JP2019177765A - Vehicle drive unit - Google Patents

Abstract

To provide a vehicle drive unit which can suppress the generation of NOx when an engine is in a cold engine state, in a vehicle which is mounted with the compression ignition type engine.SOLUTION: A vehicle drive unit comprises an automatic transmission in which a plurality of gear stages are automatically switched according to an engine rotation number by connecting an output shaft of an engine and wheels, and an electric supercharger 70 is arranged in an intake passage. Then, the automatic transmission is controlled so that the engine rotation number at which the gear stages are switched is lowered when the engine is in a warmup state in the case that the engine is confirmed to be in a cold engine state compared with the other case, and the electric supercharger 70 is driven when an engine load is equal to at least a prescribed reference load or larger.SELECTED DRAWING: Figure 1

Description

  The present invention includes a vehicle equipped with a compression ignition engine that includes a cylinder and fuel supply means for supplying fuel to the cylinder, and is configured such that a mixture of air and fuel is subjected to compression ignition combustion in the cylinder. The present invention relates to a device to be controlled.

  Conventionally, in the field of engines, various studies have been made in order to solve the problems that occur when the engine is in a cold state (the temperature of the piston and the cylinder in which the piston is fitted is low) and the temperature of the intake air is low. ing.

  For example, Patent Document 1 discloses an engine provided with an electric supercharger driven by electric energy. Patent Document 1 discloses a configuration in which intake air is supercharged by an electric supercharger when the temperature of intake air introduced into a cylinder is low. According to this configuration, the compression end temperature / pressure can be increased by increasing the pressure of the intake air by supercharging by the electric supercharger, and the ignitability of the fuel / air mixture even when the intake air temperature is low Can be improved.

JP 2010-180710 A

  By the way, in diesel engines and some gasoline engines, compression ignition combustion is performed in which a mixture of fuel and air is compressed in a cylinder and burned by self-ignition.

  In such a compression ignition type engine, when the engine is in a cold state (the temperature of the cylinder in which the piston or piston is fitted is low), the engine is in a warm state (a cylinder in which the piston or piston is fitted). There is a problem that NOx is more easily generated than when the temperature is high. Specifically, when the engine is in a cold state, the fuel is not sufficiently atomized (vaporized or atomized) as the temperature in the cylinder is low, so the fuel does not sufficiently diffuse into the cylinder and is compressed. As a result, when the temperature in the cylinder reaches a predetermined temperature, the fuel burns in a short time. As a result, the combustion temperature becomes very high and a relatively large amount of NOx is generated.

  The present invention has been made in view of the above circumstances, and is a vehicle drive device that can suppress the generation of NOx when the engine is in a cold state in a vehicle equipped with a compression ignition engine. The purpose is to provide.

  In order to solve the above-mentioned problems, the present invention includes a compression ignition engine that includes an engine body including a cylinder, and is configured so that a mixture of air and fuel is subjected to compression ignition combustion in the cylinder, An automatic transmission that connects the output shaft and wheels of the engine body and automatically switches a plurality of gears according to the engine speed, and is provided in the intake passage and driven by electric energy to supercharge intake air An electric supercharger, a temperature detection unit that detects the temperature of the engine body, a control unit that controls the automatic transmission and the electric supercharger, and the control unit is detected by the temperature detection unit The engine speed at which the gear is switched is lower when the engine is confirmed to be cold based on the temperature than when it is confirmed that the engine is warm. A vehicle that controls the automatic transmission and drives the electric supercharger at least when the engine load is equal to or higher than a predetermined reference load when it is confirmed that the engine is in a cold state. A driving device is provided.

  According to this configuration, when the engine is in the cold state, the engine speed at which the gear stage of the automatic transmission is switched is lowered. For this reason, when the engine is in a cold state, the chance of operating the engine in a region where the engine speed is high can be reduced, and the amount of NOx generated can be reduced.

  Specifically, the amount of NOx produced increases as the combustion temperature increases. The combustion temperature is higher when the combustion speed is higher, that is, when the combustion time is shorter. Therefore, when the engine speed is low, the amount of heat generated per unit time (the number of combustions) is small and the temperature in the cylinder is low, and the strength of the intake flow flowing into the cylinder is also higher than when the engine speed is high. By being weak, the combustion time is long, the combustion speed is kept low, and the amount of NOx produced is kept low. Therefore, when the engine is in a cold state in which the amount of NOx generated is likely to increase as the amount of fuel supplied into the cylinder is increased compared to when the engine is in a warm state, the engine as described above. By suppressing the opportunity for the engine to operate in a region where the rotational speed is high, the total amount of NOx generated during vehicle travel can be reduced.

