System for measuring the height above ground level of vehicles

A system for measuring a vehicle's height above ground level including a sensor which is preassembled and incorporated in the shock absorber of the vehicle eliminating assembly operations and fasteners in attaching the unit to the vehicle and protecting the sensor from impacts and the action of external agents due to its shielded position within the shock absorber.

BACKGROUND OF THE INVENTION 
The present invention relates to a system for measuring a vehicle's height 
above ground level. More particularly, the system represents a 
considerable technical improvement as compared to such systems presently 
in use, both in regard to reliability and simplicity and consequent cost 
effectivenss in manufacture and assembly. 
When the height above ground level of a vehicle must be known, measurement 
systems presently employed typically include a sensor located between the 
body (suspended mass) and the wheels (nonsuspended mass) of the vehicle. 
The sensor is physically housed in a container which can be any of many 
different shapes for being fitted between the body and a part connected to 
the wheels, such as an axle, trailing arm, stab axle, etc. 
One or more body areas suitable for fitting the sensor must be selected, 
and one or more fasteners for securing the movable part of the sensor to 
the nonsuspended parts of the vehicle and for attaching the in-line 
assembly of the sensor must be provided. 
The system to which the present invention relates eliminates these 
requirements since it employs at least one sensor that is preassembled and 
incorporated within the shock absorber of the vehicle. Fitting the sensor 
inside the shock absorber assures its physical protection and does away 
with the mounting operations and fasteners required for the sensors 
presently available on the market. 
The system sensor may be any of the presently known and available types. 
Four sensor types contemplated for use in the invention are: 
A potentiometric contact version, a version involving at least one 
Hall-effect sensor, a version involving an eddy current detector, and a 
version with an ultrasonic distance detector. Other sensors can be devised 
and the invention is not to be considered limited to these sensors. 
SUMMARY OF THE INVENTION 
The present invention overcomes the shortcomings of the prior art by 
providing a position sensor incorporated into the shock absorber of the 
vehicle for sensing the position of the piston rod of the shock absorber 
relative to the bottom of the shock absorber. 
According to a preferred embodiment of the invention, a resistance film is 
deposited on an inside wall of a working cylinder of the shock absorber 
and is contacted by an elctrical slide contact on the piston of the shock 
absorber. 
According to another embodiment of the invention, a Hall-effect transducer 
is employed including a magnet on the shock absorber piston and an end 
instrument on the working cylinder. 
Another embodiment of the invention provides for a coil having primary and 
secondary windings to be affixed to the working cylinder for developing a 
magnetic field in one coil and inducing a current in the second coil as 
modulated by the moving piston of the shock absorber. 
A still further embodiment of the invention provides for an ultrasonic 
emitter mounted on the piston of the shock absorber and a reflecting 
element on the bottom of the shock absorber. Reflected sound is processed 
for providing an indication of the position of the piston relative to the 
bottom of the shock absorber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the different figures in the drawings, it is to be understood 
that they show, merely as an example, a Mac Pherson strut, but this in no 
way shall restrict the application of the system according to the present 
invention to this particular type of shock absorber. Identical reference 
numbers indicate identical or equivalent parts of the system versions 
illustrated herein. 
FIG. 1 shows an embodiment incorporating a potentiometrical contact. 
A resistance film 2, across which a voltage V is applied, is deposited on 
an inside wall of a work cylinder 1 mounted within the container 1 which 
is closed at its lower end by a closure member 11 of a shock absorber. A 
pick-up slide 3 secured either to a piston rod 4 or to a piston 5 of the 
shock absorber slides along the resistance film 2 and picks up a voltage 
signal V', which changes with the axial position of the piston 5 within 
the working cylinder 1, so that a direct reading of its height from the 
ground may be displayed on a suitably calibrated scale located, for 
instance, on the instrument panel of the vehicle. 
FIG. 2 shows an embodiment incorporating a sensor operating on the 
principle of the well-known Hall effect incorporating a permanent magnet. 
A ring-shaped magnet 7 is secured to the piston rod 4 of the shock absorber 
and a Hall-effect sensor 6 is fixed to the outer face of cylinder 1 which, 
in this case, is made of a nonmagnetic material. The sensor 6 supplies a 
voltage signal, V, modulated according to the axial distance between the 
magnet and the sensor. It is also possible to use more than one magnet 
and/or more than one sensor and to invert their mutual position. 
FIG. 3 shows an embodiment incorporating an eddy current detector. A 
cylindrical coil 10 having a primary winding and a secondary winding 
incorporated into an insulating material is coupled to a 
voltage/frequency, V,f generator and is affixed onto the outer surface of 
the cylinder 1. When the magnetic flux, which is present within the coil, 
is interrupted by a conductive material such as, for example, the piston 5 
moving within the cylinder 1, a decrease in the strength of the 
high-frequency signal across the coil will take place by the action of the 
induced currents. 
