GB2140289A - Crank mechanism - Google Patents

Abstract

A crank mechanism for moving the blades of a windscreen wiping mechanism to a parking position displaced with respect to its normal stop position has a crank which is formed of two parts (1, 2) which are interconnected by a hinge (C). One coupling end (1b) is flat, while the other is fork- shaped (2a, 2b) to receive and guide the flat end. The flat end has two radial angularly offset shoulders (4, 5), abutting with corresponding radial shoulders (6, 7) in the fork bottom. Because of the shoulders, during the normal operation of the windscreen wiping mechanism, the two crank parts assume an angled configuration, while, when the wiping mechanism is operated to move the blades to the parking position, by reverse rotation of the driving electric motor, these parts are arranged in aligned relationship and the blades reach the parking position by an additional stroke. <IMAGE>

Description

SPECIFICATION Crank mechanism suitable for windscreen wipers This invention relates to a crank mechanism for moving the blades of a windscreen wiper and the like to a parking position which is displaced with respect to the normal position of end of stroke or stop, and wherein the parking position is attained by an additional stroke of the blades as caused by the reversal of the direction of rotation of the electric motor by the extension of the crank which on one side is keyed to the outlet shaft of the geared motor and on the other side is rotatably restrained to the connecting rod pin.

The invention also relates to the windscreen wiper and the like incorporating the crank mechanism, as well as the electric control circuit for the windscreen wiper enabling inter alia to provide the reversal of rotation to move the blades to parking position.

Known are windscreen wiper crank mechanisms in which the additional stroke of the blades to move from stop position to parking position, which is normally a concealed position, is provided by an extension of the crank as caused by reversal of the direction of rotation of the motor.

According to a known crank mechanism, the crank is formed of two superposed parts, which are interconnected by means of a pin carried by one of said parts engaging in a preset profile on the other part, so that in said profile said pin takes two limit positions depending on whether the windscreen wiper is controlled for normal operation or for causing the additional stroke of the blades. Additionally, the pin cooperates with guide means to be moved back to position of normal operation at the end of the additional stroke of the blades of the windscreen wiper. Of course, such a solution involves some friction between the connected parts and accordingly possibility of jamming thereof. Moreover, such a solution is constructively complex and costly.

According to another solution the two crank parts are connected by means of a cam and with the aid of guide springs.

Also this embodiment is somewhat complex and the operation thereof is of poor or low reliability.

It is an object of the present invention to provide a crank mechanism of the above type, in which the crank overcomes the above mentioned drawbacks and, particularly, which is of simple and inexpensive implementation, of minimum floor space, reliable in operation and interchangeable with standard cranks.

According to the invention the above objects are achieved by a crank mechanism, in which the crank is formed of two coplanar parts which are interconnected by a hinge, and in which the coupling end of each part has two radial angularly offset shoulders cooperating with corresponding radial shoulders of the other end, so that during normal operation of the windscreen wiper the two crank parts assume owing to abutment of two corresponding shoulders a first angular position, at which the distance between the axis of the geared motor shaft and the axis of the connecting rod pin is minimum while, when the windscreen wiper is operated to move the blades to parking position by a reverse rotation of the electric motor, said crank parts owing to abutment of other two corresponding shoulders assume a second angular position, at which the distance between the axis of the rotational shaft of the geared motor and the axis of the connecting rod pin is larger than the distance between said axis when the two crank parts assume the first angular position.

According to an advantageous embodiment, the two crank parts at the second angular position are aligned and the distance between the axis of the geared motor shaft and the axis of the connecting rod pin is maximum.

Additionally, in order to provide a good coupling function, one of the hinged ends is flat, while the other is in the shape of a fork to receive and guide the flat end.

The control circuit for blade parking operation is characterized by comprising electromechanical and/or electronic means which, upon operation of suitable manual control under operating condition, provide for: (a) controlling the rotation of the motor in the same direction of its rotation in normal operation of the windscreen wiper until the crank, as drawn by the geared motor shaft, from the position of end of stroke, has rotated through about 180 , during which rotation it maintains the first angled configuration (Fig.

