Disc brakes normally either have a fixed caliper or a sliding caliper. The present invention is directed to disc brakes having a fixed or sliding caliper and one or more brake discs, of which at least one is sliding. The present invention concerns disc brakes in which the brake pads only are to act on a restricted part of a full circle. ("Teilbe- lag") There are also brakes in which the brake pads act on almost a full circle along the brake discs. ("Vollbelag") The present invention could not be implemented with the latter type of brakes.

Prior Art Sliding brake discs are normally received on a sleeve, hub or the like by means of teeth, splines or the like, or by any other means giving a fixed connection in rotational direction but a sliding connection in axial di- rection. The hub, sleeve etc. is received on and connected to the wheel axle. Depending on type and make of the brake the brake disc may either be received on a sleeve on the hub, connected to the wheel axle, or the brake disc may be received directly on the hub, without the use of any sleeve. In order to give sliding there has to be a certain play between the teeth, splines or the like on the inner circumference of the brake disc and the teeth, splines or the like on the outer circumference of the hub or sleeve.

In a released condition the disc is free to move in axial direction to some extent.

If, in released condition, the brake disc is put in an inclined position in relation to the rotational axis of the hub or sleeve, the disc will be translated in an axial direction by influence of wheel rotation. The direction of travel is dictated by the direction of the inclination and the direction of wheel rotation. Inclination of a brake disc in released condition is inevitable and occurs ran- domly in most brakes of this type. The maximal inclination of each brake disc is generally limited either by the dis- tance between the brake pads on both sides of the brake disc or the play in the teeth or splines connection. The brake disc may normally travel until it comes into contact with a brake pad. Such a contact between brake pad and brake disc in a released condition causes an unwanted brak- ing action when the wheel rotates normally called dragging.

Dragging may not lead to any serious problems regarding the driving of the vehicle, however, heating of the disc and brake pad, wear of pad and disc, extra energy consumption etc. may occur. Thus, the longevity of the brake pads, and possibly the brake as such, may be negatively influenced by dragging.

In the contact with the brake pad in the released condition there is a risk that the brake disc may be locked in a position in direct contact with the brake pad. This effect is often referred to as self-locking. The driver will not observe when the brake is applied by self-locking, and it may lead to serious damages of the brake and possi- bly the wheel assembly. Furthermore, if a brake is applied suddenly and unexpected by self-locking it may lead to a hazardous situation. The risk of self-locking may be influ- enced by a number of factors, such as the radial play be- tween hub and disc, the distance between the brake pads, the position of the brake pads, the rotational direction of the hub etc.

If and as soon as the brake disc is in a vertical po- sition, i. e. in right angles to the sleeve or hub, it may not travel axially along the hub or sleeve.

Summary of the Invention One object of the present invention is to hinder or at least reduce the risk that dragging occurs. Furthermore, the risk of self-locking in a released condition should also be avoided or at least reduced.

One part of the present invention is the understand- ing that the risk of dragging should not be ignored.

According to the present invention the caliper or more precisely the brake pads are positioned to automati- cally reduce the inclination of the brake discs, without the risk of dragging.

In one aspect of the present invention the maximal inclination of the brake discs in relation to the wheel axle, is limited by the distance between each brake disc and adjacent brake pads. By such an arrangement certain benefits are achieved.

Brief Description of the Drawings Fig. 1 is an exploded view of one example of a disc brake, Fig. 2 is a principal sketch illustrating the posi- tion of a caliper in relation to a brake disc, and Fig. 3 is a principal sketch used to explain how dragging may occur and showing the brake from above.

Detailed Description of Preferred Embodiments As used in this description the expressions"axial", "radial"and similar expressions are in relation to a wheel axle associated with the brake.

In Fig. 1 one example of a disc brake is shown. A person skilled in the art realises that the principals of

the present invention apply for disc brakes having many different structures. Only parts important for the under- standing of the present invention will be specifically re- ferred to in the description below.

The disc brake as shown has a caliper 1 surrounding two brake discs 2 received on a hub 3. The brake discs 2 have splines 4 on an inner circumference, which splines 4 are to mesh with splines 4 on the outer circumference of the hub 3. Brake pads 8 are received slidable in the cali- per 1 in a normal way. The brake pads 8 are applied by means of a thrust plate 6 and a brake mechanism 11, re- ceived in the caliper 1. Braking torque is transferred from the discs 2 to the hub 3, and thus the wheel, by means of the splines 4 or teeth of the brake discs 2 and hub 3, re- spectively.

