JP2927308B2 - Hydraulic control 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 control circuit applied to a vehicle such as a forklift, and more particularly to a hydraulic control circuit capable of always providing a stable pilot pressure.

[0002]

2. Description of the Related Art A conventional hydraulic control circuit has, for example, a configuration as shown in FIG. First, there is a pump P,
A priority valve PV is connected to the pump P. Control flow port 101 of the priority valve PV is connected to the first circuit system S _1. The first circuit system S ₁ is for controlling the cylinder for power steering. Moreover, surplus flow port 103 of the priority valve PV is connected to the second circuit system S _2. The second circuit system S ₂ is for controlling the actuators of the working machine system. The priority valve PV is connected to the control flow port 101.
Pressurized oil at a constant flow rate on the side is preferentially shunted to supply excess flow above the control flow in the second circuit system S _2.

[0003] above the second circuit system S _2, from the upstream side, a first control valve V ₁ which controls the lift cylinder, a second control valve for controlling the tilt cylinder V _2, the third control valve for controlling the attachment cylinder V ₃ is provided. The above first to third
Control valves V ₁ ~V _3, the spool unit 105,107,10
9 faces the pilot chambers 111, 113, and 115, and the pilot chambers 111, 113,
Reference numeral 115 is connected to the pump P via a pressure reducing valve 117. Therefore, the maximum value of the pilot pressure acting on the pilot chambers 111, 113, and 115 is controlled by the pressure reducing valve 117. Also, the individual pilot rooms 111, 11
3 and 115 are proportional solenoids 119 and 121,
123.

When the first to third control valves V _{1 to} V ₃ are held at the neutral position (the state shown in FIG. 1), the neutral port 12
5, 127, 129 are opened, and the hydraulic oil supplied through the excess flow port 103 is supplied to the tank T through the neutral flow path 131.
Return to Further, on the downstream side of the third control valve V ₃ back pressure valve 133 is interposed. This is to generate a predetermined pressure in the neutral passage 131 when the hydraulic oil flows through the neutral passage 131. Said first control valve V ₁ was lowered position even when switched to (switching position located on the left side in the figure), the neutral port 125 remains open while the side ports communicating with the actuator in communication with the tank T It is. That is,
In this lowered position, the lift cylinder is lowered by its own weight.

The inflow ports of the _first to third control valves V _{1 to} V ₃ are:
Communicate with each other through the parallel feeder 135, it is switched to either of the control valve V ₁ ~V _3, hydraulic oil is supplied to the actuator via the parallel feeder 135. An unload valve 137 is connected to the parallel feeder 135. The pressure chamber 139 of the unload valve 137 is connected to the neutral flow path 131 via a solenoid valve 141.

The solenoid valve 141 is open in a normal state. When exciting the first to third proportional solenoid 119,121,123 of the control valve V ₁ ~V _3,
The solenoid valve 141 is also excited and closes. That is, when switching the first to third control valve V ₁ ~V ₃ in a position other than the neutral position, the solenoid valve 141 is switched to the closed position. When the solenoid valve 141 is open, the pressure chamber 139 of the unload valve 137 is connected to the tank T, so that the unload valve 137 is opened. Then, the pressure oil of the parallel feeder 135 is returned to the tank T.

The operation will be described based on the above configuration. When the discharge flow rate of the pump P is equal to or greater than the certain flow rate, the excess flow rate is supplied to the second circuit system S _2. At that time, each control valve
If V ₁ -V ₃ are in the neutral position as shown in the figure, the hydraulic oil is returned to the tank T via the neutral flow path 131 and the back pressure valve 133. Thus, hydraulic oil back pressure is generated by way of the back pressure valve 133, the back pressure acting on the control valves V ₁ ~V ₃ as a pilot pressure. Therefore, if any one of the _first to third control valves V _{1 to} V ₃ is operated in a state where such back pressure is applied, a pilot pressure corresponding to the operation amount is applied to each pilot chamber. And each control valve V ₁
Switch the V _3.

