GB2313629A - Directional control valve - Google Patents

Abstract

A directional control valve, useful in a pressurized fluid feed system, comprises: ```a spool bore housing a spool and having a pump port 222 a first 223 and a second 224 load pressure detecting port, a first 225 and a second 226 actuator port and a first 227 and a second 228 tank port arranged in such a manner that said first and second load pressure detecting ports may communicate with each other (see channel 229) ; wherein ```said spool can be displaced from a neutral position to assume a first or second pressurized fluid feed position to communicate said pump port with said second or first load pressure detecting port, to communicate said first or second load pressure detecting port with said first or second actuator port and to communicate said second or first actuator port with said second or first tank port; ```said spool can be displaced by a given distance Ll from said neutral position toward one of said first and said second pressurized fluid feed position to communicate said first actuator port with said second actuator port via a load checking valve 236; and wherein ```said main spool can thereafter be further displaced to communicate one of said first and second actuator ports with said pump port while communicating the other of said first and second actuator ports with one of said-first and second tank ports.

Description

DIRECTIONAL CONTROL VALVE This invention relates to a directional control valve which is useful in a pressurized. fluid feed system for supplying a pressurized discharge fluid(s) from a single hydraulic pump or a plurality of hydraulic pumps to a plurality of hydraulic actuators, especially to a turning motor for a power shovel and a cylinder for a boom. The invention has been divided out of Application No. 9606348.2 (Publication No. 2300027).

A pressurized discharge fluid from a hydraulic pump, when it is supplied simultaneously into a plurality of hydraulic actuators, is forced to flow preferentially into an actuator of a lowest external load among various external loads acting on the respective actuators and hence cannot be supplied into a plurality of hydraulic actuators with varied external loads simultaneously.

In order to resolve this problem, there has hitherto been known, for example, a pressurized fluid feed apparatus as shown in Fig. 1 of the accompanying drawings hereof (see Japanese Laid-Open Patent Publication No. Sho 60-11706).

As shown in the Figure, which is a hydraulic circuit diagram schematically illustrating the prior pressurized fluid feed system, the apparatus is provided in the discharge path 2 of a hydraulic pump 1 with a plurality of pressure compensating valves 3, each of the pressure compensating valves 3 being connected at its outlet side to an actuator 5 via a directional control valve 4.

By setting these respective pressure compensating valves 3 at a highest load pressure, the actuators 5 having varying loads can be supplied simultaneously with a pressurized discharge fluid from the hydraulic pump 1.

In such a pressurized fluid feed system, each directional control valve is provided at an inlet side thereof with a pressure compensating valve. which is set by a highest load pressure among a variety of actuators so that the pressurized discharge fluid from the hydraulic pump may be supplied simultaneously to the actuators of various load pressures.

In this pressurized fluid feed system, a directional control valve is made capable of detecting a load pressure in order to enable load pressures of hydraulic actuators to be detected.

For example, as shown in Fig. 2 of the accompanying drawings hereof, which is a cross sectional view substantially illustrating the prior directional control valve, a valve body 201 is formed in its spool bore 202 with a pump port 203, a first and a second load pressure detecting port 204 and 205, a first and a second actuator port 206 and 207, and a first and a second tank port 208 and 209. In this construction, a communication is established between the first and second load pressure detecting ports 204 and 205. A main spool 210 that is fittedly inserted in the above mentioned spool bore 202 can be displaced leftwards and rightwards from a neutral position thereof to assume a first and a second pressurized fluid feed position, thereby enabling the pump port 203 to communicate with the first or the second actuator port 20 or 2C7 via the first and second load pressure detecting ports 204 and 205 while enabling the second or the first actuator port 207 or 206 to communicate with the second or first tank port 209 or 208 so that a load pressure of an actuator may be detected by the second load pressure detecting port 205.

In a directional control valve so constructed, it ensues that a pressurized fluid of a rate of flow that is proportional to the area of the aperture between the first actuator port 206 and the first load pressure detecting port 204 and the area of the aperture between the second actuator port 207 and the second load pressure detecting port 205, that is, say, which is proportional to the distance of displacement of the main spool 210 without regard to the magnitude of the load, even with a finely controlled but a slightly displaced position of the main spool 210, is supplied to an actuator and that as a consequence of a rapidly motivated acceleration of the actuator that is ready to move, the actuator comes to abruptly commence moving.

