JP2003003883A - Method for detecting combustion state of diesel engine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for detecting a combustion state of a diesel engine, which is capable of improving detection accuracy. SOLUTION: The combustion state detecting method for a diesel engine of the present invention detects a combustion state using a vibration sensor 12 attached to a lower end of an engine block 6. in this case,
As the detection frequency of the engine block vibration, a frequency band including the resonance frequency of a reciprocating component system combining the piston 1, the piston pin 2, the connecting rod 3, the connecting rod metal, and the crank is used, so that the vibration level due to combustion is large. Therefore, a high S / N ratio can be detected, and the pilot injection amount can be accurately controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion state detecting method for a diesel engine which employs a pilot injection system in which fuel pressurized by a fuel pressure pump is pilot-injected into a combustion chamber by a fuel injection valve prior to main injection. Regarding

[0002]

2. Description of the Related Art Conventionally, at the time of fuel injection of a diesel engine, it is difficult to reduce the initial injection rate of the diesel engine or to perform a pilot injection, because of noise of the diesel engine or harmful exhaust gas (especially NO _x ). It is known that there is a reduction effect of. However, in the control of the injection rate as described above, particularly in the case of pilot injection, unless it is performed with extremely high accuracy, noise is deteriorated, which is rather an adverse effect.

Therefore, conventionally, as a technique for accurately controlling the pilot injection amount to suppress noise generation, there is a fuel injection device known from Japanese Patent Laid-Open No. 7-2002. This fuel injection device sequentially increases the pilot injection amount by a set amount until the vibration level information by the engine acceleration sensor falls below the set threshold value, and when it falls below the threshold value, controls so as to hold the pilot injection amount immediately before that. Then, it is possible to ensure a state in which the vibration level is reliably kept low by the action of the pilot injection. However, since the point of control accuracy of this known technique is the S / N ratio of vibration detection, there is a problem that the effect cannot be exhibited unless the vibration detection method is accurate.

Further, according to the fuel injection rate control method for a diesel engine disclosed in Japanese Patent Laid-Open No. 62-267546, the diesel engine is designed to reduce the combustion noise in response to a signal indicating the combustion noise of the fuel of the diesel engine. The fuel injection rate of the fuel supplied to the engine is controlled. In this case, the signal from the vibration sensor is used as the signal indicating the combustion sound. The pressure wave generated by combustion is transmitted from the combustion chamber to the outer wall of the engine through the cylinder wall surface, cylinder head, cylinder block, etc.
This is because the vibration is radiated into the air as the outer wall vibrates, so that the combustion state can be estimated by measuring the vibration state of the outer wall of the engine. The frequency of the vibration used at this time is the frequency of the self-ignition phenomenon in the compression ignition engine (2
〜3KHz). However, according to this method, even if the combustion pressure changes at 2 to 3 KHz, the S / N ratio deteriorates due to the vibration transfer characteristics up to the vibration detection position on the outer wall of the engine. Further, since the transmission characteristics differ from engine to engine, the S / N ratio differs from engine to engine, which causes a problem of deterioration of control accuracy.

[0005]

As described above, in order to detect the combustion state by measuring the noise and the vibration of the engine block, the transmission from the inside of the burning cylinder to the noise detection position and the vibration detection position is performed. If the characteristics of the system are not taken into consideration, a large amount of combustion information to be detected cannot be obtained for the noise level, and accurate detection cannot be performed. Further, if the combustion information cannot be detected accurately, the combustion cannot be controlled accurately. Therefore, an object of the present invention is to improve the detection accuracy of the combustion state in a diesel engine.

[0006]

The present invention provides a method for detecting a combustion state of a diesel engine according to each of the claims as a means for solving the above-mentioned problems.
The method for detecting the combustion state of a diesel engine according to claim 1, wherein the resonance frequency of a reciprocating motion component system that combines a piston, a piston pin, a connecting rod, a connecting rod metal, and a crank is used as the detection frequency of engine block vibration for detecting the combustion state. By using the included frequency band, it is possible to detect engine block vibrations that include particularly large vibrations at the resonance frequency of the reciprocating motion component system,
Since the vibration level due to combustion can be made large, detection with a high S / N ratio becomes possible.

