_■• ELECTRIC DRIVE TRAIN FOR A VEHICLE"

FIELD OF THE INVENTION

This invention relates to a drive train particularly

5. for use in a vehicle.

BRIEF DISCUSSION OF THE PRIOR ART

Traditionally the main contender for an alternative to the heat engine has been electrical traction. However the prohibitive inadequacy of electrical traction has 10. _" been the low on-hoard energy storage capacity. Thus chemical fuel on-board storage of energy is considered ^,, the only practical source of power for the majority of

road vehicles.

It is known that a heat engine such as a diesel engine, a sparlc ignition petrol engine or gas turbine

15 produces maximum power over a relatively narrow range of rotational speeds. Similarly the efficiency of such an engine reaches its maximum value at a particular speed. Also of particular importance is the control of 20. pollutant engine emissions to the atmosphere. Since the

co position of the engine exhaust varies with engine speed the* design of- ar efficient .pollution, free engine or the design of a catalytic exhaust treatment device becomes considerably more dif icult if the engine is to ^* 5. be run at widely varying speeds.

SITMMARY OF THE PRESENT INVENTION According* to the present invention a drive train comprises a primary drive, a rotatable shaft driven by said primary drive, a flywheel rotatable with the shaft

10. for the storage of inertial energy thereby being operable to absorb or rapidly give up angular kinetic energy as required, clutch means between the primary drive and the flywheel, an electrically operated transmission comprisin an electrical machine having a magnetic field structure

15. and an independently rotatable armature, one of the field structure and armature being connected to the driven shaft and the other being connected to a rotatable drive shaft, for rotation about a common axis, an electrical storage cell, and electrical control means connected with

20. the electrical machine and with the electrical storage cell, for regulating current and thereby controlling the power transmitted to the drive shaft such that when it is desired to rotate the drive shaft at a speed of rotation less than the speed of rotation of the driven shaft then

25. the electrical control means is operated so as to cause excess power to be tapped to the electrical storage cell to be stored thereby whereas, when it is desired to

rotate the drive shaft at a speed of rotation greater than the speed of rotation of the driven shaft, the electrical control means is operated so as to cause the power required in excess of the power provided by the 5. primary drive to be tapped from the electrical storage cell.

The drive train of the invention when in a vehicle enablespower to be shared between the wheels and the batteries during use in other words power not required is 10. stored by the batteries for later use.

Thus, although torque generated by the primary drive unit is transmitted to the wheels, the power is varied by the electric transmission to permit regulation of speed. The regulation of the power is effected by an 15. electrical control means regulating the armature current which determines the generator torque and hence the torque applied to the wheels.

The drive train includes a clutch between the primar drive and the flywheel so that an internal combustion 20. primary drive may be started by disengaging the clutch and passing current to the armature to cause rotation of the flywheel. The clutch is then engaged, and the inertia of the flywheel is sufficient to turn over the primary drive unit. The field structure is now driven 25. by the primary drive unit and rotates relative to the armature causing the generation of electrical current. Thus with the wheels braked the relative velocity of the

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field structure and the armature is at its maximum and the electrically operated transmission is generating at maximum capacity.

As soon as the armature is released the generator 5. reaction torque causes rotation of the armature in the same direction as the field structure. The speed of rotation of the armature is then controlled by the electrical control device which is used to tap electrical power to the battery so that only a proportion of the

10. power generated is available for use in driving the armature and thus the wheels of a vehicle. At a cruising speed where the armature and field structure are rotating together no electric current is tapped by the control device so* that all the power from the heat engine

15. passes to the wheels. In fact in practice at this cruising speed a certain amount of electricity is fed from the batteries to the armature to provide the torque required of the electrical unit.

If it is desired to increase velocity this may be

20. done for a limited period, by supplying current from the battery to the armature so that the transmission operates as an electric motor.

