DE10359224B4 - Optimized detection of the tracking voltage in DC motors - Google Patents

Abstract

Method for detecting the trailing voltage of a DC motor (100), wherein the DC motor (100) has a clocked drive with a predefinable pulse / pulse pause ratio and a first evaluation unit (210, 220, 230),
wherein the first evaluation unit (210, 220, 230) has at least one capacitor (230) which is charged in accordance with the motor voltage (UMot) detected at the DC motor (100) when a switching means (200) is closed by a corresponding signal,
and wherein the tracking voltage is determined as a function of the charge of the capacitor (230),
wherein after the motor voltage has dropped to a minimum value of zero or less than zero in a pulse pause,
a second evaluation unit (310)
with a rise of the motor voltage (UMot)
above a threshold
the switching means (200) drives in such a way
the motor voltage (UMot) is detected on the capacitor (230).

Description

State of the art

The invention relates to a method for detecting the tracking voltage of a DC motor.

For various applications, it is necessary to detect the speed of DC motors. In this case, the speed can be derived from the tracking voltage in a clocked control of the motor. For example, in the DE 199 14 404 A1 used the post-tensioning voltage of the pump motor in the untimed pulse pause to determine the speed of the pump.

The publication DE 195 39 395 A 1 discloses an apparatus for monitoring the delivery of an electrically driven liquid pump in a wet cleaning machine to its delivery condition. To drive a permanently energized electric motor is provided in the supply circuit an electronically controllable switching means is connected. The switching means is driven by a control device with a pulse-shaped drive signal with a controllable duty cycle to control the electric motor by pulse width modulation. A measuring circuit is connected to sense the generator voltage generated by the electric motor at time intervals in which the supply circuit of the electric motor is interrupted.

The DE 32 21 146 C2 an interrupt circuit arranged in the motor circuit, a sampling and storage circuit sampling and storing the motor voltage, a controller for the controllable voltage source to which a control voltage and as the actual value of the respective motor voltage value stored by the sample and storage circuit are fed, and a timing circuit, which repeatedly causes the breaker circuit to temporarily interrupt the motor current and cause the sample and memory circuit to delay the start of the interruption of the motor current, but prior to its termination, to sample the motor voltage value.

The DE 30 13 402 A1 discloses a method for controlling the speed of a third-drive DC motor, the armature current is clocked with a series-connected to the DC motor and a DC power supply DC-controlled actuator in pulse width or pulse sequence, wherein in the pulse intervals of the clocked armature current, the voltage output from the externally excited DC motor generator voltage is measured, and as a measure of the actual speed value of the externally excited DC motor is supplied to the control circuit for controlling the DC adjuster.

In the DE 195 28 697 A1 a method is described in which, starting from a variable which represents a measure of the rotational speed of the feed pump, a pressure variable at a feed pump, for example in a brake system, is determined.

From the DE 199 46 777 A1 is a method for estimating a pressure prevailing between a master cylinder and an intake valve of a wheel brake cylinder of a motor vehicle brake system, wherein the form is estimated taking into account a trailing voltage of a clocked motor of a pump for delivering brake fluid.

The detection of the tracking voltage in the prior art usually takes place via an averaging of instantaneous values of the motor voltage in the pulse interval. This averaging is necessary because the regenerative tracking voltage is interspersed by the so-called. Brush fire with quite large interference signals. The recording of the instantaneous values is controlled, for example, by the timing of a microprocessor, with several instantaneous values having to be taken in order to obtain a measurement signal of sufficient quality, since the scattering of the instantaneous values can be very large. From the mean value thus obtained, the speed of the DC motor is then calculated.

Advantages of the invention

The invention describes a device and a method for detecting the trailing voltage of a DC motor, wherein the DC motor is operated by a clocked drive. In this case, the clocked drive at least during the switch-on of the engine to a predeterminable pulse / pulse pause ratio. The core of the invention is at least one evaluation unit which detects the tracking voltage from a tracking voltage variable representing the tailing voltage of the DC motor. According to the invention, the evaluation unit has at least one capacitor which is charged in accordance with the motor voltage detected at the DC motor when a switching means is closed by a corresponding signal,
wherein the tracking voltage is determined in dependence on the charge of the capacitor (230). In this case - after the motor voltage has dropped to a minimum value of zero or less than zero in a pulse pause, the switching means is controlled by a second evaluation means with a rise of the motor voltage over a threshold value such that the motor voltage is detected on the capacitor.

