JPH0735754B2 - Combustion state measuring device for internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an apparatus for measuring a combustion state provided for various control data of an internal combustion engine.

(Prior Art) In recent years, the control of the internal combustion engine and its peripheral devices has also been electronically controlled, enabling more precise control. Various data such as the combustion state of the internal combustion engine is used for such control.

The indicated mean effective pressure Pi of the combustion pressure, which is one of the combustion states, is also one of the important data as showing the output torque, and the indicated mean effective pressure Pi is, for example, ignition control, fuel injection control, idle speed control, etc. Is an important control factor for the accurate execution of. Such Pi represents the average work amount due to the combustion pressure in the cylinder (hereinafter referred to as the in-cylinder pressure) which changes as shown in FIG. 5 for each combustion cycle, and is calculated by the following equation.

However, Vs: Stroke volume P: Combustion pressure This Pi specifically corresponds to the area within the closed curve divided by the stroke volume in the P-V diagram shown in FIG. The amount of work in the combustion cycle increases.

As a conventional combustion state measuring state of an internal combustion engine for obtaining such Pi, there is, for example, the one described in JP-A-60-22046. With this device, the specified crank angle (5 °)
The in-cylinder pressure is detected every time, and the indicated average effective pressure Pi is calculated based on that value.
Is calculated according to the following equation.

Where θ: Crank angle P _θ : In-cylinder pressure at each crank angle, that is, Pi is the product of the in-cylinder pressure at each crank angle and the volume change within the range of 0 ° → 360 ° in one combustion cycle.
It is calculated as / D converted, added, and divided by the stroke volume. This is TDC ± 180 including the peak value of cylinder pressure.
Corresponds to the portion of °. Then, by measuring this Pi, the amount of work in each combustion cycle in each cylinder can be known as one of the parameters representing the combustion state. Therefore, engine control is performed based on this information, and high drivability is ensured. .

(Problems to be Solved by the Invention) However, in such a conventional combustion state measuring apparatus for an internal combustion engine, a predetermined crank angle range (TDC ± 180 °)
Since the in-cylinder pressure at is converted to A / D and Pi is calculated based on the above equation, the in-cylinder pressure in the part excluding TDC ± 180 ° is not shown in the calculation result, and Pi measurement accuracy is indispensable. Sushi is not enough. This is because Pi has a character as an integrated value of the in-cylinder pressure in the entire stroke (0 ° → 720 °) as described above.

Although the above description is for the combustion state and Pi is a parameter, similar problems are pointed out for other parameters that represent the combustion state of the entire stroke.

(Object of the invention) Therefore, the present invention focuses on the fact that there is no large difference in the change waveform of the in-cylinder pressure except near TDC as long as the operating conditions are the same, and detects the actual in-cylinder pressure in a predetermined section near TDC, The other sections are intended to improve the measurement accuracy of parameters related to the combustion state of the engine by calculating the approximate value of the in-cylinder pressure in all strokes by determining the approximate value according to the operating conditions.

(Means for Solving Problems) In order to achieve the above object, the combustion state measuring apparatus for an internal combustion engine according to the present invention has a pressure detecting means for detecting the combustion pressure of the engine as shown in the basic conceptual diagram of FIG. a, a crank angle detecting means b for detecting the crank angle of the engine, an operating condition detecting means c for detecting at least information on the number of revolutions and a load indicating the operating state of the engine, and a crank angle at the compression top dead center. Sampling means d for sampling a plurality of combustion pressures in one crank angle range, and for the first crank angle range, while calculating the range of parameters related to the combustion state based on the output of the sampling means d, Within one combustion cycle and for a second crank angle range other than the first crank angle range, based on the output of the operating condition detecting means c, The calculation means e calculates a parameter related to the combustion state in one entire combustion cycle by calculating the range of the parameter related to the combustion state and adding these two calculated values.

