GB2609534A

GB2609534A - Systems and methods for hydro-pneumatic suspension and leveling circuit

Info

Publication number: GB2609534A
Application number: GB2207132.8A
Authority: GB
Inventors: Joyce David
Original assignee: Husco International Inc
Current assignee: Husco International Inc
Priority date: 2021-05-14
Filing date: 2022-05-16
Publication date: 2023-02-08
Also published as: GB202207132D0

Abstract

A hydro-pneumatic suspension system 10 and a method for an off-road vehicle are provided. The suspension system 10 is operable with a hydraulic cylinder 50 defining a piston side 52 and a rod side 56 configured to receive fluid from a pump 12. The suspension system 10 comprises: a proportional rod control valve 26; a piston control valve 24; a pilot operated check valve 66; a blocking valve 60; and a controller 40 configured to control a stiffness of the suspension system to maintain a target natural frequency for the vehicle.

Description

SYSTEMS AND METHODS FOR A HYDRO-PNEUMATIC SUSPENSION AND

LEVELING CIRCUIT

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] The present application is based on, claims priority to, and incorporates herein by reference in its entirety, U.S. Provisional Patent Application No. 63/188,924, filed on May 14, 2021, and entitled "Hydro-Pneumatic Suspension Systems and Methods".

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] Not Applicable.

BACKGROUND

[0003] Off-highway machines typically include suspension systems.

BRIEF SUMMARY

[0004] Aspects of the present invention provide a hydro-pneumatic suspension system designed for off-highway vehicles with varying load. The systems and methods described herein provide an ability to vary the pressure in the rod-side of a hydraulic cylinder to greater control suspension system stiffness. In some non-limiting examples, a suspension system includes an electronically-controlled valve to control the pressure in the rod-side of the cylinder(s), in either open or closed loop control strategies. In some non-limiting examples, the suspension system controls suspension stiffness by varying rod-side pressures in response to axle load changes (e.g., piston-side pressure changes) to maintain a target natural frequency of the vehicle. This builds and improves on conventional systems and methods and adds improved functional capabilities and reduced component costs.

[0005] According to one aspect, the present disclosure provides a suspension system for an off-highway vehicle. The suspension system is operable with a hydraulic cylinder defining a piston side and a rod side, in which each of the piston side and the rod side are configured to receive a flow of fluid from a pump configured to draw fluid from a reservoir and furnish pressurized fluid to a pump outlet. The suspension system includes a proportional rod control valve in fluid -1 -communication with the pump outlet to selectively provide pressurized fluid to the rod side of the hydraulic cylinder along a rod supply conduit, a piston control valve in fluid communication with the pump outlet to selectively provide pressurized fluid to the piston side of the hydraulic cylinder along a piston supply conduit, a pilot operated check valve arranged along the rod supply conduit between the proportional rod control valve and the rod side, a blocking valve arranged along the piston supply conduit between the piston control valve and the piston side, a piston-side pressure sensor arranged along the piston supply conduit between the blocking valve and the piston side, and a controller configured to control a stiffness of the suspension system to maintain a-target natural frequency for the vehicle. The blocking valve is movable between an open position and a closed position. The controller is configured to monitor, with the piston-side pressure sensor, pressure in the piston side of the hydraulic cylinder, determine an output command to the proportional rod control valve based on a first predetermined relationship between a target rod-side pressure and a valve command and a second predetermined relationship between the target rod-side pressure and a piston-side pressure for the target natural frequency, and provide the output command to the proportional rod control valve to provide the target rod-side pressure to the rod side of the hydraulic cylinder.

[0006] According to one aspect, the present disclosure provides a method for adjusting a stiffness of a suspension system of an off-highway vehicle. The suspension system is operable with a hydraulic cylinder defining a piston side and a rod side. The method includes monitoring, with a piston-side pressure sensor in fluid communication with the piston side of the hydraulic cylinder, pressure in the piston side of the hydraulic cylinder, determining, with the controller, an output command to a proportional rod control valve configured to selectively provide pressurized fluid from a pump to the rod side of the hydraulic cylinder along a rod supply conduit. The output command is based on a first predetermined relationship between a target rod-side pressure and a valve command and a second predetermined relationship between the target rod-side pressure and a piston-side pressure for a target natural frequency. The method further includes providing the output command, with the controller, to the proportional rod control valve to provide the target rod-side pressure to the rod side of the hydraulic cylinder.

[0007] The foregoing and other aspects and advantages of the disclosure will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred configuration of -2 -the disclosure. Such configuration does not necessarily represent the full scope of the disclosure, however, and reference is made therefore to the claims and herein for interpreting the scope of the disclosure.

BRIEF DESCRIPTION OF DRAWINGS

100081 The invention will be better understood and features, aspects and advantages other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such detailed description makes reference to the following drawings.

100091 Fig. lA is a schematic illustration of a suspension system having a hydraulic control circuit according to one aspect of the present disclosure.

[0010] Fig. 1B is a schematic illustration of a controller for the suspension system of Fig. 1A.

100111 Fig. 2A is a schematic illustration of the hydraulic control circuit of Fig. lA including a pressure transducer in fluid communication with a piston-side of a hydraulic cylinder.

[0012] Fig. 2B is a schematic illustration of the hydraulic control circuit of Fig. 1A including a pressure transducer on a piston-side and a rod-side of a hydraulic cylinder.

[0013] Fig 3 is a schematic illustration of the hydraulic control circuit of Fig. 1A without a shuttle valve.

[0014] Fig 4 is a schematic illustration of the hydraulic control circuit of Fig. 3 with a first valve orifice arranged adjacent to a work port of a piston control valve.

100151 Fig. 5 is a schematic illustration of the hydraulic control circuit of Fig. 1A including a proportional control valve between a piston-side accumulator and a piston side of a cylinder.

100161 Fig. 6 is a schematic illustration of the hydraulic control circuit of Fig. lA including a proportional control valve between a piston-side accumulator and a piston-side of a cylinder and between a rod-side accumulator and a rod-side of the cylinder.

100171 Fig. 7 is a schematic illustration of the hydraulic control circuit of Fig. 1A operable [0018] Fig. 8 is a schematic illustration of suspension system having a hydraulic control circuit operable with two hydraulic cylinders connected to a common axle.

[0019] Fig. 9 is a graph illustrating a predetermined relationship between a valve command for a rod control valve and a target rod-side pressure. -3 -

[0020] Fig. 10 illustrates a diagram of an open loop control strategy according to an aspect of

the present disclosure.

[0021] Fig. 11 illustrates a relationship between natural frequency and axle load.

[0022] Fig. 12 illustrates a relationship between a target rod-side pressure and axle load.

[0023] Fig. 13 illustrates a relationship between a target rod-side pressure and a piston-side pressure for a range of axle loads.

[0024] Fig. 14 illustrates a relationship between a piston-side pressure and the valve command for the rod control valve [0025] Fig. 15 illustrates a diagram of a closed loop control strategy utilizing piston-side pressure feedback according to an aspect of the present disclosure.

[0026] Fig. 16 illustrates a diagram of a closed loop control strategy utilizing piston-side and rod-side pressure feedback according to an aspect of the present disclosure.

DETAILED DESCRIPTION

[0027] Before any aspect of the present disclosure are explained in detail, it is to be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The present disclosure is capable of other configurations and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted," -connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings.

[0028] As used herein, the term line" is synonymous with "conduit" or "hose" or "flow path." For example, hydraulic hoses can be replaced with hard lines, or other forms of fluid conduit, or configured as passageways within a manifold or valve block. As such, "line is intended to broadly encompass fluid passageways that provide fluid communication between one or more components arranged along the fluid passageway. As also used herein, the term "off-highway" vehicles is -4 -intended to broadly encompass many forms of vehicles configured for off-highway use. Non-limiting examples of off-highway vehicles can include, among others, tractors, loaders, sprayers, dump trucks, off-road trucks, cranes, material handling equipment, excavators, motor graders, back hoes, and other agricultural or construction-type vehicles. As also used herein, the term "about", "approximately", or equivalents thereof is used to refer to a range of values within 25% of a stated value (e.g., within about 10 seconds can refer to a range between 7.5 to 12.5 seconds).

[0029] The following discussion is presented to enable a person skilled in the art to make and use aspects of the present disclosure. Various modifications to the illustrated configurations will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other configurations and applications without departing from aspects of the present disclosure. Thus, aspects of the present disclosure are not intended to be limited to configurations shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected configurations and are not intended to limit the scope of the present disclosure. Skilled artisans will recognize the non-limiting examples provided herein have many useful alternatives and fall within the scope of the present disclosure.

[0030] In general, hydro-pneumatic suspension systems may include one or more cylinders (e.g., actuators) linking rigid elements between the vehicle's wheels and chassis, which are then connected to one or more hydro-pneumatic actuators (e.g., accumulators) that provide a suspension and/or leveling functionality. When the system sees a change in physical load (e.g. different implements being attached to front or rear of the tractor), the off-highway vehicle (e.g., an agricultural tractor) may sit higher or lower within the range of cylinder travel, as the volume of gas displaced by oil in the accumulator changes. For ideal suspension performance, the suspension system may include an ideal target position, mostly to avoid reaching the end stops in operation. As such, a suspension system may include an automatic leveling (raise or lower) functionality, following feedback from some form of position sensing arrangement.

