WO2008071578A1

WO2008071578A1 - Separate detection of application and friction forces on a brake

Info

Publication number: WO2008071578A1
Application number: PCT/EP2007/063173
Authority: WO
Inventors: Andreas Grätz; Stefan Breitschuh
Original assignee: Continental Automotive Gmbh
Priority date: 2006-12-13
Filing date: 2007-12-03
Publication date: 2008-06-19
Also published as: DE102006058882B4; DE102006058882A1

Abstract

The invention relates to a device for detecting a normal force (N), which occurs between a friction lining (1, 5) and an object (6) displaceably arranged relative thereto, and a friction force (R) brought about between the friction lining (1, 5) and the object (6) transmitted via the normal force (N), wherein the device comprises a first sensor element (14), which is designed for the conversion of a first deformation component (e(a)) into a first electrically detectable characteristic representing the first deformation component. The device comprises a second sensor element (15), which is designed for the conversion of a second deformation component (e(-a)) into a second electrically detectable characteristic representing the second deformation component. The device further comprises a processing unit (20) for processing at least the first electrically detectable characteristic and the second electrically detectable value. The first deformation component and the second deformation component each represent a component of a deformation of a body (1, 5, 9, 11), wherein the first deformation component assumes an angle a to the frictional direction and the second deformation component assumes an angle -a to the frictional direction and a is different from zero.

Description

description

Separate detection of application and friction forces on a brake

The present invention relates to the separate detection of application force and braking force to a braking device.

In a braking arrangement based on a friction effect, in order to achieve a braking effect, a friction lining is generally pressed against a surface, referred to as a braking surface, of a subject movably arranged relative to the friction lining, the braking object. By pressing the friction lining against the brake object, a frictional force arises therebetween, which is proportional to the proportion of the pressure force that is normal to the contact surface between the friction lining and the braking object. This frictional force is called braking force below.

In vehicle brakes, the brake object is usually designed as a brake disc. Depending on the type of brake arrangement used, however, the brake object can also assume other configurations; in motor vehicles, for example, the form of a hollow drum, or in rail vehicles, e.g. the shape of an impeller. If not the object movably arranged relative to the brake lining itself, but the device bearing the friction lining is delayed or held, then, as is usual with a rail brake, the braking object can also assume a rail-shaped formation.

In machine tools and machine-driven vehicles, high demands are placed on the control of the braking force. Especially in motor vehicles, the high demands on driving dynamics, driving safety and comfort can only be met if the braking force of the vehicle brakes can be accurately controlled, and in this case, not differing from the usual German usage in this document between the terms tax and rules. Much more Both terms and their grammatical modifications are used synonymously, unless explicitly stated otherwise, which includes both a control by means of a manipulated variable and a control in which a control variable is compared with a reference variable.

In a braking system, the normal force is the manipulated variable and the braking force is the controlled variable. Since the coefficient of friction between friction lining and object to be braked is greatly influenced by the temperature at the interface, but also environmental conditions such as moisture or variations in the roughness of the braking surface can lead to a change in the coefficient of friction, can not close directly on the friction or braking force achieved by the normal force. To control the braking force, therefore, the frictional force itself must be detected.

In disc brakes, the determination of the normal force usually takes place via the measurement of the application force. For this purpose, force sensors are often used in the support of a friction lining on the brake caliper. Instead of this direct detection of the application force, this can also be derived indirectly from the widening of the brake caliper when applying the brake. The measurement of the widening is carried out by means of displacement sensors, wherein the clamping force is usually deduced from the different widening of a loaded and an unloaded arm of the brake caliper. Another way of determining the application force is to perform a strain measurement on a representative point of the caliper followed by a conversion of the strain into the application force.

In order to determine the frictional force or braking force, measuring hubs are currently used in vehicle construction. The friction force is determined by recalculation via the friction wheel. Corresponding systems can be integrated into the vehicle rim or mounted on the suspension of a vehicle. Due to their size, however, they are only as development can be used and not used as part of a braking force control.

Proceeding from this, the object of the invention is to provide a device which detects the normal force and frictional force occurring between a friction lining and a movable object arranged movably relative to the friction lining separately and has a small overall size.

The object is achieved according to the independent claims of the invention.

