WO2007003451A1

WO2007003451A1 - Protective circuit and method for monitoring the temperature of a dropping resistor

Info

Publication number: WO2007003451A1
Application number: PCT/EP2006/061660
Authority: WO
Inventors: Richard Vogt; Andreas Ewert; Michael Strupp
Original assignee: Robert Bosch Gmbh
Priority date: 2005-06-30
Filing date: 2006-04-19
Publication date: 2007-01-11
Also published as: DE102005030539A1

Abstract

A protective circuit (10, 100) is disclosed, for at least one dropping resistor (12) on a DC motor (14), comprising at least one temperature-sensitive component (28) for monitoring the temperature (T) of the at least one dropping resistance (12) and a switching means (20) with a first (26) and a second switch position (32), wherein, in the first switch position (26) of the switching means (20), the DC motor (14) is operated across the at least one dropping resistance (12) and a corresponding method for monitoring the temperature of the at least one dropping resistance. Said protective circuit (10, 100) and said method are characterised in that, in case of overload, the switching means (20) are switched to the second switch position (32) by a switch signal (S) dependent on the temperature-sensitive component (28), in order to deactivate the DC motor (14) and a renewed switching of the switching means (20) into the first switch position (26) first occurs after the isolation of a power supply (U) and/or by means of an additional control signal (C). Furthermore, a DC motor (14) is disclosed, in particular, a fan motor (36), comprising said protective circuit (10, 100).

Description

Protection circuit and method for monitoring the temperature of a series resistor

State of the art

The invention relates to a protective circuit for at least one series resistor of a DC motor and a method for monitoring the temperature of the at least one series resistor according to the preamble of the independent claims.

It is known to use at least one series resistor for DC motors, in particular blower motors, for the stepwise speed setting. In order to avoid overheating of the series resistor and thus a fire hazard in case of overload - especially when blocking the DC motor - it is also known to use temperature-controlled fuses (microtemperature protection - MTS, Thermal Cut-Off Switch - TCO), which are integrated in the current path of the DC motor are. In this case, the response of the thermal fuse is achieved by the proximity to the series resistance, so that when it overheats and possibly at the same time failure of a fan air flow in the case of a blocked DC motor, a trip threshold of the thermal fuse is exceeded.

The WO-2004109902 Al shows a Vorwiderstandsbaugruppe for an electric motor, in particular for an electrically driven fan blower in a motor vehicle, comprising a series resistor for speed control of the electric motor in one or more speed levels with a possibly connected in series to the series resistor thermal fuse, wherein a reversible

Switching element is integrated for at least one of the speed levels. In this case, the switching element is a reversible

Thermal protection switch, as a semiconductor device or as a temperature-dependent resistor with a positive temperature coefficient (PTC) is formed. Furthermore, DE 69604435 T2 discloses a control circuit for controlling the drive of a DC motor, wherein the temperature of a PTC is increased by an excess current resulting from an overloaded state of the DC motor. As a result, the PTC increases its own resistance and reduces the current flowing through a relay coil so that it opens a relay contact and stops the DC motor.

Advantages of the invention

Compared to the prior art, the protection circuit according to the invention for at least one series resistor of a DC motor, comprising at least a temperature-sensitive component for monitoring the temperature of the at least one series resistor and a switching means having a first and a second switching position, wherein in the first switching position of the switching means of the DC motor over the at least one series resistor is operable, the advantage that it does not come in an overload case to an automatic switching on and off of the DC motor and thus the switching means, the

DC motor and other electrical components from overload and excessive wear due to a periodic switching of the blocked DC motor and the resulting high switching currents are protected. In the event of an overload, the switching means switches to the second switching position by means of a switching signal dependent on the temperature-sensitive component in order to deactivate the DC motor. A renewed switching of the switching means in the first switching position takes place only after switching off a supply voltage and / or by means of an additional control signal. The manual reversibility of the overload circuit is achieved even at high currents> 15 A in an advantageous manner that after temporary disturbances, such as overloading of an engine cooling fan when passing through a water area or blocking a fan at cryogenic temperature and thus caused ice formation, the

DC motor can go back to normal operating mode without repair. Furthermore, it is easier to use and robust components, the advantage of waiving a cost-intensive and especially at high ambient temperatures error-prone sensor and evaluation.

