GB2518901A

GB2518901A - Vehicle suspension with a double acting suspension circuit

Info

Publication number: GB2518901A
Application number: GB1317691.2A
Authority: GB
Inventors: David James Cousins
Original assignee: HUSCO INTERNAT Ltd
Current assignee: HUSCO INTERNAT Ltd
Priority date: 2013-10-07
Filing date: 2013-10-07
Publication date: 2015-04-08
Anticipated expiration: 2033-10-07
Also published as: GB201317691D0; GB2518901B

Abstract

A hydraulic circuit 22 has a first node 68 and a second node 74. A first control valve 60 creates a first path between the first node 68 and a pump supply line 54 in a first position, and a second path between the first node 68 and a tank return line 58 in a second position. A second control valve 84 has a first port 82 coupled to the second node 74 and a second port 83 connected to a first chamber 34. A pilot operated check-valve 100 controls a path connected to a valve port 101. In a deactivated state, fluid can flow through the path only from the valve port toward a second chamber 32. In an activated state fluid can flow through the path in both directions. Pressure at the first node 68 exceeding a predefined threshold activates the pilot operated check-valve 100. A pressure control device 70 manages pressure at the valve port 101 selectively to pressure derived from the first node 68 or pressure in the tank return line 58.

Description

VEHICLE SUSPENSION WITH A DOUBLE ACTING SUSPENSION CIRCUIT

Cross-Reference to Related Applications

Not Applicable

Statement Regarding Federally

Sponsored Research or Development Not Applicable

Background of the Invention

1. Field of the Invention

100011 The present invention relates to vehicle suspension systems for maintaining vehicle stability while the vehicle is wider varying loads; and more particularly to vehicle suspension systems that employ a double acting hydraulic cylinder to maintain vehicle stability.

2. Description of the Related Art

100021 Most vehicle suspension systems include at last one hydraulic suspension cylinder connected between the vehicle chassis and a wheel and/or vehicle axle. Simple suspension systems primarily employ a conventional shock absorber that comprises a sealed cyhnder having an internal piston with an orifice that controls flow of fluid between a head chamber and a rod chamber on opposite sides of the internal piston. The constrained rate of fluid flow governs piston movement, thereby damping motion between the chassis and the wheel and/or axle.

100031 More sophisticated vehicle suspension systems are adjustable with damping characteristic that can be varied dynamically in response to changes in tile load on tile vehicle. In one system of this type, a gas-charged accumulator pressurizes at least one of the cyhnder chambers, which allows resilient displacement of the piston. A vaive arrangement known as a double acthg circuit selectively connects the head chamber and rod chamber to a pressure source and a tank of the hydraulic system.

100041 Another more sophisticated vehicle suspension system includes a regenerative hydraulic circuit that can reduce the number of components when compared to a conventional double acting circuit. A regenerative hydraulic circuit reduces the accumulator capacity requirement, which helps to reduce system costs. Yet, an issue with regenerative systems is that the natural frequency changes with the load applied to the vehicle suspension, leading to suspension performance changes as the loading changes. This is particularly noticeable at low loads when the suspension system will often over travel. A work around has been to increase the number of accumulators and set accumulator pre-charges differently to maximize the working range. The work around comes with unwanted added cost.

100051 As a consequence, there remains a need for a vehicle suspension system that provides a more sophisticated vehicle suspension, yet without the added cost.

Summary of the Invention

100061 A double acting vehic'e suspension system maintains vehicle stability while under varying loads.

100071 A hydraulic circuit for controlling a suspension of a vehicle and having a first cylinder with a piston that defines a first chamber and a second chamber within the first cylinder. The hydraulic circuit has a first node and a second node. A first control valve has a first position in which a first path is created between the first node and a pump supply line of the vehicle and a second position in which a second path is created between the first node and a tank return line of the vehicle. A first orifice provides a fluid path between the first node and the second node. A second control valve has a first port coupled to the second node and a second port connected to the first chamber, wherein the second control valve selectively controls fluid flow between the first port and the second port. A pilot operated check valve selectively controls a managed path connected to a valve port and being operatively connected wherein in a deactivated state fluid can flow through the managed path only in a direction from the valve port toward the second chamber, and in an activated state fluid can flow through the managed path in both directions between the valve port and the second chamber, wherein the pilot operated check valve is placed into the activated state by pressure at the first node exceeding a predefined threshold. A pressure control device manages pressure at the valve port selectively to one of pressure derived from the first node and pressure in the tank return line.

100081 Another aspect of the present hydraulic circuit has a first node, a second node, and a control node. A first control valve has a first position in which a first path is created between the first node and a pump supply line of the vehicle and a second position in which a second path is created between the first node and a tank return line of the vehicle. A first orifice provides a fluid path between the first node and the second node. A second control valve has a first port coupled to the second node and a second port connected to tile first chamber, wherein the second control valve selectively controls fluid flow between the first port and the second port. A rod orifice provides a path between the first node and the control node. A pilot operated check valve is operatively connected wherein in a deactivated state a fluid can flow only from the control node to the second chamber, and in an activated state the fluid can flow in either direction between the control node and the second chamber, wherein the pilot operated check valve is placed into the activated state by a pressure at the first node exceeding a predefined threshold. A pressure control device provides a tank path between the control node and the tank return line in response to pressure at the control node exceeding a defined pressure setting.