The advantage of this arrangement is the ability of the drive train to have a primary drive unit operating

25. at constant RPM whilst varying the speed of the vehicle. Moreover the ability of the electrically operated transmission to generate electricity below cruising speed

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overco es the difficulties previously encountered by electrical traction.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example 5. with reference to the accompanying drawings in which: Figure 1 is a cross-sectional elevation of an electrically operated transmission for a drive-train according to the invention;

Figure 2 is a schematic diagram of a drive-train 10. employing the electrically operated transmission;

Figure 3 is a schematic diagram of a further vehicle drive-train wherein, in an alternative embodiment of the invention, the transmission-drive unit functions as a differential unit; and 15. Figure 4 is a schematic representation of a hybrid petro-electric vehicle drive-train with a flywheel, of the type shown in Figure 3, and employing two disc armature DC transmission-drive units.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 20. In Figure 1, the input shaft h is driven, usually at constant speed, by a heat engine 30 (shown in Figures 2 and 3). The casing 3 of the transmission-drive unit 13 is fixed to the chassis of the vehicle (not shown) and a field structure 3i is connected to the shaft •_ is free to 25. rotate. in the bearings 32. Within the hollow field structure 31, lies an armature 1 the central shaft 5 of . which is free to rotate in the two sets of bearings 33

ounted, respectively, in a hollow section 34 of the inpu ^•" shaft 4 ^* and ^* a- tubular member--35.--the parts 3 and 35- bein concentric with the shaft 5 and connected to the field structure. 5 _^ An electrical current connection for the armature 1 and, in this case an electromagnetic field structure is made by brushes 37 and 39 which makes sliding contact wit slip rings 36 and 38. One of each of the slip rings 3β and 38 are connected to brushes 80 which are in electrica i0. connection with their respective armature coils (not shown).

In use of the unit 13 as a transmission unit electrical contact is made between the brushes 39.; electrical contact is also made between the brushes 37.

15 Electrical currents induced in the armature coils by the rotation of the field structure 3i circulate in the armature coils and their electromagnetic linkage with the armature i tends to cause the armature 1 and the associated shaft 5 to rotate in the same direction as the

20. input shaft 4. However in the stopped position of a vehicle the armature is prevented from rotation by a brake 42 acting upon the shaft 5 thus electricity is generated and transmitted to a battery source 81 (Figure 2 or 3). The unit 13 may be operated as a conventional 25. motor by disconnecting the shaft 4 from the drive unit 30 by operating _, a clutch 41 (see Figure 2) and then braking

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the shaft 4 with a brake 40. This may be done, for example, by drawing current from the battery into the coils of the armature so that the unit becomes the sole power unit for the vehicle when driven over short 5. distances around a town.

To start the drive unit 30, the brake 40 is released and electrical current applied to the armature 1 causing the field structure to rotate. Rotation of the field structure 31 causes rotation -of a flywheel 12. The 10. clutch 41 is then engaged and the inertia in the flywheel turns over the drive unit 30.

Figure 2 shows a practical layout for a vehicle drive-train for a high efficiency vehicle using a combination of electrical drive for use around town (when 15. the unit 13 is used as the sole drive unit) and for highe speed motorway cruising (when the drive unit 30 is used in conjunction with the unit 13, which unit may be used to -provide acceleration or deceleration. Power from the output shaft 5 passes to the driven wheels 15 and 16 via 20. a differential unit 14.

In the layout shown in Figure 3, the differential unit may be a transmission-drive unit 43 which has two armatures 21 and 22, each capable of independent rotation and contained within the field structure 44. 5 The field structure is driven via gears (not shown) from the shaft 27. Power output from the unit 43 is fed to the driven wheels 15 and 16 via step-down gearboxes 23

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and 24. A flywheel 29 is connected to the drive-unit output shaft 27 via the ^" gear and clutch system 28. The flywheel-operates- to -absorb* or- rapidly give .up angular... kinetic energy as required. 5. Thus, in conjunction with suitable electrical and mechanical control systems, the unit of the invention may be used to provide a vehicle drive-train exhibiting high efficiency and versatility.

Figure 4 shows in detail a preferred vehicle drive-

10. train for practical operation. Two disc-armature DC transmission-drive units 50 are used so as to provide a differential action.

The engine 30 is designed to provide base load i.e. total power requirement at cruising speed.

15. The transmission-drive units 50 are basically conventional electrical motors with both their armatures and field structures free to rotate, the field structures 31 being driven by the heat engine 30 and flywheel 29, and the armatures 52 driving the wheels. Their

20. armatures 52 are connected in series to provide the necessary differential element. Although many electrica motor designs could be used for this purpose the disc- armature DC motor design is most suitable having high efficiency both acting as motor or generator, high power/

25. weight ratio, low volume, simplicity of construction (and thereby low manufacturing cost) high inertia of the field structure 31 and low inertia of the armature 52, and torq

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output directly proportional to armature current.