  Moreover, in this configuration, when the engine is in the cold state, the engine speed at which the gear stage is switched is lowered, and the upshift is performed early during acceleration. Therefore, as described above, it is possible to suppress the opportunity for the engine to operate in a region where the engine speed is high and to suppress the generation amount of NOx.

  Here, it is necessary to increase the engine torque in order to respond to the same acceleration request as when the engine is in the warm-up state by making the engine speed at which the gear stage is switched lower than when the engine is in the warm-up state. is there. On the other hand, in this configuration, when the engine is in the cold state, the electric supercharger is driven and the intake air is supercharged at least under the condition that the engine load is equal to or higher than the reference load. Therefore, the acceleration performance of the vehicle can be improved.

  When the engine is in a warm-up state and the amount of NOx generated can be kept low, the drive of the electric supercharger can be stopped or the drive force of the electric supercharger can be reduced by not having to increase the engine torque. it can.

  In the above-described configuration, a bypass passage that is connected to the intake passage and bypasses the electric supercharger, and a portion of the intake passage that is provided on the downstream side of a portion to which a downstream end of the bypass passage is connected. An intake throttle valve that opens and closes the passage, and the control unit is configured to take in the intake air supercharged by the electric supercharger when the engine is operated in the cold state and the engine load is at least less than a predetermined load. Preferably, the intake throttle valve is controlled so that an intake air circulation flow is formed in which a part of the intake air is returned to the electric supercharger through the bypass passage.

  According to this configuration, when the engine is in a cold state, the engine load is low, and the temperature in the cylinder is particularly low, the intake air is repeatedly compressed by the electric supercharger due to the formation of the intake air circulation flow. The temperature of the introduced intake air is increased. Therefore, when the engine is in a cold state, the temperature in the cylinder can be increased to promote fuel atomization, and the combustion rate of the air-fuel mixture can be decreased to suppress the generation of NOx.

  In the above-described configuration, the automatic transmission may have a gear stage of 6 speeds or more.

  In diesel engines with a relatively low geometric compression ratio of 13 or more and 16 or less, especially when the engine is in a cold state, the compression end temperature is kept low, fuel atomization is inhibited, and NOx is likely to be generated. . Therefore, if the above configuration is applied to such an engine, the amount of NOx produced can be effectively reduced (claim 4).

  As described above, according to the vehicle drive device of the present invention, it is possible to suppress the generation of NOx when the engine is in a cold state in a vehicle on which a compression ignition type engine is mounted.

1 is a system diagram showing a preferred embodiment of an engine to which a vehicle drive device of the present invention is applied. It is a block diagram which shows the control system of a vehicle. It is the figure which showed the shift map of the automatic transmission at the time of warm. It is the figure which compared and showed the shift map of the automatic transmission at the time of cold machine, and warm. It is the figure which showed an example of the time change of each parameter at the time of acceleration. It is the figure which compared and showed the driving | operation area | region of the engine at the time of cold machine and warm. It is a figure for demonstrating an intake air circulation flow. It is the flowchart which showed the flow of control.

(1) Overall Configuration of Engine FIG. 1 is a system diagram of an engine showing an embodiment according to the present invention. The engine shown in the figure is a four-cycle diesel engine mounted on a vehicle as a driving power source. The engine body 1, an intake passage 30 through which intake air introduced into the engine body 1 flows, and the engine body 1, an exhaust passage 50 through which exhaust gas exhausted from 1 circulates, a turbocharger 60 and an electric supercharger 70 that send out the intake air flowing through the intake passage 30 to the engine body 1 while compressing, and the exhaust passage 50. A high-pressure EGR device 80A and a low-pressure EGR device 80B that recirculate a part of the exhaust gas to the intake passage 30 are provided.

