Patent Grant
9115702
This is a U.S. National Phase patent application of PCT/SE2011/050919, filed Jul. 6, 2011, which claims priority to the Swedish Patent Application No. 1050845-5, filed Aug. 9, 2010, each of which is hereby incorporated by reference in the present disclosure in its entirety.
The present invention relates to hydraulic or oil pressure control systems which are used in oil circuits for driving actuators for stationary or mobile machines, in particular to an oil pressure control system in which a flow control valve is provided in a combined oil input and output circuit of an actuator to control the flow control valve under the control of a pilot valve.
Hydraulic or oil pressure control systems, which are used in oil circuits for driving actuators for stationary or mobile machines, may sometimes be subjected to sudden changes in pressure. For instance, when activating or starting up a hydraulic system from an inactive state an abrupt increase in pressure may cause a pressure pulse, sometimes referred to as a hydraulic ram. Although such pressure pulses are generally not a problem for hydraulic devices or valves in the system, but may cause undesirable noise and/or vibrations that are noticeable to an operator.
An example of a hydraulic system that may give rise to such problems is shown in
In operation with the flow control valve 1 in its inactive state, the flow control valve 1 is maintained in its closed position by high pressure from the accumulator A and the spring 4 at the spring side of the poppet 3 in the flow control valve 1. Under transition from active to inactive state of the flow control valve 1, the sum of forces created by the pressure from the accumulator A acting on the input/output port 5 and any pressure from the consumer C acting on the output/input port 6 will be less than the force created by the pressure from the accumulator A acting on the spring side 8 of the poppet 3. Over time, internal leakage through the consumer C, indicated as a throttle 7 between the consumer and the tank T, will cause the pressure at the consumer C to drop to tank, or reservoir, pressure.
In order to operate the consumer C with pressurized hydraulic fluid from the accumulator A, the solenoid valve 2 is actuated in order to pressurize the said consumer C. When the solenoid valve 2 is displaced to its actuated position, hydraulic fluid acting on the spring side 8 of the poppet 3 in the flow control valve 1 is drained to the tank T through a damping throttle 9. High pressure from the accumulator A at the input/output port 5 acting on a poppet ring area of the poppet 3 opens the flow control valve 1. The relatively high pressure difference across the flow control valve 1 causes a relatively abrupt rise in pressure in the consumer C.
An inherent feature of a flow control valve of this type is that a relatively small displacement of the poppet to open the valve will open up a relatively large flow area. The abrupt pressure rise in the flow control valve 1 creates an uncontrolled pressure transient in the consumer, causing a distinct noise similar to a fluid hammer. Immediately after opening, a pressure pulse caused by the pressure transient may cause the pressure in the consumer C to be higher than the pressure in the accumulator A. The damping throttle 9 will only have a limited effect on the rate at which the hydraulic fluid is drained from the spring side 8 and can not eliminate this noise.
A further problem that may occur in hydraulic or oil pressure control systems is a sudden loss of pressure in a consumer or actuator. In the example shown in
Alternatively, the consumer C may be a hydraulic pump/motor. Under certain conditions, such as a sudden overload of the pump/motor, hydraulic fluid may leak from the cylinders of the pump/motor into the housing surrounding the pump/motor. If the flow of hydraulic fluid is interrupted, the hydraulic pump/motor may resume operation after the excess fluid has been drained out of the said housing. Should the flow of fluid continue, then the pressurized fluid may cause the housing to burst, requiring substantial repairs to the hydraulic pump/motor. The prior art arrangement as shown in
A common way of solving this problem is to provide the system with a hose burst valve. However, this solution requires the mounting of an additional valve in the system and increases the complexity, weight and cost of the system.
One object of the invention is to overcome the above problems by providing an improved hydraulic system that will minimize generation of undesirable noise and/or vibrations caused by pressure pulses. A further object of the invention is to provide an improved hydraulic system that will prevent an uncontrolled flow of hydraulic fluid from the supply of hydraulic pressure caused by a sudden loss of pressure in the consumer.