100091 Yet another aspect of the present hydraulic circuit has a first node and a second node. A first control valve has a first position in which a first path is created between the first node and a pump supply line of the vehicle and a second position in which a second path is created between the first node and a tank return line of the vehicle. A first orifice provides a fluid path between the first node and the second node.

A second control valve has a first port and a second port, the second control valve for selectively controlling fluid flow between the first port and the second port, wherein the second port is connected to the first chamber. A second orifice provides a fluid path between the second node and the first port. A pressure control device has a third port connected to the first node, a fourth port connected to the tank return line, and a fifth port. A pilot operated check valve is operatively connected wherein in a deactivated state a fluid can flow only from the fifth port to the second chamber, and in an activated state the fluid can flow in either direction between the fifth port and the second chamber, wherein the pilot operated check valve is placed into the activated state by a pressure at tile first node exceeding a predefined threshoid.

Brief Description of the Drawings

100101 FIG. 1 is a front view of a vehicle that incorporates a double acting suspension circuit according to the present invention; 100111 FIG. 2 is a schematic diagram of a double acting suspension circuit according to the present invention; 100121 FIG. 3 is a scilenlatic diagranl of another embodiment of a double acting suspension circuit according to the present invention, including circuit velocity control; 100131 FIG. 4 is a schematic diagram of another embodiment of a double acting suspension circuit according to the present invention, including variable rod chamber control with respect to head chamber pressure; 100141 FIGS. 5 and 6 are schematic diagrams of another embodiment of a double acting suspension circuit according to the present invention, including a load sense shuttling device; and 100151 FIG. 7 is a schematic diagram of another embodiment of a double acting suspension circuit according to the present invention, with an alternative pressure control configuration.

Detailed Description of the Tnvention

100161 The term "directly connected" as used herein means that the associated components are connected together by a conduit without any intervening element, such as a valve, an orifice or other device, which restricts or controls the flow of fluid beyond the inherent restriction of any conduit. Likewise, the term "coupled" as used herein means that the associated components can be directly connected, or can be indirectly connected with one or more intervening elements.

100171 With initial reference to FIGS. 1 and 2, a vehicle 20, such as an agricultural tractor, can carry widely varying loads. In order to maintain vehicle stability under varying loads, a hydraulic circuit 22 controls flow of fluid to and from a pair of cylinders 24 that are positioned in the vehicle suspension between the vehicle body 26 and the front wheels 28. The cylinders 24 have internal bores in which a piston 30 is slidably received, thereby forming a rod chamber 32 and a head chamber 34 within the cylinder 24 on opposite sides of the piston 30. The volume within the rod chamber 32 and the head chamber 34 vary as the piston 30 moves within the cylinder. hi one configuration, a cylinder 24 is attached to the frame of the vehicle body 26 while the piston rod 38 is attached to the vehicle axle 44 for either the front or rear wheels 28. In another configuration, the piston rod 38 is attached to the frame of the vehicle body 26 and the cylinder 24 is attached to the vehicle axle 44 for either the front or rear wheels 28.

100181 The pair of cylinders 24 are part of the hydraulic circuit 22 controlled by a controller 46. The controfler 46 may be a microcomputer-based device that includes processor which executes instructions of a software control program, to be described, and a memory for storing the instructions and data for the control program. A position sensor 47 detects the distance that one of the piston rods 38 extends from one cylinder 24 and provides a suspension position sial 40 to the controller 46. The hydraulic circuit 22 comprises a fluid tank 48 and a variable displacement WTI 50 that can be driven by tile engine (not shown) of the vehicle 20. The pump 50 draws fluid from the tank 48 and sends it through a pump supply line 54 to a valve assembly 56. The valve assembly 56 selectively couples the rod chambers 32 and head chambers 34 to the supply line 54. The valve assembly 56 also conveys the fluid from the cylinders 24 back to the tank 48 via a tank return line 58. The pump supply line 54 is connected in the valve assembly 56 to an inlet of an electrohydraulic first control valve 60 that has a spool that is driven by a solenoid 62. The controller 46 is coupled to the solenoid 62 to activate the first control valve 60. Depending upon the position of the spool, an outlet 64 of the first control valve 60 is connected either to the supply line 54 or to the tank return line 58. The connection to the tank return line 58 occurs when the solenoid is de-energized.

100191 The outlet 64 of the first control valve 60 is connected to a first node 68 in the valve assembly 56. A first orifice 72 couples the first node 68 to a second node 74 in the valve assembly 56. A load sense line 76 (indicated by a dotted line) is coupled to the second node 74 to provide a control signal for varying the displacement of the pump 50 on the vehicle 20. A second orifice 80 couples the first node 68 to an electrohydraulic second control valve 84 in the valve assembly 56.

