FI72579C - Transmission. - Google Patents

Description

72579 1 Transmission 5 The present invention relates to a hydraulic control system comprising a hydraulic actuator having opposite channel openings arranged to alternatively act as inputs and outputs for moving an actuator element in opposite directions; a pump for directing fluid to said actuator via supply valve devices being controlled by a control pressure, the fluid being alternately supplied to it at a control pressure to direct flow through a pair of hydraulic lines extending from said supply valve devices to one actuator channel opening to control the direction of actuator movement; 15 return lines from exhaust valve devices for returning fluid to the tank; and control pressure controlled exhaust valve means separate for each actuator passage and each located between the green 20 return line and the hydraulic line of each actuator passage to control fluid flow therebetween.

U.S. Patent No. 4,201,052, incorporated herein by reference, discloses a control pressure driven high pressure load sensing valve system 25 connected to a valve body for mounting directly on a controllable actuator, such as a hydraulic cylinder or hydraulic motor. The valve system precisely controls the position of the actuator and its operating speed.

Briefly, the valve system disclosed in the aforementioned patent comprises an independent hydraulically pre-controlled supply element, a pair of load relief shut-off valves, a pair of independently operating normally closed discharge elements, a pair of load pressure controlled valves and a pair of anti-cavitation valves. A supply element was provided to direct the fluid to flow into either of the actuator channels. Normally closed discharge elements are connected to each of the actuator channels to direct fluid flow to a channel 2 72579 opposite the actuator channel to which the supply element directs fluid. The discharge elements act as adjustable nozzles that dispense liquid between a suitable actuator channel and a low pressure range such as a storage tank.

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Both discharge elements are connected to load pressure-controlled valves which act on the discharge elements according to the load pressure, so that the discharge elements can also provide pressure equalization protection. The anti-cavitation valves are connected to both channels of the actuator and are arranged to open a suitable channel in the tank.

The valve system is mounted directly in the actuator duct assembly pipe and is supplied with one main flow high pressure pipe, a pair of control pressure pipes and a load detection pipe. The operation of the valve-15 system is controlled via control pipes from a manually controlled hydraulic remote control valve. In the absence of a control signal from the hydraulic remote control, the supply element assumes a centralized or neutral position with the shut-off valves, outlet elements, pressure-controlled valves and anti-cavitation valves all in the closed position. In the neutral position, the valve system prevents uncontrolled reduction of loads and in excess loads prevents fluid flow from the high pressure fluid source to the actuator even when the pipe is broken. Since the valve system is a load sensing system, the power of the pump is made to match the power 25 required by the load. Conversely, in a non-load sensing system, the power of the pump exceeds the power required by the load, whereby the excess force is dissipated as heat.

In some circumstances, it may be impossible or undesirable to install the 30 valve system directly on the actuator. Such conditions may occur due to space constraints on the actuator or when it is desirable to limit the number of supply and control tubes to the top of the telescopic boom or when braking, as in winch type applications, is required between the actuator and valve system. Under these conditions, the valve system is mounted on top of the device away from the actuator, with a pair of tubes passing into the actuator manifold of the actuator. In one of these situations,

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3 72579 1 It is possible to place a conventional back pressure valve between the actuator ducts and the valve system. The non-return valve takes care of the controlled load reduction and maintenance in the duct manifold of the actuator.

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In another situation, when a stable load is required, it may be desirable to place a hydraulically pre-controlled shut-off valve between the actuator channel and the valve system. The hydraulically pre-controlled shut-off valve takes care of the positive pi-10 of the load, i.e. keeps the load at steady zero.

Also, many applications require a linear hydraulic cylinder that must have a float position or a rotating hydraulic motor with a free rotate or "roll" position. In either case, a rotary actuator at the cylinder end of the device or for the boom is allowed to roll into the stop due to frictional forces in the system.

The valve system disclosed in the above-mentioned patent cannot be used in the above-mentioned circuit applications "namely in applications of free-floating or rotating non-return valves, hydraulically pre-controlled control valves, brakes and actuator. This is mainly due to the normally closed space of the exhaust valve elements.

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Thus, it is an object of the present invention to provide a valve system of the above-mentioned type which operates when using back-pressure valves, hydraulically pre-controlled control valves, brakes and free floating or rotation of the actuator.

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The hydraulic control system according to the invention is characterized in that at least one of said exhaust valve devices controlled by: a control pressure corresponding to simultaneously controlling the supply valve device is connected to one of said actuator channel openings 35 so as to be open when no control pressure is applied to the supply valve devices .

'* 725 79 1 According to the invention, the above control valve system is provided with a pair of normally open exhaust valves located between the tank passage and the actuator passages so that when the supply valve is in the neutral position, both actuator passages are open to the tank passage through normally open exhaust valves and the actuator is free to move, as in the case of a freely rolling boom. However, when the control signal is applied to the supply valve to move the actuator in one direction, control pressure is also used to close a suitable exhaust valve 10 to prevent fluid flow from the pump to the tank slot, leaving the second exhaust valve open in the tank slot. When a back pressure valve is used in connection with the second channel of the actuator to control the reduction and holding of the load, a single normally open exhaust valve is provided between the channel of this actuator and the tank slot. When an external brake is provided to hold the load, a single normally open exhaust valve is also provided between the actuator orifice and the tank slot.

