Device for verifying disturbances in signal transmission in motor vehicles

A device is disclosed which can detect and document tampering in the signal transmission path between speed measurement and/or mileage counting devices and the speed transmitters which are associated with these devices using the simplest possible means and so as to be suitable for large-scale series manufacture. The device provides that at least one movement transmitter, which senses forces which are typical of driving, is arranged inside the respective measurement device, and that an evaluating circuit is also provided, which delivers a signal which controls a recording arrangement when signals of a speed transmitter do not correspond with those of the movement transmitter.

FIELD OF THE INVENTION 
The present invention pertains to a device for verifying disturbances in 
signal transmission in motor vehicles, and in particular, the signal 
transmission which occurs between speedometers and/or mileage counters and 
speed (rate of rotation) transmitters which are arranged external to these 
devices and are accompanied by the use of a recording arrangement. 
BACKGROUND OF THE INVENTION 
It is well known that the data which is determined and recorded by 
tachographs and the like devices, which are installed in motor vehicles, 
is valuable insofar as it serves to clarify traffic accidents, to 
determine the type and extent of the use of a vehicle, and to verify the 
work times and the rest periods for the driver who is employing the 
vehicle. This necessarily entails the risk that the recordings of these 
devices may be altered for fraudulent purposes or that attempts may be 
made to prevent these recordings. On the other hand, there is also the 
problem of verifying that the power supply of the respective devices, or 
the associated signal transmission, may have been tampered with. There are 
many opportunities for tampering, especially since the speed transmitter 
is externally situated and is connected with the respective devices via 
electrical lines and plug-in connections. 
In order to verify interruptions in the operating voltage, which result in 
a compression of the driving time, and which may be effected, for 
instance, by means of a flasher or a windshield wiper interval timer, so 
as not to be recognized immediately as tampering, it is known to provide a 
storage circuit, which records a mark, which is atypical of driving, e.g. 
a radial line over the entire speed recording field in conventional 
tachographs, when the operating voltage is switched on again. 
Further, it is also known to effect the signal transmission twice and to 
transmit an inverted signal sequence of one and the same speed transmitter 
via a second signal line. An Exclusive OR gate, located on the device 
side, serves as an evaluating or recognition circuit which, in the case of 
a tachograph recording on diagram charts, controls the speed recording 
member during a disruption in the signal transmission, in such a manner, 
that it is deflected in a defined manner and records a bar chart if the 
disturbance persists. 
This known device may verify whether or not the speed transmitter is 
completely severed, whether one of the transmitter lines is interrupted or 
short-circuited with other lines, or whether the power supply of the 
transmitter is interrupted. To this extent, this device also offers a 
relatively reliable self-monitoring of the speed transmitter, including 
the signal lines and contacts. 
In spite of the above, however, there are known methods of tampering with 
these devices which cannot be detected by the devices described above 
since they meet the conditions of phase inversion. In other words, they 
simulate an orderly operation of transmitter and signal transmission. In 
this manner, the work time codes which are applicable to commercial 
transportation, and which are often ignored in this highly competitive 
branch of industry, may be circumvented. In particular, adherence to 
prescribed rest periods may be falsified or, in the case of taxis or 
rental cars, illegal trips may be made without any mileage record. Another 
known practice is the simulation of a speed chart, which makes it possible 
to exceed legally prescribed speed limits without detection. 
SUMMARY OF THE INVENTION 
The present invention provides a device for verifying disturbances in 
signal transmission in motor vehicles which overcomes the shortcomings in 
the prior art. The object of the present invention is therefore to detect 
previously undetectable disruptions in the signal transmission and signals 
which do not correspond to the driving record while employing means which 
are as simple as possible and which are suited for large-scale series 
production. 
The device of the present invention provides that at least one movement 
transmitter, which senses forces which are typical of driving, is arranged 
inside a respective measurement device and that an evaluating circuit is 
provided, which delivers a disturbance signal which controls a recording 
arrangement when signals of the speed transmitter do not correspond with 
those of the movement transmitter. 
A preferred embodiment which specifically relates to tampering is 
characterized in that, in order to verify the disruption of signals from 
the speed transmitter, the evaluating circuit delivers a disturbance 
signal when a pulse of the movement transmitter, which is stored in the 
evaluating circuit, is not canceled by a pulse of the speed transmitter 
after a determined period of time has elapsed. 
The evaluating circuit of this embodiment contains a flip-flop stage, the 
set input of which is associated with the movement transmitter and the 
reset input of which is connected with the signal input of the speed 
transmitter on the device side. A timer is also provided which is 
controllable by the pulses of the movement transmitter and the output of 
which is linked with the output of the flip-flop stage via an AND 
operation. 
