US 4,572,619 AGranted

Electrically dimmable rear-view mirror for motor vehicles

AssigneeDaimler-Benz Aktiengesellschaft

InventorsSiegfried Reininger, Albert Wiesmeier

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Abstract

An electrically dimmable rear-view mirror for motor vehicles of simple and robust construction, suitable for use as an outside mirror or as an interior mirror possessing a transmission layer which is composed of a PLZT ceramic, on which a linear birefringence can be imposed by means of a controlling electric field. The transmission layer is located between a linear polarizer and a reflective layer, the latter being designed as a dielectric multilayer arrangement. Suitable comb-type electrodes are located on that side of the reflective layer which faces away from the transmission layer and, if appropriate, on that side of the polarizer which faces the transmission layer, the function of these comb-type electrodes being to generate the controlling field. The polarizer defines the direction of polarization, which is inclined at 45.degree. with respect to the field direction and/or the optical axis of the transmission layer. The strength of the electric field controlling the dimming effect is regulated in a manner such that the effective reflectivity of the rear-view mirror is reduced to suit the prevailing situation, this field-strength regulation being accomplished by a photoelectric control system which reacts, on the one hand, to the brightness of the surroundings and, on the other hand, to the intensity of a luminous flux passing through the polarizer and the transmission layer.

Claims13

Dependent claims

An electrically dimmable rear-view mirror comprising:

a linear polarizing means with a transmission axis receiving incident light for generating a light output,
a transmission layer means for receiving at least a portion of light output from the linear polarizing means to transmit a portion of the light received thereby and including a ceramic means exhibiting an electro-optical effect in response to an electric field for controlling the effective reflectivity of the rear-view mirror,
a reflecting layer means including at least a multi-layer dielectric arrangement receiving light output from the transmission layer means,
spaced electrode means disposed on at least one side of the transmission layer means for generating an electric field substantially parallel to the transmission layer means in response to a voltage applied to the electrode means to provide a linear birefringence in the transmission layer,
a transmission window means in the reflecting layer means for transmitting a luminous flux from the transmission layer,
a second polarizer for receiving said transmitted luminous flux, the transmission axis of the second polarizer coinciding with that of the linear polarizer,
a light sensor means receiving the transmitted luminous flux from the second polarizer for generating a voltage output signal which increases monotonically with the intensity of the transmitted luminous flux from the second polarizer,
a control voltage source responsive to the voltage output signal to produce a voltage which, in its turn, increases monotonically with the output voltage from the light sensor means for generating the electric field which effects the linear birefringence of the transmission layer.

5 more elements

Dependencies are inferred from the claim text.