In the present description and in the enclosed claims the expression"brake pad assembly"is sometimes used, which expression is intended to cover the brake pads, in- cluding brake lining material, back plate, thrust plate, guiding means and/or support means. As used here the ex- pressions"friction area", "surface area"and similar ex- pressions, refer to the parts of the pads in connection with the brake disc (s) during braking.

By means of the splines 4 the discs 2 are received giving a fixed connection in rotational direction but a sliding connection in axial direction. In order for the disc to be able to move axially there must be a play in the splines contact between the disc 2 and the hub 3. This play, in combination with gravity, will give the disc 2 a position with its centre somewhat lower than the centre of the hub 3, when the brake is released. This vertical dis- placement of the disc 2 concentrates the points of contact between the disc 2 and the hub 3 to the upper part of their interface. The rotation of the hub 3, originating from the wheel, is transferred to the disc 2 by means of these

points of contact. Thus, the driving forces are concen- trated to the upper part of the interface. In the lower part of the interface between disc 2 and hub 3 there is no point of contact between disc 2 and hub 3 in the released condition of the brake. This is true in the released condi- tion independent of if the brake disc 2 inclines or not.

This could be referred to as a rolling contact type, i. e. the points of contact appear between changing pairs of splines 4 on the disc 2 and the hub 3, respectively, during rotation.

In other embodiments (not shown) other number of discs 2 are used and one disc 2 may be fixed in axial di- rection. Brake pads 8 are placed on both sides of each brake discs 2. Also the brake pads 8 are received moveable in axial direction in the caliper 1, even though the brake pad 8 furthest from the thrust plate may be fixed. During braking the brake mechanism 11 will press the thrust plate 6 against the adjacent brake pad 8, which will be pressed against the brake disc 2 and so on. Braking will occur as the brake pads 8 and brake discs 2 are pressed against each other.

The brake pads 8 have circumferential extensions, which are only parts of a full circle, preferably less than 180°. A person skilled in the art realises that the exact form of the brake pads may vary, without influencing the invention as such. The position of each brake pad 8 or brake pad assembly in relation to the brake discs 2 will influence the risk of dragging. In Fig. 2 an imaginary point 5 is shown on the top of the brake disc 2. Said imaginary point 5 is placed vertically above the centre of the wheel axle, and at the outer periphery of the brake disc 2. The imaginary point 5 represents the angular posi- tion of the action point of the resultant driving forces from the hub 3 on the disc 2 when the brake is released.

This is due to the fact that the points of contact are

placed at the upper part of the interface between disc 2 and hub 3, as described above. The caliper 1, and, thus the brake pads 8 or at least a predominant portion of the fric- tion area of the brake pads 8, is placed in such a position that the pads are placed 0° to 180° behind (to the right as seen in Fig. 2) the imaginary point 5, when seen in the di- rection 7 of disc rotation. In this description, said posi- tion of the caliper 1 is referred to as a"lagging posi- tion". Correspondingly if the caliper 1 is placed with the pads 0° to 180°, or at least a predominant part of the friction area of the brake pads 8, before (to the left as seen in Fig. 2) the imaginary point 5 in the direction 7 of disc rotation, said position is referred to as a"leading position".

By placing the predominant part of the friction area of the pads 8 or the brake pad assembly in the lagging po- sition, a major portion of a surface area of the pads 8 acts on the disc 2 in the region of the lagging position which serves to reduce dragging. Preferably, greater than 75% of the surface area of the pads 8 acts on the disc 2 in the lagging position to reduce dragging. Most preferably, nearly all of the surface area of the pads 8 acts on the disc 2 in the lagging position to reduce dragging. It is understood that due to application or other engineering considerations, such as for example, space constraints on some axles and in some vehicles, it may not be possible for the entire surface area of the pad 8 to act in the lagging position of the disc 2, but this does not negate the inven- tion.

The shown direction 7 of disc rotation is when the vehicle is driven in forward direction. If the vehicle is driven in reverse the brake disc 2 will rotate in the oppo- site direction.

In relation to the direction 7 of rotation of the discs 2 the brake pads 8 have a front edge 9 and a trailing

edge 10. As used in this description the front edge 9 is the first part of the brake pad 8 one would encounter if one were placed on the rotating brake disc 2, rotating in the direction of the arrow 7 of Fig. 2.