The invention comprises a device for detecting a, occurring between a friction lining and a relative to this movable lent arranged object, normal force and mediated by the normal force between the friction lining and the article caused frictional force. The device has a first sensor element, a second sensor element and a processing device. The first sensor element is configured to convert a first deformation component into a first electrically detectable parameter representing the first deformation component, the second sensor element is configured to convert a second deformation component into a secondelectrically detectable parameter representing the second deformation component, the first deformation component and the second deformation component in each case represent a component of a deformation of a body and the first deformation component and the second deformation component each represent a component of a deformation of a body, and wherein the first deformation component occupies an angle α to the rubbing direction and the second deformation component an angle -α to the rubbing direction, and α is different from zero.

In this context, it should be noted that the terms "comprise", "comprise", "include" and "with" used in this description and the claims for claiming features and their grammatical variations generally indicate the presence of features such as process steps, facilities, areas, sizes, and the like, but in no way exclude the presence of other or additional features or groupings of other or additional features.

The device has a small size and is thus easily integrated into conventional brake systems. The detection of normal force and a mediated by the normal force between the friction lining and the object caused

Frictional force allows accurate control of the braking force of motor vehicles, machine tools or other machines.

The invention is further developed in its dependent claims.

In an advantageous development of the invention, the angle between the rubbing direction and the two deformation components is ± 45 degrees, so that a high sensitivity and measuring quality of the force determination are achieved.

For an immediate detection of normal and frictional force, the processing device is expediently designed to determine the normal force and the frictional force on the basis of the first electrically detectable parameter and the second electrically detectable parameter. In this case, the processing device is expediently designed to determine the normal force on the basis of an additive combination of the first electrically detectable parameter and the secondelectrically detectable parameter and the frictional force on the basis of a subtractive combination of the first electrically detectable parameter and the second electrically detectable parameter ,

So that the sensor elements do not have to be attached directly to the wear-resistant friction linings of the brake, the friction lining can be accommodated in a support device which has a rigid, for example non-positive, positive fit or cohesively executed connection with at least one, rigidly connected to the friction lining, thrust field, wherein the thrust field is adapted to receive the first sensor element and the second sensor element. To increase the redundancy as well as the accuracy of the measurement, the support device with several, rigidly connected to the friction lining shear fields in turn is rigidly connected.

An inexpensive and mechanically very stable design of the device is characterized by a one-piece design of the

Supporting achieved with the one or more shear fields.

For detecting normal and frictional force via the direct deformation of a friction lining, the first sensor element and the second sensor element are each arranged in the interior of the friction lining.

Further features of the invention will become apparent from the following description of inventive embodiments in conjunction with the claims and the figures. The individual features can be realized in one embodiment according to the invention depending on one or more. In the following explanation of some embodiments of the invention düng reference is made to the accompanying figures, of which

FIG. 1 shows a disk brake in a schematic representation,

FIG. 2 shows the deformation of a body caused by the frictional force and normal force,

FIG. 3 illustrates the tensioning and shear stress caused by the normal force and the frictional force, as well as their components in the respective measuring directions, Figure 4 shows an embodiment of a device for separate detection of acting on a friction lining normal and frictional force shows, and

Figure 5 shows a block diagram of the electronic component of a device for separately detecting the forces acting on a friction lining normal and frictional force.

FIG. 1 shows an example of a disk brake 10 in a schematic representation. The brake object is formed by the brake disc 6 only partially shown. The braking of the brake disc 6 is effected by means of two, arranged on opposite sides of the brake disc 6 and received in a floating caliper 4, friction linings 1 and 5. The active friction lining 1 is attached to an application device having a fixedly connected to the caliper part 4 and 3 comprises a relative to the caliper 4 slidable part 2. The passive friction lining 5 is firmly connected to the brake caliper. To brake the brake disk 6, the active friction lining 1 of the brake 10 is pressed by the application device with a normal force N against a side surface of the brake disk 6. When pressing the caliper 4 designed as a floating caliper shifts relative to the brake object 6, whereby the passive friction lining 5 is also pressed with the normal force N against the second side of the brake disc 6.