With such an evaluation device according to the invention, the tracking voltage can be detected faster than with the methods or devices known from the prior art. This rapid detection allows a more rapid determination of the speed of the DC motor and thus a better adaptation of the flow rate of a pump connected to the motor. Furthermore, only the physically minimum time required for detecting the trailing voltage is used, since the detection can be adapted automatically to the operating state of the motor and thus a shortening of the switch-off time of the motor can be achieved. By such an adaptation, it is possible to operate the engine with a higher-frequency control. Such a control has positive effects on the noise, the engine dynamics and the speed stability.

When using an integrating AD converter, as can be realized, for example, by a delta-sigma converter, moreover, it is possible to obtain exact average values of the tracking voltage. The corresponding values are available without delay and continuously. With a sigma-delta converter, shorter cycles can be achieved for the detection of regenerative follow-up voltage, which also allow a higher-frequency control of the motor.

In one embodiment of the invention, the first time duration t _{mess_off} and / or the pulse / pulse _{pause ratio} which controls the timing of the drive of the DC motor is modified during the operation of the DC motor. This can be done, for example, depending on the time course of the tracking voltage. Advantageously, however, the first time duration t _{mess_off} and / or the pulse / pulse _{pause ratio} is given by the same fixed value at each restart, and it may well be provided that the last values can be used before the shutdown of the DC motor for the restart of the engine.

Advantageously, the tracking voltage magnitude is detected by the first evaluation means during the pulse pause in a second time period τ. However, in the case of the second time period τ, it should be noted that the entire time duration from the first time duration t _{mess_off} and the second time duration τ must not exceed the third time duration of the pulse interval T _out . Furthermore, it is provided in particular that the second time duration τ can be predetermined, for example when the motor is restarted, but also during the entire detection. In a further embodiment of the invention, however, the second time duration τ can be modified as a function of the course of the tracking voltage during the detection of the tracking voltage.

Furthermore, it is provided in one embodiment of the invention that the first evaluation means comprises at least one capacitor, in particular as part of a low-pass filter, wherein the switching means controls the charge of the capacitor. Preferably, the charge is controlled as a function of the tracking voltage magnitude. The tracking voltage is then determined as a function of the charge of the capacitor, for example via the voltage applied to the capacitor. In a further embodiment of the invention, an integrating AD converter can also be provided as first evaluation means.

In a particular embodiment of the invention, the switching means is designed as a sample and hold circuit element. Furthermore, it can be provided that the second evaluation means at least partially takes over the control of the switching means.

Advantageously, the DC motor controls a pump, for example a return pump in a vehicle. In addition, it can also be provided that the tracking voltage is used to estimate the delivery rate of a pump.

By the proposed invention, a rapid detection of the regenerative tracking voltage can be achieved, which is generated by the movement of the motor in the pulse break. This can be done for example by the rapid charging of a suitably dimensioned capacitor. Furthermore, can be shortened by the rapid detection of the trailing voltage, the switch-off of the engine. Thus, an operation of the engine with a higher-frequency clocked control is possible. A reduction in the engine off time, for example, in the context of a higher-frequency control can have a positive effect on the noise, engine dynamics and speed stability.

Another advantage of the invention is that the regenerative tracking voltage is not detected directly, but for example via a sample and hold stage. Thus, a temporally optimized detection of the tracking voltage is possible. The shortened measuring time makes the motor smoother so that the speed of the motor can be regulated better. Furthermore, the capacitor of a low-pass filter is not constantly discharged to zero by the sample and hold circuit, so that during the sample time in the capacitor only the amount of charge must be recharged, which is the difference to the last measurement.

Advantageously, the invention can be used with different drive variants of the motor, ie with clocked drive with lückenendem current, for example at a 50Hz clocking, or non-licking current, for example at a 20kHz clocking or RF clocking. By a targeted interruption of the power supply, however, the tracking voltage and thus the speed of a DC motor can be detected, which is operated with a continuous control. For this purpose, the tracking voltage is detected during the interruption according to the invention.