By considering the assembly as a transformer, the effects due to the energy 
dissipated by the secondary winding are carried out to the primary winding 
by introducing an equivalent impedance. 
By operating over limited distances and with a suitable calibration range, 
it is possible to obtain a linear relationship between the output voltage 
of the coil and the axial position of the piston 5 within the coil 10. 
Other embodiments incorporating the eddy current-type sensor system are 
also possible. For example, the primary and secondary windings of the coil 
10 can be separated and arranged in a different manner, such as, for 
instance, field coils can be affixed to the cylinder 1 and induced coils 
can be keyed onto the piston rod 4. In any case, the system measures the 
position of the piston and, therefore, the body of the vehicle relative to 
the bottom of the shock absorber. 
FIG. 4 shows the embodiment incorporating an ultrasonic distance detector. 
On the piston rod 4 under the piston 5 there is fitted an ultrasonic 
quartz emitter 8 which sends a reference signal to an acoustically 
reflecting plate 9. A reflected signal returns to the quartz emitter 8 
which also acts as an end instrument and which is coupled to an electronic 
device which receives, recognizes, demodulates, and converts the incoming 
signal into a voltage which is proportional to the distance covered by the 
ultrasonic wave in reaching the reflecting plate 9. 
In all of the above mentioned embodiments, that is, according to FIGS. 1, 
2, 3 and 4 a continuous output signal from the particular sensor varies 
between two values indicating the two extreme position of the wheels with 
respect to the body. 
Moreover, in the embodiment involving the Hall-effect sensor, it is not 
necessary that the sensor exciter consists of a permanent magnet but it 
may be replaced by any means made of suitable magnetic material, as it is 
evident from the further versions of this embodiment, illustrated in FIGS. 
5 to 7. 
FIG. 5 shows a first variation of the embodiment involving Hall-effect 
sensor. On the outer surface of the cylinder 1, which in this case is made 
of nonmagnetic material (e.g. aluminum alloy, stainless steel and so 
forth), there are fixed two Hall-effect sensors 7 capable to provide a 
voltage signal when faced by a magnetized piston 5 or any other magnetized 
material such as 13. When the magnetized piston 5 or the ring 13 passes by 
the sensors 7, signals forming a position reading code of the piston 5 are 
released. 
FIG. 6 shows a second variation of the embodiment involving the Hall-effect 
sensors. Two spark plug formed supports 7' each supporting a Hall-effect 
sensor 7 are fixed to the shock absorber housing 1'; the sensing surface 
of said sensor is facing the nonmagnetic material cylinder 1. The 
operation is the same as that described in relation to the embodiment of 
FIG. 5. When the piston 5 or the ring 13 passes by the sensors 7, signals 
defining a position of the piston 5 are obtained. 
In this case, it is sufficient to drill two holes in the shock absorber's 
outer case 1' to mount the sensors with the evident greatest ease in using 
the system. 
FIG. 7 shows a third variation of the embodiment involving the Hall-effect 
sensors. The sensors 7 can be wall mounted, either inside the shock 
absorber housing 1' on the outer surface of cylinder 1, as shown in FIG. 
5, or screwed into the shock absorber housing 1 as shown in FIG. 6. Both 
sensors 7 sense the eventual presence of the piston rod/piston (4,5) 
assembly in front of them and not just the passage of the piston 5 or the 
ring 13 as in the other variations of the embodiment. The voltage signals 
obtained from sensors 7 define a position of the piston 5. A further 
system variation, also shown in FIG. 7, includes fixing to the piston rod 
4 a cylindrical pierced cage 12 made of magnetic material which permits 
the passage of the oil during the operation of the shock absorber and 
provides the magnetic material mass capable of exciting the sensors 7. 
Such solution can be used when the piston rod is too far from sensors 7. 
It can be seen that the system, according to the present invention, solves 
in a simple manner the problem of fitting the sensors inside the shock 
absorber and offers a wide range of solutions and advantages over present 
techniques. 
The inside construction of the shock absorber provides for placement of the 
sensor in an area protected against accidental impacts and environmental 
conditions. 
The main advantage of the present invention is found in the fact that 
nothing must be added to the vehicle to accommodate the system, no 
fastening areas must be provided and no assembly and adjustment time is 
required. 
It must also be stressed that numerous variations, changes, additions 
and/or modifications may be made and those changes, additions, and 
modifications are to be considered to be within the scope of the appended 
claims.