2), in which the distance between the extreme axes of rotation of the two parts thereof is minimum, and the blades travel through the going or forward stroke to reach the extreme position corresponding to that attained in normal operation of the windscreen wiper; and then (b) controlling the reverse rotation of the motor until the crank through a reverse rotation of about 1 80' moves back to rest (or start) position, during which rotation said crank assumes the second configuration (Fig.

6), in which the distance between said axes of rotation is larger than the minimum distance, and the blades travel through return stroke to reach the parking position by an additional stroke.

Further details and advantages of the present invention will become apparent from the description of a preferred embodiment of the crank mechanism shown with reference to the accompanying drawings, in which: Figure 1 is a schematic view showing the windscreen wiper crank mechanism incorporating a crank according to the invention, under normal operating conditions; Figure 2 is a plan view of the crank of Fig.

1 shown under said normal operating conditions; Figure 3 is a sectional view of the crank of Fig. 2 taken along line Ill-Ill; Figure 4 is a plan view of the two separated parts of a crank according to the invention, with the pivoting pin; Figure 5 is a schematic view of the crank mechanism of Fig. 1 during "parking" control of the blades; Figure 6 is a plan view of the crank of Fig.

5 shown during said "parking" control; Figure 7 is a view showing the crank of Fig.

2 provided with retaining means for the taken position; Figure 8 is a sectional view of the crank of Fig. 7 taken along line Vlil-Vlli; Figure 9 is a view showing the crank of Fig.

6 provided with retaining means for the taken position; Figure 10 is a plan view showing a small plate forming part of the retaining means; and Fig. 11 is the electric diagram for a control circuit of a windscreen wiper comprising a crank according to the invention.

Referring to the crank mechanism of Fig. 1, reference letter A denotes the outlet shaft of the geared motor (not shown) and reference letter M the crank according to the invention, controlling the blade S, through the connecting rod Bz, the rocking lever C, oscillating about pin P1, and the wiping arm T1 and blade S2 through the hinged connecting rods B, B2, the rocking levers C2, oscillating about pin P2, and the wiping arm T2. By a there is shown the wiping angle travelled by each blade during the normal operation of the windscreen wiper. The blades Si, S2 are shown at normal position of end of stroke or stop position.

According to the invention, the crank M is formed of two coplanar parts 1 and 2, which are interconnected by a hinge C and connected by the other two ends to shaft A and connecting rod B,, respectively.

As better shown in Figs. 2, 3 and 4, part 1 comprises a small plate carrying a pin B for articulated connection with connecting rod B, and a hole 1 'a to provide the hinge.

Part 2 is also a small plate and on the hinge side is in the shape of a fork 2a,. 2b to receive and guide the flat end 1 b of small plate 1, while having at the opposite end a conical hole 2cfor receiving and clamping the end of said shaft A. Both sides of the fork are provided with holes 2d.

The hinge is provided by means of a pin 3 passing through the holes 2d and 1 a of the two ends of coupled small plates. On one side said pin has a head 3a and on the other side 3b is riveted to hold parts 1 and 2 by an articulated connection.

Pin 3 (see Fig. 4) comprises a central cylindrical portion 3 c cooperating with hole 1 a of small plate 1, and two faceted or prismatic side portions 3dand 3e, which are differently oriented and the function of which will be discussed in the following.

According to an important aspect of the invention, the coupling end for small plate 1 has two angularly offset radial shoulders 4, 5 cooperating with corresponding radial shoulders 6, 7 on the coupling end of the other small plate 2, so that the two hinged parts 1 and 2 may assume two angular limit positions by abutment of shoulders 4, 6 or 5, 7, respectively.

For the sake of simple construction, the shoulders 4, 5 of small plate 1 will lie on a single plane through the axis of pin 3, while the shoulders 6, 7 of small plate 2 are provided at the two ends of bottom of fork 2a, 2b, and lie on two converging planes also through the axis of pin 3.

Thus, the contact between corresponding shoulders occurs on planar surfaces.

