JPH08338404A - Load sensing hydraulic circuit - Google Patents

Abstract

PURPOSE: To form a vehicle so that its straight advancing property can be compensated, even when a work error is provided in a switching valve and a pressure compensating valve or in the other flow path. CONSTITUTION: Full speed running positions a to d are provided in switching valves 4, 5, also to provide a communication path 64 of connecting actuator ports 32, 33 and 35, 36 of the switching valves 4, 5 in these full speed running positions a to d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a pair of traveling system actuators and other work machine system actuators, and a load sensing circuit for detecting the maximum load pressure of these actuators and controlling the pump discharge pressure. Regarding

[0002]

2. Description of the Related Art A conventional load sensing circuit shown in FIG. 2 is provided with a pair of traveling system actuators 1 and 2 and a working machine system actuator 3. The actuators 1 to 3 are provided with switching valves 4 to 6 respectively. Are connected. Each of the switching valves 4 to 6 forms an inflow port 7 to 9 connected to the variable pump P and a relay port 13 to 15 connected to the inflow side of the pressure compensation valve 10 to 12. When the switching valves 4 to 6 are switched to the left or right, the inflow ports 7 to 9 and the relay ports 13 to 15 communicate with each other, and
The opening degree of the variable throttles 16 to 18 formed in the communication process is proportional to the switching amount of the switching valves 4 to 6.

Downstream of the relay ports 13-15,
Although the pressure compensating valves 10 to 12 are connected as described above,
The downstream side of the pressure compensating valves 10 to 12 is the first communication port 1
9 to 21 and the second communication ports 22 to 24. The first and second communication ports 19 to 24 communicate with the tank line 31 via the return ports 25 to 30 when the switching valves 4 to 6 are in the illustrated neutral position. Then, the switching valve 4 to
When 6 is switched to the left position in the drawing, the first communication port 19
˜21 communicate with one of the actuator ports 32-34, while the other actuator port 35-37 communicates with the tank line 31 via the return ports 26, 28, 30.
Communicate with

When the switching valves 4 to 6 are switched to the right position in the drawing, the second communication ports 22 to 24 communicate with the other actuator ports 35 to 37, while the one actuator ports 32 to 34 are connected. Returns to port 2
It communicates with the tank line 31 via 5, 27 and 29.
Each of the switching valves 4 to 6 as described above connects the pilot chambers 38 and 39, 40 and 41, and 42 and 43 provided on both sides thereof to a pilot pressure reducing valve (not shown). This pilot pressure reducing valve guides the pilot pressure to one of the pilot chambers 38, 39, 40 or 41, 42 or 43 depending on the direction in which the lever is tilted, and the other pilot chamber 39, 38, 4 or
Any one of 1 or 40, 43 or 42 is communicated with the tank through the tank passage.

Further, the pilot pressure reducing valve is capable of controlling the magnitude of the pilot pressure according to the tilt amount of the lever. The variable pump P is a regulator 4
The maximum load pressure of each actuator selected by the shuttle valves 45 to 47 is guided to the regulator 44. That is, the shuttle valves 45 to 47 are connected in a tournament system, and the shuttle valve 47 at the final stage selects the highest pressure. And, the shuttle valve 45 on one side is
Pressure compensating valve 1 for controlling traveling system actuators 1, 2
It is connected to the downstream side of 0 and 11. Therefore, the shuttle valve 45 is provided with a pair of traveling system actuators 1, 2
Whichever is higher, directs it to the final stage shuttle valve 47.

The shuttle valve 46 is connected to the downstream side of the pressure compensation valve 12 of the actuator 3 of the working machine system. Therefore, the shuttle valve 46 selects the highest load pressure on the working machine side and sets it to the final stage shuttle valve 47.
Lead to. Further, the shuttle valve 47 at the final stage selects the higher one of the load pressures of the working machine system and the traveling system as described above, and transmits it to the regulator 44. Therefore, the maximum load pressure of the circuit is guided to the regulator 44. At this time, the regulator 44 controls the variable pump P so that the discharge pressure thereof becomes higher than the maximum load pressure by a predetermined pressure. . In the figure, reference numeral 48
Is a main relief valve provided in the process of communication between the shuttle valve 47 and the regulator 44.