Regardless of the specific embodiment of a brake device, the normal force N on each of the brake linings 1 or 5 causes a frictional force R, the direction of the movement of the braking surface, ie the covered by the respective friction lining side surface of the brake disc 6, is opposite to the friction linings , In the disk brake shown in FIG. 1, normal force and friction force are arranged orthogonal to one another. When a friction lining is pressed on, the normal force N leads to a compression, while the friction force R leads to a distortion of a physical object subjected to these forces. The rectangular cross-section of the friction lining 1 shown in FIG. 1 would thus have a diamond-shaped distortion during a braking operation. This is illustrated in Figure 2, wherein the unloaded body or object 11 with a solid, the deformed under the respective forces body 12, however, is shown with a dashed line.

In the representation a of Figure 2, the deformation of the article 11 by the friction force R is shown schematically. The frictional force acts on the surface of the object 11, which bears against the braking surface of the brake object, and displaces it, due to the elastic deformability of the object 11, parallel to the opposite surface. If the surface shown in the illustration is marked with a measuring cross 13 whose bars form the diagonals of a square, then the measuring cross 13 is distorted under the influence of the frictional force R to the shape shown in dash-dotted line representation a.

Representation b of FIG. 2 shows the effect of the normal force N on the shape of the object 11. The force N acting over the entire surface leads to a compression of the elastically deformable object, so that essentially changes its thickness in the form shown. The effect of a combination of frictional force R and normal force N is illustrated in figure c of the figure, wherein the loading of the article 11 with these forces results in a distortion resulting in an upset, parallelogram shaped cross-sectional shape. The elastic distortion is also expressed in the form of the illustrated mitverzerrten measuring cross 13, which forms the diagonal of a square in the unloaded state of the article 11. The distortion, exaggerated in FIG. 2, of the force-loaded body 12 can be detected by means of strain sensors, each of the sensors being designed to measure a strain component in only one direction. The measuring directions of the two sensors are arranged opposite attacking friction and normal force each at an angle and are also at an angle to each other.

The following describes the strains ε _ζ and ε _η along the measuring directions ζ and η of the respective strain sensors with reference to FIG. In FIG. 3 a, the object 11 subjected to the normal force N and the frictional force R is shown in the non-distorted state. The normal force N is directed against the ordinate y, the frictional force R in the direction of the abscissa x of a Cartesian coordinate system. The normal force causes a compressive stress inside the article 11

σ _y = N / A, (1)

which has only one component in the y-direction, ie O _x = 0. A in Equation 1 denotes the area over which the normal force acts on the brake object 11. The friction force R causes a shear stress

τ _xy = R / A, (2)

whose surface normal corresponds to the x-axis and whose direction corresponds to the y-axis. In Figure 3b, the surface element shown in Figure 3a with a dashed line is shown enlarged, indicating the voltages. In order to calculate the stresses along the measuring directions α or -α to the rubbing direction illustrated in FIG. 3c, the voltages O _y , O _x , τ _xy and τ _{yx must be transformed} into the ζ-η coordinate system of the measuring directions. For the following calculations a Cartesian ζ-η coordinate system is assumed without restriction of generality, but only with a view to a clear representation Angle α is rotated relative to the xy coordinate system. This gives you for the tension in the respective measuring direction:

σ _ζ = 0.5- (σ _x + σ _y ) + 0.5- (σ _x -σ _y ) -cos 2α + τ _xy -sin 2α; (3a)

σ _η = 0.5- (σ _x + σ _y ) - 0.5- (σ _x - σ _y ) -cos 2α - τ _xy -sin 2α; (3b)

For the shear stress τ _ζη we obtain:

τ _ζη = -0.5- (σ _x - σ _y ) -sin 2α + τ _xy -cos 2α; (4)

Since σ _x = 0, equations 3a and 3b simplify to:

σ _ζ = 0.5-Gy - 0.5-σ _y -cos2α + τ _xy -sin2α; (5a)

σ _η = 0.5-Gy - 0.5-σ _y -cos2α - τ _xy -sin2α; (5b)

For the strain ε _ζ = ε (α) in the α-direction, ie the strain that is absorbed by the first strain sensor, the following applies:

ε (α) = {0, 5σ _y - (1-v) • (l-cos2α) + (1 + v) • τ _xy -sin2α} / E (6a)

where E is the modulus of elasticity and v is the transverse contraction number of the material from which the shear field is made.