According to a second aspect of the present invention, in the combustion state detecting method, a piston, a piston pin, a connecting rod, a connecting rod metal,
The frequency band including the resonance frequency of the reciprocating motion component system in which the cranks are combined is utilized, which enables detection with a high S / N ratio similar to detection of engine block vibration. The combustion state detection method according to claim 3, wherein a signal indicating engine block vibration is detected as detection of the combustion state, and this is compared with a value stored in advance to detect combustion abnormality in the engine block. As the detection frequency of, a frequency band including the resonance frequency of the reciprocating motion component system that combines the piston, piston pin, connecting rod, connecting rod metal, and crank is used.
As a result, a high S / N ratio can be detected, and a lighter abnormal combustion can be detected. Therefore, since the abnormal state of the engine can be detected earlier, appropriate measures can be taken and damage to the engine can be further reduced.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A method for detecting a combustion state of a diesel engine according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a side partial sectional view showing a configuration of a diesel engine to which a combustion state detecting method according to a first embodiment of the present invention is applied. Engine block (cylinder block)
Reference numeral 6 denotes a skeleton of the engine, which internally supports a crankshaft 4, a camshaft (not shown), and the like through a metal, a cylinder head 7 is attached to an upper portion, and an oil pan 11 is attached to a lower portion. There is. Engine block 6
A cylinder liner (not shown) is fitted in
In addition to forming a combustion chamber with the cylinder head 7 and the piston 1, it also functions as a cylinder for the piston 1 to smoothly move up and down.

The piston 1 is connected to the connecting rod 3 via a piston pin 2 and reciprocates in the cylinder while receiving a compression pressure or an explosion pressure. Connecting rod 3 is cap 1
It is connected to the crankshaft 4 by a bolt through a connecting rod metal (not shown) in cooperation with the motor 3. The crankshaft 4 is supported by a crank cap 5 fixed to the engine block 6. Cylinder head 7
A fuel injection valve 10 is attached to the fuel injection valve 10, and an intake pipe 8 and an exhaust pipe 9 are connected.

Generally, in the engine constructed as described above, when the fuel injected by the fuel injection valve 10 burns in the cylinder, the combustion pressure acts on the piston 1, the cylinder head 7, and the cylinder. In a diesel engine with a high compression ratio, since the gap between the piston 1 and the cylinder head 7 is small at the compression top dead center, the combustion pressure mainly acts on the piston 1 and the cylinder head 7. In this case, the cylinder head 7 includes an intake pipe 8, an exhaust pipe 9 and a fuel injection valve 1.
In addition to 0, a large number of components such as an intake valve, an exhaust valve, a camshaft, a head cover, etc., which are not shown, are mounted, the pressure transmission system is complicated, and the seating vibration of the valve occurs. Therefore, it is not suitable for vibration detection.

On the other hand, the force acting on the piston 1 due to the combustion pressure is transmitted from the piston pin 2 to the connecting rod 3 and from the large end of the connecting rod 3 to the crankshaft 4.
Since the crankshaft 4 is supported by the crankcap 5, the force is transmitted to the crankcap 5. Since the crank cap 5 is fixed to the engine block 6,
Power is transmitted to the engine block 6. Engine block 6
Since the oil pan 11 is mounted on the bottom of the cylinder, the number of parts to be mounted is smaller than that of the cylinder head 7, and the force transmission system is not complicated, which is an advantageous location for vibration detection.

As described above, the combustion pressure is transmitted to the engine block 6 through the reciprocating motion component system of the piston 1, the piston pin 2, the connecting rod 3, the connecting rod metal, and the crank. Therefore, when the vibration of the engine block 6 is detected,
Information on combustion is obtained.

FIG. 2 is a graph showing frequency characteristics of vibration of the reciprocating component system during engine operation. The vibration has a peak level at the resonance frequency, and also a vibration at the lower end of the engine block has a peak at that frequency. That is, when the pilot injection amount is extremely large, the vibration also becomes large. Therefore, if the pilot injection amount is increased and a vibration sensor (measuring sensor whose characteristics are known) is attached to the lower end of the engine block, frequency analysis is performed. ,
As shown in FIG. 3, the resonance frequency can be determined because it has a peak at a certain frequency. As described above, the vibration of the engine block 6 particularly greatly includes the vibration at the resonance frequency of the reciprocating motion component system that is the transmission system. Therefore, if the engine block vibration in the frequency band including the resonance frequency of the reciprocating component system is detected, the level of vibration due to combustion can be made large, so that detection with a high S / N ratio becomes possible.

