WO2017123495A2

WO2017123495A2 - Single engine sweeper with infinitely variable transmission

Info

Publication number: WO2017123495A2
Application number: PCT/US2017/012693
Authority: WO
Inventors: Hao Zhang; Rajineesh KUMAR; Blake Adam Carl
Original assignee: Parker-Hannifin Corporation
Priority date: 2016-01-12
Filing date: 2017-01-09
Publication date: 2017-07-20
Also published as: WO2017123495A3

Abstract

A vehicle drive system includes a prime mover, a first power pathway that directs power from the prime mover to drive a wheel assembly, an accessory load mechanically separate from the wheel assembly, and a second power pathway that directs power from the prime mover to drive the accessory load. The second power pathway includes a variator that converts an engine speed of the prime mover to a drive speed suitable for driving the accessory load. The first power pathway may include an infinitely variable transmission, and the second power pathway may include a power takeoff or a transfer case that draws power from the prime mover. An exemplary vehicle may be a street sweeper with multiple accessory loads, with a portion of the accessory loads being driven directly from the engine using a speed ratio assembly, and a portion of the accessory loads being driven using a hydrostatic transmission.

Description

TITLE: SINGLE ENGINE SWEEPER WITH INFINITELY VARIABLE

TRANSMISSION

Field of Invention The present invention relates to hybrid vehicles with accessory loads, such as for example a street sweeper or similar vehicle with an accessory load other than driving, and arrangements for drive mechanisms for operating such accessory loads based on a single engine configuration.

Background

There are various types of construction and maintenance related vehicles that require operating one or more accessory loads in addition to ordinary driving. An example of such a vehicle is a street sweeper. In addition to ordinary driving, an exemplary street sweeper may include multiple accessory loads, such as for example a vacuum fan, a high pressure water pump, a sweeper brush assembly, and a lift cylinder for moving the sweeper brush assembly into and from a cleaning position.

Existing street sweeper configurations (and configurations of similar type vehicles) employ two separate internal combustion engines to support driving and operating accessory loads. Fig. 1 is a drawing depicting a schematic view of a conventional vehicle drive system 10 for ordinary driving and operating accessory loads. The drive system 10 may include a first drive system 12 for performing ordinary driving, and a second drive system 14 for operating accessory loads. The first drive system 12 for driving may include a first chassis engine 16 that employs a clutch 18 to engage a drive transmission 20. The chassis engine may be configured as an internal combustion engine, and may be referred to more generally as a prime mover. The chassis engine or prime mover 16 drives a wheel assembly 22 for performing ordinary driving. A transmission power takeoff 24 may draw engine power from the transmission to operate certain load components associated with driving, such as for example a low pressure water pump 26.

In conventional configurations of such a vehicle with one or more accessory loads, the second drive system 14 is provided that includes a second auxiliary engine 28, which typically is a second internal combustion engine to drive the various accessory loads. In other words, the auxiliary engine 28 is provided in addition to the first chassis engine 16 that drives the wheels. As referenced above, in the example of a street sweeper as may utilize the drive system 10 shown in Fig. 1 , the multiple accessory loads may include a vacuum fan 30, a high pressure water pump 32, a sweeper brush assembly 34, and lift cylinders 36 for moving the sweeper brush assembly into and from a cleaning position. The accessory loads may be engaged by operation of an auxiliary clutch 38 that engages a gear train 40 that provides for operation of the accessory loads. In the example of Fig. 1 , the vacuum fan and high-pressure water pump are operated using portions of the gear train with appropriate speed ratios to achieve the desired speed of the given accessory. The lift cylinders and brush assembly may be driven by a hydrostatic transmission 42 including a hydraulic pump 44 coupled to a hydraulic motor 46.

As seen in Fig. 1 , therefore, the various accessory loads are powered by the auxiliary engine 28 during the street cleaning operation. During such an operation, the chassis engine 16 is running at near idle speed to maintain a very low vehicle speed. On the other hand, the auxiliary engine 28 is non-functional during regular driving. Accordingly, the two engines have very different duty cycles and non- overlapping power requirements. The use of two internal combustion engines has particular substantial disadvantages. Increasingly stringent regulations governing engine emissions provide for the use of after-treatment systems for the emissions. After-treatment systems tend to be expensive, so two engines requiring two respective after- treatment systems represents a significant cost. In addition, vehicles such as street sweepers tend to be relatively compact, and therefore based on space availability, the provision of two engines with two respective after-treatment systems can be difficult to achieve. Accordingly, there are incentives to configure the power sources on street sweepers and similar vehicles with accessory loads to provide superior propulsion while maintaining the adequate power distribution to the vehicle drive system and the accessory loads in a compact size. Summary of Invention

The present invention provides for an enhanced configuration of a vehicle with accessory loads, in which ordinary driving and operation of the accessory loads is achieved by distributing power off of a single prime mover or engine. Such a configuration overcomes the deficiencies of the conventional two-engine

configuration described above. The single prime mover or engine, therefore, results in an architecture vehicle design for a combined power source with optimal power distribution as between the vehicle drive system and the drive system for operating the accessory loads. The configuration of the present invention further permits brake energy recovery and better energy efficiency in the accessory loads. In this manner, power losses are reduced and system cost is managed while maintaining such braking energy recovery with an improved user "feel" during both driving and operating the accessory loads. Efficient switching between such operations also is achieved. An aspect of the invention is a vehicle drive system that drives both a wheel assembly for normal driving, and one or more accessory loads mechanically separate from the wheel assembly, using a single engine or prime mover. In exemplary embodiments, the vehicle drive system may include a prime mover, a first power pathway configured to direct power from the prime mover to drive a wheel assembly, and a second power pathway configured to direct power from the prime mover to drive the accessory load, the second power pathway including a variator that operates to convert an engine speed of the prime mover to a drive speed suitable for driving the accessory load. The first power pathway may include an infinitely variable transmission, and the second power pathway may include a power takeoff (PTO) that draws a portion of the power from the prime mover to drive the accessory load. Alternatively, the vehicle drive system may include a transfer case that is selectively operable to direct full power from the prime mover to either the first power pathway or the second power pathway.

The first power pathway for driving the wheel assembly may be configured in a variety of ways. Example configurations include a series hybrid transmission including a first hydraulic unit connected to the prime mover, and a second hydraulic unit in series with the first hydraulic unit and connected to a drive shaft that drives the wheel assembly. Another potential configuration of the first power pathway is an advanced series hybrid layout including a series hybrid transmission and a direct mechanical link that mechanically connects the prime mover to the drive shaft that drives the wheel assembly. Another potential configuration of the first power pathway is a power-split transmission system including a series hybrid transmission and a planetary gear train operable to split power from the engine between the series hybrid transmission and a direct mechanical link that mechanically connects the prime mover to drive shaft that drives the wheel assembly.