The above problems have been solved by a hydraulic system and a method for controlling such a system, according to the appended claims.
According to a preferred embodiment, the invention relates to a hydraulic system comprising a source of high pressure, a consumer connectable to the source of high pressure via a flow control valve, and a solenoid valve arranged to control the flow control valve. The source of high pressure may be any suitable accumulator or pump that is able to supply fluid at a desired working pressure for operating the consumer. The consumer may be any type of device intended to be operated by means of fluid pressure, such as a fluid cylinder or a hydraulic pump/motor. In this context the term “pump/motor” may include fixed displacement pumps/motors as well as variable displacement pumps/motors. Such pumps/motors can be operated as a pump or be driven as a motor. Although the solenoid valve described in the examples below is an electrically operated two-position valve, the invention is not limited to this valve.
The hydraulic system further comprises a hydraulic pilot valve that is selectively controllable by the solenoid valve to connect a control chamber in the flow control valve either to the source of high pressure or to a low pressure side, such as a tank or reservoir, via a drain conduit, preferably comprising a throttle. The invention is not limited to this throttle being included in the hydraulic pilot valve drain conduit.
The flow control valve has an input/output port connected to the source of high pressure and an output/input port connected to the consumer. A poppet or a similar valve body has one operating position which disconnects the input/output port from the output/input port and one operating position which connects the input/output port to the output/input port. The poppet is acted on by a spring force combined with the force created by the pressure in the control chamber on one side and by the combined forces from the pressures of the input/output port and the output/input port on the opposite side. The area of the poppet acted on by the pressure in the control chamber is equal to the combined areas acted on by the pressures in the input/output port and the output/input port. The poppet will remain in its closed position as long as the control chamber is connected to the input/output port and the pressure level at the output/input port is lower than a threshold pressure level. The threshold pressure level is higher than the pressure of the source of high pressure by a difference which is determined by the spring force and the poppet area acted on by the output/input pressure. Threshold pressure can be achieved only if hydraulic fluid flows in direction from the output/input port towards the input/output port. Hence, as long as the control chamber is connected to the input/output port, the flow control valve will remain closed in direction from the input/output port towards the output/input port.
The hydraulic pilot valve has a first end acted on by the force from the pressure of the source of high pressure and a second end acted on by a spring force combined with the force from the pressure at the second end. The spring is arranged to provide a force which is lower than the force from the supply pressure acting on the first end of the hydraulic pilot valve.
The solenoid valve has a supply port connected to the source of high pressure, a load port connected to the second end of the hydraulic pilot valve and the consumer, and a drain port connected to the low pressure side.
When the solenoid valve is non-actuated, the solenoid valve is arranged to connect the second end of the hydraulic pilot valve to the low pressure side via a drain conduit, preferably comprising a throttle. The invention is not limited to this throttle being included in the solenoid valve drain conduit. Hence, as long as the solenoid valve is non-actuated, the source of high pressure acting on the first end of the hydraulic pilot valve will hold the hydraulic pilot valve in a first position wherein the control chamber is connected to the source of high pressure and the flow control valve is closed in direction from the input/output port towards the output/input port.
When the solenoid valve is actuated, the solenoid valve is arranged to connect the source of high pressure to the consumer via a by-pass conduit in order to pre-pressurize the consumer prior to the opening of the flow control valve.
At the same time, the solenoid valve is arranged to connect the source of high pressure to the second end of the hydraulic pilot valve via the by-pass conduit. As soon as the combined forces from the spring and the pressure at the second end of the hydraulic pilot valve exceed the force from the pressure at the first end of the hydraulic pilot valve, the hydraulic pilot valve will displace into a second position in which the control chamber is connected to the low pressure side and the flow control valve is opened. In order to prevent an excessive opening velocity of the control valve poppet, a throttle, acting as a resistance to an abrupt outflow of fluid, may be located in the conduit connecting the control chamber in the flow control valve to the low pressure side. In this way, the throttle acts to prevent an abrupt change in the pressure of the control chamber, whereby the valve body can be smoothly shifted.
