Pistons, gear selectors and shift levers

Abstract

The invention relates to a piston (7), in particular for a gear selector (2), comprising a piston body (8) with a piston skirt (10) and a piston end face (9), which can be pressurized with a working fluid. The piston (7) comprises a first sealing portion (19) and a second sealing portion (20). The piston body (8) and the first sealing portion (19) have mutually complementary geometric shapes, so that a first ventilation channel (15) is formed. The first ventilation channel (15) is arranged in a hydraulic circuit in series with the second sealing portion (20). The second sealing portion (20) prevents ventilation up to a first pressure (P1) and allows ventilation above the first pressure (P1). The invention also relates to a gear selector and a gear shift lever for a vehicle.

Description

Technical Field

[0001] The invention relates to a hydraulic piston, a hydraulic gear selector for a motor vehicle transmission, and a gear lever with a corresponding gear selector for a motor vehicle. Background Art

[0002] Hydraulic actuators in the form of single-acting or double-acting hydraulic cylinders are used in various applications, described here by way of example in the context of gear selectors for motor vehicle transmissions.

[0003] A gear selector is provided to actuate the shift forks on the transmission so as to engage the various gears. A hydraulically actuated gear selector comprises a plurality of hydraulic cylinders for this purpose.

[0004] A hydraulic cylinder is a fluid-driven working cylinder, also known as a hydraulic linear motor. It converts the energy of a hydraulic fluid, supplied by a hydraulic accumulator or hydraulic pump, into linear motion. A hydraulic cylinder typically consists of a piston that is capable of translational adjustment within a cylindrical tube.

[0005] Single-acting cylinders have only one piston end, which is loaded with hydraulic fluid. Therefore, they can only work in one direction. The return movement is ensured by their own mass or an external force (e.g. a return spring).

[0006] In a double-acting cylinder, there are two opposing pistons and surfaces that are usually alternately loaded with hydraulic fluid. Therefore, the cylinder has two effective directions of movement.

[0007] Hydraulic cylinders must be ventilated at least before the initial commissioning of a hydraulic system and after any intervention in the system (e.g. repairs). Continuous ventilation prevents air inclusions from accumulating in the hydraulic cylinder over time.

[0008] At high pressures or pressure fluctuations, air inclusions in the working medium or working fluid (hydraulic fluid) can lead to the so-called diesel effect, which causes fluid degradation and loss of sealing due to a significant temperature increase. Another negative effect is the diffusion of air through the sealing material toward the lower-pressure side. Because the pressure drop at the seal surface is so large, the air inclusions suddenly expand, leading to premature seal wear.

[0009] Another disadvantage of existing ventilation solutions is that the working fluid is constantly exhausted through the ventilation element. Especially during longer periods of non-use, this can cause the hydraulic system to suck in air and in extreme cases run dry. Summary of the Invention

[0010] The object of the present invention is therefore to improve a piston of the initially cited type in such a way that it can be ventilated during prolonged periods of non-use without air being drawn in or running dry via a formed venting element.

[0011] According to the invention, this object is achieved by a piston, in particular for a gear selector, comprising a piston body with a piston skirt and a piston end face which can be pressurized with a working fluid.

[0012] According to one aspect, the piston includes a first sealing portion and a second sealing portion. Here, the piston body and the first sealing portion have complementary geometries, forming a first ventilation channel that is arranged in series with the second sealing portion in the hydraulic circuit. The second sealing portion prevents ventilation up to a first pressure. The second sealing portion allows ventilation above the first pressure. This reliably prevents air ingress or dry running of the cylinder during extended periods of non-use.

[0013] According to an advantageous aspect, the piston end face may have a recess in which a rubber-elastic sealing element is arranged. The first sealing portion may in particular be a part of the sealing element. The piston body and the sealing element may have mutually complementary geometric shapes so as to form a first ventilation channel with a first free cross-sectional area, and in a pressure-reduced state, a second ventilation channel with a second free cross-sectional area is formed between the mutually opposite surfaces of the recess and the first sealing portion of the sealing element. The first ventilation channel and the second ventilation channel may preferably be hydraulically connected in parallel. In addition, the recess and the sealing element may be configured so that as the temperature of the sealing element increases, its elastic modulus decreases, and the pressurization of the sealing element by the working fluid causes an elastic deformation of the sealing element that depends on temperature and pressure. The elastic deformation in turn causes the free cross-sectional area of ​​the second ventilation channel to decrease.