Also, in a case where the main spool 210 of the directional valve is stopped at an intermediate position between the pressurized fluid feed positions from its neutral position, it should ensue that a pressurized fluid of a rate of flow that is proportional to the area of the aperture is supplied to an actuator even though the actuator is in a high load state. Here again, the result is a lack of stability of the actuator.

Accordingly, the present applicant has previously filed a patent application for a directional control valve that is designed to resolve the above mentioned inconveniences.

More specifically, as schematically shown in the cross sectional view of Fig. 3 of the accompanying drawings hereof, the directional control valve of our prior application has a main spool 210 which is formed with a communicating bore 211 designed to communicate the first load pressure detecting port 204 and the first actuator port 206 with each other and an opening 212 designed to communicate the second load pressure detecting port 205 and the second actuator port 207 with each other within a range in which the main spool 210 is slidably displaced by a given distance from its neutral position and in which the above mentioned communicating bore 211 is provided with a load checking valve 213 for blocking a flow of pressurized fluid from the first actuator port 206 to the first load pressure detecting port 204.

In such a directional control valve, if lying in a range in which the main spool 210 is displaced by a given distance from its neutral position, the pressurized discharge fluid of the hydraulic pump that is introduced in the first load pressure detecting port 204 will be prevented by the load checking valve 213 from flowing into the first actuator port 206 until the fluid pressure is elevated to a level that is commensurate with the load pressure of the actuator. In addition, a portion of the pressurized fluid will be caused to flow out of the opening 212 into the second tank port 209 via the second actuator port 207 in a rate of flow that is proportional to the load of an actuator. Thus, depending upon the load, the actuator will be slow to move in its initial period of movement, and the stability of an actuator is enhanced owing to the fact that the attenuation of movement is increased by the rate of flow of the fluid flowing out into the tank port.

If a directional control valve of this type is used with an actuator that is operated by an external force, however, an inconvenience does take place, for example, with a power shovel whose upper vehicle body needs to be turned by a turning motor and where, operating on a slope, the upper vehicle body attempts to be turned downwards by its own gravity.

For example, in a case where a turning motor 214 attempts to allow the upper vehicle body to turn in the direction of arrow by its own gravity, if the main spool 210 is displaced rightwards to feed the pressurized fluid from the first actuator port 206 into the first port 214a so that the turning motor 214 may rotate at a very low speed in the direction of arrow, it can be seen that although the second actuator port 207 and the second tank port 209 may communicate with each other when the main spool 210 is slightly displaced, it will be unable for the first load pressure detecting port 204 to communicate with the first actuator port 206.

For this reason, the pressurized fluid of the second port 214b of the turning motor 214 will flow into the second tank port 209 from the second actuator port 207 to allow the turning motor 214 to rotate in the direction of arrow. Since the first port 14a is, however, then not to be fed with a pressurized fluid and thus is to be correspondingly evacuated, a cavitation will tend to develop in the first port 214a of the turning motor 214.

In order to obviate this deficiency, it may be conceived to provide at the side of the first and second ports 214a and 214b of the turning motor, a suction valve 215 which acts to suck the pressurized fluid into the first port 214a from a reservoir 216. Since, however, this is in a controlled state in which the turning motor 214 is operating at a very low speed, the pressure in the reservoir circuit will not be at a full level and the pressurized fluid will not be supplied in an amount that is sufficient to fill the vacuum into the first port 214a of the turning motor 214.

Hence, there will still remain a strong tendency for a cavitation to develop in the first port 214a.

When a cavitation develops in the first port 214a of the turning motor 214, a vibration will be induced in the turning motor 214 and its operability to carry out a very low speed control will become extremely difficult.

Accordingly, it is an object of the present invention to provide a directional control valve which has an enhanced operability and which, with a turning motor in allowing an upper vehicle body to turn in a given direction by its own weight, is capable of eliminating the development of a cavitation when it is attempted to rotate the said turning motor at a very low speed in the said direction.