A throttle may be located in the by-pass conduit between the first and second ends of the hydraulic pilot valve, preferably between the first end of the hydraulic pilot valve and the solenoid valve. The purpose of this throttle is to create a pressure drop that delays the equalization of pressure between the first and second ends of the hydraulic pilot valve, so that the consumer is at least partially pre-pressurized via the by-pass conduit prior to the switching of the hydraulic pilot valve into its second position and the subsequent opening of the flow control valve.
Pre-pressurization of the consumer may be initiated as soon as the pressure after the throttle is greater than the pressure in the consumer. The consumer may have an internal leakage which, over time, will reduce the pressure in the consumer to ambient pressure, that is, the pressure in the tank or reservoir. The internal leakage must have a flow rate that is less than the flow rate through the throttle.
The throttle between the first and second ends of the hydraulic pilot valve provides a safety function protection the system from a sudden pressure loss in the consumer. This safety function will be described in detail below.
A non-return valve may be located in the by-pass conduit between the second end of the hydraulic pilot valve and the consumer, in order to prevent fluid flow from the consumer towards the second end of the hydraulic pilot valve and the solenoid valve.
Alternatively, the non-return valve may be excluded, if separate by-pass conduits to the consumer and the hydraulic pilot valve are connected to separate load ports in the solenoid valve. Then, the solenoid valve must be of a type which disconnects the load port to which the by-pass conduit to the consumer is connected from the drain port of the solenoid valve when the solenoid valve is non-actuated. However, this alternative solution will require the throttle to be located between the first end of the hydraulic pilot valve and the solenoid valve if protection from a sudden pressure loss in the consumer is required.
The hydraulic system as described above has a safety function that allows the source of high pressure to be disconnected from the consumer if an extensive leak flow occurs in the said consumer. When the solenoid valve and the hydraulic pilot valve are in their actuated positions, the flow control valve is open and enables flow of fluid under pressure flows from the source of high pressure to the consumer. Should an extensive leak occur in the consumer, for instance by a burst fluid conduit or a temporary malfunction in a fluid pump, then it is desired to close the flow control valve in order to prevent an extensive flow level from causing damage to the source of high pressure or to components at the low pressure side.
An extensive leak in the consumer will cause an extensive flow level through the flow control valve in direction from the supply port to the consumer port. That extensive flow will cause a pressure drop across the flow control valve, wherein the pressure at the consumer port will become significantly lower than the pressure at the supply port. However, as long as the pressure available from the source of high pressure is sufficient to counteract the force of the spring, the poppet will not close. At the same time, the pressure will drop in the by-pass conduit. If a non-return valve is located in the by-pass conduit between the second end of the hydraulic pilot valve and the consumer, then the pressure drop across the flow control valve will cause the non-return valve to open. This causes a reduction of the pressure acting on the second end of the hydraulic pilot valve. If the loss of pressure at the consumer is sufficient, the fluid flow rate through the by-pass conduit and the solenoid valve is sufficient to create a pressure drop across the throttle between the first and the second ends of the hydraulic pilot valve. If the pressure at the first end of the hydraulic pilot valve is greater than the pressure at the second end and the force applied by the spring, then the hydraulic pilot valve will be displaced to its non-actuated position by the pressure from the source of high pressure. The source of high pressure will then be connected to the control chamber and the flow control valve will close.
A relatively small amount of fluid will continue to leak past the throttle, the solenoid valve and the non-return valve, towards the consumer, as long as the solenoid valve remains in its actuated position. However, as long as the pressure drop across the throttle is sufficient, the pressure at the first end of the hydraulic pilot valve is greater than the pressure at the second end and the force of the spring. Hence, the hydraulic pilot valve will be held in its non-actuated position and the flow control valve will remain closed. When the pressure loss is detected, e.g. by an operator or a pressure sensor, the solenoid valve may be de-actuated manually or automatically to close the flow control valve.