Figure 1 is a schematic representation of a hydraulic circuit 20 according to the invention.

Figure 2 is a schematic representation of another modified hydraulic circuit.

Figure 3 is a schematic representation of another modified hydraulic circuit.

Figure 4 is a schematic representation of another modified hydraulic circuit.

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Figure 5 is a partial sectional view of the outlet valve used in the system.

Referring to Figure 1, a hydraulic system according to the invention comprises an actuator 20, shown herein as a linear hydraulic cylinder, having a power take-off shaft 21 displaced in opposite directions by hydraulic fluid supplied from an adjustable piston-pump system 22 having a load sensing control in the conventional manner. 5 72579 1 according to a specific structure. The hydraulic system further includes a manually operated regulator, not shown herein, that directs control pressure to the valve system 24 to control the direction of movement of the actuator, as described above. The fluid from the pump 22 is directed to a pipe 25 and a pipe 26 and a supply valve 27 which acts to direct and direct the flow of hydraulic fluid to one or the other end of the actuator 20. The supply valve 27 is hydraulically pre-controlled by a regulator, not shown, through pipes 28,29 and pipes 30,31 at its opposite ends, as described above. Depending on the direction of movement of the valve, the hydraulic fluid passes through pipes 32,33 to either end of the actuator 20.

The hydraulic system further includes a normally open exhaust valve 34,35 located between the tubes 32,33 and the tank slot 36 at each end 15 of the actuator. Exhaust valves control the flow of fluid between the actuator and the tank slot 36, as explained above.

The hydraulic system further includes spring-loaded poppet valves 37.38 in tubes 32.33 and spring-loaded anti-cavitation valves 39.40 adapted to open the tubes 32.33 in the tank slot 36. In addition, spring-loaded poppet valves (not shown) are connected to each valve 34 , 35, which act as hydraulically pre-controlled compensating valves. The pipe 47 connects the outlet valve 25 33 to the control control pipe 28 and the pipe 48 connects the valve 34 to the control control pipe 29, so that when the control pressure is applied to the other side of the supply valve 27, the corresponding valve 34,35 is closed.

The system also includes a non-return valve 44 connected to a pa-30 supply or tank pipe. The non-return valve 44 operates to minimize cavitation as the overloading or decreasing load tends to drive the actuator down. The supply pump equalization valve is arranged to take the excess flow over the supply requirements of the pump 22 and use it to the non-return valve 44 to increase the available fluid-35 of the actuator.

The supply valve 27 comprises a hole in which the control piston _____ 1 6 72579 1 is placed and in the absence of control pressure the control piston is kept in a neutral position by means of springs. The control piston normally blocks the flow from the pressure cell 26 to the slot 32,33. When the control pressure is applied to either end of the steering piston, the steering piston moves until there is a force equal to 5 weight in the steering pressure, spring load and flow forces. The direction of movement determines which Solista is supplied with the fluid under pressure

When control pressure is applied to either pipe 28 or 29 leading to exhaust valves 34 or 35, the valve is caused to close the flow 10 from the pressurized pipe 32 or 33 to the tank slot 36.

Thus, it can be seen that the same control pressure acting in the direction of opening of the inlet valve and thus in the direction of movement of the actuator also works to close a suitable exhaust valve so that the nes-15 te flows into the actuator. The opposite exhaust valve is not affected by the control pressure and thus remains open in the tank slot and allows fluid from the opposite end of the actuator to flow into the tank.

A maximum load pressure indication is provided in one of a plurality of 20 valve systems 24 that control a plurality of actuators and apply a higher pressure to a load dependent adjustable piston pump 22. Each valve system 24 includes a pipe 81 extending to a diverter valve 80 receiving The diverter valve 80 25 indicates which of the pressures is higher and moves to apply a higher pressure to the pump 22. Thus, each valve system in a row includes diverter valves 80,82 that compare the load pressure to the adjacent valve system load pressure and transfer the higher pressure to the pump system 22.

A single supply valve 27 may be replaced by two supply valves, as disclosed in co-pending application No. 117,936, filed February 4, 1980, by the same applicant as in this application.

Details of the preferred structure 7,72579 1 of other elements of the hydraulic circuit are described in more detail in the aforementioned U.S. Patent 4,201,052.

According to the invention, one or both valves 34,35 are normally open exhaust valves rather than normally closed exhaust valves, as in the aforementioned U.S. patent. In the case where both exhaust valves are normally open, as shown in Figures 1 and 2, the exhaust valves are discharged, as shown above, through exhaust lines 47a or 48a. When only one exhaust valve 10 is normally open, as shown in Figures 3 and 4, both the exhaust valve 35b or 35c and the normally closed exhaust valve 34b or 34c have outlets through a common outlet line 29a.

