Start control apparatus of internal combustion engine

A start control apparatus of an internal combustion engine includes: a gas sensor configured to detect a gas concentration of the liquefied gas fuel in a gasified state at a position near a combustion chamber; a scavenging pump configured to perform scavenging from a position upstream of the combustion chamber to a position downstream of the combustion chamber; and a control unit configured to prohibit a start of the internal combustion engine and operate the scavenging pump when the gas concentration detected by the gas sensor before the start of the internal combustion engine is equal to or greater than a predetermined threshold value.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is entitled to the benefit of Japanese Patent Application No. 2022-153586, filed on Sep. 27, 2022, the disclosure of which including the specification, drawings and abstract is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a start control apparatus of an internal combustion engine.

BACKGROUND ART

Internal combustion engines, in particular diesel engines (compression-ignition internal combustion engines) that use liquefied gas fuel, in particular DME (Di-Methyl Ether) fuel have substantially the same configuration as that of typical diesel engines that use light oil fuel, and the same applies to the starting method.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

Incidentally, DME fuel is gas at room temperature and is easier to ignite than light oil. On the other hand, when defects of the injector such as seat defects of the injector nozzle occur, the fuel leaks from the seat part of the nozzle in some situation when the engine is stopped. In this case, when the starter motor is turned on to start the engine next time and the cranking is started, the leaked fuel may ignite at locations not intended in the design immediately after the start of the piston compression and the like. In such cases, repeated impacts to pistons and liners may cause damage to piston rings and liners.

In view of this, an object of the present disclosure is to provide a start control apparatus of an internal combustion engine that can prevent damages to the engine due to the leakage of liquefied gas fuel.

Solution to Problem

A start control apparatus of an internal combustion engine according to an aspect of the present disclosure uses liquefied gas fuel, the start control apparatus including: a gas sensor configured to detect a gas concentration of the liquefied gas fuel in a gasified state at a position near a combustion chamber; a scavenging pump configured to perform scavenging from a position upstream of the combustion chamber to a position downstream of the combustion chamber; and a control unit configured to prohibit a start of the internal combustion engine and operate the scavenging pump when the gas concentration detected by the gas sensor before the start of the internal combustion engine is equal to or greater than a predetermined threshold value.

Preferably, the control unit opens an EGR valve when a predetermined time has elapsed after an operation of the scavenging pump is started.

Preferably, the gas sensor is provided at a position upstream of the combustion chamber.

Preferably, the start control apparatus further includes an additional gas sensor configured to detect a gas concentration of the liquefied gas fuel in a gasified state at a position downstream of the combustion chamber. The control unit allows the start of the internal combustion engine and stops the scavenging pump when a gas concentration detected by the gas sensor becomes equal to or smaller than a predetermined threshold value after a start of an operation of the scavenging pump, and a gas concentration detected by the additional gas sensor becomes equal to or smaller than a predetermined threshold value.

Advantageous Effects of Invention

According to the present disclosure, damages to the engine due to the leakage of liquefied gas fuel can be prevented.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure are described below with reference to the accompanying drawings. Note that present disclosure is not limited to the following embodiments.

FIG.1is a schematic view of an internal combustion engine according to an embodiment of the present disclosure. Internal combustion engine1is a multi-cylinder (four-cylinder) diesel engine for vehicles, in particular a diesel engine that uses DME fuel, which is liquefied gas fuel. The vehicle is a large vehicle such as a truck. Note that the type of the vehicle is not limited to this, and may be a small-sized vehicle such as a passenger car, for example.

Note that the engine may be applied to a moving machine other than a vehicle, such as a ship, construction equipment and industrial equipment, and may be of a stationary type.

Engine1includes engine body2, suction passage3and exhaust passage4connected to engine body2, and fuel injection apparatus5. Engine body2includes structural components such as a cylinder head, a cylinder block and a crank case, and movable components such as a piston, a crankshaft and a valve housed inside the structural components. Flows of suction and exhaust airs are indicated by white and black arrows.

