JP3072804B2 - Vehicle straight-running control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for controlling, for example, the straight running of a construction vehicle.

[0002]

Conventional control circuit shown in the Related Art FIG. 2, the first pump P _1, with connecting the first circuit system consisting traveling switching valve 1 and switching valve 2-3 Prefecture, the second pump P ₂ is connected to a second circuit system including a traveling switching valve 4 and switching valves 5 to 6. The traveling switching valve 4, and the switching valve 2,3,5,6 is a normally open type, when in the neutral position shown, the first pump P _1, and a second discharge oil of the pump P ₂ is, It is returned to the tank T via the neutral flow paths 7, 8 and the tank passages 9, 10.

The pressure ports of the most upstream switching valves 1 and 4 of the first and second circuit systems are connected to the first and second pumps P ₁ and P ₁ , respectively.
₂ and the traveling switching valve 1 of the first circuit system controls a right traveling motor (not shown), and the traveling switching valve 4 of the second circuit system controls a left traveling motor (not shown). I have. Further, a passage 11 communicating with a pressure port of the switching valve 2 is connected to the neutral flow path 7 between the traveling switching valve 1 and the switching valve 2, and a pair of check valves 13 and 14 are connected in series to the passage 11. Provided. The check valves 13 and 14 are configured to allow only the flow from the neutral flow path 7 to the pressure port.

The pressure ports of the switching valves 2, 3, 5 and 6 are connected via parallel passages 17 and 18, and one end of the parallel passage 17 is connected to check valves 13 and 14.
It communicates between. Further, in the third pump P _3, connects the third circuit system consisting of switching valves 21 to 23 and the straight traveling valve V. The switching valve 21 to 23 and the straight traveling valve V is first, and second circuit system as well as normally open, when they are in the neutral position shown, oil discharged from the third pump P ₃ is neutral flow It is returned to the tank T via the path 25 and the tank passages 26, 10.

The straight traveling valve V is located at the most upstream position in the third circuit system, and switches when a pilot pressure acts on its pilot chamber 27. The straight traveling valve V, the first inlet port 31 communicating with the second pump P ₂
When, a second inlet port 32 which communicates with the third neutral flow passage 25 of the pump P _3, a first connection port 33 which communicates with the parallel path 17 of the first circuit system, the parallel passages 18 of the second circuit system And a second connection port 34 that is in communication. When the traveling straight valve V is at the normal position shown in the figure, the first inflow port 31 and the second connection port 34
And the second inflow port 32 is communicated with the tank passage 10. When the pilot pressure is applied to the pilot chamber 27 of the travel straight valve V and the travel straight valve V is switched, the first and second connection ports 33 and 34 communicate with each other, and the second inflow port 32 is connected to both of them. It also communicates with the connection ports 33,34. And the first inflow port 3
1 is closed.

The pilot chamber 27 of the straight traveling valve V is
The first pilot passage 29 and the second pilot passage 30 are connected. The first pilot passage 29 is connected in parallel to the traveling switching valve 1 and the traveling switching valve 4. When the traveling switching valves 1 and 4 are at the neutral position in the drawing, the first pilot passage 29 communicates with the tank passage 10 via the traveling switching valves 1 and 4. The communication between the first pilot passage 29 and the tank passage 10 is cut off only when the traveling switching valves 1 and 4 are simultaneously switched.

The second pilot passage 30 is connected in series to the switching valves 2, 3, 5, and 6, and the switching valves 2, 3, 5, and 6 are connected in series.
When the positions 3, 5, and 6 are in the neutral position shown in the figure, they communicate with the tank passage 10 through the switching valves 2, 3, 5, and 6.
However, if any one of the switching valves 2, 3, 5, and 6 is switched to a position other than the neutral position, communication between the second pilot passage 30 and the tank passage is interrupted. As described above, when both the first pilot passage 29 and the second pilot passage 30 are disconnected from the tank passage 10, a pilot pressure is generated in the pilot chamber 27 of the traveling straight valve V. V is switched from the illustrated normal position to the switching position.

In such a conventional control circuit, when the switching valves for traveling 1 and 4 are maintained at the neutral position shown in the figure, the vehicle is stopped because pressure oil is not supplied to the left and right traveling motors. At the same time, since the first pilot passage 29 communicates with the tank passage 10, the pilot chamber 27 of the straight traveling valve V is also maintained at the pilot pressure. Therefore, the straight traveling valve V also maintains the illustrated normal position. When the straight traveling valve V is in the normal position, the communication between parallel passages 17, 18 of the first and second circuit system is interrupted, at this time, the second hydraulic fluid pump P ₂ is, first of straight traveling valve V It is supplied from one inflow port 31 to the parallel passage 18 of the second circuit system via the second connection port 34.
In this state, when one of the switching valves 2 and 3 of the first circuit system is switched to a position other than the neutral position, the neutral flow path 7 is closed, so that the pressure oil that has passed through the traveling switching valve 1 passes through the passageway. 11 to the parallel path 17. Therefore, if the switching valves 21 to 23 of the third circuit system are in the neutral position, the pressure oil from the third pump P3 can be supplied to the actuator (not shown) connected to the switching valves 2 and ₃ .