If the back pressure valve 133 is not provided, the following problem occurs. For example, the first control valve V ₁ in order to lower the lift cylinder in an effort to full stroke, it required pilot pressure may not occur. That is, when lowering the lift cylinder by its own weight, the first control valve V ₁ switches on the left side in the figure, but in switching the position of the left, neutral port 1
25 is left open, and the hydraulic oil returns to the tank T via the neutral flow path 131. Accordingly, proportional to switch the first control valve V ₁ solenoid 11
Be excited 9, the pressure of the pump P will be insufficient pilot pressure without stand sufficiently, the first control valve V ₁ is no longer able to full stroke. When the first control valve V ₁ is not possible full stroke, lowering speed of the lift cylinder is delayed. Therefore, the back pressure valve 1 already described
33 interposed.

The proportional solenoids 119 to 119 of the control valves V _{1 to} V ₃
When the valve 123 is operated, the solenoid valve 141 is also excited, and switches from the illustrated open position to the closed position. Therefore, the unload valve 137 is also closed.

If an emergency occurs during the operation of each actuator, the proportional solenoid of the control valve that controls the actuator is demagnetized. Thus, the solenoid valve 141 is also demagnetized. As a result, the solenoid valve 141 is switched to the open position, and the pressure chamber 139 of the unload valve 137 is connected to the tank T. When the pressure in the pressure chamber 139 reaches the tank pressure, the unload valve 13
7 is opened, and the hydraulic oil from the surplus flow port 103 is returned to the tank T via the parallel feeder 135 and the unload valve 137. Therefore, no hydraulic oil is supplied to the actuator, and the operation of the actuator stops.

When the first to third control valves V _{1 to} V ₃ are in the neutral position, the unload valve 137 is connected to the second circuit system.
The hydraulic fluid that has flowed into S ₂ is returned to tank T,
Also it has the function of preventing the rise of the oil temperature of S _2.

[0012]

According to the invention Problems to be Solved] The above conventional configuration, when switching the control valves V ₁ ~V _3, sufficient pilot pressure there is a problem that may not occur. For example, in the state the discharge flow rate is low the pump P, the switching the second control valve V ₂ to tilted forward tilt cylinder, by the action of the load of the fork, the negative pressure in each of the neutral flow passage 131 and a parallel feeder 135 Occur. Therefore, the pilot pressure is not sufficiently generated, the second control valve V ₂ has a problem that it becomes impossible to full stroke.

When the proportional solenoid is suddenly operated and stopped, the actuator slightly moves due to the back pressure generated by the back pressure valve 133 at that moment. However, if the neutral ports 125, 127, 129 are not fully closed,
Since most of the pressure oil is returned to the tank T via the neutral flow path 131, there is also a problem that the actuator does not operate halfway.

The present invention has been made based on such a point, and an object of the present invention is to provide a hydraulic control circuit which can always generate a stable pilot pressure.

[0015]

In order to achieve the above object, a hydraulic control circuit according to the present invention connects a priority valve to a pump, connects a first circuit system to a control flow port side of the priority valve, and generates an excess flow. Connect the second circuit system to the port side,
A plurality of control valves for controlling the actuators are connected to the circuit system.The discharge pressure of the pump is applied to the pilot chamber of these control valves, and this pressure is controlled by a proportional solenoid. When the control valve is in the neutral position, In a hydraulic control circuit configured so that the hydraulic oil supplied from the surplus flow port returns to the tank via the neutral flow path, a solenoid valve is disposed between the control flow port of the priority valve and the first circuit system. A switching valve having an orifice is arranged in parallel with the solenoid valve, an unload valve is arranged between the surplus flow port and the tank, and the solenoid valve is de-energized when the proportional solenoid of the control valve is de-energized. To open the valve and supply the hydraulic oil from the control flow port to the first circuit system via at least the solenoid valve. When the proportional solenoid is energized it is closed it by energizing the solenoid valve,
Hydraulic oil from the control flow port is supplied to the first circuit system through the orifice of the switching valve, and when the solenoid valve is not energized, the unload valve is opened by the action of the switching valve to generate an excess flow rate. An excess flow from the port is unloaded, and when the solenoid valve is excited, the unload valve is closed by the action of the switching valve.

