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.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will be described in detail, with references to the following figures, wherein:
FIG. 1 is a side view of an exemplary embodiment of a vehicle equipped with the invention;
FIG. 2 is an illustration of an exemplary embodiment of the invention;
FIG. 3 is schematic of an exemplary embodiment of the ride control valve;
FIG. 4 is an illustration of an exemplary embodiment of the invention with respect to signals received and transmitted by the controller;
FIG. 5 is a schematic of an exemplary embodiment of the hydraulic pump and the E-H main control valve;
FIG. 6 is an exemplary embodiment of the algorithm followed by the controller to obtain ride control on demand;
FIG. 7 is an illustration of a system for ride control in the prior art which utilizes an accumulator;
FIG. 8 is an illustration of a prior art accumulator with a sufficient load applied; and
FIG. 9 is an illustration of the accumulator of FIG. 9 with an insufficient load applied.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a side view of an exemplary embodiment of a work vehicle 1 employing the invention. The particular work vehicle 1 illustrated in FIG. 1 includes a frame 10 which includes a cab 34, a front frame portion 20, a rear frame portion 30, front wheels 22, rear wheels 32, a work tool 70, a boom 50 and a hydraulic cylinder 60 pivotally connected to the front frame portion 20 at pivot point 60 and pivotally connected to the boom at pivot point 60a. The front and rear wheels 22 and 32 propel the work vehicle 1 along the ground in a manner well known in the art.
As can be seen in FIG. 1, when the hydraulic cylinder 60 is supporting a load from the boom 50 without the aid of ride control, the boom 50 and the hydraulic cylinder 60 are positionally rigid with respect to the front frame portion 20. Thus a weight of the boom 50 as well as the linkage 80 and the work tool 70 is supported at a relatively rigid or fixed position with respect to the front frame portion 70, adding to a gravitational load experienced by the front wheels 22 and providing a new center of gravity due to that gravitational load. The rigidity of the boom 50 with respect to the front frame portion 20 has the effect of making the boom 20 an equivalent rigid portion of the front frame portion 20. This particular arrangement can cause roughness in the ride of the vehicle 1 as well less stable handling as the vehicle 1 travels along rough terrain at speed.
FIG. 2 is a schematic of an exemplary embodiment of a circuit 100 for the invention. The circuit 100 includes: a hydraulic cylinder 60, a ride control valve 110, an electro-hydraulic (E-H) main control valve 120, a hydraulic pump 125, a controller 130, a mode switch 140 having at least a first mode switch state and a second mode switch state, and a load 95 which, in this case, includes at least the boom 50 and the work tool 70. A weight of the load 95 may be increased by adding material to be transported to the work tool 70.
The hydraulic cylinder 60 includes a piston 67 with a first piston surface 67a and a second piston surface 67b, a rod 64, a piston side 61, a rod side 62, a cylindrical wall 63, a first end wall 65 and a second end wall 66. The piston side 61 includes the first surface 67a the first end wall 65 and a first cylindrical portion 63a of the cylindrical wall 63 between the first piston surface 67a and the first end wall 65. The rod side 52 includes the second piston surface 67b, the second end wall 66 and a second cylindrical portion 63b of the cylindrical wall 63 between the second piston surface and the second end wall 66. The volumes of the piston side 61 and the rod side 62, as well as the lengths of the first and second cylindrical portions 63a, 63b, change as the hydraulic cylinder 60 extends and retracts.
FIG. 3 is a schematic of an exemplary embodiment of the ride control valve 110. As illustrated in FIG. 3, this particular embodiment includes: a first valve portion 111 fluidly connected to the head end 61 and a fluid reservoir 90; and a second valve portion which includes one solenoid valve 112 fluidly connected to the rod side 62 and the fluid reservoir 90. The first valve portion 111 includes a two position three port E-H ride control activation valve 111a, a two position two port pilot controlled flow control valve 111b, and an E-H adjustable pressure relief valve 111c for adjusting ride control. The second valve portion includes an E-H shut off valve 112 that connects the rod end 62 to the fluid reservoir 90. The ride control valve 110 is fluidly connected to the piston side 61, the rod side 62 and the fluid reservoir at ports 110a, 110b and 110c, respectively.
FIG. 4 illustrates the flow of signals received and distributed by the controller 130. As shown in FIG. 4, the controller 130 distributes control signals to the E-H main control valve 120 and the ride control valve 120 via the E-H ride control activation valve 111a, the E-H adjustable pressure relief valve, and the E-H shut off valve 112. The controller 130 bases the signals distributed on signals received from the pressure transducer 145, the angle sensor 135, the mode switch 140 and the joystick 150.
