Positioning of a brake caliper

The present invention concerns a disc brake having a caliper encircling one or more brake discs. At least one of said brake discs is received sliding on a hub or a part connected to the hub. According to the invention the caliper is to be mounted in a lagging position. In said lagging position at least a portion of the brake pad assemblies is positioned 0°-180° behind an imaginary point vertically above the centre of a wheel axle, when seen in the normal direction of disc rotation. The invention is intended for brakes, in which the brake pads only act on a restricted part of a full circle.

FIELD OF THE INVENTION

The present invention concerns disc brakes. Especially it concerns the behaviour of the brake in a released condition.

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. (“Teilbelag”) 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 direction. 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 randomly in most brakes of this type. The maximal inclination of each brake disc is generally limited either by the distance 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 braking 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 possibly 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 influenced by a number of factors, such as the radial play between 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 position, 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 understanding 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 automatically 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.

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.

InFIG. 1one 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 understanding of the present invention will be specifically referred to in the description below.

The disc brake as shown has a caliper1surrounding two brake discs2received on a hub3. The brake discs2have splines4on an inner circumference, which splines4are to mesh with splines4on the outer circumference of the hub3. Brake pads8are received slidable in the caliper1in a normal way. The brake pads8are applied by means of a thrust plate6and a brake mechanism11, received in the caliper1. Braking torque is transferred from the discs2to the hub3, and thus the wheel, by means of the splines4or teeth of the brake discs2and hub3, respectively.

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, including brake lining material, back plate, thrust plate, guiding means and/or support means. As used here the expressions “friction area”, “surface area” and similar expressions, refer to the parts of the pads in connection with the brake disc(s) during braking.

By means of the splines4the discs2are 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 disc2and the hub3. This play, in combination with gravity, will give the disc2a position with its centre somewhat lower than the centre of the hub3, when the brake is released. This vertical displacement of the disc2concentrates the points of contact between the disc2and the hub3to the upper part of their interface. The rotation of the hub3, originating from the wheel, is transferred to the disc2by means of these points of contact. Thus, the driving forces are concentrated to the upper part of the interface. In the lower part of the interface between disc2and hub3there is no point of contact between disc2and hub3in the released condition of the brake. This is true in the released condition independent of if the brake disc2inclines or not. This could be referred to as a rolling contact type, i.e. the points of contact appear between changing pairs of splines4on the disc2and the hub3, respectively, during rotation.

In other embodiments (not shown) other number of discs2are used and one disc2may be fixed in axial direction. Brake pads8are placed on both sides of each brake discs2. Also the brake pads8are received moveable in axial direction in the caliper1, even though the brake pad8furthest from the thrust plate may be fixed. During braking the brake mechanism11will press the thrust plate6against the adjacent brake pad8, which will be pressed against the brake disc2and so on. Braking will occur as the brake pads8and brake discs2are pressed against each other.

The brake pads8have 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 pad8or brake pad assembly in relation to the brake discs2will influence the risk of dragging. InFIG. 2an imaginary point5is shown on the top of the brake disc2. Said imaginary point5is placed vertically above the centre of the wheel axle, and at the outer periphery of the brake disc2. The imaginary point5represents the angular position of the action point of the resultant driving forces from the hub3on the disc2when 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 disc2and hub3, as described above. The caliper1, and, thus the brake pads8or at least a predominant portion of the friction area of the brake pads8, is placed in such a position that the pads are placed 0° to 180° behind (to the right as seen inFIG. 2) the imaginary point5, when seen in the direction7of disc rotation. In this description, said position of the caliper1is referred to as a “lagging position”. Correspondingly if the caliper1is placed with the pads 0° to 180°, or at least a predominant part of the friction area of the brake pads8, before (to the left as seen inFIG. 2) the imaginary point5in the direction7of disc rotation, said position is referred to as a “leading position”.

By placing the predominant part of the friction area of the pads8or the brake pad assembly in the lagging position, a major portion of a surface area of the pads8acts on the disc2in the region of the lagging position which serves to reduce dragging. Preferably, greater than 75% of the surface area of the pads8acts on the disc2in the lagging position to reduce dragging. Most preferably, nearly all of the surface area of the pads8acts on the disc2in 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 pad8to act in the lagging position of the disc2, but this does not negate the invention.

