DE102016201696A1 - hydraulic valve - Google Patents

Abstract

Hydraulic valve for a hydraulic system, in particular for a hydraulic circuit in a vehicle, having a valve housing (1) having an inlet (E) and an outlet (A) for the hydraulic fluid, with a valve element (2) having at least one position in which a connection between inlet (E) and outlet (A) is released, and at least one position in which no connection between inlet (E) and outlet (A) is released, and with at least one return element (5 , 7), which exerts a force on the valve element (2) in the direction of a rest position of the valve element (2), wherein the hydraulic valve is designed so that the valve element (2) assumes the rest position when no differential pressure between the inlet (E) and Outlet (A) is applied, and that the valve element (2) assumes an overpressure position in which the connection between the inlet (E) and outlet (A) is released when the inlet (E) bears a differential pressure, the gr is greater than a second threshold, wherein the hydraulic valve is designed so that in the rest position, a connection between the inlet (E) and outlet (A) is released, and wherein the valve element (2) fluid controlled assumes a closed position in which no connection between Inlet (E) and outlet (A) is released when at the inlet (E) is applied a differential pressure which is between a first and the second threshold.

Description

The invention relates to a hydraulic valve for a hydraulic system, in particular for a hydraulic circuit in a vehicle, having a valve housing, which has an inlet and an outlet for the hydraulic fluid, with a valve element, the at least one position in which a connection between inlet and Outlet is released, and at least a position in which no connection between the inlet and outlet is released, and at least one return element, which exerts a force on the valve element in the direction of a rest position, wherein the hydraulic valve is designed so that Valve element assumes the rest position when there is no differential pressure between the inlet and outlet, and that the valve element assumes a positive pressure position in which the connection between the inlet and outlet is released when the inlet is subjected to a differential pressure which is greater than a second threshold value.

In a hydraulic system there is usually a pressure generating unit, for example a hydraulic pump, and hydraulic consumers such as a hydraulic motor. Most are still a filter, a heat exchanger or other aggregates available. In vehicles that are operated with an internal combustion engine, there are often hydraulic consumers, for example, for ancillaries, which are operated by a hydraulic system, in particular via a hydraulic circuit. The hydraulic pump for pressure generation can be driven via a transmission from the engine. In such hydraulic systems hydraulic valves are used as pressure relief valves.

Such pressure relief valves are known to protect a hydraulic system and the units therein such as a heat exchanger from excessive pressure. If a certain threshold value - corresponding to the above-mentioned second threshold value - is reached or exceeded for the pressure of the hydraulic fluid at the inlet of the valve, the hydraulic valve opens by bringing the valve element into an overpressure position at which a connection between inlet and outlet is released. For example, the hydraulic fluid can drain into an overflow or into an oil sump. The circuit in the overpressure position is fluid-controlled, i. due to the pressure in the hydraulic fluid which acts against the force of the return element. By way of the restoring force and the travel of the valve element required for opening, this threshold value at which the hydraulic valve releases the connection can be set. If the pressure of the hydraulic fluid in the inlet is less than this threshold, the connection between inlet and outlet is blocked. Thus, the required pressure for the operation of the hydraulic system can be built or maintained. At a pressure below the first threshold value, the valve element remains in its rest position, in which the connection between inlet and outlet is also blocked.

From the DE 10 2009 049 995 A1 Furthermore, a hydraulic valve is known as a cold start valve, that in addition to the function of the fluid-controlled pressure limiter also has the function that it can be forcibly switched by an external control and thus switched independently of the pressure level in the system to the overpressure position. This is necessary in order to catch occurring pressure peaks during the cold start of the system when the hydraulic fluid is still cold and thus has a high viscosity. The short term pressure spikes would not be enough to trigger the pressure limiting mechanism fast enough, but could damage aggregates in the plant. Due to the additional forced switching mechanism, for example an electromagnetic mechanism, the valve can be switched to the overpressure position in advance during the cold start, so that the connection between inlet and outlet is released. As soon as the starting process is completed, the additional positive circuit is switched off and the hydraulic valve functions as a fluid-controlled pressure limiting valve, which releases the connection between inlet and outlet only when a pressure threshold is exceeded.

A corresponding cold start function is necessary in particular in hydraulic systems in vehicles.

A disadvantage of the known hydraulic valve, which can take over pressure limiting function and cold start function, however, is that an additional forced switching mechanism is necessary to enable the cold start function. This makes the valve more complex and prone to malfunction.

