JPH05248537A - Hydraulic drive device for hydraulically driven vehicle - Google Patents

Abstract

PURPOSE:To prevent a prime mover from undesirable overrunning during the decelerated travel of a hydraulically driven vehicle, in particular at the time of beginning a decelerated travel from the state of a high-speed travel. CONSTITUTION:A hydraulic drive device comprising a hydraulic motor 4 connected to a variable displacement hydraulic pump 2 in the form of a closed circuit via a pair of main pipe lines 3a and 3b, is provided with a brake pressure detecting section 22 for detecting the occurrence of brake pressure in the closed circuit, and a rolling amount detecting sensor 12 for detecting the displacement capacity of the pump 2. Furthermore, the hydraulic device is equipped with an arithmetic processing section 21 for operating the target set pressure of relief valves 8 and 9 on the basis of the displacement capacity detected with the sensor 12 and the specified input torque, and proportional solenoids 8a and 9a for setting the objective pressure of the valves 8 and 9 at the calculated values, when the occurrence of the brake pressure is detected with the section 22. As a result, the pressure of the relief valves 8 and 9 becomes small, according to an increase in the displacement capacity of the pump 2, while the set pressure of the valves 8 and 9 increases, according to the drop of the displacement capacity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic drive system for a hydraulically driven vehicle such as a wheel loader.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional closed hydraulic circuit for traveling.
In FIG. 3, a double displacement type variable displacement hydraulic pump 2 driven by a diesel engine 1 which is a prime mover is a main pipeline 3
It is connected to the hydraulic motor 4 via a and 3b in a closed circuit, and the maximum pressure in the pipeline is a pair of crossover load relief valves 1.
Limited by 5,16. When, for example, a forward command is given by operating a forward / reverse switching lever (not shown) and the traveling pedal 5 is depressed, a signal corresponding to the amount of depression of the pedal 5 is input from the signal generator 5a to the controller 6, and the controller 6 operates the regulator 7. Let Regulator 7
The hydraulic pump 2 is controlled to discharge the pressure oil in the direction of the conduit 3a in response to a command from the forward / reverse switching lever, and a tilt amount of the variable displacement hydraulic pump 2 (also referred to as displacement volume) is controlled by a signal input from the controller 6. ) Control. Further, the engine speed is increased or decreased according to the amount of depression of the travel pedal 5. Therefore, the hydraulic oil having a flow rate corresponding to the depression amount of the traveling pedal 5 is discharged from the hydraulic pump 2 to the pipe 3a, and the hydraulic motor 4 is driven by this discharged oil. As a result, the wheels connected to the hydraulic motor 4 are driven via the traveling drive system, and the vehicle moves forward at a speed that depends on the operation amount of the traveling pedal 5.

When the operating pedal 5 is decelerated while the vehicle is traveling, the engine speed decreases and the hydraulic pump 2
The displacement volume of is reduced and the amount of oil flowing into the hydraulic motor 4 is reduced. At this time, the hydraulic motor 4 receives a driving force from the outside due to the traveling inertial force and rotates, and subsequently discharges the oil to the return side conduit 3b. Since the displacement volume of the hydraulic pump 2 is decreasing toward zero, the pressure in the return side pipe line 3b is increased and the crossover load relief valve 16 is relieved.
A hydraulic brake is applied to the hydraulic motor 4 according to the relief pressure.

[0004]

When such a brake pressure is generated in the return side pipe line 3b, the hydraulic pump 2 is driven by the brake pressure. Set the displacement volume of the hydraulic pump 2 to q
When p and the brake pressure are Pb, a drive torque Tb of Pb * qp acts on the hydraulic pump 2. When the drive torque Tb exceeds the loss torque Tm during engine no-load operation, the engine 1 is accelerated. Since the traveling inertial force is large during high-speed traveling, the brake pressure becomes high, and the engine 1 may be accelerated and overrun.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a hydraulic drive system for a hydraulic drive vehicle that prevents an undesired overrun of a prime mover when the hydraulic drive vehicle decelerates, particularly when traveling from high speed to deceleration. ..