[0016]

First, when the proportional solenoid of the control valve is de-energized, the solenoid valve is de-energized and opened. At that time, the operating oil from the control flow port is supplied to the first circuit system via at least the solenoid valve. This is at least because the solenoid valve is de-energized, and there are two possible cases: closing the switching valve and allowing hydraulic oil to flow through the orifice. On the other hand, when the proportional solenoid of the control valve is excited, the solenoid valve is excited and closed. At that time, the hydraulic oil from the control flow port is supplied to the first circuit system via the orifice of the switching valve. That is, when the proportional solenoid of the control valve is excited, hydraulic oil is supplied to the first circuit system through the orifice of the switching valve, and at this time, a differential pressure is generated by the action of the orifice. Is supplied with a predetermined pilot pressure. When the solenoid valve is not energized, the unload valve is opened by the action of the switching valve to unload the excess flow from the excess flow port. Then, when the solenoid valve is excited, the unload valve is closed by the action of the switching valve.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. First, there is a pump P, which has a priority valve
PV is connected. Control flow port 1 of the priority valve PV is connected to the first circuit system S _1. This first circuit system S ₁
Is for controlling a cylinder for power steering. Moreover, surplus flow port 3 of the priority valve PV is connected to the second circuit system S _2. The second circuit system S ₂ is for controlling the actuators of the working machine system. And priority valve PV
The pressure oil of a constant flow rate control flow port 1 side is preferentially shunted to supply excess flow above the control flow in the second circuit system S _2.

[0018] The second circuit system S _2, from the upstream side, a first control valve V _1, the second control valve V ₂ is provided. The first and second control valves V ₁ and V ₂ have both ends of the spool portions 5 and 7 facing pilot chambers 9 and 11, and the pilot chambers 9 and 11 are pumped through a pressure reducing valve 13. It is connected to P. Therefore, the maximum value of the pilot pressure acting on the pilot chambers 9 and 11 is controlled by the pressure reducing valve 13. The pressure in each of the pilot chambers 9 and 11 is controlled by proportional solenoids 14 and 15.

When the first and second control valves V ₁ and V ₂ are held at the neutral position (the state shown in the figure), the neutral port 17
19 is opened, and the pressure oil supplied via the surplus flow port 3 returns to the tank T via the neutral flow path 21. Also, the first and second
The inflow ports of the control valves V ₁ and V ₂ are connected through a parallel feeder 23, and pressure oil is supplied to the actuator through the parallel feeder 23 regardless of which control valve V ₁ or V ₂ is switched. You.

Control flow port 1 of priority valve PV and first circuit system
Unload solenoid valve 25 as a solenoid valve is interposed between the S _1. The unloading solenoid valve 25 has an open position 25a and a closed position 25b, and is switched to the open position 25a by the coil spring 29 when the solenoid 27 is not excited. On the other hand, when the solenoid 27 is excited, it switches to the closed position 25b. The solenoid 27 is energized and de-energized by the proportional solenoid 1 of the first and second control valves V ₁ and V _2.
4 and 15 are synchronized at the time of excitation and proportionality.

The unloading solenoid valve 25 has an unloading pilot pressure switching valve 3 as a switching valve.
1 are connected in parallel. An orifice 33 is interposed on the primary side of the unloading pilot pressure switching valve 31. Further, an unload valve 35 is interposed between the excess flow port 3 of the priority valve PV and the tank T.

