GB2486730A

GB2486730A - A control system for a power takeoff (PTO) stub of an agricultural tractor

Info

Publication number: GB2486730A
Application number: GB1021950.9A
Authority: GB
Inventors: Aleksi Vesala
Original assignee: Valtra Oy AB
Current assignee: Valtra Oy AB
Priority date: 2010-12-24
Filing date: 2010-12-24
Publication date: 2012-06-27
Also published as: GB201021950D0

Abstract

A tractor control system comprises an engine 26 drivingly connected, via drive shaft 28 and PTO clutch 32, to a PTO stub 30, and an electronic control unit or ECU 42 for receiving a maximum PTO torque value. A driving torque delivered to the PTO stub is limited to the maximum PTO torque value to provide overload protection to the PTO shaft 22 and implement 12. Two speed sensors 38, 40 are placed adjacent the drive shaft 28 in either side of the PTO clutch 32, the signals from which are transmitted to the ECU 42. The ECU 42 then controls the pressure delivered to the PTO clutch 32 via pressure controller 36, there being a potentiometer with a dial 44 which enables a driver to preselect a maximum PTO torque value which is dependent on the implement 12 attached.

Description

DESCRIPTION

TRACTOR CONTROL SYSTEM

The invention relates to control systems for agricultural tractors which include a power takeoff (PTO) stub driven by an engine.

The ever-increasing demand for more efficient food production has driven the trend for agricultural farm machinery to get bigger and more powerful through the years. Modem combine harvesters, for example, have increased capacity and working width to speed up the harvesting process whilst agricultural tractors have increased in size and power to cater for larger farm implements requiring less passes across a field.

Larger implements, such as balers, seed drills and hay equipment, are more power-consuming than older, smaller models. For example, large modem tillage equipment requires a more powerful tractor to drive such. In addition to propulsion of the implement, power is often delivered from the tractor via a PTO shaft connected to the implement. As the power consumption of larger implements increases so too must the torque and/or speed of the PTO shaft in order to deliver the power demanded. PTO shafts for larger equipment, therefore, are built with a more robust construction.

PTO couplings for all tractors and implements are typically constructed to meet a standard so that any implement PTO shaft can be attached to any tractor PTO output. However, when lighter, more delicate implements are attached to more powerful tractors which are capable of delivering high torque levels, the PTO shafts must be provided with overload protection measures to prevent excessive torques being delivered to the implement and thus causing damage. Such measures may comprise a shear bolt provided in the driveline or a more complex torque limiting device. This adds cost and complexity in constmction to the farm implement. Furthermore, in the case of the shear bolts, replacement thereof is costly in both time and money.

It is an object of the invention to provide PTO overload protection in a more simple and less costly way.

In accordance with the invention there is provided a tractor control system comprising an engine drivingly connected to a PTO stub, and an electric control unit (ECU) for receiving a maximum PTO torque value, wherein a driving torque delivered to the PTO stub is limited to the maximum PTO torque value. Advantageously, by limiting the maximum output torque of the PTO stub at the tractor, the provision of expensive overload protection measures are not required on any attached implement. Tn any case, the overload protection provided by the inventive control system prevents any existing shear bolts in the driveline from breaking thus reducing downtime.

Torque increases can resuh from a blockage in the implement or simply placing too much demand upon the implement. For example a rotary topper may strike a rigid object such as an obscured tree stump which causes a sudden increase in torque along the PTO driveline. In another example, a small square baler may become overloaded when processing hay with a high moisture content to an extent where excessive load on the working parts runs the risk of damage. In both cases overload protection measures are required to prevent damage to the implement.

In accordance with a preferred embodiment of the invention the control system further comprises a PTO clutch located in a driveline between the engine and the PTO stub and comprises at least a pair of clutch plates held together by an adjustable clutch pressure, wherein the driving torque delivered to the PTO stub is limited to the maximum PTO torque value by controlling the clutch pressure. All modem tractors include a PTO clutch to allow selective engagement of the PTO output as required. In this preferred embodiment, the existing PTO clutch is exploited to provide a means of limiting the maximum torque delivered to the PTO stub. By controlling the clutch pressure appropriately, any demand in torque above the predetermined maximum threshold, causes the clutch plates to slip thereby preventing excessive torque being conveyed to the implement.

The PTO clutch preferably comprises hydraulic actuators to adjust the clutch pressure wherein the hydraulic actuators are controlled by means of known hydraulic control technology including solenoid-activated valves controlled with electronic signals from the ECU.