[0006]

Referring to FIG. 1 showing an embodiment, the present invention comprises a variable displacement hydraulic pump 2 driven by a prime mover 1 and a pair of main pipelines 3a, 3b having input / output ports. The present invention is applied to a hydraulic drive system for a hydraulically driven vehicle that includes a hydraulic motor 4 connected to an input / output port of the hydraulic pump 2 in a closed circuit, and a displacement volume setting means 7 that sets the displacement volume of the hydraulic pump 2. Then, the brake pressure detecting means 22 for detecting the generation of the brake pressure in the pipeline, the displacement volume detecting means 12 for detecting the displacement volume of the hydraulic pump 2, and the displacement volume detecting means 12 for detecting the displacement volume are detected. Calculation means 21 for calculating a target value of the brake pressure based on the displacement volume and a predetermined pump limit torque.
When the brake pressure is detected by the brake detection means 22, the outflow amount of the pressure oil from the return side pipeline to the discharge side pipeline is controlled so that the brake pressure becomes the calculated target value. The above object is achieved by providing a pressure control means for The calculation unit 21 may repeatedly calculate the target brake pressure, and the pressure control unit may control the pressure oil outflow amount so that the target value is sequentially calculated. The pressure control means has variable relief valves 8 and 9 arranged in the pipeline connecting the pair of pipelines 3a and 3b, and controls the brake pressure by changing the set pressure of the relief valves 8 and 9. can do. The pressure control means has a variable throttle provided in a pipeline connecting the pair of pipelines 3a and 3b, and the brake pressure can be controlled by changing the throttle opening.

[0007]

The calculating means 21 calculates the target value of the brake pressure based on the displacement volume detected by the displacement volume detection means 12 and the predetermined pump limit torque. When the brake pressure detecting means 22 detects that the brake pressure is generated, the pressure control means controls the amount of the pressure oil flowing out from the return side pipeline to the discharge side pipeline so that the brake pressure becomes the target value. Control. As a result, if the pump limit torque used for the above target value calculation is set to, for example, the maximum loss torque during the no-load maximum rotation operation of the prime mover 1, the prime mover 1 will not overrun the allowable maximum speed. .. When the target brake pressure is sequentially calculated and the amount of the pressure oil flowing from the return side pipe to the discharge side pipe is sequentially controlled so as to reach the target value, the pump displacement volume can be increased. As the brake pressure decreases, the brake pressure gradually increases, and a shock-free hydraulic brake can be generated.

Incidentally, in the section of means and action for solving the above-mentioned problems for explaining the constitution of the present invention, the drawings of the embodiments are used to make the present invention easy to understand. It is not limited to.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. The same parts as those in FIG. 3 are designated by the same reference numerals, and the differences are mainly described. In FIG. 1, a pair of main pipelines 3 connecting the variable displacement hydraulic pump 2 and the hydraulic motor 4 to each other.
A pair of crossover load relief valves 8 and 9 are connected in parallel in opposite directions between a and 3b. The set pressures of the crossover load relief valves 8 and 9 are proportional electromagnetic solenoids 8a, which are driven by a signal from the calculation unit 21,
It is determined according to the operation amount of 9a. That is, each crossover load relief valve 8 and 9 is a variable relief valve.

Pressure sensors 10 and 11 are connected to the main pipelines 3a and 3b, respectively, and detection signals of these pressure sensors 10 and 11 are input to a brake pressure detector 22.
Further, 12 is a tilt amount sensor, and this tilt amount sensor 1
Reference numeral 2 detects the discharge direction of the variable displacement hydraulic pump 2 and the tilt amount corresponding to the displacement volume, and the detection signal is input to the brake pressure detection unit 22 and the above-described calculation unit 21. Here, the calculation unit 21 and the brake pressure detection unit 22 are provided in the control circuit 20 mainly including a microcomputer.

In the brake pressure detecting unit 22, the main pipe lines 3a and 3b are operated by the hydraulic pump 2 in response to a signal from the tilt amount sensor 12.
Discriminating the discharge side or the return side, the brake pressure is calculated by the following equation, brake pressure = return side pipeline pressure−discharge side pipeline pressure ....
The brake pressure obtained in (1) is input to the calculation unit 21 as a signal Pb. The calculation unit 21 calculates the target set pressure of the relief valve according to the procedure of FIG. 2 and applies a drive signal to the proportional solenoid of the relief valve.

