JP2013133813A - Control device for compression-ignition internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for a compression-ignition internal combustion engine, which does not cause upsizing, and which enhances exhaust emission performance by properly controlling switching between a spark-ignition operation and a compression-ignition operation while having a simple configuration.SOLUTION: The control device for the compression-ignition internal combustion engine switches an operation of the compression-ignition internal combustion engine (engine) between the compression-ignition operation of bringing about premixed compression-ignition combustion of an air-fuel mixture supplied to a combustion chamber and the spark-ignition operation of bringing about spark-ignition combustion of the air-fuel mixture via a spark plug of the combustion chamber. The control device detects a temperature Tc of a catalyst for exhaust emission control, which is arranged in an exhaust system of the engine (S12 and S20), performs switching from the compression-ignition operation to the spark-ignition operation when the catalyst temperature Tc detected during the compression-ignition operation of the engine is lower than a first predetermined value Tc1 (S14 and S18), and performs switching from the spark-ignition operation to the compression-ignition operation when the catalyst temperature Tc detected during the spark-ignition operation of the engine is higher than a second predetermined value Tc2 (S22 and S26).

Description

  The present invention relates to a control device for a compression ignition internal combustion engine. More specifically, a premixed gas obtained by mixing fuel and air is supplied to a combustion chamber, and this is self-ignited under a high compression ratio. The present invention relates to an improvement in a control device for a premixed compression self-ignition internal combustion engine that achieves thermal efficiency.

  A premixed compression self-ignition internal combustion engine, for example, as disclosed in Patent Document 1, is a compression ignition operation (HCCI (Homogeneous Charge Compression) for premixed compression ignition combustion of an air-fuel mixture (premixed gas) supplied to a combustion chamber. Ignition operation) and spark ignition operation (SI (Spark Ignition) operation) in which the air-fuel mixture is spark-ignited and combusted via the spark plug. In such an internal combustion engine, the pre-mixed gas is compressed under a high compression ratio (higher than the compression ratio of a normal spark ignition type internal combustion engine), and thus self-ignition is performed simultaneously at multiple points. There is an advantage that the flame can be propagated quickly and the combustion is completed in a short time, thereby improving the thermal efficiency and reducing the NOx emission while improving the fuel efficiency.

  The above-described internal combustion engine is configured to perform a spark ignition operation at the start, and then switch to a compression ignition operation when the warm-up is completed. However, in the case of the compression ignition operation, since the exhaust temperature is lowered, the temperature of the exhaust purification catalyst is also lowered, and the active state cannot be maintained, and there is a possibility that the exhaust emission performance deteriorates.

  Therefore, for example, it is conceivable to provide an additional device such as a heater for heating the exhaust. Further, as described in Patent Document 2, the exhaust purification catalyst is divided into two parts and arranged on the upstream side and the downstream side, and even if the exhaust gas temperature decreases, the activity of the catalyst on the downstream side is reduced. Techniques have been proposed that maintain the state as long as possible.

JP 2005-69097 A JP 2007-309251 A

  However, if an additional device such as a heater is provided or configured as in the technique described in Patent Document 2, the structure is complicated by the amount of the additional device and the exhaust purification catalyst divided into two parts, and the entire engine is increased in size. There was a bug.

  Therefore, the object of the present invention is to solve the above-mentioned problems, and not to increase the size, and to appropriately control switching between the spark ignition operation and the compression ignition operation with a simple configuration, thereby improving the exhaust emission performance. An object of the present invention is to provide a control device for a compression ignition internal combustion engine.

  In order to solve the above-described problem, in claim 1, the ignition means disposed in the combustion chamber of the compression ignition internal combustion engine and the air-fuel mixture supplied to the combustion chamber are premixed and compressed to operate the engine. In a control apparatus for a compression ignition internal combustion engine, comprising an operation switching means for switching between a compression ignition operation for igniting combustion and a spark ignition operation for spark ignition combustion of the air-fuel mixture via the ignition means, an exhaust system of the engine And a catalyst temperature detection means for detecting the temperature of the catalyst, and the operation switching means has a first predetermined catalyst temperature detected during the compression ignition operation of the engine. If it is less than the value, the compression ignition operation is switched to the spark ignition operation, and if the catalyst temperature detected during the spark ignition operation of the engine is greater than a second predetermined value, the spark ignition operation is performed. It was composed as switching to the compression ignition operation.