Reference numeral 12 in FIG. 1 is a vibration sensor, and its mounting position is preferably close to the mounting position of the crank cap 5 to which the vibration of the reciprocating component system is transmitted. The vibration sensor 12 may be attached to the crank cap 5, but it is necessary to reliably seal the oil. Therefore, the first embodiment shown in FIG. 1 shows the case where the engine block 6 is attached to the lower end of the engine block 6 as the outside of the engine that does not require oil sealing.

FIG. 4 is a graph showing the relationship between the pilot injection amount and the vibration level at the lower end of the engine block when the vibration sensor 12 is attached to the lower end of the engine block 6 as shown in FIG. Further, FIG. 5 shows the injection rate, and the pilot injections P1, P2, P3 correspond to the pilot amounts P1, P2, P3 of FIG. In FIG. 4, the solid line shows the vibration level at the lower end of the engine block at the resonance frequency of the reciprocating component system, and the broken line shows the vibration level at the lower end of the engine block at frequencies other than the resonance frequency. Therefore, as can be seen from FIG. 4, when the resonance frequency is used, the sensitivity (gradient) regarding the pilot (injection) amount can be increased.

The combustion state detecting method according to the first embodiment of the present invention is utilized for injection rate control to detect the vibration level at the lower end of the engine block at the resonance frequency of the reciprocating motion component system,
If the pilot injection rate is controlled so as to reduce this, highly accurate injection rate control becomes possible.

The vibration sensor 12 may be a resonance type matching the resonance frequency of the reciprocating component system, or a bandpass filter may be used for the output of the vibration sensor 12,
The resonance frequency of the reciprocating component system may be included.

Further, as a method of processing the signal from the vibration sensor 12, since it is desired to detect the state of combustion, the period including the combustion period is adjusted in accordance with the timing of combustion so that the signal in the non-combustion period is not detected. If only the signal of (4) is taken out, detection with a higher S / N ratio becomes possible. Of the detection timing, the detection start timing is
The injection command signal may be used as a trigger, and the detection end timing is crank angle 4 TDC after top dead center (TDC).
If the angle is 5 °, combustion ends and vibration reaches the sensor position, so it is preferable to detect the signal in the above range. As the signal, a signal for detecting a peak value or an effective value in the detection period may be used. For peak detection or effective value, a peak hold circuit or an effective value calculation circuit may be used, or a signal may be AD-converted to obtain the peak value or effective value.

The resonance frequency of the reciprocating component system is obtained as follows. Since the peak of the resonance frequency of the engine block itself may appear largely, as shown in FIG. 6, the piston 1, the piston pin 2,
A system with connecting rod 3 and crankshaft 4 assembled,
The vibration sensor 21 whose characteristics are known to the piston 1, the connecting rod 3, or the crankshaft 4 when the top surface of the piston 1 is vibrated by being mounted on the support 23 via the rubber sheet 22. Attached
By measuring the vertical vibration of FIG. 6 and obtaining the transfer function,
The resonance frequency is determined.

FIG. 7 is a side partial sectional view showing the structure of a diesel engine to which the combustion state detecting method according to the second embodiment of the present invention is applied. The structural difference from FIG. 1 is that instead of the vibration sensor 12 provided at the lower end of the engine block 6,
The noise detection sensor 14 is provided near the bottom of the engine block 6, and other configurations are the same. That is,
In the first embodiment, an example in which engine block vibration is detected as detection of the combustion state has been shown, but in the second embodiment, noise generated due to vibration is measured. By extracting a frequency band including the resonance frequency of the reciprocating motion component system from the noise signal detected by the noise detection sensor 14, it is possible to detect with a high S / N ratio as in the case of vibration detection. In this case, it is preferable that the position of the noise detection sensor 14 is near the bottom of the engine block 6, which includes a large resonance frequency of the reciprocating component system as in the case of detecting vibration.