The detailed procedure of the calculation unit 21 will be described with reference to FIG. In step S1, it is determined whether the brake pressure Pb calculated by the equation (1) is greater than zero. If it is less than zero, the target set pressure Pset is set to the maximum set pressure Pmax in step S5, and the relief valve 8 is set in step S4. , 9 are applied to the proportional solenoids 8a, 9a so that the set pressures of P ,. When it is determined in step S1 that Pb is larger than zero, the target set pressure Pset is calculated by the following equation in step S2. Pset = (200π · Tm) / | qp | (2) However, Tm is the loss torque when the engine is operated at the maximum unloaded engine speed, and whether the calculated Pset in step S3 is less than or equal to the maximum set pressure Pmax. If it is affirmative, the process proceeds to step S4, and the signal indicating the target set pressure Pset calculated by the equation (2) is sent to the proportional solenoids 8a and 9a.
Apply to. Target set pressure Pset calculated by equation (2)
Is larger than the maximum set pressure Pmax, the process proceeds from step S5 to step S4, and a signal indicating the maximum set pressure Pmax is applied to the proportional solenoids 8a and 9a.

The operation of the above embodiment will be described. When forward travel is commanded by a forward / backward lever (not shown) and the traveling pedal 5 is stepped on, the hydraulic pump 2 discharges high-pressure oil according to the traveling load to the discharge side conduit 3a, and the hydraulic motor 4 is driven by the pressure oil. The low-pressure oil is rotatively driven and the low-pressure oil is discharged to the return side pipe line 3b. Since the tilt amount sensor 12 outputs a positive predetermined value according to the tilt amount, the brake pressure detection unit 22 causes the brake pressure P to be increased.
b is the pressure of the main pipeline 3b detected by the pressure sensor 10-
It is calculated by the pressure of the main pipeline 3a detected by the pressure sensor 11. Since the brake pressure Pb thus calculated is negative during acceleration, the procedure of FIG. 2 proceeds from step S1 to step S5, and the set pressure of the crossover load relief valves 8 and 9 reaches the maximum value Pmax. The proportional solenoids 8a and 9a are driven so that Therefore, the motor drive torque during traveling acceleration can be maximized.

Next, the traveling pedal 5 is decelerated while traveling,
For example, when the foot is completely released from the traveling pedal 5, the engine speed decreases toward the idle speed, and the tilt amount of the hydraulic pump 2 also decreases toward zero. Therefore, a high pressure is generated in the return pipe 3b, and the brake pressure calculated by the brake pressure detector 22 (pressure of the main pipe 3b detected by the pressure sensor 10-pressure of the main pipe 3a detected by the pressure sensor 11). Is positive. Therefore, the process proceeds from step S1 to steps S2 and 3, and the brake torque is the loss torque T of the engine no-load maximum rotation speed according to the equation (2).
The target set pressure Pset is calculated so as not to exceed m,
If the target set pressure Pset is less than or equal to the maximum value, the set pressure of the crossover load relief valves 8 and 9 is set to this value. Therefore, the brake pressure Pb is limited by the relief pressure of the relief valve 9.

According to the above procedure, when the pressure generated in the pump return side pipeline is larger than the pressure generated in the pump discharge side pipeline, that is, when the brake pressure Pb in the equation (1) is positive, the crossover is performed. The set pressure of the load relief valves 8 and 9 is set to the target set pressure calculated by the equation (2). Therefore, the larger the displacement volume of the hydraulic pump 2, the lower the set pressure of the crossover load relief valves 8 and 9, and the smaller the displacement volume, the higher the target set pressure. That is, as can be seen from the equation (2), the relief of the crossover load relief valves 8 and 9 is adjusted so that the pump drive torque acting on the hydraulic pump 2 by the return pressure becomes constant regardless of the displacement volume of the hydraulic pump 2. The pressure is determined. Here, the maximum loss torque T when the value of the pump drive torque is operated at the engine no-load maximum rotation speed
If it is set to m, the engine 1 will not be speeded up regardless of the value of the brake pressure acting between the input and output ports of the hydraulic pump 2, and the overrun can be prevented.