Fuel injection apparatus5is composed of a common rail type fuel injection apparatus, and includes a fuel injection valve, i.e., injector7provided in each cylinder, and common rail8connected to each injector7. In addition, fuel injection apparatus5includes feed pump51for suctioning and discharging the fuel inside fuel tank50, and supply pump52for pressurizing the fuel discharged from feed pump51to high pressure and supplying it to common rail8. Feed pump51of the present embodiment is composed of an in-tank pump disposed in fuel tank50. Supply pump52is driven by a crankshaft of engine1, and includes a volume regulation valve for regulating the discharging fuel volume.

Suction passage3is mainly defined by suction manifold10connected to engine body2(in particular, the cylinder head), and suction pipe11connected to the upstream end of suction manifold10. Air cleaner12, airflow meter13, compressor14C of turbocharger14, inter cooler15, and electronic control type suction throttle valve16are provided in suction pipe11in this order from the upstream side in the direction in which suctioned air flows toward combustion chamber9of engine body2. Airflow meter13is a sensor (suction amount sensor) for detecting the intake air volume (suction flow rate) per unit time of engine1.

Exhaust passage4is mainly defined by exhaust manifold20connected to engine body2(in particular, the cylinder head), and exhaust pipe21disposed on the downstream side of exhaust manifold20in the flow direction of the exhaust air from combustion chamber9of engine body2. Turbine14T of turbocharger14is provided between exhaust pipe21or exhaust manifold20and exhaust pipe21. An exhaust post-processing apparatus not illustrated in the drawing is provided in exhaust pipe21on the downstream side of turbine14T. The exhaust post-processing apparatus includes an oxidation catalyst, a particulate filter, a SCR (Selective Catalytic Reduction) catalyst and an ammonia oxidation catalyst in this order from the upstream side in the flow direction of the exhaust air, for example.

Engine1also includes EGR (Exhaust Gas Recirculation) apparatus30. EGR apparatus30includes EGR passage31for causing reflux of a part of the exhaust air (referred to as EGR gas) in exhaust passage4(in particular, exhaust manifold20) into suction passage3(in particular, suction manifold10), EGR cooler32for cooling EGR gas flowing through EGR passage31, and EGR valve33for regulating the flow rate of the EGR gas.

In addition, electronic control unit (referred to as ECU)100, which is a control unit, a circuit element (circuitry) or a controller for controlling engine1is also provided. ECU100includes a CPU (Central Processing Unit) with computation functions, a ROM (Read Only Memory) and a RAM (Random Access Memory) as storage medium, input/output ports, storage devices other than the ROM and RAM, and the like.

Further, in addition to the above-described airflow meter13, crank angle sensor40for detecting the crank angle and the rotational speed (more specifically, revolutions per minute (rpm)) of the engine, accelerator position sensor41for detecting the accelerator position, and common rail pressure sensor54for detecting the common rail pressure are provided. The output signals of these sensors are sent to ECU100.

ECU100controls various devices, i.e., injector7, the volume regulation valve of supply pump52, suction throttle valve16, and EGR valve33on the basis of the outputs of the sensors.

Engine body2is provided with starter motor22for starting the engine. Engine switch42for instructing the start and stop of the engine is connected to ECU100.

As described above, DME fuel is gas at room temperature and is easier to ignite than light oil. On the other hand, when defects of injector7such as seat defects of the injector nozzle occur, the fuel leaks from the seat part of the nozzle in some situation when the engine is stopped. In this case, when starter motor22is turned on to start the engine next time and the cranking is started, abnormal combustion may occur immediately after the start of piston compression and the like, and the leaked fuel may ignite at the location not intended in the design. In such cases, repeated impacts to pistons and liners may cause damage to piston rings and liners.

The start control apparatus of the present embodiment is configured to solve the above-described problems. The start control apparatus of the present embodiment includes first gas sensor43(which corresponds to the gas sensor in the claims) for detecting the gas concentration of the gasified DME fuel at a position near combustion chamber9, scavenging pump23for performing scavenging in the location from the upstream side to the downstream side of combustion chamber9, and the above-described ECU100. ECU100is configured to prohibit the start of engine1and operate scavenging pump23when DME gas concentration C1detected by first gas sensor43before the start of the engine is equal to or greater than predetermined threshold value of C1s.

In addition, the start control apparatus of the present embodiment includes second gas sensor44(which corresponds to the additional gas sensor in the claims) for detecting gas concentration C2of the gasified DME fuel at a position downstream of combustion chamber9.

