GB2290178A

GB2290178A - Device for operating an electric motor

Info

Publication number: GB2290178A
Application number: GB9511119A
Authority: GB
Inventors: Veit-Michael Brenner; Lukas Thull
Original assignee: GKR Gesellschaft fuer Fahrzeugklimaregelung mbH
Current assignee: GKR Gesellschaft fuer Fahrzeugklimaregelung mbH
Priority date: 1994-06-07
Filing date: 1995-06-01
Publication date: 1995-12-13
Anticipated expiration: 2015-06-01
Also published as: FR2721456A1; JPH089691A; GB9511119D0; DE4419813A1; GB2290178B; FR2721456B1

Description

2290178 Device for olperatincr an electric motor

Prior art

The invention proceeds from a device for operating an electric motor according to the generic type of the independent claims. German Patent 28 20 330 discloses a circuit arrangement for an electric window lift drive which has an anti-jamming device. An evaluation arrangement detects a current flowing through an electric motor, and a te=oral current change referred to time. The two characteristics determined for the current flowing through the electric motor are added and compared with a prescribed threshold value. After an overshoot of the threshold value, the electric motor is, for example, reversed, so that an object possibly jammed by a pane is released again. The evaluation arrangement contains a plurality of capacitors which implement low-pass filters with the aid of further components in each case. in addition to suppressing interference signals, the suppression of higher- frequency signal components in the determination of the characteristics also effects suppression cf the detection of the starting operation, Li the case of which a high motor current occurs which can he a multiple above the value of the steady-state motor current.

EP-A 0 116 904 discloses a drive device for a flap in air conditioning systems of motor vehicles. The flap is actuated by a stepping motor. It is ensured that the flap actuated by the stepping motor reliably reaches mechanical end stops due to the fact that, on the one hand, independently of the position of the flap which in to be prescribed the control device applies to the stepping motor at the beginning of an operating phase a maximum number of steps which suffices for one of the end stops of the f lap to be reached. On the other hand, in the case of each further setting of the flap in each of the mechanical end stops, in addition to the steps required for this purpose the stepping motor has further steps applied to it in the direction of movement of the flap, in order reliably to reach the respective end stop of the flap owing to this number of extra steps, and to compensate for possible lost steps of the stepping motor.

it is the object of the invention to specify a device for operating an electric motor, which uses simple means to detect an overload or a blocked state of the electric motor, in particular a stepping motor.

The object is respectively achieved by =cans of the features specified in the independent claims.

Advantages of the invention The device according to the invention has the advantage that an overload state, for example a blocked state, can be detected by determining at least one characteristic of the current flowing through a =tor, in particular a stepping motor.

It is provided in accordance with a first embodiment that the determination of the at least one characteristic is provided within an interval which, starting from the at least approximately de-energized state, begins at a prescribed time after starting the electric motor and ends before the steady-state motor current is reached. it is possible with the aid of this measure to detect an overload state or blocked state an early as the starting phase of the electric motor. The device according to the invention is therefore particularly suitable in the case of stepping motors to which individual starting pulses are applied to prescribe the number of steps, the flow of current through the motor starting at least approximately from the de-energized state in each case. A comparable operating state can occur in the case of a DC motor which has a clocked operation. It is provided within the framework of such a clocked operation 1 that a prescribed operating voltage in connected to the DC motor for a prescribed interpulne period and in subsequently switched off again for a prescribed interpulse period. Both the ratio of pulse duration to interpulse period, and the frequency can be variable. A precondition f or the proper functioning of the device according to the invention in the case of clocked operation of the DC motor is that the current f lowing through the DC motor decreases within the interpulse periods at least approximately to the value zero.

in accordance with another embodiment of the device according to the invention, it in provided that the determination of the at least one characteristic in provided at a prescribed instant 'which occurs af ter is starting the electric =tor, starting from the at least approximately de-energized state, and bef ore the steady-state motor current in reached.