In this embodiment, the pressure set value of the variable relief valve is changed to control the brake pressure. Therefore, if the pressure set value of the relief valve is set to the set pressure calculated by the above equation (2). Often, the pressure set value is uniquely determined by the amount of flexure of the set spring, and therefore the amount of flexure of the set spring due to the operation amount of the proportional solenoid is controlled in correspondence with the calculated set pressure.

In the above embodiment, the pair of main pipe lines 3a, 3
Although b is connected by a pair of crossover load relief valves 8 and 9 and the crossover load relief valves 8 and 9 are variable relief valves, a pair or a single variable valve is used instead of the crossover load relief valve. A diaphragm may be used, and the diaphragm opening may be changed according to the calculation result of the calculation unit 21 using a similar proportional solenoid. In this case, the pressure obtained by the equation (2) is considered as the target brake pressure, the throttle opening area for achieving this target brake pressure is obtained in advance, and further, based on the operation amount of the proportional solenoid with respect to the throttle opening area, ( The manipulated variable of the proportional solenoid is calculated from the target pressure value, which is the calculation result of equation (2), to drive the proportional solenoid. In the configuration of the above embodiment, the regulator 7 constitutes the displacement volume control means, and the tilt amount sensor 12 constitutes the displacement volume detection means.

[0018]

As described above in detail, according to the present invention, when the brake pressure is generated, the target brake pressure is calculated based on the displacement volume and the predetermined pump limit torque, and the target brake pressure is the target brake pressure. By controlling the amount of pressure oil flowing from the return line side to the discharge line side so that the value becomes a value, the pump drive torque due to the brake pressure is limited to within a predetermined value, so overrun of the prime mover is prevented. It If the amount of the pressure oil flowing out from the return conduit side to the discharge conduit side is successively controlled according to the target brake pressure calculated successively as in claim 2, the brake pressure gradually increases as the pump displacement volume decreases. It is possible to generate a hydraulic brake that is large and has little shock.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a hydraulic closed circuit and a control device of a hydraulic drive system according to the present invention.

FIG. 2 is a flowchart showing a procedure of target set pressure calculation executed by the control device of FIG.

FIG. 3 is a diagram showing an example of a conventional hydraulic closed circuit.

[Explanation of symbols]

 1: Engine 2: Variable displacement hydraulic pump 3a, 3b: Main line 4: Hydraulic motor 5: Travel pedal 5a: Signal generator 6: Controller 7: Regulator 8,9: Crossover load relief valve 8a, 9a: Proportional solenoid 10 , 11: Pressure sensor 12: Tilt amount sensor 20: Control circuit 21: Calculation unit 22: Brake pressure detection unit

Claims (4)

[Claims] 1. A variable displacement hydraulic pump driven by a prime mover, a hydraulic motor having an input / output port connected in a closed circuit to the input / output port of the hydraulic pump by a pair of main pipes, and a displacement volume of the hydraulic pump. In a hydraulic drive system for a hydraulically driven vehicle, comprising: a displacement volume setting means for setting a displacement volume, brake pressure detection means for detecting generation of brake pressure in the pipeline, and displacement volume for the hydraulic pump are detected. Displacement volume detection means, calculation means for calculating a target value of the brake pressure based on the displacement volume detected by the displacement volume detection means and a predetermined pump limit torque, and the brake detection means When it is detected that pressure has been generated, the amount of pressure oil flowing from the return side pipeline to the discharge side pipeline is controlled so that the brake pressure becomes the target value. Hydraulic drive system for a hydraulic drive vehicle, comprising a pressure control unit that. 2. The hydraulic pressure according to claim 1, wherein the calculation means repeatedly calculates the target value of the brake pressure, and the pressure control means successively controls the outflow amount of the pressure oil so that the target brake pressure is calculated sequentially. Hydraulic drive system for drive vehicle. 3. The pressure control means has a variable relief valve arranged in a pipe line connecting the pair of main pipe lines, and a set pressure of the relief valve is set so that the brake pressure becomes a target value. The hydraulic drive system for a hydraulic drive vehicle according to claim 1 or 2, wherein 4. The pressure control means has a variable throttle provided in a pipeline connecting the pair of pipelines, and the throttle area of the variable throttle is changed so that the brake pressure becomes a target value. A hydraulic drive system for a hydraulically driven vehicle according to claim 1 or 2.