Pressure relief valve and hydrostatic drive

Abstract

Pressure relief valve with shockless function, with a pressure connection (26) and a discharge connection, as well as a valve body which is acted upon in the closing direction by a spring (20, 22) and a control pressure in a pressure chamber, and with a control oil path which connects the pressure connection (26) to the pressure chamber and in which a first nozzle (50) is arranged and which is connected via a second nozzle (66) to a damping chamber (52) which is delimited by a damping element (54), characterized in that the damping element (54) is designed such that, with increasing displacement from a basic position in which the damping chamber (52) is minimal, it opens a pressure medium discharge path controlled by the valve body, which throttles from the pressure connection (26) to the discharge connection, wherein the damping element (54) is designed such that its inner circumferential surface delimits a gap designed as an annular gap (76) with increasing adjustment,which forms an outflow cross-section which causes the said throttling in the said pressure medium outflow path.

Description

[0001] The invention relates to a pressure relief valve with shockless function with the features of the patent claim and to a hydrostatic drive designed with such a pressure relief valve.

[0002] Conventional travel drives, such as those described in DE 42 34 139 C2, DE 198 50 162 C1, and DE 103 03 487 B4, have a hydraulic motor supplied with pressure fluid by a pump in an open circuit. The direction of rotation of the hydraulic motor is determined by a travel direction valve, via which one of the two connections of the hydraulic motor can be connected to the pump and the other connection to the tank.

[0003] A brake valve is arranged between the travel direction valve and the hydraulic motor. This valve can influence the outflow of pressure medium from the hydraulic motor and is adjusted by the pressure difference between the high-pressure side and the low-pressure side into a position in which the pressure medium can flow away from the hydraulic motor largely unthrottled in the direction set on the travel direction valve. The inflow of pressure medium from the pump to the hydraulic motor is not influenced by the brake valve, as this inflow occurs via a bypass with a check valve opening towards the hydraulic motor. During coasting, the pressure on the high-pressure side drops, so that the brake valve is adjusted towards its neutral position and throttles the outflow of pressure medium from the hydraulic motor to the tank or blocks it off completely. This means that the hydraulic motor is slowed down by the pressure building up in the outflow, thus achieving a braking effect.The familiar drive system is also equipped with two pressure relief valves, which limit the system pressure to a maximum value. Especially during braking, it can happen that the maximum set pressure is reached during deceleration, causing the associated pressure relief valve to open. If this opening occurs quickly, undesirable sudden pressure fluctuations occur in the drive system, resulting in changes in the driving condition.

[0004] To avoid this, in a travel drive known from US 5 335 495 A, each pressure relief valve is assigned a damping element which is acted upon in one direction by the pressure at the inlet connection of the pressure relief valve. This pressure is tapped via two throttles, with the valve body of the pressure relief valve being acted upon in the closing direction by the pressure between the two throttles. When pressure builds up at the inlet of the pressure relief valve, the damping element is initially displaced towards a stop, resulting in a control oil flow via the two nozzles. This control oil flow reduces the pressure effective in the closing direction, so that the pressure relief valve opens at a comparatively low pressure.When the damping element reaches its stop, the control oil flow through the nozzles approaches zero, so that pressure builds up at the inlet of the pressure relief valve in the control chamber acting in the closing direction. The valve body is designed with an area difference, so that only the force component corresponding to the area difference acts in the opening direction – the pressure at which the valve opens is thus significantly higher than at the beginning of the pressure relief function (damping element not yet at its stop). In this way, the pressure jumps in the pressure relief function explained above can be dampened.

[0005] DE 197 34 020 A1 shows a pressure relief valve with a shockless function in which a valve cone of a main stage is preloaded against a valve seat by a spring. Similar to the previously described prior art, a spring chamber for this spring is connected via a throttle / nozzle to a damping chamber which is delimited at the front by a damping element designed as an annular piston. The pressure at the pressure connection also acts on the spring chamber via another nozzle. If the pressure at the pressure connection increases, the damping element is displaced due to the pressure acting in the damping chamber, so that the volume of the damping chamber increases and the volume of the spring chamber and thus the pressure in the spring chamber decreases accordingly. The valve cone then lifts off its valve seat against the force of the spring, whereby this pressure is at a significantly lower level than the system pressure that is to be limited by the pressure relief valve.If the pressure at the pressure port continues to rise, the damping element reaches a stop position, allowing the inlet pressure to build up again in the spring chamber, and the valve cone blocks the pressure medium connection from the pressure port to the low-pressure port. The pressure relief valve then only opens again when the system pressure reaches the above-mentioned level.

