JP2019108876A - Control device for engine - Google Patents

Abstract

To secure good fuel economy performance without deteriorating combustion stability when an engine is in a half warming-up state.SOLUTION: A control device is applied to an engine including: an intake passage 30; an electric supercharger 51 provided in the intake passage 30; and an intake throttle valve 32 provided in the intake passage 30 on the downstream side of the electric supercharger 51 so as to enable opening/closing. The control device determines whether an engine is in a half warming-up state where a temperature difference obtained by subtracting a cylinder wall surface temperature from a piston temperature becomes a predetermined value or more or in a warming-up state where a cylinder wall surface temperature is higher than that in the half warming-up state and the temperature difference becomes less than the predetermined value, and when determining that the engine is in the half warming-up state, drives the electric supercharger 51 to supercharge intake air and lowers an opening of the intake throttle valve 32 compared to the engine is in the warming-up state.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a device for controlling an engine in which an electric supercharger and an intake throttle valve are provided in an intake passage.

  Immediately after the cold engine is started, that is, immediately after cold start, the temperature of the engine body is low and the fuel has low ignitability, so it is necessary to promote warm-up of the engine while securing the ignitability .

  For example, in Patent Document 1 below, the flow of exhaust gas on the upstream side of the intake throttle valve provided in the intake passage, the turbocharger driven by the energy of the exhaust gas, and the turbine of the turbocharger is At cold start of a diesel engine equipped with a throttling VGT (variable nozzle mechanism), control for closing the VGT and opening the intake throttle valve (hereinafter referred to as first control) is executed for a predetermined period, and then the VGT is opened for intake It is disclosed to execute control for closing the throttle valve (hereinafter referred to as second control).

  According to the diesel engine of Patent Document 1, the temperature of the cylinder is raised by the first control for closing the VGT to improve the ignitability, and then the catalyst is heated by the second control for closing the intake throttle valve. It can promote activation. That is, when the VGT is closed by the first control, the flow resistance (exhaust resistance) of the exhaust gas is increased, and the high temperature burnt gas remains in the cylinder (in other words, the internal EGR is performed). Increase rapidly, and the fuel's ignitability improves. Then, when the intake throttle valve is closed by the second control executed in that state, the amount of intake decreases and the air-fuel ratio becomes rich, and the unburned component of the fuel discharged together with the exhaust gas increases. The temperature of the exhaust gas is increased to promote the activation of the catalyst.

Patent No. 4453145

  Here, after the engine has been cold-started, although the temperature of the piston rises rapidly due to combustion heat, the temperature of the cylinder wall (hereinafter referred to as cylinder wall) mainly affected by the temperature of the cooling water is It only rises gradually. For this reason, at a time when a short time after the cold start, the temperature of the piston becomes significantly higher than the temperature of the cylinder wall. This state (hereinafter, referred to as a semi-warmed state) continues until the engine warm-up is almost completed and the temperature of the cylinder wall rises sufficiently.

  In the semi-warmed state, the amount of expansion of the piston (particularly the amount of expansion in the radial direction of the skirt thereof) is larger than the amount of expansion of the cylinder wall, so the mechanical friction force or compression received when the piston slides The reaction force (the force by which the intake air compressed in the cylinder pushes back the piston) increases. That is, when the outer periphery of the relatively expanded piston approaches the cylinder wall and the contact area between the two increases, the mechanical friction force of the piston increases. Also, by reducing the amount of intake air leaking through the gap around the piston (especially the gap between the piston ring and the cylinder wall) during the compression stroke, this increases the amount of intake air actually compressed in the cylinder, The compression reaction force applied to the piston is increased. Hereinafter, these resistances (frictional force, compression reaction force, etc.) received when the piston slides are generically referred to as the sliding resistance of the piston.

  As described above, in the semi-warming state in which the sliding resistance of the piston is increased, it is necessary to increase the fuel injection amount to secure the same piston speed (or output torque), so the fuel efficiency is likely to deteriorate. There's a problem.

  On the other hand, the invention of Patent Document 1 aims at promoting warm-up of the engine and catalyst at the cold start of the engine, and the problem concerning the fuel efficiency performance at the time of semi-warm-up and the countermeasure therefor Is not mentioned in particular.

  In Patent Document 1, if the engine is started in a state relatively close to half-warming, either the first control or the second control described above overlaps the period of the half-warming state. there is a possibility. However, even if either the first control or the second control is performed in the semi-warmed state, the fuel efficiency performance of the engine will be degraded.

  That is, in the first control, since the VGT is closed in order to cause the high temperature burned gas to remain in the cylinder, the exhaust resistance and hence the pumping loss are greatly increased, resulting in deterioration of the fuel efficiency. In the second control, the air-fuel ratio is greatly enriched (to λ <1) to activate the catalyst and unburned fuel is supplied to the exhaust passage. The amount increases, which also leads to the deterioration of the fuel efficiency performance.

  The present invention has been made in view of the above circumstances, and provides an engine control device capable of ensuring good fuel consumption performance without losing combustion stability when the engine is partially warmed up. With the goal.

  In order to solve the above-mentioned problems, the present invention is provided in a cylinder in which combustion is performed, a piston reciprocating in the cylinder, an intake passage through which intake air introduced into the cylinder flows, and an intake passage. An apparatus for controlling an engine comprising: an electric turbocharger driven by energy; and an intake throttle valve openably and closably provided in an intake passage downstream of the electric turbocharger, the temperature of the piston The temperature difference obtained by subtracting the wall surface temperature of the cylinder is equal to or greater than a predetermined value, or the wall temperature of the cylinder is higher and the temperature difference is less than the predetermined value than in the half-warmed state. The electric supercharger is driven to supercharge the intake air, and when the engine determines that the engine is in the half-warmed state by the determination unit that determines whether the engine is in the warm-up state, the engine If you are in a warm condition And and a control unit for reducing the opening degree of the intake throttle valve, it is characterized in that (claim 1).