In the present embodiment, first gas sensor43is provided at a position upstream of combustion chamber9, or more specifically at suction manifold10. To avoid abnormal combustion in combustion chamber9, it is preferable to detect concentration C1of the gas entering the combustion chamber9, i.e., the DME gas at a position near combustion chamber9on the upstream side immediately after the start of the cranking in a case where it is assumed that cranking is started. Therefore, it is preferable to provide first gas sensor43in suction manifold10as in the present embodiment. It should be noted that the position of first gas sensor43may be changed.

The DME leaked in the cylinder due to defects of injector7leaks from the inside of the cylinder where the intake/exhaust valve is open, to the outside of the cylinder, and the DME is retained mainly inside suction manifold10and exhaust manifold20. In the present embodiment, scavenging pump23is provided in order to remove the retained DME through scavenging. Scavenging pump23is controlled by ECU100.

In the present embodiment, suction manifold10and suction pipe11are connected through scavenging pipe24, and scavenging pump23is provided in scavenging pipe24. One end (entrance end) of scavenging pipe24is connected to the entrance of suction pipe11, i.e., to the position between air cleaner12and airflow meter13in suction pipe11, but this connection position can be changed.

In the present embodiment, second gas sensor44is provided at exhaust pipe21, or more specifically, at a position downstream of turbine14T and upstream of the exhaust post-processing apparatus not illustrated in the drawing. In the present embodiment, second gas sensor44is not provided at exhaust manifold20, but is provided at a position downstream of turbine14T separated away from combustion chamber9. It should be noted that the position of second gas sensor44can also be changed, and it may be provided at exhaust manifold20.

Next, a control of the present embodiment is described.

FIG.2illustrates a control method of the present embodiment. The routine illustrated in the drawing is repeatedly executed by ECU100at predetermined computation cycle T (e.g., 10 msec).

When the engine is stopped, EGR valve33is fully closed. When the driver turns on engine switch42to start the engine in the state where the engine is stopped, the routine is started.

First, at step S101, ECU100determines whether the DME gas concentration near combustion chamber9is high concentration. For convenience, the determination whether the concentration is high is referred to as “high concentration determination”, and the determination whether the concentration is not high (that is, the determination whether the concentration is low concentration) is referred to as “low concentration determination”. The high concentration determination is continuously performed from the time when the high concentration determination start condition described below is satisfied first, to the time when the high concentration determination termination condition is satisfied.

In the present embodiment, the high concentration determination start condition is satisfied when DME gas concentration C1detected by first gas sensor43is equal to or greater than predetermined threshold value (first start threshold value) C1sH. Threshold value C1sH is set in advance to a minimum or near minimum value of DME gas concentration C1at which abnormal combustion may occur if the cranking is started.

When it is determined at step S101that the concentration is high (step S101: Yes), i.e., when DME gas concentration C1is determined to be equal to or greater than threshold value C1sH, ECU100proceeds to step S102to prohibit the start of the engine, and operates (turns on (ON)) scavenging pump23at step S103.

Then, as indicated by the broken arrow a inFIG.1, the air is introduced to scavenging pipe24from suction pipe11so as to enter suction manifold10through scavenging pipe24. Then, the air passes through combustion chamber9of the cylinder where the intake/exhaust valve is open, and then through exhaust manifold20, turbine14T, and exhaust pipe21in this order. Along with this air flow, the DME gas retained mainly in suction manifold10and exhaust manifold20can be discharged to the exhaust side, and thus scavenging of the DME gas can be achieved.

As described above, scavenging pump23performs scavenging from a position upstream of combustion chamber9to a position downstream of combustion chamber9.

The start of the engine is prohibited by prohibiting the operation of starter motor22, for example.

Subsequently, at step S104, ECU100determines whether elapsed time t from the start of the operation of scavenging pump23has reached predetermined time ts or more. When elapsed time t has not reached predetermined time ts, the process skips step S105. When elapsed time t has reached predetermined time ts, the process proceeds to step S105to open EGR valve33. Preferably, the level of the opening at this time is the fully opened level, but it may be an intermediate level smaller than the fully opened level.

