WO1998022709A1

WO1998022709A1 - Arrangements and procedure for ionisation detection within multi-cylinder combustion engines

Info

Publication number: WO1998022709A1
Application number: PCT/SE1997/001929
Authority: WO
Inventors: Jan Nytomt
Original assignee: Mecel Ab
Priority date: 1996-11-18
Filing date: 1997-11-17
Publication date: 1998-05-28
Also published as: DE19781522T1; SE9604245D0; SE9604245L; SE507394C2; DE19781522B4

Abstract

The invention concerns an arrangement and procedure for detection of ionisation in the combustion chamber of a multi-cylinder, four-stroke engine, in which at least the pistons of the first and second chambers run in parallel, but phase-displaced as of the working phases of the four-stroke cycle. Two measuring circuits (39a, 39b) respectively connected to a measuring gap (24a-24d) in the first and second combustion chamber are employed for detection of ionisation in the combustion chambers. In order to reduce the costs incurred upon the system, a switch (51) has been used which alternately connects each measuring circuit to a signal-processing unit (44). Hereby, a cylinder identification can be accomplished by detection of the ionisation degree in the combustion chamber by using one signal-processing unit only. The invention entails a complete utilisation of ionisation detection where a cam-shaft sensor is not of required use for cylinder identification, and where a number of combustion related parameters can be detected at low system cost by using only one signal processing unit comprising a number of signal processing stages (52a, 53a and 52b, 53b).

Description

ARRANGEMENTS AND PROCEDURE FOR IONISATION DETECTION WITHIN MULTI- CYLINDER COMBUSTION ENGINES.

Present invention refers to an arrangement for ionisation detection in multi-cylinder combustion engines in accordance with the preamble of claim 1 , and a procedure for detection of ionisation within multi- cylinder combustion engines in accordance with the preamble of claim 7.

STATE OF THE ART

The ignition sequence must be defined as regard to ignition systems in four-stroke combustion engines equipped with at least one pair of pistons running in parallel but displaced by 360 crank-shaft degrees as of working phase. This is carried out conventionally with a sensor arranged on the cam shaft. The cam shaft rotates by half the speed of the crank shaft, whereby a cylinder identification/ignition-sequence may be defined. By detection of the ionisation level within the combustion chamber, preferably via the spark-plug gap, a cylinder identification may however be accomplish without such a cam-shaft sensor. In a cylinder being subjected to the expansion stroke, during which stroke the combustion occurs, the ionisation level becomes substantially higher than in the cylinder being subjected to the intake stroke. However, it is necessary that the signal-processing circuits for ionisation in those two cylinders which have the pistons running in parallel are kept separated. Consequently, a four- cylinder, four-stroke engine furnished with two pair of pistons running in parallel requires at least two signal-processing circuits.

Patent US,A,4648367 presents an ignition system designed for a four-cylinder, four-stroke combustion engine, where a cylinder identification might be obtained by two ionisation current detection circuits intended for those two cylinders which have pistons running in parallel, but displaced 360 crank-shaft degrees as of working phase.

Patent EP,A,260177 show a solution where one detection circuit and one signal processing circuit is sufficient for all the cylinders. However, this arrangement can be implemented only in purpose of knock detection, not when the object of operation is cylinder identification which requires a cam-shaft sensor with this arrangement. In a cam-shaft sensor based system the ignition sequence is set by the cam-shaft sensor enabling the system to detect the specific cylinders being subjected to the expansion stroke. This is of particular interest as the knocking condition may exist during the expansion stroke only.

The configurations of detection circuits exposed in DE,A,4239803, e.g. those of US,A,4648367 and EP, A, 260177, purports to illustrates how to reduce costs incurred upon the system. Hereby, a high frequency filter was used in order to extract the relevant information from the ionisation current excluding any kind of ability to separate signals deriving from cylinders where pistons are running in parallel. Under these conditions a cylinder identification cannot be accomplished. Thus, several solutions are known where configuration of detection circuits and signal processing circuits have been optimised in order to restrict the number of circuits. The well known technique has however always required at least two signal-processing circuits in four-stroke engines having at least two pistons running in parallel and with a ignition system being able to carry out a cylinder identification with an ionisation current detection technique.

OBJECT OF THE INVENTION

The object of the invention is to restrict the number of signal-processing circuits for ionisation current in four-stroke combustion engines furnished with at least two pistons running in parallel where the cylinder identification can be obtained by an analysis of ionisation current within the combustion chamber during the combustion.

