JPH0318139B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a knocking detection device for a diesel engine.

In a diesel engine, the combustion reaction rapidly progresses from the start of fuel injection to the ignition timing at which the combustion pressure rapidly increases, that is, the ignition delay has a significant effect on subsequent combustion. As the ignition delay increases, the amount of combustible mixture formed before ignition increases, which is then combusted all at once, resulting in a sudden pressure rise, making quiet operation impossible, and generating vibrations and knocking noises. do.

This kind of diesel knock is based on the large rate of pressure rise per angle: dP/dθ, and it is known that if this value exceeds 5 atm/deg, it will generate a significant knock noise and have a negative impact on the engine. . In a diesel engine, since the compression ratio is originally high, the vibration of the base is large, and the vibration of the engine block is drowned out by the noise caused by the vibration of the base. It is difficult to detect knocking based on the detection of vibrations.

The purpose of the present invention is to use a differential output type pressure detector to detect the pressure change per angle after correcting the rotation speed, and to detect the above-mentioned value at which knocking occurs, that is, 5 atm/deg. The concept of detecting the value and the differential value of pressure P with respect to time t, the value when ignition occurs and the pressure reaches the maximum
The phenomenon that the quotient obtained by dividing dP/dt (MAX) by the value dP/dt (t = T _l ) immediately before ignition is greater than a certain value when knocking occurs, regardless of the rotation speed. Based on the concept of utilizing this technology, the objective is to more accurately detect knocking in diesel engines.

The present invention includes a pressure detector that detects a rate of change in combustion pressure using a piezoelectric element, an angle detector that detects engine rotation, a timing calculation circuit that calculates measurement timing based on the output of the angle detector, and a sample hold circuit that captures the output value of the pressure detector at the time of trigger output at a predetermined crank angle of the timing calculation circuit; a peak hold circuit that captures the maximum output value of the output of the pressure detector; and a sample hold circuit that captures the maximum output value of the output of the pressure detector; It has a division circuit that divides by the output of the hold circuit, receives the outputs of the pressure detector and the timing calculation circuit, and makes a knocking determination that determines that knocking has occurred when the output of the division circuit becomes larger than a predetermined value. A knocking detection device for a diesel engine is provided, which is characterized by comprising a knocking detection circuit.

A knocking detection device for a diesel engine as an embodiment of the present invention is shown in FIG.

In FIG. 1, E is an in-line four-cylinder diesel engine. 1 is a pressure detector for detecting the rate of change in combustion pressure, and since a piezoelectric element is used, its output S1 represents the rate of change in pressure per hour. 2 is an angle detector, and 3 is a knocking detection circuit. 4
calculates the basic injection timing from the rotation speed n, accelerator amount θ _A , etc., and if there is a knocking signal from the knocking detection circuit, the injection timing is delayed by a predetermined amount, and if not, it is advanced to the basic injection timing. This is an injection timing control circuit with the following functions. 5 is an injection pump, and 61 to 64 are injection ports for injecting fuel into each cylinder.

In the angle detector 2, 21 is a rotation detection section;
2 is an angular position detection circuit, 23 is a reference position detection circuit, and 24 is a timing calculation circuit.

In the knocking detection circuit 3, 32 is a peak hold circuit, 33 is a sample hold circuit, 3
4 is a division circuit, 35 is a reference voltage generation circuit, and 36 is a comparison circuit.

An example of the pressure detector 1 used in the present invention is shown in FIG.

A pressure receiving plug 103 serving as a pressure medium is inserted between the piezoelectric element 101 and the diaphragm 102.
Reference numeral 104 denotes an output electrode, which is connected to a terminal 106 of a connector 105 with a lead wire 107. 108 is a grounding electrode, and the pressure receiving plug 103
and the housing 1 via the diaphragm 102
Grounded at 09. Insulators 110 and 111 insulate the piezoelectric element 101 from the sensor body 112. Similarly, 113 is an insulator and an output electrode 104
is insulated from the sensor body 112.

The sensor subassembly is assembled using the following procedure. Insert the insulator 110, electrode 104, piezoelectric body 101, pressure plug 103, and insulator 111 from the bottom of the sensor body 112, and then insert the pressure plug 103.
The piezoelectric element 101 and the pressure receiving plug 103 are fixed to the sensor body by caulking the caulking part 116 of the sensor body to the outer circumference of the sensor body through the metal hollow ring 114 and the spacer 115. On the other hand, an insulator 113 is inserted from the upper part of the sensor body 112, and a spacer 117 is press-fitted to form a sensor subassembly. Note that a preload is applied to the piezoelectric element 101 due to the springiness of the metal hollow ring 114.

The sensor subassembly is located in the housing 109
The diaphragm 102 is welded to the protrusion 1031 at the tip of the pressure receiving plug and the protrusion 1091 at the tip of the housing 109.

The connector 105 is connected to the caulking portion 1 of the housing 109 via a spacer 118 and an O-ring 119.
By caulking 092, it is fixed to the housing 109.

Pressure detectors use piezoelectric elements, so
A signal S1 representing pressure change per time, ie, dP/dt, is output.

The configuration of the angle detector 2 is shown in FIG.

22 is an angular position detection circuit.

The rotor 211 is a combination of a rotor having a plurality of protrusions on the outer periphery and a rotor having one protrusion on the outer periphery, and is fixed to a distributor shaft (not shown) and rotates together with the distributor shaft.

Reference numerals 212 and 213 designate electromagnetic pickups facing the respective protrusions of the rotor 211.

221, 231 are transistors, 222, 23
2 is a resistor, 223 and 233 are one-shot multivibrators, and 224 and 234 are drivers.

