GB2115995A

GB2115995A - Electric road vehicle

Info

Publication number: GB2115995A
Application number: GB08305050A
Authority: GB
Inventors: Erich Pohlmann; Bernd Stoy
Original assignee: Rheinisch Westfaelisches Elektrizitaetswerk AG
Current assignee: RWE AG
Priority date: 1982-02-24
Filing date: 1983-02-23
Publication date: 1983-09-14
Also published as: GB2115995B; FR2521923A1; GB8305050D0; DE3206492A1; DE3206492C2; GB2163018B; GB2163018A; IT8319726A0; IT8319726A1; GB8523559D0; IT1161091B; FR2521923B1; GB8518796D0; GB8519940D0

Abstract

The vehicle includes a battery- supplied electric motor drive in which series-wound motors are used with at least one driving motor or one pair of driving motors (17, 18) provided for each of at least two driving wheels (2). The series-wound motors are connected to the wheels they respectively drive by non-rigid transmission systems (11, 12, 13). Town-street and high- speed road operating conditions are selected by a control unit (5) varying the circuit arrangements. For town traffic a series system is adopted, while for high-speed operation at least some of the series-wound motors are connected in parallel, as determined by a preprogramming device (22) having a preselector (23), forming part of the control unit(S) and linked to the speedometer (19), with a driving pedal (21) having a resistance (24) coming into action after the vehicle has achieved a preprogrammed speed, so that the high-speed setting is initiated by a kickdown effect. <IMAGE>

Description

SPECIFICATION Electric road vehicle This invention relates to a road vehicle driven by electric motors and having at least two driving wheels, an electric motor driving system fr each driving wheel, an accumulator battery system, and a control unit, in which the electric motor driving systems can be operated at a high starting torque and switched by means of the control unit between starting conditions and running conditions at various speeds, and in which the driving shafts on the electric motor driving systems are connected to their driving wheels by means of non-rigid transmissions (e.g., toothed belts or chains).

In one known road vehicle of this type (U.S. Patent Specification 31 82742 of 1965), the electric motor driving systems are electric motors of a specific type, in which the armature winding on the one hand and the field winding on the other hand are functionally separated one from the other in the sense that they are each connected to their own accumulator batteries and can be independently controlled with respect to their voltage and current supplies. Technologically speaking, such electric motors must be classed as separately excited shunt-wound machines. In this way, an attempt is made to combine the advantages of series- and shunt-wound motors respectively.

However, the circuitry requirements are expensive.

The resulting system cannot be regarded as simple.

Admittedly, it develops a high starting torque, but it does not meet the requirements for efficient highspeed operation. However, modern traffic conditions in town streets on the one hand and high-speed roads on the other hand require certain specific operating behaviours; thus rapid starting and acceleration are required in town streets, to reach speeds of about 60 km/h even on a repetitive basis, while an adequate maximum speed is also required for rapid transit on high-speed roads, notably between satellite towns and city centres. Hitherto, it has only been possible to meet these requirements by adopting road vehicles having an internal combustion engine and a suitably adapted mechanical transmission system.

In this context, the object of the invention is to provide a road vehicle driven by electric motors and which is particularly well adapted not only to town traffic, by providing rapid starting and acceleration, but also to high-speed road traffic, does not resort to mechanical transmissions which would lower its performance but uses simple, proven and functionally reliable components, with particular reference to the motors.

According to the present invention, the electric motor driving systems of a road vehicle of the type initially described consist of at least one serieswound motor each arranged to be connected in series by means of the control unit for operation in town streets and arranged to be connected in parallel by means of the control unit for high-speed operation, and the control unit, which is designed in accordance with the rules of power electronics, incorporates a device for current limitation and a stop which only permits parallel connection when a prescribed road speed has been reached. In many cases when neither extreme acceleration nor ex tremely high maximum speed is required, for exam ple in road vehicles used mainly for town traffic, it is sufficient to provide a single series-wound motor for each driving wheel and operate on two driving wheels.Where a wide distinction must be made between acceleration and speed, it is preferred under the invention to assemble each electric motor driving system from a town-traffic series-wound motor and a rapid-transit series-wound motor, cou pled together mechanically by a free-wheeling device, the control unit being used to connect the town-traffic series-wound motors in the electric motor driving systems in electrical series for starting and town-traffic purposes, the control unit being further used during high-speed running to connect the rapid-transit series-wound motors in the electric motor driving systems electrically in series with each other and simultaneously in parallel with the towntraffic series-wound motors while the control unit, incorporates a current limiting device and a stop which only permits the electrically parallel connection of the rapid-transit series-wound motors when a prescribed road speed has been reached.

