GB2311424A

GB2311424A - Motor braking control for a windscreen wiper

Info

Publication number: GB2311424A
Application number: GB9705734A
Authority: GB
Inventors: Hubert Hietl
Original assignee: Temic Telefunken Microelectronic GmbH
Current assignee: Conti Temic Microelectronic GmbH
Priority date: 1996-03-21
Filing date: 1997-03-19
Publication date: 1997-09-24
Anticipated expiration: 2017-03-19
Also published as: DE19611064C2; GB9705734D0; ITMI962582A1; FR2746559A1; GB2311424B; IT1286465B1; FR2746559B1; ITMI962582A0; DE19611064A1

Description

0 2311424 1 Windscreen Wiper Circuit The invention relates to an

electrical circuit for activating windscreen wiper, especially one for a motor vehicle, at plurality of stepped speeds.

The arrangement includes an electric motor which has a plurality of windings corresponding to the controllable steps in speed of the windscreen wiper, the one end of the windings being at earth potential and the other ends being connectible over power leads to a suitable operating potential, preferably the positive terminal voltage of a motor vehicle battery, by means of a number of relays that are used f or activating a respective winding or, f or the purposes of rapidly braking the electric motor, being connectible via an electronic switching member, preferably an FET, to earth potential and also, to a method of operating this circuit.

An electrical circuit of this type is known from DE 42 41 996 A1 for example.

These days, the windscreen wiper assemblies used in modern motor vehicles are equipped with electrical circuits which permit the wiping action to occur at several, usually two, different speed steps (fast and slow) in dependence on the amount of precipitation that is actually occurring.

As a result of the inertia of this system, the electric motor will continue to run for a certain time after the actuation of the corresponding switch contact in the interior of the vehicle when switching the electric motor for the windscreen wiper from an operational state involving a faster or slower speed step into its state of rest so that the wiper blade of the windscreen wiper could come to a stop at an undefined position on its particular screen. In order to prevent this, in the case 1 1 0 2 of modern windscreen wiper circuits, the electric motor is connected to earth via the power lead of the currently activated winding of the electric motor precisely at that moment when the wiper arm is positioned at its lowest point, in a wiper compartment for example, so that a braking current produced in the generator mode of the electric motor can flow at once and the electric motor will then come to an immediate halt.

In order to relieve the rest contact of the corresponding switching relay and also the wiper motor's parking-position switch from the braking current, it is proposed in the above cited DE 42 41 996 A1 that a braking control circuit for the windscreen wiper should comprise at least one relay for switching the motor current via a working contact. For this purpose, a shorting circuit that is controllable via a rest contact of this relay isconstructed in the form of a contactless switching element, in particular in the form of a MOSFET, via which a braking current occurring during the stoppage of the,wiper motor can be short-circuited directly to earth without loading a switching element having moveable contacts.

It is disadvantageous in this known circuit however, that in the event of the contactless switching element switching through unexpectedly during one of the operational steps, something that can be caused by a defective component in the electronic control means for example or by the ingress of damp into the controlling electronic circuitry, an immediate and intense short-circuiting of the operating poz:ential to earth via the contactless switching element will be produced whereby the contactless switching element, and in general, other 3 components of the electrical circuit, will be damaged or destroyed.

It is of further disadvantage in the case of the known windscreen wiper circuit that the different stepped speeds are switched independently of one another and hence any chattering of the switching relay will be directly passed on to the contactless switching element so that this will "chatter" too. As a result, there will, on the one hand, be a very high rate of wear of the relay contacts and a heavy dynamic loading on the contactless switching element on the other.

It is therefore, the object of the present invention to propose an electrical circuit of the type described hereinabove in which on the one hand, it will not be possible to short-circuit the operating potential to earth via the contactless switching element in the event that the electronic switching member should switch-through unintentionally and in which chattering of a relay when switching the electric motor from an operational state into the quiescent state by means of a braking circuit will not necessarily result in chattering in the electronic switching member.

In accordance with the invention, this object is achieved in a manner, that is as amazingly simple as it is effective, wherein the relays are arranged successively in a series circuit in such a way that the relay which is situated furthest away from the electric motor can switch a common power lead coming from the windings, between the operating potential and the electronic switching member and that the relays located more closely to the electric motor can electrically connect the power lead for that particular winding of the electric motor that is to be activated to the common power lead.

0 4 Thus, in the case of the circuit in accordance with the invention and in contrast to known circuits, each winding of the electric motor is not switched individually by its own relay between the operating potential and the "braking path" independently of the other windings but rather, the appropriate power lead for activating the currently selected winding of the electric motor is initially built-up by one or more of the series connected relays and then, using the relay situated furthest away from the electric motor, a common power lead is either activated by being connected to the operating potential, or, it is deactivated by virtue of a connection to the electronic switching member and the latter's own connection through to earth, whereby any corresponding braking current then flows out of the relevant winding of the electric motor via the electronic switching member to earth.

