Hydraulically actuatable brake having ventilation function

Abstract

The invention relates to a hydraulically actuatable brake (100) comprising a first housing part (105) and a second housing part (110), wherein: the housing parts (105, 110) are interconnected by means of a screw (115); an external thread (120) of the screw (115) is screwed into a blind hole (125) in the first or second housing part (105, 110), which blind hole has an internal thread (130); the blind hole (125) is fluidically connected to a piston chamber (140) of the brake (100) via a connection channel (145); and a ventilation channel (150) is provided, which fluidically connects the blind hole (125) to an outside atmosphere (152).

Description

[0001] Hydraulically operated brake with bleed function

[0002] The present invention relates to a hydraulically actuated brake, in particular for automatic transmissions, comprising at least two housing parts connected to one another by one or more screws. The screws are each screwed into a blind hole in the first or second housing part to fix the housing parts to one another.

[0003] Hydraulically actuated or operated brakes often have the problem that there is initially air in the piston chamber or pressure chamber, or that air accumulates there over time, for example due to oil exchange and outgassing or the accumulation of small bubbles in the oil. The hydraulic medium, such as hydraulic oil, is heavier than air, so the air rises to the top and collects there. The brake piston is usually spring-loaded in the open state and closes the brake by pressurizing the piston chamber. Since air changes volume under pressure, the accumulation of air within the system changes the relationship between pressure in the hydraulic system and the associated piston travel. As a result, precise positioning of the piston by pressure control is no longer possible or only possible with increased effort. It is therefore necessary to vent the piston chamber or pressure chamber or to discharge the air from the piston chamber.

[0004] KR 1999-0031639 U further discloses a clutch booster for a vehicle that performs a reliable venting process by completely blocking the inflow of atmospheric pressure during the venting process, which discharges the air within the clutch device to the outside. The venting device of the clutch booster includes a vent groove through which air is discharged to the outside, as well as a vent screw that is screwed into the vent groove and opens and closes the vent groove by loosening and tightening. Furthermore, a means for blocking the atmospheric pressure is provided, which is arranged between the vent screw and the vent groove to block the inflow of atmospheric pressure.One object of the invention is to provide a hydraulically actuated brake that has a venting function that is resistant to clogging or clogging. The invention achieves this object by means of the subject matter of the independent claims. Subclaims specify preferred embodiments.

[0005] A hydraulically actuated brake according to the invention comprises a first housing part and a second housing part, wherein the housing parts are connected to one another by means of a screw, wherein the screw is screwed with an external thread into a blind bore of the first or second housing part, which has an internal thread, wherein the blind bore is fluidically connected to a piston chamber of the brake via a connecting channel, and wherein a venting channel is provided which fluidly connects the blind bore to an outside atmosphere. In other words, venting of the piston chamber via at least one screw is proposed, wherein the screw can be a screw that is already used for component fixation, i.e. for fixing the first housing part to the second housing part, or vice versa. The screw implements a venting function of the piston chamber of the brake.

[0006] The venting channel between the clamped housing parts connects the blind bore, which is fluidically, particularly pneumatically, connected to the piston chamber, to the outside atmosphere. The fluidic connection between the connecting channel and the venting channel is made possible by the flank clearance between the external thread of the screw and the complementary internal thread of the respective housing part. With a standard thread, the screw thread (or external thread) and the nut thread (or internal thread) of the respective housing part have a common flank clearance after tightening, which is permeable to air. The air thus enters at the end of the screw and is guided helically along the thread.The flank clearance created by the length of the thread spiral automatically creates a relatively high hydraulic resistance, which, while making the aforementioned venting possible, also represents a high resistance for the hydraulic medium within the brake and thus prevents fluid loss. When the screw is assembled or tightened, there is a complex gap geometry between the external and internal threads, with a circular gap at the root circle of the external screw thread, a flank gap between the flanks of the internal and external threads, and a circular gap at the root circle of the internal or nut thread. This gap geometry ensures that the helical gap in the engaged thread area between the screw and the housing part can never become completely blocked by particles or the like. Instead, a certain degree of venting is always guaranteed.In other words, it is not possible to completely seal such a complex gap geometry with solid particles.

[0007] The vent channel is preferably located at the point where the internal thread of the respective housing part ends, so that the air from the thread can flow directly into the vent channel. This allows the path between the piston chamber and the outside atmosphere to be kept short, which has a positive effect on pressure equalization.

