GB2273373A

GB2273373A - Braking control circuit for a windscreen/headlight wiper drive

Info

Publication number: GB2273373A
Application number: GB9324869A
Authority: GB
Inventors: Michael Geber; Wilfried Weyer
Original assignee: Daimler Benz AG; Mercedes Benz AG
Current assignee: Daimler Benz AG
Priority date: 1992-12-12
Filing date: 1993-12-03
Publication date: 1994-06-15
Also published as: GB9324869D0; DE4241996C2; DE4241996A1

Description

2273373 1 Braking control circuit for a windscreen/headlight wiper drive

The invention relates to a braking control circuit for a windscreen/headlight wiper drive, in which a braking current, produced when braking an electric wiper motor into a parking position, which motor is controllable via a first relay into at least one speed level, is passed via a shortcircuiting circuit which circuit, depending on the position of the first relay which switches off the motor current of the wiper motor, is switchable to relieve the load on a normallyclosed contact of said relay.

A circuit having these features is known from the installation in the Type W- 140 vehicle produced by the applicant; Figure 3 shows schematically the essential components of this circuit, which consists mainly of relays. The circuit diagram uses the normal terminal designations for motor vehicle electrical systems, that is to say 1115R" for radio position and ignition on, 113011 for continuous positive from the battery, 113111 for earth, 1131b" for signals from a parking position switch P, 115311 and 1153b" for the motor terminals of the first and second wiping speeds. The vehicle wiper motor M is permanently connected to earth on one side.

A terminal 11willi is connected both to a windscreen/headlight wiper control switch (level I for slow continuous operation) and to one output of an interval control apparatus (indicated by an OR gate having two inputs), in order to supply a switchable positive potential to the relay circuit. In addition to the starting pulse which initiates every intermittent wiping cycle, a stop signal, which always moves the wiper motor to its quiescent position, is also supplied - as a function of the position of the parking position switch P - via this control apparatus output, to the control circuit. A resistor Pu is used as a pull-up resistor for the lead 1131b", which is connected to the parking position switch P and supplies to the control apparatus a feedback message on the operating mode of the wiper motor M.

2 A relay RA is provided f or relieving the load on the ignition switch, and switches on the control circuit in the continuous positive (113011) driving mode.

A change-over relay RB controls the slow continuous wiping mode of the wiper motor via 115311; relay RB normally pulls in when a positive signal is applied to the input "Will'.

A relay RC having a normally-closed contact and a normally-open contact controls the fast continuous mode of the wiper motor via 1153b11. It is activated by means of an earth signal, which is produced by the control apparatus, to an input terminal "All and receives a positive voltage via the normally-closed contact of the relay RB.

Whenever the wiper motor is switched off (relays RB and RC and the parking position switch P are in the quiescent position shown), a control relay RE pulls in, activated by a positive signal from the electronic intermittent control apparatus via a terminal "B", and changes over a braking current relay RD, delayed by an RC timer, so that the braking current of the wiper motor is short-circuited via a normallyopen contact of the relay RD. The braking current, which may amount to up to 60A, in this case admittedly runs via the parking position switch, but advantageously not via the normally-closed contacts of the motor current relays RB or RC.

While, overall, this circuit operates in a satisfactory and reliable manner, the control and braking relays switch relatively slowly and, as a result of contact erosion on the braking current contact relay RD, its contact resistance increases. Under unfavourable circumstances, this leads to the wiper motor running slightly beyond the required nominal parking position of the windscreen/headlight wiper. In addition, in the intermittent operation mode.. a slight but audible amount of noise is developed since the three relays RB, RE and RD are switched at intervals of milliseconds during every wiper motor braking process.

In the case of other known windscreen/headlight. wiper controllers (DE 36 27 561 Cl, DE 36 43 414 Al), the braking current of the wiper motor is directly short-circuited via 4 v 1 3 normally-closed contacts of motor current relays.

In a further known windscreen/headlight wiper controller (DE 39 22 230 Al), admittedly the power circuit breakers for the wiper motor are represented by field-effect transistors (FETs) in one embodiment, but in this case no dedicated shortcircuiting circuit is disclosed for the braking current which is produced while the wiper motor is stopping.

The present invention to construct a braking control circuit for a windscreen/headlight wiper drive such that long term reliable maintenance of the parking position is achieved with a more compact construction.

According to the present invention there is provided a braking control circuit for a windscreen/headlight wiper drive, in which a braking current, produced when braking an electric wiper motor into a parking position, which motor is controllable via a first relay into at least one speed level, is passed via a short-circuiting circuit which circuit, depending on the position of the first relay which switches off the motor current of the wiper motor, is switchable to relieve the load on a normally-closed contact of said relay, wherein, via the normally-closed contact and in its normallyclosed position, the first relay switches on a solid-state switching element in the short-circuiting circuit, via which switching element the braking current of the wiper motor is directly short-circuited, the intermediate circuit having no switching elements with moving contacts.

In a preferred embodiment, the solid-state switching element comprises a power transistor, which may be a MOSFET, to whose gate a voltage can be applied via the normally-closed contact of the relay, and the-braking current is passed via the drain-source junction of the MOSFET. The wiper motor may be permanently connected to earth on one side, and the connection on the other side of the wiper motor is adapted to be connected to earth via the solid-state switching element after the switching contact of the first relay has tripped.