[0014] Since the working fluid often has a highly temperature-dependent viscosity, i.e., is more viscous at lower temperatures, a ventilation channel with a constant free cross section can result in a volume flow that is too low at low temperatures to adequately ventilate the piston. However, at high temperatures, the volume flow through a ventilation channel with a constant cross section is unnecessarily high, thus leading to high losses.

[0015] The influence of the pressure on the piston end face or the ventilation channel by the working fluid or the pressure difference formed on the ventilation channel is similar. At low pressure, the volume flow through the ventilation channel with a fixed cross-sectional area will be small, but at high pressure, the efficiency may not be high enough.

[0016] By suitable combinations of the above aspects, it is possible to provide hydraulic pistons with ventilation channels having a pressure- and temperature-dependent (variable) free cross-sectional area.

[0017] The pressure- and temperature-dependent free cross-sectional area changes automatically, purely due to physical effects, so that the volume flow for ventilation is large enough at a first temperature and / or first pressure, but not too large at a second (higher) pressure and second (higher) temperature.

[0018] Advantageously, the piston body and the sealing element can be configured so that the temperature- and pressure-dependent elastic deformation of the sealing element reduces the free cross-sectional area of ​​the second ventilation channel to a greater extent than the free cross-sectional area of ​​the first ventilation channel. Depending on the design, it may even be preferable if the cross-sectional area of ​​the first ventilation channel is substantially independent of pressure and temperature. This can be achieved, for example, if the first ventilation channel extends from the piston end face (or another point of the piston loaded with the operating pressure) through the piston body without the sealing element acting on the free cross-sectional area of ​​the first ventilation channel or partially covering the channel inlet.

[0019] According to another advantageous aspect, the first and second ventilation channels are arranged in a hydraulic circuit in series with a second sealing portion. The second sealing portion is preferably configured to seal the ventilation opening in the piston body against the first and second ventilation channels up to a first pressure, and to open the ventilation opening above the first pressure. This prevents the piston from running dry, particularly during extended periods of non-use.

[0020] In various embodiments, the recess can have an outer region on the piston end face, in which the rubber-elastic sealing element is arranged. Furthermore, the recess then includes an inner region in which the ventilation opening is arranged. A second sealing portion, preferably in the form of a sealing lip, is arranged between the inner and outer regions. The sealing lip has proven particularly suitable for the proposed purpose.

[0021] Preferably, the recess may have one or more ventilation grooves in its (side) wall, which together with the first sealing portion form a second ventilation channel. The ventilation grooves extend from the piston end face in the direction of the inner region to the rear of the outer region.

[0022] The corresponding ventilation groove is advantageously configured and dimensioned such that the second ventilation channel is not closed by the sealing element at the first pressure and / or first temperature, but rather has a maximum free cross-sectional area.

[0023] In this advantageous embodiment, it is further provided that, as the pressure and / or temperature increases compared to the first pressure and / or the first temperature, the sealing element elastically deforms according to the temperature and pressure so as to gradually close the free cross-sectional area of ​​the second ventilation channel, preferably until the second ventilation channel is essentially completely closed by the deformed sealing element at a pressure above the second pressure and / or above the second temperature.

[0024] In this state, the free total cross-sectional area of ​​the ventilation channel is minimal, so that at correspondingly high pressure or temperature-induced low-viscosity flow characteristics of the working medium, the volume flow through the ventilation channel is limited by means of the sealing element.

[0025] According to another advantageous aspect, at least one second ventilation groove has a flat free cross section. In this context, "flat" means that the height of the free cross section (in the radial direction) is smaller than the width (in the circumferential direction). The flat free cross section with rounded transitions can be partially or even completely closed by a sealing element that deforms under applied pressure.

[0026] In one embodiment variant, the recess can have one or more ventilation recesses in its wall, which in each case form, together with the first sealing portion, a first ventilation channel (or channels).