  When the engine is in the semi-warmed state, the sliding resistance of the piston is increased due to the relatively large expansion of the piston which is considerably hotter than the wall surface of the cylinder, and the clearance around the piston is Leakage loss is reduced. For this reason, if the opening degree of the intake throttle valve is temporarily set to the same value as in the warm-up state, the sliding resistance of the piston is further increased due to an increase in the amount of intake actually compressed by the piston. Resulting in. This leads to an increase in the amount of fuel injection necessary to maintain the same rising speed of the piston and a deterioration in the fuel efficiency performance. On the other hand, in the present invention, when the engine is in the semi-warming state, the intake filling amount to the cylinder is reduced by the decrease in the opening degree of the intake throttle valve, so the sliding resistance of the piston can be reduced. Fuel efficiency can be maintained well.

  However, simply reducing the intake charge amount to the cylinder lowers the compression end temperature of the cylinder (the temperature in the cylinder at the compression top dead center) and deteriorates the ignitability of the fuel, resulting in unstable combustion, or In the worst case, it may cause a misfire. On the other hand, in the present invention, since the electric supercharger is driven in a state where the opening degree of the intake throttle valve is reduced, the temperature increase effect due to the intake being compressed by the electric supercharger and the low opening degree The temperature of the intake can be raised quickly by the heat energy generated from the resistance when the intake passes through the gap around the intake throttle valve. As a result, the temperature inside the cylinder can be raised to improve the ignitability of the fuel, and the combustion stability can be favorably maintained.

  Preferably, a bypass passage bypassing the electric supercharger is provided in the intake passage, and the control unit determines the opening degree of the intake throttle valve when it is determined that the engine is in the semi-warmed state. A part of the intake air supercharged by the electric supercharger is reduced to an opening degree at which an intake circulation flow is formed, which is returned to the electric supercharger through the bypass passage (claim 2).

  As described above, when the intake circulation flow is formed by utilizing the bypass passage, the intake can be repeatedly compressed by the electric supercharger, so that the temperature of the intake can be greatly increased in a very short time. It is possible to further enhance the ignition performance improvement effect described above.

  In the above configuration, more preferably, the bypass passage is provided with an openable / closable bypass valve, and the control unit determines the degree of opening of the bypass valve when it is determined that the engine is in the semi-warmed state. The opening degree is lowered to a predetermined opening degree lower than the opening degree of the flow rate saturation point where the pressure difference before and behind the bypass valve substantially disappears and higher than the opening degree of the intake throttle valve (claim 3).

  According to this configuration, the bypass valve can be closed in a range where the intake air flowing backward in the bypass passage is not blocked by the bypass valve (the intake circulation flow does not disappear), and the backflow intake air has a low opening bypass valve. The thermal energy resulting from the resistance as it passes through the surrounding gap can further raise the temperature of the intake air. Thereby, the ignitability of the fuel can be more effectively improved.

  Preferably, the determination unit determines whether the semi-warmup state or the warm-up state at least when the engine is started, and the control unit is determined to be in the semi-warmup state when the engine is started The electric supercharger is driven to supercharge the intake air, and the opening degree of the intake throttle valve is reduced as compared with that at the time of starting the engine in the warm-up state (claim 4).

  According to this configuration, at the time of starting the engine in a semi-warmed state, good fuel consumption performance can be secured without losing combustion stability.

  More preferably, the control device further includes a start motor for cranking the engine at start-up, and a water temperature sensor for detecting a temperature of cooling water of the engine, and the determination unit determines the start motor at the start of the engine. Based on a predetermined parameter correlated with the generated torque and the temperature of the cooling water detected by the water temperature sensor, it is determined whether the engine is in the semi-warming state or in the warming-up state (claim 5) .

  According to this configuration, based on both the actual temperature of the engine and the generated torque of the starter motor (that is, the required torque for cranking the engine), the engine is in a semi-warmed state, that is, the wall surface of the cylinder It is possible to properly determine that the temperature difference between the piston and the piston is large and the sliding resistance of the piston is likely to increase, separately from the engine warm-up state.

  The type of engine to which the control device of the present invention is applied is not particularly limited. For example, in a compression ignition engine having a geometric compression ratio of 14 or more, the sliding resistance of the piston at the time of semi-warming becomes particularly large. It can be said that it is easy. For this reason, the present invention is suitable for a compression ignition engine having a geometric compression ratio of 14 or more (claim 6).

  When the engine is a compression-ignition engine as described above, a sufficient amount of intake air is introduced into the cylinder at the time of engine start in a state other than half warm-up to reduce pumping loss and ensure ignition performance. Is preferred. That is, the control unit sets the opening degree of the intake throttle valve at the engine start in the warm-up state and at the engine start in the cold state which is neither the warm-up state nor the semi-warm-up state. It is preferable that the pressure difference before and after the valve is substantially equal to or more than the opening of the flow saturation point (claim 7).

  As described above, according to the control device for an engine of the present invention, good fuel consumption performance can be ensured without impairing the combustion stability when the engine is partially warmed up.

It is a system figure showing a desirable embodiment of an engine to which a control device of the present invention was applied. It is a block diagram showing a control system of an engine. It is a flowchart which shows the detail of restart control which restarts the engine which stopped automatically. It is a graph which shows the time change of each temperature of the piston and cylinder wall after the engine in a low temperature state is key-started. It is a graph which each shows the sliding resistance and leakage loss of a piston which change with temperature change of FIG. It is a figure in order to explain the flow of intake air when control (intake air heating control) of Step S4 of Drawing 3 is performed.

(1) Overall Configuration of Engine FIG. 1 is a system diagram showing a preferred embodiment of an engine to which a control device of the present invention is applied. The engine shown in the figure is a four-cycle diesel engine mounted on a vehicle as a power source for traveling, and includes an engine body 1, an intake passage 30 through which intake air introduced into the engine body 1 flows, and an engine body 1, an exhaust passage 40 through which exhaust gas discharged from the engine 1 flows, a supercharging device 50 for feeding the engine main body 1 while compressing the intake air flowing through the intake passage 30, and a portion of the exhaust gas circulating through the exhaust passage 40 And an EGR device 70 for returning to the passage 30.

