JP2882998B2 - Hydraulic motor drive 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 hydraulic circuit for a construction machine, and more particularly to a drive circuit for a hydraulic motor capable of switching between high and low speeds.

[0002]

2. Description of the Related Art There is known a hydraulic motor used in a hydraulic circuit of a construction machine, in which a tilting angle is changed by an adjusting cylinder so that the speed can be switched between high and low. When the hydraulic motor is switched to the low-speed mode, the flow per rotation of the hydraulic motor is large and the torque is high. Therefore, a shock is likely to occur when starting the hydraulic motor. In addition, during driving while switching to the high-speed mode after driving the hydraulic motor, when braking is performed, the hydraulic pressure of one of the main pipelines rises and a shock occurs.

A circuit shown in FIG. 4 is known as a hydraulic circuit for reducing a shock generated when starting and braking a hydraulic motor. The hydraulic pump 1 and the hydraulic motor 2 are connected by two main pipelines 3 and 4, and a directional control valve 5 and a counterbalance valve 6 are interposed midway between the two main pipelines 3 and 4. A bypass oil passage 7 is connected between the two main pipelines 3 and 4 to provide relief valves 8 and 9 in a crossover, and a free piston 10 is provided downstream of the poppet back pressure chamber of each relief valve 8 and 9. Provide.

For example, when the directional control valve 5 is operated from the neutral position to the side 5a, the counterbalance valve 6 is also switched in the same direction, the pressure oil is led out to one main pipeline 3, and the hydraulic motor 2 is started. At this time, the pressure oil in the main conduit 3 is also led out to the bypass oil passage 7 and acts on both the relief valves 8 and 9. Here, FIG. 5 shows the internal structure of the relief valves 8 and 9 and the free piston 10. The pressure oil in the bypass oil passage 7 is diverted to the oil passage 7a on the outflow side of the relief valve 8 and the oil passage 7b on the inflow side of the relief valve 9, but the pressure receiving areas of the relief valves 8 and 9 are closer to the inflow side than the outflow side. Is larger, first the poppet 9a of the relief valve 9 is opened. At this time, the pressure oil passes through the throttle 9b in the poppet 9a and flows into the back pressure chamber 9c.
Is pressed upward in the figure. Until the free piston 10 moves to the upper end of the cylinder, the relief valve 9 continues to relieve at a relatively low pressure. Thus, in the initial stage of starting / braking the hydraulic motor 2, the relief pressure is set low and the shock is reduced.

After the free piston 10 moves to the upper end of the cylinder, the pressure difference between the front and rear of the poppet 9a disappears, and the poppet 9a is closed. Accordingly, when the pressures in the oil passages 7a and 7b continue to rise and the pressure acting on the outlet side of the relief valve 8 becomes larger than the spring pressure of the spring 8d, the poppet 8a is opened. Thus, during the latter half of braking of the hydraulic motor 2, the relief pressure is set slightly higher to improve the deceleration effect.

[0006]

In the conventional hydraulic motor drive circuit, as described above, a free piston is provided downstream of the poppet back pressure chamber of the relief valve to reduce the shock at the time of low-speed startup. However, if the relief pressure at the time of operating the free piston is set extremely low, the deceleration effect at the time of high-speed braking is lost, which is dangerous, and the shock when the relief pressure rises immediately before stopping becomes large. For this reason,
The relief pressure at the time of operating the free piston was set at an intermediate point between the shock absorption at the time of low speed and the shock absorption immediately before the high speed stop, and the shock at the start and stop of the low speed traveling was large.

[0007] Therefore, in any of the low-speed mode and the high-speed mode, there arises a technical problem to be solved in order to reduce the shock generated when starting and braking the hydraulic motor. The purpose is to solve.

[0008]

SUMMARY OF THE INVENTION The present invention has been proposed to achieve the above-mentioned object, and connects a discharge oil of a hydraulic pump to a hydraulic motor through two main pipelines via a directional control valve. When a bypass oil passage is connected between the two main pipelines and a relief valve is provided in the crossover, a free piston is provided downstream of the poppet back pressure chamber of each relief valve, and the poppet of one relief valve is opened At the same time, the free piston is actuated by the pressure oil that has passed through the throttle inside the poppet to temporarily set the relief pressure to a low pressure, and the poppet of the one relief valve is closed when the free piston reaches the stroke end. Then, in the hydraulic circuit in which the poppet of the other relief valve is opened after that, between the poppet back pressure chamber of each of the relief valves and the free piston. A switching valve is installed, a plurality of passages having different opening areas are provided in the switching valve, and when the hydraulic motor is in a low-speed mode, the switching valve is set to a larger opening area, and when the hydraulic motor is in a high-speed mode. Is a drive circuit of a hydraulic motor formed so as to switch the switching valve to the small opening area side, and a cylinder capacity such that when the body is braked in a substantially horizontal state, the free piston does not reach the stroke end until the body stops. The present invention provides a drive circuit for a hydraulic motor formed as described above.

