JPH0578452B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a transmission device for a travel motor for a hydraulic excavator.

BACKGROUND ART FIG. 3 is a hydraulic circuit diagram of a hydraulic excavator equipped with a two-speed traveling motor. The left and right travel motors are
The symmetrical arrangement shows the hydraulic circuit of the right travel motor. In the figure, 1L and 1R are respectively variable hydraulic pumps, 2L and 2R are left and right travel valves, 3 is a right travel motor assembly, 4 is a right travel motor assembly 3 as a hydraulic motor, and 5 is a slope for changing the capacity of the hydraulic motor 4. plate, 6 is a speed change cylinder, 7 is a counterbalance valve that reliably maintains the hydraulic motor 4 in a stopped state when the right travel valve 2R is in the neutral position, 8, 9
are oil passages, 10 and 11 are oil passages 8 and 11, respectively.
9 a pressure limiting valve that regulates the maximum pressure; 12 a solenoid valve; 13 an excitation coil for the solenoid valve 12; 14 a switch installed near the driver's seat; 15 a power supply; 16
is the pilot pump, 17 is the pilot valve, 18
is a pilot pressure receiving portion of the pilot valve 17. Next, the structure and operating function of the transmission of the conventional travel motor will be described with reference to FIG. When the switch 14 is turned on, the excitation coil 13 is energized and the solenoid valve 12 is switched from the A position to the B position.
Then, the discharged pressure oil from the pilot pump 16 passes through the A position of the solenoid valve 12 and the oil passage 19, and acts on the pilot pressure receiving portion 18 of the pilot valve 17, thereby switching the pilot valve 17 from the C position to the N position. Therefore, the pressure oil discharged from the pilot pump 16 is branched at the oil path 19, and the check valve 20,
Oil passage 21, pilot valve 17 position 2, throttle part 2
2, the oil is sent to the transmission cylinder 6. For this purpose, the piston 23 of the speed change cylinder 6 is
The hydraulic motor 4 is moved to the left in the figure against the spring force of the hydraulic motor 4, and the swash plate 5 of the hydraulic motor 4 connected to the piston rod 25 is actuated. As a result, the hydraulic motor 4
The displacement volume of is reduced, and the hydraulic motor 4 is switched to high speed rotation.

Problems to be Solved by the Invention When a hydraulic excavator travels, the driver selects and performs a switching operation between high speed and low speed depending on the ground conditions, etc., and performs high speed or low speed travel. For example, when changing direction while driving at high speed on flat ground, or when approaching a steep slope, the vehicle changes from high speed to low speed. The reason for this is that although the rotational speed of the travel motor is high during high-speed travel, its output torque is low. Therefore, if the vehicle climbs a hill while traveling at high speed, the oil pressure in the travel circuit increases, which tends to cause a relief state, and the travel motor may stop. Therefore, when the hydraulic excavator is running at high speed and begins to change directions or climb slopes, it switches to low speed driving, and once it has finished changing direction or climbing slopes, it switches to high speed driving again. It continued. For this reason, the driver had to frequently switch between high speed and low speed while driving, which was very bothersome.

This invention solves the above problems and provides a transmission device for a travel motor that automatically switches from high-speed travel to low-speed travel when a hydraulic excavator is under high load, such as when changing direction during high-speed travel or climbing on slopes. The purpose is to

Means for Solving the Problem The means of the present invention taken to solve the above problem are as follows: The pilot pump discharge pressure is applied to the speed change cylinder of the hydraulic motor to operate the swash plate of the hydraulic motor. In a hydraulic circuit configured to change the height of the hydraulic motor, (b) a pilot switching valve is provided in the middle of the oil path between the shuttle valve between the inlet port and outlet port of the travel hydraulic motor and the transmission cylinder, and (c) the above-mentioned pilot. Connecting the pilot pressure receiving part on the large area side of the switching valve and the discharge side of the pilot pump via a solenoid valve; (e) The pilot pressure receiving part on the large area side and the pilot pressure receiving part on the small area side of the pilot switching valve are connected via a check valve.

Operation (a) When the switch installed near the driver's seat is turned on, the solenoid valve changes, so the pressure oil discharged from the pilot pump is sent to the variable speed cylinder of the hydraulic motor. This causes the transmission cylinder to extend and actuate the swash plate connected to its piston rod. Therefore, the displacement volume of the hydraulic motor is reduced, and the hydraulic motor rotates at a high speed.

(b) When the above hydraulic motor is rotating at high speed,
A high load may be applied to the hydraulic motor.
Then, the hydraulic pressure on the inlet port side of the hydraulic motor increases to high pressure Pm. this high pressure
Pm is a higher pressure than the pilot pump discharge pressure pi. For this purpose, the high pressure Pm acts on the pilot pressure receiving portion on the small area side of the pilot switching valve, and switches the pilot switching valve to the tank communication oil path position. As a result, the speed change cylinder of the hydraulic motor is contracted by the spring force.
Therefore, the swash plate of the hydraulic motor connecting the piston rod of the speed change cylinder is operated, and the hydraulic motor is automatically switched to low speed rotation.