[0008] In one embodiment, the vent channel is formed between abutting surfaces of the two housing parts. The vent channel can be a groove or a recess formed only on the first housing part, only on the second housing part, or on both the first and second housing parts. If the groove or recess is provided on only one housing part, the other housing part, which is essentially flat in the area of ​​the vent channel, serves to spatially define the vent channel. In this case, the vent channel extends radially outward from the blind bore.

[0009] In an alternative design, the venting channel is formed as a bore within the screw. In other words, the venting channel is integrated or incorporated into the screw head. The bore connects the blind hole to the outside atmosphere in order to vent the piston chamber. The bore is preferably formed parallel to the longitudinal axis of the screw and, for example, extends through the screw head. The bore can also be formed obliquely to the longitudinal axis of the screw. In a further alternative design, the venting channel is formed between a screw head of the screw and an abutting surface of the housing part facing the screw head. In other words, the venting channel is formed beneath the screw head.The venting channel can be a groove or a recess formed only on the screw head, only on the housing part facing the screw head, or both on the screw head and on the housing part facing the screw head. In this case, the venting channel extends radially outward from the blind hole.

[0010] The connecting channel and / or the venting channel preferably have a diameter that is essentially constant or variable along its length. Alternatively or additionally, the connecting channel and / or the venting channel has a baffle. This can further prevent particles from reaching the screw thread, thus not impairing the venting function. Furthermore, alternatively or additionally, a filter medium or sieve can be inserted in the connecting channel and / or the venting valve. This can prevent or at least reduce the ingress of dirt.

[0011] Preferably, the connecting channel is coaxial with the blind bore. The connecting channel can thus be designed as an axial extension of the blind bore. This simplifies and accelerates brake production. Alternatively, the connecting channel can be designed as a bore formed at an angle to the blind bore. This increases design flexibility, as the screw can be positioned independently of the design and arrangement of the piston chamber, and vice versa, with the connecting channel connecting the blind bore and the piston chamber.

[0012] During brake operation, the connecting channel is preferably arranged above a fluid level within the piston chamber. Since air is lighter than the hydraulic medium, it can thus be easily discharged at the essentially uppermost point of the piston chamber with respect to gravity, thus reducing spray losses. The brake according to the invention is advantageously usable in an automatic transmission of a motor vehicle having at least one hydraulically actuated brake.

[0013] The invention will now be described in more detail with reference to the accompanying figures, in which:

[0014] Figure 1 is a schematic partial sectional view of a hydraulically actuated brake according to the invention;

[0015] Figure 2 is a schematic perspective view of a first housing part of the brake according to the invention shown in Figure 1 to illustrate the arrangement and design of a venting channel; and

[0016] Figure 3 is a highly schematic partial sectional view of a threaded engagement between an external thread of a screw and an internal thread of the first housing part of the brake according to the invention according to Figures 1 and 2.

[0017] Figure 1 shows a partial longitudinal section of a hydraulically actuated brake 100 according to the invention. The brake 100 can advantageously be used in an automatic transmission (not shown here), in particular in a clutch of the automatic transmission. The brake 100 comprises a first housing part 105 and a second housing part 110. The housing parts 105, 110 are connected or screwed together by means of a screw 115. The screw 115 (shown here) performs several functions. On the one hand, it fixes the housing parts 105, 110 together, and on the other hand, the screw 115 vents the brake 100 or equalizes the pressure. The screw 115 has an external thread 120 and is passed through a recess 122 of the second housing part 110 and is screwed into a blind hole 125 of the first housing part 105, which has a complementary internal thread 130, in order to fix the housing parts 105, 110 to one another.Further screws - not shown here - may be provided to fix the housing parts 105, 110 together.

[0018] Within the first housing part 105, a piston chamber 140 is formed, in which a piston 135 is guided. Particularly during operation of the brake 100, air can accumulate within the piston chamber 140, for example, due to bubbles in a hydraulic medium (not shown here), which, if not vented, could lead to malfunction of the brake 100. The piston chamber 140 is sealed by sealing elements 142, 143 arranged on the piston 135. To achieve pressure equalization in the piston chamber 140, the blind bore 125 is pneumatically connected to the piston chamber 140 via a connecting channel 145 at the end opposite the screw 115.In the present case, the connecting channel 145 is designed as a bore formed at an angle to the longitudinal axis of the blind bore 125, such that the blind bore 125 is located above the piston chamber 140 with respect to gravity during operation, so that air within the piston chamber 140 can always flow upwards relative to the heavier hydraulic medium and be discharged. Alternatively, if the piston chamber 140 is arranged accordingly, the connecting channel 145 can be formed coaxially with the blind bore 125. This would significantly simplify the manufacture of the brake 100 and the implementation of the venting function.

