GB2311208A

GB2311208A - A wiper system

Info

Publication number: GB2311208A
Application number: GB9606005A
Authority: GB
Inventors: Nicholas Philip Webb
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1996-03-21
Filing date: 1996-03-21
Publication date: 1997-09-24
Also published as: GB9606005D0

Abstract

A wiper system comprises a wiper motor 13 which causes oscillation of a wiper blade 17 and a controller 10 supplying drive signals to said motor which are continuously variable to control the motor speed. The drive signals may be pulse width modulated signals in which the mark to space ration is continuously variable (figure 2). Feedback means 19 in the form of a target wheel 191 and photo-electric emitter/receiver 194/195 may be used for the controller to determine the wiper blade speed, position and direction of movement. The controller may be arranged to control the acceleration of the wiper blade at the start of a wiper stroke, to control the deceleration of the wiper blade at the end of a wiper stroke, to achieve a constant speed of the wiper blade across a wiper stroke or to vary the speed of the wiper motor in response to a signal indicative of the road speed of a vehicle upon which the wiper system is mounted, from a sensor 12.

Description

A Wiper System For A Motor Vehicle This invention relates to wiper systems for motor vehicle windscreens.

It is known to provide a motor vehicle with a windscreen wiper system which operates at more than a single speed. These systems commonly achieve two speed operation by including a third brush in the wiper motor and switching a fixed voltage between the alternative brush arrangements.

It is also known to provide a self switching feature in such prior art systems by including a limit switch in the wiper motor gearbox to set the wiper blades at the end of their wiping stroke or to park them when they are not required.

It is an object of this invention to provide an improved windscreen wiper system.

According to the invention there is provided a wiper system for a motor vehicle comprising a wiper motor arranged to cause oscillation of a wiper blade across a surface made of a transparent material and a controller arranged to supply drive signals for driving the wiper motor wherein the drive signals are continuously variable to control the speed of the wiper motor. The transparent material could be, for example, a front or rear windscreen or a headlamp lens or cover.

The drive signals may be pulsed signals and may be made continuously variable by pulse width modulation.

The wiper system may further comprise a feedback means from which the controller can determine a speed, direction of movement or position of the wiper blade.

The controller may be arranged to modulate the drive signals to control the acceleration of the wiper blade at the start of a wiper stroke and to control the deceleration of the wiper blade at the end of a wiper stroke.

The controller may be arranged to vary the pulse width modulated signals to achieve a constant speed of the wiper blade across said surface.

The controller may be provided with a signal indicative of the vehicle road speed and may be arranged to vary the speed of said wiper motor as a result of the road speed signal.

The invention will now be described by way of example with reference to the accompanying drawings in which: figure 1 is a schematic diagram of a wiper system according to the invention: and figure 2 is a graphical representation of control signals used by the system of figure 1.

Figure l shows a wiper system comprising a wiper blade 17 moveable by an output shaft 16 of a gearbox 15 on a surface in the form of a windscreen 18 between a bottom position DN and a top position UP. The wiper system further comprises a gearbox input shaft 14 driven by a wiper motor 13 which is controlled by a controller 10.

The controller 10 receives driver inputs of chosen wiper speed from a wiper switch 11 and receives an input from a road speed sensor 12 indicative of the road speed of the vehicle (not shown). The wiper system further comprises a feedback means 19 to provide feedback from the output shaft 16 to the controller 10.

The wiper switch 11 is in the form of a stalk on the steering column (not shown) and has five positions representing the following wipe functions: OFF, flick FL, intermittent IT, low LO and high HI speeds.

The OFF, intermittent IT, low LO and high HI positions are mutually exclusive and are selected by moving the wiper switch 11 to a fixed position, in which it is retained until deselected. The flick wipe FL is instigated by pulling up on the wiper switch 11 and can be selected whenever the wiper switch 11 is in the OFF or intermittent IT positions.

The feedback means 19 is in the form of a target wheel 191 mounted on the output shaft 16 having holes 192 through it and a photo-electric emitter 194 associated with a light receiver 195 under the control of the controller 10.