100201 The second control valve 84 includes a first port 82 and a second port 83, and also has a spooi that is driven by a solenoid 85. The controller 46 is also coupled to the solenoid 85 to activate the second control valve 84. The second control valve 84 is connected between the second orifice 80 and a third node 86 to which the head chambers 34 of the two cylinders 24 are connected. One or more first gas charged head accumulators 90 are also direcfly connected to the third node 86. When the solenoid 85 is energized, the second control valve 84 creates a flow path between the second orifice 80 and the third node 86.

100211 The first node 68 is also coupled to a pressure control device 70. The pressure control device 70 includes a third port 94 coupled to the first node 68, a fourth port 96 coupled to the tank return line 58, and a fifth port 98, and is pilot opeTated by a pressure differential between the tank return line 58 and the fifth port 98. When the pressure at the fifth port 98 exceeds a predetermined evel, the pressure contr& device creates a flow path between the fifth port 98 and the tank return line 58.

100221 The pressure control device 70 is biased into a first position to create a flow path between the first node 68 and the fifth port 98. In the biased position, the pressure control device 70 couples the first node 68 to the rod chambers 32 of the two cylinders 24 by way of a pilot operated check valve 100 having a valve port 101. In a deactivated state, the pilot operated check valve 100 allows fluid to flow from the pressure control device 70 to the rod chambers 32. In an activated state, the pflot operated check valve 100 allows fluid to flow in either direction between the pressure control device 70 and the rod chambers 32. The pilot operated check valve 100 is placed into the activated state by a pressure at the first node 68 exceeding a predefined threshold. One or more second gas charged rod accumulators 102 (one is shown) are connected to the rod chambers 32.

100231 Still referring to FIG. 2, a pressure relief valve 104 is coupled to the third node 86 to provide protection from overpressure. The pressure relief valve 104 opens a flow path between the head chambers 34 and the tank return line 58 when a pressure at the third node 86 exceeds a predefined maximum pressure. A first rnanualy operated valve 108 is also coupled to the third node 86 to provide a flow path between the third node 86 and the tank return line 58. A second manually operated valve 110 is coupled between the rod chambers 32 and the tank return line 58.

100241 When the position sensor 47 detects that the front of the vehicle drops too low, the controller 46 responds by operating the hydraulic circuit 22 to raise the front suspension by introducing fluid into the head chambers 34 and draining fluid from the rod chambers 32. To accomplish this, the first and second control valves 60 and 84 are activated. When the supply line pressure is higher than the head chamber pressure and the rod chamber pressure, fluid is conveyed from the pump 50 to the supply line 54 and to the first node 68 from which the fluid will flow from a higher pressure to a lower pressure and into the rod chambers 32. At this point the pump outlet pressure and the load sense pressure are the same, and the pump 50 will increase it's displacement to maximum to increase the pump outlet pressure to the load sense pressure plus a predetermined margin. As the rod chamber pressure increases, fluid will begin to flow across first orifice 72 causing the load sense pressure to increase and the pump 50 to de-stroke, reducing the flow to the rod chambers 32. As a result, flow is diverted from the first node 68 through the first and second orifices 72 and 80 and second control valve 84 into the head chambers 34. Pressure in the load sense line 76 will begin to rise due to the lack of fluid flow into the head chambers 34. When the pump pressure builds high enough, the flow of fluid to the head chambers 34 estabhshes a pressure drop across the first orifice 72, and when the pressure drop across 72 plus a pressure drop across valve 60 is equal to the pump margin, the pump will no longer increase its displacement, and tile flow rate from the pump wifi remain steady. This defines the flow rate to the head chambers 34 and that produces a pressure drop across the second orifice 80, thereby intensifying the load sense signal 76. The second orifice 80 is appropriately sized to ensure pump supply pressure is high enough to satisfy the pressure setting of the pressure control device 70. The pressure control device 70 regulates the pressure level in the rod chambers 32 to a preset pressure level. When the position sensor 47 detects that the suspension is at the proper position, the controller 46 deactivates the first and second control valves 60 and 84.

100251 When the front of the vehicle rises too high, the controller 46 operates the hydraulic circuit 22 to lower the front suspension by introducing fluid into the rod chambers 32. To do that, the second control valve 84 is activated into the open state, thereby draining fluid from the head chambers 34 causing the piston rods 38 to retract into the cylinders 24. The fluid draining from head chambers 34 is conveyed to the first node 68 and then through the first control valve 60 to the tank 48. The first and second orifices 72 and 80 control the flow rate of that fluid and thus the velocity at which the suspension lowers. Fluid is supplied from rod accumulator 102 to the expanding rod chambers 32. When the position sensor 47 detects that the suspension is at the proper position, the controller 46 deactivates the second control valve 84.

100261 When the first and second control valves 60 and 84 are deactivated, the first control valve 60 creates a flow path from the first node 68 to the tank return line 58.

The tank pressure level is applied as the pilot pressure to the pilot operated check valve 100, thereby causing that valve to act as a simple check valve. In this state, the position of each piston 30 within the cylinders 24 is maintained because fluid is trapped in the head chambers 34 by the closed second control valve 84 and in the rod chambers 32 by the check valve 100. Now, any transient change in the force acting on the cylinders 24, such as resulting from the vehicle traveling over uneven terrain, is absorbed by forcing fluid from the respective cylinder chamber 32 or 34 into the associated accumulators 102 or 90.

