Optical height sensor and levelling system for vehicles

Abstract: An improved vehicle height sensor and automotive leveling system (90) are described using, in a preferred embodiment, two optical emitter-receiver pairs (44,46) mounted in the sidewall (22) or dust cover of a standard automotive air shock (40). The emitter-­ receiver pairs (44,46) are arranged to operate by reflecting light from the central shaft (16) of the shock absorber (40) . Each emitter-­ receiver pair (44, 46) provides a light path (52,53) that lies in a plane substantially perpendicular to the extension direction (28) of the shock (40). The two emitter receiver pairs (44,46) are spaced apart along the extension direction (28) of the shock (40) . Movement of the internal piston (18) of the shock (40) successively interrupts (by absorption) the light paths (52,53) of the emitter-receiver pairs (44,46) so as to provide a positive indication of the location of the movable piston (18) and hence the height of the shock (40) and the height of vehicle body above the road. The emitter-receiver pairs (44,46) are mounted in a common assembly (60) and seal to the shock dust cover (22) through a single hole. They are convenient to manufacture in a single module (42) which includes the control logic (93) needed to add or remove fluid from the shock (40) to maintain it in the reference position independent of the vehicle load. This makes possible a particularly compact unit.

Description: Field of the Invention This invention relates in general to the field of vehicle height sensors and, more particularly, optical sensing apparatus for use preferably within a vehicle load leveling means for sensing and controlling vehicle height. Background of the Invention It is well known in the vehicle art, particularly the automotive art, to provide air cylinders coupled between the frame or body of a vehicle and the axles to adjust the body height above the road in response to varying vehicle loads. In their most common embodiment, such air cylinders are often combined with shock absorbers to provide what are referred in the art as "air shocks". The air shocks combine the damping action of a shock absorber with the load leveling features of an air cylinder. By adjusting the length of the air shock, the body-axle separation and the height of the body above the road may be varied. A typical prior art system is described in U.S. Patent 3,558,155 to Jackson, et al. The fluid (either liquid or gas) inside the air shock acts as a variable spring. If the vehicle load is increased, the shock is compressed until it balances the added load and the height of the vehicle above the roadway decreases. The vehicle body may be returned to its initial position by forcing more fluid into the shock. Thus, when air shocks are employed, widely different loads may be carried in the vehicle while still maintaining the body at a substantially constant height above the road. This is highly desirable. There is an increasing desire to provide automatic load leveling equipment on vehicles, particularly automobiles, wherein the height of the vehicle body above the roadway is automatically maintained at a constant distance. In order to do this, it is necessary to have some means for detecting the height of the body above the axles so that the fluid pressure or volume in the air shock may be varied as the vehicle load changes to return the vehicle to its predetermined height. A number of systems have been used in the prior art to sense vehicle position. For example, a mechanical positioning system is described in U.S. Patent 3,510,143 to Carpenter. Systems using electrical switches are described in U.S. Patents 3,610,611 to Elliott and U.S. Patent 4,293,139 to Brown. A height sensing system utilizing electrical potentiometers is described in U.S. Patent 4,659,104 to Tanaka et al. The use of optical devices for sensing vehicle height is described in U.S. Patent 4,017,099 to Hegel et al., and U.S. 4,391,452 to Ohmori. All of these prior art height sensing arrangements suffer from a number of disadvantages well known in the art. Among these disadvantages are comparatively high cost, difficulty of manufacture, and/or poor reliability. Thus, there is an ongoing need for vehicle height sensors and vehicle height control systems having improved properties. US Patent No. US-A-4,141,572 discloses a height sensing apparatus attached to a vehicle air shock which senses vehicle height using a non-reflective optical arrangement. An emitter is mounted at one end of a long flexible member and receivers are mounted at the other end of the member. When the flexible member is mounted within a hole in the dust cover of the shock, the member