EP1585908A1

EP1585908A1 - Parking brake device and vehicle brake system provided with a parking brake device

Info

Publication number: EP1585908A1
Application number: EP04704236A
Authority: EP
Inventors: Ralf Leiter; Ralf Erben; Gregor Poertzgen
Original assignee: Lucas Automotive GmbH
Current assignee: ZF Active Safety GmbH
Priority date: 2003-01-22
Filing date: 2004-01-22
Publication date: 2005-10-19
Also published as: US20050252736A1; WO2004065814A1; US20080196984A1; DE10302357B3

Abstract

The invention relates to a parking brake device provided with a spring element (42) and with an actuating element (52) that acts upon the spring element (42). The parking brake device can be displaced by applying an actuating force (F) onto the actuating element (52) between a braking-ineffective released position and a braking-active engaged position. The invention provides that the spring element (42) is pretensioned in the released position and that the spring element (42), when passing from the released position into the engaged position, gives way once an actuating force threshold value is reached that is determined by the prestensioning.

Description

Parking brake device and vehicle brake system designed with a parking brake device

The present invention relates to a parking brake device with a spring element and an actuating element acting on the spring element, the parking brake device being displaceable between an inoperative release position and a braking-effective locking position by applying an actuating force to the actuating member.

Parking brake devices of this type are known from the prior art. They are provided in a vehicle brake system in order to provide a parking brake effect in addition to providing a braking effect of the brake system triggered by actuation of the brake pedal when the vehicle is in operation, for example initiated by actuating a hand brake lever.

Such a parking brake device is known for example from DE 197 11 382 C2. The parking brake device is provided on a brake caliper of a vehicle brake system. It comprises an actuator which can be driven rotatably by means of an electric motor and a worm gear. The actuator is drivingly coupled to a threaded sleeve, which can interact via a spring element with a brake piston of the vehicle brake system to achieve a parking brake effect. By rotating the actuating member, the threaded sleeve can be moved back and forth between the release position and the locking position. In the release position there is no interaction between the threaded sleeve and the brake piston. During the transition from the release position into the actuation position, the threaded sleeve moves towards the spring element, comes into contact with it and presses it onto the brake piston of the vehicle brake system, which then presses a brake lining onto a brake disc in order to achieve a parking brake effect. The spring element is compressed. If the brake pads and brake disc shrink due to cooling, the spring element can then expand again and, despite the shrinkage of the brake pads and brake disc, provide a sufficiently good parking brake effect.

However, the parking brake device according to DE 197 11 382 C2 has the disadvantage that a relatively long feed path of the threaded sleeve is required in order to to achieve a transition from the release position to the locking position. This is due to the fact that no interaction between the threaded sleeve and the brake piston is desired in the release position and the threaded sleeve must therefore be moved correspondingly far away from the spring element. Another reason for the long feed path is that the threaded sleeve acts on the completely relaxed spring element during the transition from the release position into the locking position and has to compress it over a relatively large distance in order to exert a sufficiently large force on the brake piston to achieve the desired parking brake effect even after the brake pads and brake disc have shrunk due to cooling. Furthermore, with increasing compression of the spring element in accordance with its force-displacement characteristic, the actuating force to be applied increases permanently, so that the electric motor has to be dimensioned powerfully in order to be able to guarantee a sufficiently long feed path.

In contrast, it is an object of the present invention to provide a parking brake device of the type described at the outset, which ensures a reliable parking brake effect with reduced actuation force and a shorter feed path, in particular even after the brake pads and brake disc have shrunk due to cooling.

This object is achieved by a parking brake device with a spring element and an actuating element acting on the spring element, the parking brake device being displaceable between a release position which has no braking action and a locking position which is effective when braking, by applying an actuating force to the actuating member, the spring element also in the position shown in FIG

Release position is biased and the spring element noticeably yields on transition from the release position to the locking position only when an actuation force threshold value determined by the preload has been reached.

The invention provides that the spring element is already under tension in the release position. If the actuating element then acts on the prestressed spring element during the transition from the release position into the actuating position, this initially behaves similarly to a rigid element, ie there is no or only slight yielding. The infeed movement is thus transmitted directly to the brake piston and from there to the brake pads. Only when the actuation force threshold value predetermined, for example, by the degree of the preload is reached, does the spring element yield and is subsequently compressed. That’s what happens to a kink in the force-displacement characteristic of the entire arrangement. The actuating force required for a further infeed movement no longer increases to the same extent as previously in the case of rigid or approximately rigid behavior of the spring element.

The actuating force threshold value is expediently chosen such that immediately before it is reached a force that is sufficient for a desired parking brake effect is exerted on the brake piston and by this on the brake lining. If the actuating force threshold value is then reached, essentially only the spring element is compressed, which, however, is due to the force-displacement characteristic of the spring element with less effort per infeed path than immediately before the actuating force threshold value is reached. This compression of the spring element can then later e.g. in the event of cooling-related shrinkage of various components of the vehicle brake system, such as brake pads and brake disc, can be used to compensate for the shrinkage by the spring element expanding again.

If the actuating force is applied by an electric motor, for example in the case of an electromotive parking brake, the invention makes it possible to use an electric motor which is less powerful and therefore less expensive than, for example, the prior art described at the outset.

In order to be able to achieve the above-mentioned behavior of the spring element with simple structural measures, it is provided in a further development of the invention that the spring element is enclosed in a spring chamber under prestress, a pressure plate being arranged in one end of the spring element Spring chamber is displaceable under deformation of the spring element. The actuator presses on the pressure plate. However, this only yields significantly under compression of the spring element when the actuating force threshold value is reached, i.e. the value of the actuating force at which the spring element can just be further compressed starting from its current preload state.

In this connection it can further be provided according to the invention that the spring chamber is formed in a hollow cylinder. In this variant of the invention, the hollow cylinder can be open on one side, the spring element and the pressure plate then being able to be introduced through the opening. Furthermore, it can be provided for this variant of the invention that the movement of the pressure plate and / or the Actuator is limited on one side within the spring chamber. Such a limitation can be realized according to the invention by means of a locking ring fixed in the hollow cylinder.

Basically, there are a multitude of options when choosing the spring element, each of which requires different structural configurations. Thus, the spring element can be designed according to the invention as a compression spring or as a tension spring. Furthermore, the spring element can be formed by a spiral spring or alternatively can comprise an elastomer body. Equally, however, it is also conceivable to use a plate spring package or a spring arrangement made up of several spring components, such as springs connected in parallel or in series.

It was explained above that when the parking brake device is activated, the pressure plate interacts with the actuator. This presupposes that the pressure plate and the actuator are formed separately from one another. To further simplify the arrangement according to the invention, a further development of the invention provides that the pressure plate and the actuating member are integrally formed. For example, the pressure plate can be formed as an end flange on the actuating element which is arranged in the spring chamber.

In one embodiment, the parking brake device according to the invention can be provided directly on a brake caliper of a hydraulic vehicle brake system. Within the scope of this embodiment, it is further possible according to the invention that the hollow cylinder is formed by a brake piston of the vehicle brake system or a spring bushing received in the brake piston. In this embodiment of the invention, the actuating force is transmitted directly to the brake piston of the brake system and from there via the brake lining to the brake disc of a wheel to be locked.

As an alternative to this, it is also possible for the actuating element to comprise a cable pull engaging the pressure plate and for another cable pull to be provided on the hollow cylinder. One of the cables is then connected to the actuating member of the parking brake device, for example the hand brake lever. The other cable interacts with the brake piston of the brake system.

The invention further relates to a vehicle brake system, in particular a hydraulic vehicle brake system, with a brake provided on a brake caliper. piston, which is displaceably guided in a pressure chamber for displacement of a brake lining in the direction of a brake disc, the vehicle brake system being designed with a parking brake device of the type described above.

In the following the invention is explained by way of example with reference to the accompanying figures. They represent:

1 shows a sectional view of a first exemplary embodiment of the area near the brake caliper of a vehicle brake system according to the invention;

2 shows a view corresponding to FIG. 1 of a second exemplary embodiment according to the invention;

3 shows a sectional view of part of a vehicle brake system according to the invention, which is designed with a cable pull, and

Fig. 4 shows a force-displacement characteristic of the parking brake device according to the invention.

1 shows a partial sectional view of the area near the brake caliper of a vehicle brake system according to the invention with a locking device in its release position. 1 shows a housing 10 with an opening 12 and an opening 14. A brake disk 16, which is only partially shown, projects into the opening 12 and is coupled to a wheel of the vehicle to be braked or locked. A brake lining 20 and 22 is arranged on the left and right of a radial end region 18 of the brake disk 16. The brake pad 20 is attached to the inside 26 of the housing 10 via a stabilizing back plate 24. The brake pad 22 is attached via a further stabilizing back plate 28 to the end face 30 of a brake piston 32 which is displaceably guided in the housing 10 along an axis A.

The housing 10 is floating relative to the brake disc 16. This makes it possible for the housing 10 to move to the right in FIG. 1 when the brake pad 22 moves against the brake disc 16 and when the brake pad 22 engages the brake disc 16, so that the brake pad 20 also comes into contact with the brake disc 16 arrives. This causes the Brake disc 16 is clamped between the brake pads 20 and 22 to act as a brake.

The brake piston 32 is hollow-cylindrical and is open on one side. It has a circumferential groove 34 on its outer circumferential surface, into which a sealing ring 36 is inserted. The sealing ring 36 lies against an inner circumferential surface 38 of the housing 10 in a fluid-tight manner. The brake piston 32 is thus guided in a fluid-tight manner in the housing 10 and encloses a hydraulic fluid pressure chamber 40 with the latter. By pressing hydraulic fluid into the pressure chamber 40, the brake piston 32 can be moved in the axial direction in the housing 10 in a known manner. The brake pads 20 and 22 can press on the brake disc 18 and brake it, as described above. By subsequently draining hydraulic fluid out of the hydraulic fluid pressure chamber 40, this braking effect can be canceled again.

In its interior, the hollow-cylindrical brake piston 32 has a compression spring 42. This abuts the end face 30 of the brake piston 32 at one end. With its other end, the compression spring 42 bears against a pressure plate 44 which, together with the brake piston 32, delimits a spring chamber 45. The pressure plate 44 is received in the axial direction in the interior of the brake piston 32. The displacement movement along the axis A is, however, limited by a locking ring 46, which is attached in a circumferential groove 48 in an inner circumferential surface 50 of the brake piston 32.

An actuating element 52 projects into the hydraulic fluid pressure chamber 40 in the axial direction and can be moved into the interior of the brake piston 32 via a not shown actuating element. The actuating member 52 is dimensioned such that it can be passed through the locking ring 46 and can engage with its end face 54 on the pressure plate 44.

The compression spring 42 is held in a partially compressed state via the pressure plate 44 and the locking ring 46, which differs significantly from a completely relaxed state of the spring. One also speaks of a “tethered spring”. In this partially compressed state, the compression spring 42 cannot be compressed in the spring chamber 45 until the compressive force acting on it reaches an amount which corresponds to the instantaneous point in the force-displacement Characteristic of the Compression spring 42 corresponds. Only when this force threshold value is reached does the compression spring 42 yield and can be compressed.

The mode of operation of the brake system according to the invention will be explained below with reference to FIGS. 1 and 4. If the parking brake device is activated, for example for parking the vehicle, by actuating the parking actuating element (not shown), the actuating member 52 is displaced in the axial direction onto the pressure plate 44 by applying an actuating force F generated, for example, by an electric motor. In Fig. 4, the point at which the infeed movement begins is designated by Pi. As soon as the end face 54 of the actuator 52 engages the pressure plate 44 with a sufficiently large actuating force F, the brake piston 32 moves in the housing 10 and brings the brake pads 20 and 22 into contact with the brake disc 18. At the beginning of this displacement movement of the brake piston 32 is Actuating force F is not large enough to further compress the compression spring 42. The compression spring 42 behaves rather like a rigid element in this operating phase. In order to bring the brake pads 20 and 22 into brake-effective contact with the brake disc 18 and to press them sufficiently strongly together, a permanent increase in the actuating force F is required. 4 increases until it reaches point P ₂ . At point P ₂ , the actuating force reaches the threshold value F _s , at which the compression spring 42 no longer behaves essentially rigidly, but can be compressed further beyond its prestressed state. The amount of the actuating force threshold value F _s is selected such that when it is reached, the brake pads 20, 22 press so hard on the brake disc 18 that a reliable parking brake effect is ensured. If the actuating force F is then increased further, essentially only the compression spring 42 is compressed, ie the force-displacement characteristic curve according to FIG. 4 is essentially determined by the behavior of the compression spring 42. For example, the actuation force threshold value F _s lies in Range between 10 and 15 kN, preferably at 13 kN.

To achieve a certain infeed path ds starting from point P ₂ up to a fictitious point P, only a relatively small increase ΔF in the actuating force F is required. The corresponding infeed movement is essentially used to compress the compression spring 42 to such an extent that it presses the brake piston 32 and can ensure a sufficiently strong parking brake effect if the brake pads 20 and 22 heated during operation of the vehicle and the brake disk 18 after parking and in the park cool the condition of the vehicle and then shrink. The cooling-related shrinkage of the brake pads 20 and 22 and the brake disc 18 can then be compensated for by expansion of the compression spring 42, the force with which the brake pads 20 and 22 press on the brake disc 18 is at least as large as the force threshold value F _s ,

Fig. 2 shows a second embodiment of the invention. To avoid repetition and in favor of a simple description, only the differences from the embodiment according to FIG. 1 will be described. The same reference numerals are used for this as in the description of FIG. 1, but preceded by the number “.

The embodiment according to FIG. 2 differs from the embodiment according to FIG. 1 essentially in that the spring chamber is not formed directly in the interior of the brake piston 132. Rather, a spring bushing 156 is inserted into the interior of the brake piston 132 and bears against the end face 130 thereof. The spring bushing 156 is hollow and is open on one side. The actuator 152 is inserted into its opening 158. The actuator 152 has at its left end in FIG. 2 a flange 160 which acts like the pressure plate 44 from FIG. 1 and is in contact with the pressure spring 142. The spring bushing 156 has a collar 162 at its opening 158, which limits the movement of the actuating member 152.