[0009]

When the hydraulic motor is in the low-speed mode, the switching valve is on the large opening area side, so that the pressure difference between the front and the rear of the poppet is large, so that the relief valve can be set to be relieved at an extremely low pressure. Shock during starting / braking can be reduced. Further, by increasing the cylinder volume of the free piston, the free piston does not reach the stroke end until the machine stops during braking, and the relief pressure does not increase immediately before the stop.

On the other hand, when the hydraulic motor is in the high-speed mode, the switching valve is switched to the small opening area side, so that the pressure oil applied to the relief valve passes through the restrictor in the poppet, flows into the back pressure chamber, and then further flows. It will pass through the throttle of the switching valve. Therefore, the pressure difference between the front and rear of the poppet becomes small, the shock absorption pressure when the free piston is operating becomes higher than in the low speed mode, the responsiveness at the start of the hydraulic motor is improved, and the braking effect at the time of braking is improved. Will also be obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to FIGS. For convenience of explanation, the same components as those of the related art will be described at the same time. FIG. 1 shows a drive circuit of a hydraulic motor, in which a hydraulic pump 11 and a hydraulic motor 12 are connected by two main lines 13 and 14, and two main lines 13 and 14 are connected.
Direction control valve 15 and counterbalance valve 1 in the middle of 14
6 is interposed. The hydraulic motor 12 is of a variable position type,
When the speed switching valve 17 is switched by the high-speed switching signal, the pressure oil in the main line 13 or 14 is led out to the bottom side of the adjusting cylinder 19 via the shuttle valve 18, and the adjusting cylinder 19 is extended to extend the hydraulic motor 12. Is formed such that the tilt angle of the small angle is small.

A bypass oil passage 20 is provided between the two main conduits 13 and 14, the bypass oil passage 20 is branched, and relief valves 21 and 22 are provided in the oil passages 20a and 20b in a crossover manner. . Relief valves 21 and 22 respectively
A free piston 25 is provided downstream of the poppet back pressure chamber through switching valves 23 and 24. When the hydraulic motor 12 is in the low-speed mode, the switching valves 23 and 24 are located on the large opening area side by the bias of the spring.
When is set to the high-speed mode, the switching valves 23 and 24 are formed to switch to the small opening area side by the high-speed switching signal.

When the tilt angle of the hydraulic motor 12 is large and the low-speed mode is set, when the direction control valve 15 is operated from the neutral position to the side 15a, the counter balance valve 16 is also switched in the same direction. The hydraulic oil is led out to the main pipeline 13 of the hydraulic motor 12 and the hydraulic motor 12 is started. At this time, the main pipeline 13
Pressure oil is also led out to the bypass oil passage 20 and acts on both the relief valves 21 and 22.

FIG. 2 shows the relief valves 21 and
2, the internal structure of the switching valves 23, 24 and the free piston 25 is shown. Oil passage 20 on the inflow side of relief valves 21 and 22
Assuming that the inner diameters of b and 20c are d and the inner diameters of the back pressure chambers 21c and 22c of the poppets 21a and 22a are D, the pressure receiving area S ₁ on the inflow side and the pressure receiving area S ₂ on the outflow side of the relief valves 21 and 22 are: It is expressed by the following equation.

[0015]

(Equation 1)

Accordingly, the pressure oil led to the bypass oil passage 20 is divided into an oil passage 20a on the outflow side of the relief valve 21 and an oil passage 20b on the inflow side of the relief valve 22, as is apparent from the equation (3). the relief valve 21 and 22 towards the pressure receiving area S ₁ of the inlet than the pressure receiving area S ₂ of the outlet-side side because it is large, first poppet 22a of the relief valve 22 is opened. At this time, the pressure oil passes through the throttle 22b in the poppet 22a, flows into the back pressure chamber 22c, and the switching valve 24
The pressure oil is located on the side of the large opening area by the bias of 4a, so that the pressure oil passes through the switching valve 24 and presses the free piston 25 upward in the drawing.