[0006] The above-described short-term internal holding at a lower pressure level results in greater driving comfort for travel drives, while the affected mechanical components for torque transmission, such as shafts and gears, are protected due to the reduction in the sudden load.

[0007] Particularly in directly controlled pressure relief valves, this time delay, up to which the pressure relief valve responds upon reaching the system pressure, is essentially determined by the annular piston-shaped damping element, which is displaced via the aforementioned throttle chain system and thereby releases a volume of the damping chamber that must be filled with pressure medium over a certain period of time. This delay time is essentially limited by the throttle cross-sections, resulting in a more or less stepped curve as the time-pressure characteristic with a steep rise between the low pressure level and the maximum pressure level corresponding to the system pressure to be limited.

[0008] Furthermore, reference is made to the subsequently published DE 10 2012 003 166 A1, which shows a pressure relief valve with the features of the preamble of claim 1.

[0009] In contrast, the invention is based on the object of creating a pressure relief valve and a travel drive designed therewith, in which the damping in the pressure relief function is improved, for example during a braking process.

[0010] This object is achieved with regard to the pressure relief valve by the features of patent claim 1 and with regard to the drive by the subordinate features of patent claim 10.

[0011] Advantageous further developments of the invention are the subject of the subclaims.

[0012] The pressure relief valve with shockless function according to the invention has a pressure connection and a low-pressure or drain connection as well as a valve body, preferably a valve cone, which is acted upon in the closing direction by a spring and pressure in a pressure chamber. Furthermore, a control oil path is formed in the pressure relief valve, which connects the pressure connection to the damping chamber and in which a first nozzle is arranged. The control oil path further connects the pressure chamber via another nozzle to a damping chamber, which in turn is delimited by a damping element. This damping element is designed such that with increasing displacement from a basic position in which the damping chamber is minimal, it throttles a pressure medium outflow path controlled by the valve body towards the low pressure.

[0013] By throttling the discharge cross-section in this way, the transition from the low pressure level to the high system pressure level can be designed to be significantly smoother, even with a directly controlled pressure relief valve, than with the previously mentioned prior art, so that the sudden loads caused by pulsation or similar events are further dampened. This design can be used with both a pilot-operated and a directly controlled pressure relief valve.

[0014] According to the invention, the damping element is designed such that, with increasing adjustment, its inner circumferential surface defines, on the one hand, a gap, preferably designed as an annular gap, which forms the outflow cross-section. Such a gap can, for example, be defined on the other hand by a valve bushing on which the damping element is guided and which forms part of a pressure medium outflow path to the low-pressure connection.

[0015] The damping function can be further optimized if an outer peripheral section of the damping element limits a further throttle cross-section with an inner peripheral wall on the housing side.

[0016] The construction of the pressure relief valve is particularly simple if the damping element is designed as a stepped sleeve with a stepped outer diameter, wherein the end section with a reduced outer diameter limits the above-mentioned further throttle cross-section and the inner diameter of the stepped sleeve limits the gap, which is preferably designed as an annular gap.

[0017] The use of separate sealing elements, such as sealing rings or the like, can be dispensed with if an inner peripheral section of the damping element is designed as a sealing surface. Eliminating the traditional sealing elements, which are also subject to wear during pulsation, significantly simplifies assembly, for example, as sealing elements cannot be forgotten or damaged.

[0018] The seal between high and low pressure can be further improved if the damping element is designed to be elastically deformable in sections, so that, for example, in its end positions it forms a sealing contact with adjacent components.

[0019] The stroke of the damping element can be limited relatively easily by an annular shoulder which is formed on the stepped sleeve and which runs onto a corresponding stop surface on the housing side.

[0020] In a preferred embodiment of the invention, the first nozzle is formed in the valve body and the second nozzle is formed in a jacket of a valve bushing receiving the valve body.

[0021] The hydrostatic drive according to the invention is preferably designed with a directly controlled pressure relief valve according to the invention.

[0022] A preferred embodiment of the invention is explained in more detail below with reference to schematic drawings.

[0023] It shows Fig. 1 a part of a circuit diagram of a hydrostatic drive, Fig. 2 a pressure relief valve of the drive according to Fig. 1 in its basic position, Fig. 3 the pressure relief valve in the pressure relief function and Fig. 4 a characteristic curve of the pressure relief valve according to the Fig. 2 and Fig. 3.