The devices according to the invention are particularly suitable for detecting mechanical end stops which can be reached by an actuator driven by an electric motor.

Advantageous developments and refinements of the devices according to the invention follow from the dependent claims.

The amplitude, of the current, occurring in the interval or the amplitude occurring at the specific instant, for example, is provided as a first characteris tic of the current to be evaluated. Another advantageous refinement provides that the current change or the imum current difference which has occurred in the prescribed interval is determined as the characteristic.

A development of this measure provides that the current change is referred to time. The relationship with time corresponds to a time derivative of the current which can be performed both within the interval (difference quo tient) and at the prescribed specific instant (differen tial quotient).

Another advantageous refinement of the first embodiment provides that the interval starts simultaneously with the starting of the electric motor. This measure ensures that the characteristic can be detected without a gap at the sarne time an the starting of the electric motor.

An advantageous development provides that the characteristic detected is compared with a prescribed threshold value which can be designed to be adjustable, for example, and that In the event of the threshold value being exceeded an overload state or a blocked state is detected and signalled. The blocked state can be used, for example, to detect the mechanical end stops, already described, of a drive actuated by the electric =tor.

Further advantageous refinements and developments follow from the further dependent claims In conjunction with the following description.

Drawing Figure 1 shows a block diagram of a device according to the invention for operating an electric motor, and Figures 2 and 3 respectively show current characteristics as a function of time which occur in the device according to the invention in accordance with Figure 1. Figure 1 shown an electric motor 10 which actuates a drive 11. The drive 11 has mechanical end stops 25 12, 13. The electric motor 10 in connected via four power supply lines 14 - 17 to a power output stage 18. The power output stage 18 is fed electric energy via power supply lines 19, 20. A control arrangement 21 outputs control signals 22 to the power output stage 18 and a starting si 1 23 to an evaluation arrangement 24. The control arrangement 21 is f ed an external control signal 25 as well as an overload signal 26 generated by the evaluation arrangement 24. Arranged In one of the power supply lines 14 - 17 is a current sensor 27 which detects the current flowing in the power supply line 14 -17 and relays it to a characteristic-determining unit 28 which is contained in the evaluation arrangement 24. The characteristic-deter. ning unit 28 outputs a characteristic signal 29 to a comparator 30 which compares the characteristic signal 29 with a prescribed threshold value 31, and outputs the overload signal 26 as a function of the result of comparison. The starting signal 23 in fed to a time generator 32 contained in the evaluation arrangement,24 and containing a time delay 33. The time generator 32 outputs an activation signal 34 to the characteristic deter=4 ning unit 28.

Figure 2 shows an a function of time t the currents 1 which can be detected by the current sensor 27. A first current 40, which has a sawtoothed characteristic, occurs in the non-overloaded operation of the is drive 11. A second current 41 occurs when the drive 11 in overloaded. The currents 40, 41 respectively start to flow after a starting instant To. After the expiry of a prescribed pulse duration T., the currents 40, 41 drop to zero again. The current characteristic in repeated after a prescribed interpulse period Tp. A prescribed time interval T. starts at a first time T, and ends at a second time T2' Figure 3 shown the same currents 40, 41 an a function of time t an does Figure 2. Instead of the time interval T. shown in Figure 2, in Figure 3 a delay time TV occurs which starts from the starting instant TO and lasts until a sampling instant TA The device according to the invention and in accordance with Figure 1 operates as follows:

The electric motor 10 actuates the drive 11, which has the two end stops 12, 13. A DC motor excited by a permanent magnet or, preferably, a stepping motor, for example, is suitable as the electric motor 10. A bipolar stepping motor requires, for example as drawn in Figure 1, at least four power supply lines 14 - 17. The power required by the electric motor 10 in provided by the power output stage 18, which draws it from an energy source (not shown in more detail) via the power supply lines 19, 20. The direction of rotation and, as the case may be, the motor output are f ixed by the control arrangement 21 as a function of the external control signal 25, which arrangement cammunicates them to the power output stage 18 via the control signals 22.

