JPS5925881B2 - hydraulic control device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a hydraulic control device.

In this case, the hydraulic control device includes a directional control valve suitable for controlling the working device, and a switching valve that returns the hydraulic fluid sent into the supply path to the directional control valve directly to the return path.

One control member in the directional control valve blocks at least one work equipment chamber leading to the work equipment in the neutral position, and
The two working positions are selectively connected to the supply or return path.

A control channel, which branches off from the supply channel and can be controlled by a control element in the directional control valve, is connected to the switching valve via a channel section, in which a throttle point is provided. is provided, and the pressure difference that occurs across this throttle point can exert an effect on the closing member of the switching valve in the opening direction against the force of a closing spring.

In the case of such a hydraulic control device, when the control member in the directional control valve is in the neutral position, part of the pump flow is returned to the tank via the control flow path as a control flow, and the rest is all The flow is returned to the return path as a bypass flow from a switching valve that opens based on the pressure difference before and after the throttle point in the control flow path.

When the control member is operated to move from the neutral position to the work position, the control flow path is narrowed and the switching valve and, by extension, the bypass flow path are controlled to close, and the pressure in the supply path increases, causing the flow path leading to the work equipment side to close. is controlled to open.

During this transient phase, the pump flow becomes three flows: a bypass flow, a working flow to the work equipment, and a control flow.

Eventually, the pump flow settles into two, a working flow and a control flow.

This type of hydraulic control device is already known (
(See US Pat. No. 2,489,435).

In this known example, the control spool in the directional control valve is provided with a transition zone with a different flow cross section for the working flow to the working device and the control flow via the control channel.

However, in practice, satisfactory fine control cannot be obtained.

That is, as the control spool is moved from the neutral position to the working position, an excessive pressure increase occurs whenever the pump flow settles into two, the working flow and the control flow.

Such an excessive pressure increase can significantly impede fine control or place an undesirable load on the pump.

SUMMARY OF THE INVENTION The object of the invention is to eliminate the aforementioned disadvantages in a hydraulic control device of the type mentioned at the outset and to make it possible to obtain better fine control characteristics by simple means.

This object was achieved by the present invention as follows.

That is, a second constriction point is provided in the flow path leading from the supply path to the working device.

This second throttling point is arranged upstream of the first throttling point in the control channel and parallel to the switching valve and has a larger flow cross section than the first throttling point. ing.

With such an arrangement, by utilizing the pressure difference occurring at the second throttling location, excessive pressure build-up in the transient range is significantly reduced and the fine control is significantly improved.

Furthermore, the advantage of the switching valve that directs the hydraulic fluid directly to the return path can be fully utilized.

Conventionally, these two advantages could not be combined.

Furthermore, the structural measures according to the invention are extremely inexpensive and can be implemented without major modifications to existing control systems.

This advantage is particularly advantageous if it is possible to influence as large a quantity of hydraulic fluid as possible in the fine control range with the smallest possible control flow.

The invention will now be explained with reference to the exemplary embodiment shown: FIG. 1 shows a hydraulic control device 10 consisting of a housing 28 with a connecting plate 11 and a directional control valve 12, and an end plate 13.

The connecting plate 11 is provided with a switching valve 14 connected between a supply channel 15 and a return channel 16 .

The switching valve 14 directs hydraulic oil from the supply path 15 to the return path 16.
It can be entered by returning it to (described later).

The closing member 17 of this switching valve 14 can be moved into the closed position by means of a closing spring 19 arranged in the pressure chamber 18, i.e. the supply channel 15
in the direction of the closed position in which communication from the control edge 21 to the return path 16 is interrupted.

The supply channel 15 connected to the pump line opens into the flange surface 24 of the connecting plate 11 and leads via an inlet channel 39 in the housing 28 and a check valve 38 to the inlet chamber 31 of the directional control valve 12. .

In the drawing, the branches of the inflow channel 39 are shown as solid lines, but
This branch implies that a similar type of directional control valve (not shown), which can be connected in parallel with the directional control valve 12, can be supplied with hydraulic fluid.

A branch passage 22 branches off within the connecting plate 11 from the supply passage 15 leading to the inlet chamber 31 .

This branch channel 22 has a first throttle point 23 and opens into the pressure chamber 18 of the switching valve 14 and into the flange surface 24 of the connecting plate 11 .

Upstream of the branch channel 22, the feed channel 15 has a second constriction point 25.

This second throttling point 25 has a larger flow cross section than the first throttling point 23 .

Further, the supply path 15 is connected to the directional control valve 1 which communicates with the return path 16.
Overpressure is prevented by a pressure limiting valve 26 connected to a hydraulic oil passage 27 from 2.

The directional control valve 12 has a casing 2 having a spool hole 29.
8, and the spool hole 29 is locally limited to form one inflow chamber 31 and two working device chambers 32, 33.2.
It is enlarged to form two hinged chambers 34, 35 and two mutually adjacent control chambers 36,37.