The solution which is proposed by the present invention provides the 
advantage that previous measures for verifying disruption may be dispensed 
with and that only one signal line may be required for the speed 
transmitter. The disruption of signals from the speed transmitter may be 
adequately detected by an evaluating circuit, which is of a simple 
construction, and one or more movement or acceleration transmitters, which 
may be of relatively simple construction and which, in order to filter out 
engine vibrations, shaking when loading and unloading, or vibrations which 
may be caused by getting into and out of the vehicle, are designed for 
detecting longitudinal and/or transverse accelerations, which are in turn, 
typical of driving and which further operate substantially in any one of 
the possible installation positions in the respective motor vehicle 
devices. 
If the respective motor vehicle device is outfitted with a microprocessor, 
the evaluating program may be carried out with the microprocessor and a 
recording may either be written into a data storage device, which may also 
be available, and/or made in legible form such as, for example, on the 
diagram chart of a tachograph. If a buffer battery is provided, which may 
exist in certain devices, such as, for example, in fare calculators, the 
verification of the disruption or tampering may also be ensured in the 
event of disruptions of power at least with an electronic recording. 
Moreover, the electronic recording is suitable particularly for mileage 
counters which are provided for the mileage-dependent taxation of motor 
vehicles insofar as wheel revolution counters, which may be arranged on 
the wheel hub of the vehicle, may not be utilized for this purpose. This 
practically rules out tampering. 
Accordingly, it is an object of the present invention to provide a device 
for verifying disturbances in signal transmission in motor vehicles which 
detects previously undetectable disruptions in the signal transmission and 
signals which do not correspond to the driving record while employing 
means which are as simple as possible and which are suitable for 
large-scale series production. 
It is another object of the present invention to provide a device for 
verifying disturbances in signal transmission in motor vehicles which 
provides that at least one movement transmitter, which senses forces which 
are typical of driving, is arranged inside the respective measurement 
device and that an evaluating circuit is provided, which delivers a 
disturbance signal which controls the recording arrangement when signals 
of the speed transmitter do not correspond with those of the movement 
transmitter. 
It is another object of the present invention to provide a device for 
verifying disturbances in signal transmission in motor vehicles which 
provides for the advantage that previous measures for verifying 
disruptions may be dispensed with and that only one signal line may be 
required for the speed transmitter. 
It is yet another object of the present invention to provide for a device 
for verifying the disturbances in signal transmission in motor vehicles so 
as to practically rule out tampering. 
Other objects and advantages of the present invention will be made apparent 
to those persons skilled in the art upon a review of the Description of 
the Preferred Embodiment taken in conjunction with the drawings which 
follow.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates an overview of a signal transmission situation between a 
speed transmitter and a tachograph. The overview in FIG. 1 illustrates 
that the speed transmitter 1 is arranged so as to be spatially separate 
from the device, which is in this instance, a tachograph 2 which counts 
and/or records the detected speed values and is connected with the latter 
via a cable 3. The transmitter housing 4, which is generally 
sleeve-shaped, is flanged on a wall 5 of the transmission casing of the 
motor vehicle in a conventional manner. The measuring head 7 of the speed 
transmitter 1, which projects into the transmission space 6, cooperates 
with a ferromagnetic clock wheel 8, which is provided on the transmission 
side, while a connector cap 9, is arranged at the opposite side of the 
transmitter housing 4. 
A plug-in connector 10, which is formed on one end of the cable 3, may be 
connected with the connector cap 9 by means of a union nut 11 which is 
sealed. A plug-in connector 12 is provided at the opposite end of the 
cable 3 and may be connected, in a locking-manner, into a suitable 
connector socket 14 which is constructed at the rear wall of the housing 
13 of the tachograph 2. This plug-in connection must also be sealed. 
The arrangement shown in FIG. 1, however, illustrates that devices, which 
are arranged in or around the dashboard, are generally weak points which 
invite tampering, especially since plated cables may not be utilized 
because of cost reasons. Since these weak points are located in areas of 
the motor vehicle which are not easily accessible, more subtle and brief 
tampering may not be easily detected, at least not by random control 
measures, such as by traffic control. 
For the sake of completeness, the tachograph 2 of FIG. 1 is described in 
more detail below. Referring once again to FIG. 1, the tachograph 2 
includes a display 15, a slot 16, keys 17 and 18, which are assigned to 
the driver and which automatically record the driving time of the 
respective driver when actuated, and a keyboard 19, all of which elements 
are visible on the front of the tachograph 2 of FIG. 1. Diagram charts, 
which serve as recording media, may be inserted or removed via the slot 
16, or a printed document, which contains driving and work time data, may 
be fed out of the tachograph 2 if such a design is desired. Keys 20 and 21 
of the keyboard 19 serve to switch on the driving times and the rest 
periods, respectively, of the respective driver, on the display 15. Keys 
22 and 23 control the insertion and the removal of a diagram chart. 
