JPS5821002A - Motor drive circuit - Google Patents

Abstract

PURPOSE:To prevent the abnormal rise in pressure at the time of additional acceleration, by providing a pressure control valve in a circuit connected between a tank and a supply/discharge circuit which connects a counterbalance valve and a directional control valve, so that the pressure control valve acts for a prescribed time. CONSTITUTION:When a directional control valve 4 is shifted to an operating position 4b, the pressure of oil from a pump 1 changes a counterbalance valve 7 to a left-hand position and the oil enters into the port 6a of a motor 6 and the oil from its other port 6b returns to a tank 2 so that the motor is driven. When the directional control valve 4 is returned to a neutral position and the driving of the motor 6 is stopped, the motor continues to rotate, because of the inertial force of the load, to perform pumping action. When the motor 6 is additionally accelerated by temporarily shifting the directional control valve 4 again to the operating position, a pressure control valve 14 keeps the pressure of an oil supply line 11a low for a response lag time to the shifting of the counterbalance valve 7 to an operating position, to avoid the enclosure of pressure between the valve 7 and the motor to prevent the abnormal rise in the pressure of the supply and the return lines.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a motor drive circuit used for turning a hydraulic excavator in a construction vehicle. When the directional control valve is returned to the neutral position from the state where it is rotating, the inertia of the swing motor causes the swing motor to perform a pumping action, reducing the circuit pressure that was previously being supplied, so the counterbalance valve returns to the neutral position. In this position, the supply/discharge valve is closed, the cross relief valve provided between the counterbalance valve and the motor is activated, the oil on the return side is circulated to the supply side, and a hydraulic brake is applied to the motor.

In actual work, in order to stop a packet, etc. that is fixed integrally with the revolving structure at the target position, the operator returns the directional control valve to the neutral position and applies the hydraulic brake, anticipating the flow while the hydraulic brake is applied. If the target position is not reached, the directional control valve is switched from the brake state to the operating position, and after giving a slight rotation to the motor, the directional control valve is returned to the neutral position again to enter the brake state and reach the final target position. It is operated to -This operation is commonly referred to as "additional acceleration" and causes a shock. This additional acceleration occurs when the counterbalance valve is in the neutral position under normal braking conditions, and oil from the motor passes through the cross relief valve and returns to the supply side. Pressure is applied to the supply side again, so the counterbalance valve shifts. Until this occurs, pressure is trapped in both boats of the motor, so the pressure on the brake side is added and abnormal peak pressure occurs. This phenomenon is due to a delay in the response of the counterbalance valve due to the throttle of the pilot signal, etc., which is installed to stabilize the counterbalance valve and prevent the hunting phenomenon.This response delay has a limit in terms of the stability of the counterbalance valve. Therefore, countermeasures required advanced technology.

The present invention has been made in view of the above-mentioned problems, and its purpose is to maintain the pressure in the supply side circuit at a low pressure while the counter balance valve is about to shift to the neutral position during additional acceleration under brake operation. Another object of the present invention is to provide a motor drive circuit in which pressure between a counterbalance valve and a motor is contained and prevented from increasing excessively.

1 and 2 showing one embodiment of the present invention will be explained below. In FIG. 1, 1 is a pump, 2 is a tank, and 3 is a main switching valve. A directional switching valve 4 provided in the main switching valve 3 has a neutral position 4a and operating positions 4b, 4c. 1 is selectively supplied to the motor 6 via the brake valve 5. 6a and 6b are ports of the motor 6, and the brake valve 5 is a circuit 8a provided between the motor 6 and a counterbalance valve 7 that responds to the operating pressure from the directional control valve 4, or a cross that opens when the internal pressure of 8b increases. A relief valve 9.10 is provided. The supply/discharge circuits 11a and llb that connect the counterbalance valve 7 of the brake valve 5 and the directional switching valve 4 in the main switching valve 3 are provided with a circuit 12.13 that connects to the tank 2.
Pressure regulating valves 14,15 are interposed therein.

The pressure regulating valves 14,15 will be explained with reference to FIG.

The valve body 16 of the pressure regulating valve 14.15 is connected to the circuit 12 or 1.
The poppet 17 has one end that receives the pressure of the inlet passage 18 and the other end that is inserted between the valve body 16 and the plug 27. It has a hole 20 that is pressed and opened by a spring 19 provided, and is provided with an orifice 23 that communicates with a throttle hole 21 that communicates the circumference 20 with the inlet passage 18 and an outlet passage 22. Piston 2 inserted into hole 20 of poppet 17
4 is pushed toward the inlet passage 18 by a spring 25 at the illustrated position so that a passage 26 provided therein communicates with the throttle 21 and the first refit 23.