When the traveling switching valves 1 and 4 are simultaneously switched, the left and right traveling motors are driven and the vehicle enters a traveling state. At this time, the neutral flow paths 7, 8 downstream of the traveling switching valves 1, 4 are almost in a closed state.
The switching valves 2, 3, 5, and 6 are hardly supplied with pressure oil. Moreover, in this state, if all of the switching valves 2, 3, 5, and 6 are maintained at the neutral position, the second pilot passage 30
Communicates with the tank passage 10 via the switching valves 5, 6, 3, and 2, so that no pilot pressure is generated in the pilot chamber 27 of the straight traveling valve V. Therefore, the straight traveling valve V remains at the normal position shown in the figure.

When any of the switching valves 2, 3, 5, and 6 is switched from the above state to a position other than the neutral position,
Since both of the pilot passages 29 and 30 are closed, a pilot pressure is generated in the pilot chamber 27 of the straight travel valve V, and the straight travel valve V is switched to the switching position by the action of the pilot pressure. A straight traveling valve V is Setsu換Ru, the left and right traveling motors discharge oil of the first pump P ₁ and second pump P ₂ is supplied separately. Therefore, the first and second pumps P ₁ ,
If at equal rotational speed of P _2, flow rate supplied to the left and right traveling motors become equal, the straight running of the vehicle can be compensated. In the straight running state, the switching valves 2, 3,.
5,6 either, or switch the all at the same time, the actuator connected thereto switching valve 2,3,5,6, oil discharged from the pump P ₃ is supplied. That is, while the vehicle is running, these switching valves 2, 3, 5, 6
Can be operated simultaneously. However, in this case, since the hydraulic oil supply system of the traveling motor and the other actuators is different, the lightness of the load does not particularly affect the operating speed of the traveling motor, and the traveling straightness of the vehicle is compensated. Is done.

The first to third circuit systems are provided with main relief valves 35 to 37, respectively. When the pressure in each circuit system exceeds the pressure set by the main relief valves 35 to 37, the main relief valves 35 to 37 are provided. 35 to 37 are opened to allow the pressure oil to escape to the tank T.

[0012]

In such a conventional control circuit, when the traveling straight valve V is switched by the action of the pilot pressure and the switching valves 21 to 23 of the third circuit system are in the neutral position, in 3 pressure oil pump P _3, although the actuator connected with the switching valve 2,3,5,6 of the first and second circuit system is driven, depending on the operation of the actuators,
The load pressure may increase and the pressure in the third circuit system may increase. For example, even if the actuator reaches the stroke end, if the switching valve of the actuator is switched, the load pressure increases, and the pressure in the third circuit system also increases. Then, when the pressure continues to rise, the pressure reaches the set pressure of the main relief valve 37 of the third circuit system, and the main relief valve 37 operates to reduce the pressure.

The main relief valve 37 sets the relief operation set pressure near the maximum allowable pressure in the third circuit system, and regulates the maximum pressure in the circuit. But,
The actuator is driven at a pressure lower than the maximum pressure. (In general, excavation work is not performed in the straight traveling state.) Therefore, when the actuator having a low pressure necessary for driving as described above reaches the stroke end and the load pressure increases, the conventional control circuit However, since the pressure in the circuit increases to the set pressure of the main relief valve 37 of the third circuit system, there is a problem that a large energy loss occurs. Also, if the relief operation is performed at the relief operation set pressure of the main relief valve 37, the oil temperature will rise sharply due to the high pressure,
There was also a problem that the operating capacity was reduced. SUMMARY OF THE INVENTION It is an object of the present invention to provide a vehicle straight-running control circuit that can control the pressure in a third circuit system according to a situation and minimize energy loss.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a first and second pumps connected to a first and a second pump.
In the second circuit system, a main relief valve is provided, and a plurality of normally open type switching valves are connected, and the most upstream switching valve of the switching valves is used to control one of the left and right traveling motors. The traveling switching valve is connected in tandem with the traveling switching valve and an adjacent downstream switching valve, and a plurality of switching valves located downstream of the traveling switching valve are connected in parallel via a parallel passage. On the other hand, a main relief valve is provided in the third circuit system to which the third pump is connected, and a plurality of normally open type switching valves are connected. When the traveling straight valve is switched and all the switching valves located upstream of the traveling straight valve are in the normal position, the third pump is turned on. A traveling straight control circuit for a vehicle, wherein discharge oil flows into a plurality of switching valves located downstream of the traveling switching valves of the first and second circuit systems via the parallel passage; A branch passage communicating with the tank passage is provided between the switching valve and a switching valve located upstream thereof, and a sub relief valve having a lower set pressure than the main relief valve of the third circuit system is provided in the branch passage.