The fork bottom has an undercut 8 of concave shape to allow the rotation of end of small plate 1 terminating with a circular surface 9. The two angular limit positions taken by crank parts 1 and 2 during operation are shown in Figs. 1 and 2 and Figs. 5 and 6, respectively. The angled arrangement of parts 1 and 2 shown in Fig. 2 is that taken by said parts during normal operation of the windscreen wiper, that is when the outlet shaft A of the geared motor and hence the crank M rotate in counterclockwise direction, as shown by arrow F, in Fig. 1.

Thus, during counterclockwise rotation of shaft A, the crank pin B reacts against such a rotation causing the parts 1 and 2 to rotate about the hinge until the abutment surfaces 4 and 6 come in contact with each other.

Such surfaces 4 and 6 remain in contact with each other throughout the windscreen wiper operation time, as well as rest time during which said blades S, and S2 are held at the position of end of stroke or stop position shown in Fig. 1.

Under said operating conditions, the distance G1 (see Fig. 2) between the axis of the connecting rod pin B and the axis of shaft A (or hole 2c) is minimum.

The aligned arrangement of the crank parts 1 and 2, shown in Fig. 6, is that taken by said parts during windscreen wiper parking operation, that is during the operation to move said blades S1 and S2 to a position which is displaced beyond that of end of stroke shown in Fig. 1.

Such an operation is provided by reversing the directions of rotation of the electric motor through an electric control circuit for the windscreen wiper, such as that shown in Fig. 11.

In Fig. 5 reference F2 shows the reversed (clockwise) direction of rotation of shaft A, for moving the blades to parking position follow ing an additional rotation through an angle P beyond the normal position of end of stroke by phantom.

However, it should be pointed out that said blades S1 and S2 reach the parking position after a to and fro travel from said position of end of stroke. Moreover, according to a further aspect of the invention shown in Fig. 11, the going travel of the blades still occurs by a counterclockwise rotation of crank (see Fig. 1) and reversed rotation is controlled only at the end of such a going stroke. In any case, under conditions of clockwise rotation of the crank, the distance G2 between the axis of connecting rod pin B and axis of shaft A (or hole 2c) is maximum. Of course, such a condition of maximum distance is fulfilled by selection of the position of the radial shoulders 5 and 7 abutting just when the two crank parts 1 and 2 are in alignment.

However, it is evident that such an abutment may occur under a condition of not alignment of such parts, in which case said distance is lower than G2, but still larger than G,. When the windscreen wiper is at rest position and blades S, and S2 are at the position of end of stroke shown in Fig. 1, or at parking position shown in Fig. 5, it may be convenient to provide the cranks with retaining means capable of holding by some pressure said parts 1 and 2 at the angular arrangement taken at said positions and which is shown in Fig. 2 and Fig. 6, respectively.

This to avoid that upon lifting of the blades either for tampering or maintenance or because of other circumstances, such as wind, the crank parts may vary the angular arrangement thereof, and hence not retaining on the glass the attained end of stroke position or parking position.

According to the invention, such means comprise two small retaining resilient plates 10 (see Fig. 10) which are respectively clamped on the two outer sides of fork 2a, 2b of small plate 2 by means of riveting 3b of pin 3.

Each resilient small plate is provided with square hole 11 engaging, as shown in Fig. 8, with a faceted part 3dand 3cof said pin 3.

As above mentioned, said parts are differently oriented, so that said two small plates define an angle 8/2 therebetween, which is a half of angle 8 to be travelled through by the crank parts 1 and 2 when moving from the first angular position (see Fig. 7) to the second angular position (see Fig. 9).

At the free end, each resilient small plate carries a projection 12 intended for pressure insertion in a corresponding notch or hole 13 in the crank part 1, so that the two holes 13 are offset to each other by the same angle 8.

The projections 12 are in the shape of a hemisphere and the inlet to the holes 13 is countersunk.

In Figs. 7 and 8 it is the lower small plate 10 which by its own projection engages in a hole of part 1, while in Fig. 9 it is the upper small plate 10 which by its own projection engages in the other hole.

Of course, the pressure by which the projections 12 are held in holes 13 is such as not to oppose the control strain aimed to vary the arrangement of the crank parts during the operation of the windscreen wiper.