Next, the operation of the present invention will be explained. First, if there is no pressure regulating valve 14.15, drive the pump 1 and set the direction. Exchange valve. When switching to Fig. 1゜neutral position 4〆 test excitation nt 4b, the counterbalance valve 7 is switched to the left position by pilot pressure, and pressure hydraulic oil is supplied to the motor port via the supply/discharge circuit 1181 circuit 8a). On the other hand, the return oil is returned to the tank 2 via the circuit 8b1 and the supply/discharge circuit 11b from the cylinder 6b, so that the motor 6 is driven.

When the driven motor 6 is stopped, the directional control valve 4 is returned to the neutral position, and in conjunction with this, the counterbalance valve 7 is switched to the neutral position.

As a result, the hydraulic oil from the pump 1 to the circuit 8a is cut off, and the return oil from the circuit 8b to the tank 2 is cut off by the counterbalance valve 7. At this time, the motor 6 is driven by the inertial force of the load in the same rotational direction as described above, so it performs a pumping action. When the pressure in the circuit 8b exceeds the set value due to this pumping action, the cross relief valve 10 opens. The oil in the operating circuit 8b flows to the supply side circuit 8a via the cross relief valve.

When the brake is activated due to such circulation of hydraulic oil, in an additional acceleration state in which the directional control valve 4 is temporarily switched to the activated position again to accelerate the motor 6, the hydraulic oil from the pump 1 is transferred to the motor port 6a. Pressure is trapped in the ports 6a, 6b of the motor 6 until the counterbalance valve 7 shifts to the operating position. Therefore, the pressure in the supply side circuits 11a and 8a of the motor 6 increases, and the pressure in the return side circuit 8a increases accordingly.
Excessive pressure is created by the increase in pressure at 8a.

Therefore, when the pressure regulating valve 14 is provided, the pressure regulating valve 14 is operated by the pressure of the circuits 11a and 8a. First, when the pressure of the inlet passage 18 is initially low, the oil in the inlet passage 18 is Throttle hole 21, passage 26, orifice 23
The poppet 17 and the piston 24 are in the position shown in the figure, since they are discharged in an unloaded state through the outlet passage 22.

Further, it retreats against the spring 25 under the pressure of the inlet passage 18, contacts the stopper at the stroke end, and the orifice 2
3 is closed, there is no flow of oil to tank 2, and it operates as a normal relief valve.

During this movement of the piston 24, the pressure in the circuits 11a, 8a can be kept low. In this way, during the response delay until the counterbalance valve 7 shifts from the neutral position, the pressure in the supply side circuit is maintained at a low pressure, thereby eliminating the pressure trapped between the counterbalance valve 7 and the motor 6. Therefore, it is possible to prevent the pressures on the supply side and the return side from increasing abnormally, and at the same time, it is possible to alleviate the sway during additional hitting acceleration.

Further, when the directional control valve 4 is in the neutral position and the brake state where hydraulic oil is circulating is switched again to the operating position 4c, the circuit 11b18b becomes the supply side,
The rotations of the counterbalance valve 7 and the motor 6 are reversed, and the pressure regulating valve 15 operates on the supply side, but everything else is the same as in the case described above, so a description thereof will be omitted.

As described above, according to the present invention, although it has a simple circuit configuration, it is possible to prevent abnormal pressure on the supply side and return side during additional acceleration without impairing the conventional turning operation. This has the effect of improving turning maneuverability by preventing

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
It is a sectional view of the pressure regulation valve in a figure. DESCRIPTION OF SYMBOLS 1... Pump, 2... Tank, 4... Directional switching valve, 5... Brake valve, 6... Motor, 7... Counter balance, 9.10... Cross relief, lla
, 11'b...supply/discharge circuit, 12.13...
Circuit, 14.15...Pressure regulating valve, %l(g) No. 4

Claims (1)

[Claims] In a motor drive circuit comprising a motor, a pump, and a directional control valve that selectively supplies pressure oil from the pump to the motor via a brake valve having a counterbalance valve and a cross relief valve, the counterbalance valve A circuit is provided that branches off from the supply/discharge circuit connecting the directional control valve and connects to the tank, and a pressure regulating valve is provided to keep the pressure in the circuit below a predetermined open value for a predetermined time when supply pressure is applied to the circuit. A motor drive circuit characterized by providing