GB2277379A - Electrical odometer with controlled motor torque - Google Patents

Description

- I- r 2277379

-1DESCRIPTION ELECTRICAL ODOMETER WITH CONTROLLED MOTOR TORQUE

The present invention concerns an electrical odometer of a type including a speed information sensor, means for transmitting this information to a display geared motor, such as to control the motor rotation,,and a set of display cylinders driven by the motor.

An odometer, or mileage indicator, makes it possible to display, by means of adjacent coaxial cylinders bearing figures, the distance travelled by a vehicle on land. The pertinent information is supplied by a sensor located at the output from the gearbox, and each cylinder rotates, under the control of a stepping motor, at an average speed which depends on this information and its relative position with respect to the other cylinders, that is to say the "weight" of the unit of measurement which it presents.

When it advances by one step, the motor drives a set of gears and the driving gear of the set of gears comes abruptly into contact with the driven gear which drives the cylinders. An annoying click results, all the more so since rebounds may occur, and a severe mechanical stress is incurred which fatigues the material of the set of gears.

The present invention aims to mitigate this -2drawback.

To this end, it provides an electrical odometer of the type mentioned above, in which the control means includes means for controlling the acceleration of the motor.

It is thus possible to reduce the transitions of the driving torque of the geared motor and greatly attenuate the noise and mechanical vibrations.

Advantageously, the means of controlling the acceleration include a shaping circuit connecting the sensor to a circuit controlling the motor and controlling its acceleration.

The acceleration may thus be regulated by an appropriate choice of the excitation transmitted to -the motor.

Advantageously again, the motor control circuit includes a transistor connected in series with a coil controlling the motor, the current of which is controlled by the shaping circuit.

The transistor makes it possible to establish and then progressively shut off the current in the coil. It will be noted that the absence of any abrupt transition in the coil eliminates the overvoltages normally appearing in an inductor, such as this coil, when the current flowing therein can no longer flow outside, and that it is therefore no longer necessary 1 -3to provide components for protecting against such overvoltages. Likewise, the voltage strength of the coil control components may be limited to the value of the supply voltage of the coil.

Still advantageously, the shaping circuit can include a low-pass filter.

It is thus possible, with a few simple components. to create, from the speed signal, the desired waveform for controlling the transistor.

It is in particular useful that the shaping circuit includes an operational amplifier arranged so as to control the transistor according to the speed information from the sensor.

It is in particular possible to produce a buffer amplifier connecting, to the coil, a part of the circuit shaping the speed signal, whilst inhibiting any return of a perturbation coming back from the coil to the shaping circuit. It is also possible to effect all or part of the shaping with the amplifier which, because of its low output impedance, strongly attenuates any perturbation originating from the coil.

Provision can be made for the means of controlling the said acceleration to include a memory containing a table of numerical values defining this acceleration.

It is then possible to be rid of the physical -4limitations due to a low-pass filter and create, in a software fashion, any desired waveform.

The invention will be understood better by means of the following description of the preferred embodiment of the odometer of the invention, which is explained, by way of example only with reference to the accompanying drawing, in which:

Figure 1 is an electrical diagram of the shaping and control circuit of an odometer in accordance with the invention, and Figures 2 to 4 illustrate the shape of pulses controlling the geared motor of this odometer.

The odometer of the invention is, in this case, housed in the instrument panel of a car, and it includes a shaping and control circuit 1 controlling a coil 11 ofa geared motor including a stepping motor 10 driving display cylinders 12 of a revolution counter for the car engine. Three other similar circuits (not shown) control three other coils of this motor, fed, like the coil 11, by a battery DC voltage 13.

A sensor 14 for the speed of rotation of the car engine, situated at the output from the gearbox and taking account of the gear ratio used, supplies, by means of a link 15, through a microcontroller 16, pertinent information on the instantaneous speed of -5the car. This information appears in the form of a speed signal 2 consisting of rectangular voltage pulses 20, the amplitude V2 of one of which is shown as a function of the time t on the X-axis in Figure 2, of predetermined amplitude and duration, and the input frequency of which is proportional to the speed of the car.

The pulses 20 of the signal 2 are applied, at the input to the circuit 1, to a terminal of a range multiplier 3 forming, with a parallel capacitor 4 connecting the other terminal of the resistor 3 to earth, a first-order low-pass filter. A resistor 5 is provided here, in parallel with the capacitor 4, the role of which is explained below.

The voltage at the terminals of the capacitor 4 is applied to the positive input of an ope rational amplifier 6 controlling, through its output, the base of an npn transistor 7, the collector of which is connected to the end of the coil 11 opposite to the end receiving the battery voltage 13.

The emitter of the transistor 7 is connected to the negative input of the amplifier 6 and to a terminal of a resistor 8 connected to earth through its opposite terminal, so as to form a current generator.