The shown direction7of disc rotation is when the vehicle is driven in forward direction. If the vehicle is driven in reverse the brake disc2will rotate in the opposite direction.

In relation to the direction7of rotation of the discs2the brake pads8have a front edge9and a trailing edge10. As used in this description the front edge9is the first part of the brake pad8one would encounter if one were placed on the rotating brake disc2, rotating in the direction of the arrow7ofFIG. 2.

When the brake is released there is a distance between each brake disc2and adjacent brake pads8. In order for the discs2to be able to move axially there must be a play in the splines contact between the discs2and the hub3. If a disc2is inclined γ in relation to the rotating hub3it will move axially. The axial movement is a consequence of that the interaction between disc2and hub3is of the rolling contact type, leaving the inclination unaffected by the rotation itself. Experimental rotation of a disc2and hub3shows clearly that the inclination does not change and that the disc2moves axially. Said axial translation of the brake disc2is indicated inFIG. 3. The possible maximal inclination γ is limited by several factors, such as the axial distance between the brake disc2and adjacent brake pads8or the play between the splines4of the brake disc2and hub3, respectively. InFIG. 3the caliper1and thus the brake pads8are shown with continuous lines in a leading position and shown with broken lines in an alternative lagging position, considering the shown direction7of rotation. With the caliper1positioned in a leading position, the brake disc2will be given a force component acting to keep the disc2in the inclined position when the disc2hits the brake pads8. However, if the caliper1or more precisely the brake pads8are placed in a lagging position, as indicated with broken lines inFIG. 3, the brake disc2will be given a force component acting to straighten the disc2when it hits the brake pad8and a friction force appears on the disc2. This is because the friction force from the pad8acts behind (as understood fromFIG. 2) the rotational driving force from the hub3. The above, i.e. the straightening of the disc2, is also working if the brake disc2inclines in the opposite direction to what is shown inFIG. 3. Then the disc2will move axially to the left in the picture instead, but still the disc2will be straightened as the friction force from the pad8on that side of the disc2also acts behind the driving force from the hub3. As mentioned earlier the resultant rotational driving force from the hub3acts in the upper part of the interface between disc2and hub3. The straightening of the disc2will thus reduce the inclination γ.

Thus, in order to hinder dragging, or even worse self-locking, according to the present invention the inclined disc2will be straightened by means of positioning of the brake pads8or brake pad assemblies. As the position of the brake pads8or brake pad assemblies are dictated by the position of the caliper1one could also say that it is the positioning of the caliper1, which assist in straightening of the brake disc2. Thus, when an inclined disc2comes into contact with one brake pad8or brake pad assembly in released condition, the brake disc2will be straightened. A straight brake disc2, i.e. without inclination (γ=0°), will not move axially and thus no dragging will occur.

It can be shown that with the caliper1placed in a lagging position, as defined above, the risk of dragging is significantly reduced compared to if the caliper1is placed in a leading position. To be more exact it is not the position of the caliper1as such, but the position of the brake pads8or brake pad assemblies that are of importance. However, for in principal all brakes the position of the caliper1coincides with the position of the brake pads8. 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 point5.

InFIG. 2an imaginary line12is placed going through the centre of the axle and through the imaginary point5at the top of the brake disc2. An angle α between the imaginary line12and the trailing edge10of the brake pad8is shown, as is an angle β between the imaginary line12and the front edge9of the brake pad8. The angle α should be >0° and the angle β should be <180°. In a preferred embodiment the angle α is between 0° and 180°, preferably between 0° and 135° and most preferred between 0° and 90°. The angle β 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 discs2in a released condition is either dictated by the clearance between the brake pads8and the brake discs2or by the play (clearance) in the connection between hub3and brake discs2or by combinations of these and/or other factors known to those of skill in the art. In the first case one may refer to a disc2guidance from the pads8. In analogy therewith the latter case may be referred to as disc2guidance from the splines4(teeth). By using guidance from the pads8there are certain benefits. One benefit is that there is no need for particular guiding devices or wide disc centres to get disc guidance from the connection with the hub3. This will save weight and avoiding the risk that the brake disc2will be jammed due to locking of the splines or teeth of the hub3(sleeve) and brake disc2, respectively. Furthermore, there is no need for close tolerances in splines (teeth) manufacturing. Thus, there will be a simplified and effective manufacture of disc2and hub3.