100271 The hydraLdic circuit 22 can be drained to tank 48 by manually operated valve 108 to drain the head chambers 34 and manually operated valve 110 to drain the rod chambers 32. Each, when opened, creates a flow path to tank 48. In each of the embodiments described herein, the manually operated valve 108 may be included to provide a flow path to tank, or the manually operated valve 108 can be eliminated and instead the second control valve 84 can be activated to create a flow path to tank 48 to drain the head chambers 34.

100281 Referring to FIG. 3, an alternative hydraulic circuit 122 can be employed to control the suspension's velocity when a load on the vehicle 20 changes dramatically.

In hydraulic circuit 122, the head chambers 34 are coupled to the head accumulators 90 via an electrohydraulic third control valve 126. The third control valve 126 can be a free flow check valve in a deactivated state to isolate the head accumulators 90, or it can be a double blocking valve in the deactivated state, to isolate the head accumulators 90. The rod chambers 32 are coupled via a fourth node 127 to the rod accumulator 102 via an electrohydraulic fourth control valve 128. The fourth control valve 128 can also be a free flow check valve in a deactivated state to isolate the rod accumulator 102, or it can be a double blocking valve in the deactivated state, to isolate the rod accumulator 102. Either or both tile third control valve 126 and the fourth control valve 128 can be proportionally controlled by the controller 46.

Proportionality gives the ability to control the suspension's up and down veiocity in response to transient forces, and it also allows the use of advanced event driven damping algorithms and semi-activate damping controls. The remaining components shown in FIG. 3 correspond to similar components shown in FIG. 2 and have been assigned identical reference numerals.

100291 Referring to FIG. 4, an alternative hydraulic circuit 142 can be employed to include variable rod chamber pressure control with respect to head chamber pressure.

I-Iydro-pneumatic suspension systems can benefit from a reduction in the rod chamber pressure as the head chamber pressure increases. This variable pressure control can improve the operation of the suspension system over a wider working window by limiting the change in the suspension system's natural frequency. In the hydraulic circuit 142 of FIG. 4, this is achieved by replacing pressure control device 70 with variable pressure control device 146. Variable pressure control device 146 includes a relief valve 150 with an additional spring loaded piston 152. The spring loaded piston 152 serves to provide variability to the pressure setting of the relief valve 150 normally provided by relief valve spring 160. The remaining components shown in FIG. 4 correspond to similar components shown in FIGS. 2 and 3 and have been assigned identical reference numerals.

100301 In operation, the variable pressure control device 146 is coupled to the first node 68 and is supplied with fluid from the pump 50 when the first control valve 60 and the second control valve 84 are in an activated position. A rod orifice 156 can be included to limit the flow from the first node 68 to a control node 158 at an input of the variable pressure control device 146 and at the valve port 101 of the pilot operated check valve 100. The fluid flows from the rod orifice 156 through the pilot operated check valve 100 to fill the rod chambers 32 until a defined pressure setting of the variable pressure control device 146 is reached, and more specifically, until the defined pressure setting of the relief valve 150 is reached. The defined pressure setting varies as a function of the head chamber pressure that is sensed at the first port 82 of the second control valve 84.

100311 In a condition where head chamber pressure is at or near zero, the relief valve spring 160 and a piston spring 162 act together to provide the force that controls a rod chamber relief pressure setting. With the first control valve 60 and the second control valve 84 activated, an increasing head chamber pressure is conveyed by way of a pilot signal passage 163 through the first port 82 of the second control valve 84 to act against the spring loaded piston 152 and opposing the force of the piston spring 162, thereby reducing the rod chamber relief pressure setting and the rod chamber pressure.

The setting of the variable pressure control device 146 ensures that when the suspension loading is low (e.g., a low head chamber pressure), the rod chamber pressure will be at an elevated level. When the suspension loading is large (e.g., a high head chamber pressure), the rod chamber pressure will be at a reduced level. The variable pressure control device 146 reduces the need for an accumulator with a larger capacity and provides a more stable natural frequency.

100321 In sonic embodiments, the spring force of the variable pressure control device 146 is configured to achieve a rod chamber pressure setting that achieves a beneficial head chamber pressure at low suspension loading. At higher suspension loading, the rod chamber pressure setting is reduced to a level that takes into account the rod accumulator 102 setting, thus not letting the rod accumulator 102 go below its working pressure. It also improves the suspension system by removing un-required artificial loading.

100331 The variable pressure control device 146 maintains the rod chamber pressure with respect to the head chamber pressure when the first control valve 60 is in an activated position, for example, during a raise operation. When the first control valve is in a deactivated position, for example, during a thwer operation, the variaHe pressure control device 146 does not participate and any operation of the pressure control device 146 will not change the rod chamber pressure. This is due to the pilot operated check valve 100 pilot signal passage 106 beitig connected to tank 58 at the first node 68. Therefore the control method of the hydraulic circuit 142 is configured to ensure the rod chamber pressure is correct by lowering the suspension system slightly beyond a mid-position and signaling a raise operation that re-centers the cylinder position and re-establishes the rod chamber pressure for a given load.