A further relay may be provided for switching a second wiping speed, and the solid-state switching element can be 4 driven by an evaluation circuit only when both relays are in the quiescent position.

The evaluation circuit preferably comprises an AND gate to whose inputs in each case one normally-closed contact of the relays is connected, which normally-closed contacts carry positive potential when the relay is switched off, and a control input of the solid-state switching element is connected to the output of the AND gate. The further relay may be adapted to be electrically locked via the normallyclosed contact of the first relay and is switchable on only when the first relay is in its quiescent position. In this case, a transistor in a control line of the further relay, may be controllable to conduct via the quiescent contact which carries the positive potential of the first relay. In addition, the first relay may be also electrically lockable via the normally-closed contact of the further relay.

An embodiment of the invention will now be described by way of example with reference to the drawings in which:- Figure 1 shows a circuit diagram with the essential components of the braking control circuit according to the invention, Figure 2 shows a detail from Figure 1 in order to illustrate in more detail logic signal evaluation of relay switching positions, Figure 3 shows the prior art which was mentioned initially. In the centre of Figure 1, the essential components of a control circuit 1 for operating and braking a wiper motor are collated in a dashed-dotted frame, the wiper motor M together with its mechanically switchable parking position switch P being shown on the right, likewise surrounded by a frame, in order to indicate the physical separation of these assemblies.

The control circuit 1 has standardized input terminals 1115Rll (switched positive; radio position of the ignition switch), 113111 (earth) and 1131b11 (position of the parking position switch), which are connected to a control apparatus 2 ("timing function relay") shown on the left, and two 1 standardized output terminals 115311 and 1153b11 which are connected to the motor windings.

A control switch 3, which is shown above the control apparatus 2, for manually switching the windscreen/headlight wiper mode on and off, has a switched-off position 0, an intermittent-operation contact J, a contact L for slow continuous operation and a contact S for fast continuous operation; the contacts J and S are directly connected to corresponding inputs of the control apparatus 2, while the contact L is connected via an OR gate OG to an input I of the control circuit 1.

This input I is directly connected to a first relay 4 in order to drive it, and its switching contact which is permanently connected to terminal 1115R11 can be switched over between a normally-closed contact 4R and a normally-open contact 4A. The latter is in turn directly connected to terminal 115311 of the control circuit and via this terminal to the wiper motor M. Thus, if the first relay 4 is permanently switched on by input 1 and the output of the OR gate OG (control switch 3 on contact L), then the wiper motor M changes into the slow continuous wiping mode, without any involvement of the control apparatus 2.

An output LA of the control apparatus 2 is also connected to a second input of the OR gate OG. In the intermittentoperation mode (control switch 3 on contact J), the control apparatus 2 passes starting pulses to the relay 4 via this output and holds said relay 4 pulled in as long as the wiper motor M holds the parking position switch P switched.

Because of the special design, it is intended once again to describe here the operation of the terminal 1131b11 and of the corresponding lead connection to the control apparatus 2. As can be seen from the circuit diagram, in the quiescent position shown, the parking position switch P is connected to earth (terminal 113111) and thus also connects the lead to the terminal 1131b11 to earth. However, as in the case of the prior art (Fig. 3), it is moved In a floating switch position when the wip2r motor M starts un:ll a complete wiping cycle has in

6 each case been completed. As can be seen, a connection between terminal 1115R11 and terminal 1131b11 exists within the control circuit via a pullup resistor Pu, so that a positive signal can always be detected on terminal 1131b11 when the parking position switch P is switched to be floating when the wiper motor M is running.

The control apparatus 2 now detects the alternating pulses on terminal 1131b11, via an input PE. In the normaloperating mode, it always supplies positive potential via the output LA and the OR gate OG whenever positive potential is detected at the input PE-.

Furthermore, these alternating pulses are evaluated in the context of monitoring the running time in order to protect the wiper motor against burning out in the event of seizure; if no alternating signal arrives at 1131b11 within a specific time interval when the motor is switched on, then the control apparatus 2 switches the wiper motor M off.

A further relay 5 of the control circuit 1 is permanently connected on one side, in the same way as its switching contact, to terminal 1115R11 and, on the other side, it is connected to a further output SA of the control apparatus 2. The control apparatus 2 supplies earth potential via said output SA when the control switch 3 is switched to its contact S. In the same way as the first relay 4, the further relay 5 has a normally- closed contact SR and a normally-open contact 5A, the latter in turn being permanently connected to the wiper motor M at terminal 1153b11.

The normally-closed contacts 4R and 5R of the two relays 4 and 5 are now in each case connected to one input of an evaluation circuit 6, which comprises at least one AND logic combination of these two inputs.