[0019] The screw 115 has a standard thread, so that after tightening the screw, a common flank clearance in the form of a gap 300 is formed between the internal and external threads 120, 130, which is permeable to air. The gap 300, with its complex cross-sectional geometry, is shown in Figure 3 between the thread flanks of the screw 115 and the first housing part 105. The air thus enters at the distal end of the screw 115 and is discharged helically along the thread engagement.

[0020] A vent channel 150 is provided, which fluidically connects the blind bore 125 to the outside atmosphere 152. The air collected in the piston chamber 140 is thus guided via the connecting channel 145, which is arranged above a fluid level (not shown here) with respect to gravity during operation of the brake 100, and the threaded connection between the screw 115 and the first housing part 105 into the vent channel 150, which is fluidly connected to the outside atmosphere 152.

[0021] In the present case, the venting channel 150 is arranged at the end of the threaded engagement facing away from the connecting channel 145 and discharges the air between abutting surfaces 155, 160 of the two housing parts 105, 110. As illustrated in Figure 2, the venting channel 150 is formed as a groove 200 on the abutting surface 155 or end face of the first housing part 105.

[0022] Alternatively, the venting channel 150 can be formed as a bore within the screw 115. Furthermore, the venting channel 150 can also be formed between a screw head 165 of the screw 115 and an abutting surface 170 of the second housing part 110 facing the screw head 165. It is conceivable that multiple venting channels are provided.

[0023] The connecting channel 145 and the venting channel 150 each have a diameter that is essentially constant along their length. Depending on the circumstances and requirements, the geometry of the connecting channel 145 or the venting channel 150 can be adapted. For example, the connecting channel 145 and / or the venting channel 150 can have a diameter that varies along its length. Furthermore, it is conceivable to arrange a diaphragm, a sieve, and / or a filter in the connecting channel 145 and / or the venting channel 150.

[0024] The arrows shown in Figure 1 in the connecting channel 145, on the threads 120, 130 and in the venting channel 150 schematically indicate the flow direction of the air from the piston chamber 140 to the area surrounding the brake 100. Reference numerals

[0025] brake

[0026] First housing part

[0027] Second housing part

[0028] screw

[0029] External thread of the screw

[0030] Recess of the second housing part

[0031] Blind hole drilling

[0032] Internal thread of the first housing part

[0033] Pistons

[0034] piston chamber

[0035] Sealing element

[0036] Sealing element

[0037] connecting channel

[0038] ventilation duct

[0039] Outdoor atmosphere

[0040] Impact surface

[0041] Impact surface

[0042] screw head

[0043] Impact surface

[0044] Nut

[0045] gap

Claims

Patent claims 1. A hydraulically actuated brake (100), comprising a first housing part (105) and a second housing part (110), wherein the housing parts (105, 110) are connected to one another by means of a screw (115), wherein the screw (115) is screwed with an external thread (120) into a blind bore (125) of the first or second housing part (105, 110), which has an internal thread (130), wherein the blind bore (125) is fluidically connected to a piston chamber (140) of the brake (100) via a connecting channel (145), and wherein a vent channel (150) is provided which fluidically connects the blind bore (125) to an external atmosphere (152).

2. Brake (100) according to claim 1, wherein the venting channel (150) is formed between abutting surfaces (155, 160) of the two housing parts (105, 110).

3. Brake (100) according to claim 1, wherein the venting channel (150) is formed as a bore within the screw (115).

4. Brake (100) according to claim 1, wherein the venting channel (150) is formed between a screw head (165) of the screw (115) and an abutting surface (170) of the housing part (105, 110) facing the screw head (165).

5. Brake (100) according to one of the preceding claims, wherein the connecting channel (145) and / or the venting channel (150) has a diameter that is substantially constant over its length.

6. Brake (100) according to one of the preceding claims, wherein the connecting channel (145) and / or the venting channel (150) has a diameter that is variable over its length.

7. Brake (100) according to claim 6, wherein the connecting channel (145) and / or the venting channel (150) has a diaphragm.

8. Brake (100) according to one of the preceding claims, wherein the connecting channel (145) is formed coaxially with the blind hole (125).

9. Brake (100) according to one of claims 1 to 7, wherein the connecting channel (145) is designed as a bore which is formed at an angle to the blind bore (125).

10. Brake (100) according to one of the preceding claims, wherein the connecting channel (145) is arranged above a fluid level within the piston chamber (140) during operation of the brake (100).

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