[0031] In systems that are referred to as double-acting (e.g., including double-acting hydraulic cylinders), or hydraulically pre-loaded, there are separate hydraulic volumes for both the piston-side (e.g., head-side) and the rod-side (e.g., annulus-side) of the cylinder, each connected to separate accumulators. The pressure in the rod-side is controlled by the hydraulic system. The -5 -pressure in the piston-side is then governed by both the external force loading from the supported mass (e.g., the axle load), and the pressure in the rod-side. As the axle load changes, there is an effect on system performance, changing the overall stiffness of the suspension system by causing changes in cylinder pressures. This can lead to undesirable effects, including, for example, changes in the natural frequency of the vehicle, which can lead to a change in the ride quality perceived by an operator of the vehicle. As used herein, the natural frequency of the vehicle is the frequency at which the vehicle (and suspension suspending the vehicle) oscillates when subjected to a non-continuous external force. These undesirable effects also persist even after the suspension system has corrected to raise or lower the suspension to the ideal target position, particularly in suspension systems with fixed or constant rod-side pressures.

[0032] It is therefore desirable to have an ability to adjust the rod-side pressure to alter suspension stiffness. As described herein, adjusting rod-side pressures can be done by operator preference, or as an automated control system using open or closed loop control strategies, to alter the rod-side pressure based on the system loads (e.g., axle loads or piston-side pressures). The present disclosure provides a double-acting suspension system configured to vary the rod-side pressure, which can be provided by electronic control, to maintain a target natural frequency for the vehicle across a broad range of axle loads. In some aspects, the suspension system can be configured to vary the rod side pressure to maintain a constant target natural frequency for the vehicle across a broad range of axle loads. Such a simplified double acting suspension system may be particularly applicable in off-highway vehicles where axle loads can vary dramatically during operation based on attached implements, or the weight of a load being supported by an implement (e.g., a full bucket, a pallet/bail supported by a set of forks, etc.).

[0033] Fig. I A illustrates a non-limiting example of a suspension system 10 for an off-highway vehicle. The illustrated suspension system 10 can include a hydraulic control circuit 20 operable with one or more hydraulic cylinders 50. In the illustrated example, the suspension system 10 is in the form of a hydro-pneumatic, double-acting, suspension system configured to provide open and closed loop control on rod-side pressures of a hydraulic cylinder 50 by a controller 40. The hydraulic cylinder can be coupled between rigid elements that are coupled between the wheels and chassis of a vehicle.

[0034] In general, the suspension system 10 can be operable with a hydraulic system capable of load sensing operation, either via a load sensing pump, as illustrated in Fig. 1A, or a load sensing -6 -unloader/compensator arrangement. The suspension system 10 illustrated in Fig. IA includes a pump 12 having a pump outlet 14. The pump 12 can be configured to draw fluid, such as oil, from a reservoir 16 (e.g., tank) and furnish the fluid under increased pressure at the pump outlet 14. In the illustrated non-limiting example, the pump 12 is configured as a pressure compensated variable displacement pump. The pressure of the fluid provided at the pump outlet 14 can be responsive to a pressure signal at a load sense port 18. The pump 12 can be configured to maintain the pressure at the pump outlet 14 to be a constant differential, known as rated margin pressure, above the pressure sensed at the load sense port 18. The pump 12 can increase or decrease its displacement in order to maintain the rated margin pressure between the pump outlet 14 and the load sense port 18. In other non-limiting examples the pump 12 can be configured as a fixed displacement pump and a bypass compensator (not shown) may be integrated into the suspension system 10 to maintain the pressure at the pump outlet 14 at a constant differential above the load sense pressure.

[0035] The pump outlet 14 can be in fluid communication with a supply conduit 22. The supply conduit 22 can be in fluid communication with the hydraulic control circuit 20 to furnish pressurized fluid thereto. The hydraulic control circuit 20 can include a piston control valve 24 and a rod control valve 26. The illustrated piston control valve 24 and the rod control valve 26 can be in the form of 2 position, 3-way valves. In the illustrated example, the rod control valve 26 is configured as a proportional electronic pressure reducing valve.

[0036] The piston control valve 24 can include a piston inlet port 28, an piston outlet port 30, and a piston work port 32. The piston inlet port 28 can be in fluid communication with the supply conduit 22 to receive pressurized fluid from the pump 12, and the piston outlet port 30 can be in fluid communication with the reservoir 16. The piston control valve 24 can be moveable, in an on/off manner, between a first position where fluid communication is provided between the piston inlet port 28 and the piston work port 32, and a second position where fluid communication is provided between the piston work port 32 and the piston outlet port 30. The illustrated piston control valve 24 can be biased into the second position by a spring (e.g., normally or de energized in the second position), and may be moveable between the first position and the second position by a solenoid 34. The solenoid 34 can be in electrical communication with the controller 40. The controller 40 can be configured to selectively command the solenoid 34 to actuate the piston control valve 24 between the first position and the second position. -7 -

100371 The rod control valve 26 can include a rod inlet port 38, a rod outlet port 42, and a rod work port 44. The rod inlet port 38 can be in fluid communication with the supply conduit 22 to receive pressurized fluid from the pump 12, and the rod outlet port 42 can be in fluid communication with the reservoir 16. In the illustrated example, the rod control valve 26 is configured as a proportional electronic pressure reducing valve. As such, the rod control valve 26 can be proportionally controlled between a first position where fluid communication is provided between the rod inlet port 38 and the rod work port 44, a second position where fluid communication is provided between the rod work port 44 and the rod outlet port 42, and an infinite number of intermediate positions between the first position and the second position to vary the rod-side pressure between a maximum pressure setting and a minimum pressure setting, and any pressure setting between the maximum and minimum pressure settings. The illustrated rod control valve 26 can be biased into the second position by a spring (e.g., normally or de-energized in the second position), and may be moveable between the first position, the second position, and a plurality of intermediate positions by a solenoid 46. The solenoid 46 can be in electrical communication with the controller 40.

100381 The rod control valve 26 is configured such that, given that the pressure at the rod inlet port 38 is sufficient, the output pressure at the rod work port 44 is proportional to the force generated by solenoid 46. The output force of the solenoid 46 is also proportional to the command (e.g., current) supplied by the controller 40. In the illustrated non-limiting example, the proportional relationship between the output pressure and the force applied by the solenoid can be governed by a diameter of a sensing element with the rod control valve 26. In operation, the position of the rod control valve 26 can be controlled by a balance of the force generated by the solenoid 46 applied to one end of a spool (or sensing element) against a force of the pressure at the rod work port 44 applied to the opposite end of the spool. In the illustrated non-limiting example, the spring biasing the spool is a low-rate, low force biasing spring that ensures the rod control valve 26 is in the second position on system start up (e.g., when no solenoid force is present, and no when pressure force is present). If the pressure force (plus the biasing spring force) is lower than the solenoid force, the rod control valve 26 will move towards the first position, and if the pressure force (plus the biasing spring force) is higher than the solenoid force, then the rod control valve 26 will move towards the second position. As will be described in greater detail below, the controller 40 can be configured to selectively command the solenoid 46 to actuate the rod control -8 -valve 26 between the first position and the second position, and the plurality of intermediate positions to achieve a desired target rod-side pressure.

[0039] With continued reference to Fig. 1A, the piston work port 32 of the piston control valve 24 can be in fluid communication with a piston side 52 of the hydraulic cylinder 50 via a piston supply conduit 54. In the illustrated example, the hydraulic control circuit 20 can include a blocking valve 60 arranged on the piston supply conduit 54 between the piston control valve 24 and a piston-side port 62 of the hydraulic cylinder 50. The illustrated blocking valve 60 can be configured as a solenoid-operated electro-hydraulic onloff valve (e.g., shutoff valve) that is movable between an open position and a closed position by a solenoid 64. The solenoid 64 can be in electrical communication with the controller 40. The controller 40 can be configured to selectively command the solenoid 64 to actuate the blocking valve 60 between the open position and the closed position. In this specific non-limiting example, the blocking valve 60 is a two-way, two-position valve. In other non-limiting examples, the blocking valve 60 can be configured as a proportional valve.

[0040] When the blocking valve 60 in the open position, the blocking valve 60 can provide fluid communication between the pump 12 or the reservoir 16, dependent on a position of the piston control valve 24, to the piston side 52 of the hydraulic cylinder 50 to, respectively, provide pressurized fluid to, or vent fluid from, the piston side 52 of the hydraulic cylinder 50. When the blocking valve 60 is in the closed position, the blocking valve 60 inhibits fluid communication along the piston supply conduit 54. That is, when the blocking valve 60 is in the closed position, the pump 12 cannot furnish pressurized fluid to, nor can fluid be vented from, the piston side 52 of the hydraulic cylinder (with the exception of relieving excess pressure via a relief valve). In the illustrated example, the blocking valve 60 can be biased into the closed position by a spring (e.g., normally or de-energized in the closed position).

