GB2029542A

GB2029542A - Power transmitting coupling for windscreen wipers

Info

Publication number: GB2029542A
Application number: GB7926700A
Authority: GB
Original assignee: SWF Spezialfabrik fuer Autozubehoer Gustav Rau GmbH
Current assignee: SWF Auto Electric GmbH
Priority date: 1978-08-24
Filing date: 1979-07-31
Publication date: 1980-03-19
Also published as: FR2434058A1; GB2029542B; DE2836998A1; AU5009979A; FR2434058B3

Abstract

A power transmitting coupling, for insertion between a windscreen wipe drive motor and a wiper blade, which automatically takes up at least part of the driving motion when movement of the wiper blade is blocked, for example by snow, in order to prevent damage to the motor. In one arrangement the coupling is located in a motor crank and is such that the crank length is shortened when the wiper blade is blocked. The crank comprises an inner lever (1) to which the driver shaft of the motor is secured (at 9) and an outer lever (18), movable relative to the inner lever (1), to which a push rod may be articulated (at 23). The inner lever (1) is guided within the outer lever and when the wiper blade movement is not blocked a spring (28) serves to keep the distance between the drive shaft (9) and the push rod articulation part (23) at a maximum. <IMAGE>

Description

SPECIFICATION Power transmitting coupling for windscreen wipers This invention relates to windscreen wiper apparatus for motor vehicles, and in particular to couplings therefor.

There exists the danger that the wiper blades of a windscreen wiper installation can no longer glide over the entire wiping angle when an obstacle becomes attached to the wiping area and their movement is therefore blocked. Especially in winter time, when snow is falling, it is possible that around one end position of the wiper blades such a thick snow bolster is formed that the motor power is no longer sufficient to move the wiper blades to the end position. It can, however, also be imagined that the movement of the wiper blades can be blocked anywhere between its two end positions.

In each case it is possible that the windscreen wiper installation is damaged to such an extend that parts of it or the entire wiper installation will have to be replaced. In particular, an electric drive motor can be destroyed, since a wiper motor blocked outside of the parking position is connected to the operating voltage even when it is switched off. Depending on the design this will result in more or less costly consequential damages.

According to the present invention there is provided windscreen wiper driving apparatus for motor vehicles, comprising a drive motor; a transmission mechanism for transforming the motor motion into wiper blade motion, and, in order to protect the motor if movement of the wiper blade becomes blocked, a power transmitting coupling in the transmission mechanism, said coupling automatically taking up at least part of the motor motion dependent on the resistance to wiper blade motion.

Power transmitting connections are known, for instance from German Specification DE-OS 2014051 which describes a motor crank consisting of two parts movable against each other which are effectively secured to each other at least initially by a spring. However this motor crank has its shortest length during normal wiper operation, so that it can only be elongated. Therefore it cannot be used as a motor protection, when the wiper blades are blocked. Thus the known coupling has the purpose to enlarge the wiping angle of the wiper blades in the second half of the wiping period by an elongation of the motor crank and enable that the wiper blades occupy a parking position outside of the wiping area.

This elongation is effected from outside via an electromagnet and a cam disk.

In a force-locking connection or coupling according to the present invention, during normal wiper operation the motion of the drive motor is transmitted to the wiper blades by the coupling and other elements of a power transmission mechanism. During normal wiper operation the coupling acts as a rigid constructional unit, so that no discontinuity appears in the wiping pattern. Only when the wiper blade motion is blocked, and due to increased load on the coupling members, is there reciprocal motion of the power transmitting elements. This motion in not controlled by the vehicle driver, but it is automatically effected by the interplay between the blocked wiper blades and the drive motor. The coupling can thereby be designed in such a manner that the force-locking connection betweem motor and wiper blades is completely interrupted.However it is more favourable not to separate the coupling members completely after release of the coupling, but to hold them together by a spring element.

During the movement of the coupling members this spring element is tensioned, so that after the obstacle on the windscreen is removed a rigid connection of the coupling members is again effected without an external influence. Thus power is transmitted to the wiper blade, too, when the movable parts of the coupling changed their position from the initial position.