  The engine body 1 is an in-line multi-cylinder engine in which a plurality of cylinders 2 are arranged in series in a direction orthogonal to the plane of FIG. In the present embodiment, the engine body 1 is provided with four cylinders 2. In FIG. 1, only one of the plurality of cylinders 2 is shown. The engine body 1 includes a cylinder block 3, a cylinder head 4, and a piston 5. A cavity 6 a that is recessed downward (in a direction away from the cylinder head 4) is formed on the crown surface of the piston 5. The cylinder block 3 has a cylinder liner 3a that forms the four cylinders 2 described above. The cylinder head 4 is attached to the upper surface of the cylinder block 3 and closes the upper opening of the cylinder 2. The piston 5 is housed in each cylinder 2 so as to be slidable back and forth, and is connected to a crankshaft 7 (an output shaft of the engine main body 1) via a connecting rod 8. In response to the reciprocating motion of the piston 5, the crankshaft 7 rotates about its central axis.

  The crankshaft 7 is connected to the automatic transmission 110 (see FIG. 2) via a torque converter (not shown). In the present embodiment, the automatic transmission 110 is a multi-stage automatic transmission (so-called 6-speed AT) capable of achieving an arbitrary gear stage from six forward speeds and one reverse speed, and includes, for example, a planetary gear mechanism, a planetary gear mechanism, and a planetary gear mechanism. Built-in a plurality of frictional engagement elements including clutches and brakes for switching the power transmission path and gear ratio by the gear mechanism, and a hydraulic control mechanism (valve body) for switching engagement / release of each frictional engagement element Yes.

  A combustion chamber 6 is formed 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. In the combustion chamber 6, the supplied fuel is combusted by compression ignition, and the piston 5 pushed down by the expansion force by the combustion reciprocates in the vertical direction. 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 13 or more and 16 or less. 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 (engine rotational speed) of the crankshaft 7. Further, the cylinder head 4 is provided with an engine water temperature sensor SN2 that detects the temperature (engine water temperature) of the cooling water flowing through the engine body 1 (the cylinder block 3 and the cylinder head 4).

  The water temperature sensor SN2 corresponds to an example of a “temperature detection unit” in the claims, and the engine water temperature detected by the water temperature sensor SN2 corresponds to an example of an “engine body temperature” in the claims.

  An intake port 9 and an exhaust port 10 communicating with the combustion chamber 6 are formed in the cylinder head 4. The bottom surface of the cylinder head 4 forms the ceiling surface of the combustion chamber 6. An intake side opening that is the downstream end of the intake port 9 and an exhaust side opening that is the upstream end of the exhaust port 10 are formed on the ceiling surface. The cylinder head 4 is assembled with an intake valve 11 for opening and closing the intake side opening and an exhaust valve 12 for opening and closing the exhaust side opening. The cylinder head 4 is provided with an intake side valve mechanism 13 and an exhaust side valve mechanism 14 for driving the intake valve 11 and the exhaust valve 12, respectively.

  The cylinder head 4 is further provided with a fuel injection valve 15 that injects fuel (light oil) into the combustion chamber 6. The fuel injection valve 15 is, for example, a multi-hole injection valve that injects fuel radially from the center of the ceiling surface of the combustion chamber 6.

  The intake passage 30 includes a single tubular intake pipe 32, and an air cleaner 31, an intercooler 41, and a surge tank 35 provided in the intake pipe 32 in order from the upstream side of the intake flow. The intake passage 30 is provided with an I / C bypass passage 36 that branches from the intake pipe 32 and bypasses the intercooler 41.

  The air cleaner 31 removes foreign matter in the intake air. The intercooler 41 is a water-cooled heat exchanger, and cools intake air that passes through the intercooler 41.

  The intake pipe 32 is formed so that a midway portion branches into two branches. That is, the intake pipe 32 has a single tubular main passage portion 32a and a bypass passage 32c that branches from a middle portion of the main passage portion 32a and joins the main passage portion 32a again on the downstream side. The main passage 32a is a passage that leads to an electric supercharger 70 (electric motor 70M) described later. The bypass passage 32 c is a passage that bypasses the electric supercharger 70. A bypass valve 321 capable of opening and closing the bypass passage 32c is provided in the bypass passage 32c. A throttle valve (intake throttle valve) 341 capable of opening and closing the main passage 32a is provided in a portion of the main passage portion 32a on the downstream side of the connection portion at the downstream end of the bypass passage 32c.

