Semi-active ride control for a mobile machine

A system and method of achieving ride control for a work vehicle that replaces a traditional accumulator with a ride control valve, a directional control valve and a fluid pressure source. The fluid pressure source may be a variable displacement hydraulic pump. The ride control valve is set to a first relief pressure that allows fluid to flow from the head end of a hydraulic cylinder when the loading on the cylinder, i.e., the pressure in the head end is equal to or greater than the first relief pressure. A work tool of the vehicle falls from a first position to a second position when fluid flows from the head end. The ride control valve is then reset to a second relief pressure, higher than the first relief pressure and sufficient to move the work tool toward the first position. Afterwards, the directional control valve is opened long enough to allow fluid from the fluid pressure source to enter the head end and move the work tool back to approximately the first position. The ride control valve may be dynamically adjusted.

FIELD OF THE INVENTION

The invention relates to ride control for a work vehicle. In particular, it relates to shock absorption by a hydraulic cylinder that manipulates a work tool on a work vehicle.

BACKGROUND OF THE INVENTION

As work vehicles move along the ground, roughness of the terrain may cause roughness in vehicle ride. A rigid mechanical relationship between the vehicle frame and the working portion of the vehicle which includes the work tool and any linkage between the work tool and the vehicle tends to increase shock loading to the vehicle and, thereby, increase the roughness of the vehicle ride. Ride control systems for four wheel drive loaders are common and usually include a valve that connects a boom cylinder to an accumulator where the accumulator, ultimately, acts as a shock absorber. All are designed to provide flexibility and to absorb shock loading between the working portion of the vehicle and the vehicle frame, thereby, increasing the comfort of the vehicle operator and improving vehicle stability. However, such systems are complex, expensive and bulky, i.e., they require a substantial amount of space on the vehicle.

SUMMARY OF THE INVENTION

As stated above, ride control systems commonly used in work vehicles are, generally, complex, expensive and bulky. Additionally, such systems are generally limited in performance and must be attuned towards operation with either an empty or a loaded bucket (i.e., a light or a heavy tool) but not both.

Described herein, is a system and method of achieving ride control without expensive, complex and bulky components such as, for example, conventional accumulators. Additionally, the system and method described may be optimized over the entire range of operating conditions for the work vehicle. In the invention, a valve system including a proportional relief valve and solenoid valve plumbed in parallel with an electrohydraulic directional control valve controls a hydraulic cylinder that manipulates the work tool. The proportional relief valve connects the head end of the hydraulic cylinder to a fluid reservoir and the solenoid valve connects the rod end of the cylinder to the fluid reservoir. A controller directs controlling signals to the solenoid valve and the electrohydraulic directional control valve.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is a side view of an exemplary embodiment of a work vehicle1employing the invention. The particular work vehicle1illustrated inFIG. 1includes a frame10which includes a cab34, a front frame portion20, a rear frame portion30, front wheels22, rear wheels32, a work tool70, a boom50and a hydraulic cylinder60pivotally connected to the front frame portion20at pivot point60and pivotally connected to the boom at pivot point60a. The front and rear wheels22and32propel the work vehicle1along the ground in a manner well known in the art.

As can be seen inFIG. 1, when the hydraulic cylinder60is supporting a load from the boom50without the aid of ride control, the boom50and the hydraulic cylinder60are positionally rigid with respect to the front frame portion20. Thus a weight of the boom50as well as the linkage80and the work tool70is supported at a relatively rigid or fixed position with respect to the front frame portion70, adding to a gravitational load experienced by the front wheels22and providing a new center of gravity due to that gravitational load. The rigidity of the boom50with respect to the front frame portion20has the effect of making the boom20an equivalent rigid portion of the front frame portion20. This particular arrangement can cause roughness in the ride of the vehicle1as well less stable handling as the vehicle1travels along rough terrain at speed.

FIG. 2is a schematic of an exemplary embodiment of a circuit100for the invention. The circuit100includes: a hydraulic cylinder60, a ride control valve110, an electro-hydraulic (E-H) main control valve120, a hydraulic pump125, a controller130, a mode switch140having at least a first mode switch state and a second mode switch state, and a load95which, in this case, includes at least the boom50and the work tool70. A weight of the load95may be increased by adding material to be transported to the work tool70.

The hydraulic cylinder60includes a piston67with a first piston surface67aand a second piston surface67b, a rod64, a piston side61, a rod side62, a cylindrical wall63, a first end wall65and a second end wall66. The piston side61includes the first surface67athe first end wall65and a first cylindrical portion63aof the cylindrical wall63between the first piston surface67aand the first end wall65. The rod side52includes the second piston surface67b, the second end wall66and a second cylindrical portion63bof the cylindrical wall63between the second piston surface and the second end wall66. The volumes of the piston side61and the rod side62, as well as the lengths of the first and second cylindrical portions63a,63b, change as the hydraulic cylinder60extends and retracts.

FIG. 3is a schematic of an exemplary embodiment of the ride control valve110. As illustrated inFIG. 3, this particular embodiment includes: a first valve portion111fluidly connected to the head end61and a fluid reservoir90; and a second valve portion which includes one solenoid valve112fluidly connected to the rod side62and the fluid reservoir90. The first valve portion111includes a two position three port E-H ride control activation valve111a, a two position two port pilot controlled flow control valve111b, and an E-H adjustable pressure relief valve111cfor adjusting ride control. The second valve portion includes an E-H shut off valve112that connects the rod end62to the fluid reservoir90. The ride control valve110is fluidly connected to the piston side61, the rod side62and the fluid reservoir at ports110a,110band110c, respectively.