Embodiments Hereinafter, a transmission device for a traveling motor according to the present invention will be explained in detail based on the drawings. FIG. 1 is a hydraulic circuit diagram according to the present invention, and first, its configuration will be described. Applying the discharge pressure of the pilot pump 16 to the variable speed cylinder 6 of the hydraulic motor 4,
By operating the swash plate 5 of the hydraulic motor 4,
In a hydraulic circuit configured to switch between high and low speeds of the traveling hydraulic motor 4, a pilot switching valve is provided between the shuttle valve 26 between the inlet port and the outlet port of the traveling hydraulic motor 4 and the oil path between the speed change cylinder 6. 27 is provided, and its pilot switching valve 2
The large-area side pilot pressure receiving section 28 of No. 7 and the discharge side of the pilot pump 16 were connected via a solenoid valve 12. On the other hand, the pilot pressure receiving portion 29 on the small area side of the pilot switching valve 27 and the shuttle valve 2
6 was connected. At the same time, the large area side pilot pressure receiving part 28 and the small area side pilot pressure receiving part 29 of the pilot switching valve 27 are connected to the check valve 3.
It was configured by connecting through 0.

The transmission device for a traveling motor according to the present invention is constructed as described above, and its operational functions will be described next. When the switch 14 installed near the driver's seat (not shown) of the hydraulic excavator is turned on, the excitation coil 13 is energized and the solenoid valve 12 is turned on.
is switched from the A position to the B position. Then, the discharge pressure pi from the pilot pump 16 is
At position 2, from the oil passage 31, one side acts on the large-area side pilot pressure receiving part 28 of the pilot switching valve 27 via the oil passage 32, and the other side acts on the large area side pilot pressure receiving part 28 of the pilot switching valve 27.
Branches at , oil path 33, check valve 30, oil path 3
4, 35, and 36, it acts on the small-area side pilot pressure receiving portion 29. Here, the large area side pilot pressure receiving part 28 and the small area side pilot pressure receiving part 29
If the pressure receiving areas are S and s, and the spring force of the spring 37 of the pilot switching valve 27 is _pB , then {pi×S}
> {(pi×s)+p _B }.
For this reason, the pilot switching valve 27 is switched from the H position to the H position, so that the pressure oil discharged from the pilot pump 16 is transferred from the oil passage 35 side to the oil passage 38, to the H position of the pilot switching valve 27, to the oil passage 39, and to the aperture. Part 2
2, the oil is sent to the transmission cylinder 6. For this purpose, the piston 23 of the speed change cylinder 6 has a spring 24
The hydraulic motor 4 is moved to the left in the figure against the spring force, and the hydraulic motor 4 is rotated at high speed. However, there are cases where a high load is applied to the hydraulic motor 4 that rotates at high speed. Then, the inlet port side hydraulic pressure of the hydraulic motor 4 increases to high pressure Pm and is led out to the shuttle valve 26. Therefore, a pressure of {(Pm×s)+p _B } is applied to the small-area side pilot pressure receiving part 29 of the pilot switching valve 27, and a pressure of {pi×S} is applied to the large-area pilot pressure receiving part 28. act.
Here, s<S, but Pm>pi, so
{(Pm×s)+p _B }>{pi×S}. Therefore, the pilot switching valve 27 is switched to the tank communication oil path position H. Therefore, the speed change cylinder 6 of the hydraulic motor 4 is contracted by the spring force of the spring 24. At this time, the hydraulic oil in the speed change cylinder 6 returns to the oil tank 49 through the throttle portion 22, the oil passage 39, and the pilot switching valve 27 at the E position. Therefore, the piston rod 25 of the transmission cylinder 6
moves to the right in the figure, so the swash plate 5 operates,
The hydraulic motor 4 automatically switches to low speed rotation.

FIG. 2 is a hydraulic circuit diagram of a modification of the transmission for a traveling motor according to the present invention. The configuration of the hydraulic circuit shown in FIG. 2 is different from the hydraulic circuit shown in FIG. Two pilot valves 40 and 41 are connected in series, and the shuttle valve 2 of the hydraulic motor 4
6, and the pilot pressure receiving part 4 of the pilot valve 40.
2 are connected. Next, the operating functions of the hydraulic circuit shown in FIG. 2 will be described. When the switch 14 is turned on when a high load is not applied to the hydraulic motor 4, the excitation coil 13 is energized and the solenoid valve 12 is switched from the A position to the B position. Then, the pressure oil discharged from the pilot pump 16 is transferred to the RO position of the solenoid valve 12, the oil passage 43, and the pilot valve 40.
It acts on the pilot pressure receiving portion 46 of the pilot valve 41 through the oil passages 44 and 45, and switches the pilot valve 41 from the R position to the N position. Therefore, the pressure oil discharged from the pilot pump 16 is branched off at the oil path 44, and the oil path 33, check valve 30,
Oil passage 47, pilot valve 41 null position, oil passage 3
9. The oil is sent to the speed change cylinder 6 of the hydraulic motor 4 through the throttle section 22. As a result, the speed change cylinder 6 is extended to operate the swash plate 5, and the hydraulic motor 4 rotates at high speed. However, when the hydraulic motor 4 is rotating at high speed, a high load may be applied to the hydraulic motor 4. Then, the hydraulic pressure on the inlet port side of the hydraulic motor 4 increases to high pressure Pm. And shuttle valve 2
The high pressure Pm led out to the pilot valve 40 acts on the pilot pressure receiving portion 42 of the pilot valve 40 through an oil passage 48. Then, the pilot valve 40 is switched from the t position to the tank communication oil passage position t, so that the speed change cylinder 4 and the oil tank 49 communicate with each other. Therefore, the piston 23 of the speed change cylinder 6 is
The swash plate 5 moves to the right in the figure due to the spring force.
is activated, and the hydraulic motor 4 automatically rotates at a low speed.

