JP3073036B2 - Travel hydraulic circuit of work vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a traveling hydraulic circuit for improving traveling performance of a work vehicle when traveling at a reduced speed.

[0002]

2. Description of the Related Art A hydraulic circuit as shown in FIG. 5 is conventionally known. In FIG. 5, reference numeral 1 denotes a hydraulic pump. The direction and flow rate of hydraulic oil discharged from the hydraulic pump 1 is controlled by a hydraulic pilot control valve 2 and supplied to a hydraulic motor 4 via a counter balance valve 3. You. The output shaft of the hydraulic motor 4 is connected to the input shaft of the transmission 5, and the output shaft of the transmission 5 is connected to the traveling drive shaft. The high / low speed switching of the transmission 5 is performed by the air cylinder 8.

The air in the air tank 6 can be introduced into the air cylinder 8 via a transmission switching valve 7. The power supply 9 is connected to the solenoid of the transmission switching valve 7 via a switch 10. When the switch 10 is turned on, the transmission switching valve 7 is switched to the position A, the air cylinder 8 is extended, and the transmission 5 is driven at a low speed. Become a step.
When the switch 10 is turned off, the transmission switching valve 7 is switched to the low position, the air cylinder 8 is contracted, and the transmission 5 is set to the high speed stage.

The switching direction and the stroke amount of the pilot control valve 2 are controlled by a pilot pressure from a pilot hydraulic circuit. The pilot hydraulic circuit includes a pilot hydraulic pump 11, a pilot valve 12 that follows the hydraulic pump 11 and controls the stroke amount of the control valve 2 to control the traveling speed of the vehicle, and a pilot valve that follows the pilot valve 12. A slow return valve 13 for delaying the return oil to the valve 12, and a forward / reverse switching valve 1 following the slow return valve 13 for selecting forward, backward or neutral of the vehicle
And 4.

FIG. 6 shows a state between the AB port and the B port of the control valve 2.
FIG. 4 is a diagram showing an opening area characteristic with respect to a stroke between a −T port (or an A−T port). In a neutral position where the stroke amount is zero, the AB port communicates with the maximum opening area, and the stroke amount is small. increase, it becomes x ₁₀ and A-B
Port is blocked, stroke increases from x ₁₀ When B
The opening area between the -T ports increases. That is, in the stroke x _10, any port is completely blocked.

FIG. 5 shows a state where the forward / reverse switching valve 14 is in the neutral position (N position) and the pilot valve 12 is not operated. Therefore, the pilot control valve 2 is in the neutral position and the hydraulic pump 1 Is returned to the tank 15 and the vehicle is stopped.

The forward / backward switching valve 14 is switched between forward (F position) and reverse (R position) to switch the pedal 12 of the pilot valve 12.
a, the oil discharged from the hydraulic pump 11 is applied to the pilot port 2a or 2a of the pilot control valve 2.
b, the control valve 2 is switched by the stroke amount corresponding 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 counter balance valve 3, and the hydraulic motor 4 is driven to drive the vehicle. The speed of the vehicle depends on the amount of depression of the pedal 12a of the pilot valve 12.

A first overload relief valve 17a, 17b and a check valve 18a, 18b are provided between the hydraulic motor 4 and the counter balance valve 3, and a pilot port 117a of the first overload relief valve 17a, 17b. , 117b are connected via a shuttle valve 19 to a first switching valve 20 of a hydraulic pilot type. When the first switching valve 20 is switched to the a position, the shuttle valve 19 is connected to the tank 21, and when the first switching valve 20 is switched to the b position, the shuttle valve 19 is switched.
Is the tank 21 via the second overload relief valve 22
Connected to. A shuttle valve 24 provided between the pilot control valve 2 and the counterbalance valve 3
A pipeline with a high pressure is selected from a and 16b. This pressure is guided to the pilot port 20a of the first switching valve 20,
When the pressure becomes equal to or higher than a predetermined value set by a spring during acceleration or steady running, the first switching valve 20 switches to the low position. If a pressure equal to or higher than a predetermined value is generated in the pipelines 16a, 16b during traveling, the first overload relief valve 17a,
The set pressure of 17b is a high set pressure obtained by adding the set pressure of the second overload relief valve 22 to the pressure of the relief spring. Therefore, a predetermined traveling driving force is obtained during normal traveling.