(Operation) In the present invention, one combustion cycle (cycle including each stroke of intake, compression, expansion, and exhaust) is divided into two crank angle ranges, and from one value calculated in each range, one combustion cycle Combustion state information, that is, a value corresponding to the indicated mean effective pressure for the entire combustion cycle (hereinafter abbreviated as PZ)
Is required. Here, one range is a first crank angle range (hereinafter, referred to as a primary range) including the compression top dead center, and the pressure associated with combustion (for convenience, is included in this primary range).
Most of P ₁ ) is included (P _{2 for} convenience). In contrast,
The other range is the remaining range within the same travel period (hereinafter, secondary range), and the pressure in this secondary range (conveniently P ₃ ) is the residual pressure not included in the primary period (conveniently P ₃ ). and ₄₎ mechanical pressure (such as compression pressure of the piston; but given total value of convenience P _5), P ₄ is
Since P ₂ much smaller than that of the, in practice no problem believe that P ₃ = P _5. Moreover, the size of P ₅ is uniformly determined by the engine operating conditions such as the number of revolutions and the load, and is hardly affected by the combustion condition, so P ₅ can be represented by a single calculated value. Therefore, the comprehensive parameter (PZ) related to the combustion state within one stroke period can be calculated from P ₂ and P _5, and the secondary range, which was conventionally ignored, can be included in the calculation target. The measurement accuracy of can be improved step by step.

(Example) Hereinafter, the present invention will be described with reference to the drawings.

2 to 5 are views showing an embodiment of the present invention.

First, the configuration will be described. In FIG. 2, 1a to 1d are in-cylinder pressure sensors (pressure detecting means), and in-cylinder pressure sensors 1a to 1d.
Are arranged for each cylinder (4 cylinders in this embodiment). The in-cylinder pressure sensors 1a to 1d output the charge output S ₁ by converting the combustion pressure in the cylinder into an electric charge by the piezoelectric element, and the charge output S ₁ is similarly output by the charge amplifiers 2a to 2d arranged for each cylinder. It is converted into a voltage signal and input to the multiplexer (MPX) 3. The multiplexer 3 selectively switches the signals from the charge amplifiers 2a to 2d based on the switching signal Sc for each cylinder,
The signal S ₂ i (i = 1 to 4, cylinder number) is output to the low pass filter (LPF) 4.

The low-pass filter 4 eliminates the high-frequency component of the signal S ₂ i, such as knocking vibration or ignition noise, that is not necessary for the PZ calculation, and causes only the low-frequency component below a predetermined frequency to pass, which causes erroneous measurement. The signal S ₃ i is output to the control unit 5. Signals from a crank angle sensor (crank angle detecting means) 6 and an intake air amount sensor (operating condition detecting means) 7 are further input to the control unit 5.

The crank angle sensor 6 has an explosion interval (18 in a 4-cylinder engine).
(0 °) each time, a reference position signal REF that becomes a pulse of [H] level is output at a predetermined position before the compression top dead center (TDC) of the angular cylinder, and at each crank angle unit angle (for example, 1 °). The unit signal POS, which is a pulse of [H] level, is output. The engine speed Ne can be known by counting the pulses of the signal REF. On the other hand, the intake air amount sensor 7 is composed of, for example, an air flow meter, and absorbs the intake air amount as one of the parameters indicating the operating state of the engine.
Detect Qa.

The control unit 5 has functions as a sampling unit and a calculation unit, and includes a CPU 11, a ROM 12, a RAM 13, and an A / D converter.
14 and I / O interface 15. CPU
11 is related to the combustion state within one stroke period while fetching the required external data from the I / O interface 15 according to the program written in the ROM 12 and exchanging data with the RAM 13. The processing value necessary for the calculation of the comprehensive parameter, that is, the value PZ corresponding to the indicated mean effective pressure of one entire combustion cycle is calculated, and the processed data is output to the I / O interface 15 as necessary. Each signal from the low-pass filter 4, the crank angle sensor 6, and the intake air amount sensor 7 is input to the I / O interface 15, and the switching signal Sc is output from the I / O interface 15.