In accordance with the present invention there is provided a directional control valve which comprises: a valve body formed in a spool bore of said valve and having a pump port, a first and a second load pressure detecting port, a first and a second actuator port and a first and a second tank port arranged in such a manner that said first and second load pressure detecting ports may communicate with each other; a main spool fittedly inserted in said spool bore; and wherein said main spool can be disposed at a neutral position thereof to block a communication of any one of said ports with another; wherein said main spool can be displaced to assume a first pressurized fluid feed position to communicate said pump port with said second load pressure detecting port, to communicate said first load pressure detecting port with said first actuator port and to communicate said second actuator port with said second tank port; wherein said main spool can be displaced to assume a second pressurized fluid feed position to communicate said pump port with said first load pressure detecting port, to communicate said first actuator port with said first tank port and to communicate said second load pressure detecting port with said second actuator port, wherein said spool can be displaced by a given distance from said neutral position toward one of said first and said second pressurized fluid feed position to communicate said first actuator port with said second actuator port via a load checking valve; and wherein said main spool can thereafter be further displaced to communicate one of said first and second actuator ports with said pump port while communicating the other of said first and second actuator ports with one of said first and second tank ports.

According to a construction as mentioned above, by virtue of the fact that when a said main spool is displaced towards one of a said first and a said second pressurized fluid feed position, there is established a communication between a said first actuator port and a said second actuator port and that when the said spool is thereafter displaced further, there are established a communication between one of the said first and second actuator ports and the said pump port and a communication between the other of the said first and second actuator ports and one of a said first and a said second tank port, it will be seen that a return pressurized fluid from an actuator that is operated by an external force can be supplied to the said actuator to prevent the said actuator from being rendered at a vacuum so that there may develop no cavitation in the said actuator.

In a construction as mentioned above, it should also be noted that it is preferred that: the said main spool is formed with a first communicating bore for establishing and blocking a communication between the said first load pressure detecting port and the said first actuator port and with a second opening for establishing and blocking a communication between the said second load pressure detecting port and the said second actuator port; the said main spool can be displaced by a given distance from the said neutral position towards the said first pressurized fluid feed position to allow the said first communicating bore to establish a communication between the said first load pressure detecting port and the said first actuator port while permitting the said second opening to establish a communication between the said second load pressure detecting port and the said second actuator port; and a said load checking valve is disposed in the said first communicating bore for blocking a flow of pressurized fluid from the said first actuator port into the said first load pressure detecting port.

A preferred embodiment of a directional control valve according to the present invention will now be described in detail with reference to Figure 4 of the accompanying drawings, which is a cross-sectional view schematically illustrating the directional control valve.

In the directional control valve in accordance with the illustrated embodiment of the present invention, a valve body 220 is formed, in a spool bore 221 thereof, with a pump port 222, a first and a second load pressure detecting port 223 and 224, a first and a second actuator port 225 and-226 and a first and a second tank port 227 and 228, and the said first and second load pressure detecting ports 223 and 224 is communicating with each other at a fluid bore 229.

A main spool 230 that is fittedly inserted in the above mentioned spool bore 221 is formed with an intermediate small diameter portion 261, a first and a second notch 262 and 263, a first small diameter portion 264, a third and a fourth notch 265 and 266, a second small diameter portion 267 and a fifth and a sixth notch 268 and 269. The said main spool 230 is held at a neutral position thereof with a left hand side and a right hand side spring 231 and 231 so as to block a communication from any one of the said ports from another. The said main spool 230 with a pressurized fluid fed into a first pressure receiving chamber 232 is also adapted to be thrusted rightwards to assume a first pressurized fluid feed position. Also. with a pressurized fluid fed into a second pressure receiving chamber 233 the said main spool 230 is adapted to be thrusted leftwards to assume a second pressurized fluid feed position.

The above mentioned main spool 230 is formed with a first communicating bore 234 for establishing and blocking a communication between the said first load pressure detecting port 223 and the said first actuator port 225 and a second communicating bore 235 for establishing and blocking a communication between the said second load pressure detecting port 224 and the said second actuator port 226.

The said first and second communicating bores 234 and 235 are each provided with a load checking valve 236 for blocking a flow of pressurized fluid from a said actuator port into a said load pressure detecting port.

The above mentioned first and second communicating bore 234 and 235 each comprise an axial bore 240 and a pair of radially extending first and second fluid bores 241 and 242 whereas the above mentioned load checking valve 236 is provided with a valve 244 in a blind hole 243 that is formed at an axial portion of the said main spool 230. A spring 246 is provided between the said valve 244 and a plug 245 to make the valve 244 in an abutting engagement with the said axial bore 240.

The above mentioned main spool 230 is formed with a first slit-like opening 247 for establishing and blocking a communication between the said first load pressure detecting port 223 and the said first actuator port 225 and a second slit-like opening 248 for establishing and blocking a communication between the said second load pressure detecting port 224 and the said second actuator port 226.