Preferably, the system further comprises means to sense slippage of the PTO clutch. For example a speed sensor may be placed on the driveshaft to each side of the PTO clutch, the signals from which are transmitted to the ECU. Slippage can, therefore, be simply detected by comparison of the signals from the respective speed sensors.

The system may further comprise a driver alarm which activates in response to a sensed slippage of the clutch plates of the PTO clutch. This allows a driver to respond accordingly

I

by disengaging the PTO drive manually and/or stopping forward propulsion of the tractor.

The PlO clutch may be disengaged automatically in response to a sensed slippage of the clutch plates of the PTO clutch for a predetermined period of slippage time. By automatically disengaging the PTO clutch in this way, overheating of the PTO clutch is avoided. The predetermined period of time may be as short as zero seconds for immediate disengagement or as long as ten seconds, for example, to give the driver adequate time to deactivate the system manually.

Alternatively, the engine output torque can be lowered in response to a sensed slippage between the clutch plates of the PlO clutch for a pre-deterniined period of time. In this case the ECU commands a lower torque output from the engine by transmitting appropriate control signals. Although this method prevents damage to the implement and reduces slippage of the P10 clutch, a result may be stalling of the engine unless the increase in P10 torque is temporary. Preferably the engine output torque is lowered to a level that produces substantially zero slippage between the clutch plates of the P10 clutch so as to avoid overheating of the P10 clutch.

In an alternative embodiment the maximum engine output torque is limited to a value dependent on the maximum PlO torque value. In this case the engine is controlled by the ECU so as to limit the maximum output torque so that the torque delivered to the P10 stub never exceeds the maximum threshold. This system carries the disadvantage that overall power of the tractor can be limited thereby affecting the power available for propulsion.

The control system may further comprise a user interface device connected to the ECU which allows a user to input the maximum input torque value. In one example the user interface device may be a simple dial on a console within reach of the driver which adjusts a potentiometer connected to the ECU. Simple rotation of the dial changes the maximum PTO torque value stored by the ECU. In another example the user interface device comprises a driver terminal having a touch sensitive display in which a displayed numeric keypad allows a driver to enter the maximum PTO torque value which is subsequently received and stored by the ECU.

In an alternative embodiment, a communications link in the form of an existing communication bus is provided between the ECU and an attached implement. In one example, the communications bus meets the ISOBUS standard. The communications link is exploited to convey a signal representative of the maximum PTO torque value from a control umt associated with the implement to the ECU located on the tractor.

Further advantages of the invention will become apparent from reading the following description of specific embodiments with reference to the appended drawings in which:-Figure 1 is a schematic diagram of a control system according to a first embodiment of the invention; and, Figure 2 is a schematic diagram of a control system according to a second embodiment of the invention.

With reference to Figure 1, an agricultural tractor represented by dashed outline 10 has an implement in the form of a rotary hay tedder 12 attached thereto by means of a three-point linkage represented diagrammatically by dotted line 14. The invention is applicable to any PTO-driven application although, for completeness, the hay tedder 12 comprises a pair of rotors 16 driven by respective rotor gear boxes 18 which derive power fi'om a main gear box 20. An implement PTO shaft 22 comprises a female coupling member 24 of known construction at one end and a connection to the tedder gearbox 20 at the other.

The tractor 10 comprises an internal combustion engine 26 having an output drive shaft 28 connected thereto. Although not shown it should be understood that power for propulsion of the tractor is taken from the output driveshaft 28 by means of various gears and clutches of a known arrangement which are omitted from the figure for clarity.

A PTO stub 30 is located at the rear of the tractor 10 and is driven by driveshaft 28 via PTO clutch 32. The female connector 24 is coupled to the PTO stub 30 by means of a splined arrangement which meets industry standards.

The PTO clutch 32 is of a known construction and may take various different forms.

However, for the sake of explanation in this example, the PTO clutch 32 comprises a pair of clutch plates 34 which are held together by an adjustable clutch pressure. The detailed construction of the PTO clutch 32 will not be described and the apparatus to control the clutch pressure is simply represented by box 36.

Two speed sensors 38, 40 are placed adjacent the driveshaft 28 on either side of the PTO clutch 32, the signals from which are transmitted to ECU 42. For sake of clarity, ECU 42 is represented by a simple box although it will be understood that the ECU 42 will typically comprise a data processor and numerous electronic components to receive, transmit and process various electronic signals associated with various fhnctions on the tractor 10. It will also be understood that the ECU may be located in a single module upon the tractor or may be distributed over several locations iii different modules.