Here, the cylinder capacity of the free piston 25 is formed larger than that of the conventional type. Therefore, the time until the free piston 25 reaches the stroke end becomes longer. The oil in the free piston 25 is discharged through the check valve 26a. After the free piston 25 reaches the stroke end, the poppet 22
The poppet 22a is closed because the pressure difference before and after a disappears. Accordingly, the pressure in the oil passages 20a and 20b increases,
The hydraulic motor 12 keeps rotating in the low speed mode. And
Even during braking, the relief pressure is set extremely low and the stroke of the free piston 25 is large, so that the shock is reduced until immediately before the stop.

On the other hand, when the tilt angle of the hydraulic motor 12 is small and the high-speed mode is set, the spools of the switching valves 23 and 24 are moved by the high-speed switching signal as shown in FIG. Switches to the smaller opening area side. Here, when the hydraulic motor 12 is started, one main pipeline 13
As described above, the pressure oil led to the bypass oil passage 20 first opens the poppet 22a of the relief valve 22, and flows into the back pressure chamber 22c through the throttle 22b. At this time, since the switching valve 24 is located on the small opening area side, pressure loss occurs in the pressure oil passing through the switching valve 24 from the back pressure chamber 22c, and the pressure difference between the front and rear of the poppet 22a becomes small.

Accordingly, the relief pressure at the start of the high-speed mode is higher than that of the low-speed mode, and a smooth feeling of acceleration without response delay can be obtained. Further, a high deceleration effect and a shockless effect are obtained even during braking, and the shock of the free piston 25 is reduced until just before the stop because the free piston 25 has a large stroke. In addition, the present invention can make various modifications without departing from the spirit of the present invention, and
Naturally, the invention extends to such modifications.

[0020]

According to the present invention, as described in detail in the above embodiment, a switching valve is provided between the poppet back pressure chamber of the relief valve and the free piston to switch the opening area, so that the low speed mode is achieved. Shock at the time of starting and braking of the vehicle and at the time of starting and braking of the high-speed mode can be significantly reduced, which can contribute to improvement of operability of the construction machine.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention and is a drive circuit diagram of a hydraulic motor.

FIG. 2 is an explanatory diagram showing an internal structure of a relief valve, a switching valve, and a free piston in a low-speed mode.

FIG. 3 is an explanatory view showing the internal structure of a relief valve, a switching valve, and a free piston in a high-speed mode.

FIG. 4 is a drive circuit diagram of a conventional hydraulic motor.

FIG. 5 is an explanatory view showing an internal structure of a conventional relief valve and a free piston.

[Description of Signs] 11 Hydraulic pump 12 Hydraulic motor 13, 14 Main line 15 Directional control valve 20 Bypass oil passage 21, 22 Relief valve 21a, 22a Poppet 21b, 22b Restrictor 21c, 22c Back pressure chamber 23, 24 Switching valve 25 Free piston

Continuation of the front page (56) References JP-A-6-287983 (JP, A) JP-A-57-129904 (JP, A) JP-A-54-86069 (JP, A) JP-A-2-57739 (JP, A) , A) Japanese Utility Model 63-123801 (JP, U) Japanese Utility Model Hei 5-94504 (JP, U) Japanese Utility Model Utility Model 61-22901 (JP, U) (58) Fields surveyed (Int. Cl. ⁶ , DB Name) F15B 11/00 E02F 9/22

Claims (2)

(57) [Claims] 1. A discharge oil of a hydraulic pump is connected to a hydraulic motor by two main lines via a directional control valve, and a bypass oil line is connected between the two main lines to provide a relief valve in a crossover. A free piston is provided downstream of the poppet back pressure chamber of each relief valve, and when the poppet of one of the relief valves is opened, the free piston is actuated by the pressure oil that has passed through the restrictor inside the poppet to temporarily operate the free piston. In the hydraulic circuit, the relief pressure is set to a low pressure, and when the free piston reaches the stroke end, the poppet of the one relief valve is closed, and then the poppet of the other relief valve is opened. A switching valve is provided between the poppet back pressure chamber of each of the relief valves and the free piston, and a plurality of passages having different opening areas are provided in the switching valves; A hydraulic motor characterized in that when the motor is in a low-speed mode, the switching valve is set to a large opening area side, and when the hydraulic motor is set to a high-speed mode, the switching valve is switched to a small opening area side. Drive circuit. 2. When the aircraft brakes in a substantially horizontal state,
2. The hydraulic motor drive circuit according to claim 1, wherein the free piston is formed in a cylinder volume such that the stroke of the free piston does not reach a stroke end until the body stops.