The second power pathway for driving the accessory loads also may be configured in a variety of ways depending upon a number and type of accessory loads. Example configurations include a hydraulic pump that provides a supply of hydraulic fluid to the accessory loads via multiple respective hydraulic motors that may be turned on or off using a respective plurality of accessory valves. Another potential configuration of the second power pathway includes a hydrostatic transmission that provides a supply of hydraulic fluid to the accessory loads, and a speed ratio assembly that is driven by an output of the hydrostatic transmission and has multiple speed ratio components for converting an engine speed of the prime mover to a suitable operating speed for each of the accessory loads. Another potential configuration of the second power pathway includes a hydrostatic transmission that provides a supply of hydraulic fluid through a hydraulic pathway to drive at least one of the accessory loads, and a speed ratio assembly outside of the hydraulic pathway for converting an engine speed of the prime mover to a suitable operating speed for driving at least one of the accessory loads by pure mechanical speed variation.

The principles of the present invention may be applied to any vehicle in which accessory loads are driven in addition to ordinary driving. An exemplary street sweeper vehicle is described in which the wheels are driven using a power-split transmission, and power is selectively directed to either the power-split transmission or to street sweeping accessory loads using a transfer case. A hydrostatic transmission provides a supply of hydraulic fluid through a hydraulic pathway to drive at least one of the accessory loads, including a rotational accessory load (e.g., a cooling fan) from the motor output and a linear accessory load (e.g., a hydraulic cylinder for moving a cleaning brush). Additional accessory loads may be driven via a speed ratio assembly outside of the hydraulic pathway that drives such additional accessory loads by pure mechanical speed variation.

These and further features of the present invention will be apparent with reference to the following description and attached drawings. In the description and drawings, particular embodiments of the invention have been disclosed in detail as being indicative of some of the ways in which the principles of the invention may be employed, but it is understood that the invention is not limited correspondingly in scope. Rather, the invention includes all changes, modifications and equivalents coming within the spirit and terms of the claims appended hereto. Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in

combination with or instead of the features of the other embodiments.

Brief Description of the Drawings Fig. 1 is a drawing depicting a schematic view of a conventional vehicle drive system for ordinary driving and operating accessory loads.

Fig. 2 is a drawing depicting a schematic view of an exemplary vehicle drive system in accordance with embodiments of the present invention, using a power takeoff to direct engine power to the accessory loads. Fig. 3 is a drawing depicting another schematic view of an exemplary vehicle drive system in accordance with embodiments of the present invention, using a transfer case to direct engine power to the accessory loads.

Fig. 4 is a drawing depicting a schematic view of an exemplary vehicle drive system similar to Fig. 2 using a power takeoff to direct engine power to the

accessory loads, showing a first embodiment of driving transmission and variator.

Fig. 5 is a drawing depicting a schematic view of an exemplary vehicle drive system similar to Fig. 3 using a transfer case to direct engine power to the accessory loads, and having the first embodiment of driving transmission and variator.

Fig. 6 is a drawing depicting a schematic view of an exemplary vehicle drive system similar to Fig. 2 using a power takeoff to direct engine power to the

accessory loads, showing a second embodiment of driving transmission and variator. Fig. 7 is a drawing depicting a schematic view of an exemplary vehicle drive system similar to Fig. 3 using a transfer case to direct engine power to the accessory loads, and having the second embodiment of driving transmission and variator of Fig. 6. Fig. 8 is a drawing depicting a schematic view of an exemplary vehicle drive system similar to Fig. 2 using a power takeoff to direct engine power to the

accessory loads, showing a third embodiment of driving transmission and variator.

Fig. 9 is a drawing depicting a schematic view of an exemplary vehicle drive system similar to Fig. 3 using a transfer case to direct engine power to the accessory loads, and having the third embodiment of driving transmission and variator of Fig. 8.

Fig. 10 is a drawing depicting a schematic view of an exemplary vehicle drive system similar to Figs. 3 and 9 using a transfer case to direct engine power to the accessory loads, and having the third embodiment of driving transmission of Fig. 9 and additionally expanded for operating multiple accessory loads. Fig. 1 1 is a drawing depicting a schematic view of an exemplary vehicle drive system similar to Fig. 10, showing an alternative embodiment for operating multiple accessory loads.

Fig. 12 is a drawing depicting a schematic view of an exemplary vehicle drive system similar to Figs. 10 and 1 1 , showing another alternative embodiment for operating multiple accessory loads.

Detailed Description

Embodiments of the present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It will be understood that the figures are not necessarily to scale.

Generally, an aspect of the invention is a vehicle drive system that drives both a wheel assembly for normal driving, and one or more accessory loads mechanically separate from the wheel assembly, using a single engine or prime mover. In exemplary embodiments, the vehicle drive system may include a prime mover, a first power pathway configured to direct power from the prime mover to drive a wheel assembly, and a second power pathway configured to direct power from the prime mover to drive the accessory load, the second power pathway including a variator that operates to convert an engine speed of the prime mover to a drive speed suitable for driving the accessory load. The first power pathway may include an infinitely variable transmission, and the second power pathway may include a power takeoff (PTO) that draws a portion of the power from the prime mover to drive the accessory load. Alternatively, the vehicle drive system may include a transfer case that is selectively operable to direct full power from the prime mover to either the first power pathway or the second power pathway.

Fig. 2 is a drawing depicting a schematic view of an exemplary vehicle drive system 50 in accordance with embodiments of the present invention. The vehicle drive system 50 has a single engine 52 for powering both a first power pathway that provides torque to a drivetrain for driving the vehicle wheels, and a second power pathway that provides torque for operating one or more accessory loads. In exemplary embodiments, the engine 52 is configured as an internal combustion engine (ICE) as is suitable for operating vehicles that utilize the present invention, although any suitable engine configuration may be employed. More generally, therefore, engine 52 may be referred to as a prime mover 52. Fig. 2 provides an overall schematic in a simplified representation, with additional details being shown in subsequent figures. In the first power pathway for driving the wheels, the ICE or prime mover 52 provides power through a transmission 54, and in the example of Fig. 2, the transmission 54 is shown configured to be an automatic transmission (AT). The transmission provides power through a drivetrain 56 to drive rotation of a wheel assembly 58. The transmission further may, more specifically, be an infinitely variable transmission. Details for various configurations of the transmission are described with respect to subsequent figures. The transmission 54 and drive train 56 convert the engine speed via an appropriate gear ratio to a suitable speed of operation of the wheel assembly 58. For a vehicle with an accessory load, such as a street sweeper, the power requirement ultimately to drive the wheel assembly varies depending upon a precise mode of operation of the vehicle. For example, during a first mode of operation corresponding to ordinary driving that does not involve use of an accessory load, the power requirement for driving is highest. Accordingly, engine power almost entirely is transmitted to the wheel assembly via the first power pathway. In contrast, in a second mode of operation corresponding to employing one or more accessory loads, the vehicle tends to be driving at most slowly, and may even be stopped or idling. During such second mode of operation, the power requirement to drive the wheel assembly is minimal. In the example of Fig. 2, therefore, the transmission 54 is provided with a power take-off (PTO) 60 that draws engine power from the transmission 54 for the purpose of driving one or more accessory loads via the second power pathway in the referenced second mode of operation. The PTO 60 may draw up to approximately 80% of the engine power off of the transmission 54, with the remaining

approximately 20% of power being available to supply the wheel assembly 58. Such 20% engine power is suitable for the low drive speed or idling of the wheel assembly during the second mode of operation using an accessory load.

