Patent GB-856338-A (GB)
Title: Improvements in or relating to windscreen wiping units
IPC: B60S1/18
Filed: 1959-09-30
Abstract: 856,338. Windscreen wipers. BOSCH G.m.b.H., R. Sept. 30, 1959 [Oct. 1, 1958], No. 33123/59. Class 138(1). A windscreen wiper unit has two oppositely movable wiper arms 1, 2 to each of which is hinged a wiper blade 1<SP>1</SP>, 2<SP>1</SP> which when the unit is switched off rest partly superimposed in the centre of the screen adjacent the frame so that their wiping areas overlap, the movements of the two arms in the overlapping area being so controlled that the blades do not come into contact with each other when in operation. In the wiper unit shown in Fig. 1, a push-rod 20 actuated by the stating crank 3 causes the swivel lever 4 of wiper arm 1 to swing about its axis 4<SP>1</SP> and, through the action of a connecting rod 21, an intermediary lever 5 about its axis 5<SP>1</SP>. This lever 5 is connected by way of a second connecting rod 22 with the swivel lever 6 of wiper arm 2, causing it to rotate about its axis 6<SP>1</SP>. The pivotal points of the two connecting rods 21, 22 are selected such that the first rod 21 traverses a longer path in its operating direction then the second rod 22. Starting from the rest position the wiper arm 1 initially leads the wiper arm 2, than both wipers reach their outer turning points at approximately the same time, the wiper arm 2 leaving its turning point somewhat more quickly than the arm 1. This difference in speed is achieved by the intermediate lever 5 which, in its resting position shown in Fig. 1, is adjusted so that the horizontal spacing A between the pivots of the rods 21, 22 on the lever increases at the beginning of the wiping operation and decreases again towards the end of the wiping operation. The disadvantage of this arrangement is that there is a rapid retardation and acceleration of the wiper arms in the reversing area which, in the case of curved panoramic screens, may interfere with the wiping operations in the marginal areas of the windscreens. This disadvantage is reduced in a second embodiment in which the connecting rod 22 swings, the swivel lever 6 of wiper arm 2 by way of a cross-link comprising two crossed toggle joints. The connecting rods 21, 22 are connected merely by means of an elastically compressible member which serves to protect the driving arrangement of the unit from damage in the event of a breakdown in the movement of the wiper blade due, e.g. to icing. In a third embodiment, the swivel lever for wiper arm 1 comprises a toothed segment intermeshing with the end, formed as a rack, of the push-rod 20. With this arrangement, while the movement of the wiper arm 1 is only slightly accelerated or retarded, the movement of arm 2 begins after a considerable delay, is then greatly accelerated, is subsequently rapidly retarded and, before reaching its turning point, is decelerated approximately at the same rate as arm 1. On its return, the arm 2 reaches the inoperative position much earlier than arm 1. Fig. 5 shows means, applicable to any of the above embodiments, to prevent jamming of the wiper unit in the centre area of the screen swept by the two arms, e.g. when the screen is heavily covered with snow. A connecting rod 23 is surrounded by a sleeve 13 in which a compression spring 14 is located supported at one end by a washer 26 and, at its other end, on the face of the rod 23. This rod is provided with a transverse pin 16 sliding in two slots in the sleeve 13, thus maintaining the length of the rod 23 constant under tensile stress but shortening it in the event of a sufficient pressure load. In Fig. 6 a similarly acting securing means is shown in the form of a resiliently suspended wiper arm. A spring 18 which is mounted in a hinge 17 of the wiper arm 2, is in contact by one shank with the arm 2, and is supported by the other shank against an abutment 19. The effective strength of the spring 18 is arranged to be the same as that of spring 14 of Fig. 5. The wiper blade arrangement shown in Fig. 7 is provided with rubber cushions 28 which prevent reciprocal contact between the metal parts of the wipers and simultaneously preclude the wiper arm 2 hitting against the frame R of the windscreen as it returns to its inoperative position.