[0041] Referring still to Fig. 1A, the rod work port 44 of the rod control valve 26 can be in fluid communication with a rod side 56 of the hydraulic cylinder 50 via a rod supply conduit 58. In the illustrated example, the hydraulic control circuit 20 can include a rod pilot operated check valve 66 arranged on the rod supply conduit 58 between the rod control valve 26 and a rod-side port 68 of the hydraulic cylinder 50. The rod pilot operated check valve 66 can lift off its seat to provide fluid communication therethrough by a pressure difference in a forward direction across the rod pilot operated check valve 66 (e.g., a direction towards the rod side 56 of the hydraulic -9 -cylinder 50). That is, a pressure differential across the rod pilot operated check valve 66 in a direction from the rod work port 44 toward the rod-side port 68 can force the rod pilot operated check valve 66 off its seat. Additionally, the rod pilot operated check valve 66 can be lifted off its seat to provide fluid communication therethrouQh by a rod pilot signal sensed by a pilot line 70. The pilot line 70 can sense a pressure at the piston work port 32 on the piston supply conduit 54. The use and design of pilot operated check valves (i.e., the rod pilot operated check valve 66) can provide superior leakage protection as the suspension system I 0 is holding the load acting on the hydraulic cylinder 50. That is, unless the rod pilot operated check valve 66 is forced open via a pressure differential or a pilot signal, the valve is mechanically forced closed to prevent fluid flow therethrough.

[0042] In the illustrated example, the hydraulic control circuit 20 can include a first piston control orifice 72 arranged on the supply conduit 22 between the pump outlet 14 of the pump 12 and the piston inlet port 28 of the piston control valve 24. A second piston control orifice 74 can be arranged on the piston supply conduit 54 between the piston work port 32 of the piston control valve 24 and the blocking valve 60. In the illustrated non-limiting example, the second piston control orifice is arranged between the blocking valve 60 and a connection between the piston supply conduit 54 and the pilot line 70. In some non-limiting examples, the first and second piston control orifices 72, 74 may be fixed orifices. In other non-limiting examples, the first and second piston control orifices 72, 74 may be bi-directional orifices. That is, the first piston control orifice 72 and/or the second piston control orifice 74 may be configured to provide a different effective flow area when fluid passes in one direction relative to another direction. In some non-limiting examples, the first and second piston control orifices 72, 74 may be variable orifices where an effective flow area may be varied, for example, via electrical communication with the controller 40. In some non-limiting examples, the first piston control orifice 72 may be integrated into the piston control valve 24. In this non-limiting example, the piston control valve 24 may include multiple orifices arranged therein to provide alternative restrictions for fluid flowing toward the hydraulic cylinder 50 and for fluid flowing from the hydraulic cylinder 50. For example, the piston control valve 24 may include one control orifice arranged between the piston inlet port 28 and the piston work port 32 in the first position and another control orifice arranged between the piston work port 32 and the piston outlet port 30 in the second position. In some non-limiting examples, the second piston control orifice 74 may be integrated into the blocking valve 60. -10-

[0043] A pressure relief valve 76 can be connected to the piston supply conduit 54 via a piston relief check valve 78 at a location between the blocking valve 60 and the piston-side port 62 of the hydraulic cylinder 50. The pressure relief valve 76 can also be connected to the rod supply conduit 58 via a rod relief check valve 80 at a location between the rod pilot operated check valve 66 and the rod-side port 68 of the hydraulic cylinder 50. An outlet 82 of the pressure relief valve 76 can be in fluid communication with the reservoir 16. A manual override valve 84 can be configured to provide a bypass around the pressure relief valve 76 to allow the hydraulic control circuit 20 to be manually relieved to the reservoir 16, for example, during servicing or calibration. The pressure relief valve 76 can be configured to provide fluid communication between the piston supply conduit 54 and/or the rod supply conduit 58 and the reservoir 16 to relieve the system pressure at a predetermined pressure setpoint to prevent excessive pressures within the suspension system 10.

[0044] By fluidly connecting both the piston and rod supply conduits 54 and 58 to the pressure relief valve 76, the hydraulic control circuit 20 can provide protection from excess pressures in both the piston side 52 and the rod side 56 of the hydraulic cylinder 50. In addition, the design of the hydraulic control circuit 20 (e.g., the functionality of the rod pilot operated check valve 66, blocking valve 60, and the pressure relief valve 76) provides a mechanism to relieve pressure in the hydraulic cylinder 50 to the reservoir 16 in the event of an electrical malfunction. For example, in the event of an electrical malfunction where electrical power is lost, the piston control valve 24 will be biased into the second position to connect a portion of the piston supply conduit 54, between the blocking valve 60 and the piston control valve 24, to the reservoir 16. This will reduce the pressure in the pilot line 70 to allow the rod pilot operated check valve 66 to be forced against the seat to block fluid from escaping from the rod side 56 of the hydraulic cylinder 50. In addition, the blocking valve 60 will be biased into the closed position to block fluid from escaping from the piston side 52 of the hydraulic cylinder 50. In that way, the suspension system 10 can continue to provide appropriate suspension functionality, while also allowing the system to vent excess pressures through the pressure relief valve 76. It should be appreciated that, in other non-limiting examples, the hydraulic control circuit 20 may include two separate pressure relief valves to independently relieve the pressure in the piston side 52 to the reservoir 16 and to relieve the pressure in the rod side 56 to the reservoir 16.

[0045] In the illustrated example of Fig. 1, the suspension system 10 can include a piston accumulator 86 connected to the piston supply conduit 54 adjacent to the piston side 52 of the hydraulic cylinder 50. The suspension system 10 can also include a rod accumulator 88 connected to the rod supply conduit 58 adjacent to the rod side 56 of the hydraulic cylinder 50. The piston accumulator 86 and the rod accumulator 88 may be in the form of a hydro-pneumatic accumulators, which are pre-pressurized (e.g., pre-charged) to a desired, predetermined pressure level with a gas (e.g., air, nitrogen gas, etc.). The gas within the piston accumulator 86 and the rod accumulator 88 may be compressed and decompressed by fluid flowing into and out of the piston and rod accumulators 86 and 88 as a load acting on the hydraulic cylinder 50 varies. The compression and decompression of the gas within the piston accumulator 86 and rod accumulator 88 can act as a spring with a rising rate on the piston side 52 and the rod side 56 of the hydraulic cylinder 50, respectively. In this way, the piston and rod accumulators 86 and 88 can provide suspension for the hydraulic cylinder 50 and the components coupled thereto. A stiffness of the suspension provided by the suspension system 10 may be correlated to the pressures within the piston and rod accumulators 86 and 88. For example, the pressures of the piston and rod accumulators 86 and 88 can change the effective spring rate of the suspension system.

[0046] As described above, the pump 12 can be configured to maintain a rated margin pressure between the pump outlet 14 and the load sense port 18. The pressure at the load sense port 18 can be sensed by a load sense line 90. The load sense line 90 can include a shuttle valve 92 arranged thereon. The shuttle valve 92 can be in fluid communication with the piston supply conduit 54 at a location between the second piston control orifice 74 and the piston control valve 24, and can be in fluid communication with the rod supply conduit 58 at a location between the rod pilot operated check valve 66 and the rod control valve 26. The shuttle valve 92 can be configured to communicate the greater of the pressure sensed from the piston supply conduit 54 and the pressure sensed from the rod supply conduit 58 to the load sense line 90 and thereby to the load sense port 18. That is, by communicating a pressure between the second piston control orifice 74 and the piston control valve 24 or a pressure between the rod pilot operated check valve 66 and the rod control valve 26 to the load sense port 18, the pressure drop between the pump outlet 14 and the second piston control orifice 74, or between the pump outlet 14 and the rod pilot operated check valve 66 can be approximately equal to the rated margin pressure, depending on whether the pressure is higher in the piston supply conduit 54 or the rod supply conduit 58 [0047] According to some non-limiting examples, the suspension system 10 can include one or more position sensors 94 that can be arranged to measure a ride height (e.g., the amount of -12 -extension or retraction of the hydraulic cylinder 50) of an off-highway vehicle on which the suspension system 10 is in use. For example, the position sensor 94 can be configured to measure a position of an axle of the off-highway vehicle relative to a chassis of the off-highway vehicle. In addition to the ride height, the position sensor 94 may provide data that can be correlated to a stiffness of the suspension system 10. For example, the data from the position sensor 94 as a function of time may enable the calculation of a frequency at which the suspension (i.e., the hydraulic cylinder 50) is oscillating. The stiffness of the suspension may be inferred from the frequency at which the suspension is oscillating,. Alternatively or additionally, the frequency of oscillation, which can provide the stiffness of the suspension system 10, may be inferred from an accelerometer (not shown). The accelerometer (not shown) may be coupled to a piston of the hydraulic cylinder 50 or a mechanism associated with a suspension linkage.

[0048] The position sensor 94 can be in electrical communication with the controller 40. It should be appreciated that various arrangements for the position sensor 94 are possible so long as the relative position of the axle relative to the chassis on the off-highway vehicle can be measured and transmitted to the controller 40. The illustrated position sensor 94 can be coupled to the hydraulic cylinder 50. It should be appreciated that the position sensor 94 can be arranged anywhere on a structure or linkage that can displace in proportion to the relative position, for example, between a chassis and an axle on an off-highway vehicle. That is, in other non-limiting examples, the position sensor 94 may be arranged on a mechanism associated with a suspension linkage, which is coupled to the hydraulic cylinder 50.

