This invention relates to a wiper device equipped with a rise-up mechanism.
In general, a rise-up mechanism is a mechanism for shifting a wiper blade to a position away from its normal wiping positions when it stops so that a driver does not see the blade in front of his eyes.
FIGS. 1a to 1c show schematically a sequence of wiping operational steps. During the starting step, the blade 18 shifts from a parked position A through the position B to the position C. Thereafter, the blade 18 reciprocates between the positions B and C during its normal wiping operation. At the stopping step, the blade 18 shifts from the position B to the position C and then again from the position C through the position B to the parked position A in which it stops.
FIGS. 2 to 4 show a conventional rise-up mechanism for a wiper device in which the effective length of a connecting rod or link is changed by reverse rotation of a motor when a wiper switch is switched off.
A cover plate 3, latch spring 4, latch 5, motor arm 6 and eccentric member 7 are assembled in order onto a motor shaft 2 of a motor 1 and fixed thereto by means of a screw 10. The cover plate 3 is attached through a grommet 11 to the motor body. The eccentric member 7 is biased into the central axial hole of the motor arm 6 by means of a spring 12. In one end thereof, a stopper 8 is attached to engage the groove 7a of the eccentric member 7 and a spring 13 is attached to bias the stopper. At the other end thereof, a joining shaft 14 is provided to be joined to a connecting rod 15 is provided. A groove 6a is formed in the lower surface of the motor arm 6 near the joint shaft 14 and engages a pawl 5a of the latch 5. A pawl 7b projects from the lower surface of the eccentric member 7 and presses the inner actuating portion 5b of the latch 5 to slide the latch 5 so that the pawl 5a becomes disengaged from the groove 6a.
In operation, first, the motor 1 rotates to the right during starting. When the motor shaft 2 starts to rotate to the right, the pawl 5a of the latch 5, which is prevented from rotating by the cover plate 3, engages the groove 6a of the motor arm 6 as shown in FIG. 4, so that the motor 1 does not rotate while the motor shaft 2 and the eccentric member 7 rotate together as shown in FIG. 4b. When they rotate by 180.degree., as shown in FIG. 4c, the stopper 8 engages the groove 7a of the eccentric member 7 by the biasing force of the spring 13. At the same time, the pawl 76 of the eccentric metal 7 presses the inner actuating portion 5b of the latch 5 to slidably shift the latch 5 to the left as shown in FIG. 4c. As a result, the pawl 5a of the latch 5 leaves the groove 6a of the motor arm 6.
Assuming that the length or distance between the center of the joint shaft 14 and the center of the eccentric member 7 is R and that the length (eccentric degree) between the center of the eccentric member 7 and the rotation center thereof is r, the effective length between the centers of the motor shaft 2 and the joint shaft 14 of the motor arm 6 changes from (R+r) to (R-r) due to the eccentric effect when the eccentric member 7 rotates by 180.degree..
From the condition of FIG. 4c, the motor arm 6 rotates as shown in FIGS. 4d to 4f in response to the rotation of the motor shaft 2 together with the eccentric member 7 resulting from engaging stopper 8 with the groove 7a. The motor arm 6 further rotates and returns from the condition of FIG. 4f to the condition of FIG. 4c. While the motor arm 6 rotates as shown in FIGS. 4c to 4f, the connecting rod 15 joined to the joint shaft 14 reciprocates to swing the wiper pivot 16 around the axis 17 so that the blade 18 reciprocates in its normal wiping range between the positions B and C in FIG. 1b.
When a wiper switch (not shown) is switched off to stop the motor shaft 2, it continues to rotate until the condition of FIG. 4c where the motor shaft 2 begins to rotate in a reverse direction. After such reverse rotation of the motor shaft 2 in the condition of FIG. 4c, the groove 6a of the motor arm 6 contacts the pawl 5a of the latch 5. (It does not contact the pawl 5a in case of the right rotation thereof). As shown in FIG. 4g, the groove 7a of the eccentric member 7 pushes the stopper 8 at its tapered surface during its reverse rotation against the biasing force of the spring 13 so that the stopper 8 is disengaged therefrom. Thus, as shown in FIG. 4g, the motor arm 6 does not rotate and only the eccentric member 7 rotates so that after its 180.degree. rotation the pawl 5a engages the groove 6a as shown in FIG. 4a. Also, the length or distance between the center of the joint shaft 14 of the motor arm 6 and the motor shaft 4 changes from (R-r) to (R+r) due to the eccentric effect of the eccentric member 7 by its 180.degree. rotation. The effective length of the connecting rod 15 changes so that the blade 18 can be received in the position A of FIG. 1.
In the above-stated conventional wiper device, however, the latch 5 slides during the rise-up operational step. The rise-up operation cannot be accomplished by rotation of the members only. For this reason, the operation is not sure and stable. In addition, as the rotating members have some sliding portions, the mechanism is apt to be complicated. Thus, assembling thereof is difficult and its production cost is high.
On the other hand, during the starting step, the blade 18 starts to operate only after the motor shaft 2 freely rotates by 180.degree.. Therefore, the response of the device is poor.
Although not shown, in another conventional rise up mechanism for a wiper device, a motor itself moves to shift a motor shaft. In such a device, a mechanism for shifting the motor is complex in construction. As compared with a general wiper device, a rise up mechanism is expensive.