The invention primarily utilises the fact that the downward gradient of the torque curve against increasing rotary speed is particularly steep in a series-wound motor, the torque on the output shaft being proportional to the square of the motor current so long as the series-wound motor is not operated near its iron saturation limit. The invention further utilises the fact that current limitation is easily effected by the means available in power electronics and can be adjusted to conform to the maximum permissible discharge current from the accumulator battery system. The invention is moreover based on the discovery that the entire speed range can be subdivided into a town-traffic range and a high-speed range by simple circuit arrangements provided exclusively series-wound motors are used.The simplest scheme is to connect the series-wound motors in series for town-traffic purposes and in parallel for high-speed running.

However, high-speed running conditions can also be provided by connecting the town-traffic serieswound motors and the high-speed series-wound motors together in a special manner. In this case, the two town-traffic series-wound motors are themselves connected in series for starting and running on town streets. The series connection acting in the starting range provides a higher traction force than a parallel connection, under the maximum current permitted by the control unit. In this case, highspeed running is brought about by parallel connection. The series connection characteristic of the two motors in a pair associated with one driving wheel, in accordance with the invention, is an important precondition ensuring that the torque in the starting and slow-running range is more favourable than the combined torque in parallel connection.The choice of motor rates and the method of using them are determined by the relationship required between traction force and speed, which depends on the operating requirements and the current limitations; various operating requirements can be satisfied in this way.

The described construction having two serieswound motors per driving wheel has the advantage that the town-traffic series-wound motors used in the starting range and the low road-speed range can have optimum traction force/speed characteristics relative to the requirements of town traffic. In particular, these motors are designed so that they develop the necessary torque for rapid starting, bearing in mind short-period over-loading and the controlled limit on starting currents. Similarly, the high-speed series-wound motors in each pair, brought into operation for high-speed running in this embodiment, can also be optimised for this duty.

These motors need not be designed for increased heat evolution in the overloaded starting range, since when switched on they are either already rotating, rapidly or started up under no load until they take up the load at high speed.

It is known in principle (German Patent Specification 333 377 of 1921) to operate a road vehicle with an electric motor driving system comprising two electric motors and an intermediate free-wheeling device, in which the two electric motors act on the driving wheels through different transmissions and are switched on under different conditions, for example for running on the level in one case and climbing gradients in the other case. It has already been proposed for similar reasons (French Patent Specification 872 152 of 1942) to drive two driving wheels by electric motors of differing rating acting through a free-wheeling device. However, none of these known systems concerns the object of the invention, viz., the distinction between town and high-speed operation.The same can be said of the known fact (German Patent Specification 967 735 of 1957) that the opposite wheels of elecrically driven vehicles can be driven by double motors the twin armatures of which are disposed in a common housing on a common shaft.

There are various possiblities in detail for the further modification and construction of a road vehicle in accordance with the invention. In particu lar, it is possible to provide simple circuit arrange ments to subdivide certain speed stages or output stages within the town-traffic operating range or within the high-speed operating range. Thus, it is possible to provide a transition range between town-traffic and high-speed operation, in which the high-speed series-wound motors are connected in series with the town-traffic series-wound motors, which themselves remain in series. In this way, further acceleration or higher performance can be maintained near the upper limit of the town-traffic operating range.In one range of high-speed opera tion, the high-speed series-wound motors in the electric motor driving systems can be connected in parallel to each other and in common parallel to the series-connected town-traffic series-wound motors.

This produces further acceleration and as it were subdivides the high-speed operating range into two partial ranges. A further subdivision of the high speed operating range can be attained by making electrically parallel connections between both the town-traffic series-wound motors and the highspeed series-wound motors near the top limit of the high-speed opera ring range. It is within the scope of the invention to provide the electric motor driving systems with a further series-wound motor, in addition to and in electrical series and/or parallel with the town-traffic series-wound motor and the high-speed series-wound motor. As already mentioned the series-wound motors in a road vehicle in accordance with the invention can be of various designs.In this connection it is preferably that the town-traffic series-wound motors have a lower rating but a higher starting torque than the high-speed series-wound motors.

A road vehicle of the invention can be controlled by a driving pedal, like the accelerator pedal in road vehicles having internal combustion engines. For this purpose, the invention teaches that the control unit has a driving pedal, whereby the conditions can be switched between town street, high-speed road and intermediate settings and controlled during town street driving, high-speed road driving and intermediate ranges. It is preferred to provide the control unit with a pre-programming device and a preselector, preselecting the switch from one operating mode to another with the aid of the driving pedal, but preselection only coming into force when the pre-programmed speed has been reached. In this case, the driving pedal can operate against an increased mechanical resistance, so that the highspeed setting is as it were obtained by a kickdown effect.Finally, it is within the scope of the invention to adopt an arrangement and design such that when negotiating curves the control unit brings about a differential speed correction and is accordingly itself controlled by the steering lock on the front wheels.

