An airspring height control device is based on an infrared light emitting diode and photo transistor receiver combination to reflect a signal from a reflector located internally to an airspring. The variable output signal given off by the receiver is proportional to the distance from the transmitter/receiver to the reflector thus allowing a height controlling mechanism to respond to the signal and make the necessary adjustments.
In automotive suspension technology it is currently desirable to have the ability to change the height of the body relative to the road depending upon the travel conditions. It is highly desirable to be able to lower the aerodynamic profile of the automobile at high speeds on smooth roads while still being able to raise the sprung portion of the automobile to a much higher level for low speed rough road travel.
While it has long been known that the height of the suspension can be adjusted by increasing the pressure in an air adjustable shock absorber in order to increase height such adjustments can only be made manually with the vehicle stopped. In order to continuously make such adjustments, it is necessary for an automatic system to be able to detect the existing height condition of the vehicle and compare it to a standard or to a selected height.
Any mechanical systems for measuring the distance between two points of the suspension which are relatively movable to each other as the body is raised and lowered have inherent reliability problems during the long service lives of such suspension members.
It is an object of this design to develop a low cost infrared height sensor which is small in size and may permit installation within the air suspension system. A further objective is to allow the driver to electronically select among an infinitely variable number of height adjustments while the vehicle is in motion.
It is the further object to allow for the replacement of the infrared height sensing device without disassembly of the strut or suspension unit in which it is mounted. A still further object is for the height sensor to be capable of withstanding the environment of the suspension over a temperature range of -40° to 100° C.
All objectives are achieved utilizing an infrared height sensing system which is mounted within an air suspension member. The air suspension member remains capable of reliable and consistent control of vehicle height throughout the environmental range of conditions to which automobiles are subjected.
This design relates to an optical sensor for selectively controlling the relative height of an air suspension system, particularly relating to automotive suspensions employing an airspring as a primary support for the sprung portion of the suspension.
FIG. 1 schematically shows the central physical elements of the infrared height sensor without reference to any particular device in which it is being used. The height sensor 10 is composed of an infrared transmitter 12 and a infrared receiver 14. The transmitter 12 provides an infrared beam directed at a reflector 16 which returns a portion of the infrared beam from the transmitter 12 to the receiver 14. A mask 18 is shown interposed between the transmitter/receiver and the reflector. The mask will be discussed in considerable detail subsequently.
FIG. 1 also schematically shows a diagram describing the upstream and downstream electronics for providing height control in the device. These functions are shown only in a very simplified schematic form. The variable output signal 20 from the receiver 14 is routed to a receiver control circuit 22 which conditions, amplifies and provides an interface for the appropriate control devices 24 and 26 for raising or lowering respectively the height of the device in which the height sensor 10 is installed.
A variable height set point 28 is provided as additional input into the receiver control circuit 22. The infrared transmitter 12 has a control module 30 which may include an optional compensation device 32 for various external conditions, including temperature, atmospheric pressure, etc. An external input to the transmitter control 30 is the height adjustment module 33 which controls the output of the transmitter 12.
The height sensor device 10 operates by optically coupling the infrared receiver 14 with the infrared transmitter 12 via the reflector 16. The transmitter 12 and receiver 14 are positioned within a single rigid unit such that the infrared light leaves the transmitter and is reflected back to the adjacent receiver 14.
With a properly designed reflector, the amount of infrared radiation reflected back to the receiver 14 will be directly proportional to the distance between the reflector and the transmitter/receiver sensing unit. As the target area on which the reflector 16 is mounted moves closer to the transmitter/receiver assembly, a greater percentage of the transmitted infrared light is returned to the receiver 14 thereby providing a greater signal output 20 from the receiver.
The transmitter is preferably an infrared light emitting diode (LED) transmitter, such infrared diode transmitters are well known although not for use in devices such as airsprings. Other LED transmitters may be suitable for use in this design and no attempt will be made here to list the various types which may have utility, one of ordinary skill in the art of infrared transmission and detection will be aware of the evolution and suitability of various products.
The essential requirement of the transmitter 12 is that it provide a constant output of infrared radiation of a given frequency and wavelength over a suitably long life. A most preferred infrared light emitting diode type is a gallium aluminum arsenide (GaAlAs) infrared type which has a high radiation output at a given forward current.
A commercially available example is the OP260SLA available from the Optoelectronics Division of TRW Electronic Components Group of Carrolton, Tex. Gallium arsenide emitters are also a preferred type. Compensation circuits for adjusting for varying output over the life of the transmitter as well as temperature and environmental compensation circuits will be described in detail later.