[0027] The ventilation recess extends from the piston end face to the rear of the outer region in the direction of the inner region. In addition, the ventilation recess is configured and dimensioned so that even under elastic deformation of the sealing element that depends on temperature and pressure, the ventilation recess cannot be closed by the sealing element.

[0028] For this purpose, the ventilation recess can preferably have a deep free cross section. In this context, "deep" means that the height of the free cross section in the radial direction is greater than the width. A deep free cross section may only be insufficiently covered by the deformed sealing element or not covered at all.

[0029] According to another advantageous aspect, the maximum distance between the second ventilation channel and the sealing element can be smaller than that between the first ventilation channel and the sealing element. Thus, when deformed, the sealing element first / only covers the second ventilation channel.

[0030] In a preferred embodiment variant, the recess is an annular groove on the end face extending in the axial direction. This shape has proven to be particularly advantageous and provides a particularly good retention force for the sealing element.

[0031] The piston may have a piston seal. The piston seal may comprise a radial circumferential groove in the piston skirt of the piston. Preferably, a self-sealing piston groove ring having a sealing lip may be arranged in the circumferential groove.

[0032] Preferably, the piston can be a double-acting piston.The piston body then has piston end faces of the above-described type on both sides.

[0033] In general, the present invention or its advantageous embodiments considers the concept of providing an annular groove on the end face of a piston, on the wall of which a plurality of ventilation grooves and at least one ventilation recess are machined.

[0034] The sealing ring is located in an annular groove which, together with the geometry of the ventilation groove and the ventilation recess, defines the free cross-sectional area of ​​the ventilation channel.

[0035] The additional sealing lip on the sealing ring ensures that the ventilation channel or ventilation opening is completely sealed below the specified operating pressure, so that the hydraulic system cannot run dry.

[0036] Depending on the operating pressure, the sealing ring, which is elastically deformed by the operating pressure, partially or completely closes the ventilation groove, while the ventilation recess remains open regardless of the operating pressure. In the lower pressure state, the free cross-sectional area is at its maximum.

[0037] At high operating temperatures, the sealing ring's stiffness decreases, resulting in a smaller free cross-sectional area at comparable operating pressures at higher temperatures. In contrast, at low temperatures, the sealing ring is very rigid, ensuring that the free cross-sectional area of ​​the ventilation channel is approximately maximized regardless of the operating pressure. This compensates for the temperature-dependent viscosity of the operating fluid.

[0038] A gear selector for the gear selector lever is also provided. The gear selector has at least one, preferably a plurality, in particular two to six, pistons as described initially. The gear selector can be used / installed particularly flexibly and easily as a gear selector module that can be mounted on the transmission.

[0039] Furthermore, a shift lever is provided which comprises a shift selector of the type described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Other features and advantages of the present invention will be apparent from the following description and the accompanying drawings, to which reference is made.

[0041] - Figure 1 A perspective view of a piston according to the present invention;

[0042] - Figure 2 A cutaway perspective view of the piston according to the present invention in an installed state;

[0043] - Figure 3 Schematic diagram of exemplary ventilation channels and their free cross-sectional areas at low and high operating pressures;

[0044] - Figure 4 A cross-sectional view of a shift selector module according to the present invention;

[0045] - Figure 5 a perspective view of the gear lever; and

[0046] - Figure 6 Another exemplary embodiment of a piston according to the invention. DETAILED DESCRIPTION

[0047] Figure 1 A piston 7 for a gear selector 2 is shown. The piston 7 comprises a piston body 8 having a piston skirt 10 and a piston end face 9 which can be pressurized with a working fluid. The piston can be made of PPA (polyphthalamide).

[0048] The piston 7 includes a first sealing portion 19 and a second sealing portion 20. The piston body 8 and the first sealing portion 19 have mutually complementary geometric shapes, so that a first ventilation channel 15 is formed. The first ventilation channel 15 is arranged in series with the second sealing portion 20 in the hydraulic circuit. The second sealing portion 20 prevents ventilation up to a first pressure P1 and allows ventilation above the first pressure P1.

[0049] The piston end face 9 has a recess 13. A rubber elastic element 18 (not shown here) is arranged in the recess 13 (see Figure 2 ).

[0050] The piston 7 is a double-acting piston. The piston body 8 has piston end faces 9 of the above-mentioned type on both sides.