The unloading pilot pressure switching valve 31
Are provided with switching positions 31a and 31b, and are appropriately switched according to the force relationship between the pilot pressure acting from the primary side and the secondary side and the coil spring 37, respectively. Then, when switched to the switching position 31a, the flow of control flow supplied from the priority valve PV is supplied to the allowed first circuit system S _1. At this time, the orifice 39 provided at the switching position 31a
And the orifice 33 already described
The back pressure is generated by also acting as a throttle function. Further, since the tank chamber 41 of the unload valve 35 and the tank T are shut off, the unload valve 35 is closed.

On the other hand, when the unloading pilot pressure switching valve 31 is switched to the switching position 31b, the valve is closed and the tank chamber 41 of the unloading valve 35 is communicated with the tank T. As a result, the unload valve 35 opens. Note that reference numerals 43 and 45 in the figure denote relief valves, and reference numeral 47 denotes a check valve. Also, according to the above description, the unloading pilot pressure switching valve 31
Is switched to the switching position 31b, the valve is closed. However, as another embodiment, the valve may be continuously opened. That always through the orifice 33 of the unloading pilot pressure switching valve 31 is configured such that hydraulic oil is supplied to the first circuit system S _1.

The operation will be described based on the above configuration. First, a case will be described in which an external electric signal is not input and the proportional solenoids 15 and 17 of the first and second control valves V ₁ and V ₂ are in a non-excited state. Hydraulic oil flows from the pump P is diverted by the priority valve PV, the inner excess flow rate is supplied to the first circuit system S ₁ via the surplus flow port 3. On the other hand, the priority flow is supplied in parallel to both the unloading solenoid valve 25 and the unloading pilot pressure switching valve 31 via the control flow port 1. At that time, since the unloading pilot pressure switching valve 31 is closed and has switched to the switching position 31b, the control flow is fed to the first circuit system S ₁ through the unloading solenoid valve 25.

The unloading pilot pressure switching valve 31
Is switched to the switching position 31b, the tank chamber 41 of the unload valve 35 is communicated with the tank T side, and the unload valve 35 is opened. Therefore, the excess flow returns to the tank T via the neutral ports 17 and 19, and also returns to the tank T via the unload valve 35.
Return to

Next, a case where the proportional solenoids 15 and 17 of the _first and second control valves V ₁ and V ₂ are excited by input of an external electric signal will be described. The above proportional solenoid 1
When the solenoids 5 and 17 are excited, the solenoid 27 of the unloading solenoid valve 25 is simultaneously excited, and the unloading solenoid valve 25 is switched to the closed position 25b. Therefore, the priority flow rate flows only to the unloading pilot pressure switching valve 31 side, whereby the pilot pressure on the left side of the unloading pilot pressure switching valve 31 in the drawing rises and switches to the switching position 31a. Accordingly, the hydraulic fluid flows to the first circuit system S ₁ direction via the orifice 33, 39.

On the other hand, the switching operation of the unloading pilot pressure switching valve 31 shuts off the pressure chamber 41 of the unloading valve 35 and the tank T, so that the unloading valve 35 is closed. At that time, the pressure (P1) on the pump P side is (steering pressure) and (orifice 3
3) and (39) and (the control pressure of the priority valve PV).

Next, the pilot pressure applied to the first and second control valves V ₁ and V ₂ in the above state will be described.
As already mentioned, the control flow through the orifice 39 of the orifice 33 and the unloading pilot pressure switching valve 31, is supplied to the first circuit system S ₁ side. At that time, a sufficient differential pressure is generated by the action of the two orifices 33 and 39, and thereby, a necessary pilot pressure can be reliably provided.

Next, the operation in an emergency will be described. The unload valve 35 is an unload solenoid valve 2
Are those operated by the fifth switching operation, the first and second control valves V _1, V ₂ proportional solenoid 15 is unloaded state when de-energized. Therefore, even if a situation occurs in which the spool portions 5 and 7 of the first and second control valves V ₁ and V ₂ stick to each other and the neutral state is cut off, the first and second control valves V ₁ and V ₂ may be disconnected. When the proportional solenoids 14 and 15 of the two control valves V ₁ and V ₂ are de-energized, an unload state is established, and an abnormal rise in pressure on the pump P side can be prevented. Incidentally, the unload valve 35 is for unloading only the surplus flow rate, so that the first circuit system S ₂
The control flow to is ensured.