resiliently engages the wall of the dust cover and the emitter and receivers are positioned relative to the piston shaft and cylinder such that the light paths between the emitter and receivers are successively interrupted by the cylinder as it moves along the shaft. The information provided by the emitter and receivers is used by a controller external to the height sensing apparatus to determine vehicle height. As used herein the words "air shock" or "shock" are intended to refer to all manner of fluid operable pistons, whether the fluid is liquid or gas, whether the air shock is of the variable length or angular displacement type, and whether or not the air shock incorporates a damping means. As used herein and unless otherwise indicated, the words "light" or "optical" or "optically" are intended to refer in general to the portion of the electromagnetic spectrum having wavelengths in the range of about 0.1 to 100 micrometers. Summary of the Invention Accordingly, it is an object of the present invention to provide an improved vehicle height sensor employing optical devices. It is a further object of the present invention to provide an improved vehicle height sensor which is compatible with existing air shocks and which does not require changes in vehicle design or attachment points. It is an additional object of the present invention to provide an improved vehicle height sensor that is adapted to be integrated into an air shock so as to provide a compact sealed unit. In achieving the above and other object and advantages of the invention there is provided, in one form, a vehicle height sensor comprising: a first portion fixed to a first end of the sensor and a second portion moveably engaging the first portion so as to be movable in a direction parallel to an axis of the first portion and fixed to a second end of the sensor, the first and second ends of the sensor for attachment to first and second portions of the vehicle, wherein the position of the first end relative to the second end varies in response to a change in height of the vehicle such that there is relative motion between the first and second portions; enclosing means extending from the first or second end of the sensor and for enclosing at least part of the first and second portions; and optical means mounted in a module which is mounted in an opening within a wall of the enclosing means, the optical means comprising at least one emitter and at least two receivers, the vehicle height sensor being characterised by: the at least one emitter and the at least two receivers being mounted in the module so as to lie within the opening; the at least one emitter providing at least two light rays directed toward the axis of the first portion, each ray being incident on a surface of the first or second portion depending on the position of the second portion relative to the first portion, each ray being substantially reflected when incident on the surface of the first portion to provide a reflected light ray to an associated receiver of the at least two receivers and providing no reflected light ray to the associated receiver when incident on the surface of the second portion; and circuitry mounted in the module and coupled to the at least two receivers for decoding signals received therefrom and for providing, in response thereto, first, second or third output signals depending on whether none, one or at least two reflected light rays were received by the at least two receivers respectively, the output signals providing information on the position of the second portion relative to the first portion which provides an indication of the height of the vehicle. An improved apparatus for automatically maintaining the height of a vehicle and incorporating the vehicle height sensor in accordance with the present invention is also disclosed and claimed in claim 8 of the accompanying claims. In a preferred embodiment suitable for use with a typical, present day, axially extensive air shock having a rubber boot closure or the like, two optical sensors or receivers and at least one (and preferably two) optical emitters are mounted on the external dust cover of the shock. The emitters and receivers are pointed at the longitudinal central shaft of the shock, and spaced along the length direction. Absent reflections, there is substantially no direct optical path between the emitter and receiver of each emitter-receiver pair. The central shaft is connected to one end of the air shock and a movable piston which slides on the central shaft is connected to the other end of the shock. When the movable piston is extended so as to be located below the reference position, i.e., below both emitter-receiver