[0049] Referring now to Figs. I A and I B, the suspension system 10 can include a controller 40. The controller 40 can be in electrical communication with the piston control valve 24, the rod control valve 26, the blocking valve 60, and the position sensor 94. The controller 40 may be configured to receive feedback signals from the position sensor 94 (or various other sensors, including the pressure sensors of Figs. 2A and 2B) and send command signals to control the positions of the piston control valve 24, the rod control valve 26, and the blocking valve 60. In one non-limiting example, the controller 40 can send command signals to the rod control valve 26 (e.g., to vary a supplied electrical current to solenoid 46) to affect a position of a spool received therein to adjust the pressure in the rod side 56 of the hydraulic cylinder 50. In the illustrated non-limiting example, the controller 40 can be configured to receive an input from an operator input device 100. In one non-limiting example, the operator input device 100 may be in the form of a -13 -position of a control lever, a switch, a control knob, a button, or other form of input actuatable by an operator (e.g., on a control panel within a cabin of the vehicle). The operator input device 100 can be in electrical communication with the controller 40 such that a command given by the operator can be received by the controller 40 as an input signal.

[0050] Referring now to Fig. 1B, the controller 40 may be a microcomputer-based device that includes a processor 102, which executes instructions of a suspension control program, to be described herein, and memory 104 for storing the executable instructions and data (e.g., look-up tables, performance parameters, vehicle geometries, etc.) for the suspension control program. In some non-limiting examples, the memory 104 may store a lookup table or function. In some non-limiting examples, the function can relate axle load to natural frequency, axle load to rod-side pressures, rod-side pressures to piston-side pressures, rod-side pressures to valve commands (e.g., current levels), and/or piston-side pressures to valve commands. The foregoing functions may be derived from vehicle geometry data and valve performance characteristics loaded or stored on the memory 104. Alternatively, the foregoing functions may be derived from a calibration procedure or algorithm based on executable instructions stored on the memory 104 and carried out by the processor 102. As will be described, the controller 40 may use the functions to adjust commands or inputs to the rod control valve 26 to adjust a pressure in the rod side 56 of the hydraulic cylinder 50, and in some cases, to maintain a target natural frequency across a range of axle loads.

[0051] The following description illustrates various arrangements or modifications to the suspension system 10 and the hydraulic control circuit 20 of Fig. IA. It is to be understood that, unless otherwise shown or described, the following suspension systems function in a substantially similar way. It is also to be understood that aspects of the following suspension systems can be combined or shared, and each possible combination of features are expressly contemplated. As one non-limiting example, one or more pressure sensors could be included in each of the following suspension systems.

[0052] Figs. 2A and 2B illustrate suspension systems 1000, 1100 that are substantially similar to the suspension system 10 of Fig. 1A, with the exception of including one or more pressure sensors in communication with the controller 40. In Figs. 2A and 2B, elements that are similar to those of Fig. 1A are labeled with like reference numbers. As such, only aspects that differ from those of Fig. IA will be described in the following paragraphs.

-14 - [0053] As illustrated in Fig. 2A, the suspension system 1000 can include a hydraulic control circuit 2000 including a piston pressure sensor 106 arranged to measure a pressure in the piston side 52 of the hydraulic cylinder 50. It should be appreciated that the location of the piston pressure sensor 106 in Fig. 2A is not meant to be limiting in any way, and, in other non-limiting examples, the piston pressure sensor 106 can be arranged in any location capable of measuring the pressure within the piston side 52 of the hydraulic cylinder 50. The piston pressure sensor 106 can be in electrical communication with the controller 40.

[0054] As illustrated in Fig. 2B, in addition to the piston pressure sensor 106 described above, the suspension system 1100 can include a hydraulic control circuit 2 100 including a rod pressure sensor 108 arranged to measure a pressure in the rod side 56 of the hydraulic cylinder 50. It should be appreciated that the location of the rod pressure sensor 108 in Fig. 2B is not meant to be limiting in any way, and, in other non-limiting examples, the rod pressure sensor 108 can be arranged in any location capable of measuring the pressure within the rod side 56 of the hydraulic cylinder 50. The rod pressure sensor 108 can be in electrical communication with the controller 40.

[0055] Figs. 3 and 4 illustrate suspension systems 1200, 1300 that are substantially similar to the suspension system 10 of Fig. 1A, with the exception of not including a shuttle valve arranged between the rod-side and piston-side supply conduits 54, 58. In Figs. 3 and 4, elements that are similar to those of Fig. IA are labeled with like reference numbers. As such, only aspects that differ from those of Fig. IA will be described in the following paragraphs.

[0056] In general, the suspension system 1200 of Fig. 3 includes a hydraulic control circuit 2200 that operates based on driving the load sensing pump 12 with pressure from the piston-side supply conduit 54. That is, due to the size of the first and second piston control orifices 72, 74, and the axle load acting on the hydraulic cylinder 50, the pressures in the piston-side supply conduit 54 may always be greater than the pressures in the rod supply conduit 58, thereby allowing the pressures from the piston-side supply conduit 54 to act on the load sense port 18 of the pump 12. In the illustrated example, the pilot line 70 operating the rod pilot operated check valve 66 is in fluid communication with the piston-side supply conduit 54 via the load sense line 90.

[0057] Turning now to Fig. 4, the suspension system 1300 includes a hydraulic control circuit 2300 that operates similar to that of the suspension system 1200 of Fig. 3, with the exception that the first piston control orifice 72 is moved to the piston work port 32 side of the piston control valve 24 (e.g., a side of the piston control valve 24 that is closer to the hydraulic cylinder 50). This -15 -may allow, for example, a different orifice sizing to balance the pump command, a speed at which the suspension is lowered, and pressure amplifications/fluctuations, and may provide an improved performance on different vehicles.

[0058] Figs. 5 and 6 illustrate suspension systems 1400, 1500 that are substantially similar to the suspension system 10 of Fig. IA, with the exception of including one or more control valves to selectively inhibit fluid flow to a respective accumulator. In Figs. 5 and 6, elements that are similar to those of Fig. IA are labeled with like reference numbers. As such, only aspects that differ from those of Fig. IA will be described in the following paragraphs.

[0059] Turning to Fig. 5, the suspension system 1400 includes a hydraulic control circuit 2400 including a piston accumulator control valve 110 to provide alternative damping/lockout functionality. In the illustrated example, the piston accumulator control valve 110 is configured as a bi-directional proportional valve. The piston accumulator control valve 110 can be selectively moveable (e.g., by a solenoid 112 in communication with the controller 40) between an open position and a closed position, and an infinite number of positions between the open position and the closed position. In the open position, the piston accumulator control valve 110 can provide fluid communication from the piston accumulator 86 to the piston supply conduit 54, which allows for full unrestricted movement of the hydraulic cylinder 50. In the closed position, the piston accumulator control valve 110 inhibits fluid communication between the piston accumulator 86 and the piston supply conduit 54 to isolate the piston accumulator 86 from the hydraulic control circuit 2400, which holds the suspension rigid (e.g., fixes the fluid volume in the piston side 52 of the hydraulic cylinder 50). The piston accumulator control valve 110, in an intermediate position, can therefore vary the amount of flow or pressure drop between the piston supply conduit 54 and the piston accumulator 86. When the piston accumulator control valve 110 is in an intermediate position, the piston accumulator control valve 110 can provide proportional or fast responding damping that can be adjustable based on the magnitude of command (e.g., current) from the controller 40. According to some non-limiting examples, the rod-side pressure may be increased to overcome the mass of the axle to avoid cavitation. In the illustrated example, the piston accumulator control valve 110 can be biased in the closed position by a spring (e.g., normally or de-energized in the closed position) [0060] Turning now to Fig. 6, in addition to the piston accumulator control valve 110 described above, the suspension system 1500 includes a hydraulic control circuit 2500 including a rod -16-accumulator control valve 114. In the illustrated example, the rod accumulator control valve 114 is configured as a bi-directional proportional valve. The rod accumulator control valve 114 can be selectively moveable (e.g., by a solenoid 116 in communication with the controller 40) between an open position and a closed position, and an infinite number of positions between the open position and the closed position. In the open position, the rod accumulator control valve 114 can provide fluid communication from the rod accumulator 88 to the rod supply conduit 58, which allows for full unrestricted movement of the hydraulic cylinder 50. In the closed position, the rod accumulator control valve 114 inhibits fluid communication between the rod accumulator 88 and the rod supply conduit 58 to isolate the rod accumulator 88 from the hydraulic control circuit 2500, which holds the suspension rigid (e.g., fixes the fluid volume in the rod side 56 of the hydraulic cylinder 50). The rod accumulator control valve 114, in an intermediate position, can therefore vary the amount of flow or pressure drop between the rod supply conduit 58 and the rod accumulator 88. When the piston accumulator control valve 110 is in an intermediate position, the piston accumulator control valve 110 can provide proportional or fast responding damping that can be adjustable based on the magnitude of command (e.g., current) from the controller 40. In the illustrated example, the rod accumulator control valve 114 can be biased in the closed position by a spring (e.g., normally or de-energized in the closed position). In some non-limiting examples, the configuration of Fig. 6 may not include the piston accumulator control valve 110.

