Patent Application
20050029056
The invention relates to a disc brake having an actuator, which has a brake actuating lever and is arranged in a caliper, as well as to a method for determining the braking force in braking operations using a disc brake brake.
In the case of many different types of brakes, particularly in the case of pneumatically operated utility vehicle brakes, the braking force transmission takes place through the use of a brake actuating lever, which is operated by a piston rod of a brake cylinder. The brake actuating lever converts the force of the actuating unit (membrane cylinder, general actuator) at the transmission ratio of the brake actuating lever, or multiplies it with the transmission ratio, and thereby increases the braking force. A special advantage of such a lever system is the possibility of generating high braking forces by using only relatively low starting forces.
For controlling and/or regulating the braking forces, the pressure is analyzed, which pressure is applied at the pneumatic cylinder. This pressure is compared with a desired value, so that regulation can take place, as required. The regulation of the pressure is based on the presence of a pneumatic actuator, which is fed with compressed air.
In the case of brakes which hydraulically or electro-mechanically actuate the lever mechanism of the brake by way of an electric motor with a linear drive, the air pressure is eliminated as an advantageous regulating variable.
It is therefore an object of the invention to further develop a disc brake of the above-mentioned type, as well as the method of determining the braking force of the disc brake of the above-mentioned type, such that it can be used for disc brakes having many different types of construction, particularly in the case of disc brakes with many different actuators, for example, in a pneumatic, hydraulic or electromechanical construction.
With respect to the disc brake, the invention achieves this goal by arranging at least one measuring sensor, particularly a tension sensor, on at least one of the brake actuating lever, the brake actuator, the caliper and a brake anchor plate. And, with respect to the process of determining the braking force, tensions at least one of the brake actuating lever, the brake actuator, the caliper and on a brake anchor plate, from which tensions the application force exercised upon the brake or the braking torque is determined.
Advantageous constructions of the invention are described and claimed herein.
At least one measuring sensor, particularly a tension sensor, is arranged at least on the brake actuating lever, on the brake actuator, on the caliper and/or on a brake anchor plate. From the tension measurements, the braking forces are then determined, for example, by the use of a comparison and/or multiplication with previously stored reference values or constants. The invention starts with the idea of determining the braking force by way of tension measurements directly at the disc brake and, for implementing the measurement at the brake, suggests elements on this brake which are particularly suitable and which, so far, have not been utilized for measuring the braking force.
According to a particularly advantageous aspect of the invention, this measuring variable is more suitable for the measurement. The fewer elements that are situated between the measuring variable and the actual braking force is better, because each transmission element may be, in turn, faulty.
The measuring point or the element, at which the measuring takes place, should not be subject to wear because otherwise the measurements would supply different values in the course of the service life of the brake. Likewise, it is important that no outside environmental influences, such as dirt, moisture and mechanical influences, for example, thrown-up rocks, can contaminate the measuring point or even impair the operation. The measuring point should be selected in a suitable manner with respect to the high temperatures occurring during the braking operation. On the whole, a low susceptibility to trouble should be ensured in order to meet the demands on this safety-relevant part. The measuring point should therefore preferably be arranged in a protected environment inside the brake or the caliper.
Surprisingly, probably the most optimal measuring point was discovered to be the brake actuating lever of the brake. It is situated in the interior of the brake housing or brake caliper and is, therefore, protected from external influences. It is not subjected to wear and is designed for the entire service life of a brake. The force of the actuating unit is introduced at the brake actuating lever. The lever acts like a transverse beam, at which, corresponding to the load, tensile stress occurs on one side and compressive stress occurs on the other side. For this reason, at least one, preferably several tension sensors are arranged at the brake actuating lever.
Instead of the brake actuating lever, the caliper itself can also be utilized as the site of the measurement. During the operation of the brake, it expands as a result of the occurring reaction forces.
A cover housing for the caliper can be utilized as another suitable measuring point. The brake actuating lever is supported by way of bearings on the interior side of the cover housing or directly at the caliper, so that here the braking forces are introduced by way of the cover housing—in the case of a multi-part construction of the caliper with screwed connections—or directly into the caliper—in the case of a one-piece construction. Here, tensions are essentially proportional to the braking force and can be used as a measuring signal for controlling the brake.
The measuring variables can be evaluated by use of correspondingly mounted wire strain gauges or by use of piezo-electric elements, which are coupled with a measuring amplifier. The received signal is directly related to the braking force or to the braking torque and can, therefore, be used as a measuring variable for regulating the brake.
Depending on the measuring point, wire strain gauges can be switched to a quarter bridge, half bridge or full bridge, and can be evaluated by the use of a simple measuring amplifier.