The A / D converter 14 performs A / D conversion of the external signal input to the I / O interface 15 according to the instruction of the CPU 11. Also ROM
Reference numeral 12 stores a calculation program in the CPU 11, and RAM 13 stores data used for calculation in the form of a map or the like. The PZ calculated by the CPU 11 is the I / O interface 15
It is output to the outside via and is used for various engine control data.

Next, the operation will be described. First, the basic principle of the present invention will be described.

In general, the change in cylinder pressure is shown as shown in FIG. In this case, the peak position of the in-cylinder pressure deviates depending on the operating condition, but except for the vicinity of TDC, the variation mode of the in-cylinder pressure is determined substantially uniquely by the operating condition at that time. That is, there is no great difference in the in-cylinder pressure waveform. This means that cylinder pressures other than near TDC can be predicted.

Therefore, in the present invention, paying attention to such a point, the primary portion (the first portion) that actually detects the in-cylinder pressure in consideration of the PZ detection accuracy.
(Corresponding to the crank angle range of 1) and a secondary portion (corresponding to the second crank angle range) that can be predicted by the operating conditions, and by summing these, the PZ detection accuracy is made extremely high.

Specifically, the primary part shall be set from BTDC 90 ° to ATD 90 °, and the secondary part shall be other than this. Then, PZ is calculated according to the following equation.

That is, PZ (the value equivalent to the indicated mean effective pressure of one entire combustion cycle) is a value obtained by integrating the product of the detected value P of the in-cylinder pressure and the volume change ΔV within the primary range (this value is the work amount for the primary range). Equivalent) and the work amount for the secondary range estimated based on the operating conditions at that time (function B (R,
It is calculated by dividing the added value given by Q)) with the stroke volume Vs. The return value of the function B (R, Q) corresponds to the work amount from the latter half of the expansion stroke to the compression stroke in the PV diagram shown in FIG. 6, and the locus drawn by that value is the intake air amount and throttle. It has been confirmed that it is almost constant unless the operating conditions such as the opening degree and the engine speed change.
Therefore, if the amount of work for the secondary range corresponding to each operating condition is found in advance by experiments, etc., and this is mapped and the table of the function B (R, Q) is created, the actual PZ calculation is performed. The optimum value corresponding to the operating condition at the time can be looked up, and a sufficient approximate value of the work amount for the secondary range can be obtained.

The primary portion is set from BTDC90 ° to ATDC90 ° in the case of a four-cylinder engine as in the present embodiment, but when it is set from BTDC60 ° to ATDC60 ° in the case of a six-cylinder engine, the PZ for one cylinder is set. The speed of the system to be calculated can be the same as in the case of four cylinders.

FIG. 3 is a flow chart showing a program for calculating the parameter PZ related to the combustion state based on the above-mentioned basic principle. When this program is inputted with the reference signal REF of BTDC 90 °, its execution is started.

First, at P ₁ , the in-cylinder pressure represented by the output S ₃ i of the low-pass filter 4 is A / D converted to a digital value P _θ, and at P ₂ , the crank angle of a predetermined cylinder is determined based on the outputs REF and POS of the crank angle sensor 6. Is counted to obtain the sample volume ΔV.
The sample volume ΔV corresponds to the timing of sampling the in-cylinder pressure for each volume, and is obtained by looking up from a predetermined table map. This can be obtained by calculation, but since it is quite complicated, it is calculated by the lookup method in the present embodiment, and the complexity of the device is avoided.

Next, at P ₃ , the current PX is calculated according to the following equation.

PX = PX ′ + P _θ × ΔV …… However, this calculation intermediate progress data for obtaining PX: PZ PX ′: Previous calculation intermediate progress data P ₄ determines whether or not the crank angle θ has reached ATDC 90 °. When θ <ATDC 90 °, the next A / D of the output S ₃ i at P ₅
Wait for conversion timing.

On the other hand, when θ = ATDC 90 °, the return value of the function B (R, Q) is obtained with P ₆ . This is based on the engine speed Ne calculated based on the output REF of the crank angle sensor 6 and the intake air amount Qa which is the output of the intake air amount sensor 7 as parameters to determine the operating condition at that time. Based on the predetermined table map, the optimum value of B (R, Q) is searched for.