To drive an accessory load via the second power pathway, a clutch

mechanism 62 may be engaged to mechanically couple the PTO 60 to a variator 64. In this manner, the clutch mechanism 62 is operable to engage and disengage one or more accessory loads 66. The variator 64 operates to convert the engine speed to a drive speed suitable for driving the one or more accessory loads 66. A variator that can vary speed or torque ratio across its input and output shafts in a continuous manner can be realized through hydraulic, mechanical, electrical or other

technologies, examples of which are described in more detail below. One suitable example is to configure the variator as a hydrostatic transmission (HST), although other configurations may be employed, again as further detailed below.

The drive speed of typical accessory loads 66 tends to be significantly different from the drive speed suitable for driving the wheel assembly 58. In addition, a given accessory load may have a suitable drive speed that significantly differs from that of another accessory load. The variator 64, therefore, is configured to

accommodate a wide range or variety of drive speeds for different loads.

Accordingly, the drive system 50 of the present invention, with a first power pathway to drive the wheels, and a second drive pathway with a variator to drive accessory loads, provides for an infinitely variable transmission system that can accommodate the different speed requirements of all the driven components. Fig. 3 is a drawing depicting a schematic view of an alternative configuration of the exemplary vehicle drive system 50. The embodiments of Figs. 2 and 3 share common components, and accordingly like components are identified in both figures with like reference numerals. In the example of Fig. 3, instead of using a PTO, the drive system 50 includes a transfer case 68 to direct engine power selectively to either the first power pathway through the transmission 54 for driving the wheel assembly 58, or to the second power pathway that includes the variator 64 for operating the accessory load(s) 66. The transfer case 68 in exemplary embodiments may be configured as a gearbox containing fixed gear ratios between the primary power pathway and the secondary power pathway, without any clutches or means of disengaging the primary or secondary power pathway. It will be appreciated that such configuration is an example, and any suitable configuration of the transfer case may be employed. In the example of Fig. 3, the transmission 54 may be configured as a manual transmission (MT). By using a transfer case, the full torque generated by the engine power is directed selectively either to the first power pathway for driving the wheel assembly 58, or to the second power pathway through the variator 64 for operating the accessory loads 66. The use of a PTO as in Fig. 2 is more suitable when slow driving remains necessary or desirable when operating an accessory load. The use of a transfer case as in Fig. 3 is more suitable when the vehicle is stopped or idling with the transmission in neutral when operating an accessory load, since no power would be needed to drive the wheel assembly.

Subsequent figures provide various embodiments of different configurations for the first and second power pathways, and particularly different configurations for use as the driving transmission and associated drive train for driving the wheels, and the variator for supplying power for operating the accessory loads. The different components and configurations represent suitable examples, and given components in certain embodiments may be interchanged with components in other

embodiments, so as to provide a full range of suitable drive systems. Fig. 4 is a drawing depicting a schematic view of an exemplary vehicle drive system 70 similar to Fig. 2, using a power takeoff to direct engine power to the accessory loads, and showing a first embodiment of the driving transmission and variator. In the example of Fig. 4, the single engine solution utilizes an ICE or other prime mover 72 with an infinite variable transmission (IVT) realized as a series hybrid transmission with an engine hot shift PTO to drive accessory loads as shown. In the first power pathway for driving the wheel assembly, a series hybrid

transmission includes a first hydraulic unit 74 that is connected to the engine or prime mover 72, either through a gear ratio (not shown) or directly. The first hydraulic unit 74, as shown, may be an over-center hydraulic system that enables driving in reverse, which acts as a pump during normal driving. A second hydraulic unit 76 is connected in series to the first hydraulic unit 74, and further is connected to a driveshaft 78 through a gear ratio 88 or directly to drive a wheel assembly 80. The second hydraulic unit 76 may act as a motor during normal driving, and is capable of going over-center and applying a resistive torque in the pumping mode to capture braking energy. In exemplary embodiments, multiple hydraulic units may be connected selectively to the drive shaft 78 during periods of high torque demands.

A high pressure (HP) accumulator 82 may be operable to store captured braking energy, and may be connected to the hydraulic circuit through an isolation valve 84 that controls a hydraulic fluid flow between the high pressure accumulator and the first and second hydraulic units. The isolation valve 84 allows disconnecting the HP accumulator 82 for better efficiency and a more responsive transmission during periods of low braking energy availability. A low pressure (LP) hydraulic source 86 may be provided for supplying hydraulic fluid to the first and second hydraulic units. As are known in the art, the hydraulic fluid source 86 may include various components configured to provide a supply of hydraulic fluid, including for example a hydraulic fluid reservoir, a charge pump, a pressure relief valve, a low pressure accumulator, and filter and oil cooler components. The wheel assembly 80 may be driven by the second hydraulic unit 76 via the driveshaft 78 through a gear train 88 having a suitable axle ratio for driving the wheels.

In the example of Fig. 4, the second power pathway to drive one or more accessory loads 92 may include an engine-mounted hot shift PTO 94 connected to the prime mover/engine 72. A clutch 96 is operable to engage and disengage the second power pathway for operating the accessory load(s) 92. The PTO 94 provides power from the prime mover through the clutch 96 to a hydrostatic transmission 98 that acts as the variator in this embodiment. The hydrostatic transmission 98 includes a hydraulic pump 100 operating in combination with a hydraulic motor 102. The pump or motor unit in the hydrostatic transmission could be variable displacement type (the motor is a variable displacement motor in the example of Fig. 4). The hydrostatic transmission in turn drives the operation of the accessory load(s) 92. Fig. 5 is a drawing depicting a schematic view of the exemplary vehicle drive system similar to Fig. 3 using a transfer case to direct engine power to the accessory loads, and having the first embodiment of driving transmission and variator comparable to that of Fig. 4. As shown in Fig. 5, this embodiment of the drive system 70 employs a transfer case 104 to selectively direct full engine power to the accessory load(s) 92. As referenced above, by using a transfer case, the full torque generated by the engine power is directed selectively either to the first power pathway for driving the wheel assembly, or to the second power pathway for operating the accessory load(s). The use of a PTO as in Fig. 4 is thus more suitable when slow driving remains necessary or desirable when operating an accessory load. The use of a transfer case as in Fig. 5 is more suitable when the vehicle is stopped or idling with the transmission in neutral when operating an accessory load, since no power would be needed to drive the wheel assembly. Full power and torque may be delivered to the second power pathway for operating the accessory load(s) by de-stroking the first hydraulic unit 74 completely. Fig. 6 is a drawing depicting a schematic view of an exemplary vehicle drive system 1 10 similar to Fig. 2 using a power takeoff to direct engine power to the accessory loads, showing a second combination of driving transmission and variator. Like components are identified with common reference numerals as in Figs. 4 and 5. In the example of Fig. 6, the first power pathway for driving the wheel assembly is configured as an advanced series hybrid layout. Generally, an advanced series hybrid layout includes a series hybrid transmission comparably as described above, and a direct mechanical link that mechanically connects the prime mover to the drive shaft that drives the wheel assembly. A first clutch is operable to engage and disengage the series hybrid transmission, and a second clutch is operable to engage and disengage the direct mechanical link. In the example advanced series hybrid layout as shown in Fig. 6, the prime mover/engine 72 may be engaged to and disengaged from the series hybrid transmission through a first clutch 1 12. As in Figs. 4 and 5, such series hybrid transmission may include the first hydraulic unit 74, the second hydraulic unit 76, the high pressure (HP) accumulator 82 engageable via the isolation valve 84, and the low pressure hydraulic source 86.

