JPH0925651A - Hydraulic controller of hydraulically traveling vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a braking force, by providing a pressure-setting means by which the maximum pressure in the exit side pipe gets to the first value when the driving pressure of a hydraulic motor is higher than a specified value and it gets to the second value lower than the first value when the driving pressure is lower than a specified value and also setting the means to the first value when increasing the braking force. SOLUTION: When reaching a downward slope on traveling on a flat road while treading a pedal 12a, a hydraulic motor 4 is rotated with tires due to the inertia of vehicle and the driving pressure is decreased. And hence, the brake pressure is increased by the same motion with the release time of the pedal 12a but since the changeover valve 20 is positioned in (X), the blake pressure is relatively low. Then, as the brake pressure becomes short, an auxiliary brake switch 55 is put on to change over an solenoid valve 52 to (A) position to act the delivery pressure of the hydraulic source 51 on the valve 20 and change over the valve to (Y). The pressure of overload relief valves 17a, 17b are set high to raise the brake pressure. In this way, the brake force during downward traveling can be increased and the travel feeling is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device used in a hydraulic traveling vehicle such as a wheel hydraulic excavator, and more particularly to improving traveling performance on a downhill.

[0002]

2. Description of the Related Art Conventionally, a hydraulic control device of this type is known as shown in FIG. Reference numeral 1 denotes a hydraulic pump driven by an engine (motor) (not shown). The discharged oil is controlled in direction and flow rate by a hydraulic pilot type control valve 2 and passes through a counter balance valve 3 to run hydraulic motor 4.
Is supplied to. The driving force of the hydraulic motor 4 is transmitted to the traveling drive shaft via the transmission 5, whereby the vehicle is driven.

The switching direction and stroke amount of the pilot type control valve 2 are controlled by the pilot pressure from the pilot hydraulic circuit. The pilot hydraulic circuit includes a pilot hydraulic pump 11, a pilot valve 12 that follows the hydraulic pump 11, controls the travel speed of the vehicle by controlling the stroke amount of the control valve 2, and the pilot valve 12.
Following this, there is a slow return valve 13 that delays the return oil to the pilot valve 12, and following this slow return valve 13, there is a forward / reverse switching valve 14 that selects forward, reverse, or neutral of the vehicle.

FIG. 6 shows a state in which the forward / reverse switching valve 14 is in the neutral position (N position) and the pilot valve 12 is not operated. At this time, the pilot control valve 2 is in the neutral position and the hydraulic pump 1 is in the neutral position. The pressure oil from the tank returns to the tank 15 and the vehicle is stopped. When the forward / reverse switching valve 14 is switched to the forward (F position) or the reverse (R position) and the pedal 12a of the pilot valve 12 is depressed, the oil discharged from the hydraulic pump 11 is discharged to the pilot port 2a of the pilot control valve 2 or 2b, the control valve 2 is switched by a stroke amount according to the pilot oil pressure. As a result, the oil discharged from the hydraulic pump 1 is guided to the hydraulic motor 4 via the control valve 2, the pipeline 16a or 16b, and the counterbalance valve 3, and the hydraulic motor 4 is driven to drive the vehicle. The speed of the vehicle depends on the depression amount of the pedal 12a of the pilot valve 12.

First overload relief valves 17a and 17b and check valves 18a and 18b are provided between the hydraulic motor 4 and the counterbalance valve 3, and the first overload relief valves 17a and 17b are provided.
The pilot ports 117a and 117b of the overload relief valves 17a and 17b are connected to a hydraulic pilot type switching valve 20 via a shuttle valve 19. When the switching valve 20 is switched to position a, the shuttle valve 19 moves to the tank 21.
When the shuttle valve 19 is connected to the
The tank 21 via the second overload relief valve 22
Connected to.

The shuttle valve 24 provided between the pilot type control valve 2 and the counter balance valve 3 has a conduit 16a,
A pipe line having a high pressure is selected from 16b, and this pressure oil is guided to the pilot port 20a of the switching valve 20. That is, the switching valve 20 is switched to the B position during acceleration or during steady traveling. Therefore, the first overload relief valve 17a, which is running, in which a predetermined pressure is generated in the pipelines 16a, 16b,
The set pressure of 17b is a high set pressure (350 kg / cm2) obtained by adding the set pressure (for example, 250 kg / cm2) of the second overload relief valve 22 to the pressure due to the relief spring (for example, 100 kg / cm2). Therefore,
A predetermined traveling drive can be obtained during normal traveling.

