JP2518112B2 - Oil control valve - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oil control valve for controlling a hydraulic cylinder for cargo handling of industrial vehicles such as forklifts.

[0002]

2. Description of the Related Art FIG. 7 shows an operation circuit diagram of a conventional hydraulic cylinder for cargo handling in a forklift. As shown, a hydraulic pump 25 driven by the engine 24
The hydraulic fluid discharged from the oil is sent to the oil control valve 21 through the high pressure circuit 28, and passes through the low pressure circuit 29 when the valve spool 22 of the oil control valve 21 is held in the illustrated neutral position. Tank 2
6, when the valve spool 22 is switched, the valve spool 22 is sent to the cargo handling hydraulic cylinder 27 to expand or contract the hydraulic cylinder 27. When the hydraulic cylinder 27 reaches the stroke end, the pressure in the high pressure circuit 28 rises, and when the pressure in the circuit reaches the pressure set by the relief valve 23 of the oil control valve 21, the relief valve 23 opens. The hydraulic oil escapes from the escape passage 30 to the tank 26 via the low pressure circuit 29, and the circuit pressure is maintained at the set pressure of the relief valve 23. Note that FIG. 8 shows the internal circuit pressure of the high pressure circuit 28 at the end of the hydraulic cylinder stroke.

[0003]

By the way, the set pressure of the relief valve 23 is set corresponding to the maximum load of the hydraulic cylinder 27, which is constant regardless of whether the engine speed is high or low. Therefore, in the case of the conventional oil control valve 21 described above, in the region where the engine speed is low and high output cannot be expected, when the hydraulic cylinder 27 is operated to the stroke end, the circuit pressure is set by the relief valve 23. Since the pressure rises to a pressure, a load larger than its output may act on the engine 24 to cause an engine stop (hereinafter referred to as engine stall). In other words, in the conventional one,
When the hydraulic cylinder 27 such as a lift cylinder or a tilt cylinder is operated to the stroke end in the idling state of the engine 24, there is a high possibility that engine stall occurs and work efficiency is poor. It should be noted that lowering the set pressure P1 of the relief valve 23 lowers the maximum load of the hydraulic cylinder 27, and thus such a countermeasure is practically impossible.

In view of the above problems, the present invention maintains the circuit internal pressure at a high pressure in the high engine speed region, and the low circuit internal pressure in the low engine speed region such as at idling. It is a technical issue to be solved to keep it.

[0005]

In order to solve the above problems, the present invention is configured as follows. That is, the oil control valve according to the present invention is an oil control valve that drives the hydraulic cylinder for cargo handling by controlling the flow of hydraulic oil discharged from the hydraulic pump driven by the engine, and the hydraulic oil is controlled by the switching operation. Is provided in the relief passage of the hydraulic oil that connects the valve spool that controls the flow direction of the high pressure circuit and the low pressure circuit,
A relief valve for holding the pressure in the high-pressure circuit at a set pressure, and an orifice provided in the relief passage, the diameter of which is set to a thickness capable of escaping at least the entire amount of hydraulic oil discharged during idling of the engine It is characterized by that.

[0006]

In the region where the engine speed is low, the total amount of hydraulic oil discharged from the hydraulic pump can pass through the orifice, so the maximum pressure in the high pressure circuit during operation of the hydraulic cylinder is controlled only by the relief valve. Therefore,
In this case, a low circuit pressure can be obtained by reducing the set pressure of the relief valve. On the other hand, in a region where the engine speed is high, as the amount of hydraulic oil discharged from the hydraulic pump increases, the restricting action of the outflow amount by the orifice, that is, the throttling action is performed. Therefore, the internal pressure of the high-pressure circuit during operation of the hydraulic cylinder is controlled to a pressure that is the sum of the pressure set by the relief valve and the pressure generated by the throttle action of the orifice. Therefore, in this case, a high in-circuit pressure proportional to the engine speed is obtained.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, a first embodiment based on FIGS. 1 and 2
Will be explained. As shown in FIG. 1, the hydraulic oil discharged from the hydraulic pump 6 driven by the engine 5 is sent to the oil control valve 1 through the high pressure circuit 9. The oil control valve 1 of the present embodiment includes a valve spool 2 that switches the direction of the flow of hydraulic oil, a relief valve 3 and an orifice 4 for controlling in-circuit pressure, and the relief valve 3 and the orifice 4 are high pressure. Circuit 9
The relief passage 11 connecting the low pressure circuit 10 and the low pressure circuit 10 is provided with the orifice 4 on the upstream side.