In the example of Fig. 6, the prime mover/engine 72 also has a direct mechanical link 1 14 to the drive shaft for the wheel assembly 80 that can be engaged and disengaged through a second clutch 1 16. In this manner, the hydraulic pathway may be isolated from power transfer off the engine to establish a direct link between the engine and the wheels. The purpose of this direct drive link is to power the wheel assembly 80 directly from the engine, in a certain high speed range, and thus avoid all the losses typically associated with the hydraulic units in the hydraulic pathway. The series hybrid transmission constituting the hydraulic pathway may be connected to the engine 72 through a first gear ratio 1 18 and the first clutch 1 12, which can be disengaged during periods of direct drive. On the output side, second hydraulic unit 76 may be connected to the drive shaft through a second gear unit 120 and a third clutch 122. During series hybrid mode, the first and third clutches 1 12 and 122 are engaged and the second clutch 1 16 is disengaged, whereas the reverse is true in direct drive mode. In exemplary embodiments, the functionality of the advanced series hybrid system can be realized without the first clutch 1 12, but the first clutch preferably is added to avoid any churning losses associated with the first hydraulic unit 74. In the example of Fig. 6, similarly as in Fig. 4, the second power pathway to drive one or more accessory loads 92 may include the engine-mounted PTO 94 connected to the prime mover/engine 72, with the hydrostatic transmission 98 being employed to operate the accessory load(s) 92. As in the previous embodiment, the clutch 96 is operable to engage and disengage the hydrostatic transmission 98 that likewise acts as the variator in this embodiment. The hydrostatic transmission again may include a hydraulic pump 100 operating in combination with a hydraulic motor 102, with either component being a variable displacement component. The hydrostatic transmission 98 in turn drives the operation of the accessory load(s) 92.

Fig. 7 is a drawing depicting a schematic view of a variation of the exemplary vehicle drive 1 10 system similar to Fig. 3 using a transfer case to direct engine power to the accessory loads, and having the second embodiment of driving transmission and variator comparable as in Fig. 6. As shown in Fig. 7, this

embodiment employs the transfer case 104 to selectively direct engine power to the accessory load(s) 92. The differences as between using a PTO as in Fig. 6 versus a transfer case as in Fig. 7 has been described above.

Fig. 8 is a drawing depicting a schematic view of an exemplary vehicle drive system 130 similar to Fig. 2 using a power takeoff to direct engine power to the accessory loads, showing a third combination of a driving transmission and variator. In the example of Fig. 8, the first power pathway that drives the wheel assembly 80 may be configured as a power-split transmission system with a mechanical pathway directly to the wheel assembly, and a hydraulic pathway that uses a series hybrid transmission. Generally, the power-split transmission may include a series hybrid transmission comparably as described above, and a planetary gear train operable to split power from the engine between the series hybrid transmission and a direct mechanical link that mechanically connects the prime mover to the drive shaft that drives the wheel assembly. In the example configuration shown in Fig. 8, a planetary gear train (PGT) 132 can be operated to effectively decouple the wheel assembly 80, thereby providing for enhanced and efficient engine management. As in previous embodiments, the hydraulic pathway portion for driving the wheel assembly likewise may be configured as a series hybrid transmission including the first hydraulic unit 74, the second hydraulic unit 76, the high pressure (HP) accumulator 82 engageable via the isolation valve 84, and the low pressure hydraulic source 86. Together with the braking energy recovery with the HP accumulator, the power-split transmission system provides a hybrid system that can split power as between mechanical and hydraulic pathways for more efficient operation.

In the example of Fig. 8, similarly as in previous embodiments, the second power pathway to drive one or more accessory loads 92 may include an engine- mounted PTO 94 connected to the prime mover/engine 72, with a hydrostatic transmission 98 being employed to operate the accessory load(s) 92. As in previous embodiments, the clutch 96 is operable to engage and disengage the hydrostatic transmission 98 that likewise acts as the variator in this embodiment. The

hydrostatic transmission again may include a hydraulic pump 100 operating in combination with a hydraulic motor 102, with either component being a variable displacement component. The hydrostatic transmission 98 in turn drives the operation of the accessory load(s) 92. Similar to the previous embodiments of Figs. 5 and 7, the transfer case 104 may be substituted for the engine PTO to provide the power for operating the accessory load(s) 92, as shown in Fig. 9.

In common vehicle configurations suitable for using the present invention, there may be multiple accessory loads with each load having a unique duty cycle that needs to be powered by the single prime mover/engine. In certain vehicles, some or all of these loads may be driven by the engine without a variator in between when the driven accessory load speeds are suitable to be tied to the engine speed. More common, however, is that the various accessory loads require an additional degree of speed ratio control that cannot be achieved by simple engine control. A variator configured in accordance with the various embodiments of the present invention is therefore appropriate in such cases. A variator could also provide more enhanced engine management in various modes of operation. For example, as referenced above, a street sweeper vehicle may have multiple accessory loads including a vacuum cooling fan, a high pressure water pump, a sweeper brush assembly, and a lift cylinder for moving the sweeper brush assembly into and from a cleaning position. For such a vehicle configuration, a variator could provide more enhanced engine management as the street sweeper goes through periods of standard operation and heavy cleaning.

Figs. 10, 1 1 , and 12 illustrate three example configurations for powering multiple accessory loads off of a single prime mover/engine 72. In these examples, the first power pathway for driving the wheel assembly is configured as a power-split transmission system comparably to that of Figs. 8 and 9, combined with using the transfer case 104 as in Fig. 9 to selectively direct full power to either driving the wheel assembly or operating one or more of the auxiliary loads. It will be

appreciated that Figs. 10-12 are examples, and other potential arrangements may be employed, including other transmission types or configurations such as in Figs. 4-9. In another set of variations of these examples, an engine or transmission PTO may be used to direct engine power to the accessory loads rather than a transfer case.