  The I / C bypass passage 36 communicates a portion of the intake pipe 32 between the throttle valve 341 and the intercooler 41 and a portion of the intake pipe 32 between the intercooler 41 and the surge tank 35. An I / C bypass valve (intercooler bypass valve) 361 capable of opening and closing the I / C bypass passage 36 is provided in the middle of the I / C bypass passage 36. When the I / C bypass valve 36 is fully opened, almost all the intake air (air) in the intake passage 30 does not pass through the intercooler 41 and passes through the I / C bypass passage 36 having a smaller flow path resistance.

  The exhaust passage 50 is an exhaust collecting portion in which a plurality of independent exhaust passages 51 (only one of which is shown in FIG. 1) extending from the exhaust ports 10 of the plurality of cylinders 2 and the independent exhaust passages 51 are gathered. And a single tubular common exhaust passage 53 extending downstream from the center. The common exhaust passage 53 is provided with a catalytic converter 55 having a built-in catalyst 55a for purifying exhaust gas. The catalyst 55a is, for example, an oxidation catalyst that oxidizes CO and HC in exhaust gas to render them harmless, a NOx catalyst that reduces and detoxifies NOx in exhaust gas using urea, and soot (soot in exhaust gas) DPF (diesel particulate filter) is included. Although not shown, a urea injector for supplying urea to the common exhaust passage 53 and thus to the catalyst 55a is provided on the upstream side of the catalyst 55a.

  The turbocharger 60 is a device that supercharges intake air using exhaust pressure as a power source, and includes a turbine 61 and a compressor 62. The turbine 61 is rotationally driven by the exhaust gas flowing through the exhaust passage 50. The compressor 62 rotates in conjunction with the turbine 61 and compresses the intake air flowing through the intake passage 30. The compressor 62 is disposed in a portion upstream of the electric supercharger 70 in the upstream intake passage 32. The turbine 61 is disposed in a portion upstream of the catalytic converter 55 in the common exhaust passage 53. The exhaust passage 50 is provided with a bypass passage 63 for bypassing the turbine 61. The bypass passage 63 is provided with a waste gate valve 64 that can open and close the bypass passage 63.

  The electric supercharger 70 is a device that supercharges intake air by using electric energy as a power source. The electric supercharger 70 receives electric power and generates a rotational driving force, and a compressor 72C that is rotationally driven by the electric motor 71M. Including. The compressor 72C supercharges the intake air flowing through the intake pipe 32. The compressor 72 </ b> C is disposed downstream of the compressor 62 of the turbocharger 60 in the intake passage 30.

  The high-pressure EGR device 80 </ b> A and the low-pressure EGR device 80 </ b> B are devices that take out the exhaust gas from the exhaust passage 50 and recirculate the exhaust gas taken out to the intake passage 30. The high pressure EGR device 80 </ b> A returns a part of the exhaust gas flowing upstream from the turbine 61 of the turbocharger 60 to the intake passage 30 downstream of the compressor 72 </ b> C of the electric supercharger 70. The low pressure EGR device 80 </ b> B returns a part of the exhaust gas flowing downstream from the catalytic converter 55 to the intake passage 30 upstream from the compressor 62.

  The high pressure EGR device 80A includes a high pressure EGR passage 81, a high pressure EGR cooler 82, and a high pressure EGR valve 83. The high-pressure EGR passage 81 communicates a portion of the exhaust passage 50 upstream of the turbine 61 and a portion of the intake passage 30 downstream of the throttle valve 341 and the bypass valve 361 (surge tank 35). The high pressure EGR cooler 82 cools the EGR gas that passes through the high pressure EGR passage 81. The high pressure EGR valve 83 opens and closes the high pressure EGR passage 81. The electric supercharger 70 supplements the reduction in the supercharging capability of the turbocharger 60 due to a decrease in the amount of exhaust gas passing through the compressor 62 as the high pressure EGR gas recirculated through the high pressure EGR passage 81 increases. Fulfill.

  The low pressure EGR device 80B includes a low pressure EGR passage 84, a chamber 87, a low pressure EGR cooler 85, and a low pressure EGR valve 86. The low pressure EGR passage 84 communicates a portion of the exhaust passage 50 downstream of the catalytic converter 55 and a portion of the intake passage 30 upstream of the compressor 62. With this arrangement, the EGR gas passing through the low-pressure EGR passage 84 contains only a small amount of HC, CO, soot, and NOx. The chamber 87 is a box-shaped member having a predetermined space inside. The chamber 87 is configured to have a larger flow area than the low pressure EGR passage 84. Along with this, the EGR gas flowing into the chamber 87 is decompressed, and a part of the water is removed from the EGR gas. That is, the exhaust gas contains water generated by combustion, and a part of this water is removed from the EGR gas passing through the EGR passage 84 in the chamber 87. The low pressure EGR cooler 85 cools the EGR gas passing through the low pressure EGR passage 84. The low pressure EGR valve 86 opens and closes the low pressure EGR passage 84.