These several provisions apply equally significantly to the embodiment having one series-wound motor per driving wheel and those having two or more series-wound motors per driving wheel.

The accruing advantages are to be seen in general in that a road vehicle in accordance with the invention not only allows town-traffic operation with rapid starting and acceleration behaviour but is also particularly adapted for high-speed running at an improved maximum speed, nevertheless using iow cost circuitry with simple, proven and functionally reliable components and avoiding mechanical trans missions which would lower its performance.

Two embodiments of the invention will now be described by way of example only, with reference to the accompanying diagrammatic drawings, in which Figure 1 shows the arrangement of the driving system in a first embodiment; Figure 2 shows that in a second embodiment; and Figure 3 to 7 shows various possible switching arrangements. for the two pairs of driving motors shown in Figure 2.

Each of Figures 2 to 7 can be considered to relate to a four-wheeled vehicle as indicated in Figure 1 in which the front wheels 1 can be steered and the rear wheels 2 are driven. In the rear 3 of the vehicle there is mounted a battery 4 (which may consist of a plurality of individual cells) connected to a control unit 5. All the motors 6,7 or 17, 18 shown in the Figures, i.e., all the motors discussed below, are series-wound motors. Merely to simplify the terminology they will be referrd to briefly as motors.

In the embodiment shown in Figure 1,two electric motors 6 and 7 are provided. The shafts 8 and 9 on the two motors 6 and 7 are coaxial. The two motors 6 and 7 are controlled from the control unit 5. Transmission from each of the motors 6 and 7 is effected by means of a chain 11, a toothed belt or the like, which runs round a sprocket 12 on the motor shaft 8 or 9 and a sprocket 13 connected to the driven wheel 2 concerned on the vehicle. This method of transmission allows vibration-free coupling between the electric motor 6 or 7 and the driving wheel 2.

The direction of rotation of the 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, again by means of the control unit 5. When connected in series, they function as for town-street operation, and when in parallel as for high-speed road operation. The motors 6 and 7 are equally rated. On bends, the control unit 5 appropriately adjusts the rotary speeds of the motors 6 and 7. This adjustment can be derived for example from the steering gear on the front wheels 1.

The embodiment shown in Figure 2 differs in that a pair of motors 17,18 is provided for each of the two driving wheels 2, comprising in the example shown a lower-rating motor 17 and a motor 18 having approximately twice the rating, both acting on a common driving shaft 16 and being connectable and separable through a free-wheeling clutch 10. Each motor pair 17, 18 can have a common housing 20 containing the motors 17 and 18 in the pair. The two motor pairs and their individual motors 17 and 18 are controlled through the control unit 5. The circuitry of the control unit 5 is devised so that during starting and town-street operation, only the series-connected driving motors 17 act on the corresponding shafts 16 and rotate the driving wheels 2 through the transmissions 11.When the vehicle has attained the required speed, the motors 18 hitherto disconnected from the driving motors 17 by the clutches 10 can be additionally brought into action, so that the driving power is thereafter developed by the two motors 17 and 18 in each motor pair. This can be brought about in various ways, provided use is made of the advantageous parallel connection effect previously described with reference to highspeed driving. In this case, the motors 17 and 18 are for example connected in series. If the speed falls below a prescribed minimum, the motors 18 are once more switched off, so that the two motors 17 alone keep the vehicle in motion though the two driving wheels 2. As an additional high-speed setting, it is optionally possible to connect all four motors 17 and 18 in parallel, provided they are suitably designed.

Instead of the pairwise arrangement of motors 17 and 18 on each driving wheel 2, it is possible to use more than two motors which can be similarly selectably connected and separated, though this is not shown in detail.

The control unit 5 can for example be connected to the vehicle speedometer 19 and the stop preventing switching to a high-speed setting can remain effective up to a preselected threshold speed. Likewise, the control unit 5 in conjunction with the speedometer 19 can bring about a return to low-speed settings if a similarly preselected second threshold speed is not maintained.

Figures 3 to 7 show various possible circuit arrangements for the driving system of the invention. Thus the upper part of Figure 3 corresponds to the embodiment as in Figure 1, having only two separate series-connected motors 6 and 7. On reaching a certain road speed, these can be switched into parallel connection.

On proceeding to the embodiment as in Figure 2, the series-connected motors now numbered 17 which cover the starting range of the vehicle are supplemented beyond a certain speed range by a pair of motors 18, also interconnected in series, in such a manner that each motor 17 is mechanically and electrically connected to a motor 18.