Another object of the invention is to replace a relatively costly signal-processing circuit with a simple switch, and thereby obtaining a significant reduction of costs incurred upon the ignition system.

SHORT DESCRIPTION OF THE INVENTION

The inventive arrangement and procedure is distinguished by the characterising part of claim 1 and 7.

By the inventive arrangement and the procedure a cylinder identification can be carried out without a cam-shaft sensor and with a restricted number of signal-processing circuits for four-stroke combustion engines having at least two pistons running in parallel.

Other distinguishing features and merits characterising the invention are evident from the characterising parts of other claims and the following description of embodiments. The description of embodiments is made by reference to figures specified in the following list of figures.

LIST OF FIGURES

Figure 1 , illustrates a combustion engine with an engine mounted ignition-control module and an engine- control module arranged at a distance in relation to the engine.

Figure 2, illustrates an inventive ignition-control module designed for a four-stroke Otto-engine. Figure 3, illustrates some adaptation circuits, i.e. interface, for bi-directional communication. Figure 4, illustrates a signal status diagram for a trigger signal, combustion-quality signal and knock signal in relation to the position of the engine (crankshaft degrees, CD).

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The invention is applied on combustion engines 20 of Otto type, Figure 1 , equipped with at least one ignition-control module (ICM) mounted on the engine and an engine-control module(ECM). The combustion engine of the exemplary embodiment is a four-cylinder four-stroke engine furnished with at least two pairs of pistons running in parallel. In motor vehicles the engine-control module is usually placed at a distance from the engine, either on the cowl wall or protected inside the passenger compartment of the vehicle. However, the engine-control module may in certain applications be fixed on the engine but at a distance from the ignition-control module.

The combustion engine is equipped with a number of sensors, e.g. -a load sensor 12, arranged inside the inlet manifold 21 (alternatively a throttle position sensor),

-an engine-temperature sensor 13, and -an engine-position sensor 14, arranged at the flywheel 25 which, by a number of cogs fixed on the flywheel, generates pulses from sensor 14, however in a well known way. A number of cogs are shaped differently whereby the position of the engine (the rotation position of the crank-shafts 26 and the position of the pistons 23, the latter arranged into the combustion chambers 22) may be determined.

The sensors 12-14 is connected to the control module ECM, whereby the ignition as well as the fuel supply is controlled by reference to the detected engine load, engine temperature and, engine position and speed.

When the ignition-control module ICM is set to generate an ignition spark, the control module ECM by reference to detected engine parameters, pursues control via the trigger-signal conductors T1-T4. The exemplary embodiment illustrates the trigger-signal wires as four individual trigger-signal wires for each ignition coil.

A four-cylinder engine preferably has its ignition coils directly connected to each spark plug (Figure 2).

The ignition module is supplied with current via two wires, P,G, each connected to a pole of the power source. Similarly, the control module ECM also receives its current via a source of power, preferably a battery 10. The wiring L between the control module ECM and the ignition-control module ICM contains at least one bi-directional communication wire, KJ^J or KQQ

Figure 2 illustrates the design of the ignition-control module ICM designed for a four-cylinder Otto- engine. In the embodiment shown is one measuring circuit 39a used for two ignition circuits 32a-33a- 34a-35a and 32b-33b-34b-35b respectively. These ignition circuits generate the ignition spark in the spark plugs 24a and 24b, arranged in two different cylinders where the pistons have a phase displacement of 180 crankshaft degrees. The unit 60a, with two ignition circuits and one common measuring circuit 39a, is identical with the other unit 60b, which generates the ignition spark in the spark plugs 24c and 24d.

The trigger signals T1-T4 are distributed, via a processor CPU, by the signal wires tl-t4 to the primary circuit-breakers 35a and 35b within unit 60a and to the primary circuit-breakers 35c and 35d within unit 60b. At least one spark plug 24a-24d is arranged within each cylinder 22. The function is more closely described by reference to the specific sequence, in which the ignition spark is generated by the spark plug 24a. The ignition voltage is generated in an ignition coil 32a, which is equipped with a primary winding 33a and a secondary winding 34a. One end of the primary winding 33a is connected to a source of power ,P, whereas an electric controlled circuit-breaker 35a is arranged in the other grounded end of the winding. When the processor by the trigger out-put tl switches the circuit-breaker 35a to a conductive state, a current begins to flow through the primary winding 33a. When the current is interrupted a step-up transformed ignition voltage is induced in the normal manner in the ignition coil's 32a secondary winding 34a and an ignition spark is generated in the spark plug gap. The current flow is adjusted (on or off) by circuit-breaker 35a (a so called dwell-time control) dependent of an ignition-angle map stored in the memory of the control module. The 'dwell-time control' ensures that the necessary primary current is reached and that the generation of ignition sparks occurs at the ignition moment required for the load case in question.