  The engine main body 1 is an in-line multi-cylinder type having a plurality of cylinders 2 (only one of which is shown in FIG. 1) arranged in a row, and the plurality of cylinders 2 are formed therein. A cylinder block 3; a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close each cylinder 2 from above; and a plurality of pistons 5 reciprocably inserted in each cylinder 2 There is. In addition, since the structure of each cylinder 2 is the same, in the following, the description will focus on only one cylinder 2 basically.

  A combustion chamber 6 is defined above the piston 5. A fuel mainly composed of light oil is supplied to the combustion chamber 6 by injection from a fuel injection valve 15 described later. Then, the supplied fuel burns (diffuse combustion) by compression ignition, and the piston 5 pushed down by the expansion force of the combustion reciprocates in the vertical direction.

  Below the piston 5, a crankshaft 7 which is an output shaft of the engine body 1 is provided. The crankshaft 7 is connected to the piston 5 via the connecting rod 8 and is rotationally driven about the central axis according to the reciprocating motion (up and down motion) of the piston 5.

  The geometric compression ratio of the cylinder 2, that is, the ratio of the volume of the combustion chamber 6 when the piston 5 is at the top dead center to the volume of the combustion chamber when the piston 5 is at the bottom dead center is 14 or more and 20 or less It is set.

  The cylinder block 3 is provided with a crank angle sensor SN1 that detects an angle (crank angle) of the crankshaft 7 and a rotational speed of the crankshaft 7 (engine rotational speed). Further, the cylinder head 4 is provided with a water temperature sensor SN2 that detects the temperature (engine water temperature) of the cooling water flowing inside the engine body 1 (the cylinder block 3 and the cylinder head 4).

  The crankshaft 7 is detachably connected to an electric start motor 20. The start motor 20 engages with the crankshaft 7 at the start of the engine to force it to rotate (crank). Further, the starting motor 20 incorporates a current sensor SN5 (FIG. 2) for detecting the operating current.

  The cylinder head 4 includes an intake port 9 and an exhaust port 10 opened to the combustion chamber 6, an intake valve 11 for opening and closing the intake port 9, an exhaust valve 12 for opening and closing the exhaust port 10, an intake valve 11 and an exhaust valve 12 The valve operating mechanisms 13 and 14 are provided to open and close in conjunction with the rotation of the crankshaft 7.

  The cylinder head 4 is further provided with a fuel injection valve 15 for injecting fuel (light oil) into the combustion chamber 6. The fuel injection valve 15 is, for example, a multi-injection hole type injection valve that injects fuel radially from the center of the ceiling surface of the combustion chamber 6. Although not shown, a recess (cavity) for receiving the fuel injected from the fuel injection valve 15 is formed on the crown surface of the piston 5.

  The intake passage 30 is connected to one side surface of the cylinder head 4 so as to communicate with the intake port 9. The air intake passage 30 includes an air cleaner 31 for removing foreign substances in the air intake, an air intake throttle valve 32 capable of opening and closing for adjusting the flow rate of air intake, and an intercooler 33 for cooling air intake compressed by the supercharging device 50; A surge tank 34 is provided in this order from the upstream side of the intake passage 30 (the side far from the engine body 1).

  An air flow sensor SN3 for detecting the flow rate of air (fresh air) introduced into the engine body 1 through the intake passage 30 is provided at a portion of the intake passage 30 downstream of the air cleaner 31. Further, the surge tank 34 is provided with an intake pressure sensor SN4 that detects the pressure of intake air therein.

  The exhaust passage 40 is connected to the other side surface of the cylinder head 4 so as to communicate with the exhaust port 10. The exhaust passage 40 is provided with a catalytic converter 41 incorporating a catalyst 41 a for purifying various harmful components contained in the exhaust gas. As the catalyst 41a, for example, one or both of an oxidation catalyst that oxidizes CO and HC in the exhaust gas to harm them and an NOx catalyst that reduces NOx in the exhaust gas to harm them are used. Although not shown, the exhaust passage 40 is additionally provided with a DPF (diesel particulate filter) for collecting soot (soot) in the exhaust gas.

  The supercharger 50 is a so-called two-stage supercharger, and has two superchargers 51 and 52 arranged in series. The turbocharger 51 is an electric turbocharger driven by electrical energy (hereinafter referred to as the electric turbocharger 51), and the turbocharger 52 is a turbocharger driven by the energy of exhaust gas (hereinafter referred to as It is called a turbocharger 52).

  The electric supercharger 51 has a motor 62 that operates by receiving power supply, and a compressor 61 that is rotationally driven by the motor 62 to compress intake air. The compressor 61 is disposed in a main passage 63 formed between the air cleaner 31 and the intake throttle valve 32 in the intake passage 30. A bypass passage 64 for bypassing the compressor 61 is provided in the intake passage 30 in parallel with the main passage 63. The bypass passage 64 is provided with an openable / closable bypass valve 65.

  The turbocharger 52 includes a turbine 67 rotationally driven by the exhaust gas flowing through the exhaust passage 40, and a compressor 66 rotatably provided in conjunction with the turbine 67 and compressing the intake air flowing through the intake passage 30 Have. The compressor 66 is disposed upstream of the electric turbocharger 51 (compressor 61) in the intake passage 30, and the turbine 67 is disposed upstream of the catalytic converter 41 in the exhaust passage 40. The exhaust passage 40 is provided with a bypass passage 68 for bypassing the turbine 67, and the bypass passage 68 is provided with an openable / closable waste gate valve 69.

  The EGR device 70 includes an EGR passage 71 connecting the exhaust passage 40 and the intake passage 30, and an EGR cooler 72 cooling the exhaust gas (EGR gas) recirculated from the exhaust passage 40 to the intake passage 30 through the EGR passage 71. An openable and closable EGR valve 73 is provided to adjust the flow rate of the EGR gas.

  Although the EGR device 70 in the present embodiment is provided so as to return part of the exhaust gas flowing on the upstream side of the turbine 67 to the intake passage 30 on the downstream side of the compressor 61, this EGR device 70 Alternatively, an EGR device may be further provided to recirculate a portion of the exhaust gas flowing downstream of the turbine 67 to the intake passage 30 upstream of the compressor 66.

