GB2347216A - Tachograph - Google Patents

Abstract

A tachograph has an electronic clock and a drive unit for time-dependent drive of tachograph chart discs which serve as recording media. A servomotor 37 engages directly with a toothed wheel 23 of the drive unit by means of a pinion 48 fixed to the motor shaft 38. A pulse generator is formed by a toothed wheel 25 of the drive unit provided with slits 35 and a light barrier 36. A further slit 33 is provided in a further toothed wheel 30 which is in engagement with the tachograph disc receiver 14. The slit 33, in conjunction with a light barrier 34, delivers a signal denoting the zero hours position of the tachograph disc receiver 14.

Description

Tachograph This invention relates to a tachograph.

As is generally known, it must be possible to synchronise the recordings of tachographs to the current time. It is conventional with tachographs-in contrast to a recording method which also provides recording of time markers on a "neutral"recording medium-to provide the tachograph chart discs with a time scale, which results in the tachograph disc receiver associated with the tachograph chart discs having to be time-dependently driven and to be synchronised with the recording elements of the tachograph which are moved, depending on readings, radially to an inserted tachograph chart disc, wherein a connection secured against torsion between the tachograph disc receiver and an inserted tachograph chart disc is guaranteed by means of a drive mandrel formed excentrically on the tachograph disc receiver.

When a tachograph is first put into operation, after power interruptions owing to repairs, at the summertime/wintertime changeover or an accumulated inaccuracy in the drive unit, there is, or there arises, a mismatch in time between, for example, the time indicated on a display of the tachograph and the time scale figure of those radials of an inserted tachograph chart disc, on which the recording elements are acting at that moment as the electronic clock, in which calendar time changes are carried out under processor control, is buffered, thus remaining in function during interruptions of the power supply to the tachograph. A known tachograph has an electronic clock and a drive unit for time-dependent drive of tachograph chart discs serving as recording media as well as with means for tracking a tachograph disc receiver which centres and drives the tachograph chart discs where there is a difference between the time reading and the position of a time scale imprinted on the tachograph chart discs relative to the recording elements of the tachograph acting on the tachograph chart discs. A servomotor is provided, which is connected by gears to the drive unit and a free-wheel device is arranged between the servomotor and a step motor which drives the drive unit. A signal generator denotes the zero hours position of the tachograph disc receiver and a pulse generator delivers pulses proportional to the time-scale. A comparator circuit serves to cut off the supply of power to the servomotor when the counted figure of the pulses delivered by the pulse generator corresponds to the current time.

Conventional tachographs, with an electronic clock and a drive unit for time-dependent transport of tachograph chart discs have hand-activated means for compensating the time mismatch, i. e. there is a gear connection between a gear element of the drive unit and a regulating element accessible outside the drive unit, wherein clutch or free-wheel means must be associated with the drive unit to allow the tachograph chart disc support to be adjusted independently of the drive unit motor, and with a power of adjustment which is still acceptable.

Apart from the fact that such intervention in the drive unit also makes manipulations possible, tracking the tachograph chart disc support by hand requires not insubstantial expenditure of time and subjective care, so there is a risk that tracking by hand, which is laborious per se, is not done or is forgotten, as the right time is always indicated on the display of the tachograph and the position of the tachograph chart disc support is not visible from outside. An indication of the time by means of indicators, the drive of which is branched off from the drive unit of the tachograph disc receiver, would certainly represent an easy-to-see reading of the position, but with the chosen tachograph concept, a solution of this kind no longer makes sense. The lack of a clearly visible reading of the position for the tachograph disc receiver is, though, another reason why tracking and adjusting the tachograph disc receiver to the right time by hand is unsatisfactory, with unfavourable assembly positions of the tachograph and the often insufficient lighting in a driver's cab adding to the difficulties.

There is therefore a requirement to track any time mismatch which has arisen between the reading on the electronic clock and the position of the tachograph disc receiver automatically in the generically described manner, and, to avoid overwriting recordings which have already been made on the tachograph chart discs, also to do this when, as previously with tracking by hand, the tachograph concerned has been opened for the purpose of inserting or changing tachograph chart discs.

The object of the present invention is therefore to keep expenditure for automatic tracking of the tachograph disc receiver as low as possible, in particular to effect integration into a given drive unit concept, wherein as small an overall height as possible is to be aimed at. According to the invention there is provided a tachograph for time-dependent drive of tachograph chart discs serving as recording media equipped with means for tracking a tachograph disc receiver which centres and drives the tachograph chart discs where there is a difference between the time reading and the position of a time scale imprinted on the tachograph chart discs relative to the recording elements of the tachograph acting on the tachograph chart discs, said tachograph comprising an electronic clock and a drive unit with a step motor and gearing for driving the tachograph chart discs, a servomotor connected by gearing to the drive unit, a freewheel device arranged between the servomotor and the step motor, a signal generator denoting the zero hours position of the tachograph disc receiver and a pulse generator delivering pulses proportional to the time-scale and a comparator circuit which interrupts the supply of power to the servomotor when the counted figure of the pulses delivered by the pulse generator corresponds to the current time, wherein the servomotor engages directly with a toothed wheel of the drive unit with a pinion fixed on the motor shaft thereof, slits are formed in one toothed wheel of the drive unit in such a way that the toothed wheel forms the pulse generator in active connection with a light barrier, another toothed wheel with a number of teeth commensurate with the disc receiver is in engagement with the tachograph disc receiver and is provided with a slit and a light barrier is allocated to the toothed wheel to serve as the signal generator.