The pressure compensating valves 10 to 12 have one of the pilot chambers 49 to 51 in communication with the shuttle valve 47 at the final stage via a load detecting flow path 58. Therefore, the maximum load pressure of the circuit is also introduced to the one pilot chamber 49 to 51. The spring force of the springs 52 to 54 is applied to the one pilot chamber 49 to 51. The other pilot chambers 55 to 57, which are opposed to the one pilot chamber, are provided in the pressure compensating valves 10 to 10.
The pressure on the upstream side of 12 is introduced. The pressure compensating valves 10 to 12 thus configured have an overlapping configuration that maintains a fully closed state in the normal position shown.

The pressure compensating valves 10 to 12 include a variable throttle 1
6-18 after pressure is higher than the maximum load pressure by the spring 52-
The passing flow rate is controlled so as to increase by a pressure corresponding to the spring force of 54. Now, for example, the pilot pressure reducing valve is operated to operate one of the pilot chambers 38, 4 of the switching valves 4-6.
When pilot pressure is introduced to 0 and 42, those switching valves 4 to 6
Switches to the left position in the drawing. Therefore, the fluid discharged from the variable pump P is transferred to one of the actuator ports 32-34.
Is supplied to the actuators 1 to 3 via the other actuator ports 35 to 37, and the return fluid of these actuators is supplied to the tank line 31 via the other actuator ports 35 to 37.
Is returned to.

When the actuators 1 to 3 are operated as described above, the load pressures of the actuators 1 to 3 are introduced to the load detection flow path 58. Is selected and regulator 4
4 is transmitted. The maximum load pressure signal controls the discharge pressure of the variable discharge pump P to be higher than the maximum load pressure by a predetermined pressure. That is, the variable pump P
Is to be controlled by a constant differential pressure. Further, since the maximum load pressure at this time is guided to one of the pilot chambers 49 to 51 of the pressure compensating valves 10 to 12, the differential pressure before and after the variable throttles 16 to 18 is combined with the constant differential pressure control function of the variable pump P. The pressure is kept constant. The pilot pressure is introduced to the other pilot chambers 39 to 43 of the switching valves 4 to 6 so that the switching valves 4 to
When 6 is switched to the right side position in the drawing, the supply side and the return side are merely opposite to the above. Further, reference numeral 59 in the drawing is a horsepower constant control mechanism for controlling the variable pump P such that the discharge pressure p and the discharge amount q of the pump are constant at p × q = p × q.

[0010]

In the conventional load sensing circuit as described above, for example, the switching valves 4, 5,
If there is a processing error in the pressure compensating valves 10 and 11 or other flow paths, when the switching valves 4 and 5 are fully switched to drive the traveling system actuators 1 and 2 at full speed, the vehicle is bent. There was a problem of doing. Further, the constant differential pressure control function of the variable pump P and the function of the pressure compensating valve are combined to keep the differential pressure around the variable throttles 16 to 18 constant, and as a result, the flow rate according to the opening degree of the variable throttle. Will be supplied to each actuator. Since the flow rate according to the opening degree of the variable throttle is supplied to each actuator in this way, for example, the switching valves 4 and 5 are fully switched to maintain the traveling system actuators 1 and 2 at the full speed traveling state. , When the load pressure of the actuator 3 of the working machine system is increased to a pressure close to the set pressure of the main relief valve 48,
A shock is given to the actuators 1 and 2 of the traveling system.

The cause is the actuator 3 of the working machine system.
Since the high load pressure of # 1 also acts on the pilot chambers 49, 50 of one of the pressure compensating valves 10, 11 of the traveling system, the openings of the pressure compensating valves 10, 11 are suddenly and extremely narrowed. When the openings of the pressure compensating valves 10 and 11 become small in this way, the rear pressure of the variable throttles provided in the switching valves 4 and 5 rises, so that the variable pump P tries to keep the differential pressure before and after the throttles constant. Increase the discharge pressure. However, the variable pump P
If the discharge pressure increases, the horsepower constant control mechanism 59 functions to reduce the discharge amount. This sudden decrease in the discharge amount gives a shock to the actuators 1 and 2 which are running at full speed. In order to prevent the occurrence of this shock, the pressure compensating valves 1 and 2 have an underlap structure,
Even if the pilot pressure in one of the pilot chambers 49 and 50 rises extremely, it is conceivable to leave the pressure compensation valve open to some extent.