In order to be able to control the reversibility of the protective circuit according to the invention in an advantageous manner, the temperature-sensitive component is connected in series with the switching means. In this regard, it is particularly advantageous if the switching means in the second switching position bypasses the temperature-sensitive component, so that it can take almost no influence on the switching signal. In this way, an automatic switching on and off of the blocked DC motor is effectively and inexpensively avoided.

In an alternative embodiment, the switching element is connected in series with a parallel circuit consisting of the series resistor and the temperature-dependent component, so that the switching signal essentially depends on the fixed resistance of the series resistor. This also prevents automatic switching of the switching element in its first switching position and consequently a re-activation of the DC motor. As a switching signal can serve both a switching current and a switching voltage.

A clear cost advantage arises when the

Switching means is a relay, wherein a relay coil, the relay is connected in series with the temperature-sensitive component and the relay coil spends a relay changeover contact in the first or second switching position. In this context, the control signal advantageously leads to a bridging of the

Relay coil, so that this releases the relay changeover contact for re-switching to the first switching position.

In order to operate the DC motor in several speed stages, it is provided that in at least a first

Speed level of the DC motor via the at least one series resistor and in another speed step directly with the - A -

Supply voltage is connected. It is advantageous if there is no intervention by the switching means for the operation of the DC motor in the further speed stage. This measure makes it possible to eliminate a blockage of the DC motor - for example due to a jammed object - by briefly applying a high current again.

Furthermore, the invention comprises a method for monitoring the temperature of a series resistor of a DC motor by means of a temperature-sensitive component and a switching means having a first and a second switching position, wherein in the first switching position of the switching means, the DC motor is operable via the at least one series resistor. The method according to the invention offers the advantages already mentioned above in that, in the event of an overload, the switching means is switched to the second switching position by a switching signal dependent on the temperature-sensitive component in order to deactivate the DC motor, wherein the switching means only after switching off a supply voltage and / or by means of an additional

Control signal is switched again to the second switching position. In the second switching position, the temperature-sensitive component is bridged in an advantageous manner, wherein an alternative embodiment provides that the switching means is connected in series with a parallel circuit consisting of the series resistor and the temperature-dependent component.

Further advantages of the invention will become apparent from the features specified in the dependent claims and from the drawings and the description below.

drawing

The invention will be explained in the following with reference to Figures 1 and 2 by way of example, wherein like reference numerals in the figures indicate the same components with the same operation. Show it Fig. 1: a first embodiment of the protection circuit according to the invention and

2 shows a second embodiment of the protection circuit according to the invention.

description

FIG. 1 shows a first exemplary embodiment of a protective circuit 10 for at least one series resistor 12 of a DC motor 14. The series resistor 12 is for a first speed level A on the one hand with a supply potential V ₊ a power source 16 and on the other via a changeover 18 a switching means 20, in particular via a Relaisumschaltkontakt 22 of a relay 24, which is in a first switching position 26 with the DC motor 14 connected. Furthermore, the DC motor 14 is connected to a reference potential V_ of the power source 16. The difference between the supply potential V ₊ and the reference potential V_ is defined as a supply voltage U.

In a to the series circuit of resistor 12, located in the first switching position 26 Relaisumschaltkontakt 22 and DC motor 14 parallel current path are a temperature-sensitive device 28 and a relay coil 30 of

Relay 24 connected in a further series circuit, which is connected to the one with the supply potential V ₊ and the other to the reference potential V_. Furthermore, there is an electrical connection between a second switching position 32 of the Relaisumschaltkontaktes 22 and a node 34, which is located between the temperature-sensitive device 28 and the relay coil 30 of the relay 24, the ability to connect the series resistor 12 and the temperature-sensitive device 28 in parallel. In this case, the resulting parallel circuit forms a series connection with the relay coil 30 of the relay 24, and the DC motor 14 is deactivated. If the relay changeover contact 22 is in the first switching position 26, the direct current motor 14 can be connected directly to the supply potential V ₊ instead of in a first speed stage A even in a second speed stage B, ie without series resistor 12. In this case, one results opposite to the first