  A flow rate of air (fresh air) introduced into the engine main body 1 through the intake passage 30 is detected in the upstream portion of the upstream intake passage 32 and between the connection port of the low pressure EGR passage 84 and the air cleaner 31. An airflow sensor SN3 is provided. The surge tank 35 is provided with an intake pressure sensor SN4 that detects the pressure of the intake air therein.

(2) Control System FIG. 2 is a block diagram showing the control system of the vehicle of this embodiment. The PCM 100 shown in this figure is a microprocessor for comprehensively controlling the engine and the automatic transmission 110, and includes a well-known CPU, ROM, RAM, and the like.

  Detection information from various sensors is input to the PCM 100. Specifically, the PCM 100 is electrically connected to the crank angle sensor SN1, the water temperature sensor SN2, the air flow sensor SN3, and the intake pressure sensor SN4 described above, and various information detected by these sensors, specifically, Information such as the engine speed, the engine water temperature, the intake air amount, the intake pressure (supercharging pressure) and the like are sequentially input to the PCM 100, respectively. The vehicle detects an outside air temperature sensor SN5 for detecting the temperature of the outside air, a vehicle speed sensor SN6 for detecting the traveling speed of the vehicle (hereinafter referred to as vehicle speed), and an accelerator pedal opening (hereinafter referred to as accelerator opening). An accelerator opening sensor SN7 is provided, and information detected by these sensors SN5 to SN7 is also sequentially input to the PCM 100.

  The PCM 100 controls each part of the engine while executing various determinations and calculations based on input information from the sensors SN1 to SN7. That is, the PCM 100 includes a fuel injection valve 15, a throttle valve 341, an electric supercharger 70 (electric motor 71M), a bypass valve 321, an I / C bypass valve 361, a wastegate valve 64, a high pressure EGR valve 83, and a low pressure EGR valve 86. These are electrically connected to an automatic transmission 110 (specifically, a hydraulic control mechanism thereof) and the like, and output control signals to these devices based on the calculation results and the like. Such a PCM 100 corresponds to a “control unit” in the claims.

  For example, the PCM 100 calculates the engine load (required torque) based on the accelerator opening detected by the accelerator opening sensor SN7, the vehicle speed detected by the vehicle speed sensor SN6, and the calculated load, and the crank angle sensor SN1. The amount of fuel to be injected into the combustion chamber 6 (target injection amount) is determined based on the engine rotational speed detected by the above, and an amount of fuel that matches the determined target injection amount is injected into the combustion chamber 6. Thus, the fuel injection valve 15 is controlled.

(3) Control of Automatic Transmission FIG. 3 is a shift map of the automatic transmission 110 showing the relationship between the vehicle speed and the accelerator opening at each gear stage. In FIG. 3, the horizontal axis represents the vehicle speed, and the vertical axis represents the accelerator opening. Lines L1 to L5 in FIG. 3 are shift lines that connect operation points at which the gear stage is changed. These shift lines L1 to L5 are lines in which switching from the first speed to the second speed, the second speed to the third speed, the third speed to the fourth speed, the fourth speed to the fifth speed, and the fifth speed to the sixth speed is performed in order. The gear stage is automatically selected depending on which one of the regions G1 to G6 divided by these lines L1 to L5 is operated. Regions G1 to G6 are regions corresponding to the first to sixth gears in order. That is, the PCM 100 determines which of the regions G1 to G6 in FIG. 3 includes the current vehicle speed and the accelerator opening, and determines the gear stage based on the determined region. Then, the PCM 100 issues a command to the automatic transmission so that the determined gear stage is realized.

  Here, FIG. 3 is a shift map when the engine is in a warm-up state (hereinafter referred to as warm). On the other hand, the map (shift line) indicated by the solid line in FIG. 4 is a shift map when the engine is in a cold state (hereinafter referred to as cold state). In FIG. 4, the shift line during warming is indicated by a broken line. As shown by the solid line and the broken line in FIG. 4, in this embodiment, the speed change line for which the gear stage is changed is set on the low vehicle speed side and thus on the low engine speed side in the cold state than in the warm state. The engine speed at which the gear stage is switched is set to be lower when the engine is cold than when it is warm.

