Acceleration pickup

An acceleration pickup has a housing of a diamagnetic or paramagnetic material enclosing a ferromagnetic ball acting as seismic mass. The ball is held in a starting position on the bottom of the housing by means of a magnetic field generated by a permanent magnet or an electromagnet. By means of four induction sensitive sensors such as for example Hall effect sensors arranged opposite each other on the circumference of the housing, the momentary value and direction of acceleration component acting on the pickup is determined. The acceleration pickup is simple in construction and cost effective in manufacture and is easily adjustable to different applications.

BACKGROUND OF THE INVENTION 
The present invention relates to an acceleration pickup for use in antislip 
regulation or similar control systems in a motor vehicle. 
In conventional pickups of this kind acting in two dimensions a spring-mass 
system is employed. From deviation of the mass under the influence of 
acceleration against the biasing force of the spring the momentary 
acceleration in two directions can be determined. In doing so, a 
Hall-effect sensor is excited by means of a permanent magnet whereby a 
precise mechanical adjustment of zero position must be guaranteed. 
In acceleration pickups acting in a single direction only it has been known 
to fix the seismic mass by means of a magnet. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an acceleration sensor 
acting in two dimensions whereby the mechanical zero position or starting 
position of the seismic mass (a ball for example) can be reliably adjusted 
by simple means. 
Another object of this invention is to provide such an improved 
acceleration pickup in which the magnetic attraction force holding the 
ball in its starting position is independent of direction. 
Another object of this invention is to reliably detect horizontal 
acceleration components from all directions in a horizontal plane of a 
motor vehicle. 
Still another object of this invention is to reduce frictional forces 
acting on the seismic mass (ball). 
An additional object of this invention is to make the acceleration pickup 
unsensitive against shocks resulting for example during the drive over 
potholes or other unevenness of the driveway. 
A further object of this invention is to provide an improved adjustability 
of the holding force of the seismic mass in its starting position. 
Furthermore, an object of the invention is to provide an acceleration 
pickup which is almost independent of aging, temperature and power supply 
interferences. 
In keeping with these objects and with which will become apparent 
hereafter, one feature of this invention resides in the provision of a 
housing of a paramagnetic or diamagnetic material in which a ferromagnetic 
body is movably arranged, the body being held in its starting position by 
means of a magnetic field. The housing is fixedly secured in a motor 
vehicle. Upon sudden vehicle acceleration, i.e. as a result of a traffic 
accident, the housing will move with the vehicle in the acceleration 
direction. Because of its inertia the body is freely movable relative to 
the housing in opposite direction to a horizontal acceleration component 
acting on the pickup. As a result the body deforms the magnetic field such 
that induction sensitive sensors arranged around the plane of movement of 
the body detect the changes of the magnetic field and thus determine 
momentary values and directions of the acceleration component. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the figures, there is illustrated an acceleration pickup 11 assembled of 
a cup-shaped housing 10 closed by a plate 12. The housing 10 and the plate 
12 are of a diamagnetic or paramagnetic material. In the center of the 
bottom 13 of the housing a seismic mass in the form of a ferromagnetic 
ball 14 is normally held in a fixed starting position by a permanent 
magnet 15. The magnetic field 16 of the permanent magnet 15 polarizes the 
ferromagnetic ball 14 and holds the same in the center starting position. 
The diameter of the ball 14 is slightly less than the height of the 
housing 10. As is shown in FIG. 3, four induction sensitive sensors 17, 
18, 19 and 20 are fixedly arranged at the outer surface of the jacket of 
the housing 10 and the sensors are spaced apart by an angle of 90.degree. 
. Each pair of diametrically opposed sensors 17, 18, and 19, 20 is 
connected to a differential input circuit of an assigned operational 
amplifier 23 or 24 where the signals from respective sensor pairs are 
subtracted. In a modification, the sensors 17 through 20 can be connected 
in a Wheatstone bridge circuit. 
