GB2172067A - Drive for a battery-powered vehicles - Google Patents

Abstract

A battery-powered electric road vehicle is provided with a drive in which the traction motor (4) is connected through a torque-limiting coupling (6) to a continuously varying ratio transmission (16, 18, 20) and the transmission ratio is regulated in dependence upon the road speed of the vehicle by a control unit (30) that receives inputs of road speed (28) and transmission ratio setting. The control unit adjusts the transmission so that the ratio of motor speed to road speed is progressively reduced with rise of road speed. The torque limiting coupling (6) is preferably of the powder type and the variator (16) is adjusted by a hydraulic actuator through a linkage. <IMAGE>

Description

SPECIFICATION Battery-powered vehicles This invention relates to battery powered electric road vehicles and is concerned particularly with the drives of such vehicles.

The economics of operation of conventional battery powered vehicles is dependent to a large extent on the life of its batteries which, in terms of the number of cycles of charge and discharge that can be obtained, is increased when the average discharge is kept within the rated capacity of the batteries. The available motive power varies in relation to the rate at which the power is drawn from the battery or batteries, so that in order to achieve commercially acceptable economy in conventional vehicles it is necessary to have a fixed measurable duty carefully matched to the battery rated capacity, which confines a vehicle to a small range of speeds and duties.

According to the present invention, there is provided a drive for a battery powered electric road vehicle comprising an electric traction motor, preferably a series-wound DC motor, connected through a torque-limiting coupling to a preferably continuously variable ratio transmission, and means for controlling said transmission in dependence upon the road speed of the vehicle so that the ratio of motor speed to road speed is progressively reduced with rise of road speed in such a manner as to substantially limit the motor current at higher speeds.

The overall transmission ratio can be automatically controlled in relation to road speed by using the output of an electronic tachometer, or a tachogenerator, to operate an electronically controlled servo actuator which mechanically varies the transmission ratio, e.g.

acting on an adjustable belt and pulley drive transmission mechanism. By appropriate de sign,- the control system can be arranged to keep the motor speed within a narrow range and hence the batteries will be required to supply a substantially constant current. During start-up it may be desired to ensure that control of the current supply does not sacrifice initial acceleration. For example, the servo actuator can be arranged to come into operation only after start-up but at a relatively low vehicle speed, e.g. at 10-20kph, and then control the current load up to the maximum road speed of the vehicle, and if required specific means may be provided to hold the control system inoperative at start-up.

At lower speeds, the torque limiting coupling can be relied on to limit the motor current sufficiently to prevent overload.

A vehicle drive in this form does not require direct driver control of the transmission ratio, although means may be provided for adjusting the setting of the torque limiting coupling and of the controlling means. The aim will generally be to achieve an average amperehour consumption for a given vehicle duty at a higher road speed than is possible for a conventional battery powered vehicle operating at lower speeds, at a comparable ampere-hour consumption.

An embodiment of the invention will be described in more detail by way of example with reference to the accompanying drawings, in which: Figs. 1, 2 and 3 are diagrammatic side, plan and end views of a drive for a battery powered vehicle according to the invention, Fig. 4 is a schematic illustration of the control means of the drive, and Fig. 5 shows in graphical form the relationship of some of the variables of the drive in relation to road speed.

The vehicle drive is shown mounted on a baseplate 2 as a unit, with a DC series wound traction motor 4 coupled to a pre-set torque limiting coupling 6 of the powder type which is connected through a flexible coupling 8 to a drive shaft 10 mounted on bearings 12, 14.

The drive shaft carries one adjustable cone pulley 16 of a variable drive transmission coupled by a V-belt 18 to a second adjustable cone pulley 20 on a driven shaft 22 suspended below the baseplate on bearing brackets 24. The driven shaft 22 is connected through a universal joint at one end to a conventional propellor shaft 26 to drive the vehicle road wheels and at the other end to a speed sensing device 28.

The sensing device 28 is connected to an electronic control unit 30 which controls a motor 32 for an actuator piston 34. The motor 32 and piston 34 form a unit pivoted through bolt 33 relative to the baseplate. The piston has an end pivot connection 36 to a lever 38 that is mounted at its opposite end 40 to the baseplate through an articulation link 41, and between its ends at 42 the lever is pivoted to a hub 44 on one side face of the driving pulley 16. A biassing spring 46 is compressed between the hub 44 and a sleeved collar 48 fixed to the other side face of the pulley so that the spring force acts to reduce the effective diameter of the pulley, the V-belt being kept in tension by the action of a biasing spring 50 on the driven pulley 20 in an analogous way to increase its effective diameter.