[0015]

With the above construction, when the straight-travel valve is switched and all the switching valves upstream of the straight-running valve are in the neutral position, the sub-circuit having a lower set pressure than the main relief valve in the third circuit system is used. The relief valve operates before the main relief valve.

[0016]

FIG. 1 shows an embodiment of the present invention. here,
A straight traveling valve V of the third pump P ₃ downstream, the neutral flow passage 25 between the switching valve 23 positioned upstream, branch passage 3
8 are provided to communicate with the tank passage 10. And
A sub-relief valve 39 is provided on the branch passage 38. The sub relief valve 39 lowers the relief operation set pressure than the main relief valve 37 of the third circuit system, and drives the actuator connected to the switching valves 2, 3, 5, and 6 of the first and second circuit systems. Slightly higher than the pressure. These are the differences from the conventional example described above,
The other points are the same as those of the conventional example, and therefore, the same components as those of the conventional example are denoted by the same reference numerals, and detailed description thereof will be omitted.

As described above, in the state where the straight traveling valve V is switched by the action of the pilot pressure and the switching valves 21 to 23 of the third circuit system are maintained in the neutral position, the first and second traveling valves are not changed.
Pressure oil from the pumps P ₁ and P ₂ is supplied to the first and second traveling switching valves 1 and 4 to compensate for the straight traveling performance of the vehicle, and at the same time, by the pressure oil of the third pump P ₃ . , Actuators connected to the switching valves 2, 3, 5, and 6 of the first and second circuit systems. In this state, the relief operation can be performed by either the main relief valve 37 or the sub relief valve 39 as can be seen from the drawing. However, since the sub-relief valve 39 is set to have a lower relief operation set pressure than the main relief valve 37, the pressure in the third circuit system increases due to an increase in the load pressure of the actuator connected to the switching valves 2, 3, 5, and 6. Rises before reaching the set pressure of the main relief valve 37, the sub relief valve 3
9 is activated. Further, since the operation set pressure of the sub-relief valve 39 is set slightly higher than the pressure required for driving the actuator, a sufficient pressure for driving the actuator is secured.

Therefore, in the third circuit system in which the traveling straight valve V is switched and the switching valves 21 to 23 maintain the neutral position, the pressure increases only to the pressure necessary for driving the actuator. So little energy loss occurs. Incidentally, one of the straight traveling valve V ₁ upstream of the switching valve 21 to 23, or all the Setsu換Ru, neutral flow passage 25 is interrupted. Therefore, in this case, the maximum pressure of the third circuit system is the main relief valve 37
Will be controlled by

[0019]

[Effect] When the straight travel valve is switched and all the switching valves upstream of the straight travel valve are in the neutral position, the sub relief valve having a lower set pressure than the main relief valve in the third circuit system is ahead of the main relief valve. , The pressure in the third circuit system does not rise more than necessary. Therefore, energy loss hardly occurs in the third circuit system. Also, during the relief operation of the sub relief valve, the rise in oil temperature is lower than when the main relief valve is operating,
The operating capacity of the entire circuit has hardly declined due to the rise in oil temperature.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of the present invention.

FIG. 2 is a circuit diagram of a conventional example.

[Explanation of symbols]

1,4 traveling switching valve 2,3,5,6 switching valve 9, 10 tank passage 17, 18 parallel passage 26 tank passage 35 to 37 the main relief valve 38 branch passage 39 sub-relief valve P ₁ first pump P ₂ first 2 pump P ₃ 3rd pump V Traveling straight valve T tank

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B62D 5/07

Claims (1)

(57) [Claims] 1. A first and a second pump connected to a first and a second pump.
In the circuit system, a main relief valve is provided, and a plurality of normally open type switching valves are connected, and the most upstream switching valve among the switching valves is used for controlling one of the left and right traveling motors. A switching valve, in which the traveling switching valve and an adjacent downstream switching valve are connected in tandem, and a plurality of switching valves located downstream of the traveling switching valve are connected in parallel via a parallel passage. On the other hand, in the third circuit system to which the third pump is connected,
A main relief valve is provided, and a plurality of normally open type switching valves are connected, and the most downstream of the switching valves is a traveling straight valve that is switched by the action of pilot pressure, and the traveling straight valve is switched, and When all the switching valves located upstream of the straight travel valve are in the normal position,
In the vehicle straight traveling control circuit, the discharge oil from the third pump flows through the parallel passage into a plurality of switching valves located downstream of the traveling switching valves of the first and second circuit systems. A branch passage communicating with the tank passage is provided between the straight traveling valve and the switching valve located upstream thereof,
A straight running control circuit for a vehicle, wherein a sub-relief valve having a lower set pressure than a main relief valve of the third circuit system is provided in the branch passage.