As above mentioned, during blade parking operation, the reversal of rotation of crank M occurs only at the end of the going stroke of the blades, that is after the latter have travelled through the angle a from the rest or normal stop position shown in Fig. 1.

Thus, during the going stroke of the blades, which is caused by a rotation through about 1 80' of the crank from rest position, the latter still rotates in counterclockwise direction (see arrow F,) to retain the angled configuration, which is the configuration causing normal oscillations of the blades of angle a. On the other hand, after about one half revolution, the crank reverses its rotation to return by a clockwise rotation (see arrow F2) of the same angle to its starting position. But a reversed rotation causes the extension or elongation of the crank, since the parts 1 and 2 thereof become aligned, so that when the crank is at the position shown in Fig. 5, the blades in addition to angle a will have also travelled through the additional angle ss, which enables the blades to move to parking position.

In other words, during parking operation the crank will rotate through about 1 80' in counterclockwise direction, retaining the configuration of Fig. 2, and then will rotate through the same angle, but in reversed direction, taking the configuration of Fig. 6.

By such an expedient and during said parking operation, the blades in going stroke do not exceed the extreme positions P,-X, P2-Y as reached in normal operation of the windscreen wiper.

Fig. 11 shows a control circuit for parking operation for providing said operating conditions, in combination with a known type or circuit for continuous and intermittent operation of the windscreen wiper.

This known type of circuit comprises: -a manual four way switch 15 with a movable element 1 5a connected to the positive pole (+) of the battery and four fixed contacts 1 sub, 1 sic, 1 5d and 1 sue by which the movable element cooperates for respectively providing the continuous operation of the windscreen wiper at a high speed (position II) and at a low speed (position I), the intermittent operation (position i) and the zero setting of the wiper blades (position O); -an electric D.C. motor 16 of the type with excitation by permanent magnets, comprising three brushes 1 6a, 1 6b and 1 6c, which drags along a cam 17, mounted on the shaft A of the geared motor, for the control of the end of stroke switch 18; and -an electric circuit 19 defined by a dashed line for the intermittent operation of the windscreen wiper and which comprises an electromagnetic switch 20 including a coil 21 and a two way switch 22, and in which the coil excitation is controlled by a transistor 23, in turn controlled by a RC type timing circuit indicated at 24.

According to the invention, the control circuit for parking operation comprises: -a two way control pushbutton 24' actuated by the operator for parking operation.

This pushbutton 24' is of unstable work position type, that is with automatic return to rest position upon release of control action; -an initial supply circuit for motor 16, which controls the rotation of the latter in the same direction of rotation during the normal operation of the windscreen wiper until said cam 17, or crank M, has rotated through about 1 80' from the end of stroke position shown in the figure. Said supply circuit is initially closed through the pair of contacts 24b of pushbutton 24' and end of stroke switch 18 at position of end of stroke (1 8a on 1 8b) and is then maintained at work position (1 8a on 1 8c) through said switch 18.In said circuit, brush 1 6a is the input to the motor and brush 1 6c is the output from the motor; -a sensor of the extreme position reached by the blades in the going stroke, which comprises a switch 25 under the control of the same cam 17 operating the switch 1 8.

This switch 25 is brought to closed position (movable contact 25a on fixed contact 25b) when the cam has rotated through about 1 80' from the position of end of stroke. Thus, closing of switch 25 coincides with the moment at which in the going stroke the blades arrive at adjacent the normal extreme position.