The servomotor may be linked to the drive unit so that the motor shaft thereof is positioned in a plane substantially intersecting axes of the components of the drive unit, i. e. the gears at right angles. Further, the toothed wheel of the signal generator and a spring barrel which serve to compensate for backlash in the drive unit may be formed as one piece. The free-wheel device may be formed as a wrapped-wire spring clutch.

The invention solves the object set in an advantageous manner in that, apart from a servomotor and two light barriers, no additional parts are required. In other words, existing wheels of a drive unit are simply modified and used repeatedly and the number of axes remains unaffected. In addition, to implement the invention, additional use is made of the conventional microprocessor in a tachograph which controls the electronic clock. Compared with a drive unit tracked by hand, both the number of components and the required amount of space are therefore reduced, the speed of tracking is increased and the accuracy of adjustment considerably improved. Further, the low overall height aimed at is achieved in that the servomotor is linked to the drive unit in such a way that the motor shaft is arranged transversely to the relevant axes of the drive unit. The pinion of the servomotor, in this case, engages in a set of crown teeth formed on a toothed wheel with radial teeth of the drive unit. Optimisation can also be seen in the fact that the chosen concept with an additional servomotor results in a minimum power consumption and the direct current motor chosen as servomotor, which, when it is not being supplied with current is automatically rotated by the step motor of the drive unit and exerts hardly any torque on the step motor.

The invention may be understood more readily, and various other aspects and features of the invention may become apparent, from consideration of the following description. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings.

In the drawings: Figure 1 is a front view of a tachograph equipped with a drawer for holding the tachograph chart discs; Figure 2 is a plan view of a drive unit for driving the tachograph chart discs and Figure 3 is a partial section of the drive unit taken along section line A in Figure 2.

In Figure 1 a cuboid housing of the tachograph representing a preferred embodiment of the invention is indicated by the reference number 1. A front wall 2 of the housing 1 has a window 3 for a display 4. A front cover of a drawer 6 contained in the housing 1 is represented by number 5. Various control buttons 7,8,9,10,11 and 12 are provided on the front wall 2. Buttons 7 and 8 and menu button 9 are assigned to the driver or co-driver for selecting at least the most important working time data. Buttons 10 and 11 are for scrolling forwards and backwards in the selected records and button 12 is for unlocking and releasing the drawer 6. Access to a diagnostics box is secured by means of a seal denoted by reference number 13.

As can be seen from Figure 2, a tachograph disc receiver 14 is driven initially by a step motor 15 via a pinion 18 fixed on a shaft 16 of a rotor 17 of the step motor 15 and via a gear connection comprising a plurality of pairs of toothed wheels. In particular it can be seen that the pinion 18 is connected via radially toothed wheel pairs 19/20,21/22,23/24,25/26, 27/28 to a set of teeth 29 formed on the tachograph disc receiver 14. A toothed wheel 30 also engages the set of teeth 29 but is located outside the gear train between the step motor 15 and the tachograph disc receiver 14. A spring barrel 31 is formed on the toothed wheel 30 and a brake spring, not illustrated, acts in the barrel 31. This serves in a manner known per se to compensate for backlash in the previously described gear connection. The toothed wheel 30 is provided with the same number of teeth as the tachograph disc receiver 14, on which a drive mandrel 32 of non-circular shape is formed in the conventional manner. A 1: 1 transmission is therefore provided between the toothed wheel 30 and the tachograph disc receiver 14. A slit 33 made in the toothed wheel 30, together with a light barrier 34, serves to generate the signal for the zero hours position of the tachograph disc receiver 14. In this position the recording elements of the tachograph are positioned on the zero hours radials of a tachograph chart disc inserted in the tachograph disc receiver 14. The zero hours signal controls the counting of pulses of a pulse generator associated with the toothed wheel pair 25/26.

In other words, the toothed wheel 25 is provided, for example, with sixty slits 35 which are scanned by a light barrier 36.