  The control apparatus for a compression ignition internal combustion engine according to claim 2 includes a variable valve mechanism capable of opening and closing an intake valve and an exhaust valve of the engine at an arbitrary timing, and the operation switching means includes the variable operation mechanism. The engine operation is switched between the spark ignition operation and the compression ignition operation by controlling the operation of the valve mechanism.

  In the control apparatus for the compression ignition internal combustion engine according to claim 3, the second predetermined value is set to a value equal to or greater than the first predetermined value.

  In the control apparatus for the compression ignition internal combustion engine according to claim 1, the temperature of the exhaust purification catalyst disposed in the exhaust system of the engine is detected, and the catalyst temperature detected during the compression ignition operation of the engine is the first. When the catalyst temperature detected during the spark ignition operation of the engine is higher than a second predetermined value, the spark ignition operation is switched to the compression ignition operation. In other words, if the catalyst temperature drops during compression ignition operation, switch from compression ignition operation to spark ignition operation, and if the catalyst temperature rises during spark ignition operation, switch from spark ignition operation to compression ignition operation Therefore, it is possible to appropriately control the switching between the spark ignition operation and the compression ignition operation, and the temperature of the exhaust purification catalyst is relatively high. Can be held, i.e., to maintain the active state of the catalyst, it is possible to improve the exhaust emission performance. Further, since an additional device such as a heater and an exhaust purification catalyst divided into two parts as in the technique described in Patent Document 2 can be eliminated, the overall size of the engine is not increased and the cost is reduced. It is advantageous.

  The control apparatus for a compression ignition internal combustion engine according to claim 2 includes a variable valve mechanism capable of opening and closing an intake valve and an exhaust valve of the engine at an arbitrary timing, and the operation switching means includes a variable valve mechanism. Since the engine operation is switched between the spark ignition operation and the compression ignition operation by controlling the operation, in addition to the above effects, the spark ignition operation and the compression ignition operation are switched with a simpler configuration. be able to.

  In the control apparatus for the compression ignition internal combustion engine according to the third aspect, since the second predetermined value is set to a value equal to or larger than the first predetermined value, in addition to the above effect, the second predetermined value is It is also possible to set a value different from the first predetermined value, specifically, a value larger than the first predetermined value, so that the spark ignition operation and the compression ignition operation are frequently switched according to the detected catalyst temperature ( Hunting can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an overall control apparatus for a compression ignition internal combustion engine according to an embodiment of the present invention. 2 is a graph showing two valve timing (and lift amount) characteristics that are switched (set) by the variable valve mechanism of the apparatus shown in FIG. 1. It is a flowchart which shows the switching control operation | movement switched between a spark ignition driving | operation and a compression ignition driving | operation by the electronic control unit shown in FIG.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment for implementing a control apparatus for a compression ignition internal combustion engine according to the invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram generally showing a control apparatus for a compression ignition internal combustion engine according to an embodiment of the present invention.

  In FIG. 1, reference numeral 10 denotes a water-cooled four-cycle single-cylinder OHV type compression ignition internal combustion engine (a premixed compression self-ignition internal combustion engine) that uses city gas (or LP gas; hereinafter simply referred to as “gas”) as fuel. (Hereinafter referred to as “engine”). The engine 10 is a general-purpose internal combustion engine used as, for example, a generator, an agricultural machine, a drive source for a cogeneration system, and the like, and has a displacement of 163 cc, for example.

  In the engine 10, the air drawn from an air cleaner (not shown) and passing through the intake pipe (intake system) 12 is adjusted in flow rate by the throttle valve 14 and flows into the combustion chamber 20 when the intake valve 16 is opened. .

  An injector (gas injector) 22 is disposed near the intake port in front of the intake valve 16. Gas fuel is pumped to the injector 22 from a fuel supply source via a fuel supply pipe (both not shown) and connected to an electronic control unit (hereinafter referred to as “ECU”) 26 through a drive circuit 24. Is done. When a drive signal indicating the valve opening time is supplied from the ECU 26 to the drive circuit 24, the injector 22 opens, and gas fuel corresponding to the valve opening time is injected into the intake port. The injected gaseous fuel flows into the combustion chamber 20 while mixing with the air that flows in to form an air-fuel mixture (pre-air mixture).

  A spark plug (ignition means) 28 is disposed in the vicinity of the combustion chamber 20. The spark plug 28 is connected to the ECU 26 via an ignition device 30 such as an igniter. When an ignition signal is supplied from the ECU 26 to the ignition device 30, a spark discharge is generated between the electrodes facing the combustion chamber 20. Thus, the air-fuel mixture is ignited and burned, and the piston 34 slidably accommodated in the cylinder 32 is driven downward.

