GB2261026A

GB2261026A - Preventing unauthorised use of spark ignition vehicle engines

Info

Publication number: GB2261026A
Application number: GB9222405A
Authority: GB
Inventors: Kenneth Gardner; John William Fahy
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-11-01
Filing date: 1992-10-26
Publication date: 1993-05-05
Also published as: GB9222405D0

Abstract

The ignition timing is set such that the engine will not operate and a correction is applied, dependent on engine speed, in response to authorised operation of an electronic coded security lock to enable engine operation. The correcting device may be integrated into an engine management unit.

Description

VEHICLE IMMOBILISER This invention relates to a tamperproof vehicle petrol engine immobiliser. Vehicle engine immobilisers are devices which attempt to stop car theft by preventing the engine from being started by the thief.

Existing immobilisers disable the engine by breaking an electric circuit, such as electric fuel pump supply or ignition supply. The devices are usually armed using a concealed switch or keyswitch.

Although effective, this class of device can be overcome by the determined thief shorting together the device input and output, a technique popularly known as "hot wiring".

According to the present invention, there is provided a vehicle petrol engine immobiliser comprising a vehicle ignition retiming device. The vehicle engine distributor or ignition sensor is deliberately moved to significantly mis-time the engine ignition system, this by adjustment on an existing vehicle, or by design on a new vehicle. Under these conditions, the engine would normally fail to start or run.

The immobiliser introduces a correcting delay to restore the ignition timing to its correct setting, so allowing the engine to start and run normally. The timing delay is related to angular rotation of the engine and is thus a function of engine speed.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 shows the location of the immobiliser within a typical vehicle ignition system; Figure 2 shows a block diagram of the immobiliser electronic circuit; and Referring to Figure 1 of the drawing, the immobiliser is positioned between the engine ignition contact breaker or equivalent device and ignition coil.

The engine is deliberately mis-timed by adjustment or design, the mis-timed pulse being input to the immobiliser. The corrected output of the immobiliser is connected to the primary of the vehicle ignition coil.

The immobiliser is disabled using an electronic coded security lock.

Referring to Figure 2 of the drawing, the input to the immobiliser drives a frequency counter which calculates the rotational speed of the engine.

This information is used to calculate the corrective delay to be applied to the input timing pulse. The corrective delay is applied to the incoming ignition pulse. The resulting retimed ignition pulse is output to the ignition coil primary. Note that the device can be applied to engines with any number of cylinders.

The formula used to derive the correct retiming delay at a given engine rotational speed, for a given ignition mistiming is: T (a) Where: T is the corrective time delay (seconds) 6 is the timing offset angle (degrees) w is the rotational speed of the engine (degrees per second) The complex nature of the immobiliser function prevents theft by shorting the immobiliser input to output ("hot wiring"). Access to the device is by coded electronic security lock to prevent unauthorised disabling of the immobiliser. The combinations of timing advance and correcting delay are several, making substitution of another engine immobiliser difficult and time consuming.

Examples of other specific embodiments are shown in further figures in which: Figure 3 shows the immobiliser added to a traditional ignition system with contact breaker.

Figure 4 shows the immobiliser added to an ignition system with existing electronic ignition (power driver).

Figure 5 shows the immobiliser added to an ignition system with simple engine control unit.

Figure 6 shows the immobiliser fitted to an ignition system with engine management unit.

Figure 7 shows the immobiliser fitted to a distributorless ignition system.

The immobiliser is thus applicable to all types of ignition system. For new designs, the immobiliser function may be integrated with the other ignition system electronic functions, e.g. engine control unit, engine management unit.

Claims

1. A vehicle petrol engine immobiliser comprising a vehicle ignition retiming device. The vehicle engine distributor or ignition sensor is deliberately moved to significantly mis-time the engine ignition system, this by adjustment on an existing vehicle, or by design on a new vehicle. Under these conditions, the engine would normally fail to start or run.

2. A vehicle engine immobiliser as claimed in Claim 1 wherein the complex nature of the immobiliser function prevents theft by shorting input to output ("hot wiring"). Access to the device is by coded security lock to prevent unauthorised disabling of the immobiliser.

3. A vehicle engine immobiliser as claimed in Claim 1 or Claim 2, wherein the combinations of mis-timing and correcting delay are several, making substitution of another similar engine immobiliser difficult and time consuming.

4. A vehicle engine immobiliser as claimed in Claim 1, Claim 2 or Claim 3, wherein the immobiliser is not only applicable to all types of ignition system, but whose function can be integrated with the other functions which comprise the vehicle ignition system.

5. A vehicle engine immobiliser substantially as described herein with reference to figures 1, 2, 3, 4, 5, 6 and 7 of the accompanying drawings.