(2) Control System FIG. 2 is a block diagram showing a control system of the engine of this embodiment. The ECU 100 shown in the figure is a microprocessor for controlling the engine in an integrated manner, and comprises a known CPU, a ROM, a RAM and the like.

  Information detected by various sensors is input to the ECU 100. Specifically, the ECU 100 is electrically connected to the crank angle sensor SN1, the water temperature sensor SN2, the air flow sensor SN3, the intake pressure sensor SN4, and the current sensor SN5 described above, and various types of information detected by these sensors For example, information such as a crank angle, an engine rotational speed, an engine water temperature, an intake flow rate, an intake pressure (supercharging pressure), and an operating current of the start motor 20 are sequentially input to the ECU 100.

  In the vehicle, a vehicle speed sensor SN6 for detecting the traveling speed (hereinafter referred to as vehicle speed) of the vehicle and an opening degree of the accelerator pedal operated by a driver driving the vehicle (hereinafter referred to as accelerator opening degree) are detected. The accelerator sensor SN7 and the brake sensor SN8 for detecting the on / off state of the brake pedal similarly operated by the driver are provided, and the detection information by the vehicle speed sensor SN6, the accelerator sensor SN7 and the brake sensor SN8 is also sent to the ECU 100. Input sequentially.

  The ECU 100 controls each part of the engine while performing various determinations and calculations based on the input information from the sensors SN1 to SN8. That is, the ECU 100 is electrically connected to the fuel injection valve 15, the start motor 20, the intake throttle valve 32, the motor 62 for the electric supercharger 51, the bypass valve 65, the waste gate valve 69, the EGR valve 73, etc. And outputs control signals to these devices based on the result of the above calculation and the like. Such an ECU 100 corresponds to a "determination unit" and a "control unit" in the claims.

  For example, the ECU 50 calculates the load (request torque) of the engine based on the accelerator opening detected by the accelerator sensor SN7, the vehicle speed detected by the vehicle speed sensor SN6, etc., and detects the calculated load and the crank angle sensor SN1. The amount of fuel to be injected into the cylinder 2 (target injection amount) is determined based on the engine rotation speed to be calculated, and fuel injection is performed such that the amount of fuel corresponding to the determined target injection amount is injected into the cylinder 2 The valve 15 is controlled.

  Further, the ECU 100 sets the target boost pressure based on the engine rotation speed / load and the like, and the intake pressure (supercharge pressure) detected by the intake pressure sensor SN4 matches the target boost pressure. And control the opening degree of the bypass valve 65 and the waste gate valve 69, the rotation of the motor 62 for the electric supercharger 51, and the like.

  Furthermore, a so-called idling stop function is added to the engine of this embodiment. That is, the ECU 100 has a function of automatically stopping or restarting the engine under predetermined specific conditions.

  For example, the ECU 100 has a plurality of requirements such as that the engine is not in the cold state, that the vehicle speed is almost zero, that the accelerator pedal is off (the accelerator opening is zero), and that the brake pedal is on. The success or failure of the engine is determined each time based on the detection values of the water temperature sensor SN2, the vehicle speed sensor SN6, the accelerator sensor SN7, the brake sensor SN8, etc., and it is confirmed that all of these requirements are satisfied. It is determined that the stop condition is satisfied. When the automatic stop condition is satisfied, the ECU 100 cuts the fuel supply from the fuel injection valve 15 to automatically stop the engine. The determination as to whether or not the engine is in the cold state is performed based on comparison between the engine water temperature detected by the water temperature sensor SN2 and a predetermined threshold value. Specifically, the threshold value of the temperature used in this determination is set to a predetermined temperature (for example, 40 ° C.) sufficiently lower than the engine water temperature at the completion of the warm-up and higher than the outside air temperature. Then, if the engine water temperature is lower than the threshold, the engine is in the cold state, and if the engine temperature is equal to or higher than the threshold, it is determined that the engine is not in the cold state (that is, it is in either a semi-warmed state or a warmed up state described later).

  Further, the ECU 100 has a plurality of requirements such as that the brake pedal has switched from the on state to the off state after the automatic stop of the engine and that the elapsed time after the automatic stop (the continuation time of the automatic stop) has reached a predetermined time. Success or failure is judged each time based on the detection value of the brake sensor SN8 or the count value of the built-in timer, and when it is confirmed that any one of these requirements is satisfied, the engine restart condition is satisfied. It is determined that When the restart condition is satisfied, the ECU 100 restarts the engine by driving the starter motor 20 to restart the fuel supply from the fuel injection valve 15 while cranking the engine body 1.

(3) Control Depending on Temperature State at Restart of Engine Next, details of control for restarting the automatically stopped engine will be described. FIG. 3 is a flowchart showing a control procedure at the time of engine restart. When the engine is automatically stopped and the control shown in this flowchart is started, the ECU 100 determines in step S1 whether the restart condition is satisfied. The details of the restart condition are as described above, and the success or failure is determined based on, for example, the detection value of the brake sensor SN8 or the count value of the timer.

  If it is determined that the restart condition is satisfied in step S1, the ECU 100 proceeds to step S2 and performs control to drive the starter motor 20 to forcibly rotate the crankshaft 7, that is, the engine Start cranking.

  After the start of the cranking, the ECU 100 shifts to step S3 and half-warms the engine based on the operating current of the starter motor 20 detected by the current sensor SN5 and the engine water temperature detected by the water temperature sensor SN2. Determine whether the machine is in the machine state or in the warm-up state. The semi-warming state refers to a state of mid-warming that is neither cold nor warm, for example, an elapsed time since the start of the engine by the ignition-on operation of the occupant, that is, the continuation of the engine operation It tends to occur when the time is relatively short. In this semi-warmed state, the temperature of the piston 5 becomes significantly higher than the temperature of the wall surface 2a of the cylinder 2 (hereinafter referred to as a cylinder wall).