100341 Referring to FIGS. 5 and 6, alternative hydraulic circuits 164 and 172 can be employed to include a load sense shuttling device 176. In FIG. 5, the load sense shuttling device 176 selects the greater of the head chamber pressure at the second node 74, and the rod chamber pressure at the fifth port 98 of the pressure control device 70 to apply to load sense line 76 as the load sense signal. In FIG. 6, the load sense shuttling device 176 is coupled between the second node 74 and the input of the variable pressure control device 146 that is connected to control node 158. The load sense shuttling device 176 returns the greater pressure at those couphng points to tile load sense line 76. In FIGS. 5 and 6, the second orifice 80 can be removed to eliminate its associated parasitic loss to the hydraulic circuit. Tile remaining components shown in FIGS. 5 and 6 correspond to similar components shown in FIGS. 2, 3 and 4, and have been assigned identical reference numerals.

100351 Referring to FIG. 7, in a simplified hydraulic circuit 182, the pressure control device 146, as seen in FIG. 4 for example, can be replaced with a pressure relief valve 184, thereby removing the variable rod chamber pressure control with respect to head chamber pressure. As with the pressure control device 146, the pressure relief vaive 184 is coupled to the first node 68 and is supplied with fluid from the pump 50 when the first control valve 60 is in an activated position. The rod orifice 156 limits the flow from the first node 68 to the control node 158 at an input of the pressure relief valve 184. The fluid flows from the rod orifice 156 through the pilot operated check valve 100 to fill the rod chambers 32 until a defined pressure setting of the pressure relief valve 184 is reached. V/hen the defined pressure setting is reached, the pressure relief valve 184 opens and allows the fluid to flow to tank 48.

100361 The remaining components shown in FIG. 7 correspond to similar components shown in FIGS. 2 and 4 and have been assigned identical reference Ilunlerals.

100371 A calibration can be performed on a suspension system incorporating any of the hydraulic circuits described above. For convenience, the hydraulic circuit 22 of FIG. 2 will be used. The c&ibration procedure starts with the hydraulic circuit 22 raising the suspension from tile lowest mechanical portion to the highest mechanical portion and the suspension system records the upper position. The raise operation activates the first controi valve 60 and the second controi valve 84. Unless the vehicle 20 is considerably unbalanced, there will be a net load generated on the cylinders 24. In this exemplary embodiment, and assuming the suspension system is sized correctly, a nominal head chamber load pressure may be in the region of 70 bar. When the first control valve 60 is activated, the fluid chooses the path of least resistance and fills the voids in the system (e.g., empty pipe work and cylinders). The fluid fills the rod chambers 32 and begins to increase rod chamber pressure. As rod chamber pressure increases, flow is diverted toward the head chamber side of the hydraulic circuit 22, including the load sense line 76. The pump 50 establishes a pump pressure margin across the first orifice 72. The first orifice 72 defines the flow rate to the head chamber side of the hydraulic circuit 22.

The flow rate causes a pressure drop across the second orifice 80, which intensifies the load sense signal 76 at the second node 74. The second orifice 80 is appropriately sized to ensure pump supply pressure is high enough to satisfy the pressure setting on the rod side pressure control device 70.

100381 If the first contr& valve 60 is maintained in an active state, the hydraulic circuit 22 raises the suspension until a maximum pump pressure is exerted on the head chambers 34. Pressure in the rod chambers 32 is regulated by the pressure control device 70. As the pilot operated check valve 100 is piloted open by the pump supply pressure, the fluid leaving the rod chambers 32 as the cylinders 24 extend is maintained at the preset pressure levels. When the cylinders 24 have fully extended as detected by position sensor 47, the first control valve 60 is deactivated by controller 46. The rod chamber pressure is maintained by tile pilot operated check vaive 100 on tile rod side, which now has its pilot input drained to tank 48, and by the second contr& valve 84 on the head side, which acts as a blocking device in a deactivated state.

100391 The hydraulic circuit 22 then performs a lower operation. This is done by activating the second control valve 84. Flud then ieaves the head chambers 34 through the second orifice 80, which controls the lower velocity. As the pistons 30 in the cylinders 24 move, the rod chamber 32 volumes increase and the rod chambers 32 are filled with fluid from the capacity of the rod accumulator 102. This ensures that even at low net external thads, the suspension system will lower. When the suspension system has come to rest, it will have found the lowest position. The highest position and lowest position are used by the controller 42 to define a mid-position; the mid-position having upper and lower operating liniits. The operating limits define tolerance bands and the positions the controller 42 targets when it is outside the tolerance bands.

100401 The hydraulic circuit then moves the pistons 30 with a raise operation to the mid-position. This happens as described above with the calibration raise, except that the first control valve 60 is deactivated when the mid-position is achieved as indicated by position sensor 47. Pressure at the rod chambers 32 are at the preset level of the pressure control device 70. If changes in the load occur, the vehicle axle changes positions, which triggers a leveling command with regards to the tolerance bands described above.