One end of the secondary winding is connected to the spark plug 24a and in its other earth connected end there is a measuring circuit 39a which detects the degree of ionisation in the combustion chamber. The measuring circuit includes a voltage accumulator, here in the form of a chargeable capacitor 40, which applies a bias voltage over the spark plug gap with an essentially constant measuring voltage. For biasing the voltage over the spark plug gap, a substantially constant measuring voltage generated by the capacitor is employed. The capacitor is equivalent to the solution shown in EP,C, 188180, where the voltage accumulator is an increased/stepped-up voltage derived from the charging circuit of a capacitive ignition system. In the design example shown in the figure the capacitor 40 is charged up to a voltage level given by the Zener diode's 41 breakdown voltage when the ignition voltage pulse is induced in the secondary winding 34a. The breakdown voltage may be within the range of 80-400 Volts. When a current level sufficient for charging the capacitor to a voltage level corresponding the zener diode's breakdown voltage level has been generated, the zener diode will open. Similarly, a second inverse protective diode 43 is in relation to resistance 42 arranged in parallel so as to protect against voltage with a reversed polarity. The current in circuit 24a-34-40/40-42-ground can be detected by using the measuring resistance 42. This current depends upon the conductivity of the existing gases in the combustion chamber, which conductivity is proportional to the ionisation degree in the combustion chamber.

Since the measuring resistance 42 is most closely connected to ground, only one connection, linking the measuring point 45 to the signal-processing unit 44, is required. The signal-processing unit 44 in this context measures the voltage over the resistance 42, and at measuring point 45 relative to ground. By analysing the current (or alternatively the voltage) over the measuring resistance, it is possible to detect knocking and preignition. During certain engine operating cases, and as described in US,A,4535740, a detection of the present mixing ratio of air and fuel might be accomplished by measuring the period of time when the ionisation current exceeds a certain level.

The signal-processing unit 44 shown will generate, in two parallel signal-processing stages 52a, 53a and 52b, 53b, signals equivalent to the combustion quality (CQ/Combustion Quality) and knock intensity (KI/Knock Intensity). A representative value in relation to a knocking condition is obtained in a signal processing stage by extracting out the typical frequency content for a knocking condition. This is done in a band-pass filter/BPF, 52b, where the band-pass filter's centre frequency is set to the knock frequency, which knock frequency is dictated by the engine geometry. For a conventional 2 litre four-cylinder Otto- engine the centre frequency can typically lie at some 5 kHertz. Thereafter the band-pass filtered signal is rectified and integrated in an integrator 53b. The signal, KI_DATΛ, which is obtained from the integrator 53b will therefore be proportional to the knock intensity.

A representative value for the combustion quality is obtained in a similar manner in an second signal processing stage, by means of blocking out high frequency components in the ion current signal. This is done in a low-pass filter 52a. Thereafter the low-pass signal is integrated in an integrator 53a. The signal, CQ_DATA, obtained from the integrator 53a will therefore be proportional to the combustion intensity, which can be used as a measure of the combustion quality.

The measuring window signals CQ_W and KI_W are sent to the respective filters 52a/52b from the processor when the filtering in respective filters 52b and 52a is to be initiated. The measuring window signals activate the filter in the measuring window, which measuring window is controlled by the control module, ECM, in a manner which is described in more detail in connection with Fig. 4.

Since the signal processing unit 44 contains relatively expensive components a change-over switch 51 is used, which depending on a signal on a wire SW from a logic circuit switches between the measuring circuit 39a in the unit 60a and a corresponding measuring circuit 39b in the unit 60b. The change-over switch 51 is schematically reproduced in the figure as a relay controlled circuit-breaker, which with conventional IC-circuits can be realised with a MUX(multiplex)-circuit, controlled by the processor CPU. This is conducted depending on the trigger signals from the control unit ECM. When the ignition sequence has been determined the change-over switch 51 begins to switch so that either the signal on wire Jl or J2 is connected to the signal processing unit 44 depending on in which cycle combustion takes place. With the ignition sequence 1-3-4-2 the change-over switch first stands in the position shown in the figure when cylinder 1 fires, after which the change-over switch changes during the time cylinder 3 and 4 fire, in order to return to the position shown when cylinder 2 fires. This sequence provides, however, that spark plug 24a is matched with cylinder 1, spark plug 24b with cylinder 2, spark plug 24c with cylinder 3 and spark plug 24d with cylinder 4.

