GB2163018A

GB2163018A - Electric road vehicle

Info

Publication number: GB2163018A
Application number: GB08523559A
Authority: GB
Inventors: Erich Pohlmann; Bernd Stot
Original assignee: Rheinisch Westfaelisches Elektrizitaetswerk AG
Current assignee: RWE AG
Priority date: 1982-02-24
Filing date: 1985-09-24
Publication date: 1986-02-12
Also published as: IT8319726A1; FR2521923B1; DE3206492C2; GB2115995A; GB8305050D0; FR2521923A1; DE3206492A1; IT8319726A0; GB2163018B; GB8519940D0; GB8523559D0; IT1161091B; GB8518796D0; GB2115995B

Abstract

The two driving wheels 2 of the vehicle are coupled via non-rigid transmissions 10, 11, 12 to respective series wound motors 6, 7 which are connected in series with one another for starting and town traffic and in parallel for high speed running, a control unit 5 inhibiting the switch to parallel connection until a predetermined road speed has been reached. The parallel connection may be initiated by a kickdown effect of an accelerator pedal 13 which acts against an increased mechanical resistance 17. The control 5 includes a current limiting device and may be responsive to the steering gear to bring about a differential speed correction when negotiating curves. <IMAGE>

Description

1

SPECIFICATION

Electric road vehicle 5This invention relates to a road vehicle driven by electric motors and having two driving wheels, a series-wound motorfor each driving wheel, an accumulator battery, and a control unitfor switching the motors.

Series-wound motors are known to have a drooping 75 torque curve against speed. The torque measured on the shaft is proportional to the square of the motor current, provided the series-wound motor is not operating nearthe iron saturation limit. In a known roadvehicle of thistype (AT-PS 115 854,1928),the series-wound motors are permanently connected in serieswhen they are operating, and cannot be connected otherwise. The control unit,which is constructed as a classical electromechanical system, effects their switching on and off and controlstheir output. The characteristic curve prescribed bythis series connection remains unchanged asthe speed is increased. There are no means wherebythe operating conditions can be selected forstarting conditions and town traffic on the one hand, and for high-speed traffic 90 on the other hand. Nevertheless, modern traffic conditions require differentiation on these lines, viz., rapid starting and acceleration behaviour in town streets and for overtaking, upto a speed of about 60 kmlh, in contrastto an adequate maximum speed for rapid transit on high-speed roads, notably between satellite towns and city centres, together with an obviously smooth changeoverfrom town to high speed operation. These are conditions which cannot be met bythe known vehicle. The fact is that the known vehicle is primarily designed as a rail vehicle, although its use as a road vehicle is not excluded. The requirements described above have hitherto only been met by road vehicles having an internal combus tion engine and a gearbox. As a means of improving 105 the performance of road vehicles driven by electric motors, it is known (US-PS 3 182 742,1965) to separate the armature winding on the one hand and the field winding on the other hand fu nctionally from each other in the electric motors, in thatthey are each connected to their own accumulator batteries and can be independently controlled with respect to their voltage and current supplies. In this way, an attempt is made to combine the advantages of series- and sh unt-wound motors respectively. In effect, one uses 115 separately excited shu nt-wound machines. The cir cuitry requirements are expensive. The resulting system is farfrom simple, and even then the system fails to meetthe requirements for efficient high-speed operation. No differentiation is made between town 120 traffic and high-speed road traffic conditions.

The object of the invention is to provide a road vehicle of the type initially described and which is particularly well adapted not onlyto town traffic, with rapid starting and acceleration behaviour, but also to 125 high-speed traffic, with a smooth changeover and an improved maximum speed, and moreover so thatthe circuitry is inexpensive, simple proven components can be used.

According to the present invention, a road vehicle 130 GB 2 163 018 A 1 driven by electric motors and having two driving wheels has a serieswound motorfor each driving wheel, an accumulator battery, and a control unit, in which the series-wound motors act on their respective driving wheels through non-rigid transmissions and are adapted to be switched by means of the control unit, which is designed in accordance with the rules of power electronics, the series-wound motors being connected electrically in series forstarting and town traffic purposes and in parallel for high-speed running, and the control unit incorporating a devicefor current limitation and a stop which only permits parallel connection when a prescribed road speed has been reached. Non-rigid power transmissions in themselves are known inroad vehicles driven by electric motors (US-PS 3 182 742).

