GB1587955A

GB1587955A - Circuit arrangement for measuring speed and distance travelled particularly for tachographs

Info

Publication number: GB1587955A
Application number: GB37547/77A
Authority: GB
Original assignee: Kienzle Apparate GmbH
Current assignee: Digital Kienzle Computersysteme GmbH and Co KG
Priority date: 1976-10-23
Filing date: 1977-09-08
Publication date: 1981-04-15
Also published as: JPS574709U; SE423460B; DE2648021C3; FR2368717A1; DE2648021A1; JPS5381172A; FR2368717B1; DE2648021B2; SE7711852L; JPS6033367Y2

Description

(54) CIRCUIT ARRANGEMENT FOR MEASURING SPEED AND DISTANCE TRAVELLED PARTICULARLY FOR TACHOGRAPHS (71) We, KIENZLE APPARATE GMBH, a German Body Corporate of Villingen-Schwenningem Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a circuit arrangement for measuring the speed and measuring the distance travelled, particularly in tachographs, the circuit comprising a pulse generator, a pulse shaper, a frequencyvoltage converter serving to measure speed and a frequency converter to provide a measurement of distance travelled.

Tachometers and tachographs are a special kind of apparatus since it is their purpose on the one hand to indicate and record speed and on the other hand to measure distances.

To obtain the desired output data the mechanical or electrical analogue values representing an angular motion or the electrical pulses representing a distance as they are produced by a suitable generator require to be processed.

For instance for electronically representing speed proportional values a certain number of pulses per distance unit must be transmitted and so that when the speed is low, the speed indicator is kept sufficiently steady and that not too many electronic parts are required. Such high minimum frequencies as are required for measuring speed, however, are rather unsuited for distance measurement for this purpose such high pulse frequency is not required. It is sufficient if one pulse per 100 metres is given. In order not to be forced to use an additional generator for the distance counting it is therefore necessary to reduce the pulse frequency delivered per distance unit by a motor or by some other kind of magnetomechanical driving means to drive the distance counter.

With conventional apparatus it is usual to fix a driving constant for simplicity, that is, a definite input number of revolutions or a definite number of pulses per distance unit as the normal input constant to which the apparatus is adjusted. On the other hand, of course, it is necessary to have adapting means to be coupled to such apparatus in order to take care of various coupling conditions due to the many types of vehicles. Of course, the number of revolutions for each distance unit depends on the kind of vehicle (the so-called distance constant) and may be taken off at a position between the vehicle wheel and the motor which is mostly only accessible to the vehicle producer. Also it is possible that for one type of vehicle varying sizes of the tires have to be taken in consideration or that problems may arise due to the nature of type of pulse generator or generators installed in the vehicle. Under all these conditions it must be possible to adapt the input constant of the apparatus to the actual numbers of revolution delivered at the gearing output.

A known pulse operated measuring and counting system comprises a pulse reduction circuit to reduce the pulses of the generator delivered per distance unit in a definite fixed ratio for controlling the distance counter. To adapt this counting system for instance because of a different diameter of the tires it is usual to exchange toothed wheels in the adaptation gearing which is arranged between the driving motor and the distance counter. To adapt this same system with respect to speed measuring the pulse width of the generator pulses is modified. In the other case when such a measuring and counting system is provided with two pulse generators one for the speed measurement and the other one for the distance counting the adaptation is normally effected in that toothed wheels in the gearing driving the pulse generators are exchanged as this is usual where a purely mechanical transmission of the measured values is effected.

A mechanical adaptation of this kind by exchanging toothed wheels is highly unsatisfactory in connection with a measuring process which is otherwise almost completely electronic. Apart from that it is possible that for the same apparatus several adaptations have to be carried out which differ from each other and which are to be achieved at different places. This is particularly unsatisfactory where the adaptation has to be effected at the pulse generator and where this pulse generator is mounted in remotely accessible corners and angles of the vehicle gearing housing. Apart from that an adaptation by exchanging toothed wheels can only be realised in steps although the most favourable combination of toothed wheels may have been chosen to achieve as close an approach to the required reduction ratio as possible.

This means high expense in production and in mounting and also organisational problems for keeping available the most suited combinations of toothed wheels, errors in measurement being still relatively high.

It is therefore the aim of the present invention to improve the adaptability of a speed measuring and distance measuring system.

insertable particularly in tachographs. with respect to varying vehicle or transmitter conditions but, in particular, to avoid high cost and to provide an advantageous spatial arrangement of the adapting means.

It is realised that a direct proportionality exists between the width or length of the generator pulses and the measured quantity of the speed formed in the frequency-voltage converter of the speed measurement circuit.

on the one hand. as well as between the width of the generator pulses and the division ratio formed in the frequency converter of the distance measuring system, on the other hand.

According to the invention we provide a circuit arrangement for measuring speed and distance travelled. especially for use in a tachograph, the arrangement comprising a pulse generator providing a predetermined number of pulses per unit distance travelled, a pulse shaper, a frequency-voltage converter providing an output to means for measuring the speed and a frequency converter providing an output to means for measuring the distance travelled, wherein both the frequency-voltage converter and the frequency converter are circuits which are linked in parallel with the output of the pulse shaper which is provided with means for changing the pulse width. the conversion coefficients of the frequency-voltage converter and of the frequency converter being dependent on the product of the pulse repetition frequency and the pulse width of the pulses from the pulse shaper.

An exemplified embodiment of the invention is characterised in that the pulse shaper, the frequency converter and a servoamplifier incorporating the frequencyvoltage converter are integrated into a circuit group that is insertable into the tachograph and in that a potentiometer is used as the means for changing the pulse width.