  That is, at the time of engine start by the ignition on operation (hereinafter referred to as “when the ignition on operation is performed, except in the case where the ignition on operation is performed again without much time after the engine is stopped by the occupant's ignition off operation. In the key start mode, the temperature of the piston 5 and the temperature of the cylinder wall 2a both have sufficiently low values similar to the outside air temperature. FIG. 4 shows the time change of the temperature of the piston 5 and the temperature of the cylinder wall 2a when such a general key start is performed. As shown in FIG. 4, when the engine is key-started at time t0, the temperature of the piston 5 rises rapidly immediately thereafter. This is because the combustion heat generated in the combustion chamber 6 directly acts on the piston 5. On the other hand, after the key start of the engine, the temperature of the cylinder wall 2a rises only gradually. This is because the temperature of the cylinder wall 2a is mainly influenced by the temperature of the engine cooling water, and the temperature of the cooling water is characteristically (inside of the mass members such as the cylinder block 3 and the cylinder head 4) Because of the nature of circulating Note that FIG. 4 also shows the temperature of the engine cooling water, and the temperature of this cooling water is rising with the same tendency as the temperature of the cylinder wall 2a. This also indicates that the temperature of the cylinder wall 2a is mainly influenced by the temperature of the cooling water.

  Due to the difference in temperature raising speed between the piston 5 and the cylinder wall 2a as described above, the temperature difference obtained by subtracting the temperature of the cylinder wall 2a from the temperature of the piston 5 is a predetermined value ΔTx It has expanded to. Then, the temperature difference shifts in the range of the predetermined value ΔTx or more until time t2 when a while from time t1. That is, the state in which the temperature of the piston 5 is higher than the temperature of the cylinder wall 2a by the predetermined value ΔTx or more continues from time t1 to t2 after the key start. This period (t1 to t2) is a half warm-up period.

  The engine is in the cold state or in the warm-up state before and after the semi-warm-up state. That is, the period (time t0 to t1) before the engine reaches the semi-warming state is the period of the cold state, and in this cold state, the temperature difference between the piston 5 and the cylinder wall 2a is less than the predetermined value .DELTA.Tx And the temperature of the cylinder wall 2a is lower than that in the semi-warming state. Further, the period (time t2-) after the half warm-up state is the warm-up state, and in this warm-up state, the temperature difference between the piston 5 and the cylinder wall 2a becomes less than the predetermined value ΔTx, And, the temperature of the cylinder wall 2a becomes higher than that in the semi-warming state.

  The temperature difference gradually decreases from ΔTx and the temperature of the cylinder wall 2a approaches the temperature of the piston 5 more and more after time t2 when the state is shifted from the half warm-up state to the warm-up state. At time t3 at which it is considered that the warm-up is completed, the temperature difference is sufficiently reduced, and both the cylinder wall 2a and the piston 5 are fully warmed.

  FIG. 5 shows the sliding resistance and the leakage loss of the piston 5 which change with the temperature change of FIG. The sliding resistance of the piston 5 is a resistance that is received when the piston 5 reciprocates in the cylinder 2, and a mechanical friction force or a compression reaction force (the intake air compressed in the combustion chamber 6 is a piston The force that pushes back 5) is the combined resistance. The leakage loss is the amount of gas leaking from the combustion chamber 6 to the outside through the gap between the piston 5 (especially the piston ring provided on the outer periphery thereof) and the cylinder wall 2a (compressed intake air or burnt gas Amount of leakage). As shown in FIG. 5, the period of the half warm-up period from time t1 to t2 is compared with the period other than that, that is, the period of cold state from time t0 to t1 and the period of warm-up state after time t2. As the sliding resistance of 5 increases, the leakage loss decreases. This is due to the large temperature difference expanded to ΔTx or more.

  That is, in the semi-warming state (time t1 to t2), the temperature of the piston 5 is significantly higher than the temperature of the cylinder wall 2a, so the expansion amount of the piston 5 is sufficiently larger than the expansion amount of the cylinder wall 2a. As a result, the area of the portion of the circumferential surface of the piston 5 (mainly its skirt) in contact with the cylinder wall 2a is increased. The increase in the contact area increases the mechanical friction of the piston 5. On the other hand, the gap between the circumferential surface of the piston 5 and the cylinder wall 2a is reduced, so the leakage loss through the gap is reduced, and the amount of intake air actually compressed in the combustion chamber 6 is increased. This causes an increase in the compression reaction force applied to the piston 5 from the compressed intake air. Thus, in the engine half-warming state, both the mechanical friction force and the compression reaction force of the piston 5 increase, so the combined resistance force, that is, the sliding resistance of the piston 5 naturally also increases. .

  The phenomenon as described above which occurs in the semi-warming state, that is, the increase in the sliding resistance of the piston becomes more remarkable as the difference between the thermal expansion coefficient of the piston 5 and the cylinder wall 2a is larger. For example, when the piston 5 is made of an aluminum alloy and the cylinder wall 2a is made of cast iron, the thermal expansion coefficient of the piston 5 becomes significantly larger than that of the cylinder wall 2a. The resistance is greater.

  As described above, in the semi-warming state, the temperature difference between the piston 5 and the cylinder wall 2a expands to ΔTx or more, in other words, the temperature of the cylinder wall 2a becomes sufficiently lower than the temperature of the piston 5 The sliding resistance of the piston 5 is increased. The reason why each detected value of the water temperature sensor SN2 and the current sensor SN5 is used in the determination of the semi-warmed state in the step S3 is to confirm the presence or absence of such a phenomenon.

  That is, when the temperature (engine water temperature) of the engine coolant detected by the water temperature sensor SN2 is lower than a predetermined reference temperature, it can be regarded that the temperature difference between the piston 5 and the cylinder wall 2a is sufficiently large. (It should be noted that since the piston 5 should already be sufficiently heated by the operation before the engine is automatically stopped, it can be considered that the temperature difference is large because the engine water temperature is low.) Also, when the operating current of the starter motor 20 detected by the current sensor SN5 is higher than a predetermined reference current, the generated torque of the starter motor 20 required for cranking the engine is large, and the sliding resistance of the piston 5 is large. Can be considered large enough. The reference temperature for confirming that the temperature difference between the piston 5 and the cylinder wall 2a is large is the threshold value of the engine water temperature for determining the possibility of the automatic stop, that is, whether the engine is in the cold state In order to make a decision, the threshold value (for example, 40 ° C.) is set to a value (for example, 70 ° C.) higher by a predetermined amount.