Fig. 4 shows the speed sensing device 28 in the form of a ferrous disc 52 with a series of equispaced pick-up holes 54, the disc rotating with the driven shaft 22 to generate a pulsing voltage in a magnetic pick-up 56. An IC rectifier 58 converts the pick-up signals into a 0-5V DC voltage proportional to the vehicle road speed. The signal voltage is transmitted to the electronic control unit 30 through input 62 and a DC signal is also received through input 64 from a potentiometer 66 connected to the actuator piston 34. By a continuous read and search process on the input signals, the control unit is able to correlate the effective driving pulley diameter with the instantaneous road speed.Continually correcting itself, it is able to produce through output 68 a 24V DC drive for the actuator motor 32 directly related to road speed so that the piston 34, and therefore the effective pulley diameter, is adjusted as required to bring the two DC signals at the inputs 62,64 into balance.

It will be understood that by choice of the relationship to be established between the input signals and the motor output power it is possible to produce a desired control characteristic and Fig. 5 illustrates one possibility. In this figure, plotted against the vehicle road speed are the motor current and the reduction ratio of the drive. The motor current shows a maximum value at start-up of the vehicle, at which point the controller is inoperative and the driving pulley is held by its biasing spring at a minimum effective diameter. If it is necessary to hold the controller inoperative, a voltage sensitive relay means (not shown) may be provided, operated by the output of the speed sensitive device, or there may even bea time delay circuit.

As the road speed and the motor rpm build up, the motor current drops until a point is reached, at a speed of approximately 20kph in this instance, where the road speed signal to the controller is able to operate the piston and increase the effective diameter of the driving pulley. Thereafter, as road speed increases further, a linear relationship is maintained between the effective reduction ratio of the drive transmission and the road speed. It will be understood that some variation of the motor current will occur while the controller is operative, but this may be limited to about 20% of the maximum current as shown in the example of Fig. 5.

In place of the magnetic pick-up means described for sensing road speed, a tacho-generator 72 may be employed, as is also shown in Figure 4. In that case a DC signal may be taken direct from the sensor to the control unit. It may be mentioned here also that, while Fig. 1 shows a speedometer drive separate from the speed sensing device, the output of the sensing device may be also employed to operate the speedometer on the vehicle instrument panel.

While the control means described are intended to operate without intervention from the driver, it will be understood that it would be easy to arrange for momentary or pre-set modification of the control characteristics, whether by the driver or as a workshop adjustment. For example, if the duty conditions require it, the road speed input signal can be arranged to increase at a slower rate in order to give a motor current rising with speed-i.e.

thereby increasing the power output at higher speeds.

It will be understood that it is also possible within the scope of the invention to provide the drive as a modification for an existing battery-powered vehicle as well as to manufacture a vehicle incorporating the drive.

Claims (14)

1. A drive for a battery-powered electric road vehicle comprising an electric traction motor connected through a torque-limiting coupling to a variable ratio transmission, and means for controlling said transmission in dependence upon the road speed of the vehicle so that the ratio of motor speed to road speed is progressively reduced with rise of road speed in such a manner as to substantially limit the motor current at higher speeds.

2. A drive according to claim 1 wherein means are provided for inhibiting operation of said controlling means below a predetermined road speed.

3. A drive according to claim 1 wherein a time delay circuit is arranged to be operated during start up of the vehicle to temporarily inhibit the operation of said controlling means and so permit rapid initial acceleration of the vehicle.

4. A drive according to any one of the preceding claims wherein driver-operated means are provided for adjusting the setting of the means for cbntrolling the variable ratio transmission.

5. A drive according to any one of the preceding claims wherein within its range of operation the controlling means is arranged to give a substantially constant motor current characteristic.

6. A drive according to any one of claims 1 to 4 wherein within its range of operation the controlling means is arranged to give a motor current characteristic that rises with vehicle speed.

7. A drive according to any one of the preceding claims comprising a continuously variable ratio transmission for the output of the traction motor.

8. A drive according to claim 7 wherein the transmission comprises an adjustable belt and pulley drive mechanism.

9. A drive according to any one of claims 1 to 3 wherein an electronic tachometer or a tacho-generator is arranged to operate servo means for varying the transmission ratio.

10. A drive according to claim 2 together with claim 9 wherein means are provided to prevent the servo means operating on the drive transmission below said predetermined minimum vehicle speed.

11. A drive according to any one of the preceding claims wherein means are provided for adjusting the setting of the torque-limiting coupling.

12. A drive according to any one of the preceding claims wherein the traction motor is a series-wound DC motor.

13. A drive for a battery-powered rcad vehicle constructed and arranged for use and operation substantially as described herein with reference to the accompanying drawings.

14. A battery-operated electric road vehicle comprising a drive according to any one of the preceding claims.