  The cold state here means a state where the engine water temperature is lower than the reference temperature and the temperature of the engine body is lower than a predetermined temperature. The reference temperature is a preset temperature, and is set to about 50 ° C., for example. The warm-up state refers to a state where the engine water temperature is equal to or higher than the reference temperature and the temperature of the engine body is equal to or higher than a predetermined temperature.

  The shift lines L1 to L5 shown in FIGS. 3 and 4 are lines that connect operation points when the gear stage is switched to the high speed stage side, that is, when a shift up is performed. The shift line connecting the operating points when the gear stage is switched to the low speed side, that is, when the downshift is performed, is set to the lower vehicle speed side than the upshift line in both warm and cold conditions. . Also for the downshift transmission line, the cold time is set to the lower vehicle speed side and the lower engine speed side than the warm time.

  With this setting, the change in engine speed during acceleration differs between cold and warm.

  Fig. 5 shows changes in the accelerator opening, vehicle speed, and engine speed over time when the accelerator is depressed and warm when the accelerator opening is stepped from 0 to 100% (fully open) with the same vehicle speed and engine speed. FIG. The solid line in FIG. 5 is when cold, and the broken line is when warm.

  As shown in FIG. 5, when the engine is cold, the gear stage is switched to the high speed stage at a timing when the engine speed is lower than that during the warm period, and the engine is operated in a region where the engine speed is low as a whole.

(4) Engine Control The PCM 100 sets a target value of engine torque (hereinafter referred to as target engine torque as appropriate) based on the accelerator opening and the like. Specifically, the PCM 100 determines a target acceleration, which is a target value of vehicle acceleration, from the accelerator opening (specifically, the amount of change in the accelerator opening per unit time and the accelerator opening after the unit time). The target engine torque is determined from the target acceleration, the engine speed, and the gear stage.

  Here, as described above, at the time of acceleration of the vehicle, the gear stage on the high speed side is switched earlier at the time of cold operation than at the time of warm operation. Therefore, when the engine is cold, the target engine torque is set to a higher value with respect to the same target acceleration than when warm.

  Thus, the engine is operated in the region A1 shown in FIG. 6 where the maximum target engine torque is relatively low during the warm time, and the engine torque is higher in the region A2 shown in FIG. The engine is operated in the region A2 including the high region.

  Further, in this embodiment, when the engine is cold and the engine load is less than a predetermined load set in advance (the target engine torque is less than a predetermined value), the opening of the throttle valve 341 is set to an opening closer to the closing side than fully opened. At the same time, the bypass valve 321 is opened. Further, the electric supercharger 70 is driven. At this time, the rotational speed of the electric motor 71M is set to be higher than the idle rotational speed. The idle rotational speed is the lowest rotational speed among the rotational speeds at which the rotation of the electric motor 71M and the compressor 72C of the electric supercharger 70 is maintained.

  As described above, the electric supercharger 70 is driven in a state where the bypass valve 321 is opened and the opening degree of the throttle valve 341 is closed, so that the intake passage 30 has an opening as shown in FIG. Then, a flow in which a part of the intake air compressed by the electric supercharger 70 flows backward through the bypass passage 32c and is introduced again into the electric supercharger 70, that is, an intake air circulation flow is formed (arrow X1 in FIG. 7). reference). In the present embodiment, the opening degree of the bypass valve 65 is set to be larger than the opening degree of the throttle valve 32 (opening side opening degree) so that the intake air circulation flow is reliably formed.

(5) Control Flow The control flow will be described with reference to the flowchart of FIG.

  First, the PCM 100 reads various information of the engine in step S1. For example, the PCM 100 reads information such as engine water temperature, engine speed, accelerator opening, and gear position.

  Next, in step S2, the PCM 100 determines whether or not it is warm. As described above, the PCM 100 determines that it is warm when the engine water temperature is equal to or higher than the reference temperature.

  If it is determined in step S2 that it is warm, the process proceeds to step S3. In step S3, the PCM 100 selects a warm time shift map as the shift map.

  After step S3, the process proceeds to step S4. In step S4, the PCM 100 determines a gear stage by extracting values corresponding to the current engine speed and vehicle speed from the warm-time shift map, and the automatic transmission 110 is implemented so that this gear stage is realized. Command.

