GB2052099A - Control of wiper drive - Google Patents

Abstract

A wiper drive (2, 5) having an electric motor (2) for moving wipers (16) to and fro, is provided with a retardation switch (6) which temporarily places a resistor (40) in series with the motor to switch the electric motor (2) to a lower speed when the wipers (16) approach the ends of their wiping paths. The retardation switch (6) has contacts (38, 39) and a switching disc (36) which rotates with a crank arm (9) provided in the wiper drive (2, 5). The reduction in wiping speed at the ends of the path of movement of the wipers (16) reduces the inertia forces exerted on the reciprocating transmission (5) and thereby reduces wear and noise. <IMAGE>

Description

SPECIFICATION Wiper drive having an electric motor The invention relates to a wiper drive comprising an electric motor and a drive transmission connected to the motor output for moving at least one wiper back and forth.

Inter alia, Published German Patent Specification (Offenlegungsschrift) No. 25 27 689 describes wiper drives in which reciprocating drive transmission in the form of, for example, a crank gear is disposed beyond the electric motor and drives at least one wiper in alternating directions.

The wiper drives are stressed to a particularly great extent when the wipers are retarded upon approaching the ends of their paths and are finally accelerated in the new direction of movement.

Therefore, wiper drives intended for high wiping frequencies hitherto had to be or particularly expensive and very robust construction and had to be adjusted in a play-free manner by means of built in adjusting means. The play-free adjustment is gradually lost as a result of wear, so that the acceleration required to initiate the change of direction of the wipers finally causes knocking sounds and increased wear.

In a wiper drive, described in U.S.A. Patent Specification No. 2,869.165, for two wipers operating in opposing directions on a so-called full-view windscreen, there is provided an energystoring spring which is coupled to one of the wiper arms and which is stressed when the wipers enter the outer ends of their wiping paths and accelerates the wipers towards the inner ends of their wiping paths after the wipers have reached the outer ends of their wiping paths. Although the energy-storing spring effects more uniform speeds of the wipers in both wiping directions, it is subjected to high alternating stresses and is thus subjected to the risk of breaking. The spring forces cause increased wear on the bearing of the wiper arm.

The present invention resides in a wiper drive comprising an electric motor, a transmission connected to the motor output for moving at least one wiper to and fro, and at least one switch which is actuated by the wiper drive and which temporarily switches the electric motor to a lower speed when the wiper approaches at least one of the two ends of its winding path.

It is an advantage that the forces acting upon the wipers due to inertia are considerably reduced by temporarily reducing the rotational speed of the electric motor and by the resultant temporary reduction in the speed of the wipers in the regions of the ends of their wiping paths. This reduction in the forces due to inertia reduces the stress on the wiper drive and the generation of sound. The wiper drive in accordance with the invention does not need an energy-storing spring which is subjected to the risk of breakage, and its mechanical construction is correspondingly simple, inexpensive and reliable.

The invention is further described, by way of example, with reference to the drawing which is a diagram of a wiper drive in accordance with one preferred embodiment of the invention.

The wiper drive has an electric motor 2 incorporating an output shaft 4, a reciprocating drive 5 driven by the shaft 4, a retarding switch 6 and a packing switch 7 which are likewise connected to the shaft 4, and a wiper switch 8.

The reciprocating drive 5 comprises a crank arm 9, a clankpin 10, a connecting rod 11 and a pivoted lever 13 which has a pivot spindle 14 and which is connected to the connecting rod 11 by way of a pin 12. The pivot spindle 14 is connected to a wiper arm 15 so as to be non-rotatable relative thereto, and carries a wiper 16. Further wiper arms provided with wipers can be connected to the reciprocating drive 5.

The electric motor has an armature (not illustrated) provided with a commutator 17, a first carbon brush 18 which abuts against the commutator 17 and is connected to the switch 6, a second carbon brush 19 for a slow wiping frequency, and a third carbon brush 20 for a higher wiping frequency.

The packing switch 7 has an annular, electrically conductive switching disc 21 incorporating an inwardly directed switching sector 22 and a sectional notch 23 located opposite the switching sector 22, and resilient sliding contacts 24, 25 and 26. The sliding contact 24 is directed towards the orbit of the switching sectional notch 23. The sliding contact 25 is located between the sliding contacts 24 and 26 and abuts against the switching disc 21.

The wiper switch 8 has two switching contactors 27 and 28 which are electrically isolated from one another and which are commonly movable into three switching positions 0, I, II by means of a switching handle 29. When in switching position 0, the switching contactor 28 interconnects two contacts 30 and 31. The contact 30 is connected to earth, while the contact 31 is connected to the sliding contact 24.

