CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINES

Abstract: In a control device (14) for fuel injection and/or spark ignition in an internal combus­ tion engine, a first datablock (16) is pro­ grammed for operation in accordance with en­ gine operating parameters (BM, p, L,n, T) but without lambda control when the engine is cold and a second datablock (18) is pro­ grammed for operation with lambda control when the engine is warm. A switching logic (26) switches in the first datablock (16) when the engine is started below a lower threshold (T₁) and switches over to the second datablock (18) when the temperature rises above a higher threshold (T₂)

Description: The present invention relates to a control device for an internal combustion engine. Such a control device is known (US- A- 4398520). This known control device controls fuel injection and spark ignition in a multi-cylinder internal combustion engine. A processor or computer includes two datablocks containing respective programs for two modes of operation and an arithmetic unit or central processing unit for controlling the injection and ignition in accordance with engine operating parameters and in accordance with a selected one of the programs. The arithmetic unit contains a switching logic or partial load recognition stage which switches from the first datablock to the second responsively to engine load. The switching logic also switches off some of the injection valves so that not all the cylinders produce power. The first and second datablocks are programmed for optimal performance in respective modes in which all cylinders are producing power or only some cylinders are producing power, the latter mode being used under low load. This known control device, however, does not deal with the problem that it is often necessary or advantageous to operate in accordance with one program when the engine is cold and in accordance with another program when the engine is hot. In particular, it is desirable to be able to operate in a "lambda control" mode in order to minimize emission of noxious or toxic fumes in the exhaust, but this is not possible when the engine is cold, i.e. when starting the engine. DE- A- 32 33 791 describes a device for calling up and/or optimizing stored data which can be used for testing which of several stored programs, e.g, starting programs, is the best for a control device of an internal combustion engine. It is possible, using an input keyboard, to select different programs and to try out each program to check which is the best during an actual test run of the vehicle. However, there is no suggestion of a changeover from one program to another responsively to an engine operating parameter. The "Mixture control apparatus for carburetor" according to US-A 4 484 554 selects data for an opening angle of a throttle valve depending on hot state and cold state of the engine via a threshold for the engine temperature, including a hysteresis (Abstract and Fig. 6c, S 8a). US-A 4 357 922 relates to "Method and apparatus for operating a fuel-supply system with lambda control". There the output signal of a threshold element (24) for an engine temperature signal controls the lambda control. This threshold element includes a hysteresis and is able to switch in both directions. It is an object of the invention to provide a control device for an internal combustion engine which changes over from one control mode, which is used on starting with the engine cold, to another normal control mode (e.g. lambda control) which, however, is unsuitable for use with a cold engine. Advantages of the invention. This object is achieved by a control device in accordance with the features of claim 1. This has the advantage that optimum performance of the engine in accordance with engine operating parameters can be obtained when the engine is cold and that optimum combustion conditions can be maintained by the use of lambda control as soon as the engine has warmed up. The air number lambda is the actual air-to-fuel ratio divided by the stoichiometric air-to-fuel ratio. A measure of the air number lambda can be obtained by means of a lambda probe which is an oxygen sensor and is placed in the exhaust system so as to detect residual oxygen in the exhaust. It comprises a solid electrolyte which is only effective when hot. The output of the lambda probe is used to provide a feedback signal for the control device when operating in the lambda control mode. Lambda control implies a lean mixture whereas a rich mixture is required when the engine is cold. Thus the control device of the invention can operate without lambda control when the engine is cold and the lambda control is brought into use as soon as the engine has warmed sufficiently. The various engine operating parameters (intake vacuum, air intakd quantity, engine speed, engine temperature) can be used as necessary and as appropriate to obtain optimum operation in each of the two modes. If the engine is alrealdy warm on starting (e.g. upon re-starting before the engine has cooled), the lambda control mode can be brought in immediately upon starting threshold value by adopting the features of claim 4. Drawings. The invention is further described, by way of example, with reference to the accompanying drawings, in which:- Fig.1 is a block circuit diagram of a control device for an internal combustion engine in accordance with the invention, and Fig.2 is a flow diagram illustrating the operation of a switching logic in the control device. Description of the Exemplary Embodiment. Fig.1 shows diagrammatically an internal combustion engine 10 operating with spark ignition and electronically controlled fuel injection. The latter includes injection valves 12 which may be of a kind opened intermittently in synchronism with rotation of the engine crankshaft, the opening duration determining the injected fuel quantity, or of a kind held open continuously to an adjustable extent so that the fuel quantity is determined by the degree of throttling by the injection valves. The injection valves 12 are controlled by a computer 14, preferably a micro-processor. The computer 14 contains two datablocks 16,18 in which are stored programs in accordance with which a processor 20 operates the injection valves 12 when the engine is cold and when it is hot, respectively. The processor 20 receives engine operating parameters which are processed in accordance with the selected program to determine the fuel quantity to be injected. These parameters include the air intake vacuum p, the air intake quantity (throttle flap position) L, the engine speed n and the engine coolant temperature T. They also include a reference mark BM derived from a pulse generator on the engine crankshaft and used for timing the injection operations and the air number λ derived from a lambda probe 22 in the exhaust system of the engine 24. The processor 20 includes a switching logic 26 for determining which of the datablocks 16,18 is selected. For this purpose, the switching logic receives the temperature signal T and signals from two reference temperature sources 28 and 30 which may be incorporated in the computer 14. The switching logic 26 also receives a start signal indicative of when the engine 10 is being started. It may be derived from the starting switch for the starter motor. The control device operates as follows: When the ignition is switched on and the starter switch is operated, the switching logic 26 receives the start signal and the temperature signals T, T₁ and T₂. Referring now to Fig.2, if the engine is cold the sensed temperature T is below a lower threshold T₁ set by the reference source 28, datablock 1 for operation under starting conditions is selected. The processor 20 controls the injection valves 12 without reference to the air number λ (lambda control switched off). As the engine warms up, the datablock 1 for operation under starting conditions remains in use until the sensed temperature T exceeds a second higher threshold T₂ determined by the reference source 30. The switching logic 26 then changes over from the first datablock 16 to the second datablock 18, as indicated diagrammatically in Fig.1. The second datablock 18 stores the program for the processor 20 to operate the injection valves 12 with lambda control. Should the engine be started warm, in that the sensed temperature T already exceeds the lower threshold T₁ when the starter switch is operated, the switching logic immediately selects datablock 2 for operation with lambda control, as shown in Fig.2. As indicated by broken lines 32, the processor 20 may also operate the engine ignition system, the programs in the datablocks 16,18 being adapted for this purpose.