[0061] Figs. 7 and 8 illustrate suspension systems 1600, 1700 that are substantially similar to the suspension system 10 of Fig. IA, with the exception of including multiple hydraulic cylinders. In Figs. 7 and 8, elements that are similar to those of Fig. IA are labeled with like reference numbers. As such, only aspects that differ from those of Fig. I A will be described in the following paragraphs.

[0062] Turning to Fig. 7, the suspension system 1600 includes a hydraulic control circuit 2600 operable with first and second hydraulic cylinders 50a, 50b arranged in parallel. In the illustrated configuration, each of the first and second hydraulic cylinders 50a, 50b operate together, without independent control. In Fig. 8, the suspension system 1700 includes a hydraulic control circuit 2700 operable with independently controllable first and second hydraulic cylinders 50a, 50b. This configuration illustrates functionality with two cylinders connected to the same axle, with a need for independent levelling (e.g., each cylinder can raise/lower independently due to each cylinder having a respective blocking valve 60a, 60b), but common stiffness settings (e.g., a single rod -17-control valve 26 controlling the rod sides 56a, 56b of the first and second hydraulic cylinders 50a, 50b). In the illustrated example, the piston work port 32 of the piston control valve 24 is in fluid communication with a first piston supply conduit 54a and a second piston supply conduit 54b arranged in parallel with the first piston supply conduit 54a.

[0063] The independent leveling control, the modes of which are described in detail below, is provided by each of the first and second cylinders 50a, 50b including a respective piston accumulator 86a, 86b, blocking valve 60a, 60b, and second piston control orifice 74a, 74b arranged along the parallel first and second piston supply conduits 54a, 54b. Due to the independent blocking valves 60a, 60b, the first and second cylinders 50a, 50b can be extended or retracted either together or independently under the control of the controller 40. In the illustrated configuration, rod-side pressures are considered as a common volume on both cylinders, and the rod side 56a of the first hydraulic cylinder 50a and the rod side Sob of the second hydraulic cylinder 50b are connected to a common rod supply conduit 58, and thereby controllable with a common rod control valve 26 to vary the rod-side pressures acting on both rod sides 56a, 56b of the hydraulic cylinder 50. To protect from over-pressurization, each of the first and second piston supply conduits 54a, 54b can be in communication with the pressure relief valve 76 via a respective piston relief check valve 78a, 78b.

[0064] The suspension systems described above (e.g., suspension systems 10, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700) may include one or more operational modes executable by the controller 40, including raising the suspension when the suspension position is below a predetermined target position, lowering the suspension when the suspension position is above the predetermined target position, increasing the rod-side pressure (e.g., increase the suspension stiffness), and/or decreasing the rod-side pressure (e.g., reduce the suspension stiffness). According to some aspects, as will be described, the suspension system can operate to adjust the rod-side pressure to maintain a target natural frequency of the vehicle across a range of axle loads. In the control modes described herein, it is to be understood that the methods described below can be implemented into anyone of the suspension systems described herein (e.g., suspension systems 10, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700), unless otherwise described.

[0065] Referring to Figs. 1A and 9, one aspect used in each of the control modes listed above is the utilization of the rod control valve 26, which is configured as an electronically-controlled proportional pressure reducing valve, to control the rod-side pressures. The use of a proportional -18-pressure reducing valve to control rod-side pressures allows the controller 40 to provide a valve command (e.g., current) to the rod control valve 26 and correlate that valve command to a known pressure output. That is, as best illustrated in Fig. 9, the rod control valve 26 can define a known performance characteristic that can be stored (e.g., in the memory) on the controller 40. The performance characteristic can define a first predetermined relationship between a magnitude of current supplied to the solenoid 46 of the rod control valve 26 and the rod-side pressures (e.g., the pressure present in the rod supply conduit 58). As such, if a desired target rod-side pressure is needed, the controller can determine the required current magnitude to supply to the solenoid 46 of the rod control valve 26 to achieve that target rod-side pressure.

[0066] In general, the solenoid 46 may provide an output force to a spool of the rod control valve 26 that is proportional to a magnitude of a current supplied (e.g., from the controller 40) to the solenoid 46. As such, the proportional rod control valve 26 differs, for example, from bi-stable or on-off solenoid valves in that it can provide an infinite amount of output forces that is only limited by the resolution in current magnitude control provided by the controller 40. In the illustrated non-limiting example, the magnitude of current supplied to the solenoid 46 of the rod control valve 26 is linearly proportional to the target rod-side pressures.

[0067] Referring still to Fig. IA, the controller 40 can be configured to operate the suspension system 10 in a raise mode. For example, the controller 40 can monitor the position of the hydraulic cylinder (e.g., by position sensor 94), and the controller 40 can control the hydraulic control circuit 20 to raise the suspension when the position is below a predetermined target position sensed by the position sensor 94. In general, to raise the suspension, the piston control valve 24 can be commanded to the first position and the blocking valve 60 may be commanded to the open position to provide pressure to the piston side 52 of the hydraulic cylinder 50. At the same time, the rod control valve 26 can be given a valve command to provide a target rod-side pressure. When the pressure in the piston side 52 of the hydraulic cylinder is sufficient to overcome the axle load and the rod-side pressure, the suspension will raise and excess fluid from the rod side 56 of the hydraulic cylinder 50 will be vented to the reservoir 16 through the rod control valve 26. When the desired suspension height is reached, the controller 40 may de-energize the piston control valve 24, the blocking valve 60, and the rod control valve 26.

100681 According to one specific non-limiting example, the raising process may begin by the controller 40 initially commanding the piston control valve 24 to the first position and -19-simultaneously commanding the blocking valve 60 to the open position, such that fluid pressure from the pump 12 can be provided to the piston supply conduit 54. Next, the controller 40 can provide a valve command to the rod control valve 26, either subsequently or simultaneously, to provide a target rode-side pressure based on the predetermined proportional relationship between the valve command and rod-side pressure (see Fig. 9). Fluid pressure from the pump 12 can therefore be provided to the rod supply conduit 58. The greater of the pressures from the piston supply conduit 54 and the rod supply conduit 58 will be communicated, via the shuttle valve 92, to the load sense line 90. The pressure in the load sense line 90 will be communicated to the load sense port 18 on the pump 12 to maintain a predetermined pressure difference above the pressure in the load sense line 90. In the illustrated non-limiting example, flow from the pump 12 may be governed based on size of the first piston control orifice 72, when pressure in the piston supply conduit 54 is greater than the pressure in the rod supply conduit 58.

[0069] In operation, for example, when a rod-side pressure is high and the axle load is low, it may be that pressure in the rod supply conduit 58 is greater than the pressure in the piston supply conduit 54. In these cases, flow rate from the pump 12, and so the speed at which the suspension is being raised, may be higher than desired. Flow from the pump 12 may then pass through the second piston control orifice 74, the blocking valve 60, into piston side 52 of the hydraulic cylinder 50, and into the piston accumulator 86. Once the pressure in the piston side 52 of the hydraulic cylinder 50 is sufficient to overcome the axle load, the hydraulic cylinder 50 will extend, thereby increasing the suspension height. Fluid is then driven from the rod side 56 of the hydraulic cylinder 50 to the rod pilot operated check valve 66, which is held open from the pilot pressure in the pilot line 70 communicating pressure within the piston supply conduit, through the rod control valve 26 to the reservoir 16. The pressure in the rod supply conduit 58 is then governed by the valve command supplied to the rod control valve 26 (e.g., by the controller 40) automatically during the raise cycle to maintain a target rod-side pressure, which will then also drive the pressure in the rod supply conduit 58, the rod side 56 of the hydraulic cylinder 50, and the rod accumulator 88. The rod-side pressure, if desired, can be increased or decreased during the raise cycle, for example, by adjusting the valve command supplied to the rod control valve 26 (see Fig. 9). According to some examples, the second piston control orifice 74 is sized to ensure that sufficient pressure is raised within the piston supply conduit 54 to open the rod pilot operated check valve 66, in the event that -20 -load-induced pressure spikes in the piston side 52 of the hydraulic cylinder 50 is lower than the target rod-side pressure.

[0070] Referring still to Fig. 1A, the controller 40 can be configured to operate the suspension system 10 in a lower mode. For example, the controller 40 can monitor the position of the hydraulic cylinder (e.g., by position sensor 94), and the controller 40 can control the hydraulic control circuit 20 to lower the suspension when the position is above a predetermined target position sensed by the position sensor 94. In general, to lower the suspension, the piston control valve 24 can remain in the second position and the blocking valve 60 may be commanded to the open position to provide fluid communication between the piston side 52 of the hydraulic cylinder 50 and the reservoir 16. At the same time, the rod control valve 26 can be given a valve command to provide a target rod-side pressure. The pressure in the rod side 56 of the hydraulic cylinder 50 overcomes the piston-side pressure, and the suspension will lower and excess fluid from the piston side 52 of the hydraulic cylinder 50 will be vented to the reservoir 16 through the piston control valve 24. When the desired suspension height is reached, the controller 40 may de-energize the blocking valve 60 and the rod control valve 26.