In this manner, EGR valve33is opened after predetermined time ts has passed from the start of the operation of scavenging pump23, or in other words, it is opened with a delay or a time difference from the start of the operation of scavenging pump23.

In the case where DME gas is retained near combustion chamber9(suction manifold10and exhaust manifold20), it is recognized that DME gas is retained also inside EGR passage31. If EGR valve33is opened simultaneously with the start of the operation of scavenging pump23, however, the air mainly flows inside EGR passage31immediately after the start of the operation, thereby less flowing inside combustion chamber9.

In view of this, in the present embodiment, EGR valve33is opened with a time difference. In this manner, immediately after the start of the operation of scavenging pump23, the air mainly passes inside combustion chamber9, and thus the scavenging of suction manifold10, combustion chamber9and exhaust manifold20can be performed with high efficiency. After predetermined time ts has passed, the scavenging of the inside of EGR passage31can be performed by opening EGR valve33. In this manner, the entire scavenging can be can be efficiently performed.

After step S105, the process is returned to step S101, and whether the DME gas concentration near combustion chamber9is still high concentration is determined. At this time, when the high concentration determination termination condition described below is not satisfied, it is determined to be high concentration. When the high concentration determination termination condition is satisfied, it is determined to be not high concentration. When it is determined to be high concentration, the process proceeds to step S102and the above-described control is repeated.

The high concentration determination termination condition is satisfied when the following conditions 1 and 2 are satisfied. Condition 1: DME gas concentration C1detected by first gas sensor43is equal to or smaller than predetermined threshold value (first termination threshold value) C1sL (C1≤C1sL). Condition 2: DME gas concentration C2detected by second gas sensor44is equal to or smaller than predetermined threshold value (second termination threshold value) C2sL (C2≤C2sL).

First termination threshold value C1sL is a value smaller than the above-described first start threshold value C1sH, and is set in advance to a sufficiently small value of DME gas concentration C1at which no abnormal combustion can occur even if the cranking is performed, such as values around zero.

Second termination threshold value C2sL is set in advance to a value equal to or substantially equal to first termination threshold value C1sL.

After the start of the operation of scavenging pump23, the value of DME gas concentration C1detected by first gas sensor43gradually decreases. On the other hand, the value of DME gas concentration C2detected by second gas sensor44increases first under the influence of the DME gas sent from the upstream side through scavenging, but then conceivably decreases toward the value of DME gas concentration C1detected by first gas sensor43. In view of this, when C1≤C1sL and C2≤C2sL are satisfied, it is determined that the scavenging of the DME gas has been completed and that the DME gas concentration near combustion chamber9is not high concentration. In this manner, the fact that the DME gas concentration near combustion chamber9is sufficiently reduced can be guaranteed in a backup manner by using the detection value of second gas sensor44, and thus the occurrence of abnormal combustion when the cranking is performed can be reliably prevented.

In short, from the time when the high concentration determination start condition (C1≥C1sH) is satisfied for the first time, the determination whether the DME gas concentration near combustion chamber9is high concentration (the high concentration determination) is started, and it is determined to be Yes step S101. Thereafter, until the high concentration determination termination condition (C1≤C1sL and C2≤C2sL) is satisfied, the determination whether it is high concentration is continued. Thereafter, from the time when the high concentration determination termination condition (C1≤C1sL and C2≤C2sL) is satisfied, the determination whether it is not high concentration (step S101: No), i.e., the low concentration determination, is started.

Then, when it is determined at step S101that it is not high concentration (step S101: No), ECU100proceeds to step S106to allow for the start of the engine, and transfers to the normal start mode at step S107to start the engine. The start of the engine is allowed by allowing for the operation of starter motor22, for example.

In the normal start mode at step S107, ECU100starts the engine in accordance with the sequence as described below. The sequence of the present embodiment is substantially the same as typical engine starting sequence.

Step S201: EGR valve33is fully closed, scavenging pump23is stopped (turned off (OFF)), and feed pump51is turned on. When feed pump51is turned on, DME fuel at a predetermined feeding pressure is supplied to supply pump52.

Step S202: starter motor22is turned on, and cranking, i.e., rotating of the crankshaft is started. In the case where engine switch42is a typical key switch, starter motor22may be turned on when the driver sets the key switch to the starter-on position. Along with the rotation of the crankshaft, supply pump52is operated, and the fuel is sent under pressure to common rail8.

