Field of the invention

The present invention relates to an engine management system for an engine having a rapid heating system for a catalytic converter or a fuel vaporiser.

Background of the invention

For any fast catalyst light off heating system (exhaust gas ignition, external fuel burner, electrically heated catalyst) and fast warm up heating system (glow plug, fuel vaporiser) , there is a risk that if the system is operated more than once in close succession damage would occur.

For example, in a vehicle equipped with such a heating system, it is desirable to have the vaporiser or the catalytic converter in full operation within seconds or even a fraction of a second as soon as the car is started, and the heating system should therefore be operated during cold starts. However, if the car stalls and is restarted immediately, the catalyst is already hot, the glow plug is still hot, the fuel vaporiser is already hot, but everything else in the car remains cold. Unless there are temperature sensors measuring these hot elements directly, the engine management microprocessor would have no indication that the second start is any different from the first and would give the heating system another dose of intense heat which could cause damage to the fuel vaporiser or the catalytic convert,sr.

A difficulty currently encountered in complying with statutory regulations is that the temperature sensing elements available do not have the required proven durability and direct temperature measurement is not currently an available solution this problem.

The invention therefore seeks to provide alternative safeguards to protect against damage through overheating.

One possible solution to this problem would be to store in a keep alive memory the coolant temperature at the time the engine is stopped or stalls and to compare the stored reading with a current measurement of the coolant temperature during the attempt to restart the engine. If the engine was hot when switched off and is now cold, then it is safe to operate the heating system but if the engine coolant was cold and is still cold, this suggests that the engine is being restarted after only a very short run and that it is therefore unsafe to operate the heating system.

The problem with this system however is that the time that has elapsed since the engine was switched off is still not' known and it is possible that an engine that was run for a very brief period may have been allowed to stand for long enough to cool down fully and in this case the heating system will fail to operate during the next start, even though it should be switched on normally.

Another situation is when the engine is stopped after it has fully warmed. The coolant temperature will continue to rise for a period because of redistribution of heat within the engine when the coolant flow is stopped and will then cool relatively slowly whereas the catalyst or the fuel vaporiser will start to cool immediately after the engine is stopped and will cool more quickly. If the engine is restarted during this period, the engine management system will read the input from the coolant temperature sensor which indicates that the engine is still hot and will prevent activation of the rapid heating system even though the catalyst or the fuel vaporiser is already cold and the heating system should be activated.

In the drawing, an engine management system 14 which may for example be a microprocessor is brought into operation by an ignition switch 10 and a power supply relay 12 each time the engine is to be started. The engine management system 14 receives a variety of input signals of which only one, from a coolant temperature sensor 18, is illustrated in the drawing.

The engine management system 14 also has several outputs that control the ignition, the engine fuelling and the operation of a heating system for raising the temperature of a catalytic converter during cold starts, or for vaporising fuel during cold starts. The operation of the engine management system is well known per se and need not therefore be described in detail in the present context.

The heating system for the catalytic converter may be any of several that have been described in the prior art . Amongst these there are known systems which ignite exhaust gases, systems which ignite fuel from an external source and electrical heating elements incorporated into the catalyst. The heating system used for vaporising the fuel in common with the means for igniting fuel or exhaust gases can take the form of a glow plug.

As so far described the illustrated system is known and suffers from the problem that when the engine is switched off the management system has no way of knowing the time that has lapsed since previous operation. When it comes to life, the management system could believe the engine to be cold based upon the signal from the engine coolant temperature sensor 18 despite the fact that the heating system has recently been heated during the cold start that has not lasted long enough to affect the engine coolant temperature, for example, if the vehicle is driven only a few feet or the engine stalls shortly after starting.

To avoid this particular problem, the engine management system 14 has an output line 16 which can be used to keep the engine management system 14 alive by activating the power supply relay 12 despite the fact that the ignition switch 10 has been turned off. In effect the relay 12 now acts as a hold-on relay that keeps the engine management system in operation, performing if necessary only a reduced function, until the management system 14 determines that it would be safe to energise the heating system normally in the next cold start. The management system can by knowing the time since the engine was switched off estimate the temperature of the

If an attempt is made to start the engine before the management system has switched itself off then the data and its own programming can determine the extent that the heating system should be energised to reach its operating state in the minimum time without overheating.

Because the management system 14 does ultimately switch itself off, there is no need to provide a constantly running clock nor to maintain the management system 14 operational at all times, both of which would place an unacceptable current drain on the battery.

The engine management system can now also take the starting conditions into consideration not only when controlling the heating system but when performing its other functions, in particular fuel metering for cold start and exhaust gas ignition. Thus the presence of fuel wetting the walls of the intake system may be taken into account to avoid over-fuelling during a rapid restart.