Speed step A higher speed of the DC motor 14. If the DC motor 14, for example, a blower motor 36 of a fan 38, which drives a fan 40, so in this way a higher air flow and thus a higher cooling performance can be achieved. Alternatively, it may also be advantageous if the switching means 20 has no influence on the second speed level B. This is the case, for example, if the second speed level B is to be used, inter alia, to make the blocked DC motor 14 passable again by briefly applying a high current. If this variant embodiment is to be used, then a connection 44 shown in dashed lines in FIG. 1, which bypasses the switching means 20, is required.

The functioning of the protective circuit 10 will now be explained in more detail below, it being assumed that the temperature-sensitive component 28 is a temperature-dependent resistor having a negative temperature coefficient (NTC) 42, which reduces its resistance value as the temperature T of the series resistor 12 increases. The relay changeover contact 22 of

Relay 24 is initially - as shown in Figure 1 - in the first switching position 26th

If there is a blockage or sluggishness of the DC motor 14, then a current flowing through the DC motor 14 and the series resistor 12 motor current I _{M increases} sharply, and the temperature T of the series resistor 12 increases significantly due to the power converted in it. Since the NTC 42 is in close proximity to the series resistor 12, its resistance decreases with increasing temperature T of the series resistor 12, which leads to an increase in a current flowing through it switching current I ₃ until the relay coil 30 of the relay 24 attracts and switching the Relaisumschaltkontaktes 22 in the second switching position 32 causes. The DC motor 14 is then turned off, and the current flowing through the relay coil 30 switching current I _s is defined by the resulting resistance of the parallel connection of series resistor 12 and NTC 42 and the series-connected relay coil 30. Since the switching current I _{s is} significantly lower than that Motor current I _M , the series resistor 12 can cool, causing the resistance of the NTC 42 increases again. Due to the parallel connection of the relatively low-impedance series resistor 12 and the NTC 42, the switching current I ₃ continues to suffice to keep the relay coil 30 and thus the relay switching contact 22 in its second switching position 32. Thus, even after cooling of the series resistor 12 no automatic switching of the Relaisumschaltkontakts 22, so that an automatic switching on and off of the DC motor 14 due to a cyclic change between over-temperature on the resistor 12, switching off the DC motor 14, drop in temperature T on the resistor 12 and reconnection the DC motor 14 can be effectively and inexpensively avoided.

The explanation of the protection circuit according to the invention or of the corresponding method for latching was based on the switching current I ₃ . Instead of the switching current I ₃ , it is also possible as a switching signal S emanating from a voltage drop across the relay coil 30 switching voltage U ₃ . If the temperature T of the series resistor 12 increases due to the blocking of the DC motor 14, this leads-as already described above-to a reduction in the resistance value of the NTC 42, and the voltage drop across it decreases. As a direct result, there is an increase in the switching voltage U ₃ across the relay coil 30 until it attracts and the Relaisumschaltkontakt 22 in the second

Switching position 32 spends. Since the resulting resistance of the parallel circuit of series resistor 12 and NTC 42 significantly depends on the low-impedance resistor 12, the switching voltage U ₃ does not break over the relay coil 30, so that the relay switching contact 22 continues to hold in the second switching position 32. In order to effect a renewed switching of the Relaisumschaltkontakt 22 in its first switching position 26, so that the DC motor 14 is operable again with the speed levels A or B, now the supply voltage U and consequently the power source 16 has disconnected or disconnected and / or an additional control signal C to the switching means 20 and the relay 24 are applied.

If, for example, the supply voltage U is switched off, the relay coil 24 releases the relay changeover contact 22 so that it can return to its first switching position 26. After renewed application of the supply voltage U then a stepwise operation of the track motor 14 is possible. Alternatively or additionally, the control signal C can also be used. This leads, for example, to a bridging of the relay coil 24, which then releases the relay changeover contact 22 into its first switching position 26.