[0051] Figure 2 A perspective cross-sectional view of the piston 7 is shown. The piston body 8 and the sealing element 18 have mutually complementary geometric shapes. The piston body and the sealing element form a first ventilation channel 15 having a first free cross-sectional area. Furthermore, at least in the pressure-reduced state, the piston body and the sealing element form a second ventilation channel 17 having a second free cross-sectional area between the mutually facing surfaces of the recess 13 and the first sealing portion 19 of the sealing element 18.

[0052] The first ventilation channel 15 and the second ventilation channel 17 are hydraulically connected in parallel. The first ventilation channel and the second ventilation channel both lead to the inner area of ​​the recess 13.

[0053] Furthermore, the recess 13 and the sealing element 18 can be configured such that as the temperature of the sealing element 18 increases, its elastic modulus decreases, and the pressurization of the sealing element 18 by the working fluid 11 causes a temperature- and pressure-dependent elastic deformation of the sealing element 18. This elastic deformation, in turn, results in a reduction in the free cross-sectional area of ​​the second ventilation channel 17.

[0054] The first ventilation channel 15 and the second ventilation channel 17 are arranged in a hydraulic circuit in series with a second sealing portion 20. The second sealing portion 20 seals the ventilation opening 12 in the piston body 8 against the first and second ventilation channels 15, 17 up to a first pressure P1. The second sealing portion 20 opens the ventilation opening above the first pressure P1.

[0055] The recess 13 has an outer region on the side of the piston end face 9, in which a rubber elastic sealing element 18 is arranged. The recess 13 further includes an inner region, which contains the ventilation opening 12. A second sealing portion 20 in the form of a sealing lip is arranged between the inner region and the outer region.

[0056] The recess 13 has a ventilation groove 16 in its wall. Together with the first sealing portion 19, the ventilation groove 16 forms a second ventilation channel 17. The ventilation groove 16 extends from the piston end face 9 in the direction of the inner region to the rear of the outer region and is configured and dimensioned such that the second ventilation channel 17 is not closed by the sealing element 18 at a first pressure P1 and / or a first temperature T1. The ventilation groove 16 is further configured and dimensioned such that as the pressure Px and / or temperature Tx increase, the sealing element 18, which has elastically deformed according to the pressure and temperature, gradually closes the free cross-sectional area of ​​the second ventilation channel 17. The second ventilation channel 17 is substantially completely closed above a second pressure P2 and / or a second temperature T2. The second pressure P2 is higher than the first pressure P1. The second temperature T2 is higher than the first temperature T1.

[0057] The recess 13 has a ventilation recess 14 in its wall, which, together with the first sealing portion 19 of the sealing element 18, forms a first ventilation channel 15. The ventilation recess 14 extends from the piston end face 9 in the direction of the inner region to the rear of the outer region. The ventilation recess 14 is configured and dimensioned such that it is not closed by the sealing element 18 even in the event of temperature- and pressure-dependent elastic deformation of the sealing element 18.

[0058] The recessed portion 13 is an end surface annular groove extending in the axial direction.

[0059] The piston 7 has a piston seal. The piston seal comprises a radial circumferential groove 22 in the piston skirt 10. A self-sealing piston groove ring 23 having a self-sealing sealing lip is arranged in the circumferential groove 22. The sealing lip is located on the inner wall 6 of the cylinder in which the piston 7 is displaceably received and seals the cylinder.

[0060] Figure 3 The free cross-sectional areas of the first and second ventilation channels 15 , 17 are schematically shown.

[0061] The piston body 8 and the sealing element 18 are configured such that a temperature- and pressure-dependent elastic deformation of the sealing element 18 reduces the free cross-sectional area of ​​the second ventilation channel 17 to a greater extent than the free cross-sectional area of ​​the first ventilation channel 15 .

[0062] At the top the ventilation channels 15, 17 are shown at a first pressure P1. Both the first and the second ventilation channels 15, 17 are open and have a maximum free cross-sectional area.

[0063] Figure 3 The lower area of ​​​​shows the ventilation channels 15, 17 at a higher pressure P2. The flat ventilation groove is completely filled by the sealing element, which has elastically deformed under the applied pressure. Therefore, the second ventilation channel 17 has no free cross-sectional area and is completely closed.