Accordingly, Fig. 10 is a drawing depicting a schematic view of an exemplary vehicle drive system 140 similar to Figs. 3 and 9 using a transfer case to direct engine power to the accessory loads, and having the power-split driving transmission similar to Figs. 8 and 9. Fig. 10 additionally shows that the drive system 140 is expanded for operating multiple accessory loads including a first accessory load 142, a second accessory load 144, and a third accessory load 146. Generally, in this first example of Fig. 10, the plurality of accessory loads are each operable at different drive speeds. The variator may include a hydraulic pump that provides a supply of hydraulic fluid to the accessory loads, and a main control valve for controlling the flow of hydraulic fluid from the hydraulic pump. A plurality of hydraulic motors is provided in fluid communication with the hydraulic pump, each hydraulic motor being operable to drive a respective one of the plurality of accessory loads. A plurality of accessory valves is provided for controlling a flow of hydraulic fluid to the plurality of hydraulic motors, each accessory valve being operable to control the hydraulic fluid flow to a respective one of the plurality of hydraulic motors.

Referring more particularly to Fig. 10, the variator is configured to have a single hydraulic pump 148 to provide a supply of hydraulic fluid to the accessory loads. In this example, the pump 148 is a fixed displacement pump, and the fluid flow may be controlled using a main control valve 150. The main control valve may be a spool valve or other valve structure that can adjust the flow depending on what portion of the accessory loads may be in operation. For example, flow may be stopped for normal driving, with the flow progressively being increased as each accessory load comes on line for operation. A maximum flow potentially could be sufficient for operating all of the accessory loads 142, 144, and 146 simultaneously. The single fixed displacement pump 148 in such manner supplies the combined flow for the accessory loads, which are driven by fixed or variable displacement hydraulic motors. As to each accessory load, a 2-way, 2-position on-off valve is located between the pump and each motor to isolate the respective load in modes of operation in which a given accessory load is not operating. When variable displacement motors are employed as shown in the example of Fig. 10, finer control of load speed can be achieved by controlling the displacement of the respective driving motor for a given load. Accordingly, in the example of Fig. 10, a first hydraulic motor 152 drives the first accessory load 142. A first accessory valve 154 is located between the pump 148 and the first hydraulic motor 152 to control the flow of hydraulic fluid to the first hydraulic motor 152. Similarly, a second hydraulic motor 156 drives the second accessory load 144. A second accessory valve 158 is located between the pump 148 and the second hydraulic motor 156 to control the flow of hydraulic fluid to the second hydraulic motor 156. A third hydraulic motor 160 drives the third accessory load 146. A third accessory valve 162 is located between the pump 148 and the third hydraulic motor 160 to control the flow of hydraulic fluid to the third hydraulic motor 160.

As referenced above, in the depicted example of Fig. 10 the hydraulic motors are variable displacement motors, although depending on the accessory loads fixed displacement motors alternatively may be used. In addition, the accessory valves are depicted as being 2-way, 2-position on-off valves to turn on or isolate the respective loads, and finer control of load speed can be achieved by controlling the displacement of the respective driving motor for a given load. Other valve and motor configurations and combinations may be employed as may be suitable to achieve such finer flow control. In addition, although three accessory loads are shown in this example, the precise number of loads may be varied as warranted for any given vehicle configuration.

Fig. 1 1 is a drawing depicting a schematic view of an exemplary vehicle drive system 170 similar to Fig. 10 on the driving side employing a power-split

transmission system, and showing an alternative embodiment for operating the accessory loads 142, 144, and 146. Generally, in this second example of Fig. 1 1 , the plurality of accessory loads again are each operable at different drive speeds. The variator may include a hydrostatic transmission that provides a supply of hydraulic fluid to drive the accessory loads, the hydrostatic transmission including a hydraulic pump and a hydraulic motor and the output of the hydraulic motor drives the accessory loads. A speed ratio assembly is driven by an output of the hydrostatic transmission, and the speed ratio assembly having multiple speed ratio components is provided for converting an engine speed of the prime mover to a suitable operating speed for each of the accessory loads.

Referring more particularly to Fig. 1 1 , the variator includes a hydrostatic transmission 172 configured as a hydraulic pump 174 combined with a hydraulic motor 176. The hydrostatic transmission 172 draws the engine power for driving the multiple accessory loads and specifically directs power through a speed ratio assembly 178. The speed ratio assembly 178 may include multiple components for converting the engine speed to a suitable operating speed for each respective load, and thus different operating speeds may be achieved for different accessory loads as may be warranted. The speed ratio assembly may employ a gear train, belt and pulley system, or drive chains (or combinations thereof) to provide the appropriate speed reductions. In the specific example of a street sweeper vehicle, belt and pulley drive systems are common for operating the accessory loads. As shown specifically in Fig. 1 1 , speed ratios between the hydraulic motor 176 and the various loads are fixed by the driving mechanisms of the speed ratio assembly 178. In exemplary embodiments, a greater degree of speed variation may be achieved by configuring the hydraulic pump as a variable displacement pump, and manipulating the pump displacement at a given engine speed to adjusts the drive speed for operating the accessory loads. Fig. 12 is a drawing depicting a schematic view of an exemplary vehicle drive system 190 similar to Figs. 9 and 10, showing another alternative embodiment for configuring the variator for operating multiple accessory loads. Generally, in the example of Fig. 12, the plurality of accessory loads again are each operable at different drive speeds. The variator may include a hydrostatic transmission that provides a supply of hydraulic fluid through a hydraulic pathway, the hydrostatic transmission including a hydraulic pump and a hydraulic motor and the output of the hydrostatic transmission drives at least one of the accessory loads. A speed ratio assembly outside of the hydraulic pathway is provided for converting an engine speed of the prime mover to a suitable operating speed for driving at least one of the accessory loads.

Referring more particularly to Fig. 12, in this example of the variator, a speed ratio assembly 192 is provided directly off the transfer case mechanically upstream relative to a hydrostatic transmission 194. As shown in this example, the speed ratio assembly 192 includes components for driving the first accessory load 142 and the second accessory load 144. In this manner, the accessory loads 142 and 144 are outside of the hydraulic pathways, and thus are subjected to pure mechanical speed variation by being driven essentially only by the prime mover/engine. As in the previous example, the speed ratio assembly 192 may employ a gear train, belt and pulley system, or drive chains to provide the appropriate speed reductions as may be suitable for any particular application.

Another output of the speed ratio assembly 192 is to drive a pump component of a hydrostatic transmission for operating additional accessory loads. Similar to previous embodiments, the hydrostatic transmission 194 is configured as a variable displacement hydraulic pump 196 driven by an output of the speed ratio assembly 192, and combined with a fixed displacement hydraulic motor 198. The hydrostatic transmission 194 may supply a flow of hydraulic fluid for driving the third accessory load 146 off of the output of the motor 198. The third accessory load, therefore, may be a rotational accessory, such as for example a cooling fan or the like. In the example of Fig. 12, the hydrostatic transmission 194 further may supply of a flow of hydraulic fluid for driving a fourth accessory load 200, such as a hydraulic cylinder or other comparable linear load (rather than a rotational load being driven off the hydraulic motor 198). An accessory valve 202 may be used to switch between operation of the third accessory load 146 and the fourth accessory load 202.