In the hydraulic circuits shown in FIGS. 1 and 2, the switch 14 is closed and the hydraulic motor 4 is driven at high speed. Therefore, if a high load is applied to the hydraulic motor 4 during high-speed rotation, the hydraulic motor 4 is automatically switched to low-speed rotation. However, when the high load is no longer applied, the high pressure Pm led to the shuttle valve 26 decreases.
The pilot switching valve 27 in FIG. 1 is automatically switched from the H position to the H position, and the pilot valve 40 in FIG. 2 is automatically switched from the H position to the H position. Therefore, high-speed rotation can be continued again without turning the switch 14 on or off.

Effects of the Invention As described above, the transmission device for a traveling motor according to the present invention has a pilot switching system located between the shuttle valve between the inlet port and outlet port of the traveling hydraulic motor of a hydraulic excavator and the oil path between the transmission cylinder and the transmission cylinder. A valve was provided, and the large-area side pilot pressure receiving part of the pilot switching valve and the pilot pump discharge side were connected via a solenoid valve. On the other hand, the small area side of the pilot switching valve is connected to the shuttle valve, and the pilot pressure receiving part on the large area side and the pilot pressure receiving part on the small area side of the pilot switching valve are connected via a check valve. did.

In conventional technology, the driver determines the ground conditions and operates a switch to turn on and off, selecting either high-speed or low-speed rotation of the hydraulic motor for fixed driving. was. For this reason, for example, if the vehicle forgets to perform a low speed switching operation while driving at high speed and performs a direction change or climbs a slope, the hydraulic motor may stop due to insufficient output torque. Therefore, when the hydraulic excavator is running at high speed and begins to change directions or climb slopes, it switches to low speed driving, and once it has finished changing direction or climbing slopes, it switches to high speed driving again. It continued. For this reason, the driver
I had to switch between high and low speeds frequently while driving, which was very bothersome.

However, the transmission device for the travel motor according to the present invention, if the switch is kept in the on state,
If a high load is applied to the hydraulic motor for driving during high-speed driving, for example when changing direction or climbing a slope, the vehicle automatically switches to low-speed driving. Then, when the load on the travel hydraulic motor decreases, the vehicle can return to high-speed travel and continue traveling. Therefore, the transmission device for the travel motor according to the present invention automatically switches between high and low speeds according to the load applied to the hydraulic motor, so that the hydraulic excavator can run smoothly and the driver can easily switch between high and low speeds. It is possible to save the labor required for the operation and improve the running performance of the hydraulic excavator.

[Brief explanation of the drawing]

FIG. 1 is a hydraulic circuit diagram of a transmission device for a traveling motor according to the present invention, FIG. 2 is a modification of the hydraulic circuit according to the present invention, and FIG. 3 is a hydraulic circuit diagram of a prior art. 4... Hydraulic motor, 6... Speed change cylinder, 12
...Solenoid valve, 14...Switch, 16...Pilot pump, 26...Shuttle valve, 27...Pilot switching valve, 28...Large area side pilot pressure receiving part, 29...Small area side pilot pressure receiving part , 4
0,41,17...Pilot valve.

Claims (1)

[Claims] 1. In a hydraulic circuit in which the hydraulic motor for traveling is switched between high and low speeds by applying the pilot pump discharge pressure to the speed change cylinder of the hydraulic motor and operating the swash plate of the hydraulic motor, A pilot switching valve is provided in the middle of the oil path between the shuttle valve and the variable speed cylinder between the let port and outlet port, and the pilot pressure receiving part on the large area side of the pilot switching valve and the pilot pump discharge side are connected via a solenoid valve. Concatenate, while
The small area side pilot pressure receiving part of the pilot switching valve is connected to the above shuttle valve, and the large area side pilot pressure receiving part and the small area side pilot pressure receiving part of the pilot switching valve are connected via a check valve. What is claimed is: 1. A transmission device for a traveling motor, characterized in that the transmission device comprises: