A SERVICE DISC BRAKE FOR A HEAVY VEHICLE

TECHNICAL FIELD

The invention relates to a service disc brake for a heavy vehicle according to the preamble of claim 1.

The invention is applicable on different type of vehicles. Although the invention is primarily described in connection with trucks, the service disc brake according to the invention can also be used for example in other heavy vehicles such as buses, wheel loaders, articulated haulers, and excavators.

BACKGROUND OF THE INVENTION

In service disc brakes for trucks which brakes have a brake disc and inner and outer brake pads, an even clamp force distribution on the inner and outer pads and a running clearance between the pads and the brake disc are desired. In order to avoid the pads from dragging and leaning against the brake disc there must be a certain axial clearance between the pads and the brake disc when the brake force is removed and the brake disc is not to be braked. Furthermore, the running clearance must be present on the both sides of the brake disc. In trucks, the service disc brake can have a fixed brake caliper and the brake force can be created on one side of the brake disc. Thus, such a service disc brake needs some arrangement for distributing the forces evenly on both the inner and outer pads and for ensuring the running clearance to be present.

According to prior art, service disc brakes having a fixed brake caliper can be designed with either a sliding brake disc or a bending brake disc so as to obtain a even clamp force distribution and the requisite running clearance between the brake pads and the brake disc. However, both a bending disc and a sliding disc have large disadvantages. A bending disc involves undesired internal stress in the brake disc and in other brake components connected thereto. This in turn can cause damage to the brake. A sliding disc results in a more complicated brake design and is further less reliable due to potential jamming caused by corrosion or dirt. Furthermore, there is a risk a rattling noise arises in

the brake. The noise is caused by the requisite radial play between the brake disc and the component arranged to support the brake disc. Wear or inadequate dimensional tolerance distribution of the brake disc and the support component can increase the rattling noise.

SUMMARY OF THE INVENTION

An object of the invention is to provide a service disc brake of the kind referred to in the introduction where at least some of the problems of such prior art devices discussed above is reduced to a substantial extent.

The object is achieved by a service brake according to claim 1.

By the provision of a third piston and the closed space containing a hydraulic fluid, which space connects the second and third pistons, both first and second pistons can be displaced and, thus, both first and second pads can be brought into contact with the brake disc without the need of displacing or bending the brake disc. When applying a brake force on the first pad by means of the braking actuator, a counterforce is created on the third piston which force is transmitted to the second piston by means of the hydraulic fluid and further to the second pad and the brake disc. Hence, during braking, the clamp force can be evenly distributed on the pads arranged on different sides of the brake disc. Once the brake force is removed the first and second pads will centre equally relative to the brake disc with substantially the same running clearance on both sides of the brake disc between the brake disc and the first and second brake pads.

The service disc brake according to the invention is also very suitable to be provided with means for adjusting the running clearances so as to compensate for wear of the pads. The invention enables the disc brake to be designed for adjustment of the axial clearance on both sides of the brake disc by operation of one adjustment means only.

The invention relates also to a vehicle comprising a service disc brake according to the invention.

Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

In the drawings:

Fig. 1 is a schematic illustration of a disc brake according to the invention, and

Fig. 2 is a schematic illustration of a variant of the disc brake in figure 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In figure 1 a service disc brake 1 according to the invention is illustrated. Such a service brake is used for retardation of a vehicle during normal operation of the vehicle, i.e. during driving of the vehicle. By use of the service brake the velocity of the vehicle can be decreased. The service brake is preferably arranged at one or more wheels of the vehicle to brake the wheels. The service disc brake 1 comprises a brake disc 2 which is arranged for rotational motion relative to a brake caliper 3 provided with a first brake pad 4 and a second brake pad 5. The first and second brake pads are 4, 5 arranged on opposite sides of the brake disc to be brought into contact with the brake disc and thus brake the rotational motion of the disc. A first displaceable piston 6 and a second displaceable piston 7 are arranged in the caliper 3 to act on the first brake pad 4 and the second brake pad 5, respectively, so as to bring the pads 4, 5 into contact with the brake disc 2 and transmit the requisite brake force. Each piston 6, 7 is displaceable to and fro in the axial direction along a geometrical line 8, and preferably the first and second pistons 6, 7 are displaceable along the same geometrical line 8. Certainly, two or more of the first and second pistons could be used on each side of the brake disc.

The service disc brake 1 further comprises a third displaceable piston 9. The third piston 9 is suitably arranged, for example in the caliper 3, for displacement motions to and fro in the axial direction along for example the same geometrical line 8 as the first piston 6. In accordance with the invention the second piston 7 and the third piston 9 are connected to each other via a closed space 10 containing a hydraulic fluid. The term hydraulic fluid is meant to comprise different liquid state fluids. The hydraulic fluid is preferably any

hydraulic oil, silicon oil or any other suitable high temperature oil. The closed space 10 can be constituted by a hydraulic line 11 arranged inside the brake structure or as a piping 11 arranged outside the brake structure. Due to the risk for heating the hydraulic fluid, the closed space 10 is preferably arranged in a well ventilated part of the brake 1. A heat shield (not illustrated) may be required to protect the fluid to be heated by hot brake components or other adjacent components.

