GB2327981A

GB2327981A - I.c. engine control system for adjusting ignition timing in response to detected detonation

Info

Publication number: GB2327981A
Application number: GB9716734A
Authority: GB
Inventors: Richard Butler; Michael John Wilmott
Original assignee: LAMBDA CONTROLS INT
Current assignee: LAMBDA CONTROLS INT
Priority date: 1997-08-08
Filing date: 1997-08-08
Publication date: 1999-02-10
Also published as: GB9716734D0

Abstract

An engine control system for gas or vapour powered spark ignition engines such as those commonly used as stationary engines for generators or pumps detects an occurrence of detonation within the engine and inhibits or reduces further detonation without stopping the engine. The control system includes a transducer for acoustic coupling to the engine, for producing an output indicating a running condition of the engine; signal processing means, for receiving the output from the transducer and for producing an output indicative of a detonation condition within the engine; and control means, coupled to the signal processing means and for coupling to the ignition system of the engine, adapted to provide a control signal for adjusting the timing of ignition of said engine. The circuitry may include a low-pass filter circuit 20 to remove signals arising from mechanical engine clatter, a Schmitt trigger circuit 30 to remove low amplitude signals and a frequency-to-voltage converter 40. The circuitry is of low cost and may be retro-fitted to existing engines. A visual display panel may be provided to show eg the detonation condition and the degree of ignition retardation.

Description

ENGINE CONTROL SYSTEM The present invention relates to engine control systems, and in particular to gas or vapour powered spark ignition engines, such as those commonly used as stationary engines for generators or pumps.

Gaseous or vapour fuels commonly used in such engines are mains gas, methane, sour gas from sewerage farms, paraffin, petrol and the like.

In normal use, the engines are required to run unattended for extended periods of time, often under fairly constant load and on fuels which can be highly variable in quality.

Thus, the engines can be particularly susceptible to the phenomenon of detonation, in which localized hot spots in the engine cylinders can cause ignition of the fuel-air mixture in one or more places in a cylinder other than the desired spark gap. This causes two or more flame fronts during combustion and can be highly destructive to the engine.

It has therefore been known to provide a simple transducer coupled to the engine to detect an occurrence of detonation and, if detonation is detected, to shut down the engine, for example, by cutting off the fuel supply. This acts as a crude form of engine protection which, while preventing damage to the engine, can be inconvenient, disruptive or even dangerous depending upon the task being performed by the engine.

It is also known to include, in modern performance engines such as those used in motor vehicles, sophisticated ignition mapping systems which monitor a plurality of parameters associated with the engine, such as cylinder temperature, engine speed, manifold depression, air inlet temperature, humidity etc, in order to determine an ignition timing to achieve optimum fuel consumption, power output etc. However, such systems are highly complex, expensive, and must be designed in to the engine at the outset owing to the number and positioning of sensors required. In addition, they are focused on engines which have a wide range of loads and operating speeds and do not take into account factors often of greater significance for stationary engines, eg. variable fuel quality.

It is an object of the present invention to provide a detonation control system for an engine which detects an occurrence of detonation within the engine and inhibits or reduces further detonation without stopping the engine.

It is a further object of the present invention to provide a detonation control system which, upon detecting a detonation condition, attempts to modify the ignition timing of the engine so as to maintain optimum temperatures within the cylinders.

It is a further object of the present invention to provide an engine control system for inhibiting detonation which can readily be retrofitted to existing engines.

According to one aspect, the present invention provides an engine control system for detecting onset of detonation in a cylinder of an engine and subsequently controlling at least one operating parameter of the engine to inhibit further detonation, said control system comprising: a transducer for acoustically coupling to the engine, for producing an output indicating a running condition of the engine; signal processing means, for receiving the output from the transducer and for producing an output indicative of whether a detonation condition exists within the engine; control means, coupled to the signal processing means and for coupling to the ignition system of the engine, adapted to provide a control signal for adjusting the timing of ignition of said engine, in response to an indication from said signal processing means that a detonation condition exists.

Embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 shows a schematic circuit diagram of an engine control system according to the present invention.

With reference to figure 1, a piezo-electric accelerometer 10 is acoustically coupled to the cylinder block of an engine (not shown) to convert the acoustic resonance of the cylinder block to an electrical signal.

Other forms of transducer as known in the art may be used for this purpose. According to the sensitivity of the transducer, the acoustic coupling between the engine cylinder block may be by direct contact with the block or via some other suitable medium.

The signal output from the transducer 10 is passed to a voltage follower circuit 12 and then to a voltage amplifier 14 having a gain which is adjustable by variable resistor 13. This enables adjustment of the sensitivity of the unit according to the requirements of the engine type and transducer type and location.

The amplified signal is passed to a low pass filter circuit 20. In the preferred embodiment, the low pass filter circuit 20 comprises two transconductance amplifiers 22, 24 in a Butterworth filter configuration.

This low pass filter 20 effectively removes transducer output signals which correspond to the mechanical clatter of the engine components.

