GB2030651A

GB2030651A - Brake Actuators

Info

Publication number: GB2030651A
Application number: GB7931474A
Authority: GB
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co OHG
Priority date: 1978-09-20
Filing date: 1979-09-11
Publication date: 1980-04-10
Also published as: IT7925854A0; FR2436892B1; SE7907474L; IT1123237B; DE2840836A1; SE438361B; FR2436892A1; GB2030651B; DE2840836C2; ES245676Y; ES245676U

Abstract

A vehicle brake actuator including a fluid-pressure actuable piston (11) for pre-loading a spring (7) via a spring cup (5), the piston (11) being connected to an operating tappet (18) via an engageable and disengageable clutch (21, 22, 23). The piston (11) is slidably guided in a cup-shaped component (2) which is secured to the actuator housing (1), and the operating tappet (18) extends into a recess (3) of the component (2). Further brake applying members (not shown) may be arranged in the recess (3) for actuation by the operating tappet (18), thus reducing the overall length of a brake actuating arrangement. <IMAGE>

Description

SPECIFICATION Brake Actuators This invention relates to an actuator including a fluid-pressure-actuatable piston for pre-loading a spring, which piston is connected to an operating tappet via an engageable and disengageable clutch. An actuator of this type for brakes is known from German published patent application DE-OS 2,714,472.

In the known brake actuator the pre-loaded spring bears directly against the pre-loading piston, i.e., the piston is arranged in front of the spring. Also in front of the brake actuator is a fluid-pressure-actuatable brake-applying member which is also adapted to be actuated by the brake actuator which, however, has normally no influence on the member, i.e. as long as the preloading piston is subjected to pressure.

An essential disadvantage of the known arrangement is its large size, in particular its length. Thus it requires much mounting space.

Further, part of the fluid-pressure-actuatable brake-applying member is directly formed at the housing of the brake actuator. Since in various vehicles such a brake-applying member is not necessary and a simple brake rigging -- possibly with other additional devices - is required instead, such cases always require the provision of a complete special brake actuator for the individual vehicle. The main disadvantage is that a plurality of such complete units have to be held in stock as replacement parts.

According to the present invention there is provided an actuator including a housing; a coiled spring arranged within the housing; a spring cup extending into the spring; a fluid-pressure actuable piston for pre-loading the spring via the spring cup, and an operating tappet, the preloading piston being connected to the tappet via an engageable and disengageable clutch, and wherein the pre-loading piston is slidably guided in a cup-shaped component which is secured to the housing and extends into the spring cup whereby to delimit a recess in the spring which is open to the exterior of the housing and in which further members actuable by the operating tappet can be arranged, the operating tappet extending out of the pre-loading piston and projecting into the recess.

Embodiments of the present invention will now be described with reference to the accompanying drawings, in which Fig. 1 is a sectional view of a first embodiment of spring pre-loading means; Fig. 2 shows a second embodiment of spring pre-loading with a brake rigging comprising an adjusting device and with a hydraulically disengageable clutch; Fig. 3 shows the spring pre-loading means of Fig. 1 with a dual-circuit brake-actuating arrangement with an adjusting device.

The actuator illustrated in Fig. 1 has a housing 1 into which a cup-shaped component 2 secured to the housing extends, such that an opening or recess 3, which is open towards the outside is formed. Arranged in the housing 1 is a spring cup 5 which is slidable on the cup-shaped component 2 and which is formed by welding three elements together. Sliding elements 6 are provided between the spring cup 5 and the cup-shaped component 2 for greater ease of slidability. A pre loadable spring 7 surrounding the spring cup 5 is engaged between an end face 1' of the housing 1 and the spring cup 5.

The opening 3 in the cup-shaped component 2 is bounded by a partition wall 8. Formed between the partition wall 8 and bottom element 9 of the spring cup 5 is a cylindrical bore 10 in the cupshaped component 2. A pre-loading piston 11 is sealed to and slidably guided in the bore 1 0. An operating chamber 12, which is defined between the pre-loading piston 11 and the partition wall 8, is connectible with a fluid pressure source, such as an accumulator (not shown), via a channel 13 and a port 14. A channel 13' provides venting of the operating chamber 12 via a valve 1 5. On its end remote from the operating chamber 12, the pre-loading piston 11 has an extension 1 6 bearing against the bottom element 9 of the spring cup 5. Openings 17 permitting volume compensation are provided in the bottom element 9.