One-shot multivibrator 223, 23
Transistors 221 and 23 are connected to the trigger terminal 3.
1 collectors are connected to each.

When the rotor 211 rotates and each protrusion crosses the electromagnetic pickups 212, 213, the electromagnetic pickups 212, 213 sometimes drop to a negative voltage, and at this moment the transistors 221, 231 become conductive, and the transistors 221, 231 become conductive. The one-shot multivibrators 223 and 233 are triggered by the falling edge, respectively.

One-shot multivibrator 223, 23
3 outputs a low level signal for a time determined by the time constant of the resistor and capacitor, and the inverting driver 224,
234 into a high level signal.

As a result of the above, the output of the angular position detection circuit 22 is
A rotation signal S22 having a frequency proportional to the rotation speed and a pulse width independent of the rotation speed is output, and the reference position detection circuit 23 outputs one pulse signal S23 per rotation.

The timing calculation circuit 24 includes a down counter 2
41-244, flip-flop 245, 24
6. One-shot multivibrator 247,2
48.

A flip-flop 245 that starts sample hold and a flip-flop 246 that starts peak hold are set by a signal S241 based on signals S22 and S23. At signal S242
In order to hold the sample before TDC, the flip-flop 245 is reset and hold is started.

Similarly, flip-flop 24 is used to hold the peak after detecting the maximum output using signal S243.
6 and start hold.

Based on S22 and S23, the output of the comparison circuit 36 is output at a predetermined crank angle.

The configuration of the knocking detection circuit is shown in FIG. The peak hold circuit 32 is, for example, BURR.
-Use BROWN's 4084/25 peak hold module. The maximum output when the control input S246 is at a high level is held, and the hold output is reset using the control input S248.

The sample and hold circuit 33 is, for example, a sample and hold module manufactured by Deitel-Intersil.
Use SHM series. Control input S
Hold when 245 is low level.

The division circuit 34 uses, for example, a division circuit module of the AD530 series manufactured by Analog Devices. Output S34 is input S32 and input S33
A voltage S34 proportional to S32/S33, which is the ratio of
Output.

35 is a reference voltage generation circuit. 36 is a comparison circuit which samples at input S247.

In the knocking detection circuit 3, the output of the peak hold 32 is divided by the output of the sample hold circuit 33, and the output of the division circuit 34 is compared with a predetermined value by the comparison operation of the comparison circuit 36. When the output of the division circuit becomes larger than a predetermined value, it is determined that knocking has occurred.

In other words, the reason for performing this division is that if the rotational speed is constant, regardless of whether or not knocking occurs, the value immediately before TDC when ignition occurs and the pressure increases is dP/dt (t=T _h ), dP/dt ( t = T _l ) is constant, and the peak value of the pressure increase rate dP / dt (MAX) (P = P _h ), dP / dt (MAX) (P = P _l ) is expressed as dP / dt (t = T _h ), dP/dt (t = T _l ) is based on the fact that the quotient obtained by dividing by dP/dt (t = T l ) is greater than a certain value when knocking occurs, regardless of the rotation speed. Knocking is detected by performing division and correcting the output of the pressure change rate detector, which varies depending on the rotational speed.

In addition, in the above, T _h and P _h represent the timing and pressure at high rotation speed, respectively, and T _l and P _l
represent the timing and pressure at low rotation speed, respectively.

In addition, as mentioned above, the peak value dP/dt (MAX) and the sample hold value at a given crank angle
In order to compare the dP/dt ratio with a reference value, correction based on the suction negative pressure, that is, the load, is automatically performed.

Signal waveforms at various parts of the device shown in FIG. 1 are shown in FIG.

In Figure 5, 1 is the top dead center timing TDC
, 2 is the output signal S1 of the pressure detector 1, 3 is the sample hold control signal S245, 4 is the output signal S33 of the sample hold circuit 33, 5 is the peak hold control signal S246, and 6 is the peak hold reset signal S248. , 7 represents the output signal S32 of the peak hold circuit 32, 8 represents the sampling timing SMP, and 9 represents the output signal S364 of the knocking detection circuit 3, respectively.

According to the present invention, knocking in a diesel engine can be detected more accurately.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a knocking detection device for a diesel engine as an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of a pressure detector in the device shown in FIG. 1, and FIGS. 4a and 4b are diagrams showing the knocking detection circuit in the device shown in FIG. 1, and FIG. 5 is a waveform diagram showing signal waveforms at various parts in the device shown in FIG. 1. 1...Pressure detector, 2...Angle detector, 21...
... Rotation detection section, 22 ... Angular position detection circuit, 23
... Reference position detection circuit, 24 ... Timing calculation circuit, 3 ... Knotting detection circuit, 32 ... Peak hold circuit, 33 ... Sample hold circuit, 34 ... Division circuit, 35 ... Reference voltage generation circuit, 36 ... Comparison circuit, 4 ... Injection timing control circuit, 5 ... Injection pump, 61, 62, 63, 64
...Injection port, E...diesel engine.

Claims (1)

[Claims] 1. A pressure detector that detects the rate of change in combustion pressure using a piezoelectric element; An angle detector that detects the rotation of the engine; A timing calculation circuit that calculates measurement timing based on the output of the angle detector; and the timing calculation circuit. a sample hold circuit that captures the output value of the pressure detector at the time of trigger output at a predetermined crank angle; a peak hold circuit that captures the maximum output value of the output of the pressure detector; and a peak hold circuit that captures the maximum output value of the output of the pressure detector; a knocking detection circuit that receives outputs from the pressure detector and the timing calculation circuit and determines that knocking has occurred when the output of the dividing circuit becomes larger than a predetermined value. A knocking detection device for a diesel engine, comprising;