pairs, then light is reflected to both receivers from the central shaft. When the movable piston is at the reference height, one emitter-receiver pair directs light to and from the central shaft and another substantially identical emitter-receiver pair directs light at the movable piston of the shock that slides axially along the central shaft. The light striking the central shaft is reflected to the first receiver while the light striking the movable piston is substantially absorbed so that little or no light is returned to the second receiver. When the movable piston is located above the reference position, light from both emitters falls on the movable piston and is absorbed so that substantially no light is reflected to either receiver. Thus, the combination of outputs from the two receivers indicates the relative position of the movable piston The two emitter-receiver pairs are mounted in a single module which is, desirably, sealed to the sidewall of the air shock. It is desirable but not essential that the sealing means be arranged so that increasing the fluid pressure inside the shock increases the sealing force. A control means responsive to the signals from the optical receivers increases and decreases the fluid pressure (and/or volume) in the shock to maintain the piston height and hence the vehicle height in the reference position. It is further desirable to provide in the module a window transparent to the light emitted by the emitters to separate the emitter-receiver pairs from the pressurizable space. The above and other objects, features, and advantages of the present invention will be better understood from the following detailed description taken in conjunction with the accompanying drawings. Brief Description of the Drawings FIG. 1 is a partial cross-sectional and cut-away view of an air shock utilizing an optical height sensing arrangement, according to the prior art, and in simplified form. FIG. 2 is an end view of the interior of the prior art shock of FIG. 1, in schematic form, indicating the light path within the shock. FIG. 3 is a view similar to that of FIG. 1 but according to the present invention. FIG. 4 is a partial cross-sectional view of the air shock of FIG. 3, according to the present invention, showing further details of the optical assembly, according to a first embodiment. FIG. 5 is a view similar to FIG. 4 but according to a further embodiment of the present invention. FIG. 6 is a view of the optical assembly portion of the embodiment shown in FIG. 5 as viewed from the central shaft of the shock absorber. FIG. 7 is a view similar to that of FIG. 6 but according to a further embodiment of the present invention. FIG. 8 is a view in schematic form corresponding to the embodiment of FIG. 7, parallel to the longitudinal axis of the air shock and at right angles to FIG. 7, and showing the optical path. FIG. 9 is a block diagram of an automatic system for adjusting a vehicle levelling air shock, according to the present invention. Detailed Description of the Figures FIG. 1 is a partial cut-away and cross-sectional view of a prior art axially extensible air shock absorber employing an optical height sensor and FIG. 2 is a highly simplified schematic view of the same air shock looking along the longitudinal axis of the shock, showing further details of the optical path within the prior art shock. Referring now to FIGS. 1 and 2, prior art shock 10 has opposed mounting brackets 12, 14 which are used for attaching air shock 10 between the vehicle body (or frame) and the vehicle axle. While mounting means 12, 14 are shown as brackets having holes 13, 15 therein for accepting attachment bolts, any means for attaching the air shock between the body and axle may be used. Central shaft 16 of air shock 10 is rigidly connected to first mounting means 12 and axial cylinder 18 is rigidly connected to second mounting means 14. Cylinder 18 slidably engages shaft 16 at seal 20. Dust cover 22 is provided extending, in this example, from first mounting means 12 toward second mounting means 14 and coaxially surrounding shaft 16 and cylinder or piston 18. Dust cover 22 could alternatively extend from mounting means 14 toward mounting means 12. Pressurizable space 23 between cover 22, piston 18 and shaft 16 is closed by rolling flexible seal 24. Seal 24 is typically a rubber impregnated fabric boot having end 24A attached to piston 18 and end 24B attached to cover 22. The pressure in space 23 will typically reach about 2MPa (300 psi) during operation of a conventional air shock. Air shock 10 has inlet 26 whereby fluid (e.g., a liquid or gas) may be introduced into space 23 thereby forcing piston 18 to slide inwardly or outwardly