Reference number 37 denotes a servomotor, preferably a direct current motor, the rotor shaft 38 of which is arranged transversely to the shaft 16 and to the associated axes 39, 40,41,42,43,44 and 45 of the drive unit on the floor 46 of the drawer 6. This contributes to the fact that the overall height of the drive unit, already designed to be flatly proportioned, can be kept as low as possible. The height is substantially determined by the height of the drive mandrel 32. The servomotor 37 is connected by gears to a toothed wheel of the drive unit, in this case to toothed wheel 23. The connection is made via a set of crown teeth 47, formed on the toothed wheel 23, into which a pinion 48 fixed on the motor shaft 38 of the servomotor 37 engages. An annular bead 49, formed on the floor 46 of the drawer 6, serves to support the toothed wheel 23 laterally. A free-wheel device 50 is superimposed on the clock drive of the step motor 15 and coupled to toothed wheel pair 21/22. The free-wheel device 50 is formed as a wrapped-wire spring clutch 51. Preferably the spring wire used for the wrapped spring clutch 51 has a rectangular cross-section, guaranteeing high functional safety with low expenditure on components and assembly. In particular, the toothed wheel 22 is provided with a shank 52, on which is formed a cylindrical running face which serves as a bearing for the toothed wheel 21. The shank 52 also has a tongue 53 with rectangular cross-section at its outer end which rotatably secures a bush 54 on the shank 52. A cylindrical face 55 is formed on the bush 54, with the same diameter as a cylindrical face 57 moulded onto a running collar 56 of the toothed wheel 21. Both faces 55 and 57 serve as a seat and friction face for the wrapped spring 51.58 denotes a plate at least partially covering the drive unit; 59 denotes a side wall of the drawer 6.

The process of tracking the tachograph disc receiver 14 is substantially as follows: if it is established or detected by the microprocessor of the tachograph that a wintertime/summertime changeover or vice versa has taken place, adjustment of the electronic clock has been carried out in the course of maintenance measures or the power supply to the tachograph has been cut off owing to repairs to the vehicle, the driver is informed by a signal, for example by flashing of the time reading. Tracking of the tachograph disc receiver 14 can take place when the vehicle is stationary but, to avoid exceeding previous recordings, conditions for tracking should prevail, i. e. at least the drawer 6 has been opened or, in particular with two-driver appliances, both tachograph chart discs have been removed or have not yet been inserted. An already required insertion check is used to recognise the presence of tachograph chart discs.

If the starting conditions have been met, the light barriers 34 and 36 are switched on and the servomotor 37 supplied with power. When the zero hours position is reached, a time counter is set back and the pulses delivered by the pulse generator 25/35/36, in the embodiment minute pulses, are counted, triggered by the zero hours signal of the signal generator 30, 33,34. When the constant comparison of time counter content and set value of the electronic clock become identical, the servomotor 37 is stopped and the light barriers 34 and 36 switched off.

For completeness it should be mentioned that the pulse generator 25/35/36 can also be employed for checking the function of the drive unit, by transmitting the minute count in a suitable manner, on condition that the light barrier 36 is continuously switched on, and by producing a continuous reading, for example by flashing of the hour/minute dividing symbols of the time reading on the display 4.

Claims (7)

1. Claims 1. A tachograph for time-dependent drive of tachograph chart discs serving as recording media equipped with means for tracking a tachograph disc receiver which centres and drives the tachograph chart discs where there is a difference between the time reading and the position of a time scale imprinted on the tachograph chart discs relative to the recording elements of the tachograph acting on the tachograph chart discs, said tachograph comprising an electronic clock and a drive unit with a step motor and gearing for driving the tachograph chart discs, a servomotor connected by gearing to the drive unit, a free-wheel device arranged between the servomotor and the step motor, a signal generator denoting the zero hours position of the tachograph disc receiver and a pulse generator delivering pulses proportional to the time-scale and a comparator circuit which interrupts the supply of power to the servomotor when the counted figure of the pulses delivered by the pulse generator corresponds to the current time, wherein the servomotor (37) engages directly with a toothed wheel (23) of the drive unit with a pinion (48) fixed on the motor shaft (38) thereof, slits (35) are formed in one toothed wheel (25) of the drive unit in such a way that the toothed wheel (25) forms the pulse generator (25/35/36) in active connection with a light barrier (36), another toothed wheel (30) with a number of teeth commensurate with the disc receiver (14) is in engagement with the tachograph disc receiver (14) and is provided with a slit (33) and a light barrier (34) is allocated to the toothed wheel (30) to serve as the signal generator (30/33/34).
2. 2. A tachograph according to claim 1, wherein the servomotor (37) is linked to the drive unit in such a way that the motor shaft (38) thereof is located in a plane substantially intersecting axes (39,40,41,42,43,44,45) of the components of the drive unit at right angles.
3. 3. A tachograph according to claim 1 or 2, wherein the toothed wheel (30) of the signal generator (30,33,34) and a spring barrel (31) serve to compensate for backlash of the drive unit and are formed as one piece.
4. 4. A tachograph according to any one of claims 1 to 3, wherein the toothed wheel (23) with which the pinion (48) of the servomotor (37) engages, is formed as a crown wheel.
5. 5. A tachograph according any one of claims 1 to 4, wherein a direct current motor is used as the servomotor (37).
6. 6. A tachograph according to any one of claims 1 to 5, wherein the free-wheel device (50) is formed as a wrapped-wire spring clutch.
7. 7. A tachograph substantially as described herein with reference to the accompanying drawings.