[0064] The ventilation groove 16 has a flat free cross section, in particular a height H2 in the radial direction that is smaller than a width B2 in the circumferential direction.

[0065] The ventilation recess 14 has a deep free cross section, in particular a height H1 in the radial direction that is greater than a width B1 in the circumferential direction.

[0066] Compared to the first ventilation channel 15 , the maximum distance between the second ventilation channel 17 and the sealing element 18 is smaller.

[0067] Due to the deep design of the ventilation groove 14 and its arrangement remote from the sealing element 18, even at a relatively high pressure P2, the deformed sealing element 18 does not fill the ventilation recess 14. Therefore, the cross-sectional area of ​​the first ventilation channel 15 remains substantially unchanged.

[0068] For example, for the hydraulic oil used in the gear selector, the minimum flow rate can be set to 0.08 l / min to 0.15 l / min at a first temperature T1 in the range of -20°C to -30°C and a first operating pressure P1 of approximately 70 psi. In contrast, the maximum flow rate can be set to 0.4 l / min to 0.7 l / min at a second temperature T2 in the range of 100°C to 130°C and a second operating pressure P2 of approximately 300 psi. At operating pressures up to 3 psi (or 15 psi), the system should be completely sealed so that the system does not drain during extended downtime and there is no risk of damage during recommissioning.

[0069] Figure 4 A cross section of a gear selector 2 for a gear shift lever is shown. The gear selector 2 has a plurality of pistons 7. The gear selector 2 is configured as a gear selector module that can be mounted on a transmission.

[0070] Figure 5At least parts of a gearshift lever are shown. The gearshift lever comprises a gear selector 2 of the type described above. The gearshift lever may be part of a motor vehicle. For greater clarity, the transmission itself is not shown.

[0071] Figure 6 Another embodiment of a piston 7 is shown. The piston 7 includes a first sealing portion 19 and a second sealing portion 20. The piston body 8 and the first sealing portion 19 have mutually complementary geometries, forming a first ventilation channel 15. The first ventilation channel 15 is arranged in series with the second sealing portion 20 in the hydraulic circuit. The second sealing portion 20 prevents ventilation up to a first pressure P1 and allows ventilation above the first pressure P1.

[0072] The piston 7 has a piston seal. The piston seal comprises a radial circumferential groove in the piston skirt 10. A self-sealing piston groove ring with a sealing lip is arranged in the circumferential groove 22.

[0073] The piston 7 is a double-acting piston. The piston body 8 has piston end faces 9 of the above-mentioned type on both sides.

Claims

1. A piston (7), comprising a piston body (8) having a piston skirt (10) and a piston end face (9), the piston end face being pressurizable with a working fluid, wherein: The piston (7) comprises a first sealing portion (19) and a second sealing portion (20), wherein the piston body (8) and the first sealing portion (19) have mutually complementary geometric shapes such that a first ventilation channel (15) is formed, wherein the first ventilation channel (15) is arranged in a hydraulic circuit in series with the second sealing portion (20), and wherein the second sealing portion (20) prevents ventilation before a first pressure (P1) is reached and allows ventilation above the first pressure (P1).

2. The piston (7) according to claim 1, wherein The piston end face (9) has a recess (13) in which a rubber-elastic sealing element (18) is arranged, wherein the first sealing portion (19) is part of the sealing element (18), wherein the piston body (8) and the sealing element (18) have mutually complementary geometric shapes, so that a first ventilation channel (15) with a first free cross-sectional area is formed, and in the pressure-reduced state, a second ventilation channel (17) with a second free cross-sectional area is formed between mutually opposite surfaces of the recess (13) and the first sealing portion (19), wherein the first ventilation channel (15) and the second ventilation channel (17) are hydraulically connected in parallel, and further wherein the recess (13) and the sealing element (18) are configured such that as the temperature of the sealing element (18) increases, its elastic modulus decreases, and the pressurization of the sealing element (18) by the working fluid causes a temperature- and pressure-dependent elastic deformation of the sealing element (18), and by means of the elastic deformation, causes a reduction in the free cross-sectional area of ​​the second ventilation channel (17).