[0024] In the Fig. The circuit diagram shown in Figure 1 shows a hydrostatic drive in an extremely simplified manner, wherein in principle only the components essential for understanding the invention are shown. For a detailed description, reference can be made to the applicant's earlier patent application DE 10 2012 003 166.1. Accordingly, such a hydrostatic drive 1 usually has a pump 2 which supplies a hydraulic motor 4 with pressure medium. In the illustrated embodiment, the hydraulic motor 4 and pump 2 are shown in an open hydraulic circuit. In principle, a closed hydraulic circuit can of course also be used. The pressure medium connection is established via working lines 6, 8, which are connected to the two working ports of a travel direction valve 10.This is designed as a continuously adjustable directional control valve, with the adjustment being electrohydraulically carried out in the illustrated embodiment. Both the hydraulic motor 4 and the pump 2 can be designed as swash plate machines, the delivery / discharge volume of which can be adjusted using a suitable adjusting device. The pressure in the working lines 6, 8 is limited by pressure relief valves 12, 14 according to the invention, which, when a predetermined pressure level is exceeded, open a pressure medium connection from one working line carrying the high pressure to the other working line carrying the low pressure. Both pressure relief valves 12, 14 are designed with a shockless function, with this shockless function being shown in the circuit diagram according to. Fig. 1 is formed by damping elements 16, 18, the function of which will be explained in more detail below. The drive also has the previously explained Fig. 1 schematically shown brake valve 19.

[0025] As further shown in the circuit diagram Fig. 1, the respective pressure in the working line 6, 8 acts on the two pressure relief valves 12, 14 in the opening direction. The following considerations focus on the pressure relief valve located in the outlet of the hydraulic motor 4, at whose pressure connection the outlet pressure rising during the braking process is applied. In the closing direction, each pressure relief valve 12, 14 is acted upon by the force of a spring 20, 22. The other Fig. The functional elements shown in Figure 1 are described using the Fig. 2 and Fig. 3 is explained in more detail.

[0026] The pressure relief valves 12, 14 are identical in design, so only the structure of the pressure relief valve 12 will be explained below. This is a cartridge-type valve and is installed in a control block 24 of the hydrostatic drive. The pressure relief valve 12 has an inlet or pressure port 26, which is connected to the respective working line, for example, the outlet-side working line 6. Reference numeral 28 designates a low-pressure or outlet port, which is connected to the other working line, for example, the inlet-side working line 8, via the channel 30 shown.

[0027] In the specific embodiment, the pressure relief valve 12 has a seat bushing 32 connected to a valve bushing 34 in which a valve cone 36 is guided. This is preloaded by the spring 20 against a seat 38 formed on the seat bushing 32. The spring 20 is accommodated in a spring chamber 40, which is delimited on the one hand by an enlarged part of the valve bushing 34 and on the other hand by a cap 42 screwed into a stepped valve bore 44 of the control block 24. The spring 20 is supported on the rear side by the cap 42 and engages a stepped pin 46 of the cone 36 via a spring plate 47.

[0028] The diameter of the pin 46 is smaller than the seat diameter, so that the cone 36 is designed with a surface difference effective in the opening direction. The spring chamber 40 is connected to the pressure port 26 via an axial bore 48 of the cone 36. A first nozzle 50 is arranged in this axial bore 48, forming part of a control oil path via which the pressure port 26 is connected to the spring chamber 40.

[0029] An outer circumference of the valve bushing 34 defines a damping chamber with an inner circumference section of the valve bore 44 (see in particular Fig. 3), which in the representation according to Fig. 2 has a minimal volume. This damping space is Fig. 2 to the right by the cap 42 and, on the other hand, by a damping member 54, which is sealingly guided on the outer circumference of the valve bushing 34 and on the inner circumferential wall of the valve bore 44. The damping member 54 is designed as an annular piston and is stepped back towards the cone 36, so that the outer circumferential surface of the remaining end section 56 of the damping member 54, together with the inner circumferential wall of the valve bore 44, defines a displacement chamber 60. This displacement chamber 60 is connected to the inlet-side channel 30 via a third nozzle / throttle cross-section. In the illustrated embodiment, this throttle cross-section, referred to below as the third nozzle 62, is limited by the end section 56 on the one hand and by a damping web 64 on the control block side on the other hand, and is also dependent on the stroke of the damping member 54 - this will be discussed in more detail below.