along shaft 16 in axial direction 28. Prior art shock 10 includes optical emitter 30 and optical receivers 32, 34 mounted in dust cover 22. Shock 10 is generally installed in the vehicle so that mounting means 12 is located higher than mounting means 14 but this is not essential. For convenience of description, the words "above" and "below" used herein, refer to this customary orientation. Emitter 30 and receivers 32, 34 of prior art shock 10 are azimuthally offset around the perimeter of dust cover 22 by angle 39 of approximately 135 degrees (see FIG. 2). The 135 degree angular displacement is important in the prior art shock, since at larger angles the light path would always be blocked by central shaft 16 and at smaller angles, the light path would never be interrupted by piston 18. When piston or cylinder 18 is extended outwardly in direction 28B in FIG. 1 so as to be remote from receiver 34, then light rays 36, 38 may travel unimpeded between emitter 30 and receivers 32, 34 without intersecting central shaft 16 or piston 18. As piston 18 moves inward, that is, in direction 28A in FIG. 1, it successively blocks first light path 38 and then light path 36. When a vehicle employing air shock 10 is lightly loaded, cylinder 18 of shock 10 will move toward its extreme extensive position, that is, in direction 28B. In this situation, light emitted from emitter 30 will reach both receivers 32, 34 along optical paths 36, 38 respectively (see FIGS. 1-2). When the vehicle height is in its reference position, then cylinder 18 will be located on shaft 16 so that end 18A of cylinder 18 lies between optical receiver 32 and optical receiver 34. This is the situation shown in FIG. 1. In these circumstances light ray 36 extending between emitter 30 and receiver 32 is unimpeded, while light ray 38 extending between emitter 30 and receiver 34 is blocked by end portion 18A of cylinder 18 at 38′. The prior art system illustrated in FIGS. 1-2 above suffers from a number of disadvantages. Among other things, the prior art optical arrangement requires that the emitter and receivers be located at different azimuthal positions about 135 degrees apart around the perimeter of the shock so as to provide a direct line of sight therebetween. Thus, three separate holes are required in the dust cover for these components. This is expensive to make and more prone to leaks. Further, because the emitter and sensors must be spaced widely apart on the dust cover it is very difficult to align and put them into a single module with the necessary control electronics. This further increases the manufacturing cost and reduces reliability. These disadvantages are overcome and other advantages achieved with the arrangement of the present invention illustrated in FIGS. 3 through 9. FIG. 3, shows a view similar to FIG. 1, but of air shock 40 according to the present invention. Air shock 40 has some features in common with prior art shock 10 which are identified by the same reference numerals. Air shock 40 of the present invention has all of the optical components mounted in unitary module 42 which requires only single entrance hole 43 in the side of dust cover 22. Other features of dust cover 22 in FIG. 3 are the same as FIG. 1. Optical height sensor 42 comprises, in a preferred embodiment, emitter-receiver pairs 44 and 46 which point radially inward from dust cover 22 toward central shaft 16 and which are spaced apart along axial direction 28 of shock 40. Emitter-receiver pairs 44, 46 are connected to integrated control module 50 by connectors 49. Optical paths 52, 53 extend between emitter-receiver pairs 44, 46 and central shaft 16. FIG. 4 provides a partial cross-sectional view through air shock 40 at the axial location indicated on FIG. 3, showing additional construction details of a first embodiment. Referring now to FIG. 4, emitter 44E and receiver 44R of emitter-receiver pair 44 are mounted in spaced-apart fashion in mounting block 48 and coupled to connectors 49. Emitter 44E and receiver 44R have lenses 47E and 47R, respectively, and are oriented so as to point at shaft 16 running along the central axis of air shock 40. Light ray 52E from emitter 44E is directed toward shaft 16 where it is reflected to form light ray 52R directed toward optical receiver 44R. Rays 52E and 52R are separated by reflection angle 54. Angle 54 should preferably be about 45 degrees or less with 20-25 degrees being convenient and about 22 degrees being preferred. It will be noted that there is no direct optical path between emitter 44E and receiver 44R. This is a particular feature of the present invention. Mounting block 48 containing emitter-receiver pairs 44, 46 is located in boss or protrusion 