The present invention relates to a method for the operation of a hydraulic vehicle brake, including a brake housing in which a hydraulic working pressure chamber is delimited by a displaceable brake piston, which is movable into operative connection with a brake disc in order to achieve a braking effect, and wherein a parking brake device acts on the brake piston and, in a condition where the brake piston is in operative connection with the brake disc, is lockable by means of a locking device, the said locking device being activated by a force-transmitting element, which is operable by means of an electromagnetic actuator comprising at least one coil, one yoke and one armature, and wherein the position of the force-transmitting element connected to the armature is determined because the change in inductance of the coil is determined depending on the armature movement. Further, the invention relates to a device for the operation of a hydraulic vehicle brake.
DE 10 2004 062 810 A1 discloses a hydraulic vehicle brake of this type. In order to determine the position of the force-transmitting element or the armature connected to the force-transmitting element, the change in inductance of the coil in dependence on the armature movement is detected. However, the method known in the art has the shortcoming of inaccuracies.
In view of the above, an object of the invention is to further improve the method as described hereinabove in order to achieve a higher rate of accuracy.
According to the invention, this object is achieved by the method in that the position of the force-transmitting element is determined in such a way that the result of the determination is independent of the ambient temperature.
In a favorable improvement of the method of the invention, the position determination is performed in such a way that the result is irrespective of the temperature of the coil and/or the yoke and the armature.
It is arranged that the position determination is performed with the following steps:
Another, especially favorable embodiment of the method of the invention provides that the temperature-responsive component of the eddy current in the yoke and in the armature is taken into consideration when measuring the current that flows through the coil, and the result of measurement is corrected accordingly. As the eddy current component distorts the current measurement, consideration of the eddy current component and a correction of the result of measurement is especially favorable.
The previously defined values of the electric resistance of the coil are found by calibration. It is arranged in this respect that the calibration takes place before the initiation of the hydraulic vehicle brake and/or in regular intervals during the operation.
In addition, this object is achieved according to the invention in that means are provided, which carry out the position determination of the force-transmitting element in such a way that the result thereof is independent of the ambient temperature, the temperature of the coil, and/or of the yoke and the armature.
In a particularly advantageous improvement of the subject matter of the invention, the means perform the following steps:
The invention will be described in detail hereinbelow by way of an embodiment, making reference to the accompanying drawings.
In the drawings:
The hydraulic vehicle brake of the invention shown in
As can be taken from
A spindle drive or a threaded-nut/spindle assembly 14, respectively, forms a locking device, which is necessary for realizing a parking brake function in the design illustrated in
The hydraulic vehicle brake is illustrated in
Subsequently, the electromagnetic actuator 3 is energized, with the result that the armature plate 23 is arrested by the electromagnetic actuator 3 in its stop position, as described above. In a following pressure reduction in the working pressure chamber 7 and in the accumulator pressure chamber 9, the brake piston 6 moves to the right in the drawing, while the accumulator piston 11 moves to the left. Arresting of the force-transmitting element 27 enables a relative movement between the force-transmitting element 27 and the accumulator piston 11, whereby the function of the central bearing 21 for the spindle 16 is canceled and the two friction surfaces 17, 18 are moved into engagement with each other. The biased spring element 12 mentioned hereinabove presses the accumulator piston 11, the spindle 16 blocked due to the friction surfaces 17, 18 being in engagement, the threaded nut 15, and thus the brake piston 6 to the left in the drawing and against the brake disc (not shown), respectively. The vehicle brake is thereby locked in its applied condition. Thereafter the electromagnetic actuator 3 is no more energized, and the armature plate 23 and the force-transmitting element 27, respectively, are no more arrested. The valve 24 adopts its de-energized state, and it is hence closed. Thus, the hydraulic vehicle brake does not require energy and hydraulic pressure in order to maintain the locking engagement in the applied condition, which is considered as an advantage.
To release the locking engagement, in turn, hydraulic pressure is built up in the working pressure chamber 7 and, after a corresponding actuation of the NC valve 24, likewise in the accumulator pressure chamber 9. The hydraulic pressure, in turn, would displace the brake piston 6 in
As can be seen in
The coil 25 of the electromagnetic actuator 3 fulfils the function of a sensor for sensing the position of the armature plate 23, which position allows detecting whether locking of the vehicle brake is or is not possible. In addition, especially the action of the armature plate 23 striking against the electromagnetic actuator 3 is a signal for the pressure generator (not referred to in detail) to terminate the pressure buildup for performing a parking brake operation in the pressure chambers 7, 9. In order to reliably determine the position of the armature plate, the change of inductance of the coil 25 of the electromagnetic actuator 3, being caused by the movements of the armature plate, is defined. This is brought about in that voltage pulses are applied to the coil 25. The variation of the current that flows through the coil 25 is simultaneously determined. This current variation indicates the position of the armature plate 23 and, thus, the position of the force-transmitting element 27. As the position of the armature plate 23 changes, the variation of the current that flows through the coil 25 will change as well. The change of inductance of the coil 25 mainly depends on the size of the slot between the armature plate 23 and the iron yoke 26 of the electromagnetic actuator 3.