According to this embodiment, the following effects can be obtained. First, the pilot pressure to the first and second control valves V ₁ and V ₂ can be always provided in a stable state. That is, when the first and second control valves V ₁ and V ₂ are in the neutral state, not only a sufficient pilot pressure is provided, but also the proportional solenoid 1 of the first and second control valves V ₁ and V _2.
If the 4, 15 is energized, the control flow is because flows in the first circuit system S ₁ via the orifice 33 and 39, whereby a large pressure difference is caused which it is supplied as Paitto pressure .

[0031] The first control valve V _1, even emergency such as the second control valve V ₂ of the spool 5 and 7 are stuck, the first control valve V _1, a second control valve V ₂ of the proportional solenoid 14, By deenergizing 15, the unload valve 35 can be opened to unload the excess flow-side hydraulic oil, thereby improving the safety, such as preventing an increase in oil temperature. be able to.

As described above, in the unloading pilot pressure switching valve 31, even when the unloading solenoid valve 25 is excited, the flow of the hydraulic oil through the orifice 39 is continuously permitted. In this case, the unloading solenoid valve 25 may be used.
Irrespective of non-excitation / excitation, the orifices 33 and 39 have a back pressure and a pilot pressure.

[0033]

As described above, according to the hydraulic control circuit of the present invention, a necessary pilot pressure can be provided even when the proportional solenoid of the control valve is excited, and a stable pilot pressure is always provided. Can be.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a hydraulic control circuit showing one embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional hydraulic control circuit.

[Explanation of symbols]

Reference Signs List 1 control flow port 3 surplus flow port 9 pilot chamber 11 pilot chamber 14 proportional solenoid 15 proportional solenoid 21 neutral flow path 25 unloading solenoid valve (solenoid valve) 31 unloading pilot pressure switching valve (switching valve) P pump PV priority Valve S ₁ First circuit S ₂ Second circuit T Tank

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-258512 (JP, A) JP-A-4-258511 (JP, A) JP-A-2-303403 (JP, A) JP-A-2- 261912 (JP, A) Fully open sho 61-23506 (JP, U) Full open sho 58-20709 (JP, U) (58) Fields studied (Int. Cl. ⁶ , DB name) F15B 11/00-11 /twenty two

Claims (1)

(57) [Claims] 1. A priority valve is connected to a pump, a first circuit system is connected to a control flow port side of the priority valve, a second circuit system is connected to a surplus flow port side, and the second circuit system is connected to the second circuit system. A plurality of control valves for controlling the actuators are connected, a discharge pressure of a pump is applied to a pilot chamber of these control valves, and this pressure is controlled by a proportional solenoid. When the control valve is in a neutral position, an excess flow port is provided. A hydraulic control circuit configured so that the hydraulic oil supplied from the control valve returns to the tank via the neutral flow path includes a solenoid valve disposed between the control flow port of the priority valve and the first circuit system. A switching valve having an orifice is disposed in parallel with the valve, an unload valve is disposed between the surplus flow port and the tank, and the solenoid is deenergized when the proportional solenoid of the control valve is not energized. The solenoid valve is de-energized and opened, and hydraulic oil from the control flow port is supplied to the first circuit system via at least the solenoid valve. When the proportional solenoid of the control valve is excited, the solenoid valve is excited. To close the valve, supply hydraulic oil from the control flow port to the first circuit system through the orifice of the switching valve, and when the solenoid valve is de-energized, unload by the action of the switching valve. A hydraulic control circuit characterized in that the valve is opened to unload the excess flow from the excess flow port, and the unload valve is closed by the action of the switching valve when the solenoid valve is excited. .