The consumer may be a reversible, variable displacement pump that can act both as a pump and a motor. In this case, the pump can be connected to an arrangement that can drive the pump or be driven by the motor. When the variable displacement pump is reversed, hydraulic fluid is arranged to flow from the variable displacement pump, past the flow control valve, to the source of high pressure when the fluid pressure delivered by the pump exceeds a predetermined value. An example of this may be a hydraulic hybrid vehicle that can be driven by hydraulic pressure stored in an accumulator.
An example of a hydraulic system in which the arrangement according to the invention may be used is a hydraulic hybrid vehicle, in particular a vehicle that can be driven by hydraulic pressure stored in an accumulator. Typically such vehicles are intended for use in urban areas and/or which is operated with a frequent start/stop cycle. When the vehicle is stationary, a hydraulic drive unit in the form of a reversible, variable displacement pump is disconnected from the supply of hydraulic pressure, such as an accumulator. To start the vehicle, the drive unit is pressurized by actuating a flow control valve according to the invention whereby the drive unit is operated as a motor connected to a transmission and the vehicle can be driven. When the vehicle is to be decelerated or stopped, the drive unit is reversed to act as a pump driven by the vehicle transmission. When the combined forces from pressures of the input/output port and the output/input ports exceed the force from the pressure in the control chamber, including any spring load acting on the poppet, the control valve will open and excess fluid pressure is stored in the accumulator. This allows energy to be regenerated and stored in the form of fluid pressure that may subsequently be used to drive the vehicle.
The invention further relates to a method for controlling a hydraulic system as described above. The method relates to connection a consumer to a source of high pressure and involves the steps of:
In addition, the method involves controlling the fluid flow through the by-pass conduit using a throttle located between the first and second ends of the hydraulic pilot valve. The pre-pressurization of the consumer may be controlled by providing a flow rate through the throttle that is greater than the internal leakage in the consumer. According to the method, fluid flow from the consumer towards the solenoid valve may be prevented by means of a non-return valve located in the by-pass conduit between the second end of the hydraulic pilot valve and the consumer.
The invention also relates to an alternative method for controlling a hydraulic system as described above. The method relates to disconnection of a consumer from a source of high pressure in case of a leakage in the consumer. This method involves the steps of:
In addition, the leakage causes a pressure drop in the by-pass conduit, thereby causing a non-return valve (34) to open and reducing the pressure at the second side (33) of the hydraulic pilot valve (31)
A primary object of the present invention is, therefore, to provide a hydraulic system in which oil pressure may be controlled by a flow control valve that is controlled according to the throttle opening of a pilot valve. Even an abrupt opening of the hydraulic pilot valve enables avoidance of generation of an over-shooting phenomenon and therefore prevention of noise or vibrations in the flow control valve caused by momentary, abrupt operation of an actuator operatively associated with the flow control valve.
A secondary object of the present invention is, therefore, to provide a hydraulic system with a safety function whereby a loss of oil pressure in the consumer may be controlled by a flow control valve that is controlled to close automatically by means of a pilot valve subjected to a pressure drop. A total loss of pressure from the source of high pressure and unnecessary loss of hydraulic oil can therefore be prevented.
The invention will be described in detail with reference to the attached figures. It is to be understood that the drawings are designed solely for the purpose of illustration and are not intended as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to schematically illustrate the structures and procedures described herein.