-a changeover circuit 26 for the polarity of the motor supply voltage, also defined by a dashed line, for connection upon closure of the position switch 25 of a reverse supply circuit of the motor, so that the latter reverses its direction of rotation. Such a circuit 26 comprises two remote controlled switches 27 and 28, each of which comprising a coil 29 and 30 and a two way switch 31 and 32. The coils are simultaneously excited under control of a transistor 33, in turn controlled by a timing circuit 34 also of RC type. In said reverse supply circuit, brush 1 6c is the input to the motor and brush 1 6a is the output from the motor.Since switch 25 is closed after rotation of cam 17 through about 1 80', this means that supply and hence reverse rotation of the motor will start after an initial rotation of crank M in the direction of arrow F, through about half a revolution from the rest position shown in Fig. 1; and -a parking sensor comprising a two way switch 35 which cuts off the reverse supply circuit of the motor, causing the latter to stop, as soon as in return stroke the blades arrive at parking position. To this end, said switch 35 may be operated by any member of the control drive of the blades when such a member arrives at the position corresponding to the blade parking position; for example, such a member may be the rocking lever C1 (see Figs. 1 and 5).

For a further explanation of the control circuit for parking operation, it should be pointed out that the initial supply circuit for motor 16 comprises, in addition to the pairs of contacts 24b of pushbutton 24' and switch 18 at the two positions, also the following contacts, all of which at rest position: movable contact 35a of switch 35, movable contact 22a of switch 22, and the two movable contacts 31a and 32a of switches 31 and 32; while the reverse supply circuit for the motor comprises the movable contact 35a of switch 35 at rest position, and the two movable contacts 31a and 32a of switches 31 and 32 at work position (31a on 31c and 32a on 32c).

Now the operation of the circuit of Fig. 11 will be briefly described, in which the various parts are shown at rest position.

Continuous operation By moving the element 15a of manual switch 15 to position I or Il, the motor 16 will rotate at low or high speed, respectively, driving the blades S1 and S2 at corresponding speed.

The low speed motor supply circuit is as follows: + battery, element 15a on 15c, contact 31a on 31b, brush 16a, motor winding, brush 16c, contact 32a on 32b and ground; while at high speed the supply circuit is as follows: + battery, element 15a on contact 15b, brush 16b, motor winding, brush 16c, contact 32a on 32b and ground. At the end of operation, by moving the switch 15 back to rest position (position 0), the motor rotates until the movable contact 18a is moved back on the fixed contact 18b, moment at which the motor winding is shorted and the motor is braked.

Intermittenf operation The contact 15a is moved to position i. The motor is supplied through the following circuit: + battery, element 15a on 15d, contact 22a on 22b, contact 31a on 31b, brush 16a, motor winding, brush 16c, contact 32a on 32b, and ground.

With the motor start, contact 18a moves on 18c, and the next supply circuit is: + battery, element 15a on 15b, contact 35a on 35b, contact 18a on 18c, contact 22a on 22c, contact 31a on 31b, brush 1boa, motor winding, brush 16c, contact 32a on 32b, and ground.

As shown, the circuit comprises the movable contact 22a on fixed contact 22c. This changeover of contact 22a is due to energization of remote controlled switch 20 caused by conduction of transistor 23 owing to charge of capacitor 36 of the timing circuit 24.

As soon as the blades terminate a complete stroke (going and back stroke), the contact 18a moves back on 18b and the motor stops because of its winding being shorted.

The stop or dwell time, during which the motor is at a standstill, is determined by the discharge time of capacitor 36 on circuit 24.

Discharge commences as soon as movable contact 18a moves back on contact 18b.

Throughout the discharge time, the transistor 23 is conductive and accordingly the remote controlled switch 20 is energized for the same time, so that the movable contact 22a remains positioned on the fixed contact 22c. At the end of discharge, the transistor 23 is shut off, the remote controlled switch 20 is deenergized and the contact 22a moves back to the rest position shown in the figure. Now, the cycle is restarted and so on until the switch 15 is moved back to rest position.

When this occurs, the motor continues to rotate until the contact 18b is on 18b, whereupon its winding is shorted and the motor is braked.