When the brake is released there is a distance be- tween each brake disc 2 and adjacent brake pads 8. In order for the discs 2 to be able to move axially there must be a play in the splines contact between the discs 2 and the hub 3. If a disc 2 is inclined y in relation to the rotating hub 3 it will move axially. The axial movement is a conse- quence of that the interaction between disc 2 and hub 3 is of the rolling contact type, leaving the inclination unaf- fected by the rotation itself. Experimental rotation of a disc 2 and hub 3 shows clearly that the inclination does not change and that the disc 2 moves axially. Said axial translation of the brake disc 2 is indicated in Fig. 3. The possible maximal inclination y is limited by several fac- tors, such as the axial distance between the brake disc 2 and adjacent brake pads 8 or the play between the splines 4 of the brake disc 2 and hub 3, respectively. In Fig. 3 the caliper 1 and thus the brake pads 8 are shown with continu- ous lines in a leading position and shown with broken lines in an alternative lagging position, considering the shown direction 7 of rotation. With the caliper 1 positioned in a leading position, the brake disc 2 will be given a force component acting to keep the disc 2 in the inclined posi- tion when the disc 2 hits the brake pads 8. However, if the caliper 1 or more precisely the brake pads 8 are placed in a lagging position, as indicated with broken lines in Fig.

3, the brake disc 2 will be given a force component acting to straighten the disc 2 when it hits the brake pad 8 and a friction force appears on the disc 2. This is because the friction force from the pad 8 acts behind (as understood from Fig. 2) the rotational driving force from the hub 3.

The above, i. e. the straightening of the disc 2, is also

working if the brake disc 2 inclines in the opposite direc- tion to what is shown in Fig. 3. Then the disc 2 will move axially to the left in the picture instead, but still the disc 2 will be straightened as the friction force from the pad 8 on that side of the disc 2 also acts behind the driv- ing force from the hub 3. As mentioned earlier the resul- tant rotational driving force from the hub 3 acts in the upper part of the interface between disc 2 and hub 3. The straightening of the disc 2 will thus reduce the inclina- tion y.

Thus, in order to hinder dragging, or even worse self-locking, according to the present invention the in- clined disc 2 will be straightened by means of positioning of the brake pads 8 or brake pad assemblies. As the posi- tion of the brake pads 8 or brake pad assemblies are dic- tated by the position of the caliper 1 one could also say that it is the positioning of the caliper 1, which assist in straightening of the brake disc 2. Thus, when an in- clined disc 2 comes into contact with one brake pad 8 or brake pad assembly in released condition, the brake disc 2 will be straightened. A straight brake disc 2, i. e. without inclination (y=0°), will not move axially and thus no drag- ging will occur.

It can be shown that with the caliper 1 placed in a lagging position, as defined above, the risk of dragging is significantly reduced compared to if the caliper 1 is placed in a leading position. To be more exact it is not the position of the caliper 1 as such, but the position of the brake pads 8 or brake pad assemblies that are of impor- tance. However, for in principal all brakes the position of the caliper 1 coincides with the position of the brake pads 8. In order to guarantee the desired effect at least some part of the brake pad assembly should be placed at least a small distance behind an imaginary line going through the centre of the axle and the imaginary point 5.

In Fig. 2 an imaginary line 12 is placed going through the centre of the axle and through the imaginary point 5 at the top of the brake disc 2. An angle a between the imaginary line 12 and the trailing edge 10 of the brake pad 8 is shown, as is an angle ß between the imaginary line 12 and the front edge 9 of the brake pad 8. The angle a should be >0° and the angle p should be <180° In a pre- ferred embodiment the angle a is between 0° and 180°, pref- erably between 0° and 135° and most preferred between 0° and 90°. The angle P is between 0° and 180°, preferably between 45° and 180° and most preferred between 90° and 180°.

As stated above the maximum inclination of the brake discs 2 in a released condition is either dictated by the clearance between the brake pads 8 and the brake discs 2 or by the play (clearance) in the connection between hub 3 and brake discs 2 or by combinations of these and/or other fac- tors known to those of skill in the art. In the first case one may refer to a disc 2 guidance from the pads 8. In analogy therewith the latter case may be referred to as disc 2 guidance from the splines 4 (teeth). By using guid- ance from the pads 8 there are certain benefits. One bene- fit is that there is no need for particular guiding devices or wide disc centres to get disc guidance from the connec- tion with the hub 3. This will save weight and avoiding the risk that the brake disc 2 will be jammed due to locking of the splines or teeth of the hub 3 (sleeve) and brake disc 2, respectively. Furthermore, there is no need for close tolerances in splines (teeth) manufacturing. Thus, there will be a simplified and effective manufacture of disc 2 and hub 3.