Technical field

The invention relates to a parking brake device according to the preamble of claim 1.

Background

When parking or holding various types of vehicles, e.g. trucks, it is important for reasons of safety to ensure stable and reliable locking of the vehicle's position. This is done by means of a parking brake which is used for vehicle parking and holding, unlike the service brake which is used when the vehicle is in motion.

There are currently various solutions for achieving this. One of the solutions used involves mechanical tightening of the brake linings against the brake discs with such force that reliable braking is effected. However, this entails using a considerable amount of space in the wheel housing if this solution is to work satisfactorily. Available space in the wheel housing is limited and it would therefore be advantageous to use a form of parking brake which does not occupy so much space. Another solution currently used is electromechanical parking brakes which are then an integral part of the service brake cylinder and use the same pushrod as the service brake. This solution is activated pneumatically and has to be post-tightened when the discs and the linings have cooled down, in order to ensure sufficient braking action. This type of system also always entails a certain undesired leakage of air, which means that a large initial braking action is essential for reliable braking of the vehicle even when the pressure in the system drops. A further disadvantage of parking brakes of this type is that they entail the release of a considerable amount of air after braking. There is therefore a need for a parking brake device which occupies a limited amount of space, provides reliable braking of vehicles during short or long halts and is easy to engage and disengage.

Summary of the invention

The object of the present invention is to eliminate the above problems. This object is achieved by a brake device according to the independent claim, in which at least one locking means is arranged adjacent to the brake yoke in order to be introduced through an aperture in the brake yoke and to proceed into or through at least one recess in the brake disc situated at the same radial distance from the centre of the brake disc as the aperture in the brake yoke and thereby lock the brake disc relative to the brake yoke when the parking brake is activated.

This parking brake device overcomes the disadvantages indicated above of previously known solutions in that the locking means results in extremely distinct and reliable locking of the brake disc relative to the brake yoke. The fact that the brake device is not affected by the length of time for which the vehicle is held is a great advantage. Nor is any post-compensation of the parking brake device required to ensure sufficient braking action, since the locking spigot which is fixed in the activated state is not affected by the passage of time. The parking brake is also easy for the user to activate/release when parking/moving off. The solution can be accommodated in or adjacent to the already existing brake yoke, thereby reducing the space requirement and hence freeing space for other components.

In an embodiment of the parking brake device, the aperture in the brake yoke takes the form of an elongate slot and said at least one locking means is adapted to being movable relative to the brake yoke along the length of the slot in order to be introduced into and locked in said at least one recess in the disc when the position of said at least one locking means corresponds to the position of said at least one recess. This embodiment prevents the vehicle from moving a certain distance before the position for said at least one recess in the brake disc corresponds to the aperture in the brake yoke and said at least one locking means can be introduced into said at least one recess. Safety is thus improved when the parking brake is applied with the vehicle in the halt position chosen by the driver.

In an embodiment of the parking brake device, said at least one locking means is moved along the aperture by the action of a mechanical device such as a spring or by a pneumatic device or an electric drive.

In a further embodiment of the invention, when the parking brake device is activated, said at least one locking means is pressed against the disc and thereafter moves over the disc's surface along the slot until said locking means is positioned in said at least one recess, into which the locking means is introduced by the action of a mechanical device such as a spring or by a pneumatic device or an electric device.

In an embodiment of the invention, the brake disc has at least two substantially circular recesses and the length of the aperture in the brake yoke is the same as or greater than the distance between two neighbouring recesses plus two recess diameters. This version has the advantage that there will always be at least one recess situated somewhere along the aperture in the brake yoke, thereby ensuring that the locking means can be engaged without the brake disc having to be rotated relative to the brake yoke.

In an advantageous embodiment of the parking brake device, the aperture in the brake yoke takes the form of a substantially circular arc with constant distance from the centre of the disc and said at least one substantially circular recess in the disc is arranged at the same radial distance from the centre of the disc as the aperture in the brake yoke. This version means that the position of said at least one recess in the brake disc will always correspond to a position of the aperture in the brake yoke, making it easier to engage and disengage the locking means and making it possible for there to be less play between the locking means, the brake disc and the brake yoke, thereby ensuring precise braking with little play.

In another embodiment of the parking brake device, the brake disc has at least two recesses in the form of elongate notches running radially from the centre of the disc and the length of the aperture in the brake yoke is the same as or greater than the distance between two neighbouring recesses at the radial distance from the centre of the disc at which the aperture in the yoke is situated, plus two recess widths. This configuration is advantageous where the brake disc is composed of a number of sections. The joints between the sections can then be used as recesses, thereby reducing the number of process steps involved in the setting up and the assembly of the various constituent parts.

Said at least one locking means has a substantially circular cross-section, since substantially circular recesses in the brake disc are the geometric shape which minimises the risk of cracks starting from the recess, which can be a problem with brake discs.

To ensure easy engagement of said at least one locking means and acceptable play between the recesses and the locking means, the diameter or width of said at least one recess is 0.2 mm to 10 mm larger than the diameter or width of said locking means. Brief description of the drawings

The invention is explained in more detail below with reference to the drawings, in which:

Figure 1 depicts schematically a first embodiment of the parking brake device according to the invention, and

Figure 2 depicts schematically a second embodiment of the invention.