  In step S3, when either of the above two requirements is satisfied, that is, the requirement that the engine water temperature is lower than the reference temperature and the requirement that the operating current of the starter motor 20 be higher than the reference current. If any one of them is established, it is determined that the engine is in the semi-warmed state. Conversely, if none of these two requirements are met, it can be said that the engine is in a warm-up state. That is, it is assumed that the engine is not at least in the cold state on the premise that the engine is automatically stopped. Therefore, the non-satisfaction of the above two requirements means that the engine is not in the semi-warm state even in the cold state; means. The determination in step S3 is usually completed before the piston 5 of the cylinder 2 stopped in the compression stroke reaches the first compression top dead center.

  If it is determined NO in step S3 and it is confirmed that the engine is in the warm-up state, the ECU 100 shifts to step S7 and restarts the engine by normal restart control. Specifically, each cylinder 2 of the engine is opened in a state where the intake throttle valve 32 and the bypass valve 65 are opened to a higher degree than in step S4 (intake air heating control) described later and the electric supercharger 51 is not driven. The fuel injection valve 15 sequentially injects and burns fuel. In this normal engine restart, for example, the opening degree of the intake air throttle valve 32 and the bypass valve 65 is set to an opening degree higher than the flow rate saturation point. The flow saturation point is an opening at which the pressure difference between the upstream and downstream sides of the intake throttle valve 32 (or the bypass valve 65) disappears, and the intake flow does not increase even if the opening is further increased. Degree. Although the opening degree of the flow rate saturation point varies depending on the operating condition of the engine, the opening degree of the flow rate saturation point is, for example, about 30% under the operating condition where the control of step S7 is executed. In this case, each opening degree of the intake air throttle valve 32 and the bypass valve 65 is about 30% or more.

  On the other hand, when it is determined YES in the above-mentioned step S3 and it is confirmed that the engine is in the semi-warming state, the ECU 100 shifts to step S4 and electrically charges the intake air supercharged by the electric supercharger 51 again. Intake air heating control that forms a circulating flow of intake air to be returned to the supercharger 51 is executed. Specifically, in this intake heating control, the opening degree of the intake throttle valve 32 is sufficiently lower than the opening degree of the flow rate saturation point (in other words, the pressure on the downstream side of the pressure on the upstream side of the intake throttle valve 32) The opening degree of the bypass valve 65 is higher than the opening degree of the intake throttle valve 32 and lower than the opening degree of the flow saturation point while being set to a predetermined low opening degree (for example, 10 to 20%) which becomes sufficiently low. The opening degree (for example, 20 to 30%) is set. Further, in this state, the motor 62 of the electric supercharger 51 is driven, and the compressor 61 performs supercharging.

  As shown in FIG. 6, a portion of the intake air compressed by the electric supercharger 51 (compressor 61) and discharged from the main passage 63 flows back to the bypass passage 64 in the intake passage 30 by the control of step S4. Then, a flow that can be introduced into the electric supercharger 51 again, that is, a circulating flow of intake air is formed (see arrow X1 in FIG. 6). That is, the compressor 61 is rotationally driven in a state where the opening degree of the intake air throttle valve 32 is lower than the opening degree of the bypass valve 65, whereby the intake air throttle valve 32 is directed to the bypass valve 65 (that is, the bypass passage 64 A flow of intake air flowing back is formed, and a flow of drawing back the intake air flowing back in the bypass passage 64 back to the compressor 61 is formed.

  When the intake circulation flow as described above is formed, the temperature of the intake air on the circulation path (main passage 63 and bypass passage 64) is a temperature increase effect due to the intake air being repeatedly compressed by electric supercharger 51 The thermal energy generated from the resistance when the intake air flowing backward through the bypass passage 64 passes through the gap around the bypass valve 65 with a low opening degree, to a temperature (eg, about 80 to 100 ° C.) sufficiently higher than the outside air temperature. It can be enhanced in a very short time. Further, when a part of the intake air is branched from such a high temperature circulating flow and passes through the intake throttle valve 32, the flow of intake air toward the engine main body 1 through the intake passage 30 on the downstream side of the intake throttle valve 32 Formed (see arrow X2). At this time, the intake air passes through a gap around the intake throttle valve 32 having a lower opening than the bypass valve 65, so that the temperature of the intake air is further raised by receiving heat energy generated from the resistance at the time of the passage. .

  After heating the intake air by formation of the intake circulation flow as described above (step S4), the ECU 100 performs the fuel injection valve at an appropriate timing such that the heated intake reaches the engine body 1 in the next step S5. Fuel is injected from 15. This fuel injection is performed first for the cylinder 2 that receives the compression stroke most quickly after the arrival of the heating intake. The injected fuel is self-ignited and burned in the combustion chamber 6 of the cylinder 2 to push down the piston 5. As a result, the autonomous rotation of the engine body 1 is started, and the engine rotational speed is rapidly increased.

  Next, the ECU 100 similarly receives fuel from the fuel injection valve 15 in the order of the cylinder that receives the compression stroke next to the cylinder (the first firing cylinder) that was first fired, and then the cylinder that receives the compression stroke next. Inject and burn. Then, it is determined whether combustion has been performed in all the cylinders 2 and the engine has completely detonated (step S6), and when complete detonation, engine restart control is ended. After completion of the restart control, the control shifts to normal control such as adjusting the fuel injection amount according to the accelerator opening degree, the vehicle speed, and the like.

(4) Operation and Effect, Etc. As described above, in this embodiment, the engine to be restarted after the automatic stop is in the semi-warming state (the state where the temperature difference between the piston 5 and the cylinder wall 2a is equal to or more than the predetermined value ΔTx) While the electric supercharger 51 is driven to supercharge the intake air, the opening degree of the intake throttle valve 32 is reduced as compared with the case where the engine is in the warm-up state. An intake circulation flow is formed in which a portion of the supplied intake air is returned to the electric turbocharger 51 through the bypass passage 64. According to such a configuration, there is an advantage that good fuel consumption performance can be secured without losing combustion stability at the time of engine restart in a semi-warmed state.