The object of the invention is now to develop a hydraulic valve for pressure limiting so that it can be used as a cold start valve, without the need for a complex forced switching mechanism is necessary. Furthermore, the object is to make the hydraulic valve as reliable as possible and less dependent on other aggregates.

The object is achieved by a hydraulic valve according to claim 1. For this purpose, the hydraulic valve is designed so that in the rest position of the valve element, a connection between the inlet and outlet is already released, and that the valve element fluid controlled a Closed position, in which no connection between the inlet and outlet is released, takes only when at the inlet a differential pressure is applied, which is between a first and the second threshold. The displacement of the valve element from the rest position in the direction of the closing position is made possible by corresponding active surfaces are provided, via which the differential pressure can exert a force in the direction of the closing position on the valve element. In this case, hydrostatic forces or hydrodynamic forces, in particular shear forces can be utilized by the flow of hydraulic fluid.

The fact that the rest position is not the same as the closed position in terms of function, but initially allows a drainage of hydraulic fluid, short-term pressure peaks can be intercepted by the viscous hydraulic fluid during cold start of the system. Thus, the problem of a normal pressure relief valve is also solved that due to the inertia and the friction of the valve element and the return element, the overpressure position at short-term pressure peaks or very quickly building up pressure peaks, such as occur during cold start, not or not reached fast enough. The valve according to the invention has the advantage that it is immediately open without inertia-related delay during cold start. The cold start function is necessary to protect units in the system from excessive pressure. In particular, heat exchangers can be easily damaged by excessive pressure. With cold hydraulic fluid and thus increased flow resistance in the heat exchanger, the risk of damage is even particularly large.

In the hydraulic valve according to the invention, the valve element is only in the closed position when the pressure in the system reaches the first threshold, and thus the desired operating pressure can be further built. This offers the advantage that the cold start function is carried out without additional switching or control and instead alone fluid-controlled by the pressure in the hydraulic system. Thus, the functions of the hydraulic valve are reliably ensured and realized without dependence on external units or controllers. This simplifies valve control and increases safety.

Due to the inertia and the friction of the valve element and the return element, the closing position is not reached at short-term pressure peaks or at very quickly building up pressure peaks, as they occur during cold start. Only when the pressure reaches the first threshold a little more constant, the valve closes. If during operation the second threshold value is exceeded by the differential pressure at the inlet, then the valve element goes into overpressure position and releases the connection between inlet and outlet.

The hydraulic valve thus has at least three functional positions for the valve element on - rest position, closed position and positive pressure position. It should be noted that the closed position and overpressure position are not exactly predetermined positions of the valve element, but are to be understood as respective areas in which the desired functional state is established. And also starting from the rest position, the valve element first passes through a transition region in a displacement in the direction of the closed position, in which a connection between the inlet and outlet is still released. The threshold values can be selectively determined on the one hand by the selection of the return element and on the other hand by the design of the valve element, especially by the size of the active surfaces on the valve element to which the applied differential pressure in the various positions.

Further advantageous features of the embodiment according to the invention, which additionally improve the reliability and the functions, can be found in the subclaims.

In particular, it is advantageous if the connection between the inlet and outlet in the rest position is narrowed by at least one throttle bore in the valve element and / or by at least one throttle element in the flow cross-section such that the flow of hydraulic fluid in the rest position is less than the flow, the occurs in the overpressure position. This prevents too much hydraulic fluid from draining off when the system starts up and prevents enough pressure for the transition to the closed position. In addition, due to the pressure loss at the throttle points, a force acts on the valve element in the direction of the closing position. Using the throttle points, the hydraulic valve can be adjusted in addition to the influence of the overall design of the flow rate of the hydraulic pump in idle.

Furthermore, a damping element may be present, which can cooperate with the valve element, that the valve element, starting from the rest position, the locking position reached only delayed, when the differential pressure at the inlet for a certain time is greater than the first threshold. In a preferred embodiment, the damping element with the valve element and / or with the valve housing forms a damping chamber, which is connected via a throttle gap or a throttle bore with the valve interior or with the sump. The interior of the valve is the flow chamber formed by the valve housing and available for the hydraulic fluid. One Damping element in this context is an additional element that delays the movement of the valve element when a differential pressure is greater than the first threshold, this delay in addition to the delay caused solely by the return element and the existing friction of the valve element. The embodiment is designed so that the damping chamber is filled with hydraulic fluid in the rest position of the valve element. If a differential pressure greater than the first threshold value is reached, a force exerted by the damping element on the hydraulic fluid in the damping chamber, which drains the hydraulic fluid through the throttle gap or the throttle bore. Throttle gap or throttle bore and viscosity of the hydraulic fluid determined the damping effect. The narrower and longer the throttle gap and the higher the viscosity, the greater the damping effect and thus the time delay that occurs. As the viscosity decreases with temperature, the positive effect is achieved that a longer time delay occurs with cold hydraulic fluid and a shorter one with warmer fluid. Thus, a particularly good and automatically adapted to the present conditions cold start function is achieved.