In this manner, as will be explained in greater detail below, any transfer of the chattering of the relay when switching from an operational state into the quiescent state can be avoided by appropriately controlling the electronic switching member. However, something else that is also particularly excluded by virtue of the circuit in accordance with the invention is the materialisation of a short-circuit during an operational mode in the event of an unintentional switch-through of the electronic switching member, since the electronic switching member is only connected to the common power lead by the relay situated furthest from the electric motor during the quiescent state but is never so connected in an operational mode.

One preferred arrangement is an embodiment of the circuit in accordance with the invention in which, in the rest position of all the relays, the power lead for the winding for the lowest speed step of the windscreen wiper is connected to the electronic switching member while the power leads for the remaining windings are open ended. In this manner, the rest contacts of the relays involved are loaded to a particularly low extent so that no increased demands need to be made on the design of the relays in respect of the durability of their rest contacts.

In a further embodiment, the number of relays corresponds to the number of windings on the electric motor. In this case, only economical standard relays that can merely switch two contacts backwards and forwards need to be used.

As an alternative thereto in the case of another embodiment of the invention, there are provided only two relays of which the one located more closely to the electric motor can electrically connect the common power"lead to each of the power leads leading to the individual windings of the electric motor in a selective manner. Thus, for the purposes of establishing a connection between the common power lead and an individual power lead leading to a selected winding, this relay has to be able to drive a number of contact points corresponding to the number of individual windings. The advantage of such a circuit vis a vis those described previously is to be found in the fact that it is substantially more compact.

A particularly preferred arrangement is an embodiment of the circuit in accordance with the invention in which, there is provided an electronic control member which controls the relays in such a way that the common power lead is electrically connected to the electronic switching member at least during the chatter period of the relay located more closely to the electric motor when switching to the lowest speed step or when 6 switching between different ones of the speed steps of the electric motor and is only connected to the operating potential after the chatter period is over. In this manner, the switching contacts of the relays located more closely to the electric motor are particularly preserved since the switch-over process and the chattering of the relays only occur in a currentless state. The chattering of the relays, which normally occurs when switching over into a current carrying state, results in increased burning of the contacts in the case of the circuits in accordance with the state of the art because sparks are constantly being created during the chatter period. In the present case, any such formation of sparks is avoided by only switching-over to the operating potential after the chatter period is over.

In advantageous manner in a further development of this embodiment, the relay situated furthest away from the electric motor has a working contact which is rated for higher loads than the working contacts of the other relays and via which contact the common power lead is connected to the operating potential. Since, as described above, the relays located more closely to the electric motor are subjected to considerably lower loadings when performing a switching action, and thus too, experience a much lower degree of wear in operation, these relays can be designed to be less robust than the relay situated furthest away from the electric motor, this being a factor that considerably reduces the costs of the circuit in accordance with the invention.

An embodiment of the circuit in accordance with the invention that is also particularly preferred is one in which, there is provided an electronic control member which controls the electronic switching member in such a way that it only switches 7 through, at the earliest, following the expiry of the chatter period of the relay situated furthest away from the electric motor when the common power lead is electrically connected to the electronic switching member. one thereby achieves the effect that the rest contact of the relay situated furthest away from the electric motor remains in a current-less condition when switchingover to the "braking path" during the relay chattering period, thus considerably lengthening its lifetime. one particular result of this is that the rest contact of this relay may then have a substantially lower rating than the working contact, thus reducing the cost of this relay. Moreover, in the case of this embodiment of the invention, any "passing-on" of the relay chatter to the electronic switching member is avoided, which considerably increases its lifetime or makes it possible to use a more economical electronic switching member that is designed for lower loads.

There also falls within the framework of the invention a method of operating an electrical circuit of the type described above which is distinguished by virtue of the feature that when switching the electric motor from its rest state to the operational state involving the lowest speed step and also when switching between different ones of the speed steps, only the relay or the relays located more closely to the electric motor are initially switched into the corresponding operating position and that the relay situated furthest away from the electric motor only connects the common power lead to the operating potential after the chatter period of the last relay to be switched on is over. Better preservation of both the rest contacts and the working contacts of the relays located more closely to the electric motor is achieved in this manner.

0 8 Likewise falling within the framework of the invention is a method of operating an electrical circuit of the type described above in which, f or the purposes of rapidly braking the electric motor to a halt, it is envisaged that the common power lead be electrically connected to the electronic switching member by the relay situated furthest away from the electric motor and that the electronic switching member should only be switched- through and the common power lead connected to earth potential at the earliest after the chattering of this relay has died down. By doing this, one preserves the rest contact of the relay situated furthest away from the electric motor on the one hand since a currentless condition exists during the chattering of the relay and, on the other hand, the chattering of the relay is not passed on to the electronic switching member because this is only switched-through to earth potential thereafter so that here too reduced wear is achieved.

