Method and circuit for detecting an open line of the sine/cosine receiver coil of a resolver

Abstract

A method for detecting an open line (10) of a receiver coil (17; 18) of a resolver (16) comprisesproviding a pull-up resistor (R.sub.1; R.sub.3) and a pull-down resistor (R.sub.2; R.sub.4) at the terminals (7a, 7b; 8a, 8b) on a control device (1) for the signal lines (13a, 13b; 14a, 14b) of the receiver coil (17; 18);measuring the voltage between the two signal line terminals (7a, 7b; 8a, 8b) of the receiver coil at two sampling times provided symmetrically at the middle of the excitation period;calculating an offset value by calculating an average value that comprises the measured values measured at the two sampling times in an excitation period; andidentifying an open line (10) if the offset value exceeds a threshold value.

Claims

1. A method for detecting an open signal line of a receiver coil of a resolver, the method comprising: providing a pull-up resistor and a pull-down resistor which are connected with their one end to terminals for the signal lines; measuring the voltage between the two signal line terminals of the receiver coil at least two sampling times located symmetrically with respect to the center of the exciter period; calculating an offset value by forming a mean value which comprises the measurement values at the two sampling times of an exciter period; and identifying an open line when the offset value exceeds a threshold value.

2. The method as claimed in claim 1, wherein the pull-up resistor and the pull-down resistor are supplied at their other end with a voltage potential which differ by a constant amount from the other which is smaller than the measuring range of the AD converter for the measurement values of the receiver coil.

3. The method as claimed in claim 1, in which the calculating of the offset value takes into consideration the measurement values at the two sampling times of only one individual exciter period.

4. The method as claimed in claim 1, in which the calculating takes into consideration the measurement values at the two sampling times of a plurality of preceding exciter periods.

5. Circuit for detecting an open line of a receiver coil of a resolver, the circuit comprising: a control device with a processor, power stages, first terminals for providing signals at the exciter lines to the exciter coil of the resolver and second terminals for connecting the signal lines for the signals of the sinusoidal and the cosinusoidal coil; two AD converters which are connected to the second terminals of the control device and the outputs of which can be read and evaluated by the processor; the exciter lines which couple the first terminals to the exciter coil of the resolver; the signal lines to be diagnosed for the sinusoidal and cosinusoidal signals provided by the resolver, which couple the resolver to the second terminals of the control device; pull-up resistors which are connected with their one end to one of the terminals for the lines of the sinusoidal coil and the cosinusoidal coil and with their other end to a first direct-voltage potential; and pull-down resistors which are connected with their one end to the other one of terminals for the lines of the sinusoidal coil and the cosinusoidal coil and with their other end to a second direct-voltage potential, the second direct-voltage potential being lower than the first direct-voltage potential, in such a manner that the voltage difference lies between and in the measuring range of the AD converters; and a display or storage device for displaying or storing the information identified by the processor, into which the positive detection of an open line of one of the receiver coils of a resolver is included.

6. The circuit as claimed in claim 5, wherein the pull-up and the pull-down resistors are integrated into the control device.

7. The circuit as claimed in claim 5, wherein the resistance values of the pull-up resistors and the pull-down resistors are large compared with the ohmic resistance of the sinusoidal coil and of the cosinusoidal coil.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a circuit according to an illustrative embodiment of the invention.

(2) FIG. 2 diagrammatically explains the steps for carrying out the method according to an illustrative embodiment of the invention.

(3) FIG. 3 shows details in the variation with time of the voltages on occurrence of the fault case.

DETAILED DESCRIPTION

(4) In FIG. 1, the control device 1 for the resolver 15 is in the center which can be integrated in the control device for a vehicle (not shown here). It has a processor 2 (or also uses one) which monitors the correct sequence of all resolver functions to be controlled and also indicates malfunctions, if necessary.

(5) The control device 1 controls, in particular, power stages 3 and 4 for providing the sinusoidal exciter signal for the exciter coil 16 of the resolver 15 at the first terminals 5 and 6. At the second terminals 7a, 7b and 8a, 8b, the signals of the sinusoidal coil 17 and of the cosinusoidal coil 18, which represent the instantaneous angular position of the object being measured (e.g. the shaft of the engine), pass to the control device 1 and, after conversion in the AD converters 21 and 22, can be processed further as digital signal by a software.

(6) The resolver exciter lines 11 and 12 represent the connection from the first terminals of the control device 1 to the resolver 15, i.e. to its exciter coil 16. From the sinusoidal coil 17 and the cosinusoidal coil 18 of resolver 15, the signal lines 13a, 13b, 14a and 14 go to the second terminals 7a, 7b, 8a and 8b of the control device 1. These lines must be monitored with respect to a break which is indicated by the potential breaks 10 in FIG. 1.