When the pedal 12a is released during traveling, the pilot valve 12 shuts off the pressure oil, and its outlet port is at the tank 25.
Is communicated with. As a result, the pressure oil acting on the pilot port 2a or 2b returns to the tank 25 via the forward / reverse switching valve 14, the slow return valve 13, and the pilot valve 12. At this time, the return oil is throttled by the throttle 13a of the slow return valve 13, so that the pilot control valve 2 is gradually switched to the neutral position. When the pilot control valve 2 returns to the neutral position, the oil discharged from the hydraulic pump 1 returns to the tank 15,
A conduit 16a between the counterbalance valve 3 and the control valve 2,
Since the pressure of 16b becomes low, the switching valve 20 is switched to the a position and the first overload relief valve 17a or 17b.
The set pressure of is low.

At this time, the counterbalance valve 3 is also switched to the neutral position shown in the figure, and the oil discharged from the hydraulic motor 4 is throttled to the throttle 3a or 3b of the counterbalance valve 3 and the throttle 2c in the pilot control valve 2. Therefore, when the flow rate is large, first the first overload relief valve 17a and the check valve 18b, or the first overload relief valve 17b and the check valve 18a are opened, and a large hydraulic brake works on the outlet side conduit of the hydraulic motor 4. The vehicle starts decelerating. At this time, the set pressure of the first overload relief valves 17a and 17b is only the pressure (100 kg / cm2) by the relief spring as described above, which is low, so that shock due to deceleration can be alleviated.

When the discharge flow rate of the hydraulic motor 4 decreases due to deceleration, the first overload relief valves 17a, 17b,
The check valves 18a and 18b are closed, and the discharge oil of the hydraulic motor 4 is again discharged via the throttle 3a or 3b of the counterbalance valve 3 and the throttle 2c in the control valve 2.
The oil flows into the circulation passage returning to, and a relatively small hydraulic brake acts on the hydraulic motor 4. As a result, the vehicle is smoothly decelerated.

[0010]

With the above arrangement, the first overload relief valve 17a is released when the pedal operation is released.
Alternatively, since the set pressure of 17b is low, a good deceleration feeling can be obtained when traveling on a flat road, but on the other hand, traveling on a downhill is hindered. That is, when the vehicle is descending, the hydraulic motor is rotated by the tire due to the inertia of the vehicle body. Therefore, even if the pedal 12a is still depressed, the driving pressure of the hydraulic motor 4 decreases and the switching valve 20 returns to the a position. . At this time, the counterbalance valve is closed and the brake pressure is increased due to the decrease in the drive pressure, but since the switching valve 20 is in the a position, the overload relief valve 17a or 17b is set to a low pressure, and therefore a sufficient braking force ( The deceleration effect) cannot be obtained. Therefore, the driver has to frequently use the foot brake when descending a long downhill, and the traveling feeling is bad.

An object of the present invention is to provide a hydraulic control system for a hydraulic traveling vehicle which improves traveling feeling when descending a slope without sacrificing the deceleration shock mitigating effect during normal deceleration.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 showing an embodiment of the present invention, the present invention will be described. According to the present invention, a hydraulic pump 1 driven by a prime mover and an oil discharged from the hydraulic pump 1 are driven. When the hydraulic motor 4 that drives the vehicle, the control valve 2 that is operated by the operating means 12a and controls the pressure oil that is guided from the hydraulic pump 1 to the hydraulic motor 4, and the drive pressure of the hydraulic motor 4 is below a predetermined value. The hydraulic brake valve 3 that applies a hydraulic brake to the outlet side pipeline of the hydraulic motor 4, the setting means 17a and 17b that sets the maximum pressure of the outlet side pipeline of the hydraulic motor 4, and the drive pressure of the hydraulic motor 4 are predetermined. When the value is equal to or more than the value, the maximum pressure in the outlet side pipeline becomes the first value, and when the driving pressure is less than the predetermined value, the maximum pressure in the outlet side pipeline becomes the second value lower than the first value. 17a, 17b Control to control means 20,22,51
The present invention is applied to a hydraulic control device for a hydraulic traveling vehicle having.
Then, the command means 55 for commanding an increase in the hydraulic braking force
The above problem is solved by providing the control means 20, 22, 51 as follows. That is, when the commanding means 55 instructs the control means 20, 22, 51 to increase the hydraulic braking force, the maximum pressure of the outlet side pipeline becomes the first value regardless of the driving pressure of the hydraulic motor 4. The setting means 17a and 17b are controlled so as to control. The invention of claim 2 uses the operation switch 55 provided in the operator's cab as the command means.

