Motor vehicles – Power – Electric
Reexamination Certificate
2000-02-22
2001-12-25
Swann, J. J. (Department: 3611)
Motor vehicles
Power
Electric
C180S065510, C180S233000
Reexamination Certificate
active
06332504
ABSTRACT:
The present invention relates to electric vehicles, and more particularly to the drive system of such vehicles.
Cars and similar vehicles have, ever since their origins a century ago, largely been driven by internal combustion engines, using either petrol or diesel fuel. Two other forms of engine, viz electric and steam, have been used at various times, but neither has achieved major success. With the growing present concerns over pollution and oil conservation, electric vehicles are receiving increased attention.
Trams and trolley-buses are powered from conductors laid on, under, or over the roadway, so they are constrained to predetermined routes. Disregarding such special cases, however, an electric vehicle is battery powered, and the battery can be charged from a suitable electric supply point fed by a public utility (typically the grid). The generation of the electricity for the battery charging will generally be more efficient and less polluting than an internal combustion engine, and can use a variety of energy sources, including renewable sources. An electric motor can also provide regenerative braking.
Electric vehicles have, however, some major problems. One is the weight of the batteries required to give an adequate performance (vehicle range and speed for a battery charge), which in turn is dependent on the efficiency of the system. Another is the cost of the system, which again is dependent to some extent on the system efficiency. Adding more batteries to increase the range adds more weight to the vehicle, making it less efficient.
A vehicle driven by internal combustion normally has a single engine which drives the wheels. Traditionally, the engine drives the rear wheels, though more recently, front wheel drive and 4 wheel drive systems have become popular. The usual position for the engine is at the front of the vehicle, so a front wheel drive system avoids the need for a transmission shaft (propeller shaft) running along the length of the vehicle. A 4 wheel drive system is more complicated than a conventional 2 wheel drive system, but gives better road grip in poor driving conditions.
The obvious way of designing an electric vehicle system is to simply take a conventional internal combustion engine system and replace the engine by an electric motor. The output shaft of the electric motor will be coupled to the wheels in substantially the same way as the output shaft of the internal combustion engine, possibly with some modifications in the gearing arrangements.
An alternative approach is more radical. Since electric motors are simpler and more flexible than internal combustion engines, it has been proposed to provide a separate electric motor for each driven wheel of the vehicle, so that the vehicle has 2 or 4 electric motors.
These two approaches both have disadvantages. A problem with the simple substitution is that an electric motor has different characteristics from an internal combustion engine, so the system is likely to have considerable inefficiencies. A problem with the separate motor for each wheel system is that the system requires 2 or 4 motors instead of 1, with the concomitant increase of cost and weight (even though the individual motors can be smaller); also, the design of a control system for this system becomes complicated.
The general object of the present invention is to provide an electric vehicle with an improved motor system.
Accordingly the present invention provides an electric vehicle having an electric motor having its armature coupled to one drive shaft and its case coupled to another drive shaft, the two drive shafts driving the front and rear axles, ie the front and back pairs of wheels, respectively, through respective differentials, characterized in that a gear-box having a plurality of ratios is included in at least one of the drive shafts.
An electric motor is normally thought of as having a fixed structure, which we here term its case, in which an armature rotates. The case includes fixed magnetic means, either fixed magnets or field windings. However, the torque is essentially developed between the armature and the case; the torque developed on the armature is matched by an equal and opposite torque on the case. In the present invention, the armature is coupled to one axle, eg the front axle, and the case is mounted so that it can also rotate and is coupled to the other axle (in this case the back axle).
In principle, of course, an internal combustion engine also generates a torque between the output shaft and the engine body. But with a conventional internal combustion engine, it would be totally impracticable to allow the engine body to rotate. With an electric motor, on the other hand, there is no major difficulty of principle in allowing the motor case to rotate as well as the armature.
The electric motor thus effectively has 2 drive shafts, one from the armature and one from the case. These are coupled to the front and rear wheels of the vehicle, preferably through respective differentials of generally conventional form. These differentials may be chosen to give a desired ratio between the two drive shafts of the motor. It will be realized that the road wheels of the vehicle all normally run at the same speed; so, analysing backwards from that fact, the relative speeds of the two drive shafts of the motor are determined by the ratio of the front and back differentials. (It is convenient to refer generally to the drive shafts, the motor driving the drive shafts, etc, even though, as will appear below, the power flow along one or both the drive shafts may in certain circumstances be from the wheels to the motor, ie driving the motor as a generator.)
Depending on the circumstances, the 2 drive shafts may drive the respective axles in either the same direction or the opposite directions. In other words, if the 4 wheels are all rotating at the same speed, the two drive shafts may be rotating in either the same direction or in opposite directions, depending on the circumstances. It is generally preferred for the rotations to be in the same direction, for reasons discussed below. However, there may be special circumstances in which rotation in opposite directions may be used.
Additionally, there may be provided an auxiliary motor, coupled to the rear drive shaft, which can be used to provide additional driving force. This auxiliary motor may be an electric motor with its armature mounted coaxially on the relevant shaft and its case fixed, so that it applies an additional torque to the shaft. When this motor is not energized, it will effectively free-wheel and have no significant effect.
Alternatively, the auxiliary motor may be coupled to the relevant drive shaft via suitable gearing. Again, when it is not energized, it will have no significant effect. However, in this position, a clutch can be incorporated between it and the relevant drive shaft if desired. If desired, an internal combustion engine can be used instead of the auxiliary motor in this configuration, as a source of additional driving force.
The present invention thus provides a more efficient and flexible motor system for an electric vehicle.
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Lowe Hauptman & Gilman & Berner LLP
Lum L.
Swann J. J.
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