[0030] A second nozzle 66 is formed in the annular jacket of the valve sleeve 34, via which the spring chamber 40 is connected to the damping chamber 52. Accordingly, this is in Fig. 2 minimum damping chamber 52 is connected via the said control oil path (axial bore 48, first nozzle 50, spring chamber 40, second nozzle 66) to the pressure connection 26, to which the pressure in the outlet from the hydraulic motor 4 is applied.

[0031] How further Fig. 2, a rear annular end face of the cone 36 is connected to the channel 30 via a bore star 68, so that this annular end face is subjected to the inlet pressure.

[0032] During "normal" operation, the cone 36 is thus preloaded into its closed position by the force of the spring 20 and the pressure acting in the spring chamber 40. Due to the inlet pressure acting on its left annular end face, the damping element 54 is in its illustrated basic position, in which the damping chamber 52 is at its minimum and the displacement chamber 60 is at its maximum.

[0033] As explained, the inner peripheral wall of the damping element 54 rests sealingly against the outer peripheral wall of the valve sleeve 34, eliminating the need for additional sealing means. To enhance the seal, recesses can be provided on the end face through which sealing lips 70 are formed, which are elastically biased by the system pressure toward a sealing contact with the outer circumference of the valve sleeve 34. Of course, these elastic regions can also be achieved by a different design of the damping element 56.

[0034] In the Fig. In the basic position shown in Figure 2, the end section 56 is located with its end face at a short distance from the third nozzle 62, so that its opening cross-section is at its maximum.

[0035] In the case of the pressure relief valve 14 arranged in the inlet, the high pressure (system pressure) acts in the spring chamber 40 in the inlet to the hydraulic motor, so that the damping element 54 is then shifted to the left in the case of the high-pressure side pressure relief valve 54.

[0036] As explained, the pressure relief valve located in the outlet, for example the pressure relief valve 14, has low pressure at the inlet connection (pressure connection) 26 during normal driving operation.

[0037] During the braking described above, the pressure in the outlet from the hydraulic motor 4, ie in the low-pressure side working line 6, increases. This pressure increase is accordingly also present at the pressure connection 26. Due to the control oil path described above, the pressure in the spring chamber 40 and subsequently also in the damping chamber 52 also increases. Since this pressure generated during braking can then exceed the pressure in the inlet, the damping element 54 is accordingly released from its Fig. 2, so that the damping chamber 52 is enlarged. The speed of movement and thus the damping effect are determined, among other things, by the cross-section of the nozzles 50, 66 of the aforementioned control oil path, through which the control oil flows from the pressure port 26 into the damping chamber 52. The control oil in the displacement chamber 60 is then displaced via the third nozzle 62 into the channel 30, which is connected to the inlet-side working line 8. This means that the effective cross-section of the third nozzle 62 also determines the damping behavior of the damping element of the pressure relief valve 12, 14.

[0038] During this displacement, the radially recessed end section 56 of the damping element 54 dips into the damping web 64, so that the effective cross section of the third nozzle 62 is reduced and the movement of the damping element 54 is slowed accordingly. The effective cross section of the third nozzle 62 is then determined by the annular gap between the outer circumference of the end section 56 and the inner circumferential wall of the damping web 64. During a partial stroke, this damping cross section of the third nozzle 62 remains constant. After a further stroke, the end section 56 of the damping element 54 dips into the area of ​​the channel 30 and then increasingly covers one or more outflow openings 72 of the valve sleeve 34, so that the outflow of the pressure medium from the pressure connection 26 into the channel 30 (now the low-pressure connection) is throttled. This throttling increases with increasing displacement of the damping element 54.After a predetermined stroke, the annular shoulder of the damping element 54 runs onto a correspondingly designed annular shoulder 74 of the control block 24; this thus acts as a stroke limiter for the damping element 54. A further change in the throttle cross-sections then does not occur, so that the pressure is then limited to the set system pressure via the pressure relief valve.

[0039] The resulting characteristic curve is shown in Fig. 4. This shows the increase in pressure p as a function of time t during the damping function of the pressure relief valve 12.

