WO1997018111A1

WO1997018111A1 - Windscreen wiper driving mechanism

Info

Publication number: WO1997018111A1
Application number: PCT/GB1996/002623
Authority: WO
Inventors: Rutland Sherman Boughton
Original assignee: Wynn Marine Ltd.
Priority date: 1995-11-14
Filing date: 1996-10-28
Publication date: 1997-05-22
Also published as: AU7318996A; GB9523291D0

Abstract

A wiper driving mechanism includes a yoke member (5) driven by a rotary crank which in turn drives a pair of symmetrical arms (14, 15) each of which drives a wiper blade (17). Either the two arms (14, 15) are connected in parallel and drive one wiper blade (17) in a pantograph motion or separate unconnected blades carry out an arcuate sweep over a wider area. The arrangement enables a smooth motion approximating to simple harmonic motion to be achieved, and this then enables shock loads to be reduced at the ends of travel.

Description

"Windscreen Wiper Driving Mechanism"

The present invention relates to windscreen wiper driving mechanisms .

The purpose of a windscreen wiper driving mechanism is to cause the wiper to move to and fro across the windscreen of a vessel or vehicle. Many known mechanisms are used for this purpose and generally a main disadvantage encountered is that in transferring motion from travelling in one direction to the other shock loads are applied to the mechanism and this promotes wear. Also, most mechanisms are not symmetrical and that adds further out of balance forces to compound the problem.

A particular mechanism where this problem arises is the so-called pantograph system, which operates via use of two parallel arms carrying a blade and causing that blade to remain parallel to its initial disposition as it transverses the screen. Usually in such systems the wiper arm or arms hang downwards to provide a form of pendulum movement.

The invention is to provide a mechanism which can be used both for a pantograph parallel blade arrangement or for separate twin bladed systems. Accordingly the present invention provides a wiper driving mechanism comprising:

a crank member which is arranged to be driven by a rotary motor;

a yoke member mechanically linked to and arranged to be driven by said crank member;

symmetrically located first and second lever members mechanically linked to and arranged to be driven by said yoke member; and

first and second shafts for carrying a wiper arm and each arranged to be rotatably mounted in a fixed position relative to a windscreen and driven by said lever members;

said crank member having a crank pin, and said yoke member having a slot within which said crank pin is located to travel and provide movement of said crank member,

each of said first and second lever members being rotatably attached to respective points on said yoke member so as to constrain movement of said yoke member in an arcuate locus and to be driven in a reciprocatory movement by the yoke member and each of said first and second shafts thereby being caused to reciprocate in a rotary motion which closely approximates to a simple harmonic motion.

The main advantage of this arrangement is that two shafts are driven by the yoke member and they are symmetrically located. This enables the wiper blade or blades to travel in a smooth motion which closely approximates to a simple harmonic motion and therefore reduces shock loads at the ends of travel. Moreover since the two lever members are symmetrieally located and each is providing drive, this means that either a twin bladed pendulum system running off these two lever members can be used, or a twin arm single blade pantograph arrangement can be employed with balanced forces being applied.

Moreover, use of a balanced system approximating to a simple harmonic motion has the further important advantage that maximum accelerations and hence torque demands on the motor are controlled to lower values than in traditional mechanisms allowing use of lower power {and cost) motors. There are very few parts in the mechanism and yet two arms are driven giving the advantage of sharing the arm forces and allowing, when used in that way, the wiping of two adjacent areas in pendulum style.

If the motion of a traditional mechanism with a short connecting-rod is analysed, then it shows that the motion is far from SHM and is different in the two directions. This results in the torque demand being higher in one direction than the other and of course the specification for the motor and drive train torques must allow for that. By use of the present invention, the torque is lowered and is the same in both directions. The distortion in the traditional mechanism would only be relieved by making the connecting rod very long, taking up precious bulkhead mounting area.

An embodiment of the invention will now be described in which:

Figure 1 is an exploded perspective view of the basic mechanism;

Figure 2 shows a front elevation of the mechanism in use on a pantograph system showing three positions of its operation; and Figure 3 shows a front elevation of a twin blade pendulum system.

Referring to Figure 1, a crank member 1 pivoted on a driving shaft 2 which is driven by a conventional motor (not shown) has a crank arm 3 carrying a crank pin 4. The driving shaft 2 can be directly driven by the motor or can be indirectly driven via a gearbox dependent on requirements .