If the pressure compensating valve is constructed as an underlap as described above and the pressure compensating valve is opened to some extent in any situation, then another problem as described below will occur. Will occur. For example, when the opening of the pressure compensating valve corresponds to the underlap, and the operator makes a steering operation by changing the traveling speeds of the left and right actuators 1 and 2, the operability is deteriorated. That is, when the traveling speeds of the left and right actuators 1 and 2 are given to perform the steering operation, a difference occurs in the load pressure between the inner wheel and the outer wheel. At this time, the pressure compensation valves 10, 1
If the opening of No. 1 is fixed to the amount of underlap, the differential pressures before and after the variable throttles 16 and 17 differ by the difference of the load pressure. Therefore, with the switching valves 4 and 5,
Since the switching amount and the proportion of the supply flow rate in proportion to the switching amount are different, the operation feeling of the operator is confused. An object of the present invention is to provide a load sensing circuit which does not bend when traveling straight ahead and has good operability even during steering operation that gives a speed difference to an actuator of a traveling system.

[0013]

A first invention is to provide a pair of traveling system actuators, a working machine system actuator other than these traveling system actuators, a pump for supplying a pressure fluid to each actuator, and this pump. A regulator that keeps the discharge pressure of each actuator higher than the maximum load pressure of each actuator by a predetermined pressure, a switching valve that is connected in parallel to the pump and that is connected individually to each actuator, and a variable valve installed in this switching valve. A pressure compensating valve for maintaining a constant differential pressure across the throttle, and a load detection flow path for detecting the maximum load pressure of a plurality of actuators are provided,
It is premised on a load sensing circuit in which one pilot chamber of the pressure compensation valve is connected to the load detection flow passage and the other pilot chamber is connected to an upstream passage of the pressure compensation valve. Based on the above-mentioned circuit, the first aspect of the present invention makes the pressure compensating valve an overlap structure,
The switching valve for controlling the actuators of the traveling system is provided with a full-speed traveling position, and at this full-speed traveling position, a communication passage for communicating the actuators of both traveling systems is provided, and this communication passage is communicated with the load detection flow passage. It is characterized by points. The second invention is based on the premise of the first invention, and is characterized in that a throttle is provided in the process of communication between the communication passage and the load detection flow passage.

[0014]

Since the first aspect of the invention is configured as described above, if the actuators of the traveling system are kept in the full-speed traveling state, both actuators will communicate with each other through the communication passage. Therefore, the supply flow rates to both actuators become equal, and straight traveling is also maintained. Further, even if the load pressure of the working machine system actuator increases, for example, to the relief set pressure, since the load detection flow path of the circuit communicates with the actuator side of the traveling system via the communication passage, The high pressure of the actuator of the working machine system is guided to the actuator side of the traveling system, and the load pressure signal of the working machine system and the load pressure signal of the traveling system are neutralized as a whole. Therefore, even if the load pressure of the actuator of the working machine system rises, the opening of the pressure compensation valve of the traveling system does not become extremely small. In addition, the pressure compensating valve effectively functions even during steering operation in which the speeds of the actuators of the traveling system are varied, so that the operability does not deteriorate. In the second aspect of the invention, since the throttle is provided in the communication process between the load detection flow passage and the communication passage, even if the load pressure of the actuator of the traveling system becomes extremely low during traveling downhill, for example, the load detection flow passage The load pressure signal of can be maintained.