The current 40, 41 flowing through the electric motor 10 is detected by the current sensor 27. In the case of a stepping motor having more than two power supply lines 14 - 17, it suf f ices when the current 40, 41 is detected in a selected power supply line 14.

io A shunt resistor or the detection of a voltage drop across an output stage component, for example, is suitable as current sensor 27. The current is preferably detected via its accompanying magnetic field. Suitable elements are, for example, Hall sensors, magnetoresistive elements or, for example, inductive clamp meters.

The current detected by the current sensor 27 is relayed to the evaluation arrangement 24 which detects at least one specific characteristic of the current 40, 41 in the characteris tie - determi ming unit 28. The character istic signal 29 resulting therefrom in c=Tared in the comparator 30 with the prescribed threshold value 31. The comparator 30 outputs the overload signal 26 to the control arrangement 21 as a function of the result of comparison.

The overload signal 26 signals that an overload state has occurred in the drive 11. Such an overload state occurs, for example, due to blocking of the elec tric motor 10 or of the drive 11. The blocking takes place, in particular, when one of the end stops 12, 13 is reached. The overload signal 26 thus signals that one of the end stops 12, 13 in reached.

in the case of an electric motor 10 embodied as a stepping motor, the control arrangement 21 can itself determine the required number of steps by purposely driving up to the two end stops 12, 13, and in this way carry out a calibration. The aim of the calibration is to assign to a prescribed position of the drive 11 between the stops 12, 13 a specific number of steps which are to be provided. Using this measure it in possible to carry i r out a calibration not only during c4 asioning, but also later during operation at any time. As a result, it is possible at any time to take account of and compensate for scatter in mass production of the drive 11, age- induced changes, changes in elasticity as a function of temperature, and time-dependent mechanical play. The device according to the invention is thus particularly suitable for operating the electric motor 10 for use in a motor vehicle which is exposed to extremely rough 10 environmental conditions. A flap drive in an air conditioning system of the motor vehicle, for example, is provided as the drive 11.

According to the invention, time-dependent determination of the characteristic is provided. The time control is taken over by the time generator 32, which contains the time delay 33. The time cycles will be explained in more detail with the aid of the current characteristics 1, shown in Figures 2 and 3, an a function of time t.

in accordance with a first embodiment of the device according to the invention, the determination of the characteristic is provided within the time interval T. shown in Figure 2, which starts at the first prescribed time T, after the starting of the electric motor 10 at the starting instant TO and ends at the second prescribed time T2. It is essential that at the starting instant T. the electric motor 10 is at least approximately in the de-energized state, and that the interval T. ends at the second time T2 before the steady- state motor current has been reached. These measures ensure that only the starting phase in used to determine the characteristic. This starting phase can be substantially shorter than the pulse duration TD.

An overload state is expressed in different characteristics of the currents 40, 41. While the nonoverloaded case corresponds to the current 40, the overload case is present in the case of the current 41. As an example, the current amplitude occurring in the interval T. can be determined as suitable characteristic and output as characteristic signal 29. A further, suitable characteristic is the current change which has occurred within the interval Ti. The detc=ination of the current change is performed by dividing the time Interval T1 into a prescribed number of subintervals in which the current differences between the start of a subinterval and end of a subinterval are respectively determined and subsequently silmed.

Another characteristic In provided by the current change within the entire Interval T.. referred to the interval time T.. instead of a difference quotient, it is possible, furthe=more, to determine the rise in the current 40, 41 at least approximately as a differential quotient. It Is possible, for example, to select the maximum value from the plurality of differential quotients determined within the time interval TI and to output it an characteristic signal 29. Another characteristic in the teinporal =can value of the current 40, 41 in the time interval T..

in trials conducted using an electric motor 10 configured as a stepping motor, it emerged that a quicker current rise occurs in the case of overloading. Consequently, higher current values occur at an earlier instant after the starting instant T. in the case of overloading than without overloading. The interval T, can be matched experimentally to these circum tances. The electric motor 10 in supplied with power within the pulse duration T,) and subsequently stopped. After the pulse duration T1), the current 40, 41 decreases again to the value zero within the interpulse period TP. Care in to be taken that the interpulse period TP is dimensioned to be so long that the current 40, 41 can decrease to zero at least approximately. Cloaked operation of a DC motor, in the case of which no current gaps occur between the individual pulse durations T., reduces the reliability of detection of the overload state.