Parking operation With the movable element 15a at rest position (position 0) and the movable contact 18a of the end of stroke switch 18 on the fixed contact 18b (blades S, and S2 at stop position of Fig. 1), by operating the pushbutton 24' the pair of contacts 24b is closed and the following circuit is formed: + battery, movable element 15a, fixed contact 15e, contact 35a of switch 35 on 35b, pair of contacts 24b, contact 18a on 18b, timing circuit 24 and ground. In this step, with the charge of capacitor 36, the transistor 23 becomes conductive, and hence the remote controlled switch 20 is energized, causing the displacement of the movable contact 22a on the fixed contact 22c.Thus, the following supply circuit for motor 16 is formed: + battery, element 15a, contact 15e, contact 35a on 35b, pair of contacts 24b, movable contact 18a on 18b, contact 22a on 22c, contact 31a of switch 31 on 31b, brush 16a, motor winding, brush 16c, contact 32a of switch 32 on 32b and ground. Thus, the motor is started and at the same time the cam 17 is dragged, so that the movable contact 18a changeovers on the fixed contact 18c.

Thus, during changeover of 18a, the remote controlled switch 20 remains energized since the transistor 23 is conductive owing to discharge of capacitor 36 on RC circuit 24.

Following said changeover, the contact 18a receives the positive (+) pole of the battery through the contact 18c, so that the motor supply circuit is still the same as that above described, with the only difference that the contacts of pushbutton 24' are excluded, which therefore can move back to rest position.

At this first step of supply, the motor rotates in the same direction as it rotates during normal operation of the windscreen wiper, so as to cause the counterclock-wise rotation of crank M. This, the positive (+) pole of the supply voltage is applied to the brush 16a, while the brush 1 6c is gounded, which is the connection just occurring during normal operation of the windscreen wiper.

The above described supply circuit is an initial supply circuit for the motor, since it remains connected until the cam 17 has effected an initial rotation of about 1 80', during which the crank rotates through about a half revolution according to arrow F, and the blades S, and S2 travel through a going stroke until reaching the extreme positions P,-X and P2-Y after rotation through angle x.

After rotation through about 180 , the cam 17 changes over the movable contact 25a on the fixed contact 25b to close the switch 25 and accordingly to close the circuit therein connected. Thus, as the switch 25 is closed, the following circuit is formed: + battery, element 15a, contact 15e, contact 35a on 35b, contact 25a on 25b, parallel coils 29 and 30, transistor 33 and ground.

Therefore, the remote controlled switches 27 and 28 are simultaneously energized, which cause the displacement of the movable contacts 31a and 32a on the fixed contacts 31c and 32c, respectively. The energization of 27 and 28 can take place since the transistor 33 is in conduction state owing to the discharge of capacitor 37 on the RC circuit 34, and the charge of which occurred at the time of operation of pushbutton 24' through the circuit: + battery, element 15, contacts 15e, contact 35a on 35b, pair of contacts 24b, timing circuit 34 and ground.As a result, from the time said switch 25 is closed, the motor is reversely supplied through the following circuit: + battery, element 15a, contact 15e, contact 35a on 35b, contact 32a on 32c, brush 16c, motor winding, brush 16a, contact 31a on 31 c and ground. Thus, at this step it will be seen that the positive (+) pole of the supply voltage is applied to brush 16c, while now it is brush 16a to be grounded.

Thus, by reversal of supply voltage the motor rotates in reverse direction, that is in the contrary direction to the direction of rotation during the first supply step.

As a result, from the position attained after about a half revolution and rotating in counterclockwise direction, the crank M will move back to rest position by a reverse rotation, that is according to arrow F2. But, as soon as such a reverse rotation commences, the crank elongates (see Fig. 6), so that upon return to said rest position (see Fig. 5), the blades S, and S2 will have reached the parking position after a return stroke corresponding to the angle a + P. (see Fig. 5).

Now, the motor stops because of interruption of its reverse final supply circuit by means of opening of switch 35.

Such an opening can be controlled by any member of the blade control drive. In Figs. 1 and 5, it was assumed that such a member is the rocking lever C, which acts upon switch 35 at the time it takes the position corresponding to the blade parking position.

By the opening of switch 35, the remote controlled switches 27 and 28 are de-energized, while the remote controlled switch 20 remains energized until the end of discharge of capacitor 36 which maintains the transistor 23 in conduction state. Thus, the following braking circuit for blocking the motor is formed: ground, pair of contacts 24a, contact 18a on 18b, contact 22a on 22c, contact 31a on 31b, brush 16a, motor winding, brush 16c, contact 32a on 32b, and ground.

