GB2202629A - Transducer arrangement for a taximeter or a tachograph - Google Patents

Abstract

A transducer arrangementt for driving a taximeter or a tachograph comprises a transducer 5-9 mounted inside the gearbox housing 2 of the vehicle. The transducer comprises an infra-red emitter 6 and a receiver 7 and a rotary shutter 8 attached to the output shaft 10 of the gearbox. The transducer is electrically connected to the taximeter or tachograph to which it supplies a pulse signal representing speed of the vehicle or distance travelled. The infrared emitter and receiver 6,7 and shutter 8 may be replaced by a toothed wheel cooperating with coils wound on magnets, or by moving magnets cooperating with reed switches or Hall effect devices. <IMAGE>

Description

TRANSDUCER ARRANGEMENT FOR TAXI METER The present invention relates to a Transducer Arrangement. Such an arrangement may be used for driving a taxi meter. or in a lorry or other commercial vehicle to supply pulses representing distance travelled to a tachograph which may be of conventional type.

The term "taxi" as used herein is defined to mean any vehicle including a taxi, hackney carriage, and mini cab which is hired for the transport of persons or goods and for which a hire charge is made on the basis, possibly among other factors, of distance travelled.

The term "taxi meter" as used herein is defined to mean any means for calculating, signalling, storing, or indicating distance travelled by or charge for hiring such a taxi.

It is known for taxis to incorporate mechanically operated taxi meters connected to an output shaft of a vehicle gearbox by a rotating cable within a stationary sleeve. However, such arrangements are relatively complex and expensive to manufacture and have been replaced in recent years by electronic taxi meters. Such electronic taxi meters are driven by a transducer mounted on a front bulkhead of the vehicle and connected to an output shaft of the vehicle gearbox by a similar rotating cable and stationery sleeve arrangement.

Although the electronic taxi meter of this type is cheaper and more convenient to manufacture, the arrangement of the transducer and drive cable is inconvenient and complicates the construction of the vehicle.

Commercial vehicle such as lorries often incorporate electrically driven tachographs, which are devices for creating a record of speed and/or distance plotted against time, speed plotted against distance. or the like. It is known to arrange a transducer for such a tachograph to be driven by the transmission of the vehicle. The transducer is located downstream of a vehicle gearbox so that the record is not confused by selection of different transmission ratios by changing gear.

According to a first aspect of the invention. there is provided a transducer arrangement for a vehicle.

comprising a transducer arranged to be mounted within a transmission housing of the vehicle and arranged to provide an output signal representative of distance travelled by or speed of the vehicle.

The transducer may be arranged to supply a pulse per unit distance travelled.

According to a second aspect of the invention, there is provided a transducer arrangement for a vehicle.

comprising an infra red emitter arranged to be mounted within a transmission housing of the vehicle, an infra red transducer arranged to be mounted within the transmission housing so as to receive emitted infra red radiation via an infra red path from the infra red emitter. and a rotary infra red shutter arranged to be mounted within the transmission housing so as to be rotated at a speed proportional to the road speed of the vehicle, the shutter having at least one first portion for passing infra red radiation and at least one second portion for interrupting infra red radiation and being arranged such that, when the shutter rotates. the or each first portion and the or each second portion alternately cross the infra red path.

The or each first portion preferably comprises an opening of the shutter, and the or each second portion preferably comprises a solid part of the shutter. The shutter may, for instance. comprise a metal disk with portions removed from the circumference so as to provide the first portions. The land" between the openings then constitutes the second portions.

Preferably the transmission housing is a vehicle gearbox housing Preferably the transducer arrangement further comprises electronic processing circuitry located within or remote from the transmission housing and connected to the infra red emitter and infra red transducer. The processing circuit may comprise at least one amplifier and/or comparator for amplifying the transducer output signals and/or for providing digital output signals.

The processing circuit may further comprise a pulse-extender or monostable multivibrator for supplying output pulses of predetermined length or of predetermined minimum length.

According to a third aspect of the invention. there is provided a vehicle including a transducer arrangement according to the first or second aspect of the invention.

It is thus possible to provide a transducer arrangement which can be connected a tachograph or to to an electronic taxi meter by a pair of wires, or possibly by a single wire when the vehicle chassis is used as an earth return. The construction of the vehicle is thus greatly simplified. For instance the mechanical connection to a taxi meter or to separate transducer for a taxi meter is avoided. Further. the transducer is protected by virtue of its location within the transmission housing and may therefore be made more cheaply. For instance. the transducer arrangement may be located within the vehicle gearbox so that the shutter is mounted on the gearbox output shaft.