[0009]

However, such a conventional traveling hydraulic circuit for a working vehicle has the following problems. When the pedal 12a is released during traveling, the pilot valve 12 shuts off the pressure oil, and the outlet port of the
It is communicated with 5. As a result, the pressure oil acting on the pilot port 2a or 2b is transferred to the tank 25 via the forward / reverse switching valve 14, the slow return valve 13, and the pilot valve 12.
Return to At this time, the throttle 13a of the slow return valve 13
The pilot-type control valve 2 is gradually switched from the operating position F or R to the neutral position.

[0010] In this case, B-T opening area between the ports is gradually decreased, the stroke x ₁₀ in B-T
The port is shut off, and there is no place for return oil from the hydraulic motor 4 to go. For this reason, when the vehicle is traveling at a high speed at a high speed, a large flow rate flows, so that a high pressure is generated in the return line for a long time (for example, 4 seconds) as shown in FIG.
That is, the two-stage relief operates for a long time, causing a shock. In the case of the low-speed stage as well, for the same reason, as shown in FIG. 8, a high pressure is applied to the return line to actuate the two-stage relief and the reduction ratio is large, so that the time for generating the high pressure is short (for example, 2). Seconds), but the shock is great. Therefore, as shown in FIG. 9, if the amount of lap between the opening area diagram between the AB port and the opening area diagram between the BT port is large, for example, about 4 mm, then the hydraulic brake becomes small, The deceleration performance deteriorates. That is, since a large amount of return oil from the motor flows into the tank, the switching pressure of the first switching valve 20 does not remain in the return line, the set pressure of the overdrive valve is low, and the hydraulic brake Is small. In addition, the amount of oil flowing into the motor may be reduced to cause cavitation. Further, the motor inlet pressure is hardly increased at the time of starting, and it becomes difficult to start. 7, 8, 10, and 11, the solid line indicates the outlet pressure of the counterbalance valve, and the broken line indicates the outlet pressure of the hydraulic motor.

An object of the present invention is to secure an optimum lap amount between the opening area diagram between the AB port and the opening area diagram between the B (or A) and T ports of the control valve. It is to provide a traveling hydraulic circuit of a vehicle.

[0012]

The present invention will be described with reference to FIG. 5 showing a traveling hydraulic circuit to which the present invention is applied.
The present invention provides a hydraulic pump 1 driven by a prime mover,
A hydraulic motor 4 driven by oil discharged from the hydraulic pump 1
A transmission 5 for shifting the output shaft rotation speed of the hydraulic motor 4 to at least two stages of a high speed and a low speed and transmitting the speed to the traveling shaft of the vehicle; and a hydraulic motor provided between the hydraulic pump 1 and the hydraulic motor 4. 4 controls the amount of oil flowing into the hydraulic motor 4 and flowing out of the hydraulic motor 4. In the neutral position, the AB port communicates, and in the operating position, the PA (or B) port communicates with the B (or A) -T port. Valve 2, which performs a switching operation as described above, delay means 13 for delaying the speed at which the control valve 2 switches from the operating position to the neutral position, operating means 12 for controlling the stroke amount of control valve 2, and hydraulic motor 4. A counterbalance valve 3 provided between the control valve 2 and a hydraulic motor 4 and a counterbalance valve 3 provided between the counterbalance valve 3 and the control valve 2. Set pressure Overload relief valve 17a that switches a two-step pressure or low pressure, and 17b, the control valve 2
And a relief pressure control means 20 for increasing the set pressure of the overload relief valves 17a and 17b when the line pressure between the valve and the counter balance valve 3 is equal to or higher than a predetermined value. Is done. At the time of deceleration of the work vehicle in which the switching speed of the control valve 2 from the operating position to the neutral position is switched at a speed dependent on the delay means 13, as shown in FIG. The A- of the control valve 2 is controlled so that the pipeline pressure between the control valve 2 and the counter balance valve 3 does not exceed a predetermined value, and at a high speed stage, the pipeline pressure exceeds the predetermined value.
The above object is achieved by configuring the control valve 2 so that the opening area diagram between the B ports and the opening area diagram between the B (or A) -T ports are overlapped by a predetermined stroke length.

[0013]

The opening area diagram between the AB port of the control valve 2 and B
The opening area diagram between (or A) and T ports is wrapped by a predetermined stroke length. For this reason, when decelerating a vehicle traveling at a low speed, the pipeline pressure between the control valve 2 and the counterbalance valve 3 does not exceed a predetermined value set in the relief setting pressure control means 20, and -The set pressure of the ballo-dry relief valves 17a, 17b remains low, and the shock is smaller than before. Also, when the vehicle traveling at the high speed stage is decelerated, a large flow rate flows as compared with the low speed traveling, so that the pipeline pressure becomes equal to or higher than a predetermined value, and the relief pressure is increased by the relief setting pressure control means 20. At this time, since the reduction ratio is not large, the shock is not so large, and an appropriate deceleration feeling can be obtained. On the other hand, when the vehicle starts moving, the pipe pressure becomes equal to or higher than a predetermined value, and the relief setting pressure becomes equal to or higher than the predetermined value, so that a predetermined driving force is obtained.