[0071] According to one specific non-limiting example, the lowering process may begin by the controller 40 commanding the blocking valve to the open position, and the controller 40 can provide a valve command to the rod control valve 26, either subsequently or simultaneously, to provide a target rod-side pressure based on the predetermine proportional relationship between the valve command and rod-side pressure (see Fig. 9). By placing the blocking valve 60 in the open position, the piston side 52 of the hydraulic cylinder 50 may now be connected to the reservoir 16. The second piston control orifice 74 may govern the flow rate in the lower direction, which will increase with axle load. As the fluid drains from piston side 52 of the hydraulic cylinder 50, the hydraulic cylinder 50 will retract, increasing the volume of the rod side 56 of the hydraulic cylinder 50. The rod side 56 is then backfilled by fluid from the pump 12 through the rod control valve 26 to maintain the target rod-side pressure.

[0072] As with the raise operation, the valve command provided to the rod control valve 26 governs the pressure in the rod side 56 of the hydraulic cylinder 50, and the rod-side pressures can be increased or decreased during the lower cycle In operation, for example, pump 12 can provide pressure to the piston supply conduit 54 through the piston control valve 24 and to the rod supply conduit 58 through the rod control valve 26. In this case, the piston control valve 24 is in the second -21 -position to vent the piston supply conduit 54 to the reservoir 16. Thus, the pressure in the rod supply conduit 58 is typically greater than the pressure in the piston supply conduit 54. Therefore pressure from the rod supply conduit can be communicated to the load sense line 90 via the shuttle valve 92. The pressure in the load sense line 90 may then drive the pump 12. The pressure from the pump 12 may then sit at a fixed margin above the pressure in the rod supply conduit 58, which is governed by the rod control valve 26. This may ensure that system pressure is only driven to what is required to drive to the target rod-side pressure.

[0073] The controller 40 can also be configured to operate the suspension system 10 in a stiffness adjustment mode. For example, the controller 40 can control the hydraulic control circuit 20 to selectively increase the rod-side pressure (e.g., increase the suspension stiffness) or decrease the rod-side pressure (e.g., reduce the suspension stiffness). In this mode, the controller 40 can provide a valve command (e.g., a predetermined target current) to the rod control valve 26 that correlates to a target rod-side pressure (see Fig. 9), command the piston control valve 24 to the first position, and maintain the blocking valve 60 to the closed position. With blocking valve 60 in the closed position, the volume of fluid in the piston side 52 of the hydraulic cylinder 50 is fixed. In general, fixing the volume of fluid in the piston side 52 of the hydraulic cylinder 50 fixes the position of the hydraulic cylinder 50 (e.g., the amount of extension/retraction). However, changes in the pressure in the rod side 56 of the hydraulic cylinder pressure may marginally adjust cylinder position, due to the pressure of the gas (and therefore the volume) in the piston accumulator 86 changing with varying rod-side pressures. With the blocking valve 60 in the closed position, the system pressure may drive to a maximum, due to the lack of fluid flow through the piston supply conduit 54 or the first piston control orifice 72, which can result in the pressure within the piston supply conduit 56 upstream of the blocking valve 60 and the load sense line 90 being equal. The system pressure can increase the pressure in the pilot line 70, which ensures that the rod pilot operated check valve 66 is shifted to an open position irrespective of the target rod-side pressure. The system pressure may also ensure that the rod control valve 26 will have sufficient pressure at the rod inlet port 38 to achieve any desired target rod-side pressure within the control range of the rod control valve 26. By providing the predetermined target current to the rod control valve 26, the pressure in the rod side 56 of the hydraulic cylinder 50 will increase to the correlating target rod-side pressure. When the adjustment is complete, the controller 40 will de-energize the piston control valve 24 and the rod control valve 26.

-22 - [0074] In some cases, as noted above, the position of the hydraulic cylinder 50 may change during rod-side pressure adjustments (e.g., stiffness adjustments). If, during this mode, the suspension position moves outside a predetermined position range (e.g., a tolerance around a target position), the controller 40 can switch into the raise or lower modes described above to adjust the position back to the desired target position. During these position adjustments, the rod control valve 26 can continues to be commanded by the controller 40 to maintain the desired target rod-side pressure, which can prevent iteration between stiffness and position adjustments.

[0075] The suspension systems 1200 and 1300 illustrated in Figs. 3 and 4 may operate differently than described above, as explained in the following paragraphs, due to the exclusion of the shuttle valve (e.g., shuttle valve 92, see Fig. 1A). Turning to Fig. 3 specifically, in general, the suspension system 1200 may operate based on driving the pump 12 with pressure only from the piston supply conduit 54. For example, in the raise mode, the first piston control orifice 72 commands pump flow vs. pressure differential in the load sensing pump arrangement to drive a set flow. This flow generates an increase in pressure as it passes through the second piston control orifice 74. As such, the pressure in the load sense line 90 and the pilot line 70 is significantly higher than pressure in the piston side 52 of the hydraulic cylinder 50 caused by the axle load. The second piston control orifice 74, can therefore be sized to ensure that, even with a minimum axle load, the pressure commanded by the pump I 2 is greater than a maximum target rod-side pressure, allowing for a full range of target rod-side pressure settings.

[0076] With continued reference to Fig. 3, in the lower mode, only blocking valve 60 is energized to the open position, and the rod pilot operated check valve 66 can remain closed. Therefore, the total volume of fluid in the rod side 56 of the hydraulic cylinder 50 remains constant. As the volume in the piston side 52 decreases as the cylinder retracts, the pressure in the piston side 52 will increase as the gas in the piston accumulator 86 is compressed. Typically, if the suspension position has risen above a nominal position, and requires a lower adjustment, that is generally because a reduction in axle load has occurred. The change in force balance on the hydraulic cylinder 50 can result in a required increase in pressure on the rod side 56 to balance the pressures in the piston and rod accumulators 86, 88. As such, height adjustments may be needed to adjust the suspension position back to the nominal position. Referring still to Fig. 3, in a stiffness adjustment mode, the stiffness adjustments can be carried out as described above with respect to Fig. 1A.

-23 - [0077] In all suspension system configurations, it may be desirable to re-adjust stiffness after adjusting the suspension position in the lower mode. In some non-limiting examples, a stiffness adjustment may also be used after fully lowering the suspension to end stops, to rigidly lock the suspension. In some non-limiting examples, to ensure cavitation does not occur due to the mass of the axle/wheels, it may be desirable to fully lower the suspension position and drain all pressure from the piston accumulator 86. In this case, a stiffness adjustment (e.g., a change in rod-side pressures) may be utilized to overcome any loading from this mass.

[0078] In all suspension system configurations, in general, the proportionality of the rod control valve 26 includes characteristics to provide predictable pressure output vs. current input (see Fig. 9). The suspension system may accordingly be operated to adjust suspension stiffness (e.g., rod-side pressures) in an open loop mode, a closed loop mode utilizing piston-side pressure feedback, or a closed loop mode utilizing piston and rod-side pressure feedback. The various modes of operation can be dependent on the number and location of, for example, feedback sensors (such as pressure sensors) arranged within the system. In general, the number of sensors within a system increase costs but also may provide increased functionality. As described herein, the suspension system can provide efficient control and functionality in varying system configurations depending on the number of sensors present.

[0079] Fig. 10 illustrates a method 200 of controlling the hydraulic control circuit (e.g., the hydraulic control circuit 20) in the open loop mode, in the following description, reference will be made to Figs. I A, I B, and 10. in the open loop mode, an operator of the vehicle can switch (e.g., with an operator input device 100) between a plurality of stiffness settings to achieve a desired suspension stiffness. For example, when the load is increased on the vehicle, the operator may desire a softer suspension setting, and can therefore adjust the operator input device 100 to a "soft" setting. Therefore, in the open loop mode, no pressure sensors are required for providing feedback to the controller 40, and the adjustments may be made independent of axle load changes (e.g., based on a desired -feel" governed by the operator).

[0080] The method 200 can begin with the controller 40 receiving an input command from the operator input device 100 at block 202. The input command can be correlated to a stiffness setting among a plurality of stiffness settings. For example, the input device can be switchable between three stiffness settings, including a first setting correlating to a "soft" suspension setting, a second setting correlating to a "medium" suspension setting, and a third setting correlating to a "hard" -24 -suspension setting. In other examples, the operator can include an infinite number of suspension stiffness settings between a "soft" setting and a "hard" setting (e.g., between minimum and maximum rod-side pressures).

[0081] The controller 40, at block 204, may then determine an output command based on the predetermined relationship between a target rod-side pressure and valve command (Fig. 9). For example, the first setting can correlate to a first target rod-side pressure requiring a first current command, the second setting can correlate to a second target rod-side pressure requiring a second current command, and the third setting can correlate to a third target rod-side pressure requiring a third current command, where the first target rod-side pressure is less than the second target rod-side pressure, and the third target rod-side pressure is greater than the second target rod-side pressure. Likewise, the magnitude of the first current command is less than the second current command, and the magnitude of the third current command is greater than the second current command.

[0082] At block 206, the controller 40 can then provide the output command to the rod control valve 26 and command the piston control valve 24 to the first position to increase the pressure in the rod side 56 of the hydraulic cylinder 50 to the target rod-side pressure. The stiffness adjustment can then be carried out by the controller 40 as previously described herein. In some non-limiting examples, the controller 40 can optionally implement a delay for a predetermined period of time, at block 208, to allow the pressures in the system to normalize. This predetermined period of time can be about I second. This normalization time can be limited based on the sizing of the first and second piston control orifices 72, 74, the pump pressure, or the pre-charge of the piston and rod accumulators 86, 88. Once the target rod-side pressure is achieved, the controller 40 can then de-energize the rod control valve 26 and the piston control valve 24 at block 210, and the rod pilot operated check valve 66 will maintain the pressure in the rod side 56 of the hydraulic cylinder 50.