Due to the design of the throttle gap or the throttle bore and the damping element itself, the throttle effect can be adjusted specifically and adapted to specific requirements.

Advantageously, the damping element is constructed in several parts, in particular as a sliding piston with a further return element, preferably with a spring. The spool has a body with a cavity and a displacer that can be moved into that cavity. The cavity forms the damping chamber. The further return element causes the damping element is in a desired starting position when the valve element is in the rest position.

Preferably, the damping element is supported on the one hand via the return element directly or indirectly against the valve element and on the other directly or indirectly on the valve housing.

The damping element can also be designed as a part of the valve element. For example, it can be designed so that it influences the flow path of the hydraulic fluid through the valve, depending on its position.

A further improvement of the function is possible if the hydraulic valve is designed such that the valve element assumes an intermediate position when the differential pressure at the inlet exceeds an intermediate threshold which is less than the first threshold value. Wherein the intermediate position is designed so that it reduces the flow cross-section of the connection between the inlet and outlet relative to the rest position. Only when the pressure then increases, the connection between inlet and outlet is completely closed. This can prevent that a sudden closing of the valve occurs. Instead, the flow rate from the valve is first reduced and only then does it close.

Particularly preferably, the hydraulic valve is designed as a sliding piston valve with a valve piston as a valve element and with one or more springs as a restoring element. Such slide piston valves are easy to manufacture and reliable in operation. Among other things, by the selection of the spring, in particular the spring stiffness of the first and the second threshold can be set selectively.

In particular, it is advantageous if the connection between inlet and outlet in the rest position is made via the interior of the valve piston. For example, it is very easy to implement throttling.

Furthermore, it is advantageous if the connection between the inlet and outlet is made in the overpressure position in the space between the valve element and valve housing and not in the interior of the valve piston. As a result, sufficiently large flow rates can be dissipated in the overpressure position.

In particular, the released connection between the inlet and outlet in the rest position can be at least partially or entirely via a different path than in the overpressure position. This makes it possible to design the flow rate for the rest position and for the overpressure position independently. Thus, the flow characteristics of the valve for the cold start function and for the overpressure function can be set differently.

By way of embodiments, further advantageous embodiments of the invention will be explained with reference to the drawings. The features mentioned can not only be implemented advantageously in the illustrated combination, but also individually combined with each other. The figures show in detail:

1 Inventive hydraulic valve in the rest position

2 Inventive hydraulic valve in an intermediate position, which lies between the rest position and closing position

3 Inventive hydraulic valve in overpressure position

4 Detail of the scheme of a hydraulic system with a hydraulic valve according to the invention

The figures are described in more detail below. The 1 to 3 show an exemplary embodiment of a hydraulic valve according to the invention 30 in a schematic representation in longitudinal section. This is this valve 30 shown in different operating positions. The valve housing 1 in this case consists of a valve body 1a , which is designed as a cylindrical hollow body, and two valve covers 1b , 1c . In the valve housing 1 There are two openings for the hydraulic fluid, an inlet E and an outlet A, present. The inlet E is connected to the hydraulic system, which is to be secured, via hydraulic lines. The internal cross-section of the valve body and the various recesses influence the flow cross-section for the connection between inlet and outlet. Furthermore, as a valve element, a first piston 2 which, by virtue of its position in the valve body, controls the flow rate through the valve by releasing or blocking the connection between inlet E and outlet A. The return element is by a first coil spring 5 and a second coil spring 7 educated. The damping element consists in this embodiment of a second piston 3 having a cavity as a damping chamber, and a pin 4 acting as a displacer. The damping chamber around the spring 7 is filled with hydraulic fluid. Between pistons 3 and pen 4 there is a throttle gap. The second spring 7 can be regarded as part of the damping element, since it also ensures that the damping element goes into its initial position when the valve element 2 at rest.