It will be seen from the foregoing that the circuit formed of the two remote controlled switches 27, 28 and timing circuit 34 makes up a changeover circuit for the supply polarity because of shutting off the normal supply circuit for the motor and connecting the reverse supply circuit. Of course, such a changeover circuit may be differently implemented from that shown, in any case its function being that of a changeover during parking operation, for said two supply circuits of the motor so that the crank M, while the first circuit or normal circuit is connected, rotates through about 1 80' maintaining the "short" configuration shown in Fig. 2 while, when the second circuit or reverse supply circuit is connected, it rotates through the same angle but in reverse direction, taking the "long" configuration shown in Fig. 6. Obviously, also the two supply circuits for the motor may vary in connection with the changeover circuit and various types of control circuit for continuous and intermittent operation of the windscreen wiper, without departing for this from the scope of the invention.

Claims (18)

1. A crank mechanism for moving the blades of a windscreen wiper and the like to a dwell or parking position which is displaced beyond the normal end of stroke or stop position and in which the parking position is attained by an additional stroke of the blades, caused by reversal of the direction of rotation of the electric motor by the elongation or extension of the crank which, on one side, is keyed to the outlet shaft of the geared motor, and on the other side is rotatably restrained to the connecting rod pin, characterized in that said crank comprises two coplanar parts interconnected by a hinge and that coupling end of each part has two radial angularly offset shoulders, cooperating with corresponding radial shoulders of the other end, so that the two crank parts, during normal operation of the windscreen wiper, owing to the abutment of two corresponding shoulders, assume a first angular position, at which the distance (G1) between the axis of the rotational shaft of the geared motor and the axis of the connecting rod pin is minimum while, when the windscreen wiper is operated to move the blades to said parking position, by reverse rotation of the electric motor, said parts owing to the abutment of the other two corresponding shoulders assume an angular position, at which the distance (G2) between the axis of the rotational shaft of the geared motor and the axis of the connecting rod pin is larger than the distance (G1) between said axes when the two crank parts assume the first angular positions.

2. A crank mechanism as claimed in Claim 1, characterized in that the two crank parts at the second angular position are aligned and the distance between the axis of the geared motor shaft and the axis of the connecting rod pin is maximum.

3. A crank mechanism as claimed in Claims 1 and 2, characterized in that one coupling end of the crank is flat, while the other end is in the shape of a fork to receive and guide the flat end.

4. A crank mechanism as claimed in Claim 3, characterized in that the two shoulders of the fork end are provided in the fork bottom, which also has a central undercut for rotation of the flat end of the other crank part.

5. A crank mechanism as claimed in any of the preceding claims, characterized in that the shoulders on the coupling end of the crank parts are provided according to planes through the axis of the hinge pin, so that contact between corresponding shoulders occurs on planar surfaces.

6. A crank mechanism as claimed in Claims 3, 4 and 5, characterized in that the shoulders provided on the flat end of the crank part are aligned on a single plane through the axis of the hinge pin.

7. A crank mechanism as claimed in any of the preceding claims, characterized by having retaining means at the hinge capable of sufficiently stabilizing the two crank parts at the first and second angular positions.

8. A crank mechanism as claimed in Claim 7, characterized in that said retaining means comprise two small resilient plates provided with square hole and clamped on the outer sides of the fork end by means of hinge pin riveting, and that said pin engages with the hole of the small plates at its faceted and differently oriented (offset) parts, to arrange said small plates according to an angle (8/2) which is one half of the angle (8) travelled by the two crank parts when moving from the first to the second angular position, and that said small plates carry at the free end convex projections intended to be pressure inserted in corresponding notches on the flat end of the crank and angularly displaced from one another by an angle (8) which is the same as said angle travelled through by the small plates.

9. A crank mechanism as claimed in Claim 8, characterized in that said notches are provided by means of two countersunk through holes at the inlet to receive the projections of the small plates which are of hemispherical shape.

10. A windscreen wiper and the like incorporating a crank mechanism comprising a crank according to any of the preceding claims.