[0015]

In the embodiment shown in FIG. 1, the switching valves 4 and 5 are formed with communication ports 60 to 63, and when the switching valves 4 and 5 are fully switched, the full speed traveling position a is a switching position. And b, c and d are provided. And
When the switching valves 4 and 5 are switched to any of the full speed traveling positions a to d, the supply side port of the communication ports 60 to 63 is the actuator port 32, 33 or 3.
It connects to 5, 36. All of the communication ports 60 to 63 configured as described above communicate with each other via a communication passage 64, and the communication passage 64 communicates with the load detection flow passage 58 via a throttle 65. The configuration other than the above is the same as the conventional one. Therefore, the same components as the conventional one will not be described in detail and will be described using the same reference numerals. The pressure compensating valves 10 to 12 in this embodiment are configured to overlap each other and are fully closed in the normal state.

Next, the operation of this embodiment will be described. now,
If the two switching valves 4 and 5 are switched to the full speed traveling positions a and c, the openings of the variable throttles 16 and 17 are maximized and the supply side actuator ports 32 and 33 are provided.
Are communicated via the communication ports 60, 62 and the communication passage 64. When the supply-side actuator ports 32 and 33 communicate with each other in this way, the supply flow rates to the actuators 1 and 2 of both traveling systems become equal, so that the straightness of the vehicle is compensated. Even if the load pressure of the actuator 3 of the working machine system rises to the set pressure of the main relief valve 48 in the above state, for example, the load detection flow path 58 → the throttle 65 → the communication passage 64 → the communication port 60, 62
The pressure in the load detection flow path 58 does not rise to the relief set pressure because the pressure is released to the actuators 1 and 2 side of the traveling system via.

Therefore, the discharge amount of the variable pump P does not decrease due to the extreme increase of the load pressure signal,
No shock will occur to the running vehicle. Further, since the pressure compensating valves 10 and 11 sufficiently function even during the steering operation in which the actuators 1 and 2 have different speeds,
Since the switching valve 4 and the switching valve 5 have the same switching amount and the same ratio of the supply flow rate, the operation feeling of the operator is not deteriorated. Furthermore, the load detection flow path 58 and the communication path 64
Since the throttle 65 is provided in the process of communicating with, even if the load pressure of the actuators 1 and 2 of the traveling system becomes extremely low, for example, when traveling down a slope, the load pressure signal of the load detection flow path 58 can be maintained.

[0018]

According to the first aspect of the present invention, the straightness of the vehicle is compensated even if there is a processing error in the switching valve, the pressure compensating valve, or other flow passages. Further, even if the load pressure of the actuator of the working machine system increases to, for example, the relief set pressure, it does not affect the traveling of the vehicle. Further, the pressure compensating valve effectively functions even during the steering operation for making a difference in the speed of the actuators of the traveling system, so that the operability is not deteriorated. In the second aspect of the invention, since the throttle is provided in the communication process between the load detection flow passage and the communication passage, even if the load pressure of the actuator of the traveling system becomes extremely low during traveling downhill, for example, the load detection flow passage The load pressure signal of can be maintained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional load sensing circuit.

[Explanation of symbols]

 1, 2 Traveling system actuator 3 Working machine system actuator 4-6 Switching valve P Variable pump 10-12 Pressure compensation valve 16-18 Variable throttle 44 Regulator 49-50 One pilot chamber 55-57 Other pilot chamber 65 Throttle ad driving position

Claims (2)

[Claims] 1. A pair of traveling system actuators, a working machine system actuator other than these traveling system actuators, a pump for supplying a pressure fluid to each actuator, and the discharge pressure of this pump, the maximum load of each actuator. A regulator that keeps a predetermined pressure higher than the pressure, a switching valve that is connected in parallel to the pump and that is individually connected to each actuator, and the differential pressure before and after the variable throttle provided in this switching valve is kept constant. Pressure compensating valve for, and a load detection flow passage for detecting the maximum load pressure of the plurality of actuators, one pilot chamber of the pressure compensation valve is connected to the load detection flow passage, the other pilot chamber In the load sensing circuit in which the pressure compensation valve is connected to the passage on the upstream side of the pressure compensation valve, The switching valve for controlling the system actuator is provided with a full-speed traveling position, and at this full-speed traveling position, a communication passage for communicating the actuators of both traveling systems is provided, and the communication passage is connected to the load detection flow passage. Sensing circuit. 2. The load sensing circuit according to claim 1, wherein a throttle is provided in a communication process between the communication passage and the load detection flow passage.