When in the said switching position, the contactor 27 connects a contact 33 to a contact bar 32 connected to the positive pole of a vehicle power supply. The contact 33 is connected to the sliding contact 26. When in switching position I, the switching contactor 27 connects a contact 34 to the contact bar 32. The contact 34 is connected to the sliding contact 25 and also to the carbon brush 19 for the low wiping frequency. Finally, when in switching position II, the switching contactor 27 connects the contact bar 32 to a further contact 35 which is connected to the carbon brush 20 for the higher wiping frequency.

The retarding switch 6 has an electrically conductive switching disc 36, whose periphery incorporates two sectional notches 37, and two resilient sliding contacts 38, 39. The notches 37 are disposed diametrically opposite to one another. The two sliding contacts 38, 39 are arranged adjacent to one another and are directed towards the orbit of the notches 37. The sliding contact 38 is connected to the carbon brush 18, while the sliding contact 39 is connected to earth.

A rotational speed regulating resistor 40 is connected between the sliding contacts 38 and 39. The notches 37 have an aperture angle of, for example, 300 to 60O and are adjusted relative to the shaft 4 such that the sliding contacts 38 and 39 are not directly electrically interconnected when the shaft 4 has moved the wiper or wipers 16 into the region of the ends of their wiping paths by means of the reciprocating transmission 5.

After the wiper switch 8 has been switched on, the opening of the electrical connection between the sliding contacts 38 and 39 causes a currrent, flowing through the carbon brush 19 or 20 to the commutator and from the latter through the carbon brush 18, to flow to earth through the rotational speed regulating resistor 40. The rotational speed regulating resistor 40 reduces the current flowing through the motor 2 such that the rotational speed of the motor 2 drops. Thus, the wiper drive operates at a lower motor speed in the region of the end positions or reversal positions of the wipers. This results in lower pivoting speeds of the wipers and thus in a considerable reduction in the forces exerted in the reciprocating transmission 5 due to inertia.As already mentioned, there is a corresponding reduction in the abrupt stresses and generation of sound occurring in the wiper drive as a result of unavoidable play. The notches 37 in the switching disc can be dimensioned and set relative to the reciprocating transmission 5 such that the speed of the motor 2 is low when the wipers enter their end positions and are accelerated in the opposite direction. On the other hand, however, according to the type of the reciprocating transmission 5 used and the wiper frequencies to be obtained, it is also possible to restore the contact between the contacts 38 and 39 when the wipers have assumed their end positions. Thus, the wipers can be rapidly accelerated from their end positions.By way of example, the value of the rotational speed regulating resistor 40 can be chosen such that the current flowing through the running electric motor 2 drops to approximately half to a quarter.

Alternatively, instead of using the switching disc 36 described, a switching disc can be used which has only one notch 37 in its periphery. The contacts 38, 39 are then arranged diametrically opposite to one another relative to the centre of the switching disc. Alternatively, however, it is also possible to use control cams instead of a switching disc 36 and to allow them to act upon sets of contact springs. If, for example, a screwthreaded spindle is used instead of the abovedescribed reciprocating transmission 5 for the forward and reverse movement of wipers, contact breakers are provided which are operable by the wipers or the arms thereof.

The sliding contact 26 is energised upon switching off the described embodiment of a wiper drive. Provided that the wipers are still located outside their parked positions, the switching disc 21 continues to feed voltage to the carbon brush 19, so that the electric motor continues to drive the wipers at a speed corresponding to the low frequency. The notch 23 switches off the voltage when the wipers enter their parked position, and the electric motor 2 is de-energized.

The switching sector 22 then immediately connects the carbon brush 19 to earth by way of the contacts 30 and 31 and the switching contactor 28. The motor 2 is thereby decelerated.

Claims (8)

1. A wiper drive comprising an electric motor, a transmission connected for the motor output for moving at least one wiper to and fro, and at least one switch which is actuated by the wiper drive and which temporarily switches the electric motor to a lower speed when the wiper approaches at least one of the two ends of its wiping path.

2. A wiper drive as claimed in claim 1, in which the electric motor has an associated rotational speed regulating resistor which is connected in parallel with the switch and which is periodically bridgeable thereby.

3. A wiper drive as claimed in claim 2, in which the rotational speed regulating resistor is connected in series with the armature of the electric motor.

4. A wiper drive as claimed in any of claims 1 to 3, in which the transmission is a reciprocating transmission comprising at least one crank arm and a crank pin.

5. A wiper drive as claimed in claim 4, in which said switch incorporates a switching disc which rotates commonly with a crank arm and which has at least one notch and two contacts directed towards the orbit of the notch.

6. A wiper drive as claimed in claim 5, in which the switching disc is made from an electrically conductive material, and two notches are arranged diametrically opposite to one another relative to the axis of rotation of the switching disc.

7. A wiper drive as claimed in claim 4, in which said switch incorporates a switching disc which has control cams and rotates in synchronism with the crank arm, and contacts actuated by the switching cams.

8. A wiper drive constructed and adapted to operate substantially as herein described with reference to the drawing.