100411 If there is a load increase, the current pressure in the head chambers 34 will not be enough to support the increased load. In order to accommodate the incTeased load, fluid passes from the head chambers 34 into the head accumulators 90 resulting in a compression of the gas in the head accumulators 90, which increases the head chamber pressure. The increased load also leads to an increase in the volume of the rod chambers 32 as the cylinders 24 compress. This increase in volume of the rod chambers 32 is filled with fluid from the rod accmuiulator 102, which results in an expansion of the gas in the rod accumulator 102 and a reduced pressure in the rod chambers 32. The increase in head chamber pressure and decrease in rod chamber pressure continue until they balance the increased load. If the cylinders 24 are outside the tolerance band after the increased load is balanced, the hydraulic circuit 22 commands a raise operation to regulate the pressure in the rod chamber 32. . Errors in rod chamber pressure due to leakage can be avoided by veri'ing the rod chamber pressure with a pressure sensor (not shown) during the raise operation.

100421 If there is a load decrease, the cylinders 24 extend as the pressure in the chambers 32 and 34 become unbalanced. This in turn reduces the rod chamber volume and increases the rod chamber pressure due to accumulator 102 gas compression. The controller 42 signals a lower operation, which removes fluid from the head chambers 34. The tower operation returns the suspension system to the mid-position, and returns the rod chamber volume to the pre-set nominal operating volume and the rod chamber pressure returns to the pre-set nominal operating pressure.

100431 In order to ensure pressure in the rod chamber is correct, a lower operation can be initiated to slightly lower the cylinders 24 beyond the mid-position and then initiating a raise operation that re-centers the cylinder position and re-establishes the rod chamber pressure.

100441 The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of die invention, it is anticipated that oiie skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.