The output 28 from low pass filter 20 is passed to a Schmitt trigger circuit 30 to effectively remove any low amplitude signals. The hysteresis of this trigger can be set using variable resistor 32. The output 33 from the Schmitt trigger circuit 30 is thus a square wave form having had the low amplitude and high frequency components of the transducer output signal removed.

The output signal 33 is passed to a frequency to voltage converter circuit 40. This circuit 40 requires a fast response to changes in frequency and in the preferred embodiment an integrated circuit TC9400 is used. The required frequency to voltage conversion could be achieved by other circuit or by appropriate digital processor and software, as will be understood by persons skilled in the art.

The output 42 from the frequency to voltage converter 40 is passed to a voltage follower 50 and then via diode Dla to a Schmitt trigger circuit 60 which has an adjustable threshold voltage controlled by variable resistor 62. This detects when detonation has occurred and the voltage needs to be set to suit the frequency of the detonation for the particular cylinder size and characteristics of the engine to which the engine control system is fitted.

The output 64 of the Schmitt trigger circuit 60 is fed via a voltage follower 66 to the next stage of the circuit which determines the duration of the detonation. This is achieved by charging a capacitor C1 through a constant current device 70 while the trigger 60 is positive. Hence, the voltage achieved on this capacitor is proportional to the duration of the detonation. When the detonation has finished, the capacitor C1 is rapidly discharged.

The voltage on the capacitor C1 is passed, via voltage follower 75 to a diode D2 which, in turn, charges the capacitor C2. The effect of this arrangement is that capacitor C2 will maintain the maximum voltage achieved on capacitor C 1. It will be understood that this effect could also be achieved using other sample and hold circuits well understood in the art.

A constant current circuit 80 incorporating variable resistor 81 and transistor Q1 which slowly discharges the capacitor C2. The voltage of capacitor C2 therefore represents the mean value of the degree of detonation. This voltage appears as the output 85 from the unit via the voltage follower 84.

The output voltage 85 can then be conditioned to suit the input requirements of an ignition timing control circuit 90 such that the timing of the ignition is retarded according to the voltage appearing on capacitor C2. This retardation of the ignition timing more towards top dead centre ensures that the cylinder temperature cools thereby inhibiting further detonation. Typically, the control system is used in conjunction with an existing engine ignition system which includes an analog input for controlling the timing angle. It will be understood that with appropriate use of analogue/digital converters, digital signal processing and timing adjustment could be effected.

The rate of discharge of capacitor C2 can be adjusted so that this system does not oscillate in and out of severe detonation. Preferably, the system is adjusted so that the ignition timing will ride at the edge of detonation, eg. at the maximum ignition advance which avoids detonation.

It will be understood that multiple transducers may be used to monitor large or multibank engines and these transducers may be provided with separate signal processing circuitry, and the circuitry may be mutually connected by diodes Dla, Dlb etc. at summing point of the diode cathodes.

The circuitry described above is low cost and can be retrofitted to existing engines without the necessity of installing numerous sensors in or around the engine to monitor different operating parameters of the engine.

The circuitry may also be provided with a display panel indicating the status of the control system and thereby the engine. Such a display panel may include a visual indicator of a detonation condition, an indication of the degree of retardation of the ignition timing, for example by a LED bargraph display or the like, and other warning signals such as sensor failure or the like.

Claims

1. An engine control system for detecting onset of detonation in a cylinder of an engine and subsequently controlling at least one operating parameter of the engine to inhibit further detonation, said control system comprising: a transducer for acoustically coupling to the engine, for producing an output indicating a running condition of the engine; signal processing means, for receiving the output from the transducer and for producing an output indicative of whether a detonation condition exists within the engine; control means, coupled to the signal processing means and for coupling to the ignition system of the engine, adapted to provide a control signal for adjusting the timing of ignition of said engine, in response to an indication from said signal processing means that a detonation condition exists.

2. An engine control system according to claim 1 in which the signal processing means includes a low pass filter to remove components of the transducer output signal corresponding to mechanical clatter of the engine.

3. An engine control system according to claim 1 or claim 2 in which the signal processing means includes a Schmitt trigger circuit to remove low amplitude components of the transducer output signal.

4. An engine control system according to claim 1, claim 2 or claim 3 in which the signal processing means includes means for determining the duration of detonation.

5. An engine control system according to claim 4 in which the control means includes means for providing a control signal to retard the ignition timing of the engine.

6. An engine control system according to claim 5 in which the control means further includes means for providing said control signal to retard the ignition timing of the engine proportional to the duration of the detonation signal.

7. An engine control system according to any preceding claim further including a plurality of transducers each for producing an output corresponding to a respective cylinder of the engine.

8. An engine control system according to claim 7 in which the signal processing means further includes means for receiving the outputs from each of the transducers and for producing corresponding outputs indicative of a detonation condition within the respective cylinder.

9. An engine control system substantially as described herein with reference to the accompanying drawings.