22B formed in the side of dust cover 22. In the embodiment shown in FIG. 4 block 48 is sealed to boss 22B by O-ring 52 but any sealing means may be used. Block 48 is conveniently retained in place by externally attached clip 55, but other retention means will also serve. With the arrangement shown in FIG. 4, the fluid pressure contained within space 23 bears upon mounting block 48 so as to force seal 52 tightly against boss 22B in dust cover 22. The higher the pressure in space 23, the greater the sealing force. Optically transparent window 56 is desirably provided over emitter-receiver pairs 44, 46 to separate the emitter-receiver pairs from pressurized space 23. Optically transparent window 56 may be attached to mounting block 48 by means of gasket 58 or by adhesive or by other sealing means well known in the art, or may be formed as an integral part of block 48. Optically transparent window 56 is desirable to reduce the leak rate from pressurized space 23, for example, around emitter receiver pairs 44, 46 and, as will be explained later, to provide improved focus and cross-talk reduction for the optical components. However, optical window 56 is not essential. FIG. 5 shows a view similar to FIG. 4 but according to a further embodiment of the present invention. FIG. 6 provides a view of the embodiment shown in FIG. 5 looking toward module 42 along optical path 52 from central shaft 16. For simplicity, dust cover 22 and module cover 77 have been omitted in FIG. 6. Referring now to FIGS. 5-6, emitter-receiver pairs 44, 46 are held at mutual angle 54 in block 60 so as to point at central shaft 16. For ease of assembly, the recesses in block 60 intended to retain emitter-receiver 44, 46, have a shape which is slightly more than a half-cylinder in extent. This permits cylindrically shaped emitter-receiver pairs 44, 46 to be snapped into place and retained therein at the desired mounting angle. Mounting block 60 is attached to circuit board 62 by any convenient means. Circuit board 62 is conveniently fabricated separately and mounted in support block 64 but this is not essential. Mounting block 60, circuit board 62 and support 64 may be separate or combined. Optically transparent window 68 analogous to window 56 extends over emitter-receiver pairs 44, 46 and engages support block 64 at engagement surface 65. Engagement surface 65 insures that optical window 68 is centered with respect to support block 64 and in turn with mounting block 60 which holds emitter-receiver pairs 44, 46. O-ring 70 is conveniently used to seal optical window 68 (and therefore module 42) against dust cover 22 in boss 22C to contain the compressed fluid within pressurizable space 23. Logic circuits 72 (see FIG. 5) for forming control module 50 (see FIG. 3) are provided on circuit board 62 and connected to output pins 74 (see FIG. 6) for coupling module 42 to the rest of the system (see FIG. 9). The arrangement shown in FIGS. 5-6 provides for particularly convenient assembly of module 42 to shock 40. Module 42 in FIGS. 5-6 need not be installed during construction of shock 40 but may be inserted into boss 22C of dust cover 22 after shock 40 has been entirely assembled. Module 42 of FIGS. 5-6 may be easily installed or replaced at any time during the manufacture of shock 40 and even after shock 40 has been mounted on the vehicle. A further advantage of the embodiment of FIG. 6 is that optical window 68 has a circular shape where it engages dust cover 22 so that a standard circular seal arrangement may be utilized. This reduces the likelihood of leaks. Outer cover 77 is provided as shown in FIG. 5, for example, to cover circuit board 62 and mounting block 64 and to retain O-ring seal 70 at the proper location within boss 22C. Optical window 68 is desirably provided with lense regions 69, 71 over emitter-receivers 44, 46. Such lense regions permit more precise adjustment of optical paths 52, 53 and makes it simple to accommodate different internal dimensions of shock 40 without having to alter lenses 47E, 47R. Thus, standard fixed focus components can be used for emitter-receiver pairs 44, 46 and module 42 adapted to operate efficiently with different shocks by providing different optical windows 68 having different lense windows 69, 71. Lense windows 69, 71 may be flat, convergent or divergent according to the focus needs of the particular air shock-optical module combination. Such windows are conveniently obtained by molding during fabrication of window 68. Polycarbonate plastic is an example of a suitable material for optical window 68 (depending upon the wavelength of light used) but other materials well known in the art that are optically transparent at the emitter