Claims

CLATMS1. A hydraulic circuit for controlling a suspension of a vehicle and having a first cyhnder with a piston that defines a first chamber and a second chamber within the first cylinder, the hydraulic circuit comprising: a first node; a second node; a first control valve having a first position in which a first path is created between the first node and a pump supply line of the vehicle and a second position in which a second path is created between the first node and a tank return line of the vehicle; a first orifice providing a fluid path between the first node and the second node; a second control valve having a first port coupled to the second node and a second port coupled to the first chamber, wherein the second control valve selectively controls fluid flow between the first port and the second port; a pilot operated check valve selectively controlling a managed path connected to a valve port and being operatively connected wherein in a deactivated state fluid can flow through the managed path only in a direction from the valve port toward the second chamber, and in an activated state fluid can flow through the managed path in both directions between the valve port and the second chamber, wherein the pilot operated check valve is placed into the activated state by pressure at the first node exceeding a predefined threshold; and a pressure control device for managing pressure at the valve port selectively to one of pressure derived from the first node and pressure in the tank return line.
2. The hydraulic circuit as recited in claim I, further comprising a load sense circuit connected to the second node.
3. The hydraulic circuit as recited in any one of the preceding claims 1-2, wherein the second control valve is normally biased in a position such that the fluid can flow only from the first port to the second port.
4. The hydraulic circuit as recited in any one of the preceding claims 1-2, wherein the second control valve has a first position that allows the fluid to flow in either direction between the first port and the second port, and a second position that blocks the fluid from flowing between the first port and the second port.
5. The hydraulic circuit as recited in any one of the preceding claims 1-4, further comprising a pressure relief valve operable to create a relief path between the first chamber and the tank return line of the vehicle.
6. The hydraulic circuit as recited in any one of the preceding claims 1-5, further comprising a manual valve operable to create a manual path between the first chamber and the tank return line of the vehicle.
7. The hydraulic circuit as recited in any one of the preceding claims 1-6, further comprising a manual valve operable to create a manual path between the second chamber and the tank return line of the vehicle.
8. The hydraulic circuit as recited in any one of the preceding claims 1-7, further comprising a controller connected to and electrically controlling the first control valve and the second control valve.
9. The hydraulic circuit as recited in any one of the preceding claims 1-8, further comprising at least a first accumulator connected to the first chamber.
10. The hydraulic circuit as recited in any one of the preceding claims 1-9, further comprising a plurality of first accumulators connected to the first chamber.
11. The hydraulic circuit as recited in any one of the preceding claims 1-10, further comprising at least a second accumulator connected to the second chamber.
12. The hydraulic circuit as recited in any one of the preceding claims 1-11, further comprising a plurality of second accumulators connected to the second chamber.
13. The hydraulic circuit as recited in claim 9, further comprising a third node; and a third control valve coupled between the at least a first accumLdator and the third node, wherein the third control valve selectively controls fluid flow between the at least a first accumulator and the third node.
14. The hydraulic circuit as recited in claim 13, wherein the third control valve is a proportional control valve.
15. The hydraulic circuit as recited in claim 13, wherein the third control valve is e]ectric&ly operated.
16. The hydraulic circuit as recited in claim 11, further comprising a fourth node; and a fourth control valve coupled between the at least a second accumulator and the fourth node, wherein the fourth control valve selectively controls fluid flow between the at least a second accumulator and the fourth node.
17. The hydraulic circuit as recited in claim 16, wherein the fourth control valve is a proportional control valve.
18. The hydraulic circuit as recited in claim 16, wherein the fourth control valve is electrically operated.
19. The hydraulic circuit as recited in any one of the preceding claims 1-18, further comprising a second orifice providing a fluid path that couples the second node to the first port of the second control v&ve.
20. The hydraulic circuit as recited in any one of the preceding claims 1-19, wherein the pressure control device comprises a third port connected to the first node, a fourth port connected to the tank return line, and a fifth port; and the pilot operated check valve in the deactivated state aflows fluid to flow only from the fifth port to tile second chamber, and in the activated state the pilot operated check valve allows fluid to flow in either direction between the fifth port and the second chamber.
21. The hydraulic circuit as recited in any one of the preceding claims 1-19, wherein the pressure control device provides a tank path between the valve port and the tank return line in response to pressure at the valve port exceeding a defined pressure setting.
22. The hydraulic circuit as recited in claim 21, wherein the defined pressure setting of the pressure control device varies in response to pressure in the first chamber.
23. The hydraulic circuit as recited in any one of the preceding ciairns 1-19 and 21-22, wherein the pressure control device comprises a variable pressure control device comprising a spring loaded piston operatively connected to a relief valve.
24. The hydraulic circuit as recited in any one of the preceding claims 1-22, wherein the pressure control device comprises a pressure relief device, the pressure rehef device operaHe to create a tank path between the vaive port and the tank return line of the vehicle.
25. The hydraulic circuit as recited in any one of the preceding ciairns 1-24, further comprising a shuttling valve having one input connected to the second node, another input connected to the valve port and an output connected to a load sense Hne.
26. The hydraulic circuit as recited in any one of the preceding claims 1-19 and 2 -25, further comprising a rod orifice providing a path between the first node and the valve port.
27. A hydraulic circuit for controlling a suspension of a vehicle, the hydraulic circuit having a first cylinder with a piston that defines a first chamber and a second chamber within the first cylinder, the hydraulic circuit comprising: a first node; a second node; a first control valve having a first position in which a first path is created between the first node and a pump supply line of the vehicle and a second position in which a second path is created between the first node and a tank return line of the vehicle; a first orifice providing a fluid path between the first node and the second node; a second control valve having a first port and a second port, the second control valve for selectively controlling fluid flow between the first port and the second port, wherein the second port is connected to the first chamber; a second orifice providing a fluid path between the second node and the first port; a pressure contr& device having a third port connected to the first node, a fourth port connected to the tank return Une, and a fifth port; and a pilot operated check valve operatively connected wherein in a deactivated state a fluid can flow only from the fifth port to the second chamber, and in an activated state the fluid can flow in either direction between the fifth port and the second chamber, wherein the pilot operated check valve is placed into the activated state by a pressure at the first node exceeding a predefined threshold.
28. The hydraulic circuit as recited in claim 27, further comprising a load sense circuit corniected to the second node.
29. The hydraulic circuit as recited in any one of the preceding claims 27-28, wherein the second control valve is normally biased in a position such that the fluid can flow only from the first port to the second port.
30. The hydraulic circuit as recited in any one of the preceding claims 27-28, wherein the second control vifive has a first position that allows the fluid to flow in either direction between the first port and the second port, and a second position that blocks the fluid from flowing between the first port and the second port.
3 1. The hydraulic circuit as recited in any one of the preceding claims 27-30, further comprising a pressure relief valve operable to create a relief path between the first chamber and the tank return line of the vehicle.