Referring to FIG. 2, if an acceleration component a acts on the pickup 11 
in the direction indicated by arrow extending parallel to the plan of the 
bottom 13 then due to inertia of seismic mass of the ball 14 the relative 
position of the ball and the housing is changed and position of the ball 
is moved in counterdirection toward a housing wall. At the same time the 
magnetic field 16 is deformed in the direction of the relative movement of 
the ball 14 as seen from FIG. 2. This deformation causes a change in the 
distribution of the magnetic field 16 in the plane which is delimited by 
the sensors 17 through 20. 
It will seen from FIG. 3 that any arbitrary direction of acceleration can 
be detected inasmuch as the vector a of the acceleration component can be 
defined by corresponding coordinates a.sub.x and a.sub.y. In this example, 
the x-axis is the connection line of sensors 19, 20 and the y-axis is the 
connection line of sensors 17, 18. The coordinates a.sub.x and a.sub.y of 
the acceleration vector a are determined by voltage of frequency of 
signals detected at respective sensors. Inasmuch as the sensor pairs 17, 
18 and 19, 20 are connected to a differential input circuit of operational 
amplifiers, it is possible to determine not only the value but also the 
direction of the momentary acceleration vector a. For example if the 
relative movement of ball 14 is toward the sensor 20 (FIG. 2) then the 
signal S.sub.2 at sensor 20 is increased by a certain amount whereas the 
signal S.sub.1 at the sensor 19 is diminished by the same amount. When the 
signals S.sub.1 and S.sub.2 of the two sensors 19, 20 are subtracted in 
the operational amplifier 24, the difference of the two signals determines 
the coordinate value a.sub.x of the acceleration component in the 
direction of the x-axis. Similarly, the coordinate a.sub.y is determined 
from the signals of sensors 17, 18 and from the ratio of the a.sub.x and 
a.sub.y coordinates the direction of the acceleration component can be 
determined. Through the differential input circuit for the signals from 
the sensors interferences caused by aging, temperature and operational 
voltage variations can be eliminated. By means of the acceleration pickup 
of this invention both analog as well as digital signals can be processed 
with a high degree of integration suitable for a microcomputer technology. 
For example, if the housing is made of ceramic or of a monolithic crystal 
then both mechanical as well as electronic components can be integrated 
into a single structural module. 
If instead of the permanent magnet 15 an electromagnet 16 is used then the 
magnetic field 16 is readily adjustable to a desired level of received 
signals. By means of an electromagnet the density of the magnetic field 16 
can be adjusted at any time such that a predetermined measuring range of 
the acceleration pickup is easily set. Alternatively, the measuring range 
of the acceleration pickup can be adjusted by changing the seismic mass or 
the permeability or magnetic inductivity of the material of the ball. 
The sensors 17 through 20 can be of any conventional type of inductive 
operating sensors known from prior art. As particularly advantageous 
sensors however are Hall-effect sensors. 
As known, when the ball 14 is subject to a jarring movement during the 
drive of the vehicle or due to free vibrations after deflection, then the 
mass of the ball may be brought into the so-called natural vibrational 
mode which may interfere with the measurement. In order to damp this 
natural oscillation, the housing 10 is filled with a liquid 25 of a high 
viscosity which damps the natural vibrations of the ball 14. 
Alternatively, the natural vibrations of the ball can be damped by eddy 
currents. For this purpose, a coil 13a, is arranged in the bottom 13 of 
the housing 10 in the area of the starting position of the ball. The coil 
is supplied with a high frequency alternating current to induce the 
damping eddy currents. 
The acceleration pickup of this invention is particularly suitable in 
antiblocking systems or in antislip systems of a motor vehicle. In both 
systems it is necessary that the detection of the momentary acceleration 
component be in two directions. In addition, it is required that the 
pickup be insensitive to vertical shocks. 
While the invention has been illustrated and described as embodied in a 
specific example of the acceleration pickup, it is not intended to be 
limited to the details shown, since various modifications and structural 
changes may be made without departing in any way from the spirit of the 
present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of the invention.