WO1990006432A1

WO1990006432A1 - Engine exhaust system

Info

Publication number: WO1990006432A1
Application number: PCT/EP1988/001105
Authority: WO
Inventors: Manfred Homeyer
Original assignee: Robert Bosch Gmbh
Priority date: 1988-12-03
Filing date: 1988-12-03
Publication date: 1990-06-14

Abstract

To avoid combustion of unburnt fuel/air mixture in the catalyser (34) of an exhaust system (30) of an internal combustion engine (10), the temperature (T1 - T4) of the exhaust gases is measured in the individual exhaust elbows (46-52). The difference ΔT between each of these temperatures and their average TM is compared with a threshold ΔTO. In the event of a mis-fire in one of the engine cylinders, the threshold is exceeded for that cylinder and a signal is supplied by a respective comparator (66-72) to the main control (74) of the electronic fuel injection system to switch off the fuel supply to that cylinder. This prevents unburnt fuel from reaching the catalyser. The mis-fire also causes a pilot lamp (86) to light up.

Description

DESCRIPTIQN

ENGINE EXHAUST SYSTEM. State of the Art.

The present invention relates to a method of and apparatus for protecting an exhaust system of a multi-cylinder internal combustion engine operable with spark ignition, particularly an exhaust system containing a catalyser, from overheating due to a misfire. It is known that exhaust gas catalysers and even the exhaust manifolds of internal combustion engines can be damaged or destroyed due to overheating. The danger of overheating arises in the event of a misfire, that is to say, the fuel/air mixture in one or more of the combustion chambers fails to ignite through faulty ignition. The uncombusted mixture when it reaches the catalyser whose working temperature is in the range of 400°C to 900^ is immediately ignited, rapidly heating the catalyser to a temperature of 1000°C or more at which the catalyst is destroyed. It is an object of the invention to provide a method and apparatus whereby faulty combustion or misfire can be immediately identified so that steps can be taken to prevent consequential overheating of the exhaust system, particularly of the catalyser. Advantages of the invention.

These disadvantages are avoided by the method claimed in claim 1, and the apparatus claimed in claim 5. Not only is a misfire promptly detected through the uncombusted gases leaving the engine being at an abnormally low temperature, but also the faultily operating cylinder or cylinder group is immediately identified. In the case of petrol injection individual to the cylinders or cylinder groups, the feeding of further fuel to the mis-firing combustion -2- cha ber can be prevented by adapting the measures of claims 2 and 6. A further advantage is that normal fluctuations in exhaust gas temperature, arising through varying loads on the engine, do not cause 5 erroneous detection of mis-fire, since in this case, all the combustion chambers behave in the same way so that no temperature difference is detected.

In the case of an engine having three or more cylinders, it is advantageous to adopt the measures 10 set forth in claims 3, 4, 8 and 9. Such measures render it easy to identify the mis-firing cylinder or cylinder group.

A pilot lamp can be provided in accordance with claim 7 for giving visual inclination of mis-fire. 15 This is particularly useful in the case of a carburettor system or a fuel injection system with a single injection valve when it is impossible or dangerous to completely switch off the fuel supply. Drawings 20 The invention is further described, by way of example, with reference to the accompanying drawings, in which:-

Fig.l is a diagrammatic plan view of an internal combustion engine having individual fuel injection 25 into the inlet manifold branches and individual temperature sensors in the exhaust manifold elbows, and

Fig.2 is a block circuit diagram of apparatus according to the invention for monitoring mis-fire in 30 the engine of Fig.l and for inhibiting fuel injection upstream of the inlet valve to the mis-firing cylinder,

Description of the preferred embodiment

Fig.l shows diagrammatically a four-cylinder internal combustion engine 10 operable with fuel 35 injection and spark ignition. An air inlet manifold 12 has branches 14,16,18 and 20 leading respectively to the inlet valves (not shown) of the four cylinders. Electrσmagnetically operable fuel injection valves 22,24,26 and 28 are arranged in the 5 inlet manifold branches so as to inject the requisite amounts of petrol into the inducted air immediately upstream of the respective engine inlet valves. Such a fuel injection system in which each cylinder has a dedicated fuel injection valve opened and closed in

10 timed relation with the cylinder cycle is a so-called SEFI system. In other electronic fuel injection systems, the fuel injection is carried out for two or more groups of cylinders, with each group having its own injection valve. l ~ The engine 10 has an exhaust system 30 which is shown diagrammatically and which includes at least one exhaust silencer 32 and an exhaust catalyser 34. The catalyser 34 is so disposed in the exhaust system that it runs at an elevated temperature for catalysing the

20 reduction of nitrogen oxides and oxidation of carbon monoxide and hydrocarbons using any residual oxygen in the exhaust gases.