The invention utilises the factthatthe series connection effective for starting and town traffic purposes develops a substantial traction force when the current setting is at the maximum allowed bythe control unit, so that the afore-mentioned requirements fortown traffic conditions can be metwithout difficulty provided the series-wound motors are aptly designed. On changing overto high-speed operation, the highervoltage across each series-wound motor when connected in parallel has an advantageous effectforthe highervehicle speed and thusfor high-speed transit.The changeover is no problem and can be brought about within a short switching period with a power-electronics control unit, while by virtue of the non-rigid power transmission the switching action in no way damagesthe electric motor and driving wheel concerned by setting up mechanical oscillations, so that a smooth changeover can be 100 made.

In orderto make the driving of a road vehicle of the invention generally similarto the driving of vehicles with an internal combustion engine, the control unit preferably has a driving pedal wherebythe switch between series connection fortown street driving and parallel connection for highspeed operation can be made. It is preferred to provide the control unitwith a pre-programming device and a preselector and adapt the drivingpedal action forthe switch to high-speed 110 operation so that it only becomes effective when the pre-programmed speed has been reached. In this case use can be made of a kickdown effect as commonly used in vehicles with an internal combustion engine and automatic transmission. To this end, the driving pedal can operate against an increased mechanical resistance so that, the high-speed setting is obtained by means of a kickdown effect. The control unit can bring about a differential speed correction when negotiating curves and can accordingly be itself controlled by the steering gear on the frontwheels.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, which is a diagrammatic plan view of a road vehicle driven by electric motors.

The Figure shows a four-wheeled vehicle in which thefrontwheels 1 can be steered and the rearwheels 2 are adapted.as driving wheels. In the rear 3 of the vehicle there is mounted a battery 4which may consist of a plurality of accumulator cel Is and is connected to a control unit 5. Two series-wound 2 electric motors 6 and 7 are provided with coaxial shafts 8 and 9 and are controlled bythe control unit 5. Transmission from each of the series- wound motors 6 and 7 is effected by means of a chain 10 ortoothed belt which runs round a sprocket 11 on the motor shaft 8 and 9 and a sprocket 12 connected to the respective driving wheel 2. This transmission allows vibrationfree coupling between the series-wound motor 6 or 7 and the respective driving wheel 2.

The direction of rotation of the series-wound motors 6 and 7 can be reversed by suitable arrangements within the control unit 5. They can be connected together electrically in series or in parallel for highspeed operation, again by means of the control unit.

The series-wound motors 6 and 7 are equally rated. On bends, the control unit 5 appropriately adjusts the rotary speeds of the series-wound motors 6 and 7. This adjustment can be derived for examplefrom the steering gear on thefrontwheels 1.

Furthermore, the control unit 5 has a driving pedal 13 through which the parallel connection for highspeed operation can be made. The control unit 5 is provided with a pre-programming device 14 and a preselector 15. The changeoverto high-speed operat- ing conditions is thus brought about by means of the driving pedal 13, but can only be made aftera pre-programmed speed has been reached. The speedometer 16 is used to measure the speed forthis changeover. The driving pedal 13 operates against an

Claims

increased mechanical resistance 17. Thus the highspeed setting is initiated by a kickdown effect. CLAIMS

1. A road vehicle driven by electric motors and having two driving wheels, a series-wound motorfor each driving wheel, an accumulator battery, and a control unit, in which the series-wound motors act on their respective driving wheels through non-rigid transmissions and are adapted to be switched by means of the control unit, which is designed in accordance with the rules of power electronics, the series-wound motors being connected electrically in series for starting and town traffic purposes and in parallel for high-speed running, and the control unit incorporating a devicefor current limitation and a stop which only permits parallel connection when a prescribed road speed has been reached.

2. A road vehicle as in Claim 1, wherein the control unit has a driving pedal, whereby the switch between series connection fortown street driving and parallel connection for high-speed operation can be made.

3. A road vehicle as in eitherof Claims land 2, wherein the control unit has a pre-prog ramming device and a preselector, and the switchoverto high-speed operation can be made through the driving pedal butwill only be effected when a pre-programmed speed has been reached.

4. A road vehicle as in Claim 3, wherein the driving pedal operates against an increased mechanical resistance so thatthe high-speed setting is obtained by means of a kickdown effect.

5. Aroadvehicleas in anyoneof Claims 1 to4, wherein the control unit brings about a differential speed correction when negotiating curves and is accordingly itself controlled bythe steering gear on thefrontwheels.

GB 2 163 018 A

6. A road vehicle substantially as hereinbefore described and with reference to the accompanying drawing.

2 Printed in the United Kingdom for Her Majesty's Stationery Office, 8818935, 2186 18996. Published at the Patent Office, 25 Southampton Buildings, London WC2A lAY, from which copies may be obtained.