The above mentioned first and second actuator ports 225 and 226 are connected to a first and a second port 249a and 249b of a turning motor 249, respectively, the turning motor being adapted to turn, for example, the upper vehicle body of a power shovel. In this case, the sides of these first and second ports 249a and 249b are in communication with a reservoir 251 via a suction valve 250.

The above mentioned pump port 222 is connected to a discharge path 255 of a hydraulic pump 254 via a check valve section 253 that constitutes a pressure compensating valve 252. The said hydraulic pump 254 is of the type in which its capacity is varied by changing the sloping angle of a swash plate 256. To this end, a load pressure detecting path 258 is provided that is connected to a pump adjustment directional control valve 257 for varying the sloping angle of the swash plate 256. Furthermore, there is provided a pressure reduction valve section 259 that constitute the above mentioned pressure compensating valve 252 and designed for establishing and blocking a communication between the said discharge path 255 of the hydraulic pump 254 and the said load pressure detecting path 258.

An explanation will now be given with respect to the operation of the illustrated directional control valve. Before further proceeding, it should be noted that the turning motor 249 is assumed to be of the type which is rotated in a direction in which the pressurized fluid is discharged into the second port 249b by virtue of the weight of the upper vehicle body.

First, assume the state in which the said main spool 230 lies in its neutral position as shown in Fig. 4: Each of the said ports will be blocked so that the pressurized fluid introduced into said the pump port 222 may find a blind end. At the same time, the pressurized fluids from the said first and said second ports 249a and 249b of the said turning motor 249 will come to a dead end. This will bring the said turning motor 249 into the state in which it cannot be rotated by an external force, and will then cause the upper vehicle body of a power shovel on a slope to come to a stop without turning by its own gravity.

Assume then the state in which the said main spool 230 is slightly displaced by a distance L1 rightwards from its neutral position: The said second opening 248 will act to establish a communication between the said second load pressure detecting port 224 and the said second actuator port 226. At the same time, the said first communicating bore 234 will act to establish a communication between the said first load pressure detecting port 223 and the said first actuator port 225.

At this time, however. the said second notch 263 will not still act to establish a communication between the said pump port 222 and the said second load pressure detecting port 224 whereas the said fourth notch 266 will not still act to establish a communication between the said first load pressure detecting port 223 and the said first actuator port 225. In addition, the said sixth notch 269 will not still act to establish a communication between the said second actuator port 226 and the said second tank port 228.

This will cause the pressurized fluid of the said second port 249b of the said turning motor 249 to flow through the said second actuator port 226, the said second opening 248, the said second load pressure detecting port 224, the said fluid bore 229, the said first load pressure detecting port 223, the said first communicating bore 235 and the said first actuator port 225 into the said first port 249a of the said turning motor 249. Since this in turn enables the pressurized fluid of the said second port 249b of the said turning motor 249 to be fed into its first port 249a before the latter is fed with the pressurized fluid of the hydraulic pump 254, the said first port 249a will no longer be rendered at a vacuum, thereby preventing a cavitation from being developed therein. Hence, a very low velocity control is made possible for the said turning motor 249.

Assume, then. the state in which the said main spool 230 is further displaced rightwards by a distance L2 ( > L1) from the preceding state: Whereas the said intermediate small diameter portion 261 and the said second notch 263 will act to communicate the said pump port 222 with the said second load pressure detecting port 224, the sixth notch 269 will still act to block a communication between the said second actuator port 226 and the said second tank port 228.

This will cause the pressurized discharge fluid from the hydraulic pump 254 to flow through the said pump port 222, the said intermediate small diameter portion 261, the said second notch 263, the said second load pressure detecting port 224, the said fluid bore 229, the said first load pressure detecting port 223 and the said first communicating bore 234 and immediately in advance of the said load checking valve 236, and will then cause the pressurized discharge fluid of the said hydraulic pump 254 to come to a blind end. Accordingly, the discharge pressure of the said hydraulic pump 254 will be elevated. When that discharge pressure is elevated to a pressure of retention acting on the said load checking valve 236, the latter will be opened and the pressurized discharge fluid of the said hydraulic pump 254 will, by the action of the said load checking valve 236, be fed through the said first bore 241 into the said first port 249a of the said turning motor 249 via the said first actuator port 225.