The exhaust system 30 includes an exhaust manifold 36 having branches or elbows 38,40,42 and 44 leading

25 from the respective exhaust valves (not shown) of the engine cylinders. Individual temperature sensors, 46,48,50 and 52 are disposed in the respective exhaust elbows so as to measure the temperatures of the gases being exhausted from the individual cylinders.

30 If there is a mis-fire in one of the cylinders, the unburnt fuel/air mixture would reach the catalyser 34 which would immediately catalyse combustion and lead to rapid destruction of the catalyst. This is avoided using the electronic apparatus of Fig.2. The

-c outputs Tτ_, To_> 3 and T^ of the four temperature sensors are connected to an averaging circuit 54. Only one of the temperature sensors is shown in Fig.2. Each of the temperature sensors is shown by way of example as comprising a PTC resistor connected between earth and a fixed or trimmer resistor 56 leading to a voltage source. Each of the four temperature sensors is also connected to the minus input of a respective one of four subtracting circuits 58,60,62 and 64. The output TM of the averaging circuit 54 is connected to the plus inputs of all the subtracting circuits. The outputs of the subtracting circuits 58-64 are connected respectively to four comparators 66,68,70 and 72 for comparison with a threshold temperature difference ΔTQ . The outputs of the comparators are connected to a main control 74 of an electronic fuel injection system which controls the opening of the individual fuel injection valves 22,24,26 and 28 to deliver the requisite amounts of petrol in accordance with engine operating parameters, ^as i-^s well known. The outputs of the comparators are also connected via an OR gate 82 to the control electrode of an electronic switch 84 which lights a pilot lamp 86.

When all of the cylinders are firing properly, the exhaust gas temperatures as measured at the four spaced points by the temperature sensors 46,48,50 and 52 are substantially equal to one another, even though they may vary considerably in accordance with engine load and other operating conditions. Thus each of the measured temperatures T^ T₂, T3 and T4 is substantially equal to the average -_ so that the temperature differences 4Tτ. - T_M - T_χ, etc., applied to the comparators 66, etc., are all less than the threshold temperature difference Δ _Q and the outputs of the comparators are all zero. In the event of a mis-fire in, say, cylinder No.l, through a dirty spark plug or through a fault in the electronic ignition system or for any other reason, the temperature T^ as measured by the corresponding sensor 46 falls rapidly due to the uncombusted and therefore relatively cool gases flowing out through the corresponding exhaust valve. The temperature difference AT^ - T_M - T_j then becomes larger than the reference value ΔT_Q and a corresponding output signal is delivered via the OR gate 82 to the switch 84 to switch on the pilot light 86. Thus the driver of the vehicle in which the engine is installed knows immediately when there is a danger of the catalyser overheating and can, if necessary, take appropriate action by stopping the vehicle as soon as it is safe to do so. The output signal is also supplied to the main control 74. The latter includes end stage amplifiers 76 connected to the individual injection valves, only one such end stage amplifier being shown. The injected fuel quantities are determined by the duration of opening of the injection valves and each injection valve is open so long as a trigger signal appears on a corresponding lead 78.

By way of example, the trigger signals are fed to the respective end stage amplifiers via respective AND gates 80. The outputs of the comparators 66-72 are connected to inverting inputs of the AND gates.80. Therefore, when a signal appears at the output of, say, the comparator 66 the AND gate 80 prevents the corresponding trigger signals on the lead 78 from reaching the end stage 76, whereby the injection valve 22 is not opened. Fuel is thereby prevented from entering the mis-firing cylinder and this prevents unburnt fuel from reaching the catalyser 34. Overheating of the catalyser and the rest of the exhaust system 30 is thereby avoided. The various electronic components of the apparatus shown in Fig.l may be incorporated in the main control 74.