[0083] The controller 40 can also be configured to operate in a closed loop mode to maintain a target natural frequency of the vehicle by automatically adjusting the stiffness of the suspension (e.g., by varying rod-side pressures) in response to changes in axle loading (e.g., as measured by changes in piston-side pressures). Figs. 11-13 illustrate a conventional system, where rod-side pressure is held constant across a range of axle loads (line 220). In this conventional system, the natural frequency of the vehicle varies as the axle load changes, which results in the performance of the suspension to vary dependent on axle load, along with the comfort for the operator of the -25 -vehicle. The closed loop methods described herein can maintain a target natural frequency across a range of axle loads (line 222), as will be described below, by varying the rod-side pressures in response to changes in piston-side pressures.

[0084] The natural frequency of the vehicle can be correlated to the performance of the suspension, therefore there are natural frequencies that can be targeted to achieve a desired suspension performance or ride comfort. In the illustrated example of Fig. 11, the controller 40 can be configured to target a natural frequency of about 1.5 Hz. In some non-limiting examples, a target natural frequency can be given as an input to the controller 40. In other non-limiting examples, the target natural frequency can be dependent on the type of vehicle, the speed of vehicle travel, and/or the axle load, among others. With a desired target natural frequency chosen, a target rod-side pressure can be mathematically determined (e.g., by the controller 40) across a range of axle loads to maintain that target natural frequency, as illustrated in Fig. 12. In the illustrated example, the target natural frequency is constant across the range of axle loads. In other non-limiting examples, the target natural frequency may vary across the range of axle loads. In some non-limiting examples, the controller 40 can include a predetermined control map of natural frequency vs. axle load in the form of a function or look up table. The natural frequency can be mathematically determined based on the geometry of the hydraulic cylinder 50, the suspension geometry of the vehicle, the piston and rod-side pressures, the size of the piston and rod accumulators 86, 88, and the pre-charges of the piston and rod accumulators 86, 88.

[0085] With the target natural frequency and target rod-side pressures determined across a range of axle loads, the axle load can be converted into the resulting piston-side pressures caused by the axle load and the target rod-side pressures, as illustrated in Fig. 13. That is, Fig. 13 illustrates a second predetermined relationship between the target rod-side pressure and a piston-side pressure for a target natural frequency. With this data known, the piston-side pressures can be measured, for example, by a pressure sensor, and a target rod-side pressure can be determined using the relationship illustrated in Fig. 13, in order to maintain a desired target natural frequency. As described above, the target rod-side pressures can be correlated to a valve command for the rod control valve 26, as illustrated in Fig. 9. Therefore, the relationships illustrated in Fig. 9 and Fig. 13 can be combined to correlate a measured piston pressure to a required valve command to provide the target rod-side pressure to provide the desired target natural frequency, as illustrated in Fig. 14. In general, the target natural frequency is built into the models shown in Figs. 11-14, -26 -therefore, upon commanding a target rod-side pressure based on a measured piston pressure, the command to the rod control valve 26 from the controller 40 is configured to maintain the target natural frequency.

[0086] According to some non-limiting examples, the models illustrated in Figs. 9 and 11-14 can be uploaded to the controller 40 for storage therein. According to other non-limiting examples, the parameters for determining natural frequency (e.g., the geometry of the hydraulic cylinder 50, the suspension geometry of the vehicle, the piston and rod-side pressures, the size of the piston and rod accumulators 86, 88, and the pre-charges of the piston and rod accumulators 86, 88) and the performance characteristics of the rod control valve 26 can be provided as an input to the controller 40 and the controller 40 can output the models illustrated in Figs. 9 and 11-14.

[0087] Fig. 15 illustrates a method 300 of controlling the hydraulic control circuit (e.g., the hydraulic control circuit 20) in the closed loop mode utilizing piston-side pressure feedback. In the following description, reference will be made to Figs. 2A and 15. In this closed loop mode, at block 302, the controller 40 can monitor the piston-side pressures using the piston pressure sensor 106 to detect changes to the axle load, and adjust rod-side pressures automatically in response to axle load changes. Optionally, at block 304, the controller 40 can then determine if the piston-side pressure is within a predetermined pressure range. This predetermined pressure range can be relative (e.g., within about 5 psi, within about 10 psi, etc.) to an average pressure determined over a set period of time to account for the suspension system undergoing undulations caused by perturbations in the surface the vehicle is traversing.

[0088] Upon determining that the piston-side pressure is within the predetermined pressure range, the controller 40 can proceed to block 302 to continue monitoring the piston-side pressures. If the controller 40 determines that the piston-side pressure is outside of the predetermined range, the controller can proceed to block 306 to determine an output command to the rod control valve 26 based on the first predetermined relationship between a target rod-side pressure and a valve command (Fig. 9) and the second predetermined relationship between the target rod-side pressure and a piston-side pressure for a target natural frequency (Fig. 13). In some cases, the controller 40 may proceed from block 302 directly to block 306 if optional block 304 is not performed. At block 308, the controller 40 can then provide the output command (e.g., current) to the rod control valve 26, and command the piston control valve 24 to the first position, to provide the target rod-side pressure to the rod side 56, thereby adjusting the stiffness of the hydraulic cylinder 50 to maintain -27 -a target natural frequency. The stiffness adjustment can then be carried out by the controller 40 as previously described herein.

[0089] The controller 40 can then proceed to block 302 to continue monitoring the piston-side pressures and resume the closed-loop control strategy. In some non-limiting examples, the controller 40 can optionally implement a delay for a predetermined period of time, at block 310, to allow the pressures in the system to normalize. This predetermined period of time can be about one second. After the delay, the controller 40 can de-energize the rod control valve 26 and the piston control valve 24, and proceed to block 302 to continue monitoring the piston-side pressure and resume the closed-loop control algorithm. In any case, once the target rod-side pressure is achieved, the controller 40 de-energizes the piston and rod control valves 24, 26 at block 312, and the rod pilot operated check valve 66 will maintain the pressure in the rod side 56 of the hydraulic cylinder 50.

[0090] Fig. 16 illustrates a method 400 of controlling the hydraulic control circuit (e.g., the hydraulic control circuit 20) in the closed loop mode utilizing piston-side and rod-side pressure feedback. In the following description, reference will be made to Figs. 2B and 16. In this closed loop mode, at block 402, the controller 40 can monitor the piston-side and rod-side pressures using the piston pressure sensor 106 to detect changes to the axle load and the rod pressure sensor 108 to monitor the rod-side pressures relative to the target rod-side pressure, and automatically adjust the rod-side pressures in response to changes in axle load. In this closed-loop control mode, the controller 40 can achieve target rod-side pressures more accurately, and may not be reliant on the tolerance of current vs. pressure of the rod control valve 26 (see Fig. 9). Optionally, at block 404, the controller 40 can then determine if the piston-side pressure is within a predetermined pressure range. This predetermined pressure range can be relative (e.g., within about 5 psi, within about 10 psi, etc.) to an average pressure determined over a set period of time to account for the suspension system undergoing undulations caused by perturbations in the surface the vehicle is traversing.

[0091] Upon determining that the piston-side pressure is within the predetermined pressure range, the controller 40 can proceed to block 402 to continue monitoring the piston-side and rod-side pressures. If the controller 40 determines that the piston-side pressure is outside of the predetermined range, the controller can proceed to block 406 to determine an output command to the rod control valve 26 based on the first predetermined relationship between a target rod-side pressure and a valve command (Fig. 9) and the second predetermined relationship between the -28 -target rod-side pressure and a piston-side pressure for a target natural frequency (Fig. 13). In some cases, the controller 40 may proceed from block 402 directly to block 406 if optional block 404 is not performed. At block 408, the controller 40 can then provide the output command (e.g., current) to the rod control valve 26, and command the piston control valve 24 to the first position, to provide the target rod-side pressure to the rod side 56, thereby adjusting the stiffness of the hydraulic cylinder 50 to maintain a target natural frequency. The stiffness adjustment can then be carried out by the controller 40 as previously described herein.

[0092] At block 410, the controller 40 can then determine if the sensed rod-side pressure, utilizing the rod pressure sensor 108, is at the target rod-side pressure within a predetermined tolerance range. In some non-limiting examples, the predetermined tolerance range can be dependent on the resolution of the rod pressure sensor. For example, the predetermined tolerance range can be about ±5 psi, about ±2 psi, about ±1 psi, about +0.5 psi, etc., relative to the target rod-side pressure. Upon determining that the rod-side pressure is at the target rod-side pressure (or within the predetermined tolerance range relative to the target rod-side pressure), the controller 40 can proceed to block 416 and block 402 to de-energize the piston and rod control valves 24, 26 and continue monitoring the piston-side and rod-side pressures. If the controller 40 determines that the rod-side pressure is not at the target rod-side pressure (or outside of the predetermined tolerance range relative to the target rod-side pressure), the controller can proceed to block 412 to modify the output command (e.g., adjust a supplied current) to the rod control valve 26 based on the first predetermined relationship between the target rod-side pressure and the valve command (Fig. 9) to provide the target rod-side pressure to the rod side of the hydraulic cylinder. In some cases, the controller 40 can return to block 410 upon modifying the output command to re-evaluate the rod-side pressures relative to the target rod-side pressure.