  That is, when the engine is in a semi-warmed state, the sliding resistance of the piston 5 is increased due to the relatively large expansion of the piston 5 that is considerably hotter than the cylinder wall 2a, and The leakage loss through the clearance around 5 is reduced (see FIG. 5). For this reason, if the opening degree of the intake throttle valve 32 is temporarily set to be the same as that in the warm-up state, the amount of intake actually compressed by the piston 5 increases, and a large pressure generated during compression As the piston ring expands in diameter, the compression reaction force applied to the piston 5 and the mechanical friction force of the piston 5 increase, and the sliding resistance of the piston 5 further increases. This leads to an increase in the amount of fuel injection necessary to maintain the rising speed of the piston 5 equally and to deterioration of the fuel efficiency performance. On the other hand, in the above embodiment, at the time of engine restart in a semi-warmed state, the intake charge amount to the combustion chamber 6 is reduced by the decrease in the opening degree of the intake throttle valve 32, so the sliding resistance of the piston 5 is reduced. It is possible to maintain good fuel economy performance.

  However, simply reducing the intake charge amount into the combustion chamber 6 lowers the compression end temperature of the combustion chamber 6 (the internal temperature of the combustion chamber 6 at the compression top dead center), and the ignitability of the fuel is deteriorated. The combustion may be destabilized or, in the worst case, misfired. On the other hand, in the above embodiment, the electric supercharger 51 is driven to supercharge the intake air, and a part of the supercharged intake air is returned to the electric supercharger 51 through the bypass passage 64 (intake circulation) Since the intake throttle valve 32 is closed to a sufficiently low degree of opening so that the flow is formed, the temperature increase effect by the intake air being repeatedly compressed by the electric supercharger 51 and the intake throttle valve 32 with a low opening degree The thermal energy resulting from the resistance of the intake air as it passes through the clearance around the can cause the temperature of the intake air to rise quickly and substantially. As a result, the combustion chamber 6 can be heated to improve the ignitability of the fuel, and the combustion stability can be favorably maintained.

  In addition, since the fuel is stably burned in a state where the intake charge amount to the combustion chamber 6 is reduced, the temperature of the exhaust gas discharged from the combustion chamber 6 can be sufficiently increased, and the catalyst by the high temperature exhaust gas 41a can be heated to promote its activation.

  Here, in order to reduce the sliding resistance of the piston 5 at the time of semi-warming, it is necessary to reduce the amount of intake which greatly exceeds the amount of intake that is increased by the expansion of the piston 5 (reduction of leakage loss). On the other hand, in the above embodiment, at the time of engine restart in the semi-warming state, the opening degree of the intake throttle valve 32 is set at the normal engine restart performed in the warm-up state (e.g. Since the opening degree (eg, 10 to 20%) is reduced to a value sufficiently smaller than 30% or more), the intake charge amount to the combustion chamber 6 can be sufficiently reduced, and the sliding resistance of the piston 5 is effectively reduced. It can be reduced.

  Further, in the above embodiment, the opening degree of the bypass valve 65 is higher than the opening degree of the intake throttle valve 32 and the opening degree of the flow saturation point (before and after the bypass valve 65) Is reduced to a predetermined opening which is substantially smaller than the opening at which the pressure difference is substantially eliminated, so that the intake air flowing back in the bypass passage 64 is not blocked by the bypass valve 65 (the intake circulation flow does not disappear). The valve 65 can be closed, and the heat energy arising from the resistance when this backflowing intake passes through the gap around the low opening bypass valve 65 can further raise the temperature of the intake. Thereby, the ignitability of the fuel can be more effectively improved.

  Further, in the above embodiment, when restarting the automatically stopped engine, the engine water temperature (temperature of the engine coolant) detected by the water temperature sensor SN2 and the operating current of the starting motor 20 detected by the current sensor SN5 Whether or not the engine is in a semi-warmed state is determined on the basis of the actual temperature of the engine and the torque generated by the starting motor 20 (that is, the required torque for cranking the engine). Since the temperature difference between the cylinder wall 2a and the piston 5 is large and the sliding resistance of the piston 5 is large, it can be reliably recognized as a half-warming state. it can.

  In the above embodiment, the electric supercharger is determined when it is determined whether the engine is in the semi-warming state or in the warming-up state when restarting the automatically stopped engine, and it is determined that the engine is in the semi-warming state. Control to close the intake throttle valve 32 while driving 51 (intake heating control shown in step S4 in FIG. 3) is executed, but the same control as this intake heating control is based on the ignition on operation of the occupant It may be performed at key start of the engine, or may be performed during idling operation of the engine. That is, even if the engine is in the semi-warming state at the time of key start or idling operation, the sliding resistance of the piston is large and the fuel consumption performance is easily deteriorated. Similar control may be performed.

  Further, in the above embodiment, when the engine is in the warm-up state when the automatically stopped engine is restarted, the normal restart control shown in step S7 of FIG. 3 is executed, and as a part thereof, the electric supercharger Although the control of opening the intake air throttle valve 32 to an opening degree above the flow saturation point (the opening degree at which the pressure difference before and after the valve substantially disappears) is stopped while stopping the driving of 51 is performed The control can naturally be performed not only at engine restart in the warm-up state but also at key start of the engine in the warm-up state. In addition, even when the engine is in the cold state, the sliding resistance of the piston is smaller than in the semi-warming state, so the same control as in step S7 above (the intake throttle valve 32 is stopped while the driving of the electric supercharger 51 is stopped). May be executed at the time of key start of the engine in a cold state, in which the control to open up to the opening degree above the flow rate saturation point may be performed.

  In the above embodiment, the bypass passage 64 for bypassing the electric supercharger 51 (the compressor 61) and the bypass valve 65 for opening and closing the passage are provided, and the opening degree of the bypass valve 65 By setting the opening degree of the intake throttle valve 32 higher, part of the intake air supercharged by the electric supercharger 51 is returned to the electric supercharger 51 through the bypass passage 64 (that is, the intake circulation flow is formed). However, the formation of the intake circulation flow is stopped by, for example, completely closing the bypass valve 65 (in other words, the flow of intake air flowing in one direction from the electric supercharger 51 to the engine main body 1). You may do so. Even in this case, the intake temperature is increased by the intake air being compressed by the electric supercharger 51, and the thermal energy generated from the resistance when the intake passes through the gap around the intake throttle valve 32 with a low opening degree. Temperature can be raised to some extent.

