Motor vehicles – Power – Electric
Patent
1995-11-13
1998-04-28
Camby, Richard M.
Motor vehicles
Power
Electric
180 22, B60K 102
Patent
active
057433470
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the manner of providing and controlling power transfer from a battery pack to the electric drive motors, and to the road wheels of an electric vehicle such as a lawn and garden tractor, for example in the 16 HP size range.
Such vehicles are common and are powered by gasoline or engines, but are not economical or efficient. The noise, fumes, etc of a gasoline tractor can be obtrusive to many users, especially since many lawn and garden tractors are used around buildings and people. Several attempts have been made to provide an electric tractor, with re-chargeable batteries, in that size range.
Given that a lawn and garden tractor is purchased because the lawn and garden is quite sizeable, and therefore the tractor will be subjected to a demanding duty cycle, it is recognised that there is sufficient space on a small tractor to contain the quantity of batteries needed for the duty cycle, if used economically. That is to say, the size available for the battery pack is sufficient for the typical heavy duty cycle, but only if the power is utilised efficiently.
In previous designs of small tractor, the power to the drive motors has been controlled, as to the speed of the wheels, by means of switched resistors. This type of control does not use the electricity economically, in that some of the power goes in heating the resistors; it is also mechanically jerky; and it also has the disadvantage that the control system employs small moving parts which can pose a service problem, given that a lawn and garden tractor can suffer long periods of mechanical neglect.
In previous designs of small electric tractors, the mechanical drive from the electric motor to the road wheels has been complex, involving drive axles, chain drives and sprockets, final drive units, differential gears, etc.
The present invention is aimed at providing a power, and power control, system for a lawn and garden tractor, in which the system uses solid state components, with no exposed moving parts (other than the road wheels). In the invention, individual motors are provided for each road wheel. Preferably, each motor feeds power to its road wheel through a respective simple parallel-shaft, enclosed, speed-reduction gearbox, and the road wheel is attached directly to the output shaft of the gearbox.
The invention thus provides respective drive motors, one for each driven wheel of the tractor. The road wheels preferably are mounted directly on the output shafts of gearboxes connected directly to, and housed with, the drive motors. The driven wheels are not connected by means of a drive axle, and no differential gear or final drive unit is required.
In the invention, the left drive motor drives the left road wheel and the right drive motor drives the right drive wheel. The drive control system is such that each motor is driven to rotate at a particular speed. The motor is supplied with the current or power it needs to maintain that speed, even if load conditions should vary. Thus, the tractor tends to travel in a straight line at a constant speed, or a steered curve, even if one wheel should encounter a small obstacle. Also, the tractor maintains wheel speed even if one wheel should run over a low-grip surface.
Preferably, the motors are arranged to feed energy back into the batteries if the motors are over-running the wheels (when the tractor is decelerating, for example.) Such regenerative braking provides a useful improvement in overall efficiency. Not only that, but an electric tractor contains a battery pack of considerable mass, and the inertia of the tractor might make close maneuvering a little difficult if the tractor were able to run on during over-run. The resistance on over-run caused by regenerative braking substantially improves the feel of the controls, whereby the driver does not feel that the tractor is running away with him.
Besides, on a lawn and garden tractor, braking requirements are not very demanding, and providing regenerative braking means that the only other braking required, if indeed any other i
REFERENCES:
patent: 4415049 (1983-11-01), Weres
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