If cylinder identification, i.e. firing order determination, takes place during start of the engine with ion current detection, the firing is generally generated in both cylinders where the pistons simultaneously reach top dead centre, when one cylinder is at the end of the exhaust phase and the other cylinder is in the end phase of compression of the fuel-air mixture. The ionisation signal becomes considerably higher from the cylinder where combustion occurs, which is used to determine the firing order. In order to ensure that the firing order is determined correctly some 10 confirmed determinations of the firing order are required. If a change-over switch 51 in accordance with Fig. 2 is used the change-over switch must stand in a fixed position until the firing order has been determined. This implies that a number of combustions in the engine must be activated before the firing order is unequivocally determined, since only combustions from two of engine's four cylinders provide the basis for the determination of the firing order. Once the firing order has been determined a spark is only generated in the cylinder where the piston reaches the end of the compression stroke, and the change-over switch 51 begins to adjust to the cylinders which are in firing position.

The processor contains an A/D-converter in which the analogous signals KIΓJATA and CQDAT are converted into digital signals, preferably pulse-width modulated (PWM) signals. The processor CPU of the ignition module transmits, via an adaptation circuit 50b, the signal KlrjATA., which corresponds to the engine-knock intensity This is accomplished by a digital signal imposed on the wire PoUT/KL having a pulse width which is proportional to the analogue integrated value from the integrator 53b. Similarly, the processor CPU of the ignition module transmits, via an adaptation circuit 50a, the signal C-QDATA- which is equivalent to the engine-knock intensity. This is done by a digital signal imposed on the conductor PøUT/CQ having ^a pulse width which is proportional to the analogue integrated value from the integrator 53a.

The adaptation circuits 50a/50b of the ignition module are described in Figure 3. This type of adaptation unit is placed at each end of the communication wires, KCQ and Kχι _j. The adaptation units 50c/50d are thus placed within the control module and 50a/50b within the ignition module. The adaptation circuit is of an active-low type, signifying the existence of a signal when the signal level at KCQ/KKJ is low. KCQ/KKJ is connected, via a resistance R2, to a voltage supply/VCC. VCC operates at a voltage level of 5 Volts if 5 Volts logic's is used. If, for example, the ignition module activates its output P₍₎UT_> SI is switched-over to a conductive state, whereby CQ/KJ^J is connected to ground and assumes a low/active signal. The low status at CQ/K^J is detected via its signal input P_jj r, by the control module at the opposite end of the communication wire

An inverter INV inverts the low/active signal at KCQ/KKJ into a high/active signal, in conformity with ECM and CPU.

The function of the matching unit is described in more detail including also reference to the signal status diagram shown in Fig. 4. At the point in time A the control unit ECM sends out a signal on the wire Tl which via the processor switches the primary switch 35a for cylinder 1 into a conductive status with a signal on the wire tl . This signal also initiates the processor in the ignition module to send up the value in the integrators 53a and 53b obtained from the previous combustion, which in Fig. 4 correspond to the pulse width CQ_cy|₂ and KI_cyl2, obtained from the combustion in cylinder 2. The previous combustion has occurred in cylinder 2 in a four-cylinder engine with the firing order 1-3-4-2. The pulse widths on CQ_cy|₂ and KI_cyi2 are preferably proportional to CQ_DATA and KI_DATA obtained from the two signal processing stages 52a, 53a and 52b,53b. At the point in time B the trigger signal on the wire Tl goes low which switches the primary switch into a non conductive status, whereby the spark is generated, which normally occurs a few crankshaft degrees/CD prior to the top dead centre. The top dead centre for cylinder 1 corresponds to 0 CD on the x-axis in Fig. 4. When combustion starts the detection of the combustion quality shall be initiated, which takes place at the point in time C controlled by the control module by means of activating the measuring window, with the signal CQ_w._cyil. The control module ECM activates its output P_0Uτ which activates SI to a conductive status, whereby K_CQ/K_KI is connected to earth and assumes a low/active signal. The low signal in the communication wire K_CQ is detected by the ignition module's processor CPU on the input P,_N/CQ, whereby the processor activates the filter 52a via the signal wire CQ_W. The pressure oscillations typical for a knocking condition always occur at a later stage of the combustion. The control of the knock measuring window is conducted in a similar manner. When knocking can occur the knock detection shall be initiated, which takes place at the point in time D controlled by the control module by activating the measuring window, with the signal KI_w__cyU. The control module ECM activates its output P₀uτ» which activates SI to a conductive status, whereby the communication wire K^ is connected to earth and assumes a low/active signal. The low signal on the communication wire K_κ, is detected by the ignition module's processor CPU on the input P_wm, whereby the processor activates the filter 52b via the signal wire KI_W. At the point in time E the control module ECM closes the measuring window for knock and combustion quality in that the respective output P₀uτ is deactivated, whereby K_KI and K_CQ assume a high non active signal.