A potentiometer with dial 44 attached is mounted to a driver console and connected to ECU 42. The dial 44 has associated therewith a scale which enables a driver to preselect a maximum PTO torque value which is dependent upon the implement attached.

Operation Before engagement of the PTO clutch 32 the driver preselects a maximum PTO torque value and inputs said value by appropriate adjustment of dial 44. ECU 42 receives the maximum torque value from dial 44 and subsequently limits the maximum clutch pressure applied to PTO clutch 32.

Therefore, when commanded by the driver by a further user interface device (not shown), PTO clutch 32 is engaged with a clutch pressure dependent on the maximum PTO torque value. In the event that the torque along the PTO shaft 22 exceeds the threshold value, the excessive torque transmitted by engine 26 is absorbed by slippage of the PTO clutch 32.

Such slippage is detected by a combination of signals from sensors 38, 40 processed by ECU 42. In response to sensed slippage of PTO clutch 32, ECU 42 activates a driver alarm (not shown) which may be audible andlor visual and located in the cab. The alarm alerts the driver that the torque on the PTO shaft 22 has exceeded the threshold value and allows the driver to take appropriate steps such as stopping the forward motion of the tractor 10 andlor manual disengagement of the PTO clutch 32.

After a predetermined period of slippage, the ECU 42 may command automatic disengagement of the PTO clutch 32 to prevent overheating thereof Alternatively, the ECU 42 may command a reduction in output torque from engine 26 to prevent further slippage of PTO clutch 32.

Figure 2 shows an alternative embodiment in which the dial 44 is omitted. Only those features which differ from the embodiment of Figure 1 will be described. The implement 12 in this example includes an onboard control unit 46 which is connected electrically to ECU 42 via a communications bus 48 which includes a female coupling member 50 associated with the tractor 10 which receives a male plug 52 from the implement 12. The implement controller 46 transmits a predetermined maximum PTO torque value to the ECU 42 via the communications bus 48. Advantageously, this alleviates the driver of the need to manually look up and input the maximum PTO torque value of the associated implement.

Ahhough the embodiment shown is described with reference to a rotary tedder it will be appreciated that the invention is applicable to any PTO driven farm implement including balers, tillage equipment, fertiliser spreaders and the like.

From reading the present disclosure, other modification will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the field of PTO drive systems and component parts therefore and which may be used instead of or in addition to features already described herein.

Claims

CLAIMSI. A tractor control system comprising an engine drivingly connected to a PTO stub, and an electronic control unit for receiving a maximum PTO torque value, wherein a driving torque delivered to the PTO stub is limited to the maximum PTO torque value.
2. A control system according to Claim I, further comprising a PTO clutch located in a driveline between the engine and the PTO stub and comprising at least a pair of clutch plates held together by an adjustable clutch pressure, wherein the driving torque delivered to the PTO stub is limited to the maximum PTO torque value by controlling the clutch pressure.
3. A control system according to Claim 2, further comprising means to sense slippage of the PTO clutch.
4. A control system according to Claim 3, further comprising a driver alarm which activates in response to a sensed slippage between the clutch plates of the PTO clutch.
5. A control system according to Claim 3 or 4, wherein the PTO clutch is disengaged in response to a sensed slippage between the clutch plates of the PTO clutch for a predetermined period of time.
6. A control system according to Claim 3 or 4, wherein the engine output torque is lowered in response to a sensed slippage between the clutch plates of the PTO clutch for a predetermined period of time.
7. A control system according to Claim 6, wherein the engine output torque is lowered to a level that produces substantially zero slippage between the clutch plates of the PTO clutch.
8. A control system according to any one of Claims 3 to 7, wherein the means to sense slippage of the PTO clutch comprises a drive-side speed sensor for sensing the rotational speed of the driveline on the engine side of the PTO clutch and a driven-side speed sensor for sensing the rotational speed of the driveline on the PTO stub side of the PTO clutch.
9. A control system according to Claim 1, wherein the maximum engine output torque is limited to a value dependent upon the maximum PTO torque value.
10. A control system according to any preceding claim, further comprising a user interface device connected to the electronic control unit which allows a user to input the maximum PTO torque value.
Ii. A control system according to any preceding claim, wherein the electronic control unit receives the maximum PTO torque value via a communications link with an implement attached to the tractor.