As referenced above, the precise configurations of Figs. 10-12 represent typical examples of variator configurations for operating multiple accessory loads. Other suitable configurations may be employed, including variations in the number and types of accessory loads, different types or combinations of speed ratio assemblies, and different combinations of mechanical and hydraulic drive systems, as may be desirable or suitable for a particular vehicle type. In addition, any of such variator configurations may be used in combination with either a PTO or a transfer case, and/or in combination with any suitable configuration of infinitely variable transmission for driving the wheel assembly. All such combinations and variations are considered within the scope of the present invention.

In addition, the principles of the present invention may be applied to any suitable vehicle that employs accessory loads in addition to a wheel assembly for ordinary driving. In one example, a street sweeper vehicle may be configured in accordance with Fig. 12. An exemplary street sweeper, therefore, may include a prime mover 72; a first power pathway 204 configured to direct power from the prime mover to drive a wheel assembly 80 for normal driving; a plurality of accessory loads (e.g., 142, 144, 146, and 200) for performing street sweeping functions, the accessory loads being mechanically separate from the wheel assembly; and a second power pathway 206 configured to direct power from the prime mover to drive the plurality of accessory loads. The second power pathway may include a variator that operates to convert an engine speed of the prime mover to a drive speed suitable for driving the accessory loads. In exemplary embodiments, the variator may include a hydrostatic transmission 194 that provides a supply of hydraulic fluid through a hydraulic pathway, the hydrostatic transmission including a hydraulic pump 196 and a hydraulic motor 198, and the output of the hydrostatic transmission drives at least one of the accessory loads (e.g., loads 146 and/or 200). A speed ratio assembly 192 outside of the hydraulic pathway is provided for converting an engine speed of the prime mover to a suitable operating speed for driving at least one of the accessory loads (e.g., loads 142, and/or 144).

In such a street sweeper, the first power pathway 204 may be configured as a power-split transmission system including a series hybrid transmission including a first hydraulic unit 74 connected to a member of a planetary gear train 132, and a second hydraulic unit 76 in series with the first hydraulic unit and connected to a drive shaft that drives the wheel assembly 80. The planetary gear train 132 is operable to split power from the engine between the series hybrid transmission and a direct mechanical link that mechanically connects the prime mover to the drive shaft that drives the wheel assembly. In a street sweeper vehicle, an output of the hydraulic motor 198 drives at least one rotational accessory load 146, such as for example a cooling fan. The hydraulic pathway further may include an accessory valve 202 that directs hydraulic fluid for driving at least one linear accessory load 200, such as for example a hydraulic cylinder for moving a street cleaner brush to and from a cleaning position. Additional accessory loads, such as for example a water pump 142 and/or a cleaning brush 144, may be operated using pure mechanical speed reduction via the speed ratio assembly 192.

The embodiments of the present invention have significant advantages over conventional configurations, such as that of Fig. 1 employing a second or auxiliary engine. The present invention eliminates the need for such a second engine for accessory power requirements on street sweepers and other utility vehicles, such that the single engine power can be distributed for normal driving and also for operating multiple accessory functions. Without the need of a second engine, the expense and bulk of after-treatment systems are reduced, as an after-treatment system for the second engine is no longer needed. The present invention is also highly versatile, with applicability to using a wide range of drive line configurations including simple mechanical, hydraulic, and/or power-split infinitely variable transmission systems with brake energy recovery capability. In addition, no engine up-sizing is required. For example, a conventional vehicle configuration may need to employ two 150 hp engines, one on the driving side and one the accessory side. With the present invention, no up-sizing is required, i.e., both the driving and accessory sides can be driven off of a single 150 hp engine (no need to up-size the engine to 300 hp or similar).

Relatedly, the present invention is applicable to using either an engine mounted hot shift PTO or transfer case, with optional brake energy recovery capability and an engine start/stop feature. Engine optimization for both drive line and accessory power and efficiency also are achieved. In this manner, power losses are reduced and system cost is managed while maintaining such braking energy recovery with an improved user "feel" during both driving and operating the accessory loads. Efficient switching between such operations also is achieved, and an accessory load can be driven without adverse impact or interference by the accessory drive system on the driving or propulsion side. Another advantage is that by using a PTO or transfer case, rather than a second engine, a vehicle can be easily retrofitted with different accessory loads along with the appropriate drive systems for driving such accessory loads. In addition, conventional two-engine vehicles similarly can be easily retrofitted by removing the second engine and installing a PTO or transfer case off of the remaining engine. An aspect of the invention, therefore, is a vehicle drive system for a vehicle including a wheel assembly and an accessory load mechanically separate from the wheel assembly, the vehicle drive system having an enhanced drive mechanism by which ordinary driving and the accessory load are powered off of a single engine or prime mover. In exemplary embodiments, the vehicle drive system includes a prime mover; a first power pathway configured to direct power from the prime mover to drive a wheel assembly; and a second power pathway configured to direct power from the prime mover to drive the accessory load, the second power pathway including a variator that operates to convert an engine speed of the prime mover to a drive speed suitable for driving the accessory load. The vehicle drive system may include one or more of the following features, either individually or in combination.

In an exemplary embodiment of the vehicle drive system, the first power pathway comprises an infinitely variable transmission, and the second power pathway comprises a power takeoff (PTO) that draws power from the prime mover to drive the accessory load.

In an exemplary embodiment of the vehicle drive system, the second power pathway has a clutch mechanism between the PTO and the variator for engaging and disengaging the accessory load.

In an exemplary embodiment of the vehicle drive system, the first power pathway comprises an infinitely variable transmission, and the vehicle drive system further comprises a transfer case that is selectively operable to direct full power from the prime mover to either the first power pathway or the second power pathway. In an exemplary embodiment of the vehicle drive system, the first power pathway comprises a series hybrid transmission including a first hydraulic unit connected to the prime mover, and a second hydraulic unit in series with the first hydraulic unit and connected to a drive shaft that drives the wheel assembly.

In an exemplary embodiment of the vehicle drive system, the series hydraulic transmission further includes: a high pressure accumulator operable to capture braking energy; an isolation valve for controlling a hydraulic fluid flow between the high pressure accumulator and the first and second hydraulic units; and a low pressure hydraulic fluid source for providing a supply of hydraulic fluid to the first and second hydraulic units. In an exemplary embodiment of the vehicle drive system, the first power pathway includes an advanced series hybrid layout, the advanced series hybrid layout including: a series hybrid transmission including a first hydraulic unit connected to the prime mover, and a second hydraulic unit in series with the first hydraulic unit and connected to a drive shaft that drives the wheel assembly; and a direct mechanical link that mechanically connects the prime mover to the drive shaft that drives the wheel assembly.

In an exemplary embodiment of the vehicle drive system, the advanced series hybrid layout further comprises a first clutch that is operable to engage and disengage the series hybrid transmission, and a second clutch that is operable to engage and disengage the direct mechanical link.

