WO1993023904A1

WO1993023904A1 - Process for monitoring an electric motor for thermal overloading

Info

Publication number: WO1993023904A1
Application number: PCT/DE1993/000356
Authority: WO
Inventors: Hubert Lamm
Original assignee: Robert Bosch Gmbh
Priority date: 1992-05-15
Filing date: 1993-04-23
Publication date: 1993-11-25
Also published as: EP0640252A1; DE4216040A1

Abstract

A process is disclosed for monitoring an electric motor for thermal overloading in order to generate a switching off signal that switches off the motor when an admissible temperature limit is exceeded. In order to keep low the technical expenditure and the required total volume of an overload protector working according to this process, the motor power loss or a value proportional thereto is calcutated then integrated while the electric motor is switched on. The integration value is compared with a predetermined limit value and when the limit value (S1) is reached or exceeded the motor switching off signal is generated.

Description

> x

10

Procedure for monitoring an electric motor for thermal overload

State of the art

20th

The invention is based on a method for monitoring an electric motor for thermal overload in order to generate a switch-off signal which causes the motor to be switched off when a permissible temperature limit is exceeded.

Such overload protection is in electromotive adjustment systems in motor vehicles, e.g. indispensable for window regulators, lifting sunroofs or seat adjustment, because

30 always with sudden stiffness of the

Adjustment elements or obstacles in the adjustment path must be expected, and in these cases it is necessary to shut down the electric motor to avoid irreparable thermal damage.

35 Previously known monitoring methods for electric motors for thermal overload use a bimetal switch thermally coupled to the motor winding, the switch contact of which is in the motor circuit and opens when a predetermined temperature is exceeded, so that the electric motor is switched off. In the case of electric motors with a commutator operated on the DC voltage network, these bimetal switches are preferably accommodated on the brush holder. However, these known bimetallic switches are expensive and require a relatively large installation space, which leads to not inconsiderable installation problems in spatially highly integrated adjustment systems.

Advantages of the invention

The method according to the Invention with the characterizing features of claim 1 has the advantage that it can be implemented in today's modern adjustment systems, all of which have a microcomputer for controlling the electric motor, without any significant additional effort and without additional installation space for any electrical or electronic components . All process steps can be implemented using suitable logic in the microcomputer. The sensors required to record the necessary motor data are usually already present in the adjustment systems for other reasons or can be easily integrated into the motor itself. With the method according to the invention, a thermal switch is simulated, which does not require any construction volume, since all the electronic components required for its replication are already present in the adjustment systems.

Advantageous further developments and improvements of the monitoring method specified in claim 1 are possible through the measures listed in the further claims. In a preferred embodiment of the method according to the invention, the motor power loss is calculated from the speed of the motor and the motor terminal voltage

PMot = (UBatt -

(1)

calculated, where RA is the resistance of the armature winding, c • <j) is the field-dependent induction constant and UBatt is the terminal voltage of the electric motor. The speed is detected by a Hall sensor, which is used in today's

Adjustment systems for reasons of positioning are already integrated in the electric motor anyway. The sensor signal supplied by the Hall sensor is already available in the control unit or microcomputer and can also be used there to calculate the engine power loss. As already mentioned at the beginning, the hardware effort required to ensure the overload protection in the adjustment systems is zero and only a small amount of software is required.

The advantages of the method according to the invention can be exploited to an increased extent if it is introduced into an adjustment system which has a multiplicity of electric motors for different adjustment processes and a central control device which has a

Multiplexer system communicates with the electric motors. In this case, the central control unit ensures the overload protection for all electric motors, so that considerable savings can be achieved compared to the individual equipment of the electric motors with thermally responsive cut-outs. drawing

The invention is explained in more detail in the following description using an exemplary embodiment illustrated in the drawing. Show it:

1 is a block diagram of an adjustment system for a lifting sunroof in motor vehicles with overload protection,

Fig. 2 is a diagram showing the course of the

Integration value of the motor power loss over the duty cycle of the motor shows

Fig. 3 is a block diagram of a circuit for

Realization of overload protection.