When the valve spool 2 is held in the neutral position shown in the figure, the working oil is returned to the tank 7 through the low pressure circuit 10. However, when the valve spool 2 is switched, the lift cylinder and It is sent to a cargo handling hydraulic cylinder 8 such as a tilt cylinder, and the hydraulic cylinder 8 is extended or contracted. During operation of the hydraulic cylinder 8, when the hydraulic cylinder 8 reaches the stroke end, the pressure in the high-pressure circuit 9 rises, and when the circuit pressure reaches the set pressure of the relief valve 3, the relief valve 3 Is opened and the working oil escapes through the orifice 4 to the tank 7 via the low pressure circuit 10 via the low pressure circuit 10, and the circuit internal pressure is maintained at a pressure controlled by the relief valve 3 and the orifice 4.

FIG. 2 shows the in-circuit pressure of the high pressure circuit 9 at the end of the stroke of the hydraulic cylinder 8. In FIG. 2, P1 indicates the pressure set by the conventional relief valve 3, and P2 indicates the present embodiment. Example relief valve 3
P3 indicates an inlet pressure generated on the upstream side of the orifice 4 by the throttling action of the orifice 4. That is, the set pressure P2 set by the relief valve 3 in this embodiment is set lower than the conventional set pressure P1, while the diameter of the orifice 4 is
For example, in a region where the engine speed is low, such as during idling, the thickness is set so that the entire amount of hydraulic oil discharged from the hydraulic pump 6 can flow.

The oil control valve 1 according to this embodiment is constructed as described above, and therefore the circuit of the high pressure circuit 9 when the hydraulic cylinder 8 is operated by the switching of the valve spool 2 and reaches the stroke end. The internal pressure is as follows.

When the engine speed is low, the amount of hydraulic oil discharged from the hydraulic pump 6 is small and the entire amount can pass through the orifice 4. Therefore, no throttling action is performed and the inlet pressure P3 becomes 0 kg / cm ^2. . Therefore, the load applied to the hydraulic pump 6 when the hydraulic cylinder 8 reaches the stroke end, that is, the load applied to the engine 5, corresponds to the pressure P2 set by the relief valve 3. Since this pressure P2 is set lower than the conventional pressure as described above, the load applied to the engine can be small. Therefore, in this case, the set pressure P2 of the relief valve 3 is preferably adjusted to the maximum pressure at which engine stalling does not occur even when a load is applied to the engine 5 in the idling state.

On the other hand, when the engine speed increases,
In proportion to this, the amount of hydraulic oil discharged from the hydraulic pump 6 increases, and the flow rate of hydraulic oil passing through the orifice 4 is accordingly limited. Therefore, the inlet pressure P3 of the orifice 4 gradually increases due to the throttling action of the orifice 4. Therefore, the pressure in the circuit at that time is the pressure P2 determined by the relief valve 3.
And the pressure P3 generated by the throttle action of the orifice 4 are added (P2 + P3).

Therefore, by setting so that the throttle action of the orifice 4 works after the idling speed is exceeded, the internal circuit pressure of the high pressure circuit 9 is, as shown in the graph of FIG. It gradually increases as the number of rotations increases, and reaches the conventional set pressure P1 on the way.
After that, this pressure is exceeded and the maximum pressure is reached at the maximum engine speed. However, the maximum pressure at this time must be set in consideration of the pressure resistance of the system equipment. In the region where the circuit pressure (P2 + P3) controlled by the relief valve 3 and the orifice 4 is lower than the set pressure P1 by the conventional relief valve, the pressure in the hydraulic cylinder 8 also becomes P2 + P3, and in this region, high load work is performed. In consideration of such a point, when the engine speed is 2/3 or less of the maximum speed, the circuit pressure (P2 +
It is desirable to adjust P3) to reach the conventional relief pressure P1.

As described above, according to the oil control valve 1 of the present embodiment, the pressure in the circuit is maintained at the pressure P2 lower than the conventional pressure in the engine in the region where the engine speed is low such as at the time of idling. The applied load can be reduced, and on the other hand, in a region where the engine speed is high, a high pressure (P2 + P3) controlled by the relief valve 3 and the orifice 4 is maintained to cope with high load work by the hydraulic cylinder 8. Is something that can be done.