FIG. 2 shows a second exemplary embodiment of the protective circuit 100 according to the invention. In contrast to Figure 1, the step-by-step control of the DC motor 14, which can also be configured here as a blower motor 36 of a blower 38 for driving a fan 40, no longer directly by a direct connection of the speed levels A and B with the DC motor 14, but over a first 46 and a second speed stage relay 48, each having a relay coil 50 and 52 and a

Relay switching contact 54 and 56 have. In this way, largely separate circuits for switching the speed levels A and B and the supply of the DC motor 14. Since now the resistor 12 is located exclusively in the supply circuit of the DC motor 14, this is no longer in the case of a turn-off due to a blocking of the DC motor 14 flowing through a stream. This results in the advantage of a faster cooling and a lower load of the series resistor 12.

For the following explanation of the operation of the protection circuit 100 according to the invention is first of it assumed that the Relaisumschaltkontakt 22 of the relay 24 is in its first switching position 26, so that the DC motor 14 is gradually operable via the speed levels A or B. Now, if the speed level A is connected to the supply voltage U, so that it is at the supply potential V ₊ , flows through the relay coil 50 of the speed stage relay 46, a current that causes a closing of the relay switching contact 54. Then, the DC motor 14 can be operated with the first speed level A via the series resistor 12. Accordingly, an operation of the track motor with maximum speed on the second speed level B and the relay 48 with the relay coil 52 and the relay switching contact 56 without series resistor 12 is possible. In the following, however, an operation in the first speed stage A is assumed.

If there is an increase in the motor current I _M as a result of a blockage or sluggishness of the DC motor 14, the temperature T of the series resistor 12 rises. Since - as already in Figure 1 - designed as NTC 42, temperature-sensitive device 28 is in spatial proximity to the series resistor 12, due to the increasing temperature T decreases its resistance, and connected by the series-connected to NTC 42 relay coil 30 of the relay 24 flowing switching current I _s increases. Thereafter, the relay coil 30 attracts and causes a switching of the relay changeover contact 22 in the second switching position 32, which is electrically connected to a node 34 between the series circuit of relay coil 30 and NTC 42. By switching the relay changeover contact 22 in the second switching position 32 is the One of the DC motor 14 off because the relay coil 50 of the speed stage relay 46 releases the relay switching contact 54 to open, and on the other hand, the NTC 42 is bridged, so that the relay coil 30 of the relay 24 directly with the

Supply potential V ₊ and the reference potential V_ is connected. If there is now a cooling of the series resistor 12 and a resulting increase in the resistance of the NTC 42, this has no effect on the switching current I _s , and the relay coil 30 keeps the Relaisumschaltkontakt 22 further in the second Switching position 32. A renewed switching is - as already described for Figure 1 - only after the switching off of the supply voltage U and / or by means of an additional control signal C possible. In this case, for example, the control signal C cause a bridging of the relay coil 30 of the relay 24, so that the relay coil 30 releases the Relaisumschaltkontakt 22 to its movement into the first switching position 26. In order that the relay changeover contact 22 in the event of bridging the relay coil 30 back to the first switching position 26, the relay 24, a device, not shown, such as a spring, a metal strip or the like, by the displacement of the Relaisumschaltkontakts 22 in the second Switching position 32 is biased.

Finally, in order to avoid overloading the relay coils 30, 50, 52, a correspondingly dimensioned resistor 58 can be arranged between the relay changeover contact 22 and the reference potential V_. Its resistance value must be chosen such that it ensures self-holding of the relay coil 30 by the switching current I _s .

It should finally be pointed out that the exemplary embodiments shown are limited neither to FIGS. 1 and 2 nor to the components described. Thus, the protective circuit according to the invention and the method according to the invention can also be used with three-stage and multi-stage drives with a corresponding number of series resistors. Likewise, an application in connection with several DC motors, for example in a double fan, conceivable. It should also be noted that the invention is not limited to the use of a relay 24 as switching means 20. With appropriate design, it is also possible to use semiconductor devices, such as transistors, gate turn-off thyristors (GTO) or the like. Finally, the protection circuit is not limited to an NTC 42 as a temperature-sensitive device 28. Possible alternatives in this context are a temperature-dependent resistor with a positive temperature coefficient (PTC), a bimetal or similar, wherein the switching means 20 would be designed accordingly.