Assume, next, the state in which the said main spool 230 is displaced rightwards by a distance L3 ( > L2) from the preceding state: A communication will now be established of the said second actuator port 226 with the said second tank port 228 via the said sixth notch 269 to allow a portion of the pressurized discharge fluid of the said hydraulic pump 254 to flow out of the said second opening 248 into the said second tank port 228 at a rate of flow that is proportional to the magnitude of a load pressure (i. e. a pressure of retention of the said turning motor 249) acting on the said first actuator port 225. Thus, when the load (i. e.

retention pressure) of the said turning motor 249 is large, the rate of flow into the said second tank port 228 will be increased. Conversely, when the load pressure is small, the rate of flow into the said second tank port 228 will be reduced. The result is that the acceleration of the said turning motor 249 when it commences moving will become gentle in accordance with the load and there will then no longer be a feel of abrupt start. In addition, there will be an enhanced stability of the said turning motor 249 by virtue of the fact that the rate of flow into the said second tank port 228 will enlarge an attenuation of movement.

In this connection, it should be noted that since the above mentioned second slit-like opening 248 is much smaller in the area of aperture than the said sixth notch 269 and the said first communicating bore 234, there will be no excessive slowing in the acceleration of the said turning motor 249 due to the rate of flow into the said second tank port 228.

Finally, assume the state in which the said main spool 230 is further displaced rightwards by a distance -L4 ( > L3) from the preceding state: The said second slit-like opening 248 will not act to establish a communication between the said second load pressure detecting port 224 and the said second actuator port 226 to allow the pressurized discharge fluid of the said hydraulic pump 254 to flow at a rate of flow that is proportional to the areas of the apertures of the said first load pressure detecting port 223 with the said first small diameter portion 264 and the said second notch 266 of the said main spool 230 and the said first actuator port 225, thereby accelerating the operating speed of the said turning motor 249.

While the foregoing explanation has been directed to the cases in which the said main spool 230 is displaced rightwards, it should be noted that in a case where the said turning motor 249 is rotated in a direction in which the pressurized fluid is discharged from the said first port 249a ousting to tile weight of the said upper vehicle body, similar cases apply when the said main spool 230 are displaced leftwards.

Also, in a case where an actuator, sucli as with a boom cylinder or an arm cylinder. is operated only in a single direction by an external force. it will suffice to provide only one of the first and second openings 247 and 248 and one of the first and second communicating bores 234 and 235.

A directional control valve of this invention may be used in the pressurized fluid feed system described in the parent Application No. 9606348.2 (Publication No. 2300027).

A preferred embodiment of such a pressurized fluid feed system is described in detail with reference to Figs. 4-8 of the parent specification.

Claims (4)

CLAIMS:

1. A directional control valve which comprises: a valve body formed in a spool bore of said valve and having a pump port, a first and a second load pressure detecting port, a first and a second actuator port and a first and a second tank port arranged in such a manner that said first and second load pressure detecting ports may communicate with each other; a main spool fittedly inserted in said spool bore; and wherein said main spool can be disposed at a neutral position thereof to block a communication of any one of said ports with another; wherein said main spool can be displaced to assume a first pressurized fluid feed position to communicate said pump port with said second load pressure detecting port, to communicate said first load pressure detecting port with said first actuator port and to communicate said second actuator port with said second tank port; wherein said main spool can be displaced to assume a second pressurized fluid feed position to communicate said pump port with said first load pressure detecting port, to communicate said first actuator port with said first tank port and to communicate said second load pressure detecting port with said second actuator port, wherein said spool can be displaced by a given distance from said neutral position toward one of said first and said second pressurized fluid feed position to communicate said first actuator port with said second actuator port via a load checking valve; and wherein said main spool can thereafter be further displaced to communicate one of said first and second actuator ports with said pump port while communicating the other of said first and second actuator ports with one of saidfirst and second tank ports.

2. A directional control valve as set forth in Claim 1, wherein said main spool is formed with a first communicating bore for establishing and blocking a communication between said first load pressure detecting port and said first actuator port and with a second opening for establishing and blocking a communication between said second load pressure detecting port and said second actuator port; said main spool can be displaced by a given distance from said neutral position towards said first pressurized fluid feed position to allow said first communicating bore to establish a communication between said first load pressure detecting port and said first actuator port while permitting said second opening to establish a communication between said second load pressure detecting port and said second actuator port; and a said load checking valve is disposed in said first communicating bore for blocking a flow of pressurized fluid from said first actuator port into said first load pressure detecting port.

3. A pressurized fluid feed system including a directional control valve according to Claim 1 or Claim 2.

4. A directional control valve substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.