  After step S4, the process proceeds to step S5. In step S5, the PCM 100 determines a target engine torque based on the gear determined in step S4, the target acceleration obtained from the accelerator opening, and the engine speed. Then, the PCM 100 determines the injection amount of the injector 11, that is, the fuel injection amount, determines the opening degree of the throttle valve 341, and issues a command to them so that the target engine torque is realized. In this embodiment, the PCM 100 fully closes the bypass valve 321 at this time.

  On the other hand, when the determination in step S2 is YES and the time is cold, the process proceeds to step S6. In step S <b> 6, the PCM 100 selects a cold speed shift map as the shift map.

  After step S6, the process proceeds to step S7. In step S7, the PCM 100 determines a gear stage by extracting values corresponding to the current engine speed and vehicle speed from the cold speed shift map, and causes the automatic transmission 110 to realize this gear stage. Issue a command.

  After step S7, the process proceeds to step S8. In step S8, as in step S5, the PCM 100 determines a target engine torque based on the gear determined in step S7, the target acceleration obtained from the accelerator opening, and the engine speed.

  After step S8, the process proceeds to step S9. In step S9, the PCM 100 determines whether or not the engine load is less than a predetermined load. Specifically, the PCM 100 determines whether or not the target engine torque set in step S8 is less than a preset reference torque. The reference torque is preset and stored in the PCM 100. For example, the reference torque is set to a value of about 20% of the maximum engine engine torque.

  When the determination in step S9 is YES and the engine load is less than the predetermined load, the process proceeds to step S10. In step S10, the PCM 100 drives the electric supercharger 70 (electric motor 71M), so that the intake air circulation flow is formed, and the target engine torque set in step S8 is realized. The opening degree of the throttle valve 341, the opening degree of the bypass valve 321 and the rotation speed of the electric motor 71M are controlled. Further, the injection amount of the injector 11 is determined and a command is issued to the injector 11 so that the target engine torque is realized. After step S10, the process ends (returns to step S1).

  On the other hand, if the determination in step S9 is NO and the engine load is greater than or equal to the predetermined load, the process proceeds to step S11. In step S11, the PCM 100 drives the electric supercharger 70 (electric motor 71M) and opens the throttle valve 341 and the rotation speed of the electric motor 71M so that the target engine torque set in step S8 is realized. Then, the injection amount of the injector 11 is determined and a command is issued to them. In step S11, the PCM 100 fully closes the bypass valve 321. After step S11, the process ends (returns to step S1).

(6) Operation, etc. As described above, in the present embodiment, the automatic transmission 110 is controlled so that the engine speed at which the gear stage is switched is lower when the engine is cold than when the engine is warm. The feeder 70 is driven.

  For this reason, when the engine is cold, it is possible to suppress the opportunity for the engine to operate in a region where the engine speed is high, and to suppress the generation amount of NOx.

  Specifically, in an engine in which compression ignition combustion is performed, when the engine is cold, the fuel is not sufficiently atomized (vaporized or atomized) due to the low temperature in the combustion chamber 6, so that the fuel is sufficiently in the combustion chamber. Does not diffuse into 6. As a result, the amount of fuel supplied into the combustion chamber 6 is more likely to be increased when the engine is cold than when the engine is warm. For this reason, when the temperature in the combustion chamber 6 reaches a predetermined temperature due to compression, the fuel burns in a short time at a stretch, and the combustion temperature rises. As a result, the amount of NOx generated increases. Here, the combustion temperature is higher when the combustion speed is higher, that is, when the combustion time is shorter. When the engine speed is low, the amount of heat generated per unit time (the number of combustions) is small, the temperature in the combustion chamber 6 is kept low, and the strength of the flow of intake air flowing into the combustion chamber 6 is also compared. By being suppressed to a low level, the combustion time is long and the combustion speed is kept low. Therefore, as described above, if the number of opportunities to operate the engine in a region where the engine speed is high can be suppressed, that is, if the opportunity to operate the engine in a region where the engine speed is low can be increased, combustion Opportunities for realizing an operating state with a long time and a small amount of NOx generation can be increased. Therefore, the total amount of NOx discharged from the vehicle can be reduced.