In operation, the embodiment according to FIG. 2 functions as explained above with reference to the embodiment according to FIG. 1 and with reference to FIG. 4. This means that the compression spring 142 initially behaves like a rigid element and only yields when an actuating force threshold value F _{s is reached} .

The embodiment according to FIG. 2 has the advantage of a simplified structural design compared to that according to FIG. 1, in particular because of the integral design of the actuator 152 and flange 160 acting as a pressure plate. It is thus possible to prefabricate the spring bushing 156 and the actuator 152 to form an assembly and to insert them into the interior of the brake piston 132 during assembly without having to take any further measures, such as, for example, attaching a locking ring. 3 shows part of a further embodiment of a parking brake device according to the invention. This embodiment is used in the case of a parking brake device which can be operated with a cable pull. For the description of this embodiment, the reference numerals used above are again used, but preceded by the number “2”.

In this embodiment, a spring assembly 266 is provided, which is arranged between two cables 268 and 270. The cable 268 is fastened at one end to a spring bushing 256 and coupled at its end (not shown in FIG. 3) to the actuating member of the parking brake device. The cable pull 270 is fastened at one end to the pressure plate 244 and coupled at its end (not shown in FIG. 3) to the brake piston of the vehicle brake system. The spring bushing, similar to that shown in FIG. 2, comprises a compression spring 242, which is prestressed via a pressure plate 246 and a locking ring 246.

When the actuating member of the parking brake device is actuated, the compression spring 242 initially acts like a rigid element due to its pretension and transmits the actuating force F introduced via the cable 268 to the cable 270 without deformation. However, as soon as the actuating force reaches and exceeds the actuating force threshold F _s , the compression spring 242 yields and is compressed without the cable 270 being moved accordingly. The compression spring 242 thus stores part of the actuating force F, so that it can later be released for a further infeed movement when required, for example due to a shrinkage of brake pads and brake disc, with the compression being reduced.

It should be pointed out that a plurality of spring assemblies 266 according to FIG. 3 can also be connected in series in order to achieve a sufficient spring action.

The invention shows a possibility of how a parking brake device can be realized with structurally simple means, which can be operated with a relatively low actuating force and yet ensures a reliable parking braking effect. This applies in particular if the brake pads and brake disc of the vehicle brake system contract when the vehicle is parked after a journey due to cooling.

Claims

Expectations

1. Parking brake device with a spring element (42; 142; 242) and an actuator acting on the spring element (42; 142; 242)

(52; 152; 270), wherein the parking brake device can be shifted between an inoperative release position and a braking effective locking position by applying an actuating force (F) to the actuating element (52; 152; 270), characterized in that the spring element (42; 142; 242) is pretensioned in the release position and that the spring element (42; 142; 242) only noticeably yields on transition from the release position into the locking position when an actuating force threshold value (F _s ) determined by the pretensioning is reached.

2. Parking brake device according to claim 1, characterized in that the spring element (42; 142; 242) is enclosed under prestress in a spring chamber (45; 145; 245), a pressure plate (44; 160; 244) at one end of the spring element. is arranged, which is displaceable in the spring chamber (45; 145; 245) while deforming the spring element (42; 142; 242).

3. Parking brake device according to claim 2, characterized in that the spring chamber (45; 145; 245) is formed in a hollow cylinder.

4. Parking brake device according to claim 2 or 3, characterized in that the movement of the pressure plate (44; 160; 244) o- and / and the actuator (52; 152; 270) within the spring chamber (45; 145; 245) limits on one side is.

5. Parking brake device according to claim 4, characterized in that the limitation is provided by means of a securing ring (46; 246) fixed in the hollow cylinder.

6. Parking brake device according to one of the preceding claims, characterized in that the spring element (42; 142; 242) comprises a compression spring, a tension spring, a spiral spring and / or an elastomer body.

7. Parking brake device according to one of the preceding claims, characterized in that the pressure plate (160) and the actuating member (152) are integrally formed.

8. Parking brake device according to one of the preceding claims, characterized in that the parking brake device is provided on a brake caliper of a hydraulic vehicle brake system.

9. Parking brake device according to claim 8, characterized in that the hollow cylinder of a brake piston (32)

Vehicle brake system or a spring bushing (156) accommodated in the brake piston (132).

10. Parking brake device according to one of claims 1 to 9, characterized in that the actuating member (270) on the pressure plate

(244) engaging cable pull (270) and that a further cable pull (268) is provided on the hollow cylinder (256).

11. Vehicle brake system, in particular hydraulic vehicle brake system, with a brake piston (32; 132) provided on a brake caliper, which for displacement of a brake lining (22; 122) on a brake disc (16; 116) is displaceably guided in a pressure chamber (40; 140) is characterized by a parking brake device according to one of the preceding claims.