(7) Furthermore, pull-up resistors R.sub.1 and R.sub.3 are provided which are connected with their one end to one of the terminals 7a and 8a for one of the lines 13a and 14a to the sinusoidal coil 17 and to the coinusoidal coil 18. At their other end, the pull-up resistors R.sub.1 and R.sub.3 are connected to a first direct-voltage potential U.sub.H. With the other terminals 7b and 8b for lines 13b and 14b to the sinusoidal coil 17 and the cosinusoidal coil 18, pull-down resistors R.sub.2 and R.sub.4 are connected with their one end and with their other end to a second direct-voltage potential U.sub.L. In this context, the second direct-voltage potential U.sub.L is lower than the first direct-voltage potential U.sub.H and the voltage difference U.sub.HU.sub.L can lie within the measuring range of AD converters 21 and 22.

(8) The method for detecting an open line 10 of a receiver coil 17 or 18 of a resolver 16, as explained symbolically in FIG. 2, is identical for both receiver coils. In step 31, it is based on providing the aforementioned pull-up resistor R.sub.1 and R.sub.3, respectively, and the pull-down resistor R.sub.2 and R.sub.4 at terminals 7a and 8a and 7b, respectively, and 8b at the control device 1 for signal lines 13a and 14a and 13b, respectively, and 14b.

(9) The next method step is the measuring 32 of the voltage between the two signal line terminals 7a and 7b and 8a and 8b, respectively, of the respective receiver coil at two sampling times R and F located symmetrically to the center of the exciter period. These measurements can take place with the AD converters 21 and 22 in addition to the operational measurements of the angular position of the rotor or the processor 2 can also select the measurement values at times R and F from these measurement values. This is followed by the calculating 33 of an offset value U.sub.DC by forming a mean value which comprises the measurement values U.sub.R, U.sub.F at the two sampling times R and F of an exciter period
U.sub.DC=*(U.sub.R+U.sub.F).

(10) FIG. 3 explains the significance of this value. It shows the variation with time of potential U.sub.High and U.sub.Low at the two terminals 7a and 7b of the sinusoidal coil in the left-hand half of the figure before and on the right after occurrence of the fault of an open signal line. The voltage difference between the two signal lines 13a and 13b, designated as high and low in FIG. 3, is indicated by vertical arrows. In faultless operation (on the left) it is caused by the exciter coil 16 and its variable coupling via the rotor. Since the two terminals 7a and 7b of the signal lines are run to the AD converter 21, it is only this difference which is the measurement value of the signal of the sinusoidal coil which is processed further by the processor. The potential of the two lines at terminals 7a and 7b to ground is additionally determined by the pull-up resistor R.sub.1 and the pull-down resistor R.sub.2 and the potentials U.sub.H and U.sub.L to which they are connected. These resistors act as voltage dividers and lead to an offset for the potentials (in FIG. 3, the potentials are designated as U.sub.High and U.sub.Low), the offset value being about 2.1 V in the example shown in FIG. 3. The comparatively low ohmic resistance of the receiver coil 17 acts as short circuit with respect to this voltage divider and prevents the formation of a significant voltage difference between U.sub.High and U.sub.Low beyond the measurement signal.

(11) If then the voltage difference between times R and F, shown by the two arrows on the left, which is switched to the AD converter for the fault detection is added up, a value close to zero is obtained. It is only if the amplitude of the resolver signal changes, which may occur under certain operating conditions, that this sum differs from zero; but it still remains small, particularly smaller than a predetermined threshold value C.sub.S. In addition, the possibility exists to include the measurement values at times R and F from one or more of the preceding exciter periods, in the formation of the mean value in order to eliminate this risk of a false diagnosis.

(12) If then the fault of an open signal line occurs (on the right in FIG. 3), the short-circuit effect of the receiver coil 17 disappears so that no more voltage divider is formed by the pull-up resistor R.sub.1 and the pull-down resistor R.sub.2. The potentials of the two line terminals 7a and 7b and, respectively, 8a and 8b are instead now pulled to the direct voltage potential U.sub.H and U.sub.L, respectively, via the pull-up resistor R.sub.1 and the pull-down resistor R.sub.2 to the direct-voltage potential U.sub.H and U.sub.L, respectively, and the voltage difference detected by the AD converter (in FIG. 4, e.g.: 2.8 V1.6 V=1.2 V) between terminals 7a (high) and 7b (low) indicated by arrows in FIG. 3, here, too, is a fixedly positive value U.sub.HU.sub.L which respectively exceeds the threshold value C.sub.S. Identifying 34 (see FIG. 2) an open line of one of the signal lines 13a, 13b of the sinusoidal coil therefore takes place by observing whether the offset value U.sub.DC at the associated AD converter 21 exceeds the threshold value C.sub.S without a clipping of an AD converter having to take place. This correspondingly applies to the signal lines 14a and 14b of the cosinusoidal coil 18.

(13) On the basis of the finding of whether the offset value U.sub.DC exceeds the threshold value C.sub.S and thus whether an open signal line 10 is diagnosed, the required measures can take place very rapidly, particularly the finding of the fault is indicated or stored, respectively, with a display and/or storage device 9. In this context, the openline can be designated, e.g., by its color or its reference number.