Thus, as shown in Figure 1, both exhaust valves 34,35 15 are normally open so that the actuator is free to move, as in the case of a rotating boom, when the supply valve is in the neutral position. However, when the control signal is arranged to move the actuator in the other direction, the control pressure is applied through pipes 47, 48 to close a suitable exhaust valve.

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Thus, when the control signal is directed to the supply valve to move the actuator in the other direction, the exhaust valve connected to the passage to the actuator through which the liquid is to be fed is closed by the control signal. When the supply valve is returned to the neutral position 25, the exhaust valve is returned to its normally closed position and the actuator is allowed to enter the float position in the case of a hydraulic cylinder or the free rotation or winding position in the case of a rotating hydraulic motor.

Although the invention has been described in connection with a flow control supply valve system in Figure 1, it may also be used in a pressure control supply valve system as shown in Figure 2. As shown in Figure 2, the pressure control supply valve system has a return pressure of pipe 83 opposite to the flow control. and a feedback pressure of pipe 84 opposite to the control pressure at 30. This provides a softer stopping and starting of loads and a more accurate placement of loads that would not otherwise be achieved in a flow control feed valve system.

When the system is used in an environment that requires a back pressure-5 valve 85, as shown in Figure 3, only one normally open exhaust valve 35b is provided between the second actuator port and the exhaust valve 35b and the exhaust valve 34b connected to the second actuator port is normally closed. Thus, the backpressure valve 85 can function to control loads in excess of the flow through the vent-10 brick. When the supply valve is caused to lift the actuator by a control signal, fluid can flow through the control valve of the back pressure valve 85 to the actuator. At the same time, the control signal coming through the pipe 87 closes the exhaust valve 35b. The drain valve 34b operates in a conventional manner to allow removal from the second slot of the actuator.

When an external brake 88 is used to control loads in excess, as in Figure 4, only one normally open exhaust valve 35c is similarly provided and connected to the second port of the rotating hydraulic actuator 20, while the normally closed exhaust valve 34c is connected to the second port. The tubes 89 extend from the brake 88 to a load tube connected to another slot.

Referring to Figure 5, each normally open exhaust valve 34, 35, 35b, 35c is identical in structure and, for clarity, only valve 35 will be explained.

The exhaust valve 35 includes compensating zone holes 60 and 72 in which a poppet valve 61 is positioned between the supply port 32 and the tank slot 36.

The valve includes a slot 62 with a nozzle 62a extending from the supply port 33 to the chamber 63 at the rear of the poppet valve. One or more slots 64 formed in the poppet valve 61 extend from the chamber 63 to the tank slot 36. The arm 65 is adapted to close the connection between the chamber 63 and the slots 64 by the action of a control pressure piston 66 located between the chambers 35 and 71. The spring 67, when no pressure is present in the system, holds the arm 65 in the open position and resiliently forces the poppet valve 61 to the closed position, as shown in Figure 5.

9 72579 1 However, in use, the valve normally functions as an open valve "for this purpose the nozzle 62a, the depth of deflection of the spring 67, and the equalization area of the poppet valve 66, i.e. the area of hole 60 minus the area of hole 72, are selected so that a low and relatively insignificant pressure in the pipe 33 61 to open and provide a flow path between the slot 33 and the tank slot 36. The slot 68 connects the chamber 69 to the guide pressure in the guide tube 28. The pressure in the chamber 69 acts on one end of the piston 66. The chamber 71 at the other end of the piston 66 is discharged through a passage 70 such as mentioned above, is associated with a suitable vent pipe 48a or 29a, as shown in Figures 1-4.

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Claims (4)

A hydraulic control system comprising a hydraulic actuator (20) in which opposite channel openings are arranged to function alternatively as inlets and outlets for displacing an element of the actuator (20) in opposite directions; a pump (22) for conducting fluid into said actuator (20) through supply valve means (27) controlled by a control pressure, fluid being alternately guided thereto with control pressure for conducting the flow through a hydraulic line pair extending from said supply valve means for a channel opening in the operating device for controlling the direction of movement of the operating device (20); a return pipe (36) from a drain valve means (34,35) for returning liquid to a tank; and control valve controlled discharge valve means (34,35), separate for respective channel opening in the actuator, and each of which is located between said return line (36) and the hydraulic line for each channel opening in the actuator for controlling the flow of liquid therebetween. characterized in that at least one of said drain valve devices (34,35), controlled by control pressure corresponding to that with which the supply valve device (27) is simultaneously controlled, is connected to one of said channel openings in the operating device and is connected in such a manner that it is open when the supply valve means (27) are not subject to control pressure. 1 Patent claim Hydraulic control system according to claim 1, characterized in that said one normally open drain valve device (34,35) in the control system is operated with the same control pressure as that arranged to control said supply valve device (27), such that when the control pressure is controlled to said supply valve means for displacing the actuator in one direction are the normally open valve means which are connected to the channel opening in the actuator through which the liquid is led closed, but which act in their normally open position and the actuator is allowed to move freely when the control pressure is broken. II