The combustion state detecting method according to the third embodiment of the present invention uses the detection of engine block vibration according to the first embodiment and utilizes this for detecting abnormal combustion in the combustion state. In general, abnormal combustion includes abnormal injection due to noise in the injection command signal and oil suction. In either case, since more fuel is supplied to the cylinder with respect to the normal fuel injection amount, abnormal combustion occurs. If abnormal combustion occurs,
Since the cylinder pressure acting on the piston 1 becomes large,
The vibrating force on the piston 1 is increased, and vibration is generated.

In the third embodiment, similarly to the above description in the first embodiment, if the resonance frequency of the reciprocating motion component system is used as the detection frequency, the S / N ratio can be increased, so that it is more mild. Abnormal combustion can be detected. Therefore, since the abnormal state of the engine can be detected earlier, appropriate measures can be taken and damage to the engine can be further reduced. In this case, the abnormal combustion determination is performed by comparing the value stored in advance with the normal value to determine the abnormality and performing the abnormal process.

[Brief description of drawings]

FIG. 1 is a side partial cross-sectional view showing a configuration of a diesel engine to which a combustion state detecting method according to a first embodiment of the present invention is applied.

FIG. 2 is a graph showing frequency characteristics of vibration of a reciprocating component system of a diesel engine.

FIG. 3 is a graph showing vibration characteristics of a lower end of an engine block of a diesel engine.

FIG. 4 is a graph showing a relationship between a pilot (injection) amount and vibration of a lower end of an engine block.

FIG. 5 is a diagram showing a relationship between a fuel injection rate and time.

FIG. 6 is a diagram showing how to obtain a resonance frequency of a reciprocating component system.

FIG. 7 is a side partial cross-sectional view showing the configuration of a diesel engine to which the combustion state detection method according to the second embodiment of the present invention is applied.

[Explanation of symbols]

1 ... Piston 2 ... Piston pin 3 ... connecting rod 4 ... crankshaft 5 ... Crank cap 6 ... Engine (cylinder) block 7 ... Cylinder head 10 ... Fuel injection valve 11 ... Oil pan 12 ... Vibration sensor 13 ... Cap 14 ... Noise detection sensor

Front page continuation (51) Int.Cl. ⁷ identification code FI theme code (reference) G01M 15/00 G01M 15/00 Z (72) Inventor Ho Kamiya 1 Toyota-cho, Toyota City, Aichi Prefecture Toyota Motor Corporation F term (reference) 2G087 AA01 AA27 BB11 CC15 FF16 3G084 AA01 BA13 DA39 EA04 EA11 EB06 EC03 FA19 3G301 HA02 JA37 MA23 MA27 NA08 NC01 PC06Z

Claims (3)

[Claims] 1. A diesel engine in injection control for detecting a combustion state of a diesel engine, detecting a signal indicating engine block vibration, and controlling a fuel injection rate of fuel supplied to the diesel engine so that the signal becomes small. In a combustion state detection method for an engine, a detection frequency of the engine block vibration is a piston,
A method for detecting a combustion state of a diesel engine, which is a frequency band including a resonance frequency of a reciprocating motion component system in which a piston pin, a connecting rod, a connecting rod metal, and a crank are combined. 2. A diesel engine in injection control for detecting a combustion state of a diesel engine, detecting a signal indicating engine noise, and controlling a fuel injection rate of fuel supplied to the diesel engine so as to reduce the signal. In the combustion state detection method for an engine, the detection frequency of the engine noise is a frequency band including a resonance frequency of a reciprocating component system in which a piston, a piston pin, a connecting rod, a connecting rod metal, and a crank are combined. Diesel engine combustion state detection method. 3. A control for detecting a combustion state of a diesel engine, detecting a signal indicating engine block vibration, comparing the detected signal with a value stored in advance to detect a combustion abnormality, and performing abnormality processing. In a combustion state detection method for a diesel engine, a detection frequency of the engine block vibration is a piston,
A method for detecting a combustion state of a diesel engine, which is a frequency band including a resonance frequency of a reciprocating motion component system in which a piston pin, a connecting rod, a connecting rod metal, and a crank are combined.