32. The hydraulic circuit as recited in any one of the preceding claims 27-31, further comprising a manual valve operable to create a manual path between the first chamber and the tank return line of the vehicle.
33. The hydraulic circuit as recited in any one of the preceding claims 27-32, further comprising a manual valve operable to create a manual path between the second chamber and the tank return line of the vehicle.
34. The hydraulic circuit as recited in any one of the preceding claims 27-33, further comprising a controller connected to and electrically controlling the first control valve and the second control valve.
35. The hydraulic circuit as recited in any one of the preceding claims 27-34, further comprising at least a first accumulator connected to the first chamber.
36. The hydraulic circuit as recited in any one of the preceding claims 27-35, further comprising a plurality of first accumulators connected to the first chamber.
37. The hydraulic circuit as recited in any one of the preceding claims 27-36, further comprising at least a second accumulator connected to the second chamber.
38. The hydraulic circuit as recited in any one of the preceding claims 27-37, further comprising a plurality of second accumulators connected to the second chamber.
39. The hydraulic circuit as recited in claim 35, further comprising a third node; and a third control valve coupled between the at least a first accumifiator and the third node, wherein the third control valve selectively controls fluid flow between the at least a first accumulator and the third node.
40. The hydraulic circuit as recited in claim 39, wherein the third control valve is a proportional control valve.
41. The hydraulic circuit as recited in claim 39, wherein the third control valve is electrically operated.
42. The hydraulic circuit as recited in claim 37, further comprising a fourth node; and a fourth control valve coupled between the at least a second accumulator and the fourth node, wherein the fourth control valve selectively controls fluid flow between the at least a second accumulator and the fourth node.
43. The hydraulic circuit as recited in claim 42, wherein the fourth control valve is a proportional control valve.
44. The hydraulic circuit as recited in claim 42, wherein the fourth control valve is electric&ly operated.
45. The hydraulic circuit as recited in any one of the preceding claims 27-44, wherein the pressure control device is a two position, three way valve.
46. The hydraulic circuit as recited in any one of the preceding claims 27-45, wherein the pressure control device is operated by a pressure at the fifth port.
47. The hydraulic circuit as recited in any one of the preceding claims 27-46, wherein the pressure control device creates a third path between the third port and the fifth port when pressure at the third port is less than a predetermined level.
48. The hydraulic circuit as recited in any one of the preceding claims 27-47, wherein when the pressure at the fifth port exceeds a predetermined level, the pressure control device creates a fourth path between the fourth port and the fifth port.
49. The hydraulic circuit as recited in any one of the preceding claims 27-48, further comprising a shuttling valve having one input connected to the second node, another input connected to the fifth port and an output connected to a load sense line.
50. A hydraulic circuit for controlling a suspension of a vehicle and having a first cylinder with a piston that defines a first chamber and a second chamber within the first cylinder, the hydraulic circuit comprising: a first node; a second node; a control node; a first control valve having a first position in which a first path is created between the first node and a pump supply line of the vehicle and a second position in which a second path is created between the first node and a tank return line of the ye lii c e; a first orifice providing a fluid path between the first node and the second node; a second control valve having a first port coupled to the second node and a second port connected to tile first chamber, wherein the second control valve selectively controls fluid flow between the first port and the second port; a rod orifice providing a path between the first node and the control node; a pilot operated check valve operatively corniected wherein in a deactivated state a fluid can flow only from the control node to the second chamber, and in an activated state the fluid can flow in either direction between the control node and the second chamber, wherein the pilot operated check valve is placed into the activated state by a pressure at the first node exceeding a predefined threshold; and a pressure control device that provides a tank path between the control node and the tank return line in response to pressure at the control node exceeding a defined pressure setting.
1. The hydraulic circuit as recited in claim 50, further comprising a load sense circuit connected to the second node.
52. The hydraulic circuit as recited in any one of the preceding claims 50-51, wherein the second control v&ve is normally biased in a position such that the fluid can flow only from the first port to the second port.
53. The hydraulic circuit as recited in any one of the preceding claims 50-51, wherein the second control valve has a first position that allows the fluid to flow in either direction between the first port and the second port, and a second position that blocks the fluid from flowing between the first port and the second port.
54. The hydraulic circuit as recited in any one of the preceding claims 50-53, further comprising a pressure relief valve operable to create a relief path between the first chamber and the tank return line of the vehicle.
55. The hydraulic circuit as recited in any one of the preceding claims 50-54, further comprising a manual valve operable to create a manual path between the first chamber and the tank return line of the vehicle.
56. The hydraulic circuit as recited in any one of the preceding claims 50-55, fUrther comprising a manual valve operable to create a manual path between the second chamber and the tank return line of the vehicle.
57. The hydraulic circuit as recited in any one of the preceding claims 50-56, fUrther comprising a controller connected to and electrically controlling the first control valve and the second control valve.
58. The hydraulic circuit as recited in any one of the preceding claims 50-57, further comprising at least a first accumulator connected to the first chamber.
59. The hydraulic circuit as recited in any one of the preceding claims 50-58, further comprising a plurality of first accumulators connected to the first chamber.
60. The hydraulic circuit as recited in any one of the preceding claims 50-59, further comprising at least a second accumulator connected to the second chamber.
61. The hydraulic circuit as recited in any one of tile preceding claims 50-60, further comprising a plurality of second accumulators connected to the second chamber.
62. The hydraulic circuit as recited in claim 58, further comprising a third node; and a third control valve coupled between the at least a first accumulator and the third node, wherein the third control valve selectively controls fluid flow between the at least a first accumulator and the third node.
63. The hydraulic circuit as recited in claim 62, wherein the third control valve is a proportional control valve.
64. The hydraulic circuit as recited in claim 62, wherein the third control valve is electrically operated.
65. The hydraulic circuit as recited in claim 60, further comprising a fourth node; and a fourth control valve coupled between the at least a second accumulator and the fourth node, wherein the fourth control valve selectively contrifis fluid flow between the at least a second accumulator and the fourth node.
66. The hydraulic circuit as recited in claim 65, wherein the fourth control valve is a proportional control valve.
67. The hydraulic circuit as recited in claim 65, wherein the fourth control valve is electrically operated.
68. The hydraulic circuit as recited in any one of the preceding claims 50-67, wherein the pressure control device provides a tank path between the control node and the tank return line in response to pressure at the control node exceeding a defined pressure setting.
69. The hydraulic circuit as recited in any one of the preceding claims 50-68, wherein the defined pressure setting of the pressure contr& device varies in response to pressure in the first chamber.
70. The hydraulic circuit as recited in any one of the preceding claims 50-69, wherein the pressure control device comprises a variable pressure control device comprising a spring loaded piston operatively connected to a relief valve.
71. The hydraulic circuit as recited in any one of the preceding claims 50-70, further comprising a shuttling valve having one input connected to the second node, another input connected to the control node and an output connected to a load sense line.
72. The hydraulic circuit as recited in any one of the preceding claims 50-7 1, further comprising a second orifice providing a fluid path tile couples the second node to the first port of the second control valve.