[0040] As explained above, the pressure relief valve 12 located in the outlet is initially closed. During braking, the pressure increases, so that the damping element 54 is displaced in the manner described above and the pressure chamber 52 increases accordingly. Due to the pressure drop in the spring chamber 40, the force acting on the cone 36 in the closing direction is reduced, so that it lifts off and the pressure accordingly reaches the lower pressure level (p min) as long as the damping element 54 is displaced. After a time t1, the damping element 54 then reaches a position in which the outflow openings 72 are covered by the end section 56, so that the outgoing pressure medium volume flow is throttled accordingly and the pressure at the pressure connection 26 continues to rise, since a corresponding control pressure effective in the spring chamber 40 is also built up. The pressure then increases continuously with increasing throttling of the outflow opening 72, so that in the illustration according to Fig.4, the slope of the characteristic curve is established. After a time t2, the damping element 54 then reaches its stop position, so that further throttling of the outflowing pressure medium volume flow no longer occurs and thus the damping element 16, 18 is no longer effective - the pressure is then limited in the conventional manner via the pressure relief valve to the set system pressure, so that the pressure in the outlet cannot exceed this system pressure.

[0041] The damping function described above can also be provided with a pilot-operated pressure relief valve.

[0042] The slope of the characteristic curve in the region t2 can be determined by appropriately designing the annular gap 76 between the inner circumferential wall of the end section 56 of the damping element 54 and the outer circumferential wall of the valve bushing 34. In principle, however, differently designed outflow cross-sections can also be formed on the valve bushing 34, which are then covered by the end section 56 during displacement in order to continuously change the outflow cross-section accordingly, preferably to reduce it.

[0043] Further influencing the damping or the throttle chain can be determined by selecting the cross-sections of the nozzles 50, 66 or the throttle cross-section of the so-called third nozzle 62. Varying these is particularly simple, since only the diameter of the damping web 64 and the outer diameter of the end section 56 need to be varied.

[0044] In principle, it is also possible to form a further throttle cross-section by matching the outer diameter of the larger part of the damping element 54 and the inner circumferential diameter of the valve bore 44 to one another in such a way that a throttle gap is created, via which the damping chamber 52 is connected to the displacement chamber 60 in a throttled manner.

[0045] A pressure relief valve with shockless function is disclosed, wherein a damping element in the shockless function controls an outflow cross-section.

Claims

[1] Pressure relief valve with shockless function, comprising a pressure port (26) and a drain port, and a valve body which is acted upon in the closing direction by a spring (20, 22) and a control pressure in a pressure chamber and with a control oil path which connects the pressure port (26) to the pressure chamber and in which a first nozzle (50) is arranged and which is connected via a second nozzle (66) to a damping chamber (52) which is bounded by a damping element (54), characterized by, that the damping element (54) is designed such that, with increasing displacement from a basic position in which the damping space (52) is minimal, it restricts a pressure medium outflow path controlled by the valve body, which throttles from the pressure port (26) to the outlet port, wherein the damping element (54) is designed such that its inner circumferential surface, with increasing adjustment, limits a gap designed as an annular gap (76) which forms an outflow cross-section that causes the said throttling in the said pressure medium outflow path. [2] Pressure relief valve according to claim 1, wherein an inner circumferential wall of the damping element (54) limits, on the one hand, a gap preferably designed as an annular gap (76) as the adjustment increases. [3] Pressure relief valve according to claim 2, wherein the gap is on the other hand limited by a circumferential section of a valve bushing (34) on which the damping element (54) is guided and which limits part of the pressure medium outflow path. [4] Pressure relief valve according to claim 2 or 3, wherein an outer circumferential section of the damping element (54) with a housing-side wall limits a third nozzle (62) or a throttle cross-section. [5] Pressure relief valve according to one of the preceding claims, wherein the damping element (54) is designed as a stepped sleeve with a stepped outer diameter, wherein an end section (56) with a reduced outer diameter limits a third nozzle (62) and an inner circumferential wall of the stepped sleeve limits the gap in the pressure medium outflow path. [6] Pressure relief valve according to one of the preceding claims, wherein an inner circumferential section of the damping element (54) is designed as a sealing surface. [7] Pressure relief valve according to one of the preceding claims, wherein the damping element (54) is elastically deformable in sections to improve the sealing, preferably with a sealing lip (70). [8] Pressure relief valve according to one of the preceding claims, with an annular shoulder (74) for limiting the stroke of the damping element (54). [9] Pressure relief valve according to one of the preceding claims, wherein the first nozzle (50) is formed in the valve body and the second nozzle (66) is formed in a sleeve of a valve bushing (34) in which the valve body is guided. [10] Hydrostatic drive system with a pilot-operated or a directly controlled pressure relief valve according to one of the preceding claims.

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