The first time T.. which corresponds to the ' start of the time interval T,, can coincide with the starting Instant T..

1 Figure 3 shown another embodiment of the device according to the invention f or operating the electric motor 10, in which instead of the time interval T:, shown in Figure 2 sampling of the current 40, 41 in provided at a prescribed sampling instant TA. The sampling instant TA is at a distance from. the starting instant T. by the prescribed delay time TV, which is prescribed by the t I e delay 33 in the time generator 32. This embodiment in particularly suitable when the instantaneous value or the amplitude of the current 40, 41 or the dif f erential quotient at the sampling instant TA is to be determined an the characteristic.

The f irst and second times T,, T2 Shown in Figures 2 and 3 and which f ix the time interval T,, an well as the delay time Tv and the sampling instant TA are respectively determined by the time generator 32 contained in the evaluation arrangement 24, and fed to the characteristic -determining unit 28 an activation signal 34. The starting point in each case is the starting signal 23, which corresponds to the starting instant Too The time delay 33 contained in the time generator 32 prescribes either the time between the starting instant T. and the first time T,, or the delay time between the starting instant T. and the sampling instant TA- 10 claims 1. Device f or operating an electric =tor, having means for detecting a current flowing through the electric motor, and having an evaluation arrangement which evaluates at least one characteristic of the current, compares it with a threshold value and outputs an over- load signal in the event of overshooting of the threshold value, characterized in that the determination of the characteristic is provided within a time interval M,) which starts at a f irst prescribed time (T1) after a starting instant (To), the electric =tor (10) being started at the starting instant (To) starting from the at least approximately deenergized state, and which ends at a second prescribed time (T2) before the steady-state motor current (40, 41) in reached.

2. Device for operating an electric motor, having 20 means for detecting a current flowing through the electric motor, and having an evaluation arrangement which evaluates at least one characteristic of the current, compares it with a threshold value and outputs an overload signal in the event of overshooting of the threshold value, characterized in that the determination of the characteristic is provided at a prescribed sampling instant (T.) which occurs after a prescribed delay time (TV) after a starting instant (T.) at which the electric motor (10) is started starting from the at least approx- imately de-energized state and which occurs before the steady-state motor current (40, 41) In reached.

Claims

3. Device according to Claim 1, characterized in that the first prescribed

time (T1) coincides with the starting instant (T,).

4. Device according to Claim 1, characterized in 1 P that the temporal mean value and/or the amplitude andlor the current change and/or the m"4=1- current difference andlor at least one difference quotient of current and time are determLined within the tine interval (T1) an the characteristic.

5. Device according to Clai= 2, characterized in that the instantaneous current (40, 41) andlor the differential quotient of current (40, 41) and time (t) are deter=ined at the sampling instant (T.) an the cha:acterist4c.

6. Device according to Claim 1 or 2, characterized in that the overload signal (26) is a blocking signal which constitutes blocking of a drive (11) actuated by the electric motor (10).

7. Device according to Claim 6, characterized in that the blocking signal indicates that an end stop (12, 13) of the drive (11) is reached.

8. Device according to Clain 1 or 2, characterized in that a stepping motor in provided as the electric motor (10).

9. Device according to Claim 1 or 2, characterized by use in an air conditioning system of a motor vehicle, in which the electric motor (10) actuates a flap which in operation reaches at least one end stop (12, 13).

10. A device substantially as herein described with reference to Figures 1 and 2, or Figures 1 and 3 of the accompanying drawings.