Reliability is also increased by the absence of any mechanical coupling. The emitter and transducer may be mounted through an opening in the gearbox housing so that. should there be a failure in either of these parts or in the electronics. the relevant parts may be removed and repaired or replaced easily and quickly.

The invention will be further described. by way of example, with reference to the accompany drawings, in which : Figure 1 if a lateral view of a transducer arrangement constituting a preferred embodiment of the invention and located in a gearbox housing: Figure 2 is a view of the transducer arrangement of Figure 1 from a longitudal end of the gearbox; Figure 3 is a circuit diagram of the transducer arrangement of Figure 1; and Figure 4 illustrates an application of the transducer arrangement shown in Figures 1 and 2.

A transducer arrangement 1 is mounted through an opening in a taxi gearbox casing 2 and is fixed to the casing by means of bolts (not shown) passing through clearance holes 3 in a flange portion of the arrangement 1 and screwed into threaded holes 4 in the gearbox casing. The transducer arrangement 1 contains an electronic processing circuit which will be described hereinafter.

The arrangement further comprises transducer means 5 mounted to a lower surface thereof and including an infra red emitter 6. such as an infra red emitting diode, and an infra red transducer 7, such as an infra red-sensitive transistor. The emitter 6 directs an infra red beam at the transducer 7 along a path therebetween.

A rotary shutter comprising a metal disc 8 and a collar 9 is attached to the output shaft 10 of the gearbox so as to rotate therewith. As shown in Figure 2 the disc 8 has formed therein four openings 11 in the circumference thereof separated by solid wall "land" portions 12. The shutter and the transducer are located such that the openings 11 and the land portions 12 alternately pass across the infra red path between the emitter 6 and the transducer 7 as the output shaft of the gearbox rotates at a speed which is porpotional to the road speed of the taxi. Although four openings 11 are shown in Figure 2, any number of such openings may be provided as required.

Figures 3 shows the electronic processing circuit of the transducer arrangement. This circuit receives power from a twelve volt battery as normally provided in the taxi and an integrated circuit three terminal voltage regulator 20 provides a five volt supply to the remainder of the circuit between supply lines OV and +5V. The coupling capacitors 21, 22, and 23 are used to de- couple the supply lines and to suppress or at least substantially attenuate any electrical interference or spikes on the supply from the vehicle battery.

The infra red emitter 6 is connected in series with a current-limiting resistor 24 between the supply lines. The transducer 7 comprises a phototransistor and is connected with a collector load resistor 25 in series between the supply lines.

The output of the transducer 7 is connected to the inverting input of an operational amplifier 26. The non-inverting input of the amplifier 26 is connected to the output thereof via a resistor 27 and to a potential divider formed by equal-valued resistors 28 and 29. The resister 27 has the same value as each of the resistors 28 and 29. The amplifier 26 therefore functions as a comparator with a large amount of hysteresis, provided that the input signals from the transducers 7 are of sufficient amplitude to exceed the hysteresis of the comparator. Otherwise, the amplifier functions as a very high gain amplifier.

The output of the amplifier 26 is connected to the inverting input of another operational amplifier 30 which, together with resistors 31 to 33, functions in the same way as the amplifier 26 and the resistors 27 to 29. The output signal from the amplifier 30 is a square wave having a high value substantially equal to +5V when the infra red radiation from the emitter is interrupted by the land portions 12 of the shutter, and a low level substantially equal to OV when infra red radiation passes from the emitter 6 through one of the openings 11 in the shutter to the transducer 7.

The output of the amplifier 30 is connected to the inverting input of an amplifier 34 which. together with the transistors 35 to 37, functions in the same way as the amplifier 30 as an inverting comparator. In effect, this arrangement functions merely as an inverter and provides output signals Q at a first output terminal 38 of the transducer arrangement. The output of the amplifier 30 is also connected to the non-inverting input of an operational amplifier 39 whose inverting input is connected to its output. The amplifier 39 therefore functions as a non-inverting buffer and supplies inverted output signals Q to the second output terminal 40.The output of the amplifier 30 is further connected to a pulse-stretching circuit comprising a timer integrated circuit 41 of the "555" type which is connected as a mono-stable multivibrator and is provided with a timing resister 42. a timing capacitor 43, and a de-coupling capacitor 44. The stretched-pulse output signals Q +t are supplied at a third output terminal 45 of the transducer arrangement.