3. The piston (7) according to claim 2, wherein The piston body (8) and the sealing element (18) are configured such that a temperature- and pressure-dependent elastic deformation of the sealing element (18) reduces the free cross-sectional area of ​​the second ventilation channel (17) to a greater extent than the free cross-sectional area of ​​the first ventilation channel (15).

4. The piston (7) according to claim 2, wherein: The first ventilation channel (15) and the second ventilation channel (17) are arranged in a hydraulic circuit in series with the second sealing portion (20), wherein the second sealing portion (20) seals the ventilation opening (12) in the piston body (8) against the first ventilation channel and the second ventilation channel (15, 17) before a first pressure (P1) is reached, and opens the ventilation opening above the first pressure (P1).

5. The piston (7) according to claim 4, wherein The recess (13) has an outer area and an inner area, the outer area being on one side of the piston end face (9), the rubber elastic sealing element (18) being arranged in the outer area, and the inner area including the ventilation opening (12), wherein the second sealing part (20) in the form of a sealing lip is arranged between the inner area and the outer area.

6. The piston (7) according to claim 5, wherein The recess (13) has a ventilation groove (16) on its wall, which together with the first sealing portion (19) forms the second ventilation channel (17), wherein the ventilation groove (16) extends from the piston end face (9) in the direction of the inner area to the rear of the outer area and is configured and dimensioned so that the second ventilation channel (17) is not closed by the sealing element (18) at a first pressure (P1) and / or at a first temperature (T1), and as the pressure (Px) increases and / or the temperature (Tx) increases, the sealing element (18) that elastically deforms in dependence on temperature and pressure gradually closes the free cross-sectional area of ​​the second ventilation channel (17).

7. The piston (7) according to claim 6, wherein The second ventilation channel (17) is substantially completely closed by the sealing element (18) above a second pressure (P2) and / or above a second temperature (T2).

8. The piston (7) according to claim 6, wherein The ventilation groove (16) has a flat free cross section.

9. The piston (7) according to claim 8, wherein The height (h) of the free cross section of the ventilation groove (16) in the radial direction is smaller than the width (b) in the circumferential direction.

10. The piston (7) according to any one of claims 5 to 9, wherein The recess (13) has a ventilation recess (14) in its wall, which together with the first sealing part (19) forms the first ventilation channel (15), wherein the ventilation recess (14) extends from the piston end face (9) in the direction of the inner area to behind the outer area and is configured and dimensioned so that the ventilation recess (14) is not closed by the sealing element (18) even in the event of temperature- and pressure-dependent elastic deformation of the sealing element (18).

11. The piston (7) according to claim 10, wherein The ventilation recess (14) has a deep free cross section.

12. The piston (7) according to claim 11, wherein The height (h) of the free cross section of the ventilation recess (14) in the radial direction is greater than the width (b) in the circumferential direction.

13. The piston (7) according to claim 2, wherein: Compared with the first ventilation channel (15), the maximum distance between the second ventilation channel (17) and the sealing element (18) is smaller.

14. The piston (7) according to claim 2, wherein: The recess (13) is an end surface annular groove extending in the axial direction.

15. The piston (7) according to any one of claims 1 to 3, wherein The piston (7) has a piston seal, wherein the piston seal comprises a radial circumferential groove (22) in the piston skirt (10).

16. The piston (7) according to claim 15, wherein A self-sealing piston groove ring (23) having a sealing lip is arranged in the circumferential groove (22).

17. The piston (7) according to any one of the preceding claims 1 to 3, wherein The piston (7) is a double-acting piston, wherein the piston body (8) has the piston end faces (9) on both sides.

18. The piston (7) according to any one of the preceding claims 1 to 3, wherein The piston is used for a gear selector (2).

19. A gear selector (2) for a gear lever, wherein: The gear selector (2) comprises at least one piston (7) according to any one of the preceding claims.

20. The gear shift selector (2) according to claim 19, wherein: The shift selector (2) comprises a plurality of pistons (7).

21. The gear selector (2) according to claim 19 or 20, wherein: The shift selector (2) is a shift selector module that can be mounted on a transmission.

22. A gear shift lever comprising a gear selector (2) according to any one of claims 19 to 21.

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