According to an optional solution, a throttle 35 can be included in the hydraulic pilot valve drain conduit. According to an alternative embodiment, the throttle 35 can be replaced by a combined throttle/non-return valve between the spring side 28 of the poppet 23 and the load part c of the hydraulic pilot valve 31 (
The solenoid valve 22 held in its non-actuated position by a spring load, wherein a supply port d of the solenoid valve 22 is connected to the accumulator A via a control throttle 37. A drain port e of the solenoid valve 22 is connected to the tank T via an optional damping throttle 29. A load port f of the solenoid valve 22 is connected to a port g on a second side 33 of the hydraulic pilot valve 31. In the non-actuated position the load port f is connected to the drain port e, in order to drain the second side 33 to the tank T. The solenoid valve 22 is further connected to the consumer C via a by-pass conduit 38 comprising a non-return valve 34, wherein fluid flow is prevented from the consumer C in the direction of the second side 33 of the hydraulic pilot valve 31 and the tank T.
When actuated, the solenoid valve 22 is displaced into its actuated position by a solenoid, wherein the supply port d of the solenoid valve 22 is arranged to connect the accumulator A to the load port f. The drain port e of the solenoid valve 22 is arranged to interrupt the connection to the tank T. When pressurized, the load port f of the solenoid valve 22 is arranged to supply pressure from the accumulator A to the second side 33 of the hydraulic pilot valve 31 and to the consumer C via the non-return valve 34.
Alternatively, by providing the solenoid valve with two load ports, replacing the single load port f, individual connections can be provided to the consumer and the second end of the hydraulic pilot valve, wherein fluid flow is prevented from the consumer C in the direction towards the solenoid valve when the solenoid valve is in its non-actuated position. When the solenoid valve is actuated, the two load ports are connected to the same supply port and are supplied with pressure from the accumulator A.
In operation with the flow control valve 21 in its inactive state, the flow control valve 21 is maintained in its closed position by high pressure from the accumulator A, supplied by the hydraulic pilot valve 31, and the spring 24 at the spring side of the poppet 23 in the flow control valve 21. While the solenoid valve 22 remains non-actuated, the first end 32 of the hydraulic pilot valve 31 is pressurized by the accumulator A and the second end 33 of the hydraulic pilot valve 31 is drained to tank T to ensure that the hydraulic pilot valve 31 is maintained in its non-actuated position.
Under transition from active to inactive state of the flow control valve 21, the sum of forces created by the pressure from the accumulator A acting on the input/output port 25 and any pressure from the consumer C acting on the output/input port 26 will be less than the force created by the pressure from the accumulator A acting on the spring side 28 of the poppet 23 in addition to the force from the spring 24. Over time, internal leakage through the consumer C, indicated as a throttle 27 between the consumer and the tank T, will cause the pressure at the consumer C to drop to tank pressure.
In order to supply the consumer C with hydraulic pressure, the solenoid valve 22 is actuated in order to connect the said consumer C to the accumulator A. When the solenoid valve 22 is displaced to its actuated position, the supply port d will be connected to the load port f. This actuation will simultaneously initiate two sequential series of events.
In a first series of events, the load port f of the solenoid valve 22 will connect the accumulator A to the consumer C via the throttle 37, located between the accumulator A and the solenoid valve 22, and the non-return valve 34. This will initiate a flow of hydraulic fluid in direction from the accumulator A into the consumer C. The flow will create a pressure drop across the throttle 37, reducing the pressure at the load port f to a level just slightly higher than the pressure in the consumer C.
The flow of hydraulic fluid into the consumer C will initiate an increasing pressure in the consumer C. In order to ensure pressure increase in the consumer C, the flow rate through the throttle 37 must be greater than the flow rate caused by internal leakage through the consumer C, indicated by the throttle 27.
In a second series of events, the load port f of the solenoid valve 22 will connect the increasing pressure downstream of the throttle 37 to the second side 33 of the hydraulic pilot valve 31. Initially, the hydraulic pilot valve 31 will remain in its non-actuated position because the force created by the pressure subjected to its second end 33 in addition to the force from the spring 36 will be lower than the force created by the pressure from the accumulator A subjected to the first end 32 of the hydraulic pilot valve 31. When the pressure at the second end 33 of the hydraulic pilot valve 31 has increased to a level where the difference between the forces created by pressures at the first and second ends 32, 33 becomes smaller than the force from the spring 36 the hydraulic pilot valve 31 will be displaced into its actuated position.