The invention could, within the scope of the claims, be modified in a number of ways. For example, in a straight six-cylinder engine with three pistons running in parallel, equipped with only one ignition module the switch can sequentially connect one signal processing unit (corresponding 44 in Figure 2) with either of three measuring circuits (corresponding 39a-39b in Figure 2) within the ignition module.

Within certain types of engines more than one ignition module can be used. This is the case of V- engines, in which an ignition module is arranged upon each cylinder bank. Engines of this type, i.e. equipped with an ignition module for each cylinder bank, may have a switch installed in each ignition module.

Claims

1 An arrangement for detection of ionisation within the combustion chamber of a multi-cylinder, four-stroke combustion engine (20), including

- at least a first and a second combustion chamber in which the pistons run in parallel, but where the pistons are phase displaced according to the working phase of the four-stroke cycle,

- a measuring gap (24a, 24d) arranged in the first and second combustion chamber, which gap is biased to a substantially constant voltage level via measuring circuits (39a, 39b) individualised for the first and second combustion chamber respectively, which measuring circuits each deliver a proportional signal in relation to the ionisation degree via signal wires (JlorJ2) characterised in that

-a signal-processing unit (44) common for the measuring circuits (39a,39b) is connected to the respective measuring circuit (39a and 39b respectively) via a switch device (51), which momentarily at detection of ionisation currents only connects one of the signal wires (Jl or J2) from a measuring circuit (39a and 39b), to the signal-processing unit (44).

2. An arrangement according claim 1 characterised in that the switch device (51) is a two- way switch.

3. An arrangement according claim 2 characterised in that the switch device (51) is controlled by a logic circuit, preferably a processor (CPU), via a wire (SW).

4. An arrangement according claim 3 characterised in that the switch (51) is a digital multiplex circuit controlled by a processor (CPU) at a digital TTL-level via the wire (SW), which processor generates an ignition spark within the cylinders (22) of the combustion engine by means of its connected circuit-breakers (35a-35d), said sparks being generated by the processor in a predetermined ignition sequence given by externally obtained trigger signals (via T1-T4), or in a predetermined sequence, and where the switch device (51) is controlled by the processor synchronously to the ignition sequence.

5. An arrangement according any of the preceding claims characterised in that the signal- processing unit (44) at least contains means (53a) for integrating the signal which is proportional to the ionisation degree during a combustion in the combustion chamber.

6. An arrangement according claim 5 characterised in that the signal-processing unit (44), containing at least two parallel signal- processing stages (52a, 53a and 53a, 53b) which signal-processing stages by processing the signal being proportional to the ionisation degree, detects two different and combustion related parameters.

7. A procedure for detection of ionisation in the combustion chamber of a multi-cylinder, four-stroke combustion engine(20), including

- at least a first and a second combustion chamber in which the pistons run in parallel, but where the pistons are phase-displaced in accordance to the working phases of the four-stroke cycle,

- a measuring gap (24a, 24d) arranged in each of the first and second combustion chamber respectively, which gap is biased to a substantially constant voltage level via a measuring circuit (39a and 39b) individualised for the first and second combustion chamber, which measuring circuits deliver a signal, via signal wires (J1,J2), which is proportional to the ionisation degree characterised in that the

- measuring circuits are individually, and alternately connected to a common signal-processing unit (44) dependent of an established ignition sequence determined by a cylinder identification.

8. A procedure according claim 7 characterised in that a cylinder identification is performed by analysis of the ionisation in the combustion chamber, and where a substantially increased ionisation signal is obtained from the combustion chamber being subjected to the expansion stroke and a combustion in progress, and that the signal-processing units, until the cylinder identification has been definitely determined, continuously is connected to one measuring circuit (39a or 39b) only.