wavelength may also be used. Optical window 68 is conveniently formed by molding. By providing optically opaque regions, as indicated for example by heavy lines 67 on window 68, the stray (out-of-path) light from emitters 44E, 46E is reduced and the sensitivity of receivers 44R, 46R to stray scattered light within the shock is also reduced. This decreases the possibility of unwanted cross-talk in the unit. For convenience of viewing the internal arrangement of mounting blocks 60, 60′ and emitter-receivers 44, 46 and 73, 75, 76, opaque regions 67 have been omitted from FIGS. 6 and 7, and windows 68 therein shown as being fully transparent. FIG. 7 is an illustration similar to FIG. 6 but showing a further embodiment of the present invention. FIG. 8 shows a highly simplified schematic diagram of the interior of shock 40 corresponding to the arrangement of FIG, 7, viewed in a plane parallel to shaft 16 and at a right angle to FIG. 7, and illustrating the optical paths within the shock. Referring now to FIGS. 7-8, single emitter 73 is used in conjunction with two receivers 75, 76 which are spaced apart in direction 28 of air shock 40. With this arrangement, emitter 73 must have sufficiently wide light dispersion angle 79 so that some portion of the light from emitter 73 reflected from shaft 16 at angles 84 along paths 80, reaches receivers 75, 76. The dispersion angle of an otherwise narrow beam emitter may be increased by including a divergent lense 69 over emitter 73 in window 68. Angles 79 and 84 are desirably less than 45 degrees and preferably in the range of about 15-25 degrees, with about 20-22 degrees being convenient. The details of cover 22 and mounting block 64 are omitted in FIG. 8 for clarity. While the arrangement of FIG. 8 allows the use of only one emitter, it is more prone to optical cross-talk than the arrangement of FIG. 6. Cross-talk may be reduced by use of opaque regions 67 covering the out-of-path portions of window 68, as has been previously described. FIG. 9 illustrates how height sensor module 42 is integrated in system 90 with air source 92 and vent valve 94 to provide actuation of air shock 40. Sensor module 42 comprises emitter-receiver pairs 44, 46 (or 73, 75, 76) and desirably includes logic block 50. Logic block 50 contains the electronic circuitry necessary to decode the responses from emitter-receiver pairs 44, 46 and actuate air source 92 and vent valve 94. When piston 18 is below the reference position, sensor module 42 with logic block 50 provides the signals to open air source 92 and direct air or other fluid via line 96 to inlet 26 of to shock 40. When piston 18 is in the reference position, then air source 92 and vent valve 94 are off. When piston 18 is above the reference position then sensor module 42 and control logic 50 provide the signal to open vent valve 94 to remove fluid from shock 40 via exhaust line 98. Air source 92 may be conveniently provided by an air pump coupled to an air reservoir, wherein the pump automatically maintains the reservoir at a pressure exceeding the highest pressure required by the air shock. A valve is conveniently included within air source 92 which, when activated by control logic 50, delivers air to shock 40 via line 96. Pumps, reservoirs and values for these purposes are well known in the art. If additional power is required to drive the air source output valve and the vent valve, power booster module 93 may be included as shown in FIG. 9. Power booster 93 may be any suitable type of electronic relay or amplifier. Those of skill in the art will understand based on the description herein how to provide the logic needed to interpret the signals from emitter-receiver pairs 44, 46 or 73, 75, 76 to turn on and off air source 92 and vent valve 94 depending on the position of piston 18 as explained above, and to provide power booster module 93 if such is required. Means for decoding the outputs of optical receivers and for boosting logic signals to actuate valves and the like are well known in the art. Emitters 44E, 46E, are preferably light emitting diodes but other emitters may also be used. Receivers 44R, 46R are preferably phototransistors or photodiodes but other types of optically sensitive electronic components well known in the art may also be used. In a typical automotive type shock absorber the distance between the central shaft and the emitter-receiver pairs is about 25 mm and the emitter-receiver pairs are spaced apart along direction 28 by about 5-25 mm, more usefully about 10-15 mm, and typically 15 mm. The emitters and receivers have a diameter of about 5 mm and a length of about 5-10mm or more. Emitter having optical wavelengths in the range of about 600-1000 