Description of the embodiment

In Fig. 1, a block diagram of an adjustment system for a lifting sunroof in motor vehicles is shown, in which a method for monitoring the electric motor 10 for thermal overload is used for the purpose of overload protection of an electric motor driving the sliding sunroof, which is in good time before the occurrence of thermal

Overloading the electric motor 10 switches it off. The electric motor 10 operated on the DC voltage network of the motor vehicle is designed as a commutator motor, which is controlled by a control unit 11 designed as a microcomputer via an output stage 12 with reversal of the direction of rotation. The control unit 11 is supplied with the command signals “lift”, “open”, “close” and “central locking (ZV)”, which converts the command signals into corresponding control signals for the output stage 12. The final stage 12- has in known

Power transistors arranged in a bridge circuit on, the power transistors in opposing bridge branches being driven simultaneously. The electric motor 10 is connected to the diagonal branch of the bridge circuit. Depending on the control of the transistor pairs, the electric motor turns to close or

Open to the right or left. Both the output stage 12 and the control unit 11 are connected to the DC mains voltage UBatt. To monitor the rotational position of the electric motor 10, a Hall sensor 13 is integrated in the latter, which delivers a signal corresponding to the rotational position of the electric motor 10 to the control unit 11. In the end positions of the lifting / sliding roof, a reference switch 14 is mechanically closed, which gives a reference signal to the control unit 11. The reference signal represents the reference variable for calculating the current rotational position of the electric motor 10 from the output signal of the Hall sensor 13. To prevent thermal overloading of the electric motor, e.g. due to the extreme stiffness of the lifting sunroof in one or the other direction, during the

Duty cycle of the electric motor 10 whose power loss Pnot or a variable proportional to this is calculated and integrated using suitable motor data. As soon as the integration value reaches or exceeds a predefined threshold value, a switch-off signal is generated that the

Control unit 11 causes the electric motor 10 to be switched off.

To calculate the engine power loss Pnot, the speed n is first measured, for which the output signal of the Hall sensor 13 is used, which the

Contains speed information. In addition, the terminal voltage UBatt of the electric motor 10, which is already available on the control unit 11, is measured. The engine power loss Pnot is thus according to

Pnot = (UBatt - c-ψ-n) ² / RA (1) calculated. RA is the resistance of the armature winding of the electric motor 10 and c- y is the field-dependent induction constant of the electric motor 10. The latter can be determined from the motor characteristic

calculate, where no is the idle speed of the electric motor 10 and Uo is the clamping voltage of the electric motor 10 at idle.

The motor power loss Pκot is now integrated during the entire operating time of the electric motor 10. The integration value, which is a measure of the thermal load on the motor, depends on the

Duty cycle shown in Fig. 2 for three different load cases. As soon as the integration value reaches or exceeds a first predetermined threshold Si, the switch-off signal for the electric motor 10 is generated. Since a cooling process starts when the electric motor 10 is stopped, this cooling process is simulated in that the integration value is reduced from the time of the switch-off after an e-function. If the integration value reaches a second predefined threshold S2, the electric motor 10 can be switched on again, unless it remains switched off for other reasons, and the method described above for calculating the motor power loss and its Au integration starts again until the first threshold Si again is reached and the shutdown signal is generated. This process after switching on the

Electric motor 10 is shown in broken lines in FIG. 2 for the three load cases.