Further advantages of the invention are apparent from the description and the drawing. Likewise, the aforesaid features and also those to be discussed hereinafter may, in accordance with the invention, be used on an individual basis or combined in any combination. The embodiments that are described and shown should not be considered to be the last words on the subject, but rather they are merely of an exemplary character for illustrating the invention.

According to one aspect of the present invention there is provided an electrical circuit for activating a windscreen wiper, at a plurality of stepped speeds, including an electric motor which has a plurality of windings corresponding to the controllable steps in speed of the windscreen wiper, one end of each winding being at earth potential and the other end being connectible via power leads to an operating potential, by means of a number of relays that are used for activating a respective winding, or, for the purposes of rapidly braking the electric motor, being connectible via an electronic switching member, to earth 0 9 potential, wherein; the relays are arranged successively in a series circuit in such a way that the relay that is furthest away from the electric motor can switch a common power lead coming f rom the windings, between the operating potential and the electronic switching member and that the relays located more closely to the electric motor can electrically connect the power lead for that particular winding of the electric motor that is to be activated to the common power lead.

The invention is illustrated in the drawings and will be explained in more detail on the basis of exemplary embodiments. Therein:

Fig. 1 shows a first embodiment of the circuit in accordance with the invention having two selectable steps in speed; 0 10 Fig. 2 a further embodiment of the circuit in accordance with the invention having three selectable steps in speed and three relays; and Fig. 3 an embodiment of the circuit in accordance with the invention having three selectable steps in speed but only two relays.

In the windscreen wiper circuit according to Fig. 1, there can be perceived an electric motor 1, the windings of which are connected to earth potential at one end and can be supplied with operating current via power leads 2 and 3 at their other ends. In its rest position, a relay 4 located more closely to the electric motor 1 connects a common power lead 5 to the power lead 2, while in its activated position, it connects it to the power lead 3. A relay 6 located remotely from the electric motor 1 connects the common power lead 5 to an electronic switching member 7 in its rest position and, in its activated position, to an operating potential 15R which is preferably tapped from the positive terminal voltage of a notillustrated motor vehicle battery. For the purposes of rapidly braking the electric motor 1, an appropriate gate signal from a not- illustrated microprocessor unit may be applied via a control lead 8 to the electronic switching member 7 so that this switches through to earth potential and the motor braking current correspondingly flows to earth via the common power lead 5.

In the rest position illustrated in Fig. 1, the electric motor 1 is connected via the power lead 2, the common power lead 5 and the electronic switching member 7 to earih so that no current flows and the motor remains at rest. In order to switch to a first one of the stepped speeds of the windscreen wiper 11 that is driven by the electric motor 1, the relay 6 located furthest from the motor 1 has to be actuated so that the common power lead 5 is electrically connected to the operating potential 15R. Due to this action, an operating current of ca 4 to 6 A flows through the electric motor 1 in its corresponding first winding so that the motor rotates at a first one of the stepped speeds.

For the purposes of switching to a second of the stepped speeds, the relay 6 is then actuated again so that the common power lead 5 is connected to the electronic switching member 7 which is not switched through at this point in time. Thereafter, by actuating the relay 4, the common power lead 5 is connected to the power lead 3 for another winding of the electric motor 1 which corresponds to a second step in speed. Finally, the common power lead 6 is connected once again to the operating voltage 15R by'the relay 6 so that current flows through the second winding of the electric motor 2 [sic] and it accordingly moves at the second one of the stepped speeds. In this manner, any chattering of the relay 4 is produced entirely during a current-less state which thereby prevents increased burning of the contacts of relay 4 during its operation.

So too, when switching back from the second of the speed steps to the first speed step, the common power lead 5 is initially connected by the relay 6 to the switching member 7 in its nonswitched-through state, the common power lead 5 is then connected at its one end to the power lead 2 of the first winding of the electric motor 1 by the switclhing action of the relay 4 and only then, by virtue of a reiterated switching of the relay 6, is the common power lead 5 and 1-ence the f irst winding of the electric motor 1 connected to the operating potential 15R so that once again relay chattering occurs 12 exclusively in a current-less state during the switching of the relay 4.

when rapidly braking the electric motor 1, the common power lead 5 is initially connected to the electronic switching member 7, which is not connected through at this point in time, by switching the relay 6 into its rest state. Only after a relay chatter period of ca 10 msecs has elapsed is the electronic switching member 7 switched-through by an appropriate signal over the control line 8 so that the common power lead 5 is then connected to earth potential. In this manner, the relatively high braking current (up to 35 A) only flows to earth via the rest contact of the relay 6 and the electronic switching member 7 when a chatter free state exists. The rest contact of the relay 6 as well as the electronic switching member 7 are thereby protected from disproportionate wear, this thus resultidg in a substantially increased lifetime for the corresponding components.