The effect of this displacement is that the load port c of the hydraulic pilot valve 31 is connected to the drain port b. Pressurized hydraulic fluid acting on the spring side 28 of the poppet 23 in the flow control valve 21 will then be drained to the tank T and release the pressure on the spring side 28. Optionally, a throttle 35 can be used to assist in controlling the displacement of the poppet 23 by restricting the fluid flow rate from the spring side 28 towards the tank T. When the pressure on the spring side 28 of the poppet 23 is released, pressure from the accumulator A at the input/output port 25 acting on an annular poppet ring area of the poppet 23 will cause the flow control valve 21 to open. The throttle 35 will assist in limiting the velocity of the poppet 23, thus limiting the impact energy transmitted from the poppet 23 to the body of the flow control valve 21 when the poppet 23 reaches its fully open position.
By selecting a suitable orifice size of the control throttle 37 and a suitable spring constant for the spring 36 acting on the second side of the hydraulic pilot valve 31 it is ensured that the pre-pressurization of the consumer C via the non-return valve 34 reaches a relatively high level before the hydraulic pilot valve 31 is displaced into its actuated position. The pressure difference across the flow control valve 21 is then relatively small when the flow control valve 21 starts to open. This relatively small pressure difference prevents a significant pressure transient from being generated in the consumer C when the flow control valve 21 opens.
Alternatively, the arrangement as shown in
The arrangement shown in
A sudden leak in the consumer C will cause a sudden increase of flow through the flow control valve 21, causing an increase of the pressure drop across the flow control valve 21, wherein the poppet 23 will be displaced to its closed position. However, as long as the pressure available from the accumulator is sufficient to counteract the force of the spring 24, the poppet 23 will not close. At the same time, the pressure difference across the flow control valve 21 will cause the non-return valve 34 to open. This causes a reduction of the pressure acting on the second end 33 of the hydraulic pilot valve 31. If the loss of pressure at the consumer C is sufficient, the fluid flow rate through the solenoid valve 22 is sufficient to create a pressure drop across the throttle 37. If the force created by the pressure at the first end 32 of the hydraulic pilot valve 31 is greater than the sum of forces created by the pressure at the second end 33 and the spring 36, then the hydraulic pilot valve 31 will be displaced to its actuated position and the flow control valve 21 will close.
A relatively small amount of fluid will continue to leak past the throttle 37, the solenoid valve 22 and the non-return valve 34, as long as the solenoid valve remains in its actuated position. However, as long as the pressure drop across the throttle 37 is sufficient, the pressure at the first end 32 of the hydraulic pilot valve 31 is greater than the pressure at the second end 33 and the force of the spring 36. Hence, the hydraulic pilot valve 31 will be held in its actuated position and the flow control valve 21 will remain closed.
In
When the solenoid valve is non-actuated the port g is instead connected to the tank T, as shown in
The invention is not limited to the above examples, but may be varied freely within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1050845 | Aug 2010 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2011/050919 | 7/6/2011 | WO | 00 | 3/22/2013 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2012/021101 | 2/16/2012 | WO | A |
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|---|---|---|---|
| 3906838 | Hofer | Sep 1975 | A |
| 5245826 | Roth et al. | Sep 1993 | A |
| 6279316 | Vigholm | Aug 2001 | B1 |
| 6351944 | Fertig et al. | Mar 2002 | B1 |
| 6370874 | Rausch et al. | Apr 2002 | B1 |
| 20130047592 | Opdenbosch et al. | Feb 2013 | A1 |
| Entry |
|---|
| International Search Report received for PCT Patent Application No. PCT/SE2011/050919, mailed on Sep. 5, 2011, 4 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20130209276 A1 | Aug 2013 | US |