  Moreover, according to the present embodiment, when the engine is cold, the electric supercharger 70 is driven and the intake air is supercharged at least under the condition that the engine load is equal to or greater than the predetermined load. Therefore, it is possible to compensate for the deterioration of the acceleration performance due to the reduction of the engine speed at which the gear stage is switched by the increase of the engine torque accompanying the supercharging of the electric supercharger 70, and also to improve the acceleration performance of the vehicle. be able to.

  Further, at the time of warm-up, the engine speed at which the gear stage is switched is increased, so that it is not necessary to increase the engine torque in order to achieve the target engine torque. Therefore, at the time of warm-up, it is necessary to increase the driving force of the electric supercharger 70 in order to increase the engine torque (in order to introduce an appropriate amount of air into the combustion chamber 6), or the electric supercharger 70 is driven. It is not necessary to reduce the driving force of the electric supercharger 70 and the energy consumed by the electric supercharger 70 can be reduced.

  Further, in the present embodiment, the intake air circulation flow is formed when the engine load during cooling is as low as less than a predetermined load. Then, the intake air is repeatedly compressed by the electric supercharger 70 due to the formation of the intake air circulation flow, whereby the temperature of the intake air introduced into the combustion chamber 6 is increased. Therefore, when the engine is cold, especially when the engine load is low and the temperature in the combustion chamber 6 tends to be low, the temperature in the combustion chamber 6 can be increased to promote atomization of the fuel. The generation of NOx can be suppressed by reducing the speed.

(7) Modified Example In the above embodiment, the case where the electric supercharger 70 is always driven when cold is described, but the electric supercharger 70 is driven only when the engine load is equal to or higher than a preset reference load when cold. You may make it do. Further, the electric supercharger 70 may be driven only both when the engine load is equal to or higher than the reference load and when the engine load is less than a predetermined load set to a value less than the reference load.

  In the above embodiment, an example in which the control device of the present invention is applied to a diesel engine that ignites a fuel mainly composed of light oil has been described. The present invention may be applied to a gasoline engine that performs compression ignition combustion of a mixture of fuel and air as components.

  However, in a diesel engine having a relatively low geometric compression ratio of 13 or more and 16 or less, especially at the time of cold, the compression end temperature is kept low, fuel atomization is inhibited, and NOx is likely to be generated. Therefore, if the above configuration is applied to such an engine, the amount of NOx generated can be effectively reduced.

  In the above-described embodiment, the case where the automatic transmission 110 has six or more gear stages has been described, but the number of gear stages of the automatic transmission 110 is not limited thereto.

2 cylinders 30 intake passage 32C bypass passage 70 electric supercharger 100 PCM (control part)
110 Automatic transmission 321 Bypass valve 341 Throttle valve (intake throttle valve)
SN2 Water temperature sensor (temperature detector)

Claims (4)

A compression ignition engine comprising an engine body including a cylinder, and configured so that a mixture of air and fuel is subjected to compression ignition combustion in the cylinder;
An automatic transmission that connects the output shaft and wheels of the engine body and automatically switches a plurality of gears according to the engine speed;
An electric supercharger provided in the intake passage and driven by electric energy to supercharge intake air;
A temperature detector for detecting the temperature of the engine body;
A control unit for controlling the automatic transmission and the electric supercharger;
The control unit switches the gear stage when it is confirmed that the engine is in a cold state based on the temperature detected by the temperature detection unit, rather than when it is confirmed that the engine is in a warm state. While controlling the automatic transmission so that the engine speed is low,
When it is confirmed that the engine is in a cold state, the electric supercharger is driven at least when the engine load is equal to or higher than a predetermined reference load. The vehicle drive device according to claim 1,
A bypass passage connected to the intake passage and bypassing the electric supercharger;
An intake throttle valve that is provided on the downstream side of the portion of the intake passage to which the downstream end of the bypass passage is connected and opens and closes the intake passage;
When the engine is operating in the cold state and the engine load is at least less than a predetermined load, a part of the intake air supercharged by the electric supercharger is passed through the bypass passage. The vehicle drive device characterized by controlling the said intake throttle valve so that the intake air circulation flow returned to a machine is formed. In the vehicle drive device according to claim 1 or 2,
The automatic transmission has a gear stage of six or more speeds, and is a vehicle drive device. In the vehicle drive device according to any one of claims 1 to 3,
The vehicle drive device according to claim 1, wherein the engine is a diesel engine having a geometric compression ratio set to 13 or more and 16 or less.