The holes 192 are cut in the target wheel 191 at 100 intervals. In the series of holes 192, there are three asymmetrically spaced blanks 193 in the form of undrilled and therefore missing holes.

The photo-electric transmitter 194 is positioned to transmit light through the holes 192 as the target wheel 191 rotates. As a hole 192 passes across the transmission path between the photo-electric transmitter 194 and the light receiver 195, light can pass through and the presence of a hole 192 is detected. When part of the target wheel 191 between the holes 192, or a blank 193, is in between the photo-electric transmitter and the light receiver, no light can pass through the target wheel 191.

The desired wiper speed is chosen by the driver moving the wiper switch 11 to one of its predefined positions.

The controller 10 controls the operation of the wiper motor 13 by applying pulse width modulated (PWM) signals to the wiper motor brushes 131, 132. To raise the power developed by the wiper motor 13, the mark to space ratio of the applied PWM signal is increased and conversely decreased to lower the power developed. Increasing the power developed by the wiper motor 13 under constant conditions will raise its speed and decreasing the power will decrease its speed.

The wiper motor 13 unidirectionally rotates the input shaft 14 of the wiper motor gearbox 15. The gearbox 15 reduces the motor speed and multiplies the motor torque and is geared to oscillate the output shaft 16 and thereby move the wiper blade 17 back and forth across the windscreen 18.

The wiper blade 17 describes an arc on the windscreen 18 between the bottom position DN and the top position UP.

The controller 10 times between successive holes 192 to calculate the rotational speed of the output shaft 16. By counting the number of holes 192 between blanks 193, the controller 10 derives the position and direction of rotation of the output shaft 16. These calculations provide the controller 10 with feedback of the speed, direction and position of the wiper blade 17.

The feedback is used by the controller 10 to alter the mark to space ratio of the PWM signal applied to the brushes 131, 132 to increase or decrease the current through the wiper motor 13 to maintain the speed defined by the position of the wiper switch 11.

In figure 2, the voltage of the control signals applied to the poles 131, 132 of the wiper motor 13 is shown as a function of time in a graphical form. The control signals comprise a series of 12V pulses of a fixed frequency and controlled maximum amplitude, the width of the pulses being modulated to control the speed of the motor.

A complete wiper stroke is described each time the wiper blade 17 moves from the bottom position DN to the top position UP and back to the bottom position DN. Each complete wiper stroke comprises six stages: acceleration from rest at the bottom position DN up to the desired low LO or high HI speed; a period maintaining the constant low LO or high HI speed; deceleration to rest at the top position UP; acceleration from rest at the top position UP in the reverse direction up to the desired low LO or high HI speed; a period maintaining the constant low LO or high HI speed in the reverse direction; and deceleration to rest at the bottom position DN. The speeds and rates of acceleration and deceleration and the duration of each period of the wiper stroke are all defined in the controller 10 for each position of the wiper switch 11.

Successive wiper strokes are repetitions of the operation described above.

The acceleration of the wiper blade 17 from rest is implemented by the controller 10 applying a ramp-up signal 20 to the brushes 131, 132. The mark to space ratio of the ramp-up signal 20 is increased smoothly to accelerate the wiper blade 17 at the required rate up to the constant low LO or high HI speed selected.

The selected speed is maintained by control of the mark to space ratio of the constant speed PWM signal 22, 23 until the wiper blade 17 approaches the end of the wiper stroke.

To maintain the low speed signal 22, the controller uses PWM to alter the mark to space ratio and provide a constant rate of 50 wiper strokes per minute. This is the speed used in response to the selection of the low LO position on the wiper switch 11.

The high HI position on the wiper switch 11 provides a constant rate of 70 wiper strokes per minute. This is implemented by altering the mark to space ratio to achieve a greater duty cycle, as represented by the high speed signal 23.

The approach of the top position UP or bottom position DN is interpolated from the feedback means 19 and the mark to space ratio is decreased smoothly to bring the wiper blade 17 to rest at that position. The deceleration of the wiper blade 17 is implemented by a ramp-down signal 21.