  The air-fuel mixture is also burned by compression ignition. That is, the engine 10 performs either a compression ignition operation in which the air-fuel mixture is premixed compression ignition combustion or a spark ignition operation in which the air-fuel mixture is combusted by spark ignition via the ignition plug 28 according to the operating state. The operation is switched between the compression ignition operation and the spark ignition operation (premixed), and is configured as a compression ignition internal combustion engine. Specifically, for example, a spark ignition operation is performed when the engine 10 is started or warmed up, and a compression ignition operation is performed after the engine 10 is warmed up. The operation switching after starting the compression ignition operation will be described in detail later.

  The exhaust gas generated by the combustion flows through the exhaust pipe (exhaust system) 40 when the exhaust valve 36 is opened. In the middle of the exhaust pipe 40, a catalyst device 42 made of an exhaust purification catalyst (specifically, an oxidation catalyst) is disposed. When the catalyst device 42 is in an active state, the exhaust gas is purified by removing harmful components such as HC (hydrocarbon) and CO (carbon monoxide), and is released to the atmosphere outside the engine.

  A crank angle sensor (shown as “ENG rotation speed sensor” in the figure) 44 is disposed near the crankshaft (not shown) of the engine 10, and a TDC signal indicating a TDC (top dead center) or a crank angle in the vicinity thereof. And a crank angle signal obtained by subdividing the TDC signal. Those outputs are input to the ECU 26.

  The ECU 26 includes a microcomputer and includes a CPU, a ROM, a RAM, and the like. The ECU 26 calculates (detects) the engine speed NE by counting the crank angle signal among the input signals.

  The throttle valve 14 is connected to an electric motor (for example, a stepping motor or actuator) 46. The electric motor 46 is connected to the ECU 26. The ECU 26 drives the electric motor 46 based on the output of each sensor that is input, and controls the opening TH of the throttle valve 14. That is, the operation of the throttle valve 14 is controlled by a DBW (Drive By Wire) method.

  A throttle opening sensor 50 is disposed in the vicinity of the throttle valve 14 and generates an output indicating the throttle opening TH. An intake air temperature sensor 52 is provided downstream of the throttle valve 14 in the intake pipe 12. The intake air temperature sensor 52 outputs a signal indicating the temperature of intake air flowing through the downstream side of the throttle valve 14 (that is, the intake air temperature of the engine 10) Tin.

  A wide-range air-fuel ratio sensor 56 is disposed upstream of the catalyst device 42 in the exhaust pipe 40, and a NOx sensor 60 is disposed downstream of the catalyst device 42. The wide area air-fuel ratio sensor 56 outputs a signal proportional to the oxygen concentration (ie, air-fuel ratio) of the exhaust gas, and the NOx sensor 60 outputs a signal indicating the amount of NOx (exactly NOx concentration) in the exhaust gas. Further, the catalyst device 42 is provided with a catalyst temperature sensor (catalyst temperature detecting means) 62, which generates an output indicating the temperature Tc [° C.] of the exhaust purification catalyst. The outputs of these sensor groups are also input to the ECU 26.

  The intake valve 16 and the exhaust valve 36 described above are connected to a variable valve mechanism 64. Although the detailed illustration of the variable valve mechanism 64 is omitted, for example, the variable valve mechanism 64 has a structure disclosed in Japanese Patent Application Laid-Open No. 2010-65565 previously proposed by the present applicant. Specifically, four cams of a first and a second intake cam and a first and a second exhaust cam are arranged adjacent to each other on a valve camshaft (camshaft). The intake lifter is in sliding contact with the first and second exhaust cams. The intake lifter and the exhaust lifter are each connected to a rocker arm via a push rod.

  During the spark ignition operation of the engine 10, by appropriately controlling the operation of an electromagnetic actuator, a control rod and the like connected to each cam, the intake lifter, the intake-side push rod and the rocker arm are controlled by the rotation operation of the first intake cam. And the intake valve 16 is driven with a valve timing (and lift amount) characteristic determined by the first intake cam.

  On the other hand, during the compression ignition operation of the engine 10, the intake lifter, the intake-side push rod and the rocker arm are operated by the rotation operation of the second intake cam, and the valve timing (and lift amount) characteristics determined by the second intake cam. Then, the intake valve 16 is driven. The exhaust valve 36 is also configured to operate in the same manner.

