GB2129878A

GB2129878A - Hydraulic actuating unit

Info

Publication number: GB2129878A
Application number: GB08323308A
Authority: GB
Inventors: Hans-Joachim Anders; Uwe Kley; Karl Stoerzel
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1982-11-08
Filing date: 1983-08-31
Publication date: 1984-05-23
Also published as: IT1169677B; IT8323623A0; DE3241164C2; ES275540U; ES275540Y; FR2535797B1; DE3241164A1; GB8323308D0; FR2535797A1; BR8305881A; GB2129878B; JPS59144834A

Abstract

The unit comprises a cylinder housing (8) and a piston (7), which latter is axially movable out of the open end (13) of the cylinder housing (8), as well as an annular seal (9) in an annular groove (10) in the cylinder housing (8). The radially outer wall (22) of the annular groove (10) extends like a truncated cone and is enlarged towards the open end (13). The annular groove (10) is confined by the back wall (24) and the front wall (25). A step (28) extends at the front wall (25) in the direction of the open end (13) of the cylinder housing (8). This step (28) enables larger piston travels without the piston (7), in motion, sliding past the seal (9) and causing an adjustment of the hydraulic actuating unit to take place much too early. The deformed seal in the step provides a retraction force to prevent heated brakes from rubbing against a disc. <IMAGE>

Description

SPECIFICATION Hydraulic actuating unit This invention relates to a hydraulic actuating unit of the kind having at least one cylinder housing and a piston that is axially movable out of the open end of the cylinder housing, and an annular seal which is arranged in an annular groove in the cylinder housing and which seals the piston in relation to the housing.

In a known hydraulic actuating unit of this kind (German published patent application 23 26 047), which serves for application of the brake pads against a brake disc, a step is designed at the back wall that is closer to the closed end of the cylinder housing. By this means the piston travel, which is caused at the piston due to impacts on the disc during cornering with the disc brake not applied, is reversed by the seal after termination of the cornering, i.e. the seal causes the piston to return to its initial position, to the end that as a result there will not ensue too much lost travel at the brake pedal upon the next hydraulic pressurisation.

In consequence of shortages of raw materials and the rise in price of energy, energy-saving automotive vehicles are currently being developed. A disc brake can contribute to save energy, if there are no residual brake torques in its non-applied condition, i.e. if a predetermined clearance is re-established at the brake after each braking action. Admittedly, for maintaining the clearance at a constant amount, a clearance chamfer is provided in the known disc brake at the front wall of the annular groove that is closer to the open end of the cylinder housing. But it has proved in practical applications that in the event of higher operating pressures such a clearance chamfer no longer suffices to keep the clearance at a constant amount. That means that the clearance becomes so small that undesired residual torque are caused at the brake.

It is therefore an object of the present invention to provide for a hydraulic actuating unit simple means wherein a predetermined clearance is always maintained at a constant amount independently of pressure and piston travel.

According to the invention in its broadest aspect, a hydraulic actuating unit of the kind referred to is characterised in that a step extending in the direction of the open end of the cylinder housing is provided at the front wall of the annular groove, the front wall being closer to the open end of the housing. It will be attained by this inventive step that the radially inner portion of the seal is pressure-responsively deformed by the step and is thus enabled to follow a larger piston travel without causing the sealing surface of the piston to slide past the sealing ring. By arranging for a small overall axial length of the step, there will result a comparatively large chamber between the step and the sealing surface of the piston into which a comparatively large amount of deformed sealing material is allowed to move.After release of the brake, the seal will draw the piston back into its initial position due to the seal being clamped between the cylinder housing and the piston. Owing to the geometry of the annular groove changed by the step, the elastic yielding travel of the seal could be increased in the event of larger piston travels, whereby the "roll-back behaviour" of seal and piston was augmented.