In an exemplary embodiment of the vehicle drive system, the advanced series hybrid layout further comprises a first gear ratio between the prime mover and the series hybrid transmission, a second gear ratio between the second hydraulic unit and the wheel assembly, and a third clutch between the second hydraulic unit and the wheel assembly to engage and disengage the wheel assembly from the series hybrid transmission. In an exemplary embodiment of the vehicle drive system, the first power pathway includes a power-split transmission system, the power-split transmission including: a series hybrid transmission; and a planetary gear train operable to split power from the engine between the series hybrid transmission and a direct mechanical link that mechanically connects the prime mover to a draft shaft that drives the wheel assembly; wherein the series hybrid transmission includes a first hydraulic unit connected to a member of the planetary gear train, and a second hydraulic unit in series with the first hydraulic unit and connected to the drive shaft that drives the wheel assembly.

In an exemplary embodiment of the vehicle drive system, the power-split transmission system further comprises a gear ratio between the second hydraulic unit and the drive shaft that drives the wheel assembly.

In an exemplary embodiment of the vehicle drive system, the variator of the second power pathway comprises a hydrostatic transmission including a hydraulic pump and a hydraulic motor. In an exemplary embodiment of the vehicle drive system, one of the hydraulic pump or hydraulic motor is a variable displacement hydraulic pump or hydraulic motor.

In an exemplary embodiment of the vehicle drive system, the accessory load comprises a plurality of accessory loads being operable at different drive speeds, wherein the variator includes: a hydraulic pump that provides a supply of hydraulic fluid to the accessory loads; a main control valve for controlling the flow of hydraulic fluid from the hydraulic pump; a plurality of hydraulic motors in fluid communication with the hydraulic pump, each hydraulic motor being operable to drive a respective one of the plurality of accessory loads; and a plurality of accessory valves for controlling a flow of hydraulic fluid to the plurality of hydraulic motors, each accessory valve being operable to control the hydraulic fluid flow to a respective one of the plurality of hydraulic motors. In an exemplary embodiment of the vehicle drive system, the hydraulic pump is a fixed displacement pump, and each of the hydraulic motors is a variable displacement motor.

In an exemplary embodiment of the vehicle drive system, the accessory load comprises a plurality of accessory loads being operable at different drive speeds, wherein the variator includes: a hydrostatic transmission that provides a supply of hydraulic fluid to the accessory loads, the hydrostatic transmission including a hydraulic pump and a hydraulic motor and the output of the hydraulic motor drives the accessory loads; and a speed ratio assembly that is driven by the output of the hydrostatic transmission, the speed ratio assembly comprising multiple speed ratio components for converting an engine speed of the prime mover to a suitable operating speed for each of the accessory loads.

In an exemplary embodiment of the vehicle drive system, the hydraulic pump is a variable displacement pump and the hydraulic motor is a fixed displacement motor.

In an exemplary embodiment of the vehicle drive system, each of the speed ratio components of the speed ratio assembly is one of a gear train, a belt and pulley system, or drive chains.

In an exemplary embodiment of the vehicle drive system, the accessory load comprises a plurality of accessory loads being operable at different drive speeds, wherein the variator includes: a hydrostatic transmission that provides a supply of hydraulic fluid through a hydraulic pathway, the hydrostatic transmission including a hydraulic pump and a hydraulic motor and an output of the hydrostatic transmission drives at least one of the accessory loads; and a speed ratio assembly outside of the hydraulic pathway for converting an engine speed of the prime mover to a suitable operating speed for driving at least one of the accessory loads.

In an exemplary embodiment of the vehicle drive system, the hydraulic pump is a variable displacement pump and the hydraulic motor is a fixed displacement motor. In an exemplary embodiment of the vehicle drive system, an output of the hydraulic motor drives at least one of the accessory loads. In an exemplary embodiment of the vehicle drive system, the hydraulic pathway includes an accessory valve the directs hydraulic fluid for driving at least one of the accessory loads.

Another aspect of the invention is street sweeper vehicle have the enhanced vehicle drive system. In exemplary embodiments, the street sweeper vehicle includes a prime mover; a first power pathway configured to direct power from the prime mover to drive a wheel assembly for normal driving; a plurality of accessory loads for performing street sweeping functions, the accessory loads being mechanically separate from the wheel assembly; and a second power pathway configured to direct power from the prime mover to drive the plurality of accessory loads, the second power pathway including a variator that operates to convert an engine speed of the prime mover to a drive speed suitable for driving the plurality of accessory loads. The variator includes: a hydrostatic transmission that provides a supply of hydraulic fluid through a hydraulic pathway, the hydrostatic transmission including a hydraulic pump and a hydraulic motor and the output of the hydrostatic transmission drives at least one of the accessory loads; and a speed ratio assembly outside of the hydraulic pathway for converting an engine speed of the prime mover to a suitable operating speed for driving at least one of the accessory loads. The street sweeper vehicle may include one or more of the following features, either individually or in combination.

In an exemplary embodiment of the street sweeper vehicle, the first power pathway comprises a power-split transmission system, the power-split transmission includes a series hybrid transmission, and a planetary gear train operable to split power from the engine between the series hybrid transmission and a direct mechanical link that mechanically connects the prime mover to a draft shaft that drives the wheel assembly. The series hybrid transmission includes a first hydraulic unit connected to a member of the planetary gear train, and a second hydraulic unit in series with the first hydraulic unit and connected to the drive shaft that drives the wheel assembly. In an exemplary embodiment of the street sweeper vehicle, the hydraulic pump is a variable displacement pump and the hydraulic motor is a fixed

displacement motor. In an exemplary embodiment of the street sweeper vehicle, an output of the hydraulic motor drives at least one rotational accessory load.

In an exemplary embodiment of the street sweeper vehicle, the at least one rotational accessory load includes a cooling fan. In an exemplary embodiment of the street sweeper vehicle, the hydraulic pathway includes an accessory valve that directs hydraulic fluid for driving at least one linear accessory load.

In an exemplary embodiment of the street sweeper vehicle, the at least one linear accessory load includes a hydraulic cylinder for moving a street cleaner brush to and from a cleaning position.

Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and

understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.

Claims

Claims What is claimed is:

1 . A vehicle drive system for a vehicle including a wheel assembly and an accessory load mechanically separate from the wheel assembly, the vehicle drive system comprising:

a prime mover;

a first power pathway configured to direct power from the prime mover to drive the wheel assembly; and

a second power pathway configured to direct power from the prime mover to drive the accessory load, the second power pathway including a variator that operates to convert an engine speed of the prime mover to a drive speed suitable for driving the accessory load.

2. The vehicle drive system of claim 1 , wherein the first power pathway comprises an infinitely variable transmission, and the second power pathway comprises a power takeoff (PTO) that draws power from the prime mover to drive the accessory load.

3. The vehicle drive system of claim 2, wherein the second power pathway has a clutch mechanism between the PTO and the variator for engaging and disengaging the accessory load.

4. The vehicle drive system of claim 1 , wherein the first power pathway comprises an infinitely variable transmission, and the vehicle drive system further comprises a transfer case that is selectively operable to direct full power from the prime mover to either the first power pathway or the second power pathway.