nanometers are useful with emitters operating at about 930 nanometers being convenient. Such emitters are commercially available, as for example, type MLED 930 light emitting diodes manufactured by Motorola, Inc. Phototransistors are useful for receivers and suitable units are commercially available, such as for example, type MRD 300 phototransistors manufactured by Motorola, Inc. The receivers must be chosen so that they are sensitive to the wavelength light provided by the emitters, and vice-versa. Further, the optical window material must be transparent to the wavelengths provided by the emitters. Those of skill in the art will understand, based on the description herein, that the spacing and angular separation of the components may be varied depending upon the diameter of shaft 16, piston 18 and dust cover 22, the size of the optical components being used, and the desired width of the reference piston position zone. In general, the greater the axial spacing of the emitter-receiver pairs, the wider the reference piston position zone. With respect to the angular spacing of each emitter-receiver combination, the larger the diameter of cover 22, the smaller the angles 54 (see FIGS. 4-5) and 79, 84 (see FIG. 8) for a given emitter-receiver spacing. An additional feature of the arrangement described in the present invention is that by making opening 43 in dust cover 22 elongated, one may change the reference height of the shock merely by changing height sensing module 42 without having to change the mechanical design of the shock itself. Since the reference height of the shock is determined by the axial location of emitter-receiver pairs 44, 46 (or 73, 75, 76), the reference height of the shock can be altered by replacing one module 42 having a particular emitter-receiver location along direction 28 with another module 42 having a different emitter-receiver location along direction 28. This permits a single shock body to be used for different car models having different reference position requirements, which is a great manufacturing convenience. A further advantage of the present arrangement is that control electronics 50 may be readily integrated into module 42 immediately adjacent emitter-receiver pairs 44, 46 or 73, 75, 76 since they are located in close proximity. Further, since only a single opening is used in dust cover 22 it is relatively easy to seal and cheaper. Additionally, the receivers may be integrated with some or all of the control logic of module 50 in a monolithic optically sensitive integrated circuit combining receivers and logic to further reduce the size of module 42. The emitters and receivers utilized in the above described module employ lenses, e.g., 47E, 47R, which are an integral part of the emitter and receiver components. The focal length of the lenses and optically transparent window 56, 68 are desirably chosen so that the combined focal length is related to the distance between the emitters and/or receivers and central shaft 16 so that the best combination of received signal strength with minimum cross-talk is obtained. The optical cross talk is reduced by arranging the lenses to that both emitters and receivers have only a limited field of view. While it is desirable to use an optically transparent window over the emitter-receiver pairs, it is not essential. For example, in FIG. 5, the portion of window 68 incorporating seal 70 may be included in mounting block 64 and the portion of window 68 over emitters-receivers 44, 46 omitted. It will also be noted that unlike the prior art devices, the invented arrangement described above operates by virtue of the moving piston 18 absorbing the light being emitted from one and/or both emitters so that it is not reflected back to the corresponding receivers. Accordingly, it is important that the outer surface of piston 18 that faces emitter-receivers pairs 44, 46 or 73, 75, 76 be blackened or otherwise rendered optically absorbant. It has been found that this is conveniently provided by having rubber boot 24 extend substantially to inboard end 18A of piston 18. Having thus described the invention it will be apparent to those of skill in the art based upon the description herein that the invention provides an improved vehicle height sensor that is readily integrated into air shocks in a particularly simple and convenient manner to give a sealed unit. Additionally, the control electronics necessary to actuate the pumps and valves required to fill and empty the air shock may be readily integrated with the emitter-receiver pairs in close proximity thereto and as part of the same module so as to provide a compact module which is simple and inexpensive to install on the shock.