Even if the drive pressure of the hydraulic motor 4 decreases during traveling on a downhill, the maximum pressure of the outlet side pipeline of the hydraulic motor 4 becomes a first value (high pressure) due to the increase command of the hydraulic braking force.
Sufficient braking force is obtained.

In the description of the means for solving the above problems for explaining the structure of the present invention, the drawings of the embodiments are used for the sake of easy understanding of the present invention. It is not limited to.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a wheel type hydraulic excavator in which the hydraulic control device according to the present invention is mounted, and 3 is a lower traveling body having tires 7 mounted thereon, 1 is an upper swinging structure that is swingably connected to an upper portion of the lower traveling body 1. It is the body. Upper revolving superstructure 1
A work front attachment 2 is connected to the vehicle, and a lower traveling body 3 is provided with a traveling hydraulic motor 4, a transmission 5, and a propeller shaft 6.

FIG. 1 shows the construction of a hydraulic control device for the wheel type hydraulic excavator. The same components as those in FIG. 6 are designated by the same reference numerals, and differences will be mainly described. The discharge pressure of the hydraulic pressure source indicated by reference numeral 51 is guided to the shuttle valve 54 via the electromagnetic valve 52 and the pipe line 53. The solenoid valve 52 can be switched between an A position that connects the hydraulic pressure source 51 and the pipeline 53 and a B position that shuts off the two. The switching is performed by operating an auxiliary brake switch 55 provided in the operator's cab. Be seen. That is, when the auxiliary brake switch 55 is off, the solenoid valve 52 holds the B position,
When the holding brake switch 55 is turned on, it switches to the A position. The shuttle valve 54 guides the higher pressure of the pressure in the conduit 53 and the selected pressure in the shuttle valve 24 to the pilot port 20a of the switching valve 20. The discharge pressure of the hydraulic pressure source 51 is sufficient to switch the switching valve 20 to the low position.

Next, the operation of the embodiment will be described with reference to FIGS. 3 and 4. (1) Traveling on a flat road The operation during traveling on a flat road will be described with reference to FIG. 3. First, when the pedal 12a is depressed (time T1), the driving pressure of the pipeline 16a or 16b rises, and the hydraulic motor 4 rotates. The vehicle runs. After that, the driving pressure gradually decreases. Since either the driving pressure of the pipe lines 16a or 16b or the discharge pressure of the hydraulic pressure source 51 is introduced to the pilot port 20a of the switching valve 20, the switching valve 20 is operated regardless of whether the auxiliary brake switch 55 is operated during pedal operation. Holds the B position, and the set pressure of the overload relief valve 17a or 17b becomes high pressure. Therefore, traveling can be performed without any trouble. When the pedal operation is released (time T2), the driving pressure is greatly reduced, so that the counterbalance valve 3 is closed and the brake pressure in the outlet side conduit 16b or 16a of the hydraulic motor 4 is increased. Normally, when traveling on a flat road, the auxiliary brake switch 55 is turned off, so that the switching valve 20 returns to the a position due to the reduction of the driving pressure, so that the brake pressure is kept relatively low and the deceleration shock is reduced. To be done.

(2) Downhill traveling The operation during downhill traveling will be described with reference to FIG. Pedal 12a
When the vehicle approaches a downhill while traveling on a flat road while stepping on (time T11), the hydraulic motor 4 is rotated by the tire due to the inertia of the vehicle body, and the driving pressure starts to decrease as shown in the figure. Therefore, although the brake pressure is increased by the same operation as when releasing the pedal, the brake pressure is relatively low because the switching valve 20 is in the a position. Since the braking force is insufficient in this state, the driver turns on the auxiliary brake switch 55 (time T12). As a result, the solenoid valve 52 is switched to the A position, the discharge pressure of the hydraulic pressure source 51 acts on the pilot port 20a of the switching valve 20 via the shuttle valve 54, and the switching valve 20 is switched to the B position. As a result, the set pressure of the overload relief valve 17a or 17b becomes high, the brake pressure increases as shown, and a large braking force acts on the vehicle. Therefore, the driver does not need to frequently use the foot brake, and a good traveling feeling can be obtained even when going downhill.

In the structure of the above embodiment, the pedal 12a serves as an operating means, the counter balance valve 3 serves as a hydraulic brake valve, and the first overload relief valves 17a, 17a.
b configures setting means, the switching valve 20, the second overload relief valve 22, and the solenoid valve 52 configure control means, and the auxiliary brake switch 55 configures command means.