A preferred embodiment of the invention allows, by the actuation of a single component, for example a variable resistor. both the speed measuring system and the distance measuring system to be simultaneously adapted, and this within a relatively wide range of possible pulse numbers/distance unit. The adaptation operation can be performed directly on the tachograph without the need for any assembly operations. The adjusting work is thus substantially simplified. Furthermore, no special conditions are laid down with respect to the attachment of the pulse generator and the part with which it is associated, and thus the vehicle manufacturer can attach the pulse generator at a point suitable for it. and for example inaccessible from the outside. within the gearbox housing.

In the following one embodiment of the invention shall be explained with reference to the enclosed drawing: In the drawing a pulse generator 1 may be seen which is mounted in suitable manner in the vehicle so that it is driven in dependence on the distance covered and so that a definite number of pulses per distance unit is produced and delivered to line 2, the pulse shape and period of the pulses being of no concern.

Pulses delivered by pulse generator 1. the frequency fe of which naturally changes with the speed, are introduced into a pulse shaping circuit where they assume a certain pulse width by means of the RC members 4. 5 and 6. These pulses are then delivered with the frequency fe' simultaneously to the inputs of a speed measuring circuit 7 and of a frequency converter 8. the speed measuring circuit 7 comprising essentially an amplifier provided with a frequency-to-voltage converter which forms the output value A as a speed proportional voltage signal of direct current. By means of this direct current voltage a setting motor 9 is controlled which serves to adjust the speed indicator and in the case of a tachograph also to the adjustment of the speed recording means. Frequency converter 8 which normally delivers a reduced frequency fs as compared with the pulse generator frequency fe controls for instance a step switch motor 10 which on its part actuates the distance recording means of the tachograph and/or the distance counter.

As an example let it be assumed that the input constant for the distance counting is 1 pulse metre. This would mean that the pulse delivered by the frequency converter 8 should be sufficiently wide to control the step switch motor 10 when the vehicle travels at the highest possible speed. One can think of arranging a pulse generator for the speed measurement which produces for instance 8 pulses/rev. of the generator driving shaft.

With an input constant of "1", that means one revolution of the driving shaft per metre distance, would deliver eight pulses per metre and this range would cover most of the usual values required.

Under the assumed conditions there is a fixed reduction ratio of 8 1 which has to be adjusted via a frequency converter 8 by means of the variable resistor 11. By means of this adjustment the loading current supplied by each input pulse to an integrator (not shown) in the converter 8 is controlled and thereby also the number of pulses is controlled until a certain switching value is reached. After adjustment the variable resistor 11 can be secured against being operated.

Before this is done the speed measuring circuit 7 has to be adjusted to the ratio assumed (8 pulses/metre). In this case adjustment of the speed measuring circuit 7 is performed by adjusting finely variable resistor 6 and variable resistor 12. A rough adjustment of the measuring range may be effected by varying the capacitor 4.

By means of a testing device the number of pulses fe is checked. It may be in a range between 3 to 25 pulses/metre. The deviation from the standard (8 pulses/metre) may be due to the fact that the apparatus is adjusted to another input constant and/or that the pulse generator 1 produces more or less pulses/revolution. An adaptation is therefore required which is carried through by means of the finely adjustable potentiometer 6 which modifies the pulse width t. For a number of pulses/meter < "8" the pulse width t has to be increased and for a number of pulses/metre > 8 it has to be decreased so that the current - time - integral of the pulses/metre (x + Ax)t always assumes the same value. since the output value A as well as the ratio fe/fs are a linear function of t the distance counting and the speed measurement is automatically adjusted when the variable resistor 6 is set.

It will be apparent that the wider the impulses fe' at the output of the pulse former 3. the fewer impulses will be required to obtain the switching threshold in the frequency converter and the fewer impulses will also be required to obtain the switching threshold in the frequency converter and the fewer impulses will also be required to obtain the mean charging value established for a certain particular speed. Both parts of the circuit supply output values which are dependent on the pulse widths. or in other words, both parts are capable of being influenced by altering the charging quantities supplied.

If we assume that a tachograph has already been calibrated at the manufacturer's works i.e. that the frequency voltage converter and the frequency converter have been adjusted to a fixed number of pulses per metre, e.g. 8 pulses per metre, and have also been sealed.

then if the number of generator impulses per metre in the vehicle in which this tachograph is to be installed is greater than the calibration values of the tachograph the two branches of the circuit will be supplied with the same excess quantity of charge. This increased amount of charge can be reduced by actuating the potentiometer 6. i.e. the width and the duration of the impulses will be reduced, until the current-time area of the new number of pulses per metre is once again in accordance with the calibration value given on the tachograph.

WHAT WE CLAIM IS: 1. A circuit arrangement for measuring speed and distance travelled, especially for use in a tachograph, the arrangement comprising a pulse generator providing a predetermined number of pulses per unit distance travelled, a pulse shaper, a frequencyvoltage converter providing an output to means for measuring the speed and a frequency converter providing an output to means for measuring the distance travelled.

wherein both the frequency-voltage converter and the frequency converter are circuits which are linked in parallel with the output of the pulse shaper which is provided with means for changing the pulse width, the conversion coefficients of the frequency-voltage converter and of the frequency converter being dependent on the product of the pulse repetition frequency and the pulse width of the pulses from the pulse shaper.

2. A circuit arrangement as claimed in claim 1. wherein the pulse shaper, the frequency converter and a servo-amplifier incorporating the frequency-voltage converter are integrated in a circuit group which is insertable into a tachograph and a variable resistor is used as the means for changing the pulse width.

3. A circuit arrangement for measuring speed and distance travelled substantially as described herein with reference to and as illustrated by the accompanying drawing.

4. A circuit arrangement for measuring speed and distance travelled as claimed in claim 1, substantially as hereinbefore described.

5. A tachograph incorporating the arrangement as claimed in any preceding

Claims

claim.