In the embodiment illustrated in figure 1, an actuator 12 for braking the brake disc is arranged between the first piston 6 and the third piston 9. The braking actuator 12 is arranged to act on the first piston 6 and the third piston 9 for displacement of the first piston 6 towards the brake disc 2 and for displacement of the third piston 9, preferably in the opposite direction, so as to displace the second piston 7 towards the brake disc 2 by means of the hydraulic fluid in the closed space 10.

The braking actuator 12 may comprise a pivotable lever 13 arranged between the first piston 6 and the third 9 piston. The lever 13 may have a first portion 14 for creating a force on the first piston 6 and a second portion 15 for creating a corresponding counterforce on the third piston 9 during pivot motion of the lever 13. The lever 13 can be actuated for example by an air cylinder 16 or an electric motor. The force applied on the first piston 6 generates an equally sized counterforce on the third piston 9. In an alternative embodiment the requisite force can be transmitted from a motor or an air cylinder to the pistons 6, 9 by means of another equipment, such as a wedge or similar, instead of using the lever 13.

Since the pressure of the hydraulic fluid is the same throughout the fluid in the closed space 10 the size of the force on the second piston 7 can be the same as on the first 6 and third 9 pistons provided that the same size of the end surface exposed to the hydraulic fluid is chosen for the second and third pistons. In the embodiment illustrated in figure 1 the size of the end surface 17 of the third piston 9 is substantially equal to the size of the end surface 18 of the second piston 7. In another embodiment, the end surfaces 17, 18 can be slightly different for fine adjustment of the brake.

The service disc brake 1 comprises a first means 19 for adjusting a first axial clearance 20 between the brake disc 2 and the first pad 4. The first adjustment means 19 preferably comprise a screw mechanism 21 arranged on the first piston 6. By such a screw

mechanism 21 the position of the first piston 6 relative to the brake disc 2 can be adjusted so as to compensate for wear of the first pad 4 and thereby keep the running clearance 20 substantially unchanged. By adjusting the position of the screw 21 relative to the piston 6, the distance from the rear surface 22 cooperating with the first portion 14 of the lever 13 to the front surface 23 of the piston 6, i.e. the total length of the piston 6, can be varied.

The disc brake 1 comprises also a second means 24 for adjusting a second axial clearance 25 between the brake disc 2 and the second pad 5 by adjusting the position of the second piston 7 relative to the brake disc 2. According to the embodiment illustrated in figure 1, the second adjustment means 24 comprises a fourth displaceable piston 25 which is connected to the second 7 and third 9 pistons via the closed space 10 containing the hydraulic fluid. The second adjustment means 24 further comprises a member 26, such as a screw mechanism arranged on the fourth piston 25, for adjusting the position of the second piston 7 by adjusting the position of the fourth piston 25 relative to the closed space 10. Thus, the position of the second piston 7 can be adjusted so as to compensate for wear of the second pad 5 and thereby keep the running clearance 25 substantially unchanged.

Each of the first and second pistons 6, 7 can be designed with a total compensation displacement length for example in the size of 20 mm, and the stroke length (axial clearance) can be in the size of 2 mm.

According to the embodiment illustrated in figure 2, the fourth piston is not needed and instead the second adjustment means 24b comprises a member 26b, such as a screw mechanism arranged on the third piston 9, for adjusting the position of the second piston 7 by adjusting the position of the third piston 9 relative to the closed space 10. In this embodiment the adjusting member 26b is provided with a counter portion 27 of the third piston 9, which counter portion 27 cooperates with the second portion 15 of the lever 13.

In all embodiments mentioned above the first adjustment means 19 and the second adjustment means 24, 24b can be coupled to each other in order to automatically adjust the second axial clearance 25 at the same time as the first axial clearance 20 is adjusted or vice versa. This is illustrated in figure 1 where the screw mechanism arranged on the first piston 6 has a first gear wheel 28 connected to a second gear wheel 29 of the screw mechanism arranged 26 on the fourth piston 25. This implies that if the first gear wheel 28

(viewed in a direction from the third piston towards the first piston) is rotated counter clockwise, the second gear wheel 29 (viewed in the opposite direction) is also rotated counter clockwise. Thus, both the first piston 6 and the second piston 7 will be displaced towards the brake disc 2.

The adjustment of the running clearance 20, 25 can be automatically or manually performed with the use of a further mechanical device and/or electrical device (not illustrated) for activation of the first adjustment means 19 and/or the second adjustment means 24, 24b. For automatic adjustment of the running clearance any kind of pad wear sensing equipment is preferably used together with the adjustment means described herein.

All pistons have to be supported and guided, and the pistons which are in connection with the hydraulic fluid of the closed space 10 have to be sealed off against the ambient environment.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.