The individual process steps described above for generating a thermal overload protection of the

Electric motor 10 are in a in the control unit 11th integrated logic. A hardware embodiment of this logic is shown as a block diagram in FIG. 3. The logic circuit 15 comprises a multiplier 16, two sub-radiators 17, 18, a squarer 19, a divider 20, an integrator 21 and a comparator 22. In the multiplier 16, the speed n is multiplied by the constant factor c-ψ. This product is subtracted from the terminal voltage UBatt in the first subtractor 17 and the result is squared in the squarer 19. The difference square is divided in the divider 20 by the constant RA. The output of divider 20 is

Motor power loss Pnot. This signal is fed to the second subtractor 18 via a first switch 23. The output of the second subtractor 18 is at the input of the integrator 21, the output of which is connected to the input of the comparator 22. The comparator 22, designed for example as a window comparator, has the two preset thresholds Si and S2. The output of the integrating element 21 is fed back via a second switch 24 to the inverting input of the second subtracting element 28. The two switches 23, 24 are switched synchronously with one another in such a way that when the electric motor 10 is switched on, the first switch 23 closes and the second switch 24 opens, and when the electric motor 10 is switched off by the switch-off signal or by another switching measure, the second switch 24 closes and the first switch 23 is set to zero.

When the electric motor 10 is switched on, the motor power loss Pnot according to Eq. (1) calculated. The motor power loss Pπot is applied directly to the integrating element 21 via the closed switch 23, since the second subtracting element 18 has no function because of the opened second switch 24. The motor power loss Mo au is integrated in the integrator 21 and the integration value present at the output of the integrator 21 is fed to the comparator 22. If the integration value exceeds the upper threshold Si, then the switch-off signal occurs at the output of the comparator 22, if the integration value falls below the lower threshold Sz, the comparator 22 emits a switch-on signal.

Instead of calculating and integrating the motor power loss Pnot, one of the

Motor power loss proportional size can be processed in the manner described. Such a size would be, for example, the power loss Pnot multiplied by the armature resistance RA

(Pwot-RA. = (UBatt - c-φ-n) ² (3)

In this case, only the thresholds Si and S2 in the comparator 22 would have to be changed accordingly, in such a way that when the just permissible temperature limit of the electric motor 10 was reached, the proportional quantity reached the value of the upper threshold Si. The divider 20 can then be omitted. The logic circuit 15 can be constructed from analog components, but is preferably implemented in digital technology. In this case, the calculated motor power loss Mo is sampled at fixed time intervals to and the sampled values are summed up in an adder or sum memory. However, the motor power loss can also be recalculated at fixed time intervals and the calculated values added up. In both cases, the integration value is obtained, which is compared with the thresholds Si and S2. The integration value simulates the temperature of the electric motor 10, so that when the upper threshold Si is reached or exceeded, the motor is switched off before thermal overload. The invention is not restricted to the exemplary embodiment described above. Thus, the monitoring method for the electric motor 10 for thermal overload can be implemented not only by a hardware-based logic circuit 15, but also by a computer program integrated in the control unit 11, which carries out the individual method steps.

The use of the speed n of the electric motor 10 for

Calculation of the engine power loss Fτiot is particularly advantageous here, since adjustment systems usually have a Hall sensor and the speed is therefore available without additional effort. If such Hall sensors are dispensed with in certain adjustment systems, the motor power loss can also be based on the measured motor current I according to

PMo t = I ² • RA (4)

be calculated. The motor current I can be detected in a simple manner by installing a shunt in the motor circuit. Instead of the power loss, a quantity proportional to this can also be calculated, e.g. the size PMot 'RA, so that only the measured motor current I has to be squared and integrated to simulate the motor temperature.

The control unit 11 is preferably spatially integrated into the electric motor 10. If several adjustment systems are present in a motor vehicle, for example electric window regulators, electric seat adjustment and the like, all adjustment motors can be controlled by a single central control device which is connected to the individual adjustment motors and the sensors integrated there via a multiplexer system. In this case, the Control device implemented monitoring procedures protect all adjusting motors when they are switched on against thermal overload, so that its effectiveness compared to conventional monitoring procedures is particularly evident.