In contrast to the prior art, no instantaneous values of the tracking voltage magnitude are detected in the present invention, but the tracking voltage quantity is integrally detected. Advantageously, in this integral detection, the transition phase from the supply voltage to the regenerative tracking voltage is hidden. Furthermore, the measuring time for the detection of the tracking voltage is shortened, since no complex recording of several instantaneous values is necessary.

By using the invention, it can be achieved with higher-frequency control of the DC motor that the supply current has fewer peaks, which leads to a lower effective value. This manifests itself advantageously on the wiring quality.

Further advantages will become apparent from the following description of exemplary embodiments or from the dependent claims.

drawings

1 shows the detection of the tracking voltage, as it is already known by the prior art. In contrast, in 2 a simple example showing the detection of the tracking voltage by means of a switching means. In 3 is a more complex example of a possible embodiment of the invention described. 4 shows the course of the motor voltage during a pulsed control of the motor. 5 shows another example of a circuit in which an integrating AD converter is used to detect the tracking voltage.

embodiment

A possible example of the realization of a clocked drive of a motor shows 1a using an equivalent circuit. In this case, the motor 100 is operated by a battery voltage U _Bat , which is applied to the motor 100 via the terminals 110 and 120 when the switch 130 is closed. By a targeted opening and closing of the switch 130, the engine can be controlled clocked. For example, as in 4 U _Mot is based on the application of the motor voltage shown at a time t _0, the switching means is closed, whereby the pulse phase of the time period starting _at T. The voltage applied to the motor voltage U _Mot corresponds approximately to the supply voltage U _bat . At time t1, the switch 130 is opened and the motor voltage falls briefly to a minimum value, which may be zero or less than zero (see 1b ). At the same time, the motor current I _Mot drops to zero. At time t1, the pulse pause begins with the time period T _out . The motor which continues to run between times t1 and t2 during the pulse break time T _off now acts as a generator. As a result, a voltage, the so-called regenerative voltage U _G or also trailing voltage is generated at the motor, which slowly decreases starting from a maximum value with the time T1 (see 1b ). At time t2, the switch 130 is closed again and the voltage rises to the supply voltage U _Bat . At the time t3 after the time T _on , the switch 130 is opened again and the motor voltage U _Mot shows the behavior already shown at time t1.

In the prior art, as exemplified in 1a and 1b is shown, the regenerative voltage or tracking voltage during the period T1 is detected by an evaluation means 140. In this case, instantaneous values of the motor voltage U _{Mot are} read into an AD converter and averaged. The times of the instantaneous value detection are predetermined by the sampling rate of a microprocessor, for example. Since the motor voltage in the follow-up operation is interspersed mainly by the brush fire with quite large interference signals, averaging of the instantaneous values over a longer period, ie over several sampling points is necessary to minimize the error or the scattering when detecting the tracking voltage as possible. A use with higher-frequency control of the DC motor is therefore not meaningful possible. With the help of the tracking voltage thus detected, it is then possible to determine the speed of the motor or, when using a pump motor, the flow rate.

A simple embodiment of the invention is exemplary in the 2a shown. In it, as already on the basis of 1a explained, a motor 100 operated by a clocked driving a supply voltage U _Bat . Contrary to the prior art, however, the motor voltage U _{Mot is} not detected at any time, but only when the switching means 200 is closed. With this switching means 200, which is preferably designed as a sample and hold member, a targeted recording of the motor voltage U _Mot and the current generated in the wake can be achieved with a suitable control. A first evaluation unit 210, to which the low-pass filter consisting of the resistor 220 and the capacitor 230 can be counted in the broader sense, then enables the detection of the tracking voltage U _Hold .