Next, at P ₇ , PZ is calculated according to the following equation.

Thus, since this PZ is determined, then outputs a switching signal Sc to the multiplexer 3 at P _8, together with the process proceeds to the next cylinder, clear the PX in P _9, the output S ₃ P ₁₀ i
Wait for the next A / D conversion timing of.

In this way, in the range of BTDC90 ° to ATDC90 ° centered on the TDC of each cylinder of the four-cylinder engine, based on the cylinder pressure, and in other ranges, the table of the function B (R, Q) is looked up. , PZ is calculated for each cylinder.
When calculating this PZ, unlike the conventional method, it is calculated as the sum of the effective pressures in all strokes as described in the basic principle, so that the PZ detection accuracy can be significantly improved.

Further, in the present embodiment, the sampling of the cylinder pressure and this A / D conversion section are narrower (BTDC90 ° to ATDC180 °) than the conventional one (BTDC180 ° to ATDC180 °), so a device system required for A / D conversion is used. It can be small.

Further, in the present embodiment, since the in-cylinder pressure detection section is limited to the vicinity of TDC, when the in-cylinder pressure detected due to various causes is biased as shown in FIG. It can prevent the deterioration.

That is, when there is a constant bias component P _{D with respect} to the true in-cylinder pressure P _θ , the first term in the above equation is transformed as follows.

Σ (P _θ + P _D ) · ΔV = ΣP _θ ΔV + ΣP _D ΔV = ΣP _θ ΔV + P _D ΣΔV ・ ・ ・ However, P _D = const If the section integrated by this equation exists symmetrically around TDC, ΣΔV = 0 and the second term of the formula is 0
Becomes This means that the influence of the bias is eliminated, and a decrease in PZ detection accuracy is prevented.

(Effect) According to the present invention, in a predetermined crank angle range (first crank angle range) near the compression TDC, a parameter related to the combustion state of the engine for the range is calculated based on the actual cylinder pressure. In another range (second crank angle range) that has been completely ignored in the past, the approximate value of the same parameter for the range is estimated based on the operating condition at that time, and therefore at least the estimated value is divided. Only, the calculation accuracy of PZ (a value corresponding to the indicated mean effective pressure of the entire combustion cycle) can be improved.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 4 are diagrams showing an embodiment of the present invention, and FIG.
FIG. 4 is a flow chart showing a program for calculating parameters relating to the combustion state, FIG. 4 is a diagram showing changes in in-cylinder pressure for explaining the action, and FIGS. 5 and 6 are conventional combustion state measuring devices for internal combustion engines. 5 is a diagram for explaining the action in FIG. 5, FIG. 5 is a diagram showing changes in the in-cylinder pressure, and FIG. 6 is a diagram showing the relationship between the combustion chamber volume and the combustion pressure. 1a to 1d ... In-cylinder pressure sensor (pressure detecting means), 5 ... Control unit (sampling means, computing means), 6 ... Crank angle sensor (crank angle detecting means), 7 ... Intake air amount sensor (operating condition) Detection means).

Claims (1)

[Claims] Claims: 1. A) pressure detection means for detecting the combustion pressure of the engine, b) crank angle detection means for detecting the crank angle of the engine, and c) at least information on the number of revolutions and load indicating the operating state of the engine. Operating condition detecting means for detecting; d) sampling means for sampling a plurality of combustion pressures in a first crank angle range including the crank angle of the compression top dead center; and e) the sample for the first crank angle range. The operating condition detecting means calculates the relevant range of parameters related to the combustion state based on the output of the means, and within a single combustion cycle and for the second crank angle range other than the first crank angle range. Based on the output of
Calculate the relevant range of parameters related to the combustion state,
A combustion state measuring apparatus for an internal combustion engine, comprising: a calculation unit that calculates a parameter related to a combustion state in one entire combustion cycle by adding these two calculated values.