In order to provide that the coupling takes place reliably in a preferred embodiment of the invention the spring element is designed in such a way that it is already tensioned during normal operation. The spring element can be simultaneously used to hold the individual coupling members in rigid engagement with each other. Thus it is possible to exactly determine the release point, i.e. the height of the wiping resistance during the release of the coupling, in that a defined initial tension for normal wiper operation is given to the spring.

If the motor crank serves as a coupling as in the preferred embodiment of the invention the motor can continue to rotate, when the blades are blocked near to both reversing points. The demand for a rigid coupling during normal operation can only be complied with with a considerably initially tensioned spring having a large force constant, because this coupling must take up the wiping resistances appearing on all wiper blades.

The coupling can more easily be rigidly designed, when it is located on the push rods leading to the respective wiper shafts. For in this case each coupling has to transmit the necessary forces to move a single wiper blade.

Independent of the fact whether a push rod transmits the motor motion to a wiper shaft only or whether it provides a connection betwen several wiper shafts, as for instance in a lateral arrangement of the wiper motor, it is however possible, when the coupling is arranged on a push rod, to design the coupling in a simple way that it responds to a blocking of the wiper blades at any point of the wiping area. If the push rod consists of two main rods and at least one connecting member articulated on the two main rods, in each articulated joint the parts can be effectively secured to one another in the initial position by an initially tensioned spring.When there are two couplings, each located on a respective push rod, upon release of one relative to the other the length of the associated push rod can be variable in the reverse sense, one coupling being released by compression and the other by tension between the two main rods. Each push rod may comprise two main rods and three connecting members, two of which are articulated on the main rods and the third jointedly connected with the two others. The four moving joints represent the corners of a square and the possibility of the parts rotating from an initial position into a direction reversing from moving joint to moving joint is prevented by stops. At each moving joint a spring element effectively secures the parts together in the initial position when the wiper blades are not blocked.

Similar advantages with respect to a "rigid" design of a motor crank are created, when the coupling is built into the rocker arm of the wiper shaft. In addition, the stability of the push rod is not weakened.

In an alternative embodiment of the present invention the rocker arm consists of two parts displaceable against each other, which are connected with each other by pins guided in oblong holes and by initially tensioned spring elements. In a particular development the oblong holes serving as guide slots are thereby inclined towards the rocker arm. This inclination causes the lateral deviation the distance between wiper shaft and pivotal point of the push rod to be also enlarged, so that a relatively big reduction of the original wiping angle can be compensated for.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a section through a motor crank employing a coupling according to one embodiment of the invention; Figure 2 is a top view on the motor crank of Fig. 1 with the cover only partially shown; Figure 3 is a top view of a rocker arm of a wiper shaft into which a coupling according to another embodiment of the invention is built, and Figure 4 is a lateral view of the rocker arm of Fig. 3.

The motor crank shown in Figs. 1 and 2 has an inner lever 1, which substantially consists of two lateral webs 2 and 3, two crossbars 4 and 5 connecting the ends of the lateral webs and a central block 6. By this arrangement two rectangular recesses 7 and 8 are created through the inner lever. There is a recess 9 in the central block 6 for a driven shaft of a motor (not shown). The two sides 10 and 11 of the central block 6 serve as stops. The central block 6 is furthermore provided with a bore 12. A bolt 13 with a threaded portion is screwed through the threaded opening 14 of the crossbar 4 and with its end 15 projects into the bore 12 of the central block 6.

The inner lever 1 is guided in an outer lever 18. This lever 18 consists of two side walls 19 and 20 and a base plate 21 on which the side walls 19 and 20 are standing, a support ing member 22 on which pivot pin 23 is fixed, and an abutment 24 through which the bolt 13 penetrates and from which two webs 25 and 26 extend into the recess 7 of the inner lever 1. The distance between abutment 24 and supporting member 22 is greater than the length of the central block 6. The driven shaft of the motor can engage into the recess 9 of the central block 6 through oblong hole 27 in the base plate 21.