The intermittent IT position on the wiper switch 11 provides a single but complete wiper stroke every 5 seconds. Each intermittent IT stroke is implemented in the same way as a single stroke of the high HI setting.

The flick FL position is provided to allow a single wiper stroke to be selected by the driver pulling upwards on the wiper switch 11 for about 0.5 seconds. The flick FL function is implemented by causing a single stroke of the high HI setting each time the wiper switch 11 is pulled up.

When the wiper switch 11 is placed in the OFF position, the wiper motor 13 is switched off as soon as the feedback means 19 indicates that the wiper blade 17 has next reached the bottom position DN. The wiper blade 17 will be brought to a halt at the bottom position DN by the ramp-down signal 21. This achieves a wiper park function.

In some conventional wiper systems, the wipers are parked by setting the blades at the end of their stroke.

This often means that a limit switch has to be included in wiper motor gearbox and regenerative braking used to overcome the momentum of the moving parts. This invention does without these requirements as the provision of the speed and position feedback means 19 enables the controller 10 to interpolate the position of the bottom position DN and top position UP of each wiper stroke and use this information to apply the ramp down signal 21 and then switch off the wiper motor 13 in the halted and parked position at the end of the wiper stroke following the selection of the OFF position on the wiper switch 11.

In some conventional wiper systems, as the vehicle speed increases wind resistance can cause the windscreen wipers to slow down noticeably. Other conditions such as snow weighing down the wiper blades can cause similar problems. This is because such prior art systems apply only a fixed potential across the wiper motor brushes for each speed. This invention provides feedback means 19 which enable the controller 10 to vary the mark to space ratio of the signal applied to the wiper motor 13 and thus maintain a constant speed wiper stroke for all conditions and selected wiper speeds. The mark to space ratio is also altered in response to road speed detected by the road speed sensor 12 and the wipe rate is thus increased or decreased in proportion to vehicle speed.

Finally, in some conventional wiper systems the system must switch to "low speed" before parking. The use of feedback means 19 and the ramp-down signal 21 allows the wiper system of this invention to maintain the high speed signal 23 up to the point when the ramp-down signal 21 must be applied. In similar fashion, the flick function FL can maintain the constant high speed signal 23 for almost the full duration of the single wiper stroke thereby selected.

This improves a conventional arrangement in which the "flick wipe" is initially at the higher speed but switches to the slower speed as soon as the wiper switch is released, so that the system can park.

Claims

1. A wiper system for a motor vehicle comprising a wiper motor arranged to cause oscillation of a wiper blade across a surface made of a transparent material and a controller arranged to supply drive signals for driving the wiper motor wherein the drive signals are continuously variable to control the speed of the wiper motor.

2. A wiper system according to claim 1 wherein the drive signals are pulsed signals and are made continuously variable by pulse width modulation.

3. A wiper system according to claim 1 or claim 2 further comprising feedback means from which the controller can determine a speed of the wiper blade.

4. A wiper system according to any one of claims 1 to 3 further comprising feedback means from which the controller can determine a direction of movement of the wiper blade.

5. A wiper system according to any one of claims 1 to 4 further comprising feedback means from which the controller can determine a position of the wiper blade.

6. A wiper system according to claim 5 wherein the controller is arranged to modulate the drive signals to control an acceleration of the wiper blade at the start of a wiper stroke.

7. A wiper system according to claim 5 or claim 6 wherein the controller is arranged to modulate the drive signals to control a deceleration of the wiper blade at the end of a wiper stroke.

8. A wiper system according to any preceding claim wherein the controller is arranged to vary the pulse width modulated signals to achieve a constant speed of the wiper blade across said surface.

9. A wiper system according to any preceding claim wherein the controller is provided with a signal indicative of the vehicle road speed and is arranged to vary the speed of said wiper motor in response to the road speed signal.

10.A wiper system substantially as described herein with reference to the accompanying drawings.