As already mentioned, the inflow chamber 31 has a check valve 38 and an inflow passage 39.
It is connected to the supply path 15 in the connection plate 11 via
The two return chambers 34, 35 communicate with each other by a further passage 41.

A further passage 42 connects the return chambers 34, 35 to the return passage 27.
is connected to.

One passage 43 connects the control chamber 36 and the branch passage 22 in the connecting plate 11 , and a passage 44 leads from the control chamber 37 to the flange surface in contact with the end plate 13 .

A control spool 45 is slidably guided in the spool hole 29.

This control spool 45 has two piston sections 46, 47
The control edge 48 has a control edge 48 formed with a fine control notch 49 for controlling the supply and return of hydraulic fluid to the double-acting working device.

The two additional piston sections 51, 52 also have control edges 53, which are provided with fine control recesses 54 for controlling the control flow from the branch channel 22.

The double-acting return device 55 holds the control spool 45 in a neutral position (the position shown), and from this position the control spool 45 can be operated into both left and right working positions as seen in the figures.

A passage 56 is provided in the end plate 13, and this passage 56
connects the passage 44 and the passage 42 on the directional control valve 12 side.

This passage 56 is the branch passage 2 which forms the first passage part of the control passage.
2 and the passage 43° 44 and the control room 36, 37 together with the supply passage 1
5 to the return path 16.

The mode of operation of the hydraulic control device according to the invention is as follows: In FIG. 1, the control device is shown with the control spool 45 of the directional control valve 12 in a neutral position; Hydraulic oil is not flowing.

When hydraulic oil is sent to the supply path 15 by a pump (not shown) in this state, only a portion of the hydraulic oil is opened in the control flow path including the branch passage 22 having the first throttle point 23. 57 and flows to the return path 16.

This is because the pressure difference occurring before and after the first throttling point 23 pushes the closing member 17 of the switching valve 14 from the closed position shown into the open position against the closing spring 19, so that most of the hydraulic fluid is dissipated. This is because the water returns directly from the supply path 15 to the return path 16 without being subjected to any throttling action.

In this case, the hydraulic fluid sequentially passes through the second throttle point with a larger flow cross section and the first throttle point with a smaller flow cross section, but the hydraulic fluid passes through the second throttle point 25 on the upstream side. does not actually work effectively.

This is because the flow cross section is wider than the first throttling point 23, so that its throttling effect is so small as to be negligible.

The total pressure drop across both throttle locations is always constant, defined by the closing spring 19, so that the total pressure drop across the first downstream throttle location 23 is always constant.
4, the flow rate of the hydraulic oil flowing through the control channel 57 is kept approximately constant by the first throttle point 23 cooperating with the switching valve 14.

When the control spool 45 is operated to the right towards one working position, one control edge 53 with a fine control notch 54
throttles the flow of hydraulic oil in the control flow path 57.

As a result, the hydraulic oil that continues to flow into the branch channel 22, that is to say via the first throttle point 23, increases the pressure in the pressure chamber 18 of the switching valve 14 via the control channel branch section shown in broken lines and opens it. The closing member 17 that has been in position is pushed toward the closing side.

This increases the pressure within the supply path 15. Supply route 15
If the pressure increase within exceeds the sum of the implement pressure and the set pressure of the check valve 38 , the hydraulic oil flows from the supply channel 15 via the check valve 38 into the inflow chamber 31 and the control edge 48 of the piston section 47 .
and flows into one of the working equipment chambers 33.

At the same time, hydraulic fluid returning from the working device can flow from the other working device chamber 32 to the return passage 16 via the return chamber 34 .

In this case, the hydraulic oil flowing from the supply channel 15 towards the working device chamber 33 also creates a distinct pressure difference across the second throttle point 25, which has a larger flow cross section than the first throttle point 23. .

That is, in the above-mentioned neutral position, only a small amount of hydraulic oil, in other words, a control flow, flows through the first throttle point 23 into the control flow path 57, and a pressure difference is created in this first throttle point 23. However, at the second throttling point 25, where the flow cross section is large, there is virtually no throttling effect.

However, if the hydraulic fluid also flows into the working device chamber 33 due to the pressure increase in the supply path 15 as described above, the second throttling point 25 will increase its throttling action and create a pressure difference.

Incidentally, the total pressure drop produced by the two throttle points 23,25 is determined by the closing spring 19 and therefore remains constant in every position of the closing member 17.

In other words, the pressure of the hydraulic fluid in the supply channel 15 acts on the left side of the closing member 17 as seen in the figure and tends to move the closing member to the right (in the opening direction), whereas the closing spring 19
The combined force of the spring force and the hydraulic pressure reduced by the first and second throttle points 23.25 acts on the right side of the closing member 17 and tends to move it to the left (in the closing direction). .

Therefore, the second throttling point 25 with the larger flow cross-section now has an increased throttling effect and produces a pressure difference, i.e. the increase in pressure drop at the second throttling point is equal to the pressure drop at the first throttling point 23. This means that it becomes correspondingly smaller.