An operating tappet 1 8 is sealed to and slidably guided through the partition wall 8 and the pre-loading piston 11 as well as through the bottom element 9 of the spring cup 5 and the end face 1' of the housing 1. Provided between the pre-loading piston 11 and the operating tappet 1 8 is an engageable and disengageable clutch in the form of a ball locking gear. For this purpose, the operating tappet 1 8 is hollow and houses axially movably therein a locking member 1 9 which is pre-loaded in the direction of the end face 1' by spring 20 and extends out of the operating tappet 1 8 in that direction.The locking member 1 9 has on its periphery ramp-like recesses 21 which ascend in the direction of the opening 3 and serve to house locking balls 22. In this arrangement, the locking balls 22 extend through radial openings in the operating tappet 18.

In a suitable position of the operating tappet 1 8 relative to the pre-loading piston 1 the locking balls 22 are urged into recesses 23 in the pre-loading piston 11 as a result of which the latter is held in positive engagement with the operating tappet.

Arranged at the end of the locking member 19 extending out of the housing 1 is a flexible boot 24 which has its other end secured to the end face 1' of the housing 1. Also secured to the end face 1' of the housing is a bearing bracket 25 which supports a pivotable lever 26. The lever 26 bears upon the locking member 19 and can be operated, i.e., pivoted, for example by means of a Bowden cable or the like, in order to disengage the clutch 21, 22, 23 by the locking member 19 being urged into the operating tappet 1 8 against the springs 20. On its end close to the opening 3, the operating tappet 1 8 has a cavity 27 in which further brake-applying members adapted to be inserted into the opening 3 can be held.

Moreover, the operating tappet 18 is adapted to bear against the end face 1' of the housing 1 by means of a step 28 in opposition to the brakeapplying direction.

If the actuator is inoperative, the operating chamber 12 is unpressurized and the clutch 21, 22, 23 is disengaged all parts being in their illustrated positions. A bearing force which may thereby act in the cavity 27 is taken up by the housing 1 directly through the step 28. If fluid under pressure is introduced into the operating chamber 12 through the channel 1 3 and the port 14, the pre-loading piston 11 will be displaced to the left. Thereby it acts upon the spring cup 5 as a result of which the spring 7 is loaded. When the pre-loading piston reaches a position in which the recesses 23 approach the area of the locking balls, these balls are urged radially outwardly into the recesses 23 via the ramps 21.In this arrangement, the springs 20 shift the locking member 1 9 axially to the left so that the locking balls 22 are prevented from returning to their previous position radially inwardiy. Thus the operating tappet 1 8 is in positive locking arrangement with the pre-loading piston 11.

If the pressure in the operating chamber 12 is reduced, the pre-loaded spring 7 will shift the piston 11 and thereby the operating tappet 1 8 to the right. The position of the operating tappet 1 8 can then be controlled by the pressurized fluid in the operating chamber 12. In the event of failure of the fluid source, however, the pre-loaded spring 7 acts fully upon the operating tappet 1 8 urging it to the right. In this event, the wheel brakes conventionally connected to the actuator are applied and the vehicle cannot be moved further. In order to be able to remove the vehicle from a danger area if such a situation occurs, first the actuator has to be released. For this purpose, the lever 26 is operated and the locking member 19 is shifted against the springs 20.Thus the locking balls 22 reassume their radially inward position so that the pre-loading piston 11 is disengaged from the operating tappet 1 8 and all parts return to their illustrated positions.

In the embodiment of Fig. 2, the actuator illustrated is substantially the same as that of Fig.

1. The locking member 19 is provided with a piston 29 which is sealed to and guided in the operating tappet 1 8. In this embodiment the clutch 21, 22, 23 for releasing the pre-loaded spring 7 is disengaged by hydrostatic pressure.

Further, the embodiment of Fig. 2 includes in the opening 3 a brake rigging with an adjusting device. In this arrangement, the brake rigging comprises a bolt 30 situated in the cavity 27 of the operating tappet 18 and carrying on its end remote from the cavity 27 an adjusting thread 31.

Arranged on the adjusting thread is a push rod 32 to which the wheel brakes can be connected.

Between the push rod 32 and the operating tappet 18 is an adjusting ring 33 which surrounds the bolt 30 and includes on its surface an oblique groove 34 into which a pin 35 engages. By means of a freewheel 36 the adjusting ring 33 is allowed to rotate relative to the bolt 30 in one direction only. The groove 34 is of such width that axial movements within the normal clearance do not cause turning of the adjusting ring. If the clearance is overcome because of wear, the adjusting ring 33 will cause turning of the thread 31 so that the brake rigging is elongated in the sense of effecting an adjustment.