1 shows the valve 30 at rest. The piston 2 lies on the lid 1b because of the first spring 5 and the second spring 7 is pressed in this position. The damping element is in the starting position. The second spring 7 in the damping chamber of the second piston 3 pushes the pin 4 from the internal cavity of the piston 3 out and against the lid 1c ,

Between inlet E and outlet A, a connection is released in the rest position. The hydraulic fluid flows through the throttle holes 10 inside the first piston 2 , through the cavity around the first spring 5 and through the throttle holes 11 to the outlet A. Thus, fluid can flow off immediately during a cold start without inertia-related delay and it can unreliable high pressure peak, which could damage the units in the system, reliably and without additional forced switching be avoided. A throttle disk 6 in the cavity around the spring 5 can additionally reduce the flow rate. By tuning the flow cross-sections, for example, on the flow rate of the pump at idle, a targeted interpretation done. The throttle holes 10 and 11 can each be one or more holes on the circumference.

He is behind the throttle bore 10 adjusting pressure acts on the active surfaces 20 and 21 and causes a force on the first and second pistons 2 , 3 in the direction of the closed position. Which flows after passing through the cavity around the spring 5 adjusting pressure acts on the surfaces 23 and 24 and counteracts the closing movement. The resulting force presses it over the spring 5 on the second piston 3 and about the second spring 7 on the pen 4 ,

If the differential pressure now rises to a level greater than the first threshold value, then the resulting force is sufficient to the spring 7 to compress, and this causes hydraulic fluid from the damping chamber through the throttle gap between the piston 3 and pen 4 in the interior of the valve body 1a is pressed. The piston 3 moves - damped by the outflow in the throttle gap - towards the lid 1c , The damping properties can be adjusted by the design targeted. The narrower and the longer the throttle gap, the stronger the damping. The longer the pen 4 in the initial position from the piston 3 protrudes, the longer the damping phase can be at otherwise constant throttle gap and constant conditions.

2 shows the valve 30 in the intermediate position, where the piston 3 on the lid 1c is applied. The damping phase is over, as the pen 4 completely in the second piston 3 is pressed in. The connection between inlet E and outlet A is greatly reduced in this embodiment in the flow cross-section, as the throttle bore 11 already from the first control edge 12 is covered. The throttle holes 11 but are not yet completely closed, it remains a smaller gap between the first piston 2 and valve housing 1 free. So it can be ensured that the valve does not close immediately after the end of the damping phase, but only when the differential pressure in the inlet E is so high that the spring 5 is compressed. Alternatively, the piston 2 be designed so that the throttle holes 11 when covering by the first control edge 12 directly from the valve body 1 locked become. In the transition region, which is present starting from the rest position until the first control edge 12 the edge of the throttle holes 11 reached, the connection between inlet E and outlet A is released unchanged.

Not specifically shown is the full closed position. In the embodiment shown here, the full closing position is reached only when the first paragraph 14 the first control edge 12 has reached. This requires the spring 5 something is compressed. Now the connection between inlet E and outlet A is completely closed. The system is now in normal operation, ie it is in the range of the normal operating pressure. The cold start function is no longer necessary and the opening for pressure limiting is not yet necessary. An essential advantage of the hydraulic valve 30 it is that the cold start function in the rest position of the valve 30 is present and that switching to the normal operating position so the closed position only fluid controlled without external forced operation works. This makes the valve easier and more reliable. Another advantage is that the valve has no additional electrical interfaces for the control and thus more independent installed and can be retrofitted easily.

Now increases the pressure in the system and thus the pressure acting on the inlet E differential pressure, so the spring 5 further compressed and the in 3 shown overpressure position is reached. The necessary force depends on the spring strength and the spring length. As soon as the second paragraph 15 at the second control edge 13 is pushed past, the connection between inlet E and outlet A is released. In the embodiment shown, this connection is realized on a different flow path than in the rest position and directly between the valve housing 1 and the valve element - the first piston 2 , There are also no other throttle points provided in this connection. As a result, larger amounts of hydraulic fluid can drain away quickly. In addition, the flow rate in the cold start function can be designed independently of the flow rate in the pressure limiting function.

Thus, by selecting the spring and the geometric design of the valve 30 the second threshold value thus the pressure limiting value at which the hydraulic valve 30 the connection between inlet E and outlet A is to be released.

4 shows the diagram of a hydraulic system with a hydraulic valve according to the invention 30 , The pump 31 promotes from the swamp 35 Hydraulic fluid for supplying hydraulic consumers, which are not shown. In addition, there is a heat exchanger 32 in the plant. From this the line goes 33 continue to the consumers. In front of the heat exchanger 32 branches off a line in the hydraulic valve according to the invention 30 sitting. This can be carried out in particular as previously in the 1 - 3 described. To cold start is in the rest position of the valve 30 a connection between the inlet E and the outlet A is released. In the normal operating range is the valve 30 in the closed position, which occupies it fluid controlled. If the differential pressure at the inlet E exceeds the second threshold value of the valve 30 , so there is a connection to the outlet A free and relieves the plant. The drained hydraulic fluid is in the sump 34 collected. Alternatively, it can also be directly into the swamp 35 running back. Furthermore, the hydraulic system can also be designed as a hydraulic circuit.