In the sections of the means for solving the above-mentioned problems and the operation, which explain the constitution of the present invention, the same reference numerals as those of the embodiment are used to facilitate understanding of the present invention. It is not limited to the embodiment.

[0015]

An embodiment will be described below with reference to FIGS. The circuit itself is a conventionally known two-stage relay shown in FIG.
The difference is in the opening area diagram of the control valve 2. As schematically shown in FIG. 1 in comparison with FIGS. 6 and 9, the lap amount of the opening area diagram between the AB ports and the opening area diagram between the BT ports or between the A and T ports is as follows.
It is smaller than that of FIG. 9 and is set by an appropriate amount.
An appropriate amount is, for example, 1 mm.

The appropriate amount is set as follows.
First, in order to reduce the shock at the time of deceleration at the low speed stage, the pressure in the motor return line at the time of deceleration must not exceed the switching pressure of the first switching valve 20. After the start of communication between the A and B ports, a predetermined amount of communication between the B and T ports is performed so that the pressure in the return line becomes equal to or higher than the switching pressure of the first switching valve 20 in the amount of oil flowing through the path, Make sure that the appropriate amount of return oil flows into the tank.

Next, the operation will be described. When the vehicle is traveling normally, the control valve 2 is switched to the operating position F (or R), and as shown in detail in FIG. 4, communication between the PA (or PB) ports is performed. The BT (or AT) port is in communication. When the pipe pressure on the motor inlet side becomes equal to or higher than a predetermined value, the first overload relief valves 17a and 17b are set to a high pressure, and a predetermined traveling driving force is obtained. At this time, the space between the ports A and B is closed.

When the vehicle is decelerated, the control valve 2 is gradually switched from the operating position F (or R) to the neutral position.
At this time, as can be seen from FIG. 4, as the stroke decreases, the opening area between the BT (AT) ports starts to decrease, and then the opening area between the PA (P-B) ports. Decreases. That is, the pressure oil flowing out of the hydraulic motor 4 starts to be gradually reduced, and thereafter, the inflow flow rate decreases. Then, beginning opens between A-B ports stroke x _1, the area between A-B ports stroke x = 0 (neutral) is maximized. In addition, at the stroke x _2, B
-T (AT) Open area between ports and PA (P-
B) The opening area between the ports is zero. Where x ₁ −
x ₂ is about 1mm.

When the vehicle is decelerated at a high speed, that is, when the vehicle is running at a high speed, the amount of oil returned from the motor is large. Therefore, the switching valve 2 is gradually returned to the neutral state by the slow return valve 13, and at the beginning of opening between the A and B ports, B-T
(A-T) Even if the ports are open, the pressure in the return line becomes equal to or higher than the switching pressure of the first switching valve 20, and the first switching valve 20 switches to the over-dry relief valve 17a. , 17b
, The set pressure increases, and a large braking force is obtained.
The pressure waveform of the return line at that time is as shown in FIG. 2. Compared with the waveform of FIG. 7, the time during which the high pressure is applied is reduced (for example, 1 second), and the shock is reduced.

On the other hand, when the vehicle is decelerated at a low speed, that is, when the vehicle is traveling at a low speed, the return oil pressure is relatively small, so that the pressure in the return line does not exceed the switching pressure of the first switching valve 20. The set pressure of the over-dry relief valves 17a and 17b remains low. Therefore, the pressure waveform in the return line is as shown in FIG. 3, and the shock is reduced as compared with FIG. 2 and 3, the solid line shows the outlet pressure of the counterbalance valve, and the broken line shows the outlet pressure of the hydraulic motor.

As described above, when the vehicle running at high speed is decelerated, the first overdrive valve 17a, 17
Since the set pressure of b becomes high for an appropriate time, the hydraulic brake can be properly applied, and the optimal deceleration filling can be obtained.
In addition, the amount of oil returned to the tank is appropriate,
Is prevented. Further, when the vehicle traveling at a low speed is decelerated, the shock at the time of deceleration is eliminated because the set pressure of the overdrive valve becomes low. On the other hand, when the vehicle starts moving, the set pressure of the overdrive valve becomes high and a predetermined driving force is obtained.