  The characteristic is shown by a solid line in FIG. 2 (16 for the intake valve 16 and 36 for the exhaust valve 36). During the compression ignition operation, the valve timing (and lift amount) is set to the characteristics shown by the solid line in FIG. Specifically, the closing timing of the exhaust valve 36 is advanced, and the opening timing of the intake valve 16 is retarded (at the crank angle). As a result, a predetermined amount of exhaust gas remains in the cylinder to increase the temperature of the air-fuel mixture (in-cylinder gas temperature), thereby enabling the compression ignition operation.

  On the other hand, during the spark ignition operation, the valve timing (and the lift amount) is set to a characteristic indicated by a broken line in FIG. Specifically, the closing timing of the exhaust valve 36 and the opening timing of the intake valve 16 are both changed to near the piston top dead center. As a result, the closing of the exhaust valve 36 is retarded and the amount of gas discharged in the combustion chamber increases, while the opening of the intake valve 16 is advanced and the inflow of intake air is accelerated, so that the exhaust gas is combusted. It is sent to the exhaust system without remaining in the chamber.

  Returning to the description of FIG. 1, the variable valve mechanism 64 is connected to the ECU 26 via the control circuit 66. The ECU 26 controls the operation of the variable valve mechanism 64 (more precisely, the electromagnetic actuator) through the control circuit 66, and sets the valve timing (and lift amount) of the intake valve 16 and the exhaust valve 36 to one of the above two characteristics. Set (change).

  Thus, the intake valve 16 and the exhaust valve 36 of the engine 10 can be freely opened and closed at any time (valve timing and lift amount) by the variable valve mechanism 64, and the operation of the engine 10 is controlled by the variable valve mechanism. Switching between the spark ignition operation and the compression ignition operation is performed by controlling the operation of 64.

  Next, the operation of the control device for the engine 10 according to the present embodiment will be described.

  FIG. 3 is a flow chart showing a switching control operation for switching the operation between the spark ignition operation and the compression ignition operation when the warm-up of the engine 10 is finished and the compression ignition operation is performed. It is a chart.

  As shown in FIG. 3, first, in S (step) 10, it is determined whether or not the warm-up of the engine 10 has ended and the spark ignition operation has been switched to the compression ignition operation. When the result in S10 is negative, the subsequent processing is skipped. When the result is affirmative, the process proceeds to S12, and the temperature Tc of the exhaust purification catalyst (catalyst device 42) is detected based on the output of the catalyst temperature sensor 62.

  Next, in S14, it is determined whether or not the detected catalyst temperature Tc is lower than a first predetermined value Tc1. The first predetermined value Tc1 is set to a lower limit value, for example, 400 [° C.], at which the temperature of the exhaust purification catalyst is relatively high and the active state of the catalyst can be maintained.

  When the result in S14 is negative, the program proceeds to S16, and the compression ignition operation is continued. When the result is affirmed, the program proceeds to S18, and the compression ignition operation is switched to the spark ignition operation. Specifically, in S18, the operation of the variable valve mechanism 64 (more precisely, the electromagnetic actuator) is controlled, and the first suction (exhaust) air for the spark ignition operation is controlled from the second intake (exhaust) cam for the compression ignition operation. Switch to cam.

  Thus, the intake valve 16 and the exhaust valve 36 are driven with the valve timing (and lift amount) characteristics determined by the first intake (exhaust) air cam, and the spark ignition operation is executed. When the spark ignition operation is performed, the exhaust temperature rises, so the catalyst temperature Tc also rises and the active state is reliably maintained (reactivated).

  Next, in S20, the catalyst temperature Tc is detected again, and in S22, it is determined whether or not the catalyst temperature Tc detected in S20 is greater than a second predetermined value Tc2. The second predetermined value Tc2 is such a value that it can be determined that the active state of the catalyst can be maintained even when the spark ignition operation is returned to the compression ignition operation when the catalyst temperature Tc is higher (even when the compression ignition operation is resumed). Specifically, it is set to a value equal to or greater than the first predetermined value Tc1 described above, more precisely, a value larger than the first predetermined value Tc1 (for example, 450 [° C.]).

  When the result in S22 is negative, the program proceeds to S24 and the spark ignition operation is continued. When the result is affirmative, the program proceeds to S26, and the spark ignition operation is switched to the compression ignition operation. Specifically, in S26, the operation of the variable valve mechanism 64 is controlled to switch from the first intake (exhaust) cam for spark ignition operation to the second intake (exhaust) cam for compression ignition operation. As a result, the intake valve 16 and the exhaust valve 36 are driven with the valve timing (and lift amount) characteristics determined by the second intake (exhaust) air cam, and the compression ignition operation is executed (restarted).