Next, a second embodiment of the present invention will be described with reference to FIGS.
It will be described based on. This embodiment is different from the above-described first embodiment in that the orifice 4 is provided on the downstream side of the relief valve 3, and the other configurations are similar to those of the first embodiment. That is, the diameter of the orifice 4 and the set pressure P2 of the relief valve 3 are the same. Therefore, also in the case of the second embodiment, the same operational effect as that of the first embodiment can be obtained.

That is, when the engine speed is low,
When the pressure in the circuit of the high pressure circuit 9 reaches the pressure P2 set by the relief valve 3, the relief valve 3 opens and the working oil escapes through the orifice 4 and is returned from the passage 11 to the tank 7 through the low pressure circuit 10. In this case, since the discharge amount of the hydraulic oil is small and the whole amount can pass through the orifice 4, the throttle action of the orifice 4 is not performed and the inlet pressure P3 is 0 kg / cm ² . Therefore, the pressure in the circuit when the hydraulic cylinder 8 reaches the stroke end can be maintained at the pressure P2 (see FIG. 4) lower than the conventional pressure, and the load applied to the engine 5 can be reduced.

On the other hand, in a region where the engine speed is high, the flow rate of the working oil after passing through the relief valve 3 is limited by the throttling action of the orifice 4, so that the inlet pressure P3 of the orifice 4 is changed accordingly. As shown in FIG. 4, the circuit pressure in the high pressure circuit 6 increases in proportion to
A value (P2 +) obtained by adding the pressure P2 set by the relief valve 3 and the pressure P3 generated by the throttle action of the orifice 4.
P3). Therefore, in a region where the engine speed is high, it is possible to maintain the circuit internal pressure at a high pressure and handle high load work.

Next, a third embodiment of the present invention will be described with reference to FIGS.
It will be described based on. In this embodiment, similarly to the first embodiment described above, the relief valve 3 and the orifice 4 are provided in the relief passage 11, and the relief passage 13 provided with the relief valve 12 for high pressure is provided in parallel to them. The set pressure of the relief valve 12 for high pressure is set to the same set pressure P1 as the conventional one.

Therefore, in this embodiment, in the region where the engine speed is low, the same operation as in the first embodiment is performed, and in the region where the engine speed is high, the circuit internal pressure becomes the set pressure P1 of the relief valve 12. Until reaching, the operation is similar to that of the first embodiment, but when the pressure (P2 + P3) in the circuit controlled by the relief valve 3 and the orifice 4 reaches the set pressure P1 of the relief valve 12, after that, the working oil is released. Return to tank 7 through 12. That is, in the case of the third embodiment, when the engine speed exceeds a certain rotation range, the circuit internal pressure can be maintained at the constant set pressure P1 determined by the high pressure relief valve 12.

[0020]

As described in detail above, according to the present invention,
Since the internal circuit pressure can be kept low at low engine speeds and high at high engine speeds, the engine load can be reduced and engine stall It is possible to prevent this, and when the engine is rotating at a high speed, it is possible to cause the hydraulic cylinder to perform high-load work, and it is possible to eliminate the annoyance due to engine stall and improve work efficiency.

[Brief description of drawings]

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

FIG. 2 is a graph showing the internal circuit pressure at the cylinder stroke end of the first embodiment.

FIG. 3 is a hydraulic circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a graph showing a circuit internal pressure at a cylinder stroke end according to a second embodiment.

FIG. 5 is a hydraulic circuit diagram showing a third embodiment of the present invention.

FIG. 6 is a graph showing a circuit internal pressure at a cylinder stroke end according to a third embodiment.

FIG. 7 is a hydraulic circuit diagram showing a conventional example.

FIG. 8 is a graph showing the pressure in the circuit at the end of the conventional cylinder stroke.

[Explanation of symbols]

 1 ... Oil control valve 2 ... Valve spool 3 ... Relief valve 4 ... Orifice 5 ... Engine 6 ... Hydraulic pump 8 ... Hydraulic cylinder 9 ... High pressure circuit 10 ... Low pressure circuit 11 ... Escape passage

Claims (1)

(57) [Claims] 1. An oil control valve for controlling a flow of hydraulic oil discharged from a hydraulic pump driven by an engine to drive a cargo handling hydraulic cylinder, the flow direction of the hydraulic oil being controlled by its switching operation. A relief valve, which is provided in the relief passage for the hydraulic oil that connects the valve spool and the high-pressure circuit and the low-pressure circuit, keeps the pressure in the high-pressure circuit at a set pressure, and the relief passage, the bore of which is at least the engine idling. An oil control valve with an orifice set to a thickness that allows all the discharged hydraulic oil to escape.