FIG. 4illustrates the flow of signals received and distributed by the controller130. As shown inFIG. 4, the controller130distributes control signals to the E-H main control valve120and the ride control valve120via the E-H ride control activation valve111a, the E-H adjustable pressure relief valve, and the E-H shut off valve112. The controller130bases the signals distributed on signals received from the pressure transducer145, the angle sensor135, the mode switch140and the joystick150.

FIG. 5is a schematic of a portion of the circuit inFIG. 2illustrating the E-H main control valve120the variable hydraulic pump125and the fluid reservoir90. The E-H main control valve120is a directional control valve well known in the art. The E-H main control valve120is fluidly connected to the piston side61, the rod side62, the hydraulic pump125and the fluid reservoir90at ports120a,120b,120cand120d, respectively, and is controlled by signals from the controller130. Thus the E-H main control valve120is controlled via at least two modes: (1) the regular work mode in which ride control is not activated and the E-H main control valve120is operated as a simple directional control valve to accomplish normal work functions; and (2) a ride control mode in which the E-H main control valve120is used as a compliment to the ride control valve110. Mode (2) will be fully explained shortly.

The controller130is a device well known in the art and may be a hard wired system, a system of relays or a digital electronic system. When the mode switch140is in the first mode switch state, the controller130controls the E-H main control valve120in the regular work mode via signals from an operator control150. However, when the mode switch140is in the second mode switch state, the E-H main control valve120is controlled in accordance with mode (2), i.e. the ride control mode. An exemplary embodiment of the mode switch140is an operator controlled toggle switch which is well known in the art.

FIG. 7illustrates a prior art hydraulic system which utilizes an accumulator160to achieve ride control. As shown inFIGS. 8 and 9, the accumulator160tends to be structurally complex and somewhat bulky. As illustrated inFIGS. 8 and 9, the accumulator160may include: an inlet port161, a piston162; a gas chamber163containing a gas163a; a cylindrical accumulator wall164having an inner surface164a; a first end wall165having an internal first end surface165awhich is inside the accumulator160; a second end wall166; and an accumulation chamber167; and a gas inlet port168. The accumulation chamber167includes: a first exposed cylindrical portion164a′ which is a portion of the inner surface164aexposed to hydraulic fluid entering the accumulator160; the first end wall165and the first piston surface162a. The gas chamber163includes: the second end wall166; the second piston surface162b; and a second exposed cylindrical portion164a″ which is a portion of the inner cylindrical surface164athat is exposed to the gas163aand located between the second piston surface162band the second end wall166.

A length of the second exposed cylindrical portion164a″ changes as pressurized fluid enters and leaves the accumulator160. As hydraulic fluid enters the accumulation chamber167, the volume of the gas chamber changes from a first volume V1to a second volume V2under a pressure of the hydraulic fluid as illustrated inFIGS. 8 and 9. As a result, a pressure of the gas163achanges from a first pressure P1to a second pressure P2as the amount of gas is approximately a constant. Thus the accumulator pressure PAat any given time tends to follow the equation PA=P2=P1*V1÷V2. The accumulator pressure PAis approximately equals the fluid pressure PFin the accumulator160.

FIG. 6is an exemplary embodiment of an algorithm200for the invention, i.e., the alternative ride control system mentioned above. The process for this exemplary algorithm has essentially three parts: (1) mode setting200a; (2) comparisons and calculations200b; and adjustments200c.

The mode setting200aof the process begins at step201with a check for the state of the mode switch140. If the mode switch140is not in the mode switch second state the process moves to step205and the ride control valve110is inactivated or remains inactivated if it is already inactive. If the mode switch is in the mode switch second state at step201, the process moves to steps210and220where an angular value (AR) is recorded from the angle sensor135, an initial static pressure (PS) is recorded from the pressure transducer and the ride control valve first state is implemented. The PSvalue is taken from filtered readings of the pressure transducer to reduce the chances of recording momentary spikes in pressure as illustrated inFIG. 4.

The comparisons and calculations200bportion of the process starts immediately after the mode setting200aand begins at step230determining if any change in boom angle was due to a manipulation of the joystick150. If the angular change was due to a manipulation of the joystick150, the process moves to step210.

If, at step230, the angular change is not due to joystick movement, the calculations begin. At step240, an angular difference (ΔA) is calculated according to the following equation: ΔA=AR−AC. ΔA and PSare, at step245, then used to calculate a theoretical accumulator pressure (PA) based on the accumulator model illustrated inFIGS. 8 and 9. The accumulator pressure (PA) for this particular accumulator160is based on the change in the volume of the gas chamber163resulting from a displacement of the piston162as the amount of gas163ain the gas chamber163remains constant. The displacement of the piston162is calculated from a movement of hydraulic fluid from the piston side to the accumulator sufficient in volume to cause the boom50to move through the angular change of ΔA. The accumulator pressure (PA) may be calculated differently when other accumulators are used.

The adjustments then begin at step250with adjusting the E-H proportional relief valve111cto the calculated accumulator pressure (PA). At step260, the E-H main control valve120is then moved to or remains in position #1and the hydraulic pump125is adjusted, as necessary, to achieve PA. If, at step270, there is no change of state in the mode switch140, the process moves to step230and further adjustments are made as necessary. If the mode switch has changed states at step270, the process moves to step201.

Having described the illustrated embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.