Similarly, for elongation, ε (-α) is obtained in -α direction, i. the strain absorbed by the second strain sensor:

ε (-α) = {0, 5Gy- (1-v) ^• (1-cos (-2α)) + (1 + v) ^• τ _xy ^• sin (-2α)} / E (6a)

With cos2α = cos (-2α) and sin2α = -sin (-2α) one obtains thus:

ε (α) -ε (-α) = 2 ^• (1 + v) ^• τ _xy ^• sin2α / E = Ci-R; (7a)

and ε (α) + ε (-α) = σ _y ^• (1 -v) ^• (l -cos2α) / E = C ₂ - N; (7a)

The difference of the strains in the respective measuring directions is therefore proportional to the friction force R according to equation 7a, while the sum of the strains in the respective measuring directions according to equation 7b is proportional to the normal force N. This result also applies generally to measuring directions ζ and η, which include a different angle from zero at right angles. However, the proportionality factor Ci assumes the maximum value for α = 45 °. C ₂ in this case assumes 0.5 times the value of the maximum gain.

The measurement of the expansion components in the directions of measurement of two strain sensors arranged at an angle to one another thus enables the separate detection of the normal force N and friction force R acting on the object 11.

For the measurement of the expansion components, all strain sensors, in particular resistive (eg strain gauges), piezoresistive, capacitive (MEMS) and fiber optic (based on the Bruggeffekt) strain sensors can be used, which in a suitable manner to a normal and frictional force directly or indirectly exposed object 11 can be applied. The strain sensors need not necessarily be mounted on the surface of the article 11, for example a friction lining 1 or 5, they may also be accommodated within the article in its volume. In any case, the strain sensors must be structurally connected to the article 11. An arrangement of the strain sensors in the interior of the article 11 can already take place during the manufacture of the object, but the strain sensors can also be subsequently introduced, for example by means of suitable adhesive, into the article. Instead of using individual strain sensors, the measuring cross can also be constructed with a strain gauge rosette. In a particularly advantageous embodiment, the strain sensors are not attached to the friction linings 1 and 5 of the brake itself, but on a non-positively connected to a friction lining shear field. An example of this is shown in FIG.

The friction lining 1 or 5 is applied to a lining carrier 7, which is accommodated in a supporting device 8 designed as a frame construction. A thrust field 9, which is rigidly connected to the frame construction 8 as well as to the lining carrier 7, for example in a non-positive, positive or materially connected manner, bridges a cavity arranged between the lining carrier and the frame construction. On the shear field 9, a measuring cross 13 with two mutually arranged at an angle strain sensors is applied so that the strain sensors can detect the expansion components of the shear field in the respective measuring directions of the strain sensors. Due to the rigid connection, the forces acting on the friction lining forces are transmitted directly to the thrust field 9 and deform it according to the transmitted forces.

Deviating from the illustration, the arrangement of FIG. 4 may comprise a plurality of shear fields 9 to which the normal and frictional forces acting on the friction lining are transmitted. In this case, the pusher fields can be connected to the lining carrier or the frame construction in each case rigidly or via a positive connection, which enables the introduction of force. In particular, supporting device 8 and thrust field or shear fields can be formed in one piece. The frame structure 8 is designed rigid enough that the forces discharged over it do not appreciably deform them. Furthermore, the strain sensors 13 can be arranged both on the surface and in the volume of the pusher fields or 9. Notwithstanding the representation, the thrust field 9 can also be arranged so that it is subjected to train. The expansion component of the thrust field 9 or of an object 11 transmitted to a strain sensor can be detected via a change in a parameter of the sensor associated with the strain. In the case of strain gauges, the characteristic is generally formed by the resistance of the sensor element, in the case of fiber-optic strain sensors by the wavelength of the light reflected at the Bragg gratings. These characteristics can be detected electrically by suitable measuring circuits and, for example, can be further processed into signals in a processing device 20 shown in FIG. 5, which in each case represent the normal force N and friction force R acting on the friction lining.