This means that Q=aJΔP1, that is, the flow rate Q is the pressure difference ΔP
As a result equal to the product of the square root of
The reduction in pressure in the flow path 22 leading to the closure member 17
This leads to a decrease in the overall force acting on the left side of .

As a result, the supply path 15 passes through the switching valve 14 and the return path 16
The closing control force that attempts to close the bypass passage leading to the supply passage 15 is immediately relaxed, the hydraulic oil is bypassed from the supply passage 15, and the pressure increase in the supply passage 15 settles down without reaching an excessive increase as in the known example.

FIG. 2 shows characteristic curves of the pressure profile associated with the movement of the control spool at various working device pressures for a known example, and FIG. 4 shows a similar pressure profile for the control device of the invention. is shown in the characteristic curve.

FIG. 3 shows characteristic curves of the flow rate associated with the movement of the control spool at various working device pressures for a known example, and FIG. 5 shows a similar flow rate for the control device of the invention. Shown as a characteristic curve.

As is clear from FIG. 4, the pressure P in the supply channel 15 increases as a function of the displacement S of the control spool 45 on the characteristic curve 6.
1 and, depending on the respective working device pressure, according to the characteristic curves 62 to 65.

The increase in pressure during the transition from characteristic curve 61 to characteristic curves 62 to 65 is relatively small due to the influence of second throttling point 25, and this influence becomes stronger as the displacement of the control spool increases.

FIG. 2 shows a corresponding characteristic curve at 66 for a known control device which does not have a second throttle point 25 according to the invention.
~69.

At this time, when the pressure of the working equipment is low, the pressure rises rapidly along the characteristic curve 61 to twice the working equipment pressure, and then decreases to a predetermined working equipment pressure along the characteristic curve 66. .

If the pressure in the working device is high, as shown by the flattening in characteristic curve 69, an excess pressure buildup will cause the pressure limiting valve to react.

The characteristic curve of the flow rate according to the present invention shown in FIG. 5 has a significantly smoother course compared to the characteristic curve according to the known example shown in FIG. It is.

Fine control is therefore very sensitive compared to known devices.

The control spool 45 cooperates with the switching valve to provide similar fine control during movement operations to other working positions.

In the case of this control device 10 according to the invention, the closing member 17 may cooperate with the pressure limiting valve 26 to form a pilot pressure control valve.

It is also possible to vary the construction of the directional control valve, for example, instead of the illustrated directional control valve with a direct-acting spool, it is possible to use a poppet-type directional control valve.

With either of these valve construction types, it does not matter whether a single control member or two control members separated from each other are used to perform the desired control function.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a hydraulic control device partially shown in cross section; FIG. FIG. 3 is a graph showing the flow rate progression in relation to the amount of movement of the control spool in the case of various working device pressures in a known example, and FIG. FIG. 5 is a graph showing the flow rate curve as a function of the control spool displacement under different working device pressures in a control device according to the invention. 10...control device, 11...connection board,
12... One-way control valve, 13... End plate,
14... All changeover valve, 15... Supply path, 1
6...Keyway, 17...--Closing member, 1
8...Pressure chamber, 19...Press spring, 2
1,48°53... Control edge, 22...
Branch passage, 23...First constriction point, 24...
... Flange surface, 25 ... Second throttle point, 26 ... Pressure limiting valve, 27 ... Return passage, 28 ... - Casing, 29...
Spool hole, 31...Inflow chamber, 32, 33...
...Working equipment room, 34.35...Return room, 36.37...Control room, 38...Check valve, 39...・Inflow passage, 41, 43° 44.
56...Aisle, 42...Aisle, 45.
...Control spool, 46, 47, 5L52...
... Piston section, 49, 54 ... Fine control notch, 55 ... Return device, 57 ... Control flow path, 61 to 69 ... Characteristic curve, P...
...Pressure, Q...First flow overflow, S...Control spool movement amount.

Claims (1)

[Claims] 1 A hydraulic control device, which is equipped with a directional control valve suitable for controlling working equipment and a switching valve that returns hydraulic oil sent into the supply path to the directional control valve directly to the return path. A movable control member in the neutral position shuts off at least one work implement chamber leading to the work implement and in the two work positions selectively communicates this work implement chamber with the supply or return path; The directional control valve is operated by a control channel which branches off from the flow path and is controllable by a control member in the directional control valve, and in which a throttle point is provided upstream of the control member. In the case of a type in which the pressure difference before and after the constriction point acts on the closing member of the switching valve in the opening direction against the force of the closing spring, in addition to the constriction point 23, there is a A second throttle point 25 is provided in the flow path leading to the device chamber 32 , 33 , which throttle point 25 is arranged upstream of the first throttle point 23 and parallel to the switching valve 14 . First drawing point 23
Hydraulic control device characterized in that it has a flow cross section larger than .