Claims

claims

1. Protection circuit (10, 100) for at least one series resistor (12) of a DC motor (14), comprising at least a temperature-sensitive component (28) for monitoring the temperature (T) of the at least one series resistor (12) and a switching means (20, 24 ) with a first (26) and a second switching position (32), wherein in the first switching position (26) of the switching means (20) of the DC motor (14) via the at least one series resistor (12) is operable, characterized in that in case of overload the switching means (20) is switched to the second switching position (32) by a switching signal (S) dependent on the temperature-sensitive component (28) in order to deactivate the DC motor (14) and that the switching means (20) is switched over again into the first switching mode Switching position (26) takes place only after switching off a supply voltage (U) and / or by means of an additional control signal (C).

2. Protection circuit (10, 100) according to claim 1, characterized in that the temperature-sensitive component (28) is connected in series with the switching means (20).

3. Protection circuit (10) according to claim 1, characterized in that the switching means (20) in the second switching position (32) bridges the temperature-sensitive component (12).

4. Protection circuit (10) according to claim 3, characterized in that the switching means (20) in the second switching position (32) connected in series with the switching means (20), from the series resistor (12) and the temperature-dependent component (28). existing parallel circuit causes.

5. Protection circuit (10, 100) according to any one of the preceding claims, characterized in that the switching means (20) is a relay (24), wherein a relay coil (30) of the relay (24) in

Row with the temperature-sensitive device (28) is connected and the relay coil (30) spends a relay changeover contact (22) in the first (26) or second shift position (32).

6. Protection circuit (10, 100) according to claim 5, characterized in that the control signal (C) leads to a bridging of the relay coil (30), so that this releases the Relaisumschaltkontakt (22) for re-switching to the first switching position (26) ,

7. Protection circuit (10, 100) according to any one of the preceding claims, characterized in that the switching signal (S) is a switching current (I ₃ ) or a switching voltage (U ₃ ).

8. Protection circuit (10, 100) according to any one of the preceding claims, characterized in that the temperature-sensitive component (28) is an NTC (42).

9. protection circuit (10, 100) according to claim 1, characterized in that the DC motor (14) in a plurality of speed stages (A, B) is operable, wherein in at least one first speed stage (A) of the DC motor (14) via the at least one Series resistor (12) and in another speed stage (B) directly to the supply voltage (U) is connected.

10. Protection circuit (10, 100) according to claim 9, characterized in that for the operation of the DC motor (14) in the further speed stage (B) no intervention by the switching means (20).

11. DC motor (14), in particular fan motor (36), with a protective circuit (10, 100) according to one of the preceding claims 1 to 10.

12. A method for monitoring the temperature (T) of at least one series resistor (12) of a DC motor (14) by means of a temperature-sensitive device (28) and a switching means (20) having a first (26) and a second switching position (32) in the first switching position (26) of the switching means (20) of the DC motor (14) via the at least one series resistor (12) is operable, characterized in that in case of overload, the switching means (20) by a temperature-sensitive component (28) dependent switching signal (S) in the second

Switching position (32) is switched to deactivate the DC motor (14), and that the switching means (20) only after switching off a supply voltage (U) and / or by means of an additional control signal (C) again in the first switching position (26) is switched.

13. The method according to claim 12, characterized in that by the switching means (20) in the second switching position (32), the temperature-sensitive component (28) is bridged.

14. The method according to claim 13, characterized in that the switching means (20) in the second switching position (32) in series with one of the series resistor (12) and the temperature-dependent component (28) existing parallel circuit is connected.

15. The method according to claim 14, characterized in that the DC motor (14) in a plurality of speed stages (A, B) is operable, wherein in at least a first speed stage (A) of the DC motor (14) via the at least one series resistor (12) and in another speed step (B) is directly connected to the supply voltage.

16. The method according to claim 15, characterized in that in the further speed stage (B) of the DC motor (14) is not intervened by the switching means (20) in the operation of the DC motor (14).