The functioning of the odometer will now be explained.

A rectangular pulse 20 of the signal 2 is filtered by the low-pass filter 3, 4, 5, the resistor serving, if necessary, to regulate the time constant T of the filter in accordance with the formula:

T = (3) A _151 x (4) - (3) + (5) where the figures in parentheses represent the value of the components given these reference numerals.

The ratio (5) / [ (3) + (5)] determines the attenuation of the filter.

The output voltage V of the amplifier 6 is marked 21 in Figure 3 and the collector current I of the transistor 7 is marked 22 in Figure 4. the time t -being on the X-axis.

The output voltage 21 and the collect-or current 22 vary according to an established law of (1 - e -t/T) during the pulse 20 and, thereafter, according to a falling law of (e -t/T). As is shown in Figure 4, the current 22 changes as the voltage 21. In fact, since T is greater than the time constant of the coil 11, the shape of the curve of the current can be perfectly defined. The driving torque being proportional to the collector current 22 of the transistor 7. the shape of this collector current 22, defined by the low-pass filter 3, 4 and 5, determines -7the change over time of this driving torque and thereby the acceleration of the motor 10 and of the cylinders 12 which it drives.

Components having an equivalent variable resistance, other than the transistor 7, may be used, for example a field effect transistor, r equiring no control current and thus ensuring all the better, through its high input impedance, the absence of any return of perturbations from the coil 11 to the shaping low-pass filter 3. 4, 5.

It will be understood that the regulation of the current 22 passing through the coil 11 may thus be of the parallel type, a transistor mounted in parallel with the coil 11 diverting from the latter a determined and adjustable proportion of a current coming from a source supplying a determine d current.

The given example relates to a shaping of the signal 20 effected by means of a first-order analogue filter. A higher- order filter could be provided, in order to create a signal 21 with a more complex shape.

In addition, the shaping could also be effected by a digital transcoding circuit, which would make it possible to produce, simply, any desired waveform by means of a transcoding table.

In particular, it would then be possible to dispense with the predetermined amplitude of the -8pulses 20 of the speed signal 2, in order to use only the fact that a pulse 20 is present. The leading, or trailing, edge of the pulse 20 would then be used as a synchronisation signal for a sequencer for generating a sequence of readings of successive values of the transcoding table, supplying a sequence of samples of digital vdlues representing the desired envelope shape of the collector current 22. A digital to analogue converter would then convert these digital samples into analogue samples applied to a low-pass filter effecting holding and smoothing between successive s amples and controlling a means of regulating the driving torque, such as the transistor 7.

It will be noted that the transcoding table would make it possible to create, during transitions of the signal 20,-a non-monotonic waveform for the current 22, which would make it possible, if necessary, to compensate accurately for the perturbations, and in particular the oscillations, of the collector current 22 generated by the coil 11.

Advantageously, the digital transcoding circuit could be used for controlling the four coils, sharing time if their respective currents, such as 22, were different or simply offset in phase.

The digital circuit and the converter could be located, in the diagram in Figure 1, at the input to -9the circuit 1, the low-pass filter 3, 4 and 5 then being calculated so as to have a higher cutoff frequency than that of the purely analogue example presented, in order to effect only a smoothing of the signal passing through it.

Finally it will be noted that, as the torque determining the acceleration of the driven gear and cylinders is equal to the difference between the driving torque of the driving gear and the resistive torque of the driven gear, it would also be possible to regulate the acceleration by means of a regulation of the resistive torque, by causing it to decrease progressively at each application of the driving torque, and vice versa when the latter disappeared.

Claims (9)

_10CLAIMS

1. Electrical odometer including a speed information sensor, means for transmitting this information to a display geared motor, means for controlling the motor, and a set of display cylinders driven by the motor, the control means including means for controlling the acceleration of the motor.

2. Odometer according to Claim 1, in which the means of controlling the acceleration include a shaping circuit connecting the sensor to a circuit for controlling the motor and controlling its acceleration.

3. Odometer according to Claim 2, in which the circuit controlling the motor includes a transistor connected in series with a coil controlling the motor and in which the current is controlled by the shaping circuit.

4. Odometer according to Claim 3, in which the transistor is of the field effect type.

5. Odometer according to one of Claims 2 to 4, in which the shaping circuit includes a low-pass filter.

6. Odometer according to any of Claims 3 to 5, In which the shaping circuit includes an operational amplifier arranged for controlling the transistor in accordance with the speed information from the sensor.

a 4

7. Odometer according to Claim 6, in which a resistor in series with the coil of the motor is connected to a feedback input of the operational amplifier.

8. Odometer according to any of Claims 1 to 7, in which said means for controlling the said acceleration include a memory containing a table of numerical values defining this acceleration.

9. An odometer substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.