Figure 4 shows the series connection of all four motors in the two motor pairs of Figure 2.

In the arrangement shown in Figure 5, the two motors 17 are interconnected in series whereas the two motors 18 are in parallel. Figure 6 shows the inverse situation, with the two motors 17 in parallel and the two motors 18 in series.

Finally, Figure 7 shows a parallel connection for all the motors 17 and 18 in the two motor pairs. This demonstrates the wide variety of possible circuit arrangements and hence the various vehicle operating conditions that can be obtained. The various possibilities can be realised by simple circuitry.

Figure 2 also shows the driving pedal 21, a pre-programming device 22 having a preselector 23, and a mechanical resistance 24 on the driving pedal 21 which comes into action when the driving pedal 21 has moved through a prescribed operating stroke.

The units 22,23 are functionally parts of the control unit 5. The embodiment shown in Figure 1 could be correspondingly adapted. The preselector 23 makes it possible to set the pre-programming device (at the manufacturer's or during use, for example) to a speed at which it will become possible to switchfrom town-traffic to high-speed road conditions. The switching is brought about by means of the driving pedal 21, but it can only be made afterthe road vehicle has attained the pre-programmed speed. The arrangement is such that the driving pedal must be operated against the mechanical resistance 24, so that the high-speed setting is initiated by a kickdown effect.

Claims

1. A road vehicle driven by electric motors and having at least two driving wheels, an electric motor driving system for each driving wheel, an accumulator battery system, and a control unit, in which the electric motor driving systems can be operated at a high starting torque and switched by means of the control unit between starting conditions and running conditions at various speeds, and in which the driving shafts on the electric motor driving systems are connected to their driving wheels by means of non-rigid transmissions, the electric motor driving systems each consisting of at least one serieswound motor arranged to be connected in series by means of the control unit for starting and operation in town streets and being arranged to be connected in parallel, by means of the control unit for highspeed operation, and the control unit, which is designed in accordance with the rules of power electronics, incorporating a device for 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 each electric motor driving system is assembled from a town-traffic series-wound motor and a rapid-transit series-wound motor coupled together mechanically by a free-wheeling device, the control unit being used to connect the town-traffic series-wound motors in series for starting and town-traffic purposes and the control unit being used during high-speed running to connect the rapid-transit series-wound motors in series with each other and simultaneously in parallel with the town-traffic series-wound motors when the control unit incorporates a current limiting device and a stop which only permits the electrically parallel connection of the rapid-transit series-wound motors when a prescribed road speed has been attained.

3. A road vehicle as in Claim 2, wherein in a transitional range between town-traffic and highspeed operation, the high-speed series-wound motors are connected in series with the town-traffic series-wound motors, which themselves remain in series.

4. A road vehicle as in Claim 2, wherein in one range of high-speed operation, the high-speed series-wound motors are connected in parallel to each other and in common parallel to the seriesconnected town-traffic series-wound motors.

5. A road vehicle as in Claim 2, wherein near the top limit of the high-speed operating range, electrically parallel connections are made between both the town-traffic series-wound motors and the highspeed series-wound motors.

6. A road vehicle as in any one of Claims 2 to 5, wherein the electric motor driving systems are provided with a further series-wound motor, in addition to and in electrical series and/or parallel with the town-traffic series-wound motor and the high-speed series-wound motor.

7. A road vehicle as in any one of Claims 2 to 6, wherein the town-traffic series-wound motors have a lower rating but a higher starting torque than the high-speed series-wound motors.

8. A road vehicle as in any one of Claims 1 to 7, wherein the control unit has a driving pedal, whereby the conditions can be switched between town street, high-speed road and intermediate settings and controlled during town street driving, highspeed road driving and intermediate ranges.

9. A road vehicle as in Claim 8, wherein the control unit has a pre-programming device and a preselector, bringing about the switch from one operating mode to another with the aid of the driving pedal, preselection only coming into force when the pre-programmed speed has been reached, in which case the driving pedal operates against an increased mechanical resistance so that the high-speed setting is obtained by a kickdown effect.

10. A road vehicle as in any one of Claims 1 to 9, wherein when negotiating curves, the control unit brings about a differential speed correction and is accordingly itself controlled by the steering gear on the front wheels.

11. A road vehicle as in any one of Claims 1 and 8 to 10, wherein two driving wheels are provided, each being associated with one series-wound motor, which motors are connected in series for town street driving and in parallel for high-speed road driving.

12. A road vehicle driven by electric motors and substantially as hereinbefore described with reference to Figure 1 and the upper part of Figure 3 of the accompanying drawings.

13. A road vehicle driven by electric motors and substantially as hereinbefore described with reference to Figures 2 to 7 of the accompanying drawings.