11. A control circuit for parking operation of blades in a windscreen wiper comprising a crank as claimed in the preceding claims, characterized by electromechanical and/or electronic means which, upon suitable manual control under operating conditions, control: (a) the rotation of the motor in the same rotation as it rotates in normal operation of the windscreen wiper until the crank (M), as dragged by the shaft (A) of the geared motor from the position of end of stroke (Fig. 1), has rotated (arrow F,) through about 1 80', during which it maintains an angled configuration (Fig. 2), at which the distance (G1) between the extreme axes of rotation (A, B) is minimum, and the blades effect the going stroke until reaching or approaching the extreme position corresponding to that attained in the normal operation of the windscreen wiper; and then (b) the reverse rotation of the motor until the crank (M), through a reverse rotation (arrow F2) of about 1 80', has moved back to rest (or start) position, during which rotation said crank assumes a second configuration (Fig. 6), at which the distance (G2) between said axes of rotation (A, B) is larger than the minimum distance, and the blades effect the return stroke until reaching the parking position by an additional stroke (P).

12. A control circuit as claimed in Claim 11, characterized in that said electromechanical and/or electronic means for parking operation comprise, in combination with a continuous and intermittent operating circuit of the windscreen wiper: -a control pushbutton (24) for the parking operating operated by the operator; -a normal (or initial) supply circuit for the motor (16) of the windscreen wiper which, upon operation of said pushbutton under operating conditions, controls the rotation of the motor in the same direction as it rotates during normal operation until the crank (M) has rotated from rest position through about 180 ;; -a reverse (or final) supply circuit for the motor of the windscreen wiper which replaces the normal supply circuit upon operation of a changeover circuit activated by a sensor of the normal extreme position of the blades in the going stroke, which reverse supply circuit controls the reverse rotation of the motor until the crank (M), from the position attained after normal rotation of about 1 80', has effected a return rotation through the same angle to move back to rest (or initial start) position;; -a changeover circuit (26) cutting off the normal supply circuit and connecting the reverse supply circuit for the motor as soon as a sensor under the control of a member associated with the movement of the blades, signals that the latter in going stroke have arrived at or adjacent the extreme position they assume in the normal operation of the windscreen wiper; and -a parking sensor capable of cutting off the reverse supply for the motor as soon as in the return stroke said blades reach the parking position by an angular amplitude (a + ,B) corresponding to a reverse rotation of about 1 80' to be travelled by the crank to move back to rest position.

13. A control circuit as claimed in Claim 12, characterized in that said control pushbutton (24) is of the type of unstable work position.

14. A control circuit as claimed in Claim 12, characterized in that said changeover circuit (26) comprises two remote controlled switches (27 and 28) which are simulatenously energized under control of a transistor (33) in turn controlled by a RC circuit

15. A control circuit as claimed in Claim 12, characterized in that said parking sensor comprises a switch (35) which is operated by a member of the control drive for the blades of the windscreen wiper when said member assumes the position corresponding to the parking position of the blades (S" S2).

16. A control circuit as claimed in Claim 12, characterized in that the sensor for the normal extreme position of the blades in the going stroke comprises a switch (25) controlled by a cam (17) of the end of stroke switch (18) after a rotation of about 180 from its rest position.

17. A control circuit as claimed in Claims 12-16, characterized in that the normal (or initial) supply circuit for the motor comprises in series the manual switch (15) at rest position (0), the contact (35a) of the parking switch (35) at rest position, a pair of contacts of the control pushbutton (24) at work position, the contact (18a) of the end of stroke switch (18), a contact (22a) of a remote controlled switch (20) in the intermittent circuit (1 9) at work position, and the contacts (31 a and 32a) of the two remote controlled switches (27, 28) of the changeover circuit (26) at rest position.

18. A control circuit as claimed in Claims 12-16, characterized in that the reverse (or final) supply circuit for the motor comprises in series the normal switch (15) at rest position (0), the contact (35a) of the parking switch (35) at rest position, and the contacts (31a and 32a) of the two remote controlled switches (27 and 28) of the changeover circuit (26) at work positions.