Piezo elements, which are pressed into a bore at the measuring point, also supply a signal corresponding to the deformation of the part.
The mounting of the wire strain gauges can take place by various methods.
The wire strain gauges may be glued onto a surface. As an advantageous variant, the wire strain gauges are applied to a metal carrier plate. Even under more unfavorable conditions, such as dirt, moisture, and the like, which may occur at the assembly line, the metal plate can then easily be welded to the measuring point. This permits an industrial production of brake actuating levers with wire strain gauges.
In contrast, the piezo elements are preferably pressed into a bore. However, for this purpose, only one bore with a defined tolerance field is required. The production can therefore take place without any problems.
Although it is known from German Patent Document DE 196 40 901 C2 to measure an elastic deformation of the application device on an electro-mechanical brake actuator by the use of a sensor, from which deformation the exercised application force is determined, this system has the disadvantage that the actuator and the operating unit represent a unit which cannot be separated. When the actuator is exchanged for an operating unit of another operating principle, the sensor is therefore eliminated. Here, the invention provides a remedy in a simple manner.
In the following, the invention will be explained in detail by means of an embodiment.
a, b are rear views of a second and a third disc brake, respectively, having constructions according to the invention;
a-5c and 6a-6c are respective views of brake actuating levers for the disc brake according to
a and 9b are diagrams which illustrate the proportional relationship between the braking force and the determined wire strain gauge signal through the use of measurements at the brake actuating lever, as well as at the caliper.
According to the invention, a suitable measuring variable for the braking force is provided, particularly for such brakes, in which case the brake application device can be operated according to different operating principles, for example, pneumatically, electromechanically or hydraulically.
One possibility of implementing the measurement is represented by the caliper 1.
An asymmetrical stressing may occur at the caliper 1 as a result of diagonal wear at the brake pads. It therefore also makes sense to absorb the tensions, as required, on both sides of the caliper 1 and to ascertain the mean value. One advantage of this arrangement is also the direct measuring of the braking force without mechanical intermediate links, which may exhibit a hysteresis effort.
As an alternative, or in addition, the wire strain gauges 7 or the piezo elements 8 may also be arranged in the area of the caliper 1 facing away from the brake disc or in the interior or exterior area of a cover housing 9 (may also correspond to a second caliper part) (
According to FIGS. 3 to 6, the wire strain gauges 7 or the piezo elements 8 are arranged as an alternative and/or in addition to the above-mentioned embodiments on the brake actuating lever 4, specifically preferably between the recess 10 for the piston rod on the top end of the brake actuating lever 4 and the lower eccentric-type section 11 of the brake actuating lever 4.
Preferably, the wire strain gauges 7 and/or the piezo elements 8 (see
In addition or as an alternative,
By way of a cable 12 connected to the brake actuating levers 4 and/or to the caliper 1 or another suitable element—if required, together with additional data and/or voltage supply lines, the measuring signal can be fed to a measuring circuit as illustrated in
By mounting one to four wire strain gauges on the front side and/or the back side of the brake actuating lever 4, a quarter, half, or full bridge can be implemented for analyzing the occurring tensions on the brake actuating lever 4.
The measuring circuit has a measuring bridge 14 consisting of four wire strain gauges, each forming one resistor RDMS1, RDMS2, RDMS3, RDMS4 respectively, to which a measuring voltage UE is applied. If required, the measuring bridge according to
As a miniature amplifier, the amplifier 13 can advantageously be integrated in the brake. The cable 12 then only has to have two supply cables with a feed voltage and two lines for the measuring signal. Likewise, it is contemplated to integrate the amplifier 13 into the back side of the wire strain gauge 7.
When measuring using two and, even better, four wire strain gauges 7, the influence of temperature on the measurement can also be eliminated.
The amplifier 13 can also be integrated directly (not shown) in the brake actuating lever 4. As a result, the lines to the amplifier can be kept short and the disturbances with respect to the measuring signal are reduced. As an alternative, the signal can be transmitted to the outside in a contactless manner by way of a transmitter on the back side of the brake actuating lever 4. This has the advantage that no lines have to be laid from the moving brake actuating lever 4 to the stationary caliper 1. In this case, the energy supply of the measuring system takes place in a contactless manner.
For controlling the brake, a relationship has to be found between the measuring signal and the braking force. When measuring the tensions at the brake actuating lever 4, a relationship according to the type of
| Number | Date | Country | Kind |
|---|---|---|---|
| 101-48-472.0 | Oct 2001 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP02/10853 | 9/27/2002 | WO |