Claims: 1. Control device for an internal combustion engine, comprising a computer (14) which contains a first datablock (16) for operation under one operating condition, a second datablock (18) for operation under another operating condition and a processor (20) for processing engine operating parameters in accordance with data from the first or second datablock, the processor including a switching device (26) responsive to at least one operating parameter for selecting the datablock to be used, wherein the switching device (26) is responsive to temperature, more particularly the cooling system temperature (T), and switches over from the first datablock(16), which is programmed for operation under starting conditions to the second datablock (18), which is programmed for normal operating conditions, when a predetermined temperature (T₂) is exceeded. and wherein the switching device (26) only switches to the first datablock (16) when the engine is started with the sensed temperature below a lower predetermined temperature (T₁) and then only switches to the second datablock (18) when the sensed temperature exceeds the upper predetermined temperature (T₂), wherein the switching device (26) switches directly to the second datablock (18) when the engine is started with the sensed temperature above said lower predetermined temperature (T₁). 2. Control device according to claim 1, for a spark-ignition engine, characterized in that the second datablock (18) programmed for normal operating conditions is programmed for lambda control in which the fuel quantity fed to the engine is adjusted responsively to the output of a lambda probe (22) disposed in the exhaust system (24) of the engine for measuring the residual oxygen content of the exhaust gases. 3. Control device according to claim 2, characterised in that the first datablock (16) is programmed to operate without lambda control.

Inventors: JUNDT, WERNER, MILLER, NORBERT, SOMMER, RAINER
Applicants: ROBERT BOSCH GMBH
Application year: 1987
Main classification: F02D41
IPC codes: F02D41