  However, according to the above method, since all the intake air passes through the electric supercharger 51 only once, as compared with the method according to the above embodiment in which the electric supercharger 51 is repeatedly compressed while circulating the intake air, The temperature must be reduced. For this reason, there is a possibility that the temperature of the intake air introduced into the combustion chamber 6 after passing through the intercooler 33 may remain at a temperature which is not much different from the non-execution time of the intake air heating control. Therefore, as a countermeasure in such a case, an intercooler bypass passage for bypassing the intercooler 33 is provided separately from the intercooler arrangement passage in which the intercooler 33 is disposed, and the intercooler arrangement passage and the intercooler It is conceivable to provide a switching valve for selectively introducing intake air into any of the bypass passages, and to control the switching valve so that intake air is introduced into the intercooler bypass passage when performing the intake air heating control. In this way, even if the intake circulation flow is not formed, it is possible to heat the intake air sufficiently to improve the ignitability.

  Further, in the above embodiment, the current sensor SN5 for detecting the operating current of the starter motor 20 is provided, and the torque generated by the starter motor 20 is specified based on the detection value of the current sensor SN5 when the engine is restarted. However, the generated torque of the starter motor 20 can be identified by detecting any parameter that correlates with the torque, and detects an appropriate parameter (for example, voltage etc.) other than the operating current, and the starter is started based on the detected value. The generated torque of the motor 20 may be specified.

  In the above embodiment, an example in which the control device of the present invention is applied to a diesel engine that press-ignites fuel mainly composed of light oil has been described, but the engine to which the present invention can be applied is not limited thereto. The present invention may be applied to a lean burn gasoline engine that burns a fuel whose main component is the lean air fuel ratio under a lean air fuel ratio.

2 cylinders 2a cylinder wall (wall of cylinder)
5 piston 20 start motor 30 intake passage 32 intake throttle valve 51 electric supercharger 64 bypass passage 65 bypass valve 100 ECU (determination unit, control unit)
SN2 water temperature sensor ΔTx (for temperature difference) predetermined value

More preferably, the control device further includes a start motor for cranking the engine at start-up, and a water temperature sensor for detecting a temperature of cooling water of the engine, and the determination unit determines that the temperature of the cooling water is a predetermined threshold. The first requirement that the operating current of the starting motor is higher than a predetermined reference current at the time of starting the engine in the above state, and the temperature of the cooling water detected by the water temperature sensor is higher than the threshold If either of the second requirement that the temperature is lower than the set reference temperature is satisfied, it is determined that the engine is in the semi-warming state, and both the first and second requirements are not satisfied. If the determines that the engine is in a warmed-up state (claim 5).

According to this configuration, the engine is in a semi-warmed state, ie, based on both the actual temperature of the engine and the operating current of the starter motor (in other words, the required torque for cranking the engine). It can be properly distinguished from the engine warm-up state that the temperature difference between the wall surface and the piston is large and the sliding resistance of the piston is likely to increase.

Claims (7)

A cylinder in which combustion is performed, a piston reciprocating in the cylinder, an intake passage through which intake air introduced into the cylinder flows, an electric supercharger provided in the intake passage and driven by electric energy, and an electric supercharger A device for controlling an engine comprising an intake throttle valve provided openably and closably in an intake passage downstream of an aircraft,
The temperature difference of the cylinder is higher than that of the cylinder in which the temperature difference between the temperature of the piston and the temperature of the cylinder is equal to or greater than a predetermined value. A determination unit that determines whether the warm-up state is less than a predetermined value;
The electric supercharger is driven to supercharge the intake air when it is determined by the determination unit that the engine is in the half warm-up state, and the intake air is compared to when the engine is in the warm-up state. An engine control device comprising: a control unit that reduces the opening degree of a throttle valve. In the engine control device according to claim 1,
A bypass passage for bypassing the electric turbocharger is provided in the intake passage;
When it is determined that the engine is in the semi-warmed state, the control unit is configured to open the intake throttle valve such that a portion of the intake air supercharged by the electric supercharger is electrically driven through the bypass passage. A control device for an engine, which reduces the degree of opening at which intake circulation flow to be returned to the supercharger is formed. In the engine control device according to claim 2,
The bypass passage is provided with an openable / closable bypass valve,
The controller determines that the opening degree of the bypass valve is larger than the opening degree of the flow saturation point where the pressure difference before and after the bypass valve substantially disappears when it is determined that the engine is in the semi-warmed state. A control device for an engine, characterized in that it is lowered to a predetermined opening degree which is low and higher than the opening degree of the intake throttle valve. In a control device of an engine according to any one of claims 1 to 3,
The determination unit determines whether the semi-warmup state or the warm-up state at least when the engine is started.
The control unit drives the electric supercharger to supercharge the intake air when it is determined that the engine is in the semi-warming state at the time of starting the engine, and the control portion compares the engine starting in the warm-up state. The control device for an engine according to claim 1, wherein the opening degree of the intake throttle valve is reduced. In the engine control device according to claim 4,
A starting motor for cranking the engine at start-up;
And a water temperature sensor for detecting the temperature of engine cooling water.
The determination unit determines whether the engine is in a semi-warmed state based on a predetermined parameter that correlates with the generated torque of the start motor and the temperature of the cooling water detected by the water temperature sensor at the time of starting the engine An engine control device that determines whether the engine is in a warm-up state. In the engine control device according to any one of claims 1 to 5,
A control device for an engine, wherein the engine is a compression ignition engine having a geometric compression ratio of 14 or more. In the engine control device according to claim 6,
The control unit sets the opening degree of the intake throttle valve to that of the intake throttle valve at the time of engine start-up in the warm-up state and at engine start-up in the cold state that is neither warm-up nor semi-warm-up. An engine control device characterized by being set to an opening degree of a flow rate saturation point at which a front / rear pressure difference is substantially eliminated.

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