Patent ID: 12228179

DETAILED DESCRIPTION

FIG.1shows a drum brake of a motor vehicle in perspective view, said drum brake comprising a circular carrier plate1and two brake shoes2and3, which are arranged concentrically with the central axis of the carrier plate1.

The brake shoes2,3are surrounded concentrically by a brake drum (not illustrated here), which is connected to a motor vehicle wheel to be braked, with the result that—when the brake shoes2,3are pressed against this brake drum—the rotating wheel is decelerated (service braking), or a stationary wheel is prevented from rotating (parking braking).

The brake shoes2,3each have a pressure end and a supporting end, wherein a spreader device4is arranged between the opposite pressure ends. This is generally a hydraulically, electromechanically or electrohydraulically actuatable device.

Between the likewise oppositely situated supporting ends there is a ram5, which transmits forces from one to the other brake shoe.

Both the spreader device4and the ram5are mounted so as to float in the circumferential direction relative to the carrier plate1, and therefore this is a “duo servo” brake, which has a strong self-energizing effect.

In order to support the braking forces, which act as frictional forces between the brake shoes2,3and the brake drum, an abutment6is provided. This is situated radially outside the spreader device4, wherein, adjacent to the force introduction points of the spreader device4, there are furthermore at the ends of the brake shoes2,3pressure heads7,8, which are supported on both sides of the abutment6. Since both the spreader device4and the ram5are mounted so as to float, the braking force is in each case transmitted only from the trailing brake shoe to the abutment6.

Considering the case where the brake drum is rotating counterclockwise in accordance with the illustrated arrow9, the brake shoe2illustrated on the left is the leading brake shoe, and the brake shoe3illustrated on the right is the trailing shoe.

The spreader device4pushes the two brake shoes2,3apart, wherein the leading brake shoe2is taken along by the brake drum in the direction of rotation thereof relative to the carrier plate1. The frictional force exerted thereon is transmitted by means of the ram5to the trailing brake shoe3as well, with the result that the pressure head8thereof is supported on the abutment6.

The supporting force is measured there, which force is a measure of the braking force and can thus be used to control the spreader device4.

For this purpose, in the simplest case, the abutment6shown inFIG.2consists of a massive but flat component which projects perpendicularly from the carrier plate1and is secured thereon, thus enabling the pressure heads7,8to rest on the edges thereof facing in the circumferential direction.

Here, the abutment6comprises a pedestal10, connected to which via a narrow central web11is a base12, against the edges of which that face in the circumferential direction the pressure heads7,8of the brake shoes2,3can be placed. Since the mutually facing edges of the pedestal10and the base12extend parallel to one another with a small clearance, two measurement gaps13,14are formed between the pedestal10and the base12, starting from the web11.

When the brake drum is rotated counterclockwise in accordance with the illustrated arrow9, the brake shoe2illustrated on the left is a leading brake shoe, and that illustrated on the right is a trailing brake shoe3. Owing to the frictional forces between the brake shoes and the brake drum, the brake shoes, because they are mounted so as to float, are taken along in the direction of rotation, with the result that the trailing brake shoe3is supported on the base12of the abutment6, and the base tilts relative to the pedestal10, as a result of which—as shown inFIG.2—the measurement gap14facing it widens and the measurement gap13facing away from it becomes narrower.

These changes can be detected by suitable sensors and represent a value for the braking force introduced, which, in turn, can be used to control the spreader device.

In the case of a different direction of rotation, the functions of the two brake shoes2,3are interchanged, that on the left becoming the trailing shoe and that on the right becoming the leading shoe, with the result that the latter is supported on the base12of the abutment6, as a result of which the left-hand measurement gap13facing it is widened and the right-hand measurement gap14facing away from it is narrowed.

Another possibility for the design of the abutment is illustrated inFIG.3. Extending out of the pedestal10secured on the carrier plate1is a central web16, which merges into a transverse web17, from each of the ends of which a respective arm18,19pointing toward the pedestal10emerges. The central web16, the transverse web17and the two arms18,19thus form a T. The pressure heads7,8of the brake shoes2,3are placed against the outer edge of the arms18,19, which faces in the circumferential direction.

Projecting laterally from the central web16are two pins20,21, which end shortly before the inner edges of the arms18,19, in each case forming a measurement gap13,14.

The respective leading brake shoe2,3bends the arm19or18on which it is supported inward, as a result of which the associated measurement gap14or13is reduced in size, which, in turn, can be detected by measurement.

At the same time, the pins20,21serve as overload protectors. If the braking forces become too great, the arms17,18are supported on the associated pin20,21.

A third embodiment, shown inFIG.4, comprises a pedestal10and a base12which are connected to one another via two struts22,23situated at the edges, thus forming a frame with a central opening. Emanating from the inner edge of the pedestal10, which delimits the opening, are two pins20,21, which reach as far as the inner edge of the base12, apart from a measurement gap13,14.

When the base12is subjected to a load in the circumferential direction, it shifts parallel to the pedestal10, with the result that the rectangular frame is transformed into a parallelogram, wherein the base12approaches the pedestal10and the ends of the pins20,21, as a result of which the measurement gaps13,14are correspondingly reduced in size.

In all the embodiments, there are various possibilities available for measuring the change in the measurement gap. Sensors which utilize the anisotropic magnetoresistive effect (AMR effect) or, alternatively, linear Hall sensors can be used.

Independently of the measurement of the measurement gap size, the respective change in shape of the abutment can be detected by means of strain gauges.

The sensors allow determination of the braking torque acting in the drum brake. This is used for controlling the braking effect of the drum brake.

The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the scope of the following claims.