JPH0318015B2 - - Google Patents

Description

[Detailed Description of the Invention] In a conventional two-pump type hydraulic power shovel, in order to save the driving power of the variable displacement pump when each actuator is not in operation, it is necessary to control the hydraulic circuit provided for each pump. A back pressure generating valve is connected between the center bypass oil passage of the switching valve and the tank to generate a constant back pressure in each center bypass oil passage when the directional switching valve is in the neutral position. The back pressure generated in each oil passage is used to minimize the pump tilt angle when the actuator is not operating, and therefore the pump discharge amount per rotation, but the engine rotation speed is approximately the same as when the actuator is operating. Since the speed is high, pump drive energy is wasted.

The present invention solves the above problem by automatically placing the engine in an idling state when all actuators are inactive, even when the engine is being driven with the speed control lever of the all-speed governor set to the rated rotation position. This is what I am trying to do.

The present invention provides hydraulic circuits for each of a plurality of pumps that are simultaneously driven by an engine equipped with an all-speed governor, and when the directional control valves of each hydraulic circuit are all in the neutral position, each of the center bypass oil passages is connected to the hydraulic circuit. In a hydraulic system in which back pressure generating valves that generate approximately equal back pressure are connected between each center bypass oil passage and a tank, the speed control lever of the all-speed governor is located between the operating levers that can be fixed at any position. a lost motion coupler having a lost motion stroke corresponding to the rotational displacement of the speed control lever between an idling position and a rated rotational position; and a lost motion coupler that extends or retracts by approximately the lost motion stroke in response to supply or discharge of the back pressure. A single-acting hydraulic cylinder is connected in series in such a manner that the idle-motion coupler causes idle movement when the single-acting hydraulic cylinder is extended at the idling position of the operating lever, and pressure is maintained between the center bypass oil passage. The present invention is characterized in that a switching valve is provided that connects the center bypass oil passage on the low pressure side to the single-acting hydraulic cylinder when a difference occurs.

An embodiment of the present invention applied to a two-pump system will be described below with reference to FIGS. 1 to 6. The first and second variable displacement pumps (axial piston pumps) 1 and 2 are simultaneously driven at a constant speed by a high-speed diesel engine 4 for construction machinery that is automatically controlled by an all-speed governor 3. The discharge oil passage 5 of the first pump 1 has a plurality of directional switching valves (multiple valves).
6, 7, etc. and a relief valve 8 are connected in parallel, and a back pressure generating valve 10 is connected between the center bypass oil passage 9 of the directional control valve and the tank T. The passage 11 is assembled into a valve block 12.

In addition, a plurality of directional switching valves (multiple valves) 1 are also installed in the discharge oil passage 13 of the second pump 2, which has the same configuration as the first pump 1.
4, 15, etc. and a relief valve 16 are connected in parallel, and a back pressure generating valve 1 same as the back pressure generating valve 10 is connected between the center bypass oil passage 17 of the directional switching valve and the tank T.
8 are connected, but these valves and their return oil passages 19
is assembled to the valve block 20. Note A, B
are the output ports of the directional control valves provided in each valve block.

The back pressure generating valves 10 and 18 are unload valves and throttle valves, and the set pressure thereof is a fraction of the set pressure of the corresponding relief valves 8 and 16, respectively. Therefore, each valve block 1
When the omnidirectional switching valves belonging to Nos. 2 and 20 are set to the neutral position shown, approximately the same back pressure is generated in the center bypass oil passages 9 and 17, but when the directional switching valve of either valve block is set to the left or right actuator. When the valve block is switched to the operating position, the back pressure in the valve block is discharged to the tank T through the drain oil passage of the corresponding back pressure generating valve and becomes zero.