As the above-mentioned method for the determination of the position of the armature plate 23 or the force-transmitting element 2 connected to the armature plate 23 exhibits inaccuracies, an object of the invention involves further improving the method described in order to achieve a higher rate of precision. The basic idea is that the magnetic resistance influences the inductance of the coil 25. In the method described hereinbelow, the eddy currents are considered temperature-responsively, whereby higher precision is achieved.
In the following, the principle of measurement of sensing the armature plate distance by measurement of the current rise will be explained in detail. Displacement of the armature plate 23 opens an air slot, which increases the magnetic resistance of the ferromagnetic circuit that is formed of yoke 26 and armature 23. The increase of the magnetic resistance causes a reduction of the inductance. This change shall be measured.
The following applies to each coil in a simplified form:
the inductance L can be determined in one single measurement of the current at an appropriate time t, when U and R are known and constant. A graph showing different values of T is illustrated in
Eddy currents develop in extensive electric conductors and are the result of a change in the magnetic field. The magnetic field of coil 25 is bunched in the magnet bowl and the armature plate 23. The magnetic field is proportional to the current. The magnetic field variation is proportional to the change in current. The eddy current is proportional to the magnetic field variation, and the eddy current magnetic field is proportional to the eddy current.
In addition, as can be seen in the sign, the eddy current magnetic field is inverse to its cause, i.e. the magnetic field of the coil 25. The eddy current in the ferromagnetic circuit 23, 26 is opposed to the current in the coil 25. From this follows that the current rise in the commencement is greater than the mere exponential function.
It applies:
From this follows:
From this follows for the induced voltage in the ferromagnetic circuit:
The eddy current is a consequence of the induced voltage in the ferromagnetic circuit, with
The induced eddy current in turn produces a magnetic field:
The addition of coil field and eddy current field has as a result:
With
follows:
It can be seen that the function is the original exponential function, with a factor at e. This factor depends on T and thus on RMagnetic.
Except for RMagnetic this formula contains only known quantities.
With temperature influence, the following formula for the current is obtained:
The corresponding formula for the magnetic resistance is:
RMagnetic, Rel.ferro and Rel.coil are temperature-responsive quantities, however. The temperature of the coil 25 can be measured by way of a calibration at the production site with a known temperature and the IMax-measurement at the beginning of an ignition cycle or an activation, respectively. It must be assumed then that the same temperature is prevailing in the ferromagnetic circuit 23, 26 as well. As the components are positioned in a confined space, this should apply. While relatively simple relations apply with respect to the electric resistances, so far only a rough approximation can be given for the temperature dependence of the magnetic resistance. It is assumed that no temperature dependence prevails in the temperature range to be used. It is applicable for the electric coil resistance:
R
el.coil
=f(T)=R(25° C.)·(1+αΔT)
For copper, α is at 0.0039 1/K.
The minimum temperature practically is at −40° C., the maximum at +140° C.
Thus, the minimum resistance is at 74.65%, the maximum at 144.48% of the nominal value.
For steel, α is at 0.0048 1/K.
Thus, the minimum resistance is at 68.80%, the maximum at 155.2% of the nominal value.
For RMagnetic, it shall be assumed initially that there is no dependence on temperature, at least the dependence at low temperatures is very insignificant.
then applies, and Rel.coil is measured directly, because the current for t=100 ms≈t→∞ is measured at a voltage of e.g. 1.8 volt. Thus, the calibration at the production site only takes influence on the assumed temperature of the iron component, i.e. on the calculation of Rel.ferro=f(ΔT)=f(l(t=100 ms, U0=1.8V,T)).
The application of the theoretic formulas is illustrated in
The same laboratory measurements, by means of which the parameters were found, can be used to produce the function s=f(RMagnetic), a graph of which is shown in
The polynomial formula can be used to transform each RMagnetic, which can now be calculated in a temperature-compensated fashion, into a distance s, which corresponds to the air slot between armature plate 23 and yoke 26 (cf.
The ohmic resistance of the coil 25 at T0=25° C. can be determined at the production site. Based on diagnosis function, it should also be possible in a workshop to initiate this measurement when replacing the brake caliper. Measuring the ohmic resistance of the coil 25 before the start of a sensing cycle allows determining the temperature of the coil 25 and, hence, of the ferromagnetic circuit 23, 26 as well. The temperature can be used to determine the applicable characteristic curve, thus, there is a defined correlation between current, temperature, on-cycle, voltage, and the result of measurement.
One significant advantage of the method lies in the temperature compensation by measuring the ohmic resistance of the coil 25 at the production site, with the temperature known and prior to each sensing operation. It becomes possible only this way to absolutely measure the armature position. Another advantage involves the mathematical consistency of the solution, a mathematical method of approximation is not necessary. Another advantage lies in the temperature-responsive consideration of the eddy currents, what leads to a higher rate of precision.
Number | Date | Country | Kind |
---|---|---|---|
102 43 226.0 | Sep 2002 | DE | national |
102 42 622.3 | Sep 2002 | DE | national |
103 11 747.4 | Mar 2003 | DE | national |
103 13 707.6 | Mar 2003 | DE | national |
103 29 694.8 | Jul 2003 | DE | national |
103 30 389.8 | Jul 2003 | DE | national |
102 58 649.7 | Dec 2003 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP05/56602 | 12/8/2005 | WO | 00 | 6/6/2007 |