As can be seen from Fig. 2, the inventive idea may also be implemented when switching an electric motor between more than two stepped speeds. In the example shown, the electric motor 21 comprises three windings (corresponding to three different steps in speed) the power leads 22 and 23 of which can be connected to a power lead 29 by means of a relay 24, while a common power lead 25 can be connected to the power lead 29 or to a power lead 20 leading to a third winding by the switching action of another relay 30. One can thus switch backwards and forwards between three stepped speeds of the electric motor 21 in this manner. At its other end, the common power lead 25 can be connected either to an operating potential 15R, or, to earth potential via the electronic switching member 27 which is 0 13 controllable via the medium of a control line 28, by a relay 26 that is located at a distance from the electric motor 21.

It is indicated in Fig. 3 how one can switch backwards and forwards between three stepped speeds of an electric motor 31 having three different windings and the corresponding appertaining power leads 32, 33 and 39 by means of a single relay 34 so that the currently selected power lead 32 or 33 or 39 is connected to a common power lead 35 which, for its part, can be connected at its other end by a relay 36 either to an operating potential 15R or to earth potential via the electronic switching member 37 which can receive a gate signal for switching it through over a control line 38.

A person skilled in the art of electronics may wish to use a transistor arrangement, or other suitable switching means, in place of the relays mentioned herein.

The advantages of the electrical circuit in accordance with the invention that has been described above may also be made use of in other electrical devices apart from windscreen wipers where the devices comprise an electric motor that can be switched between any of a plurality of speed steps and a rapid braking step.

0

Claims

Claims

14 An electrical circuit for activating a windscre en wiper, at a plurality of stepped speeds, including an electric motor which has a plurality of windings corresponding to the controllable steps in speed of the windscreen wiper, one end of each winding being at earth potential and the other end being connectible via power leads to an operating potential, by means of a number of relays that are used for activating a respective winding, or, for the purposes of rapidly braking the electric motor, being connectible via an electronic switching member, to earth potential, wherein; the relays are arranged successively in a series circuit in such a way that the relay that is furthest away from the electric motor can switch a common power lead coming from the windings, between the operating potential and the electronic switching member and that the relays located more closely to the electric motor can electrically connect the power lead for that particular winding of the electric motor that is to be activated to the common power lead.

2. A circuit in accordance with claim 1, wherein, in the rest position of all the relays the power lead f or the winding f or the lowest speed step of the windscreen wiper is connected to the electronic switching member while the power leads for the remaining windings are open ended.

3. A circuit in accordance with claim 1 or 2 wherein; the number of relays corresponds to the number of windings on the electric motor.

A circuit in accordance with claim 1 or 2, wherein there are provided only two relays of which the one located more closely to the electric motor can electrically connect the common power lead to each of the power leads leading to the individual windings of the electric motor in a selective manner.

0 5. A circuit in accordance with any preceding claim, wherein there is provided an electronic control member which controls the relays in such a way that the common power lead is electrically connected to the electronic switching member at least during the chatter period of the relay located more closely to the electric motor when switching to the lowest speed step or when switching between different speed steps of the electric motor and is only connected to the operating potential after the chatter period is over.

6. A circuit in accordance with claim 5, wherein the relay which is furthest away from the electric motor has a working contact which is rated for higher loads than the working contacts of the or the other relays and via which contact the common power lead is connected to the operating potential.

7. A circuit in accordance with any preceding claim, wherein there is provided an electronic control member which controls the electronic switching member in such a way that it only switches through at the earliest following the expiry of the chatter period of the relay which is furthest away from the electric motor when the common power lead is electrically connected to the electronic switching member.

8. A circuit in accordance with any preceding claim wherein, the electronic switching member, included for the purpose of rapidly braking the electric motor, is an FET device.

9. A motor vehicle including an electrical circuit according to any preceding claim and a battery, the positive terminal voltage of which constitutes said operating potential.

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

1 G 16 11. A method of operating an electrical circuit in accordance with any of claims 1 to 8, wherein, when switching the electric motor from its rest state into the operational state involving the lowest speed step or when switching between different speed steps, only the relay or the relays located more closely to the electric motor are initially switched into the corresponding operating position and that the relay which is furthest away from the electric motor only connects the common power lead to the operating potential after the chatter period of the last relay to be switched-on is over.

12. A method of operating an electrical circuit in accordance with any of Claims 1 to 8 or in accordance with Claim 11, wherein, for the purposes of rapidly braking the electric motor to a halt, the common power lead is electrically connected to the electronic switching member by the relay which is furthest away from the electric motor and that the electronic switching member is only switched through and the common power lead connected to earth potential, at the earliest, after the chattering of this relay has died down.

i 1