5. The vehicle drive system of claim any of claims 1 -4, wherein the first power pathway comprises a series hybrid transmission including a first hydraulic unit connected to the prime mover, and a second hydraulic unit in series with the first hydraulic unit and connected to a drive shaft that drives the wheel assembly.

6. The vehicle drive system of claim 5, wherein the series hydraulic transmission further comprises:

a high pressure accumulator operable to capture braking energy;

an isolation valve for controlling a hydraulic fluid flow between the high pressure accumulator and the first and second hydraulic units; and

a low pressure hydraulic fluid source for providing a supply of hydraulic fluid to the first and second hydraulic units.

7. The vehicle drive system of any of claims 1 -4, wherein the first power pathway comprises an advanced series hybrid layout, the advanced series hybrid layout comprising:

a series hybrid transmission including a first hydraulic unit connected to the prime mover, and a second hydraulic unit in series with the first hydraulic unit and connected to a drive shaft that drives the wheel assembly; and

a direct mechanical link that mechanically connects the prime mover to the drive shaft that drives the wheel assembly.

8. The vehicle drive system of claim 7, wherein the advanced series hybrid layout further comprises a first clutch that is operable to engage and disengage the series hybrid transmission, and a second clutch that is operable to engage and disengage the direct mechanical link.

9. The vehicle drive system of claim 8, wherein the advanced series hybrid layout further comprises a first gear ratio between the prime mover and the series hybrid transmission, a second gear ratio between the second hydraulic unit and the wheel assembly, and a third clutch between the second hydraulic unit and the wheel assembly to engage and disengage the wheel assembly from the series hybrid transmission.

10. The vehicle drive system of any of claims 1 -4, wherein the first power pathway comprises a power-split transmission system, the power-split transmission comprising:

a series hybrid transmission; and a planetary gear train operable to split power from the engine between the series hybrid transmission and a direct mechanical link that mechanically connects the prime mover to a draft shaft that drives the wheel assembly;

wherein the series hybrid transmission includes a first hydraulic unit connected to a member of the planetary gear train, and a second hydraulic unit in series with the first hydraulic unit and connected to the drive shaft that drives the wheel assembly.

1 1 . The vehicle drive system of claim 10, wherein the power-split transmission system further comprises a gear ratio between the second hydraulic unit and the drive shaft that drives the wheel assembly.

12. The vehicle drive system of any of claims 1 -1 1 , wherein the variator of the second power pathway comprises a hydrostatic transmission including a hydraulic pump and a hydraulic motor.

13. The vehicle drive system of claim 12, wherein one of the hydraulic pump or hydraulic motor is a variable displacement hydraulic pump or hydraulic motor.

14. The vehicle drive system of any of claims 1 -1 1 , wherein the accessory load comprises a plurality of accessory loads being operable at different drive speeds, wherein the variator comprises:

a hydraulic pump that provides a supply of hydraulic fluid to the accessory loads;

a main control valve for controlling the flow of hydraulic fluid from the hydraulic pump;

a plurality of hydraulic motors in fluid communication with the hydraulic pump, each hydraulic motor being operable to drive a respective one of the plurality of accessory loads; and

a plurality of accessory valves for controlling a flow of hydraulic fluid to the plurality of hydraulic motors, each accessory valve being operable to control the hydraulic fluid flow to a respective one of the plurality of hydraulic motors.

15. The vehicle drive system of claim 14, wherein the hydraulic pump is a fixed displacement pump, and each of the hydraulic motors is a variable

displacement motor.

16. The vehicle drive system of any of claims 1 -1 1 , wherein the accessory load comprises a plurality of accessory loads being operable at different drive speeds, wherein the variator comprises:

a hydrostatic transmission that provides a supply of hydraulic fluid to the accessory loads, the hydrostatic transmission including a hydraulic pump and a hydraulic motor and the output of the hydraulic motor drives the accessory loads; and

a speed ratio assembly that is driven by the output of the hydrostatic transmission, the speed ratio assembly comprising multiple speed ratio components for converting an engine speed of the prime mover to a suitable operating speed for each of the accessory loads.

17. The vehicle drive system of claim 16, wherein the hydraulic pump is a variable displacement pump and the hydraulic motor is a fixed displacement motor.

18. The vehicle drive system of any of claims 16-17, wherein each of the speed ratio components of the speed ratio assembly is one of a gear train, a belt and pulley system, or drive chains.

19. The vehicle drive system of any of claims 1 -1 1 , wherein the accessory load comprises a plurality of accessory loads being operable at different drive speeds, wherein the variator comprises:

a hydrostatic transmission that provides a supply of hydraulic fluid through a hydraulic pathway, the hydrostatic transmission including a hydraulic pump and a hydraulic motor and an output of the hydrostatic transmission drives at least one of the accessory loads; and

a speed ratio assembly outside of the hydraulic pathway for converting an engine speed of the prime mover to a suitable operating speed for driving at least one of the accessory loads.

20. The vehicle drive system of claim 19, wherein the hydraulic pump is a variable displacement pump and the hydraulic motor is a fixed displacement motor.

21 . The vehicle drive system of any of claims 19-20, wherein an output of the hydraulic motor drives at least one of the accessory loads.

22. The vehicle drive system of claim 21 , wherein the hydraulic pathway includes an accessory valve the directs hydraulic fluid for driving at least one of the accessory loads.

23. A street sweeper vehicle comprising:

a prime mover;

a first power pathway configured to direct power from the prime mover to drive a wheel assembly for normal driving;

a plurality of accessory loads for performing street sweeping functions, the accessory loads being mechanically separate from the wheel assembly; and

a second power pathway configured to direct power from the prime mover to drive the plurality of accessory loads, the second power pathway including a variator that operates to convert an engine speed of the prime mover to a drive speed suitable for driving the plurality of accessory loads;

wherein the variator comprises:

a hydrostatic transmission that provides a supply of hydraulic fluid through a hydraulic pathway, the hydrostatic transmission including a hydraulic pump and a hydraulic motor and the output of the hydrostatic transmission drives at least one of the accessory loads; and

24. The street sweeper vehicle of claim 23, wherein the first power pathway comprises a power-split transmission system, the power-split transm^' comprising:

25. The street sweeper vehicle of any of claims 23-24, wherein the hydraulic pump is a variable displacement pump and the hydraulic motor is a fixed displacement motor.

26. The street sweeper vehicle of any of claims 23-25, wherein an output of the hydraulic motor drives at least one rotational accessory load.

27. The street sweeper vehicle of claim 26, wherein the at least one rotational accessory load includes a cooling fan.

28. The street sweeper vehicle of any of claims 23-27, wherein the hydraulic pathway includes an accessory valve that directs hydraulic fluid for driving at least one linear accessory load.

29. The street sweeper vehicle of claim 28, wherein the at least one linear accessory load includes a hydraulic cylinder for moving a street cleaner brush to and from a cleaning position.