  As described above, in the embodiment of the present invention, the ignition means (ignition plug) 28 disposed in the combustion chamber 20 of the compression ignition internal combustion engine (engine) 10 and the operation of the engine 10 are supplied to the combustion chamber. Compression ignition internal combustion engine having operation switching means (ECU 26) for switching between compression ignition operation for premixed compression ignition combustion of the air-fuel mixture to be performed and spark ignition operation for spark ignition combustion of the air-fuel mixture via the ignition means In the engine control device, an exhaust purification catalyst (catalyst device) 42 disposed in the exhaust system (exhaust pipe) 40 of the engine 10 and catalyst temperature detection means (catalyst temperature sensor 62,) for detecting the temperature Tc of the catalyst. ECU 26. S12, S20), and when the catalyst temperature Tc detected during the compression ignition operation of the engine is lower than a first predetermined value Tc1, the compression ignition is performed. When switching from the operation to the spark ignition operation (S14, S18) and the catalyst temperature Tc detected during the spark ignition operation of the engine is larger than a second predetermined value Tc2, the spark ignition operation is changed to the compression ignition operation. It was configured to switch (S22, S26).

  This makes it possible to appropriately control the switching between the spark ignition operation and the compression ignition operation with a simple configuration, so that the temperature of the exhaust purification catalyst (catalyst device) 42 can be kept relatively high, that is, the active state of the catalyst can be changed. It is possible to maintain the exhaust emission performance. Further, since an additional device such as a heater and an exhaust purification catalyst divided into two parts as in the technique described in Patent Document 2 can be eliminated, the overall size of the engine is not increased, and the cost is reduced. It is advantageous.

  The engine (engine) 10 includes a variable valve mechanism 64 that can freely open and close the intake valve 16 and the exhaust valve 36 at an arbitrary timing, and the operation switching means controls the operation of the variable valve mechanism 64. Thus, since the engine 10 is switched between the spark ignition operation and the compression ignition operation (S18, S26), the spark ignition operation and the compression ignition operation can be switched with a simpler configuration. Can do.

  Further, since the second predetermined value Tc2 is set to be equal to or greater than the first predetermined value Tc1, the second predetermined value Tc2 is different from the first predetermined value Tc1, specifically, the first It is also possible to set a value larger than the predetermined value Tc1, and thus it is possible to prevent the spark ignition operation and the compression ignition operation from being switched frequently (hunting occurs) in accordance with the detected catalyst temperature Tc.

  In the above description, the catalyst temperature Tc is detected by using the catalyst temperature sensor 62. However, the present invention is not limited to this, and it may be detected by other methods. In addition, the first and second predetermined values, the displacement of the engine 10 and the like are shown as specific values, but these are examples and are not limited.

  DESCRIPTION OF SYMBOLS 10 engine (compression ignition internal combustion engine), 16 intake valve, 20 combustion chamber, 28 spark plug (ignition means), 26 ECU (electronic control unit), 36 exhaust valve, 40 exhaust pipe (exhaust system), 42 catalyst device (exhaust) Purification catalyst), 62 catalyst temperature sensor (catalyst temperature detection means), 64 variable valve mechanism

Claims (3)

  Ignition means arranged in a combustion chamber of a compression ignition internal combustion engine, compression ignition operation for premixed compression ignition combustion of an air-fuel mixture supplied to the combustion chamber and operation of the engine, and the mixture through the ignition means In a control apparatus for a compression ignition internal combustion engine provided with an operation switching means for switching between spark ignition operation for spark ignition combustion, an exhaust purification catalyst disposed in an exhaust system of the engine, and a temperature of the catalyst are detected A catalyst temperature detecting means, and the operation switching means switches from the compression ignition operation to the spark ignition operation when the catalyst temperature detected during the compression ignition operation of the engine is less than a first predetermined value. When the catalyst temperature detected during the spark ignition operation of the engine is larger than a second predetermined value, the compression ignition operation is switched to the compression ignition operation. The control device of fire internal combustion engine.   A variable valve mechanism that can freely open and close the intake valve and the exhaust valve of the engine at any time is provided, and the operation switching means controls the operation of the variable valve mechanism to control the operation of the engine by the spark ignition. 2. The control apparatus for a compression ignition internal combustion engine according to claim 1, wherein the control is switched between an operation and the compression ignition operation.   The control apparatus for a compression ignition internal combustion engine according to claim 1 or 2, wherein the second predetermined value is set to a value equal to or greater than the first predetermined value.

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