A spring 28 is composed of individual cup springs is guided on the bolt 13. Bolt 13 and spring 28 are located in a groove 29 formed between the two webs 25 and 26. The spring 28 supports on the abutment 24 of the outer lever 2 and on stop 30 of the bolt 13. It is initially tensioned in a way that it acts as a pressure spring. Therefore the stop side 11 of the central block 6 is pressed against the abutment 24. A cover plate 31 which is screwed to the outer lever 18, ensures that inner and outer levers of the motor crank are reliably held together. A recess 32 in the cover plate 31 enables fastening of the driven shaft of the motor to the inner lever 1 to be made.

When the windscreen wiper installation is operated the driven shaft of the motor always rotates at the same spot. All parts of the motor crank are moved in orbits around the axis of rotation of the driven shaft of the motor. If movement of a wiper blade is blocked near to one of its reversing points, it is not possible to continue the movement of the pivot pin 23 on its orbit. The outer lever 18 and the inner lever 1 are displaced relative to each other against the force of the spring 28, so that the distance between the recess 9 and the pivot pin 23 becomes smaller and the pivot pin can glide over the point on its orbit which corresponds to the reversing point of the wiper blade. The distance becomes bigger again until the central block 6 rests on the abutment 24 anew. Then the wiper blade again is moved. This adjustment of the cou pling formed by the inner and outer levers is repeated during each wiping cycle until the obstacle causing the blocking is removed.

When the windscreen wiper installation is switched off, the motor can then run into the position corresponding to the rest position of the wiper blade in which the motor comes to a standstill, even if the wiper blade is retained in a blocked position. Only after the blocking has ceased are the inner lever 1 and the outer lever 2 slid apart by the spring 28, so that the wiper blade is moved to its end position. The just described operations are possible when the wiper blade is blocked within a given angular range near its reversing points. This angular range is defined by the distance dthe stop 11 of central block 6 is from the supporting member 22 during normal operation of the windscreen wiper installation.

Figs. 3 and 4 show a coupling according to another embodiment of the invention which is installed into a rocker arm of a wiper shaft. A lever 40 with T-shaped projection has a bore 42 in its longitudinal part 41 in which wiper shaft 43 is riveted. A yoke 45 is placed over crosspiece 44 of the lever 40. Said yoke 45 is provided with two oblong holes 46 in which two bolts 47 are guided which are fixed on the crosspiece 44. Thereby the bolts 47 with their heads 48 extend beyond the width of the oblong holes, so that the yoke 45 is undetachably held on the lever 40. The yoke 45 carries a pivot 49 on which a connecting rod can be articulated. An oblong hole 50 in the crosspiece 44 serves only to receive rivet head 51 of pivot pin 49 which projects on one side of the yoke 45.

Because the oblong holes 46 are inclined to the longitudinal direction of the yoke 45, the yoke and the crosspiece 44 are displaced transversally with respect to one another when they move relative to one another. In order to provide that the yoke 45 thereby rests upon a surface of the same size on the crosspiece 44, the latter is broader than the yoke 45.

A plate 52 from which a holder 53 is cut out and bent is held by the bolts 47 on the crosspiece 44. A spring support 54 is put in one opening each on the holder 53 and a leg 55 of the yoke 45 and guides a pressure spring 56 which supports on the leg 55 and via a locking member 57 formed on the spring support 54 on the holder 53. Eye 58 which is firmly connected with the spring support 54 serves for the suspension of pull spring 59 which furthermore acts upon leg 60 of the yoke 45.

During normal wiper operation the crosspiece 44 and the yoke 45 under the force of the springs 56 and 59 occupy the relative positions to one another which is shown in Figs. 3 and 4, in which the bolts 47 touch left end 61 of the oblong holes. The springs 56 and 59 are dimensioned in such a way that the connection of all parts can be regarded as rigid in this case.

If, however, the wiper blade is blocked near to one of its reversing points-the angular range of this embodiment is about 30"When the yoke 45 can be displaced by the connecting rod in the longitudinal and transverse directions to the crosspiece 44, so that the motor crank can glide over the point on its orbit which corresponds to the reversing point of the wiper blade and the motor can continue to run. The wiping angle remains diminished until the obstacle on the windscreen is removed.

The embodiments show that by such a coupling in a windscreen wiper installation the motor thereof is effectively protected against damage resulting from wiper blade blocking and the windscreen wiper installation is fully operable, with the effective wiping angle reduced, when a wiper blade is blocked.