21 is a pilot oil passage that transmits the oil pressure of the center bypass oil passage 9 to the tilt angle control device 1a of the first pump 1; 22 is a pilot oil passage that transmits the oil pressure of the center bypass oil passage 17 to the tilt angle control device 2a of the second pump 2; This figure shows the pilot oil passage for transmission, and as in the past, when the back pressure is transmitted to the tilting angle control device, the tilting angle of the corresponding pump or the pump discharge amount per rotation becomes the minimum.

Reference numeral 23 indicates a speed control lever 25 pivoted on the base 24 of the all-speed governor 3, and the speed control lever 23 is always urged to return to the idling position shown in FIG. When the speed control lever 23 is rotated to the position shown in FIG. 4, the fuel injection amount increases and the engine reaches its rated rotational speed.

Reference numeral 28 denotes an operating lever attached to a base body 29 in the driver's cab so as to rotate about a shaft 30, and the operating lever 28 is fixed at an arbitrary rotational position by a friction braking mechanism 31 provided coaxially with the shaft 30. . A single acting hydraulic cylinder 33 and a lost motion coupler 34 are connected in series between the lower end of the operating lever 28 and the tip of the speed control lever 23 via a connecting rod 32 .

The lost movement coupler 34 is fixed to the tip of the piston rod 35 of the hydraulic cylinder 33, and the pin 36 implanted in the speed control lever 23 is positioned on the axis of the piston rod and inserted into the elongated hole 37 provided in the lost movement coupler 34. The idle stroke is between the idling position (Fig. 1) and the rated rotation position (Fig. 4).
This corresponds to the rotational displacement of the speed control lever 23 during the period shown in FIG. It is preferable that an adjusting screw 38 is screwed onto the tip of the lost motion coupler 34 to adjust the length of the elongated hole 37 or the lost motion stroke. 39 indicates a lock nut of the adjusting screw 38.

The base end of the hydraulic cylinder 33 is supported by the base body 24 via a link 40, so that the hydraulic cylinder and the idle movement coupler 34 are always supported substantially horizontally by the speed control lever 23 and the link 40, The connecting rod 32 is connected to an arm 41 installed in the middle of the hydraulic cylinder 33. Hydraulic cylinder 33
is equipped with a compression spring 43 that always urges its piston 42 to return to the most retracted position shown in FIG. Extend only the movement stroke. That is, the hydraulic cylinder 33 and the idle movement coupler 34 are connected so that when the hydraulic cylinder is extended while the operating lever 28 is rotated to the idling position A, the idle movement coupler 34 moves idle.

Reference numerals 45 and 46 indicate back pressure transmission oil passages whose ends are connected to the pilot oil passages 21 and 22, respectively.
The other ends of 5 and 46 are connected to the cylinder chamber 44 via a pilot-operated switching valve 47 and an oil passage 48 in sequence. The switching valve 47 is at a central position A where the hydraulic pressures of the oil passages 45 and 46 on both sides are equal, and the oil passages on both sides are simultaneously communicated with the oil passage 48, and when a pressure difference is created between the oil passages 45 and 46 on both sides. Only the oil passage on the low pressure side is connected to oil passage 4.
8. Positions B and C are provided.

The specific structure of the switching valve 47 is, as shown in FIG. 5, a ball valve 52 which closes conical valve seats 50 and 51 symmetrically provided on both sides of a valve housing 49 by hydraulic pressure of oil passages 45 and 46, respectively. 53, and a rod 5 is installed between the ball valves 52 and 53 to prevent both ball valves from closing at the same time.
4 may be sandwiched between them, or it may be a spool valve in which a spool 56 is fitted in the inner cavity of a valve housing 55 so as to be slidable within a certain range as shown in FIG.
The spool 56 has annular grooves 56a, 56b arranged symmetrically on its outer periphery, and its sliding range is regulated by retaining rings 57, 58 symmetrically attached to the inner cavity of the valve casing. When the spool 56 is located at the center between the retaining rings on both sides, both the annular grooves 56a and 56b communicate with the oil passage 48, and the spool slides to the right end position as shown in the figure or to the left end position. Depending on the case, the left annular groove 56a or the right annular groove 56b is the oil passage 48.
communicate with. The subur 56 has an annular groove 5 on the left side.
Holes 56c and 56d are provided to communicate the right annular groove 6a to the right oil passage 46 and the right annular groove 56b to the left oil passage 45, respectively, so that the above-mentioned switching valve 47 can be operated.