The electrically operated transmission units 50 can be arranged to match that of the engine to facilitate maximum energy recovery during standstill operation or 5. can be varied to meet any specific operating requirement. The clutch 41 is opened when the heat engine is not being used. When required the flywheel 29 is run up to speed by the electrical transmission-drive unit at which time the clutch 41 is closed to start the heat engine 30. 10. A uni-directional clutch 5i also enables the system to run without the heat engine 30.

The size of battery 53 required is primarily governed by the maximum power absorption of the electricaJ transmission-drive unit 50. 15. During normal operation the heat engine 30 is run at constant speed and the vehicle's speed is controlled solely by the electrical transmission-drive unit. At standstill the field structure 31 is rotated by the heat engine 30 whilst the armature 52 is braked, thus power is 20. generated and stored in the batteries 53.

When the armature 52 is released it tends to rotate in the same direction as the rotating field structure 3i and consequently drives the wheels, the torque being dependent on the armature current tapped by an electrical 25. control 54. The electrical control 5 is a variable resistance which varies the smount of current tapped. The current is tapped through slip rings 57 and 58 and

brushes 55 and 5 which cooperate with a commutator (not shown) on the armature 52. The DC current connection to the slip rings- 57- and 8 is by cooperating brushes 60 and** 59 respectively. 5. The field structure 31 consists of a series of sixtee permanent magnets 61 arranged adjacent to and on either side of the armature 52. The rotatable field structure 3 is driven by the shaft 27 through the unidirectional clutch 51 and the gears 62.

10. Drive from each armature 52 is fed to the respective output shaft 45 or 46 via the reduction gears 62. The power from the heat engine is divided between the wheels and the batteries at rates proportional to the vehicle speed.

15. Up to cruising speed the electricity generated by the relative velocity between the field structure 3i and the armature 52 is sufficient not only to drive the wheels but also to allow a certain amount of electricity to be tapped to replenish the batteries. The control of the sharing o

20. power between the wheels and the batteries being effected by altering the effective impedance of the electrical control 54. At cruising speed the field structure 3 and the armatures 52 rotate together, thus all the power from the heat engine 30 goes to the wheels with a trickle

25. of power from the batteries 53 to provide the torque required of the electrical unit 50. Above cruising speed the batteries 53 provide the extra power.

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Duriπg braking both the batteries 53 and the flywhe 29 are- recharged. ^" This is calculated to give a much higher regenerative efficiency than possible with just a electrical transmission-drive unit operating without a 5. flywheel.

It is possible to use the system without the heat engine 30 for operation over limited ranges (dependent on battery,capacity) up to cruising speed. This 25 mos advantageous for short intown journeys where the 10.. resulting pollution free operation is particularly welcome; in addition to making unnecessary the use of the heat engine for what, as a result, of the warming up . period required, must be its most inefficient applicatio After such operation the batteries 53 can either be 15.. recharged by the heat engine 30 or directly from the mains«- -

The system comprises as. efficient generating set, the 20 KW output of which (considering a medium size European saloon) would supply amply" the requirements of 20.. any home or indeed small factory.

As an electrical transmission-drive unit of the disc-armature DC motor design is capable of developing torque five times its rated value, there is no need for gear changes and the unit has an effective top power, 25. ten times that of the heat engine with corresponding attractive performance characteristics.

The advantages of the present invention may be

summarised as follows:—

1. High efficiency with considerable fuel saving due to the primary- drive* being able to operate at constant RPM whilst variations in speed are effected by the

5. transmission.

2. Low pollution because the pollution from the heat engine can more easily be reduced because it runs at constant speed.

3. Low maintenance: maintenance levels of electrical 10. units are very low. Heat engines running at optimum speed generally requires much less maintenan

4. Low cost: simplicity of construction results in low manufacturing cost, especially as the design incorporates only present day proven technology. i5- 5. Compatibility with conventional road vehicle design. 6. Adaptability: to different heat engines, gas turbine, etc. to one, two, four or multi-wheel drive.