It will be advantageous if a portion of the front wall of the annular groove is adjacent to the bottom of the step. Part of the front wall of the annular groove will thereby be maintained so that, upon pressurisation, the radially outer area of the seal has a first axial stop in the actuating direction of the piston and, upon continued pressure increase, part of the seal will be elastically pressed into the chamber formed by the step and the peripheral surface of the piston and will re-deform upon termination of the hydraulic actuation.

Expediently, the radially outer wall of the step extends in parallel to the cylinder axis. As a result, the sealing material which flows into the step during pressure build-up of the hydraulic actuating unit is displaced preponderantly in parallel to the peripheral surface of the piston so that forces that act radially on the sealing surface of the piston are avoided to the greatest possible extent and the friction between sealing ring and piston is low, whereby the life of the sealing ring is prolonged. It is, however, likewise possible to design the bottom of the step inclined or to make it pass over into a radius.

The step permits particular ease of manufacture, if the recess of the step has a rectangular or square cross-section. If the sides of the squared cross-section of the step are 1 mm long and if the aspect ratio of the front wall of the annular groove in relation to the side wall of the step is approximately 3 :1 , there results in tests with disc brakes, in particular floating-caliper disc brakes for passenger cars and commercial vehicles, a clearance which is optimal for these brakes and which will not even be changed by the test collectives prescribed for passenger car disc brakes. Also the life of the seal will be prolonged thereby.

It will be ensured that the seal is at all times held stationarily at the front wall of the annular groove if the radial wall of the annular groove forms a truncated cone shaped peripheral surface which is enlarged towards the open end of the cylinder housing. This is true also in the event of the width of the seal being smaller in the built-in state than the distance between the front wall and the back wall of the annular groove.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a longitudinal cross-section taken through a spot-type disc brake, Figure 2 is an enlarged cross-sectional view of the sealing arrangement in the non-applied condition of the spot-type disc brake according to Figure 1, and Figure 3 is an enlarged cross-sectional view of the sealing arrangement in the applied condition of the spot-type disc brake according to Figure 1.

The spot-type disc brake illustrated in Figure 1 comprises a brake carrier 1 that is fastened to a wheel carrier or steering knuckle (not shown), on which brake carrier a brake caliper 3 is axially slidably guided which embraces the edge of a brake disc 2 from the outside. The brake caliper 3 embraces the brake disc 2 like a U and encloses a respective brake shoe 4, 5 on either side of the brake disc 2. Serving for the actuation of the brake shoes 4, 5 which are supported in the brake carrier 1 or in the brake caliper 3 is a piston 7 that is axially slidable in the cylinder bore 6 of the brake caliper 3. Via a line (not shown), the piston 7 is connected to a (also not shown) master cylinder generating the braking pressure. This line terminates in the fluid inlet (not shown) which leads into the closed end of the cylinder housing 8.

A seal 9 formed in annular groove 10 of the cylinder housing 8 is, with its radially inner cylindrical peripheral surface 11, in sealing abutment on the cylindrical peripheral surface 1 2 of the piston 7. The piston 7 projects from the open end 13 of the cylinder housing 8 and bears with its end surface 14 against the end surface 1 5 of the carrier plate 1 6 of the brake shoe 4.

The clearance of the spot-type disc brake which is not shown in the drawing is defined after actuation of the brake by the distance between the end surface 14 of the piston 7 and the end surface 1 7 of the brake caliper 3 minus the thickness of the brake disc 2 and of the two brake shoes 4, 5. The end surfaces 14, 1 5 as well as the brake shoes 4, 5 extend in parallel to the friction surfaces 18, 1 9 of the brake disc 2. The cylinder axis 20 extends vertically to the friction surfaces 18,19.