Claims

Expectations

1. Method for monitoring an electric motor for thermal overload in order to generate a when a permissible temperature limit is exceeded

Switch-off signal causing the motor to be switched off, characterized in that during the switch-on period of the electric motor (10) its power loss (PMot) or a quantity proportional to this is calculated and integrated on the basis of measured motor data (ÜBatt n) and that the integration value with a predetermined threshold value is obtained to obtain the switch-off signal (Si) is compared.

2. The method according to claim 1, characterized in that the continuously calculated motor power loss (PMot) is sampled at fixed time intervals (to) and the integration value is obtained by summing up the samples.

3. The method according to claim 1, characterized in that the motor power loss (PMot) is calculated at fixed time intervals (to) and the integration value is obtained by adding up the calculated values.

4. The method according to any one of claims 1-3, characterized in that when the threshold value (Si) is reached or exceeded by the integration value, the shutdown signal is generated and at the same time a reduction in the integration value after a de «cooling process of the electric motor (10) approximated function, preferably an e-function is performed.

5. The method according to claim 4, characterized in that when a predetermined lower threshold value (S2) is reached or undershot, a switch-on signal for the electric motor (10) is generated by the integration value.

6. The method according to any one of claims 1-5, characterized in that in the case of an electric motor (10) operated on a direct voltage network, its speed (n) is measured and the motor power loss (PMot) according to

PMot = (ÜBatt - c-ψ-n) ² / RA

is calculated, where RA is the resistance of the armature winding, c- ^ the field-dependent

Induction constant and UBatt is the terminal voltage of the electric motor (10).

7. The method according to any one of claims 1-5, characterized in that in the case of an electric motor (10) operated on a direct voltage network, its speed (n) is measured and a variable proportional to the motor power loss (PMot) (P ot RA)

(PMot «RA) = (Uβat - c><j> -n) ²

is calculated, where UBatt is the terminal voltage and C _'is the field-dependent induction constant of the electric motor (10).

8. The method according to any one of claims 1-5, characterized in that at one to one

DC motor operated electric motor (10) whose motor current I measured and the motor power loss (PMot) according

Pπot = I ² -RA

is calculated, where RA is the resistance of the armature winding of the electric motor (10).

9. The method according to any one of claims 1-5, characterized in that in the case of an electric motor (10) operated on a direct voltage network, its motor current (I) is measured and squared to calculate a quantity proportional to the motor power loss (PMot) (PMot-Rλ).

10. The device for performing the method according to any one of claims 1-9, characterized by a control unit (11) designed as a microcomputer for controlling the electric motor (10), sensors (13) connected to the control unit (11) for detecting the

He current motor data during the duty cycle of the electric motor (10) and by a logic (15) integrated in the control unit (11) for the calculation of the motor power loss (PMot), its integration and the comparison with the predetermined threshold values (Sι, Sz).

11. The device according to claim 10 for a plurality of electric motors to be monitored, characterized in that each electric motor (10) is assigned a control unit (11) which is preferably integrated in the associated electric motor (10).

12. The apparatus according to claim 10 for several electric motors to be monitored, characterized in that a single control device (11) is provided which controls all electric motors (10) via a preferably integrated multiplexer.

13. Device according to one of claims 10 - 12, characterized in that a as a sensor for speed measurement

Hall sensor (13) is used.

14. Device according to one of claims 10-13, characterized in that an integrating element (21) is provided for motor power loss integration, that a subtracting element (18) is connected to the input of the integrating element (21), the non-inverting input of which is connected via a first switch ( 23) is assigned an input signal corresponding to the motor power loss (PMot) or a variable proportional to it (PMot • R), and its inverting input is connected to the output of the integrating element (21) via a second switch (24), and that the two Switches (23, 24) are controlled so that when the motor is switched on, the first switch (23)

REPLACEMENT LEAF closed and the second switch (24) opened and with engine shutdown the first switch is set to zero and the second switch (24) is closed.