When the main control 74 is in the form of a computer, it can be programmed to carry out the necessary comparisons digitally in accordance with the computer program. It then becomes simpler not to calculate the mean temperature T_M but instead to compare each of the temperatures T^ to T4 with the other. Thus, for a four-cylinder engine, six comparisons are made and for a six-cylinder engine, fifteen comparisons are made. In the case of such a direct temperature comparison, a rapid detection of a temperature change for one or several cylinders can be made since the temperature difference in this case is unaffected by the number of cylinders which fail and the cylinder or cylinders whose exhaust gas temperature is lower by, say, at least 100 °C than that of the others can have its fuel supply switched off immediately. When a comparison is made with an average value T^, as in Fig.2, the average value is itself lowered upon mis-fire, so that response is not so rapid.

In the case of an engine fitted with "group" injection, that is, an injection system in which each injection valve is common to a respective group of two or more cylinders, it is sufficient to provide one temperature sensor for each group and that sensor can be placed in the Y-pipe for that group, since it is not possible to switch off the fuel supply to a single cylinder in such case.

In the case of a carburettor fuel supply system or fuel injection employing a single injection valve or nozzle, it is not possible for safety reasons to switch off the fuel supply automatically when misfire -7- is detected. In such case reliance must be placed on the driver to observe the pilot lamp 86 coming on and to take the appropriate actions to bring the vehicle and the engine to rest as soon as possible.

Whilst individual AND gates 80 are shown in Fig.2 for each injection valve which is provided with its own end stage amplifier 76, it is conventional for a single end stage amplifier to be provided for all injection valves. In that event, each of the

10 energising leads from the common end stage amplifier to the individual injection valves must be provided with its own relay or electronic switch controlled by the respective one of the comparators 66 to 72.

It is a relatively simple matter, particularly in ■ic the case of a computerised fuel injection system, to modify an existing system to provide for mis-fire detection in accordance with the invention.

Claims

1. Method of protecting an exhaust system of a multi-cylinder internal combustion engine operable with spark ignition, particularly an exhaust system containing a catalyser, from overheating due to a mis-fire, characterized in that the temperatures of the exhaust gases coming from at least two cylinders or groups of cylinders are measured and compared with one another and when the difference between the measured temperatures exceeds a predetermined threshold, a signal representative of a mis-fire is produced.

2. Method according to claim 1 for an engine operable with fuel injection, characterised in that said signal is used to switch off the delivery of fuel to at least that cylinder or cylinder group which is the source of the lower temperature.

3. Method according to claim 1 or 2, characterized in that the average of the temperatures of the exhaust gases coming from at least three and preferably four or more cylinders or cylinder groups is calculated and each temperature measured is compared with the average.

4. Method according to claim 1 or 2, characterised in that all of the measured temperatures are compared with one another.

5. Apparatus for protecting an exhaust system of a multi-cylinder internal combustion engine operable with spark ignition, particularly an exhaust system containing a catalyser, from overheating due to a mis-fire, characterized in that one temperature sensor (46,48,50,52) is placed in each of several different branches of the exhaust gas tract (36) leading from individual cylinders or groups of cylinders, and the outputs of the temperature sensors are fed to at least one subtractor (58,60,62,64) which calculates the difference between the measured temperatures (Ti , T_2> T3, T4), and in that the calculated difference is applied to a comparator (66,68,70,72) which compares the calculated difference with a threshold (ΔTQ) to provide an output signal when this threshold is exceeded.

6. Apparatus according to claim 5 for an engine operable with fuel injection and having several injection valves, one for each cylinder or group of cylinders, characterised by means (80) for switching off the fuel supply to the cylinder or group of cylinders in which a mis-fire is detected.

7. Apparatus according to claim 5 or 6, in which the outputs of the comparator (66,68,70,72) are connected to control a pilot lamp (86) .

8. Apparatus according to claim 5, 6 or 7, characterized in that an averaging circuit (54) is provided for calculating the average T^) of the temperatures measured at at least three and preferably four or more different positions in respective branches of the exhaust tract (36) and the subtractor (58,60,62,64) calculates the difference between the average (T_M) and each of the measured temperatures

9. Apparatus according to claim 5, 6 or 7, characterised in that, in the case of a computerised fuel injection system, the computer is programmed to compare each measured temperature with all of the others.