Step S203: on the basis of the output of crank angle sensor40, the rotational frequency of the engine and the top dead center position of the reference cylinder (in the present embodiment, # one-cylinder) are detected. Then, the target fuel injection timing corresponding to the engine rotational frequency and the target common rail pressure required for the starting are calculated. The volume regulation valve of supply pump52is controlled such that the actual common rail pressure detected by common rail pressure sensor54is close to the target common rail pressure.

Step S204: when the actual common rail pressure reaches near the target common rail pressure and the actual crank angle detected by crank angle sensor40reaches the target fuel injection timing, a predetermined amount of fuel suitable for the starting is jetted from injector7.

Step S205: when the engine starts to perform self-driving, starter motor22is turned off. Note that in the case where engine switch42is a key switch, starter motor22may be turned off when the driver confirms the self-driving and returns the key switch from the starter-on position.

In this manner, according to the present embodiment, when DME gas concentration C1detected by first gas sensor43before the start of the engine is equal to or greater than first start threshold value C1sH, the start of the engine is prohibited and scavenging pump23is operated. In this manner, the engine can be started after preliminarily performing scavenging of the DME gas retained near combustion chamber9before the start of the engine, and thus damages to the engine due to the leakage of the DME fuel can be reliably prevented.

The above is a detailed description of the embodiments of the present disclosure, but there are various possible embodiments and variations of the present disclosure.

(1) For example, an electric turbocharger may be used as turbocharger14, and a compressor of the electric turbocharger may be used as a scavenging pump. In this case, when the electric turbocharger is turned on, the scavenging of the inside of suction passage3can be performed on the downstream side of the compressor and on the upstream side of suction manifold10(see virtual line arrow b inFIG.1), and thus the scavenging of DME gas can be more reliably performed in a wider range. Note that in this case, scavenging pipe24is naturally omitted.

(2) Second gas sensor44may be provided at a position closer to combustion chamber9, e.g., at exhaust manifold20, and the high concentration determination start condition may be set on the basis of second gas concentration C2detected by second gas sensor44. For example, when DME gas concentration C2detected by second gas sensor44is equal to or greater than predetermined threshold value (second start threshold value) C2sH, it is possible to determine that it is high concentration (step S101: Yes) so as to prohibit the start of the engine (step S102) and turn on scavenging pump23(step S103).

Alternatively, it is possible to determine that it is high concentration when both DME gas concentration C1detected by first gas sensor43and DME gas concentration C2detected by second gas sensor44are equal to or greater than threshold value C1sH and C2sH, respectively.

Alternatively, it is possible to determine that it is high concentration when one of DME gas concentration C1detected by first gas sensor43and DME gas concentration C2detected by second gas sensor44is equal to or greater than threshold value C1sH or C2sH.

(3) The high concentration determination termination condition may be set with only the detection value of first gas sensor43by omitting second gas sensor44. For example, it is possible to determine that it is not high concentration on the condition that DME gas concentration C1detected by first gas sensor43is equal to or smaller than first termination threshold value C1sL (the above-described condition 1) alone.

(4) Conversely, the high concentration determination termination condition may be set based only on the detection value of second gas sensor44. For example, it is possible to determine that it is not high concentration on the condition that DME gas concentration C2detected by second gas sensor44is equal to or smaller than second termination threshold value C2sL (the above-described condition 2) alone.

(5) In the embodiment, the scavenging pump is provided on the upstream side of the combustion chamber, and the scavenging of the DME gas is performed by pushing the air. Conversely, the scavenging pump may be provided on the downstream side of the combustion chamber so as to perform the scavenging of the DME gas by suctioning the air.

(6) The liquefied gas fuel is not limited to the DME fuel, but may be any liquefied gas fuel. For example, it may be natural gas, hydrogen and the like.

The embodiments of the present disclosure are not limited to the aforementioned embodiments only, and all variations, applications, and equivalents encompassed by the idea of the present disclosure as defined by the claims are included in the present disclosure. Accordingly, the present disclosure should not be construed as limiting, but can be applied to any other technology that falls within the scope of the idea of the present disclosure.