The coupling described with reference to Figs. 1 and 2 especially distinguishes itself in that it can be used independently of the direction of rotation of the motor. During normal operation the coupling described with reference to Figs. 3 and 4 has only to take up the wiping resistance of one wiper and therefore can easily be rigidly designed.

The present invention provides a coupling for a windscreen wiper installation by means of which the wiper motor can continue to rotate, when the wiper blades are blocked, and in which the motor comes to a standstill in the parking position, when it is switched off. Blocking of a wiper blade near to at least one reversing point does not result in a standstill of the motor.

Claims

1. Windscreen wiper driving apparatus for motor vehicles, comprising a drive motor; a transmission mechanism for transforming the motor motion into wiper blade motion, and, in order to protect the motor if movement of the wiper blade becomes blocked, power transmitting coupling in the transmission mechanism, said coupling automatically taking up at least part of the motor motion dependent on the resistance to wiper blade motion.

2. Apparatus as claimed in claim 1, the coupling comprising several first elements which are movable relative to one another by the motor out of an initial position against the force of at least one spring element, which first elements are returned to the initial position by the spring element or elements, when the increased wiping resistance has ceased.

3. Apparatus as claimed in claim 2, wherein the first elements are provided with stops and when the wiper blade is not blocked the first elements are effectively secured together by the spring element or elements, each spring element comprising a spring supported or suspended between two first elements.

4. Apparatus as claimed in claim 3, wherein the coupling is located on the motor crank the length of which is shortened thereby when the wiper blade is blocked.

5. Apparatus as claimed in claim 4, wherein the motor crank has an inner lever firmly connected to a driven shaft of the motor and an outer lever movable relative to said inner lever and carrying at least one bolt for articulating at least one push rod, wherein the two levers are guided in one another and wherein in the initial position the distance between a recess for the driven shaft of the motor and the articulation bolt is a maximum.

6. Apparatus as claimed in claim 3 wherein the coupling is located on a push rod leading to a wiper shaft.

7. Apparatus as claimed in claim 6, wherein the push rod consists of two main rods and at least one'connecting member articulated on the two main rods, and wherein in each articulated joint the parts connected there are effectively secured to one another in the initial position by an initially tensioned spring.

8. Apparatus as claimed in claim 7, in combination with a second coupling located on a respective push rod, wherein upon release of the second coupling the length of the associated push rod in comparison to the release of the first coupling is variable in reverse sense and wherein one coupling may be released by compression and the other by tension between the two main rods.

9. A combination as claimed in claim 8, wherein at least one push rod consists of two main rods and three connecting members of which two are articulated on the main rods and the third is jointedly connected with the two others, wherein the four moving joints represents the corners of a square, wherein the possibility of the parts rotating from an initial position into a direction reversing from moving joint to moving joint is prevented by stops and wherein in each moving joint a spring element effectively secures the parts together in the initial position when the wiper blades are not blocked.

10. Apparatus as claimed in claim 3 wherein the coupling is installed in a rocker arm of a wiper shaft.

11. Apparatus as claimed in claim 10, wherein the wiper shaft rocker arm has a Tpiece and a yoke, which parts are connected via pins guided in oblong holes, wherein the yoke carries means to articulate a push rod and wherein the T-piece and the yoke are effectively secured in the initial position relative to one another by at least one spring element and stopping of the pins at one end of the oblong holes.

12. Apparatus as claimed in claim 11, wherein the oblong holes are inclined towards the yoke, so that upon displacement of the Tpiece and the yoke relative to one another the distance between the wiper shaft and the pivotal point of the push rod varies.

13. Apparatus as claimed in any one of claims 10 to 12, wherein the first elements are coupled by two spring elements each which is initially tensioned in reversed sense to the other.

14. A coupling for insertion in a power transmission path between a windscreen wiper drive motor and a wiper blade substantially as herein described with reference to Figs. 1 ånd:2 or Figs. 3 and 4 of the accompånying drawings.

15. windscreen wiper installation including an appåratus òr combination or a coupling as claimed-in-;any one of the preceding claims.