In the 2 B Time curves of some quantities are plotted to e, which are relevant in the pulsed control of the motor 100 or in the detection of the tracking voltage. Thus, the course of the motor current I _Mot via the terminals 110 and 120 until the time t1 a constant value which drops when opening the switch 130 to zero and only rises again when the supply voltage U _Bat after the time T2 by the closure of the switch 130 rests again on the motor 100. The course of the motor voltage U _Mot is in contrast to 4 portrayed in a slightly idealistic way. So the voltage rises after switching off the supply voltage U _Bat in 4 steadily until he has reached the maximum value in the pulse break. As with the 2c However, the principle of the invention is to be shown, this difference should not be considered further below. After the motor current I _{Mot has} dropped to zero, the switching means is activated to allow recording of the motor voltage U _Mot . Since in comparison with the prior art with the proposed invention, the recording of the _{tracking voltage magnitude} within the time T2 (corresponds to t _{mess_on} in 4 ), is a significant drop in motor voltage U _Mot , as in 1b or also dashed in 2c is shown not to watch. At the same time, the shortened measuring time can lead to a premature switching on of the pulse phase, ie the supply voltage can be applied to the motor 100 again before t ₂ . This has the consequence that with the present invention, higher clock frequencies in the control of the DC motor can be achieved because the faster detection of the tracking voltage size, the measuring time compared to the standard method can be reduced by T3.

After the switching means by a corresponding signal ( 2d ) has been closed, the capacitor 230 is charged according to the detected motor voltage U _Mot ( 2e ), wherein the charge height of the capacitor can be used as a measure of the tracking voltage. If the charge of the capacitor no longer changes, or if the pulse pause ends after time T2, then the connection is opened again by the switching means, the detection of the cascade voltage quantity is ended and the motor is actuated again by the supply voltage U _Bat . The motor current I _Mot rises until it has reached its maximum value again. The evaluation unit 210 can then determine on the capacitor 230, the tracking voltage U _Hold , without a direct connection to the engine must be maintained.

Another embodiment is in 3a shown. In this case, the timing of the drive of the motor, that is, the pulse / pulse pause ratio and the frequency of the clock is generated by a control unit 320 which controls the switch 130. The control unit 320 transmits the information regarding the pulse phase and pulse pause phase to a second evaluation unit 310, which controls the switching means 200 or the sample and hold element as a function of this data. For example, it is provided that by a control, as in 2d and 3d shown, the switching means 200 is closed, and thus a recording of the motor voltage U _Mot in the low-pass 300 is made possible. In this illustration, the low-pass filter 300 is a part of the first evaluation unit, wherein the illustration of other parts which are provided for detection and possibly for evaluation of the tracking voltage in the first evaluation unit has been omitted for reasons of clarity. As an output value, the first evaluation unit supplies, for example, a quantity U _Hold , which represents the tracking voltage and / or the rotational speed of the motor 100.

In the 3b to e is the time behavior of the variables relevant for the detection of the tracking voltage according to the exemplary embodiment in FIG 3a shown. In 3b the timing is shown, with which the motor 100 is driven. The effects of the clocked control on the motor voltage U _Mot shows 3c , In contrast to 2c Here, however, the increase of the motor voltage after switching off the switch 130 by a flank 350 is shown. If the rise of the motor voltage U _Mot or the edge 350 is detected by the evaluation unit 310, for example by the motor voltage U _Mot exceeding a threshold value or the motor voltage U _Mot remaining almost unchanged for a certain time after the edge 350, then the switching means 200 is activated in this way ( 3d ), that the motor voltage U _Mot can be detected in the evaluation unit 300, for example on the capacitor. Thus, the control of the switching means 200 may result in that 3e the capacitor only has to be recharged or charged with the amount of charge representing the difference .DELTA.U to the last detection operation.

After the successful charging of the capacitor, the conditions for detecting the tracking voltage are given, which is why the pulse pause can be terminated. The end of the pulse pause is reported back from the evaluation unit 310 to the control unit 320 (see 3a ). Thus, for example, the timing of the control of the DC motor can be adjusted to the detection of the tracking voltage by the constancy of the time change of the charge of the capacitor is taken as an indication of the end of the detection of the motor voltage U _Mot . Thus, an adaptation of both the pulse / pulse pause ratio, represented by the ratio T _on / T _off , as well as the clock frequency of the drive in response to the detection of the tracking voltage conceivable.