FIG. 5 is a schematic hydraulic circuit diagram showing another embodiment, and the same components as those in FIG. 1 are designated by the same reference numerals. 61a and 61b are hydraulic cylinders for changing the set pressure of the overload relief valves 17a and 17b, and these hydraulic cylinders 61a and 61b are connected to the shuttle valve 54. The shuttle valve 54 selects the higher pressure of the pressure in the conduit 53 and the selected pressure of the shuttle valve 24 and guides it to the hydraulic cylinders 61a, 61b.

With the above structure, the same effect as that of FIG. 1 can be obtained. That is, when the pedal 12a (FIG. 1) is stepped on a flat road, either the driving pressure of the pipeline 16a or 16b or the pressure of the hydraulic source 51 is guided to the hydraulic cylinders 61a and 61b, and the overload relief valve 1
The set pressure of 7a or 17b becomes high. On the other hand, if the pedal operation is released while the auxiliary brake switch 55 is off, the driving pressure is reduced and the hydraulic cylinders 61a and 61b are reduced.
The pressure introduced to the valve also drops and the overload relief valve 1
The set pressure of 7a or 17b becomes low pressure. Further, when the auxiliary brake switch 55 is turned on during traveling on a downhill, the discharge pressure of the hydraulic power source 51 is guided to the hydraulic cylinders 61a and 61b, so that the overload relief valve 1 can be operated even if the driving pressure decreases.
The set pressure of 7a or 17b is high.

Although the example in which the driver operates the auxiliary brake switch 55 to switch the electromagnetic valve 52 to the A position has been described above, for example, downhill traveling is automatically determined and the electromagnetic valve 52 is moved to the A position. You may switch to. To achieve this, a tilt sensor that detects the tilt angle of the vehicle and a control circuit that controls the solenoid valve 52 according to the output thereof may be provided. Further, the configurations of the setting unit and the control unit are not limited to those in the above embodiment, and various configurations are conceivable. Further, the hydraulic control device for the wheel hydraulic excavator has been described, but the present invention can be applied to the hydraulic control device for other self-propelled hydraulic traveling vehicles.

[0023]

According to the present invention, when the increase of the hydraulic braking force is commanded, the maximum pressure of the outlet side pipeline of the hydraulic motor becomes high regardless of the driving pressure of the hydraulic motor. As a result, sufficient braking force can be obtained when traveling downhill, and it is not necessary to frequently operate the foot brake as in the conventional case, and a good traveling feeling can be obtained.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing a hydraulic control device for a hydraulic traveling vehicle according to an embodiment of the present invention.

FIG. 2 is a side view showing a wheel type hydraulic excavator on which the hydraulic control device of FIG. 1 is mounted.

FIG. 3 is a diagram showing a change over time of a pedal stroke, an inlet / outlet pressure of a hydraulic motor, and an auxiliary brake switch, showing a state when traveling on a flat road.

FIG. 4 is a view similar to FIG. 3, showing a state when traveling on a downhill road.

FIG. 5 is a schematic diagram showing a hydraulic control device according to another embodiment.

FIG. 6 is a hydraulic circuit diagram showing a conventional hydraulic control device.

[Explanation of symbols]

 1 hydraulic motor 2 pilot control valve 3 counter balance valve 4 hydraulic motor 12a pedals 17a, 17b first overload relief valve 20 switching valve 22 second overload relief valve 51 hydraulic source 52 solenoid valve 54 shuttle valve 55 auxiliary brake switch

Claims (2)

[Claims] 1. A hydraulic pump driven by a prime mover, a hydraulic motor driven by discharge oil of the hydraulic pump to drive a vehicle, and a hydraulic oil operated by an operating means and guided from the hydraulic pump to the hydraulic motor. A control valve for controlling, a hydraulic brake valve for applying a hydraulic brake to the outlet side pipeline of the hydraulic motor when the drive pressure of the hydraulic motor becomes less than a predetermined value, and a maximum of the outlet side pipeline of the hydraulic motor. Setting means for setting a pressure, and a maximum pressure of the outlet side pipeline becomes a first value when the drive pressure of the hydraulic motor is a predetermined value or more, and a maximum pressure of the outlet side pipeline when the drive pressure is less than a predetermined value. A hydraulic control device for a hydraulic traveling vehicle, comprising: a control unit that controls the setting unit so that the maximum pressure becomes a second value that is lower than the first value. When a command to increase the hydraulic braking force is given by the command means, the control means has a maximum pressure of the outlet side pipeline regardless of the driving pressure of the hydraulic motor. A hydraulic control device for a hydraulic traveling vehicle, characterized in that the setting means is controlled so that the value becomes 1. 2. The hydraulic control device for a hydraulically traveling vehicle according to claim 1, wherein the command means is an operation switch provided in a driver's cab.