A check valve 59 is installed in the middle of the oil passage 48 as shown in Fig. 1.
and a variable throttle valve 60 are connected in parallel. This corresponds to the throttling resistance when the hydraulic pressure in the cylinder chamber 44 is discharged from the back pressure generating valve 10 or 18 via the check valve 59 and the switching valve 47.
This is because the variable throttle valve 60 provides throttle resistance when the back pressure of 17 is supplied from the switching valve 47 to the cylinder chamber 44 . It goes without saying that the oil passage 48 between the check valve 59 and the variable throttle valve 60 and the hydraulic cylinder 33 is a hydraulic hose to enable free movement of the hydraulic cylinder.

Next, the operation of the present invention will be explained. FIG. 1 shows the stopped state of the engine 4, and the hydraulic cylinder 33
The speed control lever 23 is contracted to the most contracted position shown in the figure by the elasticity of the spring 43, and the operating lever 28 is in the idling position A, so the speed control lever 23 is returned to the idling position by the elasticity of the governor spring 26.
The pin 36 is engaged with the rear end (left end in the figure) of the elongated hole 37 of the lost motion coupler 34.

When the engine 4 is started and idled in this state, the omni-directional switching valves of each valve block 12, 20 are in the neutral position, and the center bypass oil passages 9, 17 are connected to the center bypass oil passages 9, 17 by valves 10, 18, respectively. To generate back pressure, the back pressure of the center bypass oil passage 9 is applied to the left port of the switching valve 47 via oil passages 21, 45, and the oil passages 22, 4 are applied to the right port of the switching valve.
6, the back pressure of the center bypass oil passage 17 is transmitted respectively. Therefore, when the back pressures of both center bypass oil passages are equal, the switching valve 47 is switched to the center position A shown in the figure, and when there is a pressure difference between the two back pressures, the switching valve 47 is switched to the B position or H position. position, and the back pressure of at least one center bypass oil passage is supplied to the cylinder chamber 44 through the oil passage 48 and the variable throttle valve 60, so the friction braking mechanism 31 restrains the cylinder at the idling position A. With respect to the operation lever 28 which is in the idling position, the hydraulic cylinder 33 extends by an idle stroke, and the elongated hole 3 is inserted into the pin 36 of the speed control lever 23 which is maintained at the idling position.
7 (right end in the figure) are engaged as shown in FIG.

Next, in order to operate the actuator, when the operating lever 28 is rotated to the rated rotational position as shown in FIG. 3, the connecting rod 32 and the hydraulic cylinder 3 in the extended position
3, the idle movement coupler 34 moves forward by approximately the idle stroke, so that the rear end of the elongated hole 37 approximately engages with the pin 36, but the speed control lever 23 maintains approximately the idling position.

Next, when the directional control valves belonging to both valve blocks 12 and 20, for example 6 and 14, are simultaneously switched to the actuator operating position, both center bypass oil passages 9 and 1
When the pump discharge hydraulic pressure is no longer supplied to the valve block 7, and only one of the directional control valves of the valve block 12 or 20 is switched to the actuator operating position, the pump discharge hydraulic pressure is supplied to the center bypass oil passage on the valve block side. It will no longer be done. That is, when the actuator is activated, the back pressure in both center bypass oil passages 9 and 17 disappears almost simultaneously, or the back pressure in one of them disappears, and the oil pressure in the cylinder chamber 44 moves the check valve 59 to the center position or to the positions on both sides thereof. , C, and is discharged to the tank T from the back pressure generating valve of the center bypass oil passage where back pressure has disappeared, and the hydraulic cylinder 33 is Shrink as shown. Therefore, the speed control lever 23 whose pin 36 is engaged with the rear end of the elongated hole 37 of the idle motion coupler 34 is connected to the governor spring 2.
The engine 4 is rotated to the rated rotational position shown in FIG. 4 against the elastic force of the engine 6, and the engine 4 produces the rated output.