die erste Zeitdauer t_{mess_off} bis zum Start der Erfassung der Nachlaufspannungsgröße zusammen mit der Messzeit τ maximal die Zeitdauer der Pulspause T_aus ergeben darf.Furthermore, with the evaluation unit 310 and the first evaluation means, the first time duration t _{mess_off} and the measurement time t _{mess_on} can also be determined and modified for further evaluation in subsequent clock cycles. However, since the period of time T may be predetermined for a given pulse / pulse ratio _and the period of time t _{mess_off} by the behavior of the engine with the supply voltage U _Bat is predetermined, it may happen that the measurement time τ in which the capacitor is charged, is less than the maximum possible measuring time t _{mess_on} is. Thus, it follows that according to $${\text{t}}_{\text{mess\_off}}+\mathrm{\tau }\le {\text{T}}_{\text{out}}\text{.}$$

the first time duration t _{mess_off,} up to the start of the acquisition of the _{tracking voltage variable,} together with the measuring time τ, may result in a maximum of the duration of the pulse interval T _out .

One way of interrogating the charge of the capacitor to determine the tracking voltage is to use an integrating AD converter as the first evaluation means.

In a further embodiment, the determination of the rotational speed of a continuously operated DC motor is possible with the present invention. For this purpose, a possibility must be provided to temporarily disconnect the motor from the supply voltage. During this brief interruption of the power supply, a detection of the tracking voltage can be carried out according to the above invention, from which in turn can be closed to the speed.

By the present invention, it is possible to reduce the cutoff frequency of the low-pass filter 300, since the charge of the capacitor can be used as a measure of the tracking voltage. By reducing the cut-off frequency of the low-pass filter, the quality of the measurement signal increases at the same time, as higher-frequency disturbances in the wake of the motor can be more effectively masked out.

In a further embodiment according to 5 An integrating AD converter is used to detect the generator trailing voltage. For example, this is a delta-sigma converter 500 that is less susceptible to short failures than "normal" AD converters that may occur during operation of an engine. With the delta-sigma converter 500, the detected tracking voltage at the motor 100 can be converted into an average value within the integration or conversion time, wherein the average value can be used as a tracking voltage variable for further processing. The advantage of using a delta-sigma converter is that the tracking voltage can be continuously detected and output as a digital signal, for example to a microprocessor for further processing. Since the regenerative tracking voltage is detected and integrated over the entire time, an exact mean value of the tracking voltage can be formed. In comparison, other AD converters capture and convert instantaneous values, with the input values needing to be filtered. Typically, one or more RC-elements are used, which cause a time delay of the signal.

The averages generated by the delta sigma converter 500 are available independent of operating system specific tasks. In this context, operating system-specific tasks are to be understood as time slices that trigger the acquisition or integration / conversion. Typically, 1-ms tasks are used, whereby the system receives the instantaneous values of the tracking voltage in the pause between 2 actuations in the 1-ms time interval. Typically, about 2 to 5 measurement points are used to form the average, which produces a relatively inaccurate and highly scattered measure of the tracking voltage. However, when using a delta-sigma converter, the conversion time can be adjusted to better utilize the available time. Since the AD converter does not have to be triggered synchronously to the tasks, the value thus obtained is not delayed by a processing time of the read-out program.

Claims (2)

Method for detecting the trailing voltage of a DC motor (100), wherein the DC motor (100) has a clocked drive with a predefinable pulse / pulse pause ratio and a first evaluation unit (210, 220, 230), wherein the first evaluation unit (210, 220, 230) has at least one capacitor (230), which is charged in accordance with the motor voltage (UMot) detected at the DC motor (100) when a switching means (200) is closed by a corresponding signal, and wherein the tracking voltage is determined depending on the charge of the capacitor (230), wherein after a pulse break the motor voltage has fallen to a minimum value of zero or less than zero, a second evaluation unit (310) when the motor voltage (UMot) rises above a threshold value, the switching means (200) controls such that the motor voltage (UMot) is detected on the capacitor (230). Method according to Claim 1 , characterized in that the capacitor (230) is part of a low-pass filter (300) and the tracking voltage is detected by the voltage applied to the capacitor (230).

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