[0093] The controller 40 can then proceed to block 416 and block 402 to de-energize the piston and rod control valves 24, 26 and continue monitoring the piston-side and rod-side pressures and resume the closed-loop control strategy. In some non-limiting examples, the controller 40 can optionally implement a delay for a predetermined period of time, at block 414, to allow the pressures in the system to normalize. This predetermined period of time can be about one second. After the delay, the controller 40 can then proceed to block 416 and block 402 and resume the closed-loop control strategy. In any case, once the target rod-side pressure is achieved, at block 416 the controller 40 can de-energize the rod control valve 26, and the piston control valve 24, and -29 -the rod pilot operated check valve 66 will maintain the pressure in the rod side 56 of the hydraulic cylinder 50.

[0094] Within this specification embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein.

[0095] Thus, while the invention has been described in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto. The entire disclosure of each patent and publication cited herein is incorporated by reference, as if each such patent or publication were individually incorporated by reference herein.

[0096] Various features and advantages of the invention are set forth in the following claims.

-30 -

Claims

CLAIMS I claim: 1. A suspension system for an off-highway vehicle, the suspension system is operable with a hydraulic cylinder defining a piston side and a rod side, wherein each of the piston side and the rod side are configured to receive a flow of fluid from a pump configured to draw fluid from a reservoir and furnish pressurized fluid to a pump outlet, the suspension system comprising: a proportional rod control valve in fluid communication with the pump outlet to selectively provide pressurized fluid to the rod side of the hydraulic cylinder along a rod supply conduit; a piston control valve in fluid communication with the pump outlet to selectively provide pressurized fluid to the piston side of the hydraulic cylinder along a piston supply conduit; a pilot operated check valve arranged along the rod supply conduit between the proportional rod control valve and the rod side; a blocking valve arranged along the piston supply conduit between the piston control valve and the piston side, the blocking valve being movable between an open position and a closed position; a piston-side pressure sensor arranged along the piston supply conduit between the blocking valve and the piston side; and a controller configured to control a stiffness of the suspension system to maintain a target natural frequency for the vehicle, the controller being configured to: monitor, with the piston-side pressure sensor, pressure in the piston side of the hydraulic cylinder; determine an output command to the proportional rod control valve based on a first predetermined relationship between a target rod-side pressure and a valve command and a second predetermined relationship between the target rod-side pressure and a piston-side pressure for the target natural frequency; and provide the output command to the proportional rod control valve to provide the target rod-side pressure to the rod side of the hydraulic cylinder.
-31 - 2. The suspension system of claim 1, wherein the controller is further configured to: determine if the pressure in the piston side is within a predetermined pressure range; and upon the determination that the pressure in the piston side is outside of the predetermined pressure range, determine the output command.
3. The suspension system of claim 1, wherein the controller is further configured to command the piston control valve in fluid communication with the pump to a position to provide pressurized fluid to the piston supply conduit, thereby shifting the pilot operated check valve that is configured to sense pilot pressure from the piston supply conduit.
4. The suspension system of claim 3, wherein the controller is further configured to de-energize the piston control valve and the rod control valve when the target rod-side pressure is achieved.
The suspension system of claim 1, wherein the output command is a current supplied to the proportional rod control valve; and wherein the magnitude of current supplied to the proportional rod control valve is proportional to the target rod-side pressure.
6. The suspension system of claim 1, further comprising a rod-side pressure sensor arranged along the rod supply conduit between the pilot operated check valve and the rod side; wherein the rod-side pressure sensor is in communication with the controller.
-32 - 7. The suspension system of claim 6, wherein the controller is further configured to: monitor, with the rod-side pressure sensor, a sensed pressure in the rod side of the hydraulic cylinder; determining if the sensed pressure is within a predetermined tolerance range relative to the target rod-side pressure; and upon the determination that the sensed pressure is outside of the predetermined tolerance range relative to the target rod-side pressure, modify the output command to the proportional rod control valve based on the first predetermined relationship between the target rod-side pressure and the valve command to provide the target rod-side pressure to the rod side of the hydraulic cylinder.
8 The suspension system of claim 1, wherein the controller is further configured to continue to monitor, with the piston-side pressure sensor, pressure in the piston side of the hydraulic cylinder after a predetermined delay following providing the output command to the proportional rod control valve.
9. The suspension system of claim I, further comprising a first piston control orifice arranged along the piston supply conduit between the piston control valve and the blocking valve.
10, The suspension system of claim 9, further comprising a second piston control orifice arranged between the pump outlet and the piston control valve Ii.
The suspension system of claim 9, further comprising a second piston control orifice arranged along the piston supply conduit between the piston control valve and the first piston control orifice.
12. The suspension system of claim 1, further comprising a piston accumulator in fluid communication with the piston side of the hydraulic cylinder and arranged between the blocking valve and the piston side; and a rod accumulator in fluid communication with the rod side of the hydraulic cylinder and arranged between the pilot operated check valve and the rod side.-33 -
13. The suspension system of claim 12, further comprising a first bi-directional proportional valve arranged between the piston accumulator and the piston supply conduit.
14. The suspension system of claim 12, further comprising a second bi-directional proportional valve arranged between the rod accumulator and the rod supply conduit.
IS. The suspension system of claim I, wherein the hydraulic cylinder includes a first hydraulic cylinder and a second hydraulic cylinder arranged in parallel with the first hydraulic cylinder.
16, The suspension system of claim I, wherein the hydraulic cylinder includes a first hydraulic cylinder and a second hydraulic cylinder; wherein a rod side of the first hydraulic cylinder and a rod side of the second hydraulic cylinder are in fluid communication with the rod supply conduit; and wherein the piston supply conduit includes a first piston supply conduit and a second piston supply conduit, the first piston supply conduit providing fluid communication between the piston control valve and a piston side of the first hydraulic cylinder and the second piston supply conduit providing fluid communication between the piston control valve and a piston side of the second hydraulic cylinder.
17. The suspension system of claim 16, wherein the blocking valve is a first blocking valve arranged along the first piston supply conduit between the piston control valve and the piston side of the first hydraulic cylinder; and wherein the suspension system further comprises a second blocking valve arranged along the second piston supply conduit between the piston control valve and the piston side of the second hydraulic cylinder.-34 -
18. The suspension system of claim 17, wherein the suspension system further includes a first piston accumulator in fluid communication with the piston side of the first hydraulic cylinder and arranged between the first blocking valve and the piston side of the first hydraulic cylinder; and a second piston accumulator in fluid communication with the piston side of the second hydraulic cylinder and arranged between the second blocking valve and the piston side of the second hydraulic cylinder.
19. The suspension system of claim I, further comprising a position sensor configured to measure a suspension position of the off-highway vehicle.
20. A method for adjusting a stiffness of a suspension system of an off-highway vehicle, the suspension system operable with a hydraulic cylinder defining a piston side and a rod side, the method comprising: monitoring, with a piston-side pressure sensor in fluid communication with the piston side of the hydraulic cylinder, pressure in the piston side of the hydraulic cylinder; determining, with the controller, an output command to a proportional rod control valve configured to selectively provide pressurized fluid from a pump to the rod side of the hydraulic cylinder along a rod supply conduit, wherein the output command is based on a first predetermined relationship between a target rod-side pressure and a valve command and a second predetermined relationship between the target rod-side pressure and a piston-side pressure for a target natural frequency; and providing the output command, with the controller, to the proportional rod control valve to provide the target rod-side pressure to the rod side of the hydraulic cylinder.
21. The method of claim 20, further comprising: determining, with a controller in communication with the piston-side pressure sensor, if the pressure in the piston side of the hydraulic cylinder is within a predetermined pressure range; and upon the determination that the pressure in the piston side is outside of the predetermined pressure range, determining, with the controller, an output command.-35 -
22. The method of claim 20, further comprising commanding a piston control valve in fluid communication with the pump to a position to provide pressurized fluid along a piston supply conduit, thereby shifting a pilot operated check valve arranged along the rod supply conduit and configured to sense pilot pressure from the piston supply conduit.
23. The method of claim 20, further comprising: monitoring, with the controller in communication with a rod-side pressure sensor in fluid communication with the rod side of the hydraulic cylinder, a sensed pressure in the rod side of the hydraulic cylinder; determining if the sensed pressure is within a predetermined tolerance range relative to the target rod-side pressure; and upon the determination that the sensed pressure is outside of the predetermined tolerance range relative to the target rod-side pressure, modifying the output command, with the controller, to the proportional rod control valve based on the first predetermined relationship between the target rod-side pressure and the valve command to provide the target rod-side pressure to the rod side of the hydraulic cylinder.
24. The method of claim 20, further comprising: continuing to monitor, with the piston-side pressure sensor, pressure in the piston side of the hydraulic cylinder after a predetermined delay following providing the output command to the proportional rod control valve.
25. The method of claim 20, wherein the output command is a current supplied to the proportional rod control valve; and wherein the magnitude of current supplied to the proportional rod control valve is proportional to the target rod-side pressure.-36 -