The first strain sensor 14 and the second strain sensor 15 of the measuring cross 13 are usually already provided with a measuring circuit which supplies an electrical output signal representing the expansion of the respective sensor element. If the sensors are not equipped with a corresponding measuring circuit, the processing device 20 comprises sensors connected to the strain sensors 14 and 15, respectively

Measuring devices 21_1 and 21_2 for electrically detecting the change associated with the deformation of the respective strain sensor whose characteristic.

The electrical measuring signals output by the measuring circuits of the sensors 14 and 15 or by the measuring devices 21 1 and 21_ 2 connected to the sensors are forwarded to a summation device 22 and a subtraction device 23 of the processing device 20. In the difference-forming device 23, an output signal is generated on the basis of a difference of the measuring signals from the sensors 14 and 15, which represents the frictional force R in an arrangement which corresponds to the representations of the figures 2 or 4. Accordingly, the output signal generated by the summation means 22 based on a sum of the measurement signals from the sensors 14 and 15 represents the normal force N. The present invention enables the separate detection of the force exerted on a friction lining of a brake normal force and thereby caused frictional force at the interface between the friction lining and the brake object. The small size of the strain sensors used to determine the forces allows the integration of the measuring apparatus in conventional brake systems, whereby a regulation of the braking force during a braking operation is possible. The measured quantities recorded are independent of the distance between the friction plane and the measuring point, so that lining wear has no effect on the measurement. Due to the measurement in the immediate vicinity of the frictional contact the disturbing influences are minimized by possibly acting inertial forces.

LIST OF REFERENCE NUMBERS

1 active friction lining

2 movable part of the application device 3 fixed part of the application device

4 caliper

5 passive friction lining

6 brake object, brake disc

7 lining carrier 8 frame construction, supporting device 9 shear field, shear plate

10 disc brake

11 unloaded item

12 loaded object 13 measuring cross

14 first strain sensor

15 second strain sensor 20 processing device 21_1 first measuring device 21 2 second measuring device

Claims

claims

1. A device for detecting a, between a friction lining (1, 5) and a relative to this movably arranged object (6) occurring, normal force (N) and one mediates the normal force (N) between the friction lining (1, 5) and the object (6) caused frictional force (R), with

a first sensor element (14), which is designed to convert a first deformation component (ε (α)) into a first electrically detectable parameter representing the first deformation component,

a second sensor element (15) which is designed to convert a second deformation component (ε (-α)) into a second electrically detectable characteristic variable representing the second deformation component, and

- A processing device (20) for processing at least the first electrically detectable characteristic and the second electrically detectable characteristic, characterized in that the first deformation component and the second deformation component each represent a component of a deformation of a body (1, 5, 9, 11) and the first deformation component occupies an angle α to the rubbing direction and the second deformation component assumes an angle -α to the friction direction, where α is different from zero.

2. Apparatus according to claim 1, characterized in that the angle (α) between the rubbing direction and the two deformation components is +45 degrees and -45 degrees, respectively.

3. Apparatus according to claim 1 or 2, characterized in that the processing device (20) is formed, the

Normal force (N) and the frictional force (R) on the basis of the first electrically detectable characteristic and the second e- lektrisch detectable characteristic to determine.

4. The device according to claim 3, characterized in that the processing device (20) is designed to determine the normal force on the basis of an additive combination of the first electrically detectable parameter and the second electrically detectable characteristic.

5. Apparatus according to claim 3 or 4, characterized in that the processing means (20) is adapted to determine the friction force on the basis of a subtractive linkage of the first electrically detectable characteristic and the second electrically detectable characteristic.

6. Device according to one of the preceding claims, characterized in that the friction lining is received in a supporting device (8) having a rigid connection with at least one, rigidly connected to the friction lining (1, 5), thrust field (9), the for receiving the first sensor element (14) and the second sensor element (15) is formed.

7. The device according to claim 6, characterized in that the supporting device (8) with a plurality of rigidly connected to the friction lining (1, 5), shear fields (9) is rigidly connected.

8. Apparatus according to claim 6 or 7, characterized in that the supporting device (8) and the one or more thrust fields (9) are made in one piece.

9. Device according to one of claims 1 to 5, characterized in that the first sensor element (14) and the second sensor element (15) are each arranged in the interior of the friction lining (1, 5).