Furthermore, when the omnidirectional switching valves of both valve blocks 12 and 20 are returned to the neutral position in the rated rotation state of the engine, the hydraulic cylinder 33 is moved as described above due to the back pressure generated in the center bypass oil passages 9 and 17. When the speed control lever 23 is extended, the elasticity of the governor spring 26 returns the speed control lever 23 to the idling position shown in FIG. 3, reducing the engine speed and saving pump drive energy.

The case of the two-pump hydraulic system has been described above, and the oil passage 48 to the switching valve 47 and the cylinder chamber 44 is
It is clear that the present invention can be applied to a three-pump type hydraulic system by connecting the second switching valve 61 between them as shown in FIG. In the illustrated case, the right input port of the second switching valve 61 is connected to the output port of the first switching valve 47, and the left input port of the second switching valve 61 is connected to the third pump through an oil passage 62. It is connected to a center bypass oil passage 63 provided in the hydraulic circuit. In FIG. 7, parts with the same reference numerals as those in FIG. 1 are corresponding parts. In addition, the back pressure generated in each center bypass oil path can be reduced by providing a very small pressure difference between the set pressures of each back pressure generation valve and by providing a difference in the oil path resistance of each valve block 12, 20, etc. If an extremely small pressure difference is provided, the switching valves 47, 61
It is clear that it is not necessarily necessary to provide a central position A for the above.

According to the present invention, even if the operating lever is at the rated rotational position, when all the actuators of the hydraulic circuit provided for each pump are stopped, the engine is automatically placed in an idling state to reduce power loss in each part of the engine. Waste of fuel can be prevented, and the cylinder chamber volume and weight of the single-acting hydraulic cylinder can be reduced, so that the expansion and contraction of the hydraulic cylinder and the operation of the operating lever can be made easier and faster.

[Brief explanation of the drawing]

Fig. 1 is a hydraulic circuit diagram of an embodiment of the present invention, Figs. 2 to 4 are longitudinal sectional side views showing the operation progress of its main parts, Figs. 5 and 6 are longitudinal sectional front views of the switching valve, respectively; FIG. 7 is a circuit diagram of main parts of another embodiment. 1, 2... Pump, 3... All speed governor, 4... Engine, 6, 7, 14, 15... Directional switching valve, 9, 17... Center bypass oil path, 1
0, 18...Back pressure generation valve, 23...Speed control lever, 28...Operation lever, 32...Connection rod, 33...
...Single-acting hydraulic cylinder, 34...Free movement coupler,
47...Switching valve.

Claims (1)

[Claims] 1 A plurality of pumps simultaneously driven by an engine equipped with an all-speed governor are each provided with a hydraulic circuit, and when the directional control valves of each hydraulic circuit are all in the neutral position, the hydraulic circuits are approximately equal to each center bypass oil path. In a hydraulic system in which a back pressure generating valve that generates back pressure is connected between each center bypass oil passage and a tank, the idling position is located between the speed control lever of the all-speed governor and the operation lever that can be fixed at any position. and a single-acting coupler having an idle stroke that corresponds to the rotational displacement of the speed control lever between the rated rotational position and the rated rotational position; type hydraulic cylinders are connected in series in such a manner that the idle movement coupler causes idle movement when the single acting type hydraulic cylinder is extended at the idling position of the operation lever, and a pressure difference is created between the center bypass oil passage. An energy-saving device for a pump-driven engine, characterized in that a switching valve is provided that connects the center bypass oil path on the low-pressure side to the single-acting hydraulic cylinder when a low-pressure side occurs.