This crank pin is located within a yoke member 5 from which in Figure 1 it is shown in an exploded relationship. The yoke member 5 is symmetrical and of cruciform shape and has a linear central slot 6 within which the crank pin 4 runs. Lateral arms of the yoke member each include a pivot seat 7.

Symmetrically located first and second lever members 8 and 9 respectively are each rotatably mounted in a fixed position relative to a windscreen, i.e. to rotate about in each case a fixed axis. On each of these fixed axes are located drive shafts 10 and 11, which provide the drive motion for the windscreen arms, and pins 12 and 13 which act as pivots located within the pivot seats 7.

Thus, the pins 12 and 13 move in an arcuate locus about the axis in each case on which the drive shaft 10 and 11 are located. These pins 12 and 13 therefore constrain the yoke member 5 to also move in the same arcuate path. However, the crank pin of crank member 1 due to its rotation moves up and down the slot 6 and thereby drives the yoke member and hence the lever members in a reciprocating arcuate movement about the drive shafts 10 and 11, as shown by the arrows between A-A' and B-B' respectively. Wiper blades mounted on the shafts 10 and 11 can therefore move in a back and forth action of the kind required for a windscreen wiper blade.

It will be seen that this layout results in symmetrical drive outputs to the shafts 10 and 11 and that the reciprocating rotary movements of these shafts

10 and 11 will be closely approximating to a simple harmonic motion.

It will be noted that the lever members 8 and 9 depend upwards from the shafts 10 and 11, however they could depend downwards so as to give a more compact layout.

Figure 2 shows the drive mechanism as applied to a pantograph parallel arm system.

Parallel wiper blade arms 14 and 15 are rigidly clamped to drive shafts 10 and 11 and are pivotally connected via a cross-piece 16 holding the outer ends of these arms in a parallel configuration. The cross-piece 16 carries a blade 17 which in the central position of the mechanism is parallel to the arms 14 and 15. As can be seen in the Figure, the blade 17 remains in a parallel configuration throughout movement from a left position (left position in the Figure) to a central position and then to a right hand position and then back.

In these figures the crank member 3 is shown upwardly offset from behind the yoke member 5 so that its rotary movement is apparent. Also the position of the pin 4 within the slot 6 can be seen. The central position shows the crank pin 4 in an upper position, but it will be appreciated that when the pin is in a lower (bottom dead centre) position the wiper blade 17 will also be in the centre of its movement.

Figure 3 shows the mechanism where two separate wiper arms 18 and 19 are attached rigidly to the drive shafts 10 and 11, and each has a wiper blade 20, 21 attached rigidly to the respective arm. The arms are set in relation to the mechanism so that in the central position they are splayed out with a separation of approximately 90°, as shown. Then in operation as the yoke arm moves to the right, the blades will move in an arc to the left so that the right hand blade sweeps towards the centre and the left hand blade moves upwards in a clockwise direction, and the movement reverses as the yoke member is moved to the left so that the full screen is covered. Various angular locations of the blade arms, and blades can be adopted to give the form of coverage required.

Claims

CLAIMS:

1. A wiper driving mechanism comprising:

a crank member which is arranged to be driven by a rotary motor;

each of said of said first and second lever members being rotatably attached to respective points on said yoke member so as to constrain movement of said yoke member in an arcuate locus and to be driven in a reciprocatory movement by the yoke member and each of said first and second shafts thereby being caused to reciprocate in a rotary motion which closely approximates to a simple harmonic motion.

2. A wiper driving mechanism according to claim 1 including first and second wiper arms, said first wiper arm being fixedly attached to said first shaft and said second wiper arm being fixedly attached to said second shaft.

3. A wiper driving mechanism according to claim 2 including a motor for rotating said crank member.

4. A wiper driving mechanism according to claim 2 in which said first and second wiper arms are joined by a linking bracket which is arranged to carry a common wiper blade which is pantographically constrained to move along a path while remaining parallel to its initial disposition.

5. A wiper driving mechanism according to any of Claims 2 to 3 in which a first wiper blade is connected to said first wiper arm and a second wiper blade is connected to said second wiper arm.

6. A wiper driving mechanism substantially as hereinbefore described with reference to the accompanying diagrammatic drawings .