Figures 2 and 3 show only that half of the sealing arrangement 21 that is disposed above the cylinder axis 20. The radially outer wall 22 of the annular groove 10 forms a truncated-cone shaped peripheral surface which is enlarged towards the open end 13 of the cylinder housing 8 and which is confined by the back wall 24 at the closed end 23 and by the front wall 25 at the open end 13. A chamfer 26 is provided at the transition from the back wall 24 to the cylinder bore 6. At the radially outer wall 22 of the annular groove 1 0, there is designed a V-shaped groove 25 opening in the direction of the seal 9 and serving for simplification of the manufacture of the annular groove 10. Adjacent to the front wall 25 of the annular groove 10 is a step 28 which extends in the direction of the open end 13 of the cylinder housing 8.A chamfer 29 is formed at the transition from step 28 to the front wall 25. The axial width of the seal 9 is slightly smaller than the distance between the front and back walls 25, 24 of the annular groove 10.

The mode of operation of the sealing arrangement 21 upon actuation of the piston 7 is as follows: Upon hydraulic pressurisation of the piston 7, the seal 9 will be urged against the front wall 25 by both the forward movement of the piston 7 caused by hydraulic pressure and by the hydraulic pressure itself. At the same time, part of the radially inner portion of the seal 9 will be pressed elastically into the chamber of the step 28. After having overcome the clearance, the brake shoes 4, 5 will now be urged against the brake disc 2 by an amount of force depending upon the magnitude of the hydraulic pressure.If the hydraulic pressure of the brake continues to rise on account of higher brake torques being necessary, the piston 7 will move further out of the cylinder housing 8 on account of the housing expansion at the brake caliper 3, the compressibility and the wear of the brake shoes 4, 5 as well as of the brake disc 2. To prevent the piston 7 from sliding past the seal 9 due to this additional travel, the chamber formed by the step 28 affords the seal 9 an optimum storage capacity so that, as a result, the inner portion of the seal 9 will always follow elastically in the direction of movement of the piston 7. The step 28 enables a better use of the spring characteristic available. Upon termination of the braking action, the seal 9, which latter has due to its deformation an axial displacing force directed in opposition to the actuating direction of the piston 7, will drawn the piston 7 back to its initial position minus the step of adjustment, while the seal 9 re-assumes its initial form to the larger extent possible.

The piston 7 will slide past the seal 9 during braking, i.e. the disc brake will adjust, only if the piston travel determined for a brake is exceeded until the beginning of an adjustment. This determined piston travel is substantially composed of the clearance and the admissible housing expansion as well as the pad compressibility.

The sealing arrangement 21 allows spot-type disc brakes of light-weight design to be realised since particularly large expansions in the brake caliper can be compensated by this sealing arrangement.

Claims

1. A hydraulic actuating unit of the kind having at least one cylinder housing and a piston that is axially movable out of the open end of the cylinder housing, and an annular seal which is arranged in an annular groove in the cylinder housing and which seals the piston in relation to the housing, characterised in that a step (28) extending in the direction of the open end (1 3) of the cylinder housing (8) is provided at the front wall (25) of the annular groove (1 0), the front wall being closer to the open end of the housing.

2. A hydraulic actuating unit as claimed in claim 1, characterised in that adjacent to the bottom of the step (28) is a portion of the front wall (25).

3. A hydraulic actuating unit as claimed in any one of the preceding claims, characterised in that the radially outer wall of the step (28) extends in parallel to the cylinder axis (20).

4. A hydraulic actuating unit as claimed in any one of the preceding claims, characterised in that the recess of the step (28) has a rectangular crosssection.

5. A hydraulic actuating unit as claimed in claim 4, characterised in that the recess of the step (28) has a square cross-section.

6. A hydraulic actuating unit as claimed in claim 5, characterised in that the sides of the square cross-section of the step (28) are 1 mm long.

7. A hydraulic actuating unit as claimed in any one of the preceding claims, characterised in that the aspect ratio of the front wall (25) of the annular groove (10) in relation to the side wall of the step (28) amounts to about 3 :1.

8. A hydraulic actuating unit as claimed in any one or in several of the preceding claims characterised in that the radial wall (22) of the annular groove (10) forms a truncated-cone shaped peripheral surface which is enlarged towards the open end of the cylinder housing (8).

9. A hydraulic actuating unit substantially as described with reference to the accompanying drawings.