As can be seen from FIG. 2, the transmitter 1, which may be a magnetic 
field transmitter, supplies a determined pulse count/mileage unit to at 
least one signal line of the cable 3 by tapping the transmission of the 
vehicle. The cable 3 may have a second signal line and, in addition, may 
contain lines for the power supply of the transmitter. These pulses, the 
frequency of which changes with the driving speed, are shaped in a 
determined pulse duration and are amplified by a pulse shaper 24 which is 
located in the tachograph 2 and which is available simultaneously at the 
frequency-voltage transformer 25 of a speed measurement circuit 26, at the 
frequency transformer 27 of a mileage counter circuit 28, and at an 
evaluating circuit 29. 
The speed measurement circuit 26 is typically a control amplifier which 
triggers a servomotor 30 with a speed-proportional d.c. signal. The 
servomotor 30, in turn, serves to follow-up the speed recording means and 
the adjustment of the display means in the event that the respective 
tachograph is outfitted with an indicator display. A comparison circuit of 
the control amplifier is designated by the reference numeral 31, while a 
control circuit, which is associated with the servomotor 30, is designated 
by the reference numeral 32. A potentiometer 33 transforms the actual 
value of the position of the servomotor 30, which is to be fed back to the 
comparison circuit 31, into a d.c. voltage. A stepping motor 35, which 
drives a mileage counter (not shown), and a mileage recording member of 
the tachograph 2, is controlled by the control circuit 34 of the mileage 
counting circuit 28. 
The evaluating circuit 29 is connected with both the speed transmitter 1 
and the movement transmitter 36, the signals of which are preferably 
signals which are based upon the longitudinal and/or the transverse 
accelerations of the vehicle, and which are transformed into pulses of a 
defined duration in a shaping and amplifying circuit 37 so as to suppress 
overshooting or bouncing of the movement transmitter 36. As is also shown 
in FIG. 2, a mono-flop 38 is controlled by the output signal of the 
evaluating circuit 29 which may be a disruption pulse. The mono-flop 38 
supplies a voltage to the comparison circuit 31 via a circuit element 39 
by the parallel connection of a resistance to the potentiometer 33, the 
voltage of which corresponds to the recording stroke which is provided for 
recording the disturbance and, accordingly, to the rotational angle of the 
servomotor 30 which is required for this purpose. In this manner, the 
disturbance is recorded by the speed recording member. 
An additional recording member, which is provided only for recording 
disruptions, may also be triggered. An exclusive or an additional storage 
of the disturbance is also envisioned, wherein real-time data entries, 
which are supplied by a timer 41, may be written into a data storage 
device 40 in order to characterize the disturbance. An accumulator 42 
serves as a buffer for the detection of an electronic disturbance. 
Further details of the evaluating circuit 29 are illustrated in FIG. 3. In 
FIG. 3, a frequency transformer 43, which is provided at the input side, 
is connected with the reset inputs of two flip-flop stages 44 and 45. The 
flip-flop stage 44 serves to store a pulse of the movement transmitter 36, 
which occurs on the line 46, while the flip-flop stage 45 serves to 
suppress the first disturbance pulse, which is advantageous, particularly 
in the event of sudden stops which may be due to traffic conditions when 
the movement transmitter 36 is not sufficiently cushioned. When a pulse of 
the movement transmitter occurs on the line 46, a mono-flop 47 is 
activated and sets the flip-flop 44, via the NOT circuit 48 and the NAND 
gate 49. When the frequency transformer 43 delivers a transmitter pulse 
within the time period, which is predetermined by the mono-flop 47, and 
which, for example, is typically 8 seconds, the flip-flop 44 is reset. For 
example, when the potential changes at the mono-flop 47, upon the 
expiration of the switching time, the AND condition is no longer met for 
the NAND gate 50, which is located at the output of the evaluating circuit 
29, and the output of a disturbance signal is prevented. Conversely, a 
disturbance signal is supplied by the evaluating circuit 29 when a 
resetting of the flip-flop 44 is not effected within the switching time of 
the mono-flop 47 and the flip-flop 45 is already set by a previous cycle. 
For the sake of completeness, it is also noted that, when a disturbance is 
recorded on a diagram chart, the pause between the two disturbance 
signals, which result from the mono-flop 47, in connection with the 
flip-flop 45, enables a sufficiently dense bar recording and prevents the 
risk of writing through. This also helps to keep the power consumption and 
the stress on the recording system as low as possible. 
While the present invention has been described in a preferred embodiment, 
such description is merely illustrative of the present invention and is 
not meant to be a limitation thereof. In this regard, the present 
invention encompasses all modifications, variations and/or alternate 
embodiments with the scope of the present invention being limited only by 
the claims which follow.