Detailed description of the invention

Figure 1 depicts a first embodiment of the parking brake device 10. The parking brake device 10 comprises a brake disc 11 and a brake yoke 12. The brake disc 11 is situated on the wheelshaft of, and rotates at the same speed as, the respective wheel of the vehicle which is to be braked. The brake yoke 12 is situated at the periphery of the brake disc 11 and accommodates brake blocks (not depicted) which are pressed against the surface of the disc in order thereby to brake the rotation of the brake disc 11 and hence also the vehicle. The brake yoke 12 has a U-shaped cross-section so that it encloses the periphery of the brake disc 11 and can accommodate brake blocks which act upon both sides of the brake disc 11. In this embodiment, the brake yoke 12 extends along almost half of the periphery of the brake disc 11 , but larger or smaller brake yokes may also be used. On one side of the brake disc 11, the brake yoke 12 is provided with an elongate aperture 13 in the form of a circular arc. A locking spigot 14 capable of linear movement is accommodated in the aperture 13. In this embodiment, the locking means takes the form of a locking spigot intended to be introduced into circular recesses 15 in the brake disc 11. Introducing the locking spigot 14 entails its movement in a direction substantially perpendicular to the surface of the brake disc 11. The recesses 15 are situated at the same radial distance from the centre of the brake disc 11 as the aperture 13 in the brake yoke 12, so that the recesses 15 become accessible via the aperture 13 in the brake yoke 12. The recesses have with advantage a diameter between 0.2 and 10 mm larger than the diameter of the locking spigot for problem-free engagement of the locking spigot 14. More play between the recesses 15 and the locking spigot 14 results in desired movement between the brake disc 11 and the brake yoke 12. Upon activation of the parking brake, the locking spigot 14 is pressed against the surface of the brake disc 11 and moves in the aperture 13 until the locking spigot 14 is situated over a recess 15 into which the locking spigot 14 is introduced by, for example, a spring or pneumatic action. The brake disc 11 is provided with a number of recesses 15 to reduce the distance between the recesses 15 and hence the distance which the locking spigot 14 has to travel along the surface of the brake disc 11 to reach a recess 15. The length of the aperture 13 in the brake yoke 12 is adapted on the basis of the distance between the recesses 15 in the brake disc and is at least as great as the distance between two recesses 15 plus two locking spigot diameters 14, to ensure that at least one recess 15 is always lockable in the aperture 13 by means of the locking spigot 14. The recess 15 is either a depression in the surface of, or a recess running through, the brake disc 11. After it has been introduced into the recess 15, the locking spigot 14 is fixed in the engaged state. This is effected close to the aperture 13 in the brake yoke 12 by a mechanical device appropriate to the purpose or, if the recess runs through the brake disc, the locking spigot may be fixed in the brake yoke 12 on the opposite side of the brake disc 11. The locking spigot 14 is moved in the aperture 13 by means of a suitable mechanical device such as a spring or a suitable pneumatic or electric drive device. Upon disengagement of the parking brake device, the locking spigot is released from its engaged state by an electric or pneumatic device.

Figure 2 depicts an alternative embodiment of a parking brake device 10 according to the invention which comprises a brake yoke 22 and a brake disc 21. In this embodiment, the brake disc 21 is composed of a number of sections 30 and the recesses take the form of grooves 31 situated between the sections 30 and extending in the radial direction across the surface of the brake disc 21. The brake yoke 22, which is of the same configuration as in the embodiment described above, has an aperture 32 in the brake yoke 22. The aperture 32, which here need not take the form of a circular arc, is straight and accommodates a locking spigot 33 adapted to being movable along the length of the aperture 32. When the parking brake is activated, the locking spigot 33 is pushed into the groove 31 between the brake disc's sections 30 and is fixed relative to the brake yoke 22 by suitable mechanical locking which needs no adjustment or tightening when the vehicle has been held for some time. The aperture 32 created in the brake yoke 22 is at least as long as the distance between two neighbouring grooves 31 at the radial position along the brake disc 21 where the aperture 32 is situated, plus two locking spigot diameters, to ensure that the locking spigot 33 can be engaged in the groove 31 without the brake disc 21 having to be rotated relative to the brake yoke 22.

Further embodiments of the invention are possible so long as the recesses in the brake disc correspond in location and shape to the aperture in the brake yoke. For example, an embodiment according to the invention might comprise two or more locking spigots which are connected together or mutually independent and which cooperate with recesses situated at the same spacing in the brake disc as the distance between the locking spigots. This embodiment may be appropriate if there is risk of large shear stresses in the locking spigot which might lead to the locking spigot giving way or becoming deformed or to heavy loads on the constituent parts of the device.

An alternative embodiment of the invention comprises a separate element in which the aperture is formed and relative to which the locking spigot is adapted to being capable of linear movement. This element is fixed to the brake yoke in a suitable manner, e.g. by a threaded connection, and otherwise functions in a manner similar to that described above.

Although it is described on the basis of some exemplifying embodiments, the invention is not limited to them but is defined on the basis of the accompanying claims.