Electricity: motive power systems – Motor-reversing – Automatic and/or with time-delay means
Patent
1986-10-03
1988-03-22
Ro, Bentsu
Electricity: motive power systems
Motor-reversing
Automatic and/or with time-delay means
15250C, B60S 108
Patent
active
047331429
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for controlling a windscreen wiper, for example for a motor vehicle.
2. Description of Related Art
The self-evident objective of a windscreen wiper system is to maximise the driver's visibility of the road ahead. Whilst under conditions of heavy rainfall this objective is likely to demand the highest possible sweep rate, under light rainfall conditions the sweep rate must be reduced to avoid smearing, blade judder and excessive wear in the system. Known methods for adjusting the sweep rate are variation of the sweep time (a multiple speed wiper motor) and variation of the delay between consecutive sweep cycles. Known systems incorporate switched motor speeds, switched delays and variable delays, all of which are controlled manually by the driver. Manual adjustment of sweep rate is a source of distraction to the driver, particularly in heavy traffic.
It is also known to employ optical or electrical sensing means for the detection of moisture on a windscreen for the purpose of activating windscreen wipers. However, such devices have not provided an economical and effective means of controlling windscreen wipers to optimise visibility and manual intervention by the driver has still been required. It is an object of the invention to provide a method and apparatus for controlling a windscreen wiper which is effective automatically to adjust the rate of operation of the wiper in dependence on the mean moisture level on the windscreen.
SUMMARY OF THE INVENTION
According to the invention there is provided a method of controlling a windscreen wiper comprising adjusting the delay between sweeps of the wiper in dependence on the time the wiper takes to sweep the screen. Preferably each single sweep is timed and the delay between successive sweeps is adjusted. However, it would be possible to time bursts of two or more sweeps of the wiper and adjust the delay between the bursts.
The invention is based on the recognition that the sweep time of a windscreen wiper depends on the wetness of the screen. Dry conditions demand a higher torque from the wiper motor than wet conditions and an electric or other motor which is limited in torque operates at a slightly lower speed under dry conditions than under wet conditions, the speed increasing monotonically between the two extremes. The speed and variation of speed with wetness have been found to be substantially independent of aerodynamic conditions. Thus by adjusting the delay between sweeps of the wiper in dependence on the sweep time the overall sweep rate of the wipers varies according to the wetness of the screen.
Preferably the sweep time is determined by monitoring operation of a limit switch of the wiper motor, for example a self-park switch which is closed after the start of each sweep cycle (the motion of the wiper from the parked position to the maximum point of travel and back to the parked position) and opened at the end of the sweep cycle. For example, the period between the time the motor starts and the time the limit switch operates at the end of a sweep cycle may be determined.
Various methods could be employed for determining the delay in terms of the sweep time. Preferably estimated maximum and minimum sweep time values are established, and the delay is determined by the relation of the measured sweep time to the maximum and minimum values. The delay could be determined from the sweep time by an open loop method in accordance with a function established by an analogue function generating circuit or digitally by means of a look-up table or algorithmic method, i. e. a scale of delay times is established for values of the measured sweep time between the maximum and minimum values. Alternatively, a closed loop technique could be used in which a desired sweep time is established (corresponding of course to a desired screen wetness) and the delay time is established in accordance with the difference between the measured sweep time and the desired sweep time.
REFERENCES:
patent: 3458889 (1969-08-01), Tann
patent: 3643145 (1972-02-01), Tann et al.
patent: 4499410 (1985-02-01), Iacoponi et al.
patent: 4625157 (1986-11-01), Phillimore
Cogent Limited
Ro Bentsu
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