In the above embodiment, the case where the control valve 2 is of a hydraulic pilot type and its stroke amount is controlled by the pilot pressure from a pilot hydraulic circuit has been described. However, this is an electromagnetic proportional valve, and its solenoid portion has a pedal. The present invention can also be applied to a circuit having a control valve for controlling the stroke amount by applying a voltage corresponding to the depression amount of 12a. In this case, naturally, the throttle return valve function is also provided electrically.

In the configuration of the above embodiment, the hydraulic pilot type control valve 2 functions as a control valve, the slow return valve 13 functions as a delay means, and the first over-dry relief valves 17a and 17b.
Is an over-dry relief valve, and the first switching valve 20 is a relief valve.
Each of the pressure setting pressure control means is configured.

[0024]

According to the present invention, when the speed of switching the operating position of the control valve from the operating position to the neutral position is reduced at a speed dependent on the delay means, the speed of the working vehicle is reduced. Works, and when decelerating at low gear, 2
The opening area diagram between the A and B ports and the opening area diagram between the B (or A) and T ports of the control valve are wrapped by a predetermined appropriate stroke amount so that the step relief does not operate. A deceleration feeling is obtained, cavitation is prevented, and a shock is reduced at low speed deceleration.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an opening area diagram of a control valve of a traveling hydraulic circuit of a work vehicle according to the present invention.

FIG. 2 is a return pressure waveform diagram when decelerating at a high speed stage when a control valve having the characteristics of FIG. 1 is used.

FIG. 3 is a return pressure waveform diagram when decelerating at a low speed stage when a control valve having the characteristics of FIG. 1 is used.

FIG. 4 is an opening area diagram between the AB port, between the B (or A) and T ports, and between the PA (or B) ports of the control valve used in the embodiment.

FIG. 5 is a hydraulic circuit diagram for a work vehicle to which the present invention is applied.

FIG. 6 is a diagram showing a conventional first opening area characteristic of the control valve shown in FIG. 5;

7 is a return pressure waveform diagram when decelerating at a high speed stage when a control valve having the characteristics of FIG. 6 is used.

8 is a return pressure waveform diagram when decelerating at a low speed stage when a control valve having the characteristics of FIG. 6 is used.

FIG. 9 is a diagram showing a second conventional opening area characteristic of the control valve shown in FIG. 5;

10 is a return pressure waveform diagram when decelerating at a high speed stage when a control valve having the characteristics of FIG. 9 is used.

11 is a return pressure waveform diagram at the time of deceleration at a low speed stage when a control valve having the characteristics of FIG. 9 is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hydraulic pump 2 Control valve 3 Counter balance valve 4 Hydraulic motor 5 Transmission 7 Transmission switching valve 17a, 17b 1st overload relief valve 20 1st switching valve 22 2nd overload relief valve

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mitsuo Kihara 650 Kandamachi, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. Construction Machinery Co., Ltd. (72) Inventor Saburo Yoshio 650, Kandamachi, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. (56) References JP-A-63-63832 (JP, A) JP-A-60-12703 (JP, U) JP-A-2-144824 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F15B 11/00 E02F 9/22

Claims (1)

(57) [Claims] 1. A hydraulic pump driven by a prime mover, a hydraulic motor driven by oil discharged from the hydraulic pump, and a rotational speed of an output shaft of the hydraulic motor is changed to at least two stages of a high speed and a low speed. A transmission for transmitting to a traveling shaft, provided between the hydraulic pump and the hydraulic motor, for controlling an amount of oil flowing into the hydraulic motor and flowing out of the hydraulic motor; Then PA
A control valve that switches so that the (or B) port communicates with the B (or A) -T port; delay means for delaying a speed at which the control valve switches from an operating position to a neutral position; Operating means for controlling the stroke amount; a counterbalance valve provided between the hydraulic motor and the control valve; a counterbalance valve and the control valve provided between the hydraulic motor and the counterbalance valve. An overload relief valve in which the set pressure switches between two stages of high pressure or low pressure in accordance with the pipeline pressure between the control valve and the counterbalance valve; the traveling hydraulic circuit of the working vehicle and a relief setting pressure control means to increase the set pressure of the load relief valve, switching to the neutral position from the operating position of the control valve intended changeover speed But the
The work vehicle that performs a switching operation at a speed that depends on delay means.
During deceleration, the transmission is such line pressure between the control valve and counterbalance valve at the low speed does not become the predetermined value or more, and such that the conduit pressure in the high speed step is the predetermined value or more In addition, AB of the control valve
Characterized in that it constitutes the opening area diagram and B (or A) -T said control valve opening area diagram such that a predetermined stroke length only rap between ports between ports.