This explains the advantages of the hydraulic valve 30 use in a hydraulic system.

LIST OF REFERENCE NUMBERS

1

 valve housing

1a

 valve body

1b, 1c

 valve cover

2

 first piston

3

 second piston

4

 pen

5

 first spring

6

 throttle element

7

 second spring

10

 first throttle opening

11

 second throttle opening

12

 first control edge

13

 second control edge

14

 first paragraph

15

 second paragraph

20, 21, 22, 23, 24

 active surfaces

30

 hydraulic valve

31

 hydraulic pump

32

 heat exchangers

33

 Hydraulic line to consumer

34

 overflow

35

 swamp

e

 inlet

A

 outlet

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009049995 A1 [0004]

Claims (11)

Hydraulic valve for a hydraulic system, in particular for a hydraulic circuit in a vehicle, having a valve housing ( 1 ) having an inlet (E) and an outlet (A) for the hydraulic fluid, with a valve element ( 2 ), which can take at least one position in which a connection between the inlet (E) and outlet (A) is released, and at least one position in which no connection between the inlet (E) and outlet (A) is released, and with at least one return element ( 5 . 7 ) acting on the valve element ( 2 ) a force in the direction of a rest position of the valve element ( 2 ), wherein the hydraulic valve is designed so that the valve element ( 2 ) assumes the rest position when no differential pressure between inlet (E) and outlet (A) is applied, and that the valve element ( 2 ) assumes an overpressure position in which the connection between inlet (E) and outlet (A) is released when the inlet (E) is subject to a differential pressure which is greater than a second threshold, characterized in that the hydraulic valve is designed such that that in the rest position, a connection between the inlet (E) and outlet (A) is released, and that the valve element ( 2 ) assumes a closed position in a fluid-controlled manner, in which no connection between inlet (E) and outlet (A) is released when a differential pressure, which lies between a first and the second threshold value, is present at the inlet (E). Hydraulic valve according to claim 1, characterized in that the connection between inlet (E) and outlet (A) in the rest position by at least one throttle bore ( 10 . 11 ) in the valve element ( 2 ) and / or by at least one throttle element ( 6 ) is narrowed in the flow cross-section such that the flow of the hydraulic fluid in the rest position is lower than the flow which occurs in the overpressure position. Hydraulic valve according to claim 1 or 2, characterized in that a damping element ( 3 . 4 . 7 ) present with the valve element ( 2 ) and / or with the valve housing ( 1 ) forms a damping chamber, which via a throttle gap or a throttle bore with the valve interior or the sump ( 35 ) connected is. Hydraulic valve according to one of the preceding claims, characterized in that the damping element ( 3 . 4 . 7 ) in several parts, in particular as a sliding piston ( 3 . 4 ) with a further return element ( 7 ), preferably with a spring. Hydraulic valve according to claim 3 or 4, characterized in that the damping element ( 3 . 4 . 7 ) on the one hand via the return element ( 5 ) directly or indirectly against the valve element ( 2 ) and on the other hand directly or indirectly on the valve housing ( 1 ) is supported. Hydraulic valve according to claim 3 or 4, characterized in that the damping element as a part of the valve element ( 2 ) is executed. Hydraulic valve according to one of the preceding claims, characterized in that the hydraulic valve is designed so that the valve element ( 2 ) assumes an intermediate position which initially reduces the flow area of the connection between inlet (E) and outlet (A) when the differential pressure at inlet (E) exceeds an intermediate threshold which is less than the first threshold. Hydraulic valve according to one of the preceding claims, characterized in that it as a sliding piston valve with a valve piston as a valve element ( 2 ) and with a spring as a restoring element ( 5 . 7 ) is trained. Hydraulic valve according to claim 8, characterized in that in the rest position the connection between inlet (E) and outlet (A) via the interior of the valve piston ( 2 ) is made. Hydraulic valve according to claim 8 or 9, characterized in that in the overpressure position, the connection between inlet (E) and outlet (A) in the space between the valve element ( 2 ) and valve housing ( 1 ) is made. Hydraulic valve according to one of the preceding claims, characterized in that in the rest position, the released connection between inlet (E) and outlet (A) at least partially or completely via a different path than in the overpressure position.

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