Claims: A vehicle height sensor comprising: a first portion (16) fixed to a first end (12) of the sensor and a second portion (18) moveably engaging the first portion (16) so as to be movable in a direction parallel to an axis of the first portion (16) and fixed to a second end (14) of the sensor, the first (12) and second (14) ends of the sensor for attachment to first and second portions of the vehicle, wherein the position of the first end (12) relative to the second end (14) varies in response to a change in height of the vehicle such that there is relative motion between the first (16) and second (18) portions; enclosing means (22) extending from the first (12) or second (14) end of the sensor and for enclosing at least part of the first (16) and second (18) portions; and optical means (73, 75, 76) mounted in a module (42) which is mounted in an opening within a wall of the enclosing means (22), the optical means (73, 75, 76) comprising at least one emitter (73) and at least two receivers (75, 76), the vehicle height sensor being characterised by: the at least one emitter (73) and the at least two receivers (75, 76) being mounted in the module (42) so as to lie within the opening; the at least one emitter (73) providing at least two light rays (52E, 53E) directed toward the axis of the first portion (16), each ray being incident on a surface of the first (16) or second (18) portion depending on the position of the second portion (18) relative to the first portion (16), each ray being substantially reflected when incident on the surface of the first portion (16) to provide a reflected light ray (52R, 53R) to an associated receiver (75 or 76) of the at least two receivers and providing no reflected light ray to the associated receiver (75 or 76) when incident on the surface of the second portion (18); and circuitry (50, 72) mounted in the module and coupled to the at least two receivers for decoding signals received therefrom and for providing, in response thereto, first, second or third output signals depending on whether none, one or at least two reflected light rays were received by the at least two receivers respectively, the output signals providing information on the position of the second portion (18) relative to the first portion (16) which provides an indication of the height of the vehicle. The sensor of claim 1 wherein the at least one emitter (73) and at least two receivers (75, 76) are mounted in a mounting block (48, 60, 64, 62) in the module (42) and the mounting block (48, 60, 64, 62) is attached to the enclosing means (22). The sensor of claim 2 further comprising a window (56, 68) attached to the mounting block (48, 60, 64, 62) such that the optical means (73, 75, 76) is separated from the first and second portions by the window (56, 68) and the at least two light rays (52E, 53E) from the at least one emitter (73) and the reflected light rays (52R, 53R) traverse the window (56, 68). The sensor of claim 3 wherein the window (68) comprises optically opaque regions (67) for reducing the stray light from the at least one emitter (44E). The sensor of claim 3 or 4 wherein the window (68) comprises lens regions (69, 71) substantially adjacent the at least one emitter (44E) and at least two receivers (46), the lens regions being any one of the following flat, convergent or divergent. The sensor of any preceding claim wherein the at least two receivers (75, 76) are spaced apart along the direction of relative motion (28). The sensor according to any preceding claim wherein a first light ray (52) of the at least two light rays and a second light ray (53) of the at least two light rays lie in substantially parallel spaced-apart planes. Apparatus (90) for sensing and controlling the height of a vehicle comprising: the vehicle height sensor according to any preceding claim, wherein the second output signal provided by the circuitry (50, 72) indicates that the second end (14) is in a predetermined location relative to the first end (12); and actuator means (92, 93, 94) coupled to receive the first, second and third output signals from the circuitry and being responsive to the first and third output signals for returning the second end (14) to the predetermined location relative to the first end (12). The apparatus according to claim 8 wherein the first portion comprises an internal longitudinal shaft (16) of an air shock and the second portion comprises a piston (18) of an air shock moving thereon, and wherein the enclosing means (22) encloses at least part of the shaft (16) and piston (18) to provide a pressurizable space (23) therearound, and wherein the module (42) in which the optical means (73, 75, 76) and circuitry (50, 72) are mounted is sealed within the opening in the wall of the enclosing means, and wherein the first, second and third output signals provide an indication of the position of the piston (18) along the shaft (16) and wherein the actuator means (92, 93, 94) comprises means (92, 94) for increasing or decreasing the pressure within the pressurizable space (23) in response to receiving the first or third output signals from the circuitry (50, 72) to return the piston (18) to the predetermined position.

Inventors: HANSON DAVID D, SEGERSON EUGEN EDWARD, VOWLES DAVID LEVERETT, HANSON, DAVID D., SEGERSON, EUGEN EDWARD, VOWLES, DAVID LEVERETT
Applicants: MOTOROLA INC, MOTOROLA, INC.
Application year: 1989
Main classification: B60G17
IPC codes: G01D5, B60G17, F16F9