FIG. 5 is a schematic of a portion of the circuit in FIG. 2 illustrating the E-H main control valve 120 the variable hydraulic pump 125 and the fluid reservoir 90. The E-H main control valve 120 is a directional control valve well known in the art. The E-H main control valve 120 is fluidly connected to the piston side 61, the rod side 62, the hydraulic pump 125 and the fluid reservoir 90 at ports 120a, 120b, 120c and 120d, respectively, and is controlled by signals from the controller 130. Thus the E-H main control valve 120 is controlled via at least two modes: (1) the regular work mode in which ride control is not activated and the E-H main control valve 120 is 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 valve 120 is used as a compliment to the ride control valve 110. Mode (2) will be fully explained shortly.
The controller 130 is 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 switch 140 is in the first mode switch state, the controller 130 controls the E-H main control valve 120 in the regular work mode via signals from an operator control 150. However, when the mode switch 140 is in the second mode switch state, the E-H main control valve 120 is controlled in accordance with mode (2), i.e. the ride control mode. An exemplary embodiment of the mode switch 140 is an operator controlled toggle switch which is well known in the art.
FIG. 7 illustrates a prior art hydraulic system which utilizes an accumulator 160 to achieve ride control. As shown in FIGS. 8 and 9, the accumulator 160 tends to be structurally complex and somewhat bulky. As illustrated in FIGS. 8 and 9, the accumulator 160 may include: an inlet port 161, a piston 162; a gas chamber 163 containing a gas 163a; a cylindrical accumulator wall 164 having an inner surface 164a; a first end wall 165 having an internal first end surface 165a which is inside the accumulator 160; a second end wall 166; and an accumulation chamber 167; and a gas inlet port 168. The accumulation chamber 167 includes: a first exposed cylindrical portion 164a′ which is a portion of the inner surface 164a exposed to hydraulic fluid entering the accumulator 160; the first end wall 165 and the first piston surface 162a. The gas chamber 163 includes: the second end wall 166; the second piston surface 162b; and a second exposed cylindrical portion 164a″ which is a portion of the inner cylindrical surface 164a that is exposed to the gas 163a and located between the second piston surface 162b and the second end wall 166.
A length of the second exposed cylindrical portion 164a″ changes as pressurized fluid enters and leaves the accumulator 160. As hydraulic fluid enters the accumulation chamber 167, the volume of the gas chamber changes from a first volume V1 to a second volume V2 under a pressure of the hydraulic fluid as illustrated in FIGS. 8 and 9. As a result, a pressure of the gas 163a changes from a first pressure P1 to a second pressure P2 as the amount of gas is approximately a constant. Thus the accumulator pressure PA at any given time tends to follow the equation PA=P2=P1*V1÷V2. The accumulator pressure PA is approximately equals the fluid pressure PF in the accumulator 160.
FIG. 6 is an exemplary embodiment of an algorithm 200 for the invention, i.e., the alternative ride control system mentioned above. The process for this exemplary algorithm has essentially three parts: (1) mode setting 200a; (2) comparisons and calculations 200b; and adjustments 200c.
The mode setting 200a of the process begins at step 201 with a check for the state of the mode switch 140. If the mode switch 140 is not in the mode switch second state the process moves to step 205 and the ride control valve 110 is inactivated or remains inactivated if it is already inactive. If the mode switch is in the mode switch second state at step 201, the process moves to steps 210 and 220 where an angular value (AR) is recorded from the angle sensor 135, an initial static pressure (PS) is recorded from the pressure transducer and the ride control valve first state is implemented. The PS value is taken from filtered readings of the pressure transducer to reduce the chances of recording momentary spikes in pressure as illustrated in FIG. 4.
The comparisons and calculations 200b portion of the process starts immediately after the mode setting 200a and begins at step 230 determining if any change in boom angle was due to a manipulation of the joystick 150. If the angular change was due to a manipulation of the joystick 150, the process moves to step 210.
If, at step 230, the angular change is not due to joystick movement, the calculations begin. At step 240, an angular difference (ΔA) is calculated according to the following equation: ΔA=AR−AC. ΔA and PS are, at step 245, then used to calculate a theoretical accumulator pressure (PA) based on the accumulator model illustrated in FIGS. 8 and 9. The accumulator pressure (PA) for this particular accumulator 160 is based on the change in the volume of the gas chamber 163 resulting from a displacement of the piston 162 as the amount of gas 163a in the gas chamber 163 remains constant. The displacement of the piston 162 is calculated from a movement of hydraulic fluid from the piston side to the accumulator sufficient in volume to cause the boom 50 to 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 step 250 with adjusting the E-H proportional relief valve 111c to the calculated accumulator pressure (PA). At step 260, the E-H main control valve 120 is then moved to or remains in position #1 and the hydraulic pump 125 is adjusted, as necessary, to achieve PA. If, at step 270, there is no change of state in the mode switch 140, the process moves to step 230 and further adjustments are made as necessary. If the mode switch has changed states at step 270, the process moves to step 201.
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.
Patent Grant
7165395
