This invention relates to a device for preventing engine over run in a motor vehicle.
When a motor vehicle, more particularly, a vehicle having a fixed gear ratio, rolls down a slope, running is accelerated by its own weight, the engine over running at a rotational speed beyond the allowable range. In such situation the wheels tend to drive the engine at a very high rpm, when the driver closes the throttle. This phenomenon happens especially in a motorcycle or moped without gear's. In the case of such vehicles, having a two-stroke engine, as the engine depends on fuel for lubrication, shortage of fuel to the engine would result in a shortage of oil in the cylinders since such engines have lubrication oil mixed with fuel. During this condition of engine overrun, the piston would seize within a short time due to lack of lubrication, causing extensive engine damage.This may lead to several mechanical failures. In order to prevent this condition, manual intervention is required in order to determine whether the engine rpm is exceeding the allowable limit and, if so, to operate a brake or a self regulating mechanism to reduce the speed of the vehicle.
According to the known art, various mechanisms have been proposed to reduce the engine speed, such as those given below:
In one such mechanism, the fuel supply is reduced so as to decrease the engine speed. This method requires additional components in the fuel system.
In another mechanism, the ignition is controlled at higher engine speed. This method has a disadvantage, namely, that if there is a fault it will result in ignition failure.
In yet another mechanism, applying a mechanical lock up is an option used in earthmovers. However, this results in a complex and bulky system, occupying more space than is desirable..
The prior art has also led to the proposal of using an exhaust brake. In this mechanism, the exhaust pipe has to accommodate the high pressures generated by this system. This can cause increase in engine oil carry-over.

The hydraulic retarder requires complex mechanisms like oil hoses and reservoirs, which are bulky and not cost effective for small vehicles.
Electric retarders utilize electrical windings on a stator attached to the chassis and rotor attached to the axle. These are space consuming and increase the weight of the vehicle.
A freewheel is used to avoid overrun, but leads to more weai* on the brakes.
In a motor vehicle with manual transrfiission, a downshift can be done to reduce the engine speed, but it is entirely dependent on the driver/operator's alertness and is prone to human error.
It is therefore an object of this invention to provide a simple, cost effective solution to overcome the problem of engine overrun especially in a vehicle having fixed gear ratio or transmission system.
This invention proposes to reduce the engine speed, when it crosses the specified limit, by increasing the electrical load on the alternator/magneto (hereinafter briefly referred to as the magneto) of the engine. As the magneto is mechanically coupled to the engine, the electrical loading will increase the load on the engine. Thus when the input signal crosses a predetermined value, the magneto is loaded completely, leading to an increase in the load on the engine forcing the rpm to come down significantly.
The electrical loading can be achieved by means of a controller, which controls the switching of the electrical loads after processing the information provided by two sensors.
To avoid engine seizure due to rise in engine rpm, a device to reduce the engine rotational speed is proposed. This control mechanism involves the use of a controller and a switching device. The controller performs the functions of shorting the output of the magneto based on a predetermined logic:
This depends on various factors like engine rpm, brake status and so on. Power is dissipated in the electrical loads so as to reduce the power developed in the engine. This proposal would prevent engine sei/nre HUP tr.

invariable increase in the engine speed. The added advantage is lesser braking effort will be required to slow down the vehicle. It provides additional stopping ability to a vehicle in motion.
This invention will now be described with further reference to the single Figure in the accompanying drawings which illustrate by way of example and not by way of limitation one of possible embodiments of the device proposed herein.
For two-wheelers, the electrical power is generated by a magneto (M) which is directly coupled to the crankshaft!. When the engine is running, the magneto converts this mechanical energy to electrical energy. The voltage produced by the magneto is regulated by the regulator cum rectifier unit (R), for supplying to the loads (LI, L2) and charging the battery B. The switches Swl and Sw2 are mechanical switches independently controlled by the driver/operator. These switches are used to switch ON or switch OFF the electrical loads (LI, L2) such as headlamp, tail lamp, position lamp, etc. Alternatively, the control unit CU can also enable or disable power supply to the loads (LI, L2).
The control unit CU receives its supply S for its functioning from the battery B. Sensors are provided for sensing input signal which can be either engine speed or the brake signal. When the signal input (I) to the control unit (CU) exceeds a predetermined value, the control unit shorts the magneto output lighting power L and charging power C to the chassis ground. The controller also receives the switch status information from Swl and Sw2. If either of the switches Swl or Sw2 is ON, then the controller does not short the magneto output (C and L). Only when both the switches (Swl and Sw2) are in the OFF condition, and the signal input I exceeds a predetermined value, the controller shorts the magneto output (C and L) to the chassis ground. Hence the load on the magneto M increases thereby loading the engine. This will reduce the engine rpm and avoid engine overrun.
It will be appreciated that various other embodiments of the device proposed herein are possible without departing from the scope and ambit of this invention.

We Claim:
1. A device for preventing engine over run in a motor vehicle comprising a magneto; a control unit, a battery for supplying power to the control unit; at least one sensor for sensing the input signal and feeding the input signal to the control unit; electrical loads and ON/OFF switches connected to the control unit, whereby when at least one of the switches is in the OFF position, and the input signal to the control unit crosses a predetermined value corresponding to a predetermined wheel speed, the control unit shorts the output of the magneto to the chassis of the vehicle (ground) thereby loading the magneto, and thus, in turn, loading the engine, to reduce the engine rpm and prevent engine over run.