JPH0552451U - Switching valve - Google Patents

Abstract

(57) [Abstract] [Purpose] When a load circuit is driven by a fixed displacement type hydraulic pressure source, the flow rate can be adjusted according to the load of the load circuit.
Moreover, it provides a switching valve that can be manufactured easily and accurately. In a switching valve provided with a spool 4 having a land portion 4a on the outer circumference, a notch 6c is formed in the land portion 4a so as to pass through the land portion 4a in the axial direction m.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to a switching valve that is preferably used for cylinder driving and the like.

[0002]

[Prior Art]

 As a specific device having a switching valve for driving a cylinder, for example, a forklift can be cited. A forklift is a lift cylinder for raising and lowering the platform along the mast, a tilt cylinder for changing the angle of the platform by tilting the mast forward / backward, and a reach cylinder for projecting and retracting the mast with respect to the vehicle body. Generally, various cylinders such as are provided, and a switching valve is connected to each cylinder correspondingly. As shown in the circuit diagram of FIG. 7, the switching valve includes a pair of actuator ports A and B connected to both side chambers 1a and 1b of the cylinder 1 and a high pressure port P communicating with a high pressure source 2 such as a pump. , And has a low-pressure port T 2 communicating with the tank 3, and normally performs a switching function of 3 positions according to the sliding position of the internal spool 4 as shown in FIG. Specifically, both actuator ports A and B are blocked at the center position of the spool 4 shown in FIG. 7, and the actuator port A or B is connected to the high pressure port P at the rightward position or the leftward position of the spool 4. At the same time, the actuator port B or A is connected to the low pressure port T. When the spool 4 blocks both actuators A and B at the center position, the high-pressure port P and the low-pressure port T are communicated with each other through the flow path 5, and the high-pressure liquid is supplied through the flow path 5 to the tank 3 Return to. The flow path 5 is blocked at the rightward position and the leftward position of the spool 4. Since the tilt cylinder and the reach cylinder are usually reciprocating type, the switching valve may have the above-mentioned configuration, but the lift cylinder is usually single-acting type, so the switching valve may be the actuator port A or B of the above-mentioned configuration. Are blocked by appropriate means.

[0003]

[Problems to be solved by the device]

 By the way, each of the cylinders 1 of the forklift described above is usually connected to a pump 2 which is a common high-pressure source, and is configured to operate by utilizing the discharge pressure liquid of the pump 2. At this time, the capacities of the pump 2 and the electric motor that drives the pump 2 are selected in accordance with the lift cylinder that requires high speed and high power, and generally have large output and large capacity. With such a configuration, however, the equivalent pressure fluid is supplied from the pump during driving to the tilt cylinder and the reach cylinder, which may have relatively low speed and low power, which is preferable in terms of operation and safety. There is something wrong. On the other hand, the pipes around the tilt cylinder and reach cylinder are made thinner to increase the pipe resistance, and when operating these cylinders, the relief valve attached to the switching valve is blown to partially discharge. There is also a method of slowing the speed by sending a small amount of liquid to the cylinder while returning the liquid to the tank.However, in this case, when the tilt cylinder or the reach cylinder is operated, the liquid pressure is always up to the relief pressure. The temperature rises unnecessarily, the current consumption of the motor increases, the installed battery becomes short-lived, and the liquid temperature rises sharply, causing a problem that the circuit is adversely affected.

In view of the above situation, for example, the one disclosed in Japanese Patent Publication No. 60-54238, as shown by the broken lines in FIGS. By-pass passages 6 are provided to connect the high-pressure port P and the low-pressure port T to each other through the throttle at the stationary and leftward positions. According to this, when the cylinder 1 such as the tilt cylinder or the lift cylinder is driven, a part of the pressurized liquid can be returned to the tank 3 through the bypass passage 6 and the flow rate to each cylinder 1 can be limited. The pump 2 can be operated at a pressure level corresponding to the load of the cylinder 1, and the power efficiency can be significantly improved.

However, in the above-mentioned prior art, the bypass passage 6 is realized by providing the bleed-off throttles 6a opening on both sides of the land portion 4a of the spool 4 as shown in FIG. For this reason, when processing the bleed-off stop 6a, a completely separate processing step is required after lathe processing, resulting in an increase in the number of processing steps, and the bleed-off stop 6a tends to have a narrowing effect. However, it is extremely difficult to set the aperture value to a precise value. Further, as shown in FIG. 9, the bypass passage 6 is formed by reducing the diameter of the outer periphery of the land portion 4a of the spool 4 to form a slight gap 6b between the bypass passage 6 and the sleeve 7 and setting this gap 6b. However, in such a case, it is necessary to carry out the polishing process of the spool 4 twice, and in actual use, the radius of the gap 6b is larger than that of the gap 6b. Since it is necessary to control the minute gaps in units of 1/1000 mm, not only will the number of processing steps increase, but the cost will be inevitably high in terms of dimensional accuracy.

[0006] The present invention has been made in view of the above problems, and generally includes a forklift, a fixed displacement type hydraulic pressure source, a hydraulic circuit and a hydraulic device. It is an object of the present invention to provide a switching valve capable of supplying a flow rate corresponding to a load to those hydraulic circuits through the switching valve when supplying the fluid, and at the same time, capable of being manufactured simply and accurately.

[0007]

[Means for Solving the Problems]

 In order to achieve such an object, the switching valve according to the present invention is characterized in that a notch is formed in the outer peripheral land portion of the spool so as to traverse the land portion in the axial direction.

As a notch machining method in that case, the end mill is placed at a position offset in a direction perpendicular to both axes with respect to a center position where the axis is orthogonal to the axis of the spool. An effective method is to dispose the end mill from the spool and dispose the end mill relative to the land along the axial center of the spool with a predetermined depth of cut from that position. Hereinafter, this processing method is referred to as an end mill method.