The brake rigging is arranged in a holding device 38 which in turn is secured in the opening 3 of the actuator. In this arrangement, a spring 39 bearing against the holding device 38 preloads the pin 30 through a bearing plate 41 and a thrust bearing 40 into the cavity 27 of the operating tappet. Also secured to the holding device 38 and to the push rod 32 is a flexible boot 42 which prevents the ingress of contaminants.

In the embodiment of Fig. 3, a cylinder 45 which is open towards the operating tappet 1 8 is arranged fast in the opening 3 of the actuator. The cylinder 45 accommodates a piston 46 and a piston 47 arranged in tandem. With its end face close to the operating tappet 18, the piston 46 forms a boundary for a first pressure chamber 48 which is connectible with a first brake circuit.

Defined between the piston 46 and 47 is a second pressure chamber 49 which is connectible with a second brake circuit. On its end remote from the second pressure chamber 49, the piston 47 has a cavity 27'. The cavity 27' receives and supports a brake rigging which corresponds substantially to that of Fig. 2.

The actuator is mostly used as a safety device or for actuation of the parking brake only, whereas the service brake is a dual-circuit fluidpressure-actuated brake. Thus the actuator is normally loaded by pressurized fluid fed into chamber 12, so that the operating tappet 28 exerts no influence on the piston 46 and 47. The brake is applied by the supply of pressurized fluid into pressure chambers 48 and 49. In the event of failure of a brake circuit, the brake continues receiving the full brake force from the other brake circuit, either by pressurized fluid acting on the piston 47 directly and the piston 46 bearing against the operating tappet 1 8 in the opposite direction, or by pressurized fluid acting on the piston 46 and mechanically on the brake rigging via the piston 47.

If the pressure in chamber 12 is reduced or fails, the spring pre-loading means is activated as a result of which the operating tappet is urged to the right. It thereby acts mechanically upon the brake rigging via the piston 46 and 47. In the event of pressurized fluid not being available for chamber 12, the actuator can be released by lever 26 as described with reference to Fig. 1.

The two embodiments shown in Figs. 2 and 3 are of very short overall length because the space within the pre-loading spring 7 accommodates further elements.

The elements of the brake actuator are combined in a very confined space and a very short distance is achieved between the two bearing areas, which distance is not determined by the length of the pre-loaded spring. On the contrary, the major part of the space within the spring can be made use of for accommodating further brake-applying members. Various types of brake-applying members can be fitted into the recess without difficulty. This can be done without the need to dismantle the actuator which would entail release of the pre-loaded spring which is, as a rule, very strong.

Claims

1. An actuator including a housing; a coiled spring arranged within the housing; a spring cup extending into the spring; a fluid-pressure actuable piston for pre-loading the spring via the spring cup, and an operating tappet, the preloading piston being connected to the tappet via an engageable and disengageable clutch, and wherein the pre-loading piston is slidably guided in a cup-shaped component which is secured to the housing and extends into the spring cup whereby to delimit a recess in the spring which is open to the exterior of the housing and in which further members actuable by the operating tappet can be arranged, the operating tappet extending out of the pre-loading piston and projecting into the recess.

2. An actuator as claimed in claim 1 in combination with a brake rigging arranged within the recess and bearing against the operating tappet, part of the brake rigging extending out of the recess being connectible with brakes, and including an adjusting device arranged substantially within the recess.

3. An actuator as claimed in claim 1 in combination with a brake rigging with an adjusting device, and a cylinder, arranged within the recess, which is open towards the operating tappet and accommodates a first piston, the first piston being actuatable by pressurized fluid and/or the operating tappet, and the brake rigging with the adjusting device bearing against the end of the first piston remote from the operating tappet.

4. An actuator as claimed in claim 3 wherein the cylinder accommodates between the first piston and the operating tappet a second piston which is actuatable in the direction of the first piston by the pressure of a second brake circuit, whereas a first brake circuit is connected to a pressure chamber defined between the first piston and the second piston.

5. An actuator as claimed in any one of the preceding claims, wherein the spring cup is slidably guided on the cup-shaped component.

6. An actuator as claimed in any one of the preceding claims, wherein the spring cup bottom is penetrated by the operating tappet and the operating tappet also extends out of the housing on the side thereof opposite to the recess.

7. An actuator as claimed in claim 7, wherein the pre-loading piston is sealed to and slidably guided in a bore of the cup-shaped component the bore being open towards the spring cup bottom and wherein the pre-loading piston has an extension bearing against the spring cup bottom and is an annular piston which is penetrated by the operating tappet.

8. A vehicle brake actuator substantially as herein described with reference to and as illustrated in Fig. 1, Fig. 2, or Fig. 3 of the accompanying drawings.