The infrared receiver 14 may be any device capable of receiving variable inputs of infrared radiation of a given wavelength and frequency. The most suitable devices known at this time are photo transistor receivers.
A most preferred type is a photodarlington transistor. A broader preferred class is a transimpedence amplifier with parallel feedback. At the present time a particularly suitable receiver is an NPN silicon photodarlington, type OP530, available from Optoelectronics Division of TRW Electronic Components Group. The photodarlington offers the advantage over conventional photo transistors of providing high current gains under low signal light levels.
The infrared transmitter 12 and receiver 14 must be precisely and properly aligned relative to each other. It is felt at this time that moving the centerlines of the transmitter and receiver as close together as possible is a desired configuration. The receiver centerline 34 and the transmitter centerline 36 are shown in parallel orientation.
It is noted that for many applications it may be highly desirable to have the centerlines 34 and 36 angularly positioned relative to each other. When the receiver 14 and transmitter 12 are placed physically very close together it is important that one be shielded from the other to prevent unwanted radiation leakage from the transmitter to the receiver which has not traveled to the reflector and back.
Such installation and orientation of the components of the sensor are known to one of ordinary skill in the art and will not be discussed in further detail. The potting materials used to secure the receiver and transmitter into an integral unit must be capable of withstanding the environment including temperature, humidity and various contaminants which may be present in the working environment.
The reflector 16 is a critical element of the height sensor 10 operation and the reflector may be mounted either on the moving component of the device or on the fixed component depending on the various design criteria. The reflector must be capable of providing constant reflectivity of the infrared wavelength being utilized despite the presence of various contaminants.
In some circumstances a highly machined metal surface may be suitable, but in most applications a special reflector should be provided with special consideration given to the environment in which the reflector is being utilized. The reflector may have reflective paint placed on the reflective surface or it may be a separate laminate or film which is applied to the work surface to form the reflector 16.
The reflector should be capable of reflecting back nearly all of the radiation which impinges on its surface without absorbing any substantial amount. One particularly suitable material is a product manufactured by the Minnesota Mining and Manufacturing Company and marketed under the product designation 3M Scotchlite.TM., High Contrast #7615 Sheeting.
This retro-reflective sheeting has a dispersion angle of 20° of the transmitted centerline. Other high reflectivity surfaces would be suitable. The size of the reflector 16 is determined experimentally by the nature of the movement between the fixed and moving surface of the device in which the height sensor is installed, but generally a large enough target area must be provided by the reflector 16 to assure a smooth, controllable return signal to the receiver 14 from the transmitter 12.
Contamination such as oil, dust, water, various other solids and fluids cause difficulty with the consistency of reflectivity of the reflector 16. These contaminants must be taken into consideration in selecting the reflective material for a particular application. It should be noted that even simple condensation of water over the surface of a reflector may render the reflective material dead or incapable of returning the incoming radiation.
A protective mask 18 may be utilized to advantage in many applications for the dual purpose of protecting the reflector 16 from contamination as well as providing a matrix for varying the reflectivity of the reflector over its surface. As to the contamination protection, the mask may be made from any suitable material which has the appropriate transparency in the desired infrared frequency range.
Materials which may be suitable for the mask include polycarbonate, polyester, polyvinyl chloride or acrylic films. The photo mask may include a matrix 38 on its surface of open transparent areas 40 interspersed with opaque areas 42 in a desired pattern. When such a matrix 38 is provided on a protective film laminate the mask will be described as a photo mask.
The matrix 38 of open transparent areas 40 and opaque non-reflective areas 42 may be provided using photographic techniques for exposing and altering the surface of the mask 18 to selectively alter the reflectivity of the surface. Many forms of the matrix may be utilized and depending upon the variability of the orientation of the reflector 16 to the centerlines 34 and 36 of the receiver 14 and transmitter 12, the matrix 38 may be varied in order to provide a desired output as the reflector moves toward the receiver 14.
A series of concentric rings is the most preferred form of mask 18.
It is to be noted in working configurations that several transmitters 12 may be positioned around a single receiver in order to augment the signal being received. The individual receivers and transmitters are preferably encapsulated in optically clear plastic or other suitable potting material.
The transmitters should be shielded to prevent unwanted cross talk or radiation which moves directly from the transmitter to the receiver without having been reflected back from the reflector 16. The materials and designs for the infrared sensor are dependent upon the environment and the specific design requirements of the application.
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