[0009]

[Action]

 A switching valve using a normal spool blocks the high and low pressure ports by the land at the rightward position or the leftward position of the spool, but the switching valve to which the spool of the present invention is applied is the rightward or leftward position of the spool. The high and low pressure ports are communicated via the notch at the row position, and a certain amount of pressure fluid is bypassed from the high pressure port to the low pressure port according to the throttle amount of the notch, and the remaining pressure fluid is passed to the load circuit. Will be supplied. Therefore, the pump can be operated at a pressure level according to the load, and the power efficiency can be significantly improved. Moreover, as in the present invention, if the bypass passage is formed by the notch that crosses the land portion, the end mill method can be applied, and the end mill is scanned along the land portion on the same lathe. It is possible to easily form a notch having a triangular groove shape in cross section. The advantage of the end mill method in that case is that the notch cross-sectional area can be controlled automatically by adjusting two independent parameters, the offset position of the end mill and the depth of cut. The processing for setting the bypass flow rate will be extremely simple, and the accuracy can be reasonably improved.

[0010]

【Example】

 An embodiment of the present invention will be described below with reference to FIGS.

This switching valve is applied, for example, to operate a cylinder of a forklift. As shown in FIG. 3, basically, the switching valve includes a pair of actuator ports A and B connected to both side chambers 1a and 1b of a cylinder 1 and a high pressure port P communicating with a pump 2 as a high pressure source. , And a low-pressure port T communicating with the tank 3, and performs a three-position switching function according to the sliding position of the internal spool 4 as shown in FIG. That is, both actuator ports A and B are blocked at the center position of the spool 4, the actuator port A or B is connected to the high pressure port P at the rightward position or the leftward position, and the actuator port B or A is at a low pressure position. Connect to port T. In the state of FIG. 3 in which the spool 4 is at the center position and blocks both actuators A and B, the high pressure port P and the tank port T are communicated with each other through the flow path 5, and the high pressure liquid is flowed. Return to tank 3 via line 5.

In such a switching valve, the spool 4 shown in FIGS. 1 and 2 has a notch 6c formed in its outer peripheral land portion 4a so as to traverse the land portion 4a in the axial direction. 6c is used as a bypass passage 6 for connecting the high pressure port P and the low pressure port T via the flow path 5 as shown in FIG. For processing the notch 6c, it is preferable to modify the end mill construction method proposed by the present inventor in Japanese Patent Application No. 2-407068. The procedure is as shown in FIGS. 4 to 6, in which the end mill 8 is moved in a direction X perpendicular to both axial centers m and n with reference to a center position where the axial center n of the end mill 8 is orthogonal to the axial center m of the spool 4. It is arranged at a position offset to the end mill 8 relative to the land 4a along the axial center m of the spool 4 with a predetermined cut amount d from that position, and then the end mill 8 is spooled. In this embodiment, the feeding operation is performed until the end mill 8 completely crosses the land portion 4a of the spool 4. As a result, as shown in FIGS. 1, 2 and 6, a triangular notch 6c having a V-shaped cross section is engraved on the spool 4, and in the present embodiment, such a notch is formed. 6c are provided at four equiangular points of the land portion 4a.

When such a spool 4 is applied to the switching valve of FIG. 3, the high port P and the low pressure port T communicate with each other through the notch 6c at the rightward position or the leftward position of the spool 4 and the notch 6c Depending on the amount of throttling, a predetermined flow rate of the pressure liquid is bypassed from the high pressure port P toward the low pressure port T, and the remaining pressure liquid is supplied to the cylinder 1. Therefore, the pump 2 can be operated at a pressure level according to the load, and the power efficiency can be markedly improved. Moreover, as in the present embodiment, when the notch 6c that crosses the land portion 4a is formed by using the end mill method and the notch 6c is used as the bypass passage 6, the notch 6c is used on the same lathe. Not only is it possible to perform machining, but the advantage of the end mill method is that the cross-sectional area of the notch 6c can be controlled freely by adjusting two independent parameters, the offset position X of the end mill 8 and the depth of cut d. The benefits will be obtained. For this reason, the processing for setting the bypass flow rate according to the load of the cylinder 1 becomes extremely simple, and the accuracy can be reasonably improved.

[0014]

[Effect of the device]

 As described above, the switching valve according to the present invention can be suitably applied to cylinder drive or the like by forming the notch that traverses the land portion in the spool. Moreover, the notch having such a shape can be easily and accurately machined by using an end mill method or the like. Therefore, this switching valve is extremely useful when it is desired to supply pressure liquid to a hydraulic circuit, a hydraulic device, etc., which is generally a fixed displacement type hydraulic pressure source, such as a forklift.

[Brief description of drawings]

FIG. 1 is a front view showing a spool installed in an embodiment of the present invention.

2 is a cross-sectional view of FIG.

FIG. 3 is a circuit diagram showing a switching valve of the same embodiment.

FIG. 4 is a perspective view showing a state of processing a notch on the spool of the embodiment.

FIG. 5 is a cross-sectional view of the same.

FIG. 6 is a front view of the same.

FIG. 7 is a circuit diagram showing a conventional switching valve.

FIG. 8 is a front view showing a conventional spool.

FIG. 9 is a front view showing another conventional spool.

[Explanation of symbols]

 4 ... Spool 4a ... Land 6c ... Notch m ... Shaft center

Claims (1)

[Scope of utility model registration request] 1. A switching valve having a spool having a land portion on its outer circumference, wherein the land portion is formed with a notch that passes through the land portion in the axial direction.