The operational amplifiers 26, 30. 34. and 39 are shown as individual amplifiers in Figure 3, but they may comprise the four parts of a quad operational amplifier integrated circuit.

Although not shown in Figure 3, a pulse divider circuit may be provided within the transducer arrangement so as to adjust the number of pulses per mile travelled by the taxi to the input requirements of the taxi meter. in combination with selection of the number of openings 11 in the shutter.

The choice of output terminals 38. 40. or 45 depends on the particular requirements of the taxi meter and normally only one of the outputs will be connected to the taxi meter, although balanced operation in order to improve noise immunity can be provided by using the complementary outputs 38 and 40. If the taxi meter requires a guaranteed minimum pulse length for correct operation, it may be necessary to use the output 45 and to select the values of the timing components 42 and 43 to ensure that this minimum period is guaranteed.

The transducer arrangement. in particular the transduc-er means 5, is located in a well protected environment. i.e. within the gearbox casing 2, and is therefore substantially free from contamination with anything which might affect the the transmission of infra red radiation between the emitter 6 and the transducer 7. The only modification to the gearbox required by the installation is the provision of an opening and threaded holes 4 in the gearbox casing and the mounting of the shutter on the gearbox output shaft.

neither of which adds substantially to the cost or complexity of the gearbox. The only connection requirements with the transducer arrangement are the signal wires and the power supply wires, the former of which can be passed easily through the taxi bulkhead and thence to the taxi meter and the latter of which can be supplied from any convenient location within the electrical system of the vehicle.

The transducer arrangement is very reliable as it contains a single moving part and does not contain any parts in relative motion. It is therefore not subject to mechanical wear and, with the high reliability of modern electronic components, should have a far greater life, possibly equaling that of the vehicle, than with conventional mechanical drive arrangements. No lubrication or maintenance is necessary. and no protective housing for the transducer means is required as it is well protected within the gearbox casing 2.

Various modifications may be made within the scope of the invention. For instance, the infra red transucer arrangement may be replaced by any other suitable arrangement, preferably providing a pulse per unit distance travelled. A light emitter and transducer may be used. Also an arrangement based on magnetism or induction may be used. Such arrangements include moving magnets operating stationary read switches or Hall effect devices and coils wound on magnets and cooperating with toothed wheels.

Although the transducer arrangement has been described for use in a taxi for driving a taxi meter, it may equally well be used in a lorry or other vehicle for driving a tachograph. Figure 4 illustrates disgrammatically such an application in which a transducer 120 of the type shown in Figures 1 and 2 is connected to signal processing electronics 121 which is connected to a tachograph 122. The signal processing electronics 121 may be of the type shown in Figure 3 or may be any type suitable for driving the tachograph 122.

Claims (9)

1. A transducer arrangement for a vehicle, comprising a transducer arranged to be mounted within a transmission housing of the vehicle and arranged to provide an output signal representative of distance travelled by or speed of the vehicle.

2. An arrangement as claimed in Claim 1, in which the transducer is arranged to supply a pulse per unit distance travelled by the vehicle.

3. A transducer arrangement for a vehicle. comprising an infra red emitter arranged to be mounted within a transmission housing of the vehicle, an infra red transducer arranged to be mounted within the transmission housing so as to receive emitted infra red radiation via an infra red path from the infra red emitter. and a rotary infra red shutted arranged to be mounted within the transmission housing so as to rotate at a speed proportional to the road speed of the vehicle. the shutter having at least one first portion for passing infra red radiation and at least one second portion for interrupting infra red radiation and being arranged such that, when the shutter rotates, the or each first portion and the or each second portion alternatively cross the infra red path.

4. An arrangement as claimed in Claim 3. in which the or each first portion comprises an opening of the shutter and the or each second portion comprises a solid part of the shutter.

5. An arrangement as claimed in Claim 4. in which the shutter comprises a metal disk with portions removed from the circumference so as to provide the first portions.

6. An arrangement as claimed in any one of the preceding claims. in which the transmission housing is a vehicle gearbox housing.

7. An arrangement as claimed in any one of the preceding claims, including a processing circuit comprising an amplifier and/or comparator for amplifying an output signal of the transducer and converting the amplified output signal to a digital signal, and a monostable multivibrator arranged to be triggered by the digital signal.

8. A transducer arrangement substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

9. A vehicle including a transducer arrangement as claimed in any one of the preceding claims.