If the two relays 4 and 5 are in the quiescent position, then a positive signal is produced at the output of the evaluation circuit 6, which positive signal leads to a noncontact making switching element switching through, in this case an MOSFET power transistor 7. The gate of the MOSFET 7 is connected to the output of the evaluation circuit 6, its 1 7 source is permanently connected to earth and the drain is connected by terminal 53 to the wiper motor M and to the normally-open contact 4A of the relay 4. A voltage-dependent conductive VDR resistor 8 is provided in parallel with the drain-source junction, as overvoltage protection for the MOSFET.

The wiring shown of the MOSFET 7 results in its drainsource junction conducting after the two relays return to their quiescent position shown (=windscreen/ headlight wiper mode or intermittent-operation pause switched off), and a connection being produced between the terminal 115311 of the wiper motor and earth. Said wiper motor is thus shortcircuited and stops instantaneously, the braking current which is still being produced passing entirely via the MOSFET without producing wear. All the contacts of the relays and of the parking position switch are now free of braking current loads.

As soon as one of the two relays pulls in again, that is to say one of the two inputs of the evaluation circuit 6 becomes floating, this instantaneously blocks the MOSFET. In contrast to the prior art, only one relay is now still switched in order to brake the wiper motor, which has a positive influence, particularly in the intermittent-operation mode, when the relay 4 is continuously switched on and off. Since the electronic arrangement having the evaluation circuit 6 and the MOSFET 7 switches off considerably faster (in the microsecond range) then the switching contact of the relay 4 can be switched from the normally-closed to the normally-open contact 4A (millisecond range), there is also no risk of a short-circuit from 4A via the MOSFET to earth.

A possible embodiment of the evaluation circuit 6 is shown schematically in Figure 2 as a detail from Figure 1, as well as electrical locking of the relay 5.

The two relays 4 and 5 can be seen once again, their normally-open contacts 4A and 5A respectively being connected to the terminals 115311 and 1153b" respectively. Their normallyclosed contacts 4R and 5R are connected to inputs of an AND 8 gate UG whose output is connected to the gate of MOSFET 7. This completes the control of the MOSFET, which control has already been mentioned with respect to Figure 1.

The collector-emitter junction of a transistor 9, whose base is connected by a resistor to the normally-closed contact 4R of the relay 4, is now also inserted into the connection, which can be regarded as a control line of the further relay 5, between this relay and the input II (switchable earth) of the control circuit 1; in addition, the normal pull- down resistor for the base electrode is also shown.

This wiring results in the relay 5 being able to switch only when the switching contact of the relay 4 is on the normally-closed contact 4R. Only then does the base of the transistor 9 receive positive potential and the collectoremitter junction becomes conductive. If, in contrast, the relay 4 is pulled in, then the relay 5 is electrically locked via the normally-closed contact 4R. It is thus impossible for both relays to switch simultaneously.

It is self-evident that the relay 4 could also be electrically locked via the normally-closed contact 5R of the relay 5; for this purpose, a transistor which is connected on the base side to the normally-closed contact 5R could be inserted in an analogous manner into the earth connection of the relay 4.

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Claims

1. A braking control circuit for a windscreen/headlight wiper drive, in which a braking current, produced when braking an electric wiper motor into a parking position, which motor is controllable via a f irst relay into at least one speed level, is passed via a short-circuiting circuit which circuit, depending on the position of the f irst relay which switches of f the motor current of the wiper motor, is switchable to relieve the load on a normally-closed contact of said relay, wherein, via the normally-closed contact and in its normallyclosed position, the f irst relay switches on a solid-state switching element in the short- circuiting circuit, via which switching element the braking current of the wiper motor is directly short-circuited, the intermediate circuit having no switching elements with moving contacts.

2. A braking control circuit according to Claim 1, wherein the solidstate switching element comprises a power transistor.

3. A braking control circuit according to Claim 1 or 2, wherein the wiper motor is permanently connected to earth on one side, and the connection on the other side of the wiper motor is adapted to be connected to earth via the solid-state switching element after the switching contact of the f irst relay has tripped.

4. A braking control circuit according to Claim 2, wherein the power transistor is a MOSFET, to whose gate a voltage can be applied via the normally-closed contact of the relay, and the braking current is passed via the drain-source junction of the MOSFET.

5. A braking control circuit according to any one of the preceding claims, wherein a further relay is provided f or switching a second wiping speed, and the solid-state switching element can be driven by an evaluation circuit only when both relays are in the quiescent position.

6. A braking control circuit according to Claim 5, wherein the evaluation circuit comprises an AND gate to whose inputs in each case one normallyclosed contact of the relays is connected, which normally-closed contacts carry positive potential when the relay is switched off, and a control input of the solid-state switching element is connected to the output of the AND gate.

7. A braking control circuit according to Claim 5 or 6, wherein the further relay is adapted to be electrically locked via the normallyclosed contact of the first relay and is switchable on only when the first relay is in its quiescent position.

8. A braking control circuit according to Claim 7, wherein a transistor in a control line of the further relay, is controllable to conduct via the quiescent contact which carries the positive potential of the first relay.

9. A braking control circuit according to Claim 7, wherein, in addition, the first relay is also be electrically lockable via the normally-closed contact of the further relay.

10. A braking control circuit for a windscreen/headlight wiper drive, substantially as described herein with reference to and as illustrated in figures 1 and 2 of the accompanying drawings.

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