JP2006090148A - Engine starter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the startability of an engine with an intake valve opened until the vicinity of the middle of a compression stroke even after a bottom dead center. <P>SOLUTION: In this engine starter for a gasoline engine 1 with the closing timing of the intake valve set to the vicinity of the middle position between the bottom dead center and top dead center of the compression stroke, a supercharger 6 using an electric motor 7 as a driving source is provided in an intake passage 4, and when the engine is started, the supercharger 6 is driven to perform supercharging. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to improvement of startability of an internal combustion engine including a supercharger driven by an electric motor.

  In order to start the engine, it is necessary to have a temperature necessary for ignition in the cylinder with the piston near top dead center, and to generate torque for continuous operation after ignition. .

  In particular, in a diesel engine, the temperature of the combustion chamber has to be increased to reach the ignition temperature of light oil, so it has been necessary to increase the compression ratio.

  However, when the compression ratio is increased in order to ensure ignitability, problems such as an increase in mechanical loss such as pumping loss and generation of smoke due to an increase in waste volume have occurred.

Therefore, in Patent Document 1, a supercharger that is driven by an electric motor is provided in the intake passage, and the pressure in the cylinder is increased by performing supercharging at the time of starting the engine, thereby improving the startability while keeping the compression ratio low. It is improving.
JP-A-6-280723

  However, in an engine with a high compression ratio such as a diesel engine, it is not necessary to further increase the compression ratio only for improving the startability by the technique of Patent Document 1, but the effect of reducing pumping loss and the like is great. In the case of a gasoline engine in which the intake valve is open even after bottom dead center and the substantial compression ratio is low, such as an engine that actively uses the engine or a Miller cycle engine, the engine of the patent document 1 can be applied to start the engine. However, by suppressing the compression ratio to a low level, problems such as deterioration of fuel consumption during normal driving and high output cannot be obtained.

  Therefore, an object of the present invention is to improve the startability of a gasoline engine whose intake valve closing timing is late without impairing fuel efficiency and output performance.

  The gasoline engine starter according to the present invention is a gasoline engine starter in which the closing timing of the intake valve is in the vicinity of an intermediate position between the bottom dead center and the top dead center of the compression stroke, and the motor is driven in the intake passage of the gasoline engine. A supercharger is provided as a source, and the supercharger is driven to perform supercharging when the engine is started.

  According to the present invention, supercharging is performed by the electric supercharger at the time of starting the engine. Therefore, even if the intake valve is opened to the middle between the bottom dead center and the top dead center of the compression stroke, the idle rotation speed after ignition by the spark plug Therefore, it is possible to supply a sufficient amount of intake air into the cylinder so as to maintain a stable engine start.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing the configuration of a system to which this embodiment is applied.

  Reference numeral 1 denotes an engine, 2 denotes an intake manifold that supplies intake air to each cylinder of the engine 1, 4 denotes an intake passage that connects an air duct (not shown) and the intake manifold 2, and 3 denotes an exhaust manifold that collects exhaust from each cylinder.

  A supercharger 6 driven by a motor 7 as an electric motor is interposed in the intake passage 4. A bypass passage 5 that bypasses the supercharger 6 and communicates the upstream side and the downstream side of the supercharger 6 is provided. A connecting portion between the intake passage 4 and the bypass passage 5 on the upstream side of the supercharger 6 is a branching portion 15, and a connecting portion between the intake passage 4 and the bypass passage 5 on the downstream side of the supercharger 6 is a joining portion 16.

  The bypass passage 5 is provided with a bypass valve 14 that opens and closes the flow path. The opening and closing of the bypass valve 14 is controlled by a control unit (ECU) 9 described later.

  A throttle valve 10 for adjusting the intake air amount is provided downstream from the merging portion 16. The opening degree of the throttle valve 10 is controlled by the ECU 9 similarly to the supercharger 6.

  The ECU 9 includes a water temperature sensor 12 that detects the cooling water temperature of the engine 1, a rotation speed sensor 13 that detects the engine rotation speed, a shaft rotation speed sensor 11 that detects the rotation speed of the supercharger 6, and a storage amount of the battery 8 described later. Based on these, the opening / closing control of the bypass valve 5, the operation of the supercharger 6, the control of the opening degree of the throttle valve 10 and the like are performed.

  In the above configuration, the engine 1 is a mirror cycle engine. Accordingly, the closing timing of the intake valve (not shown) is near the middle of the compression stroke, and the compression ratio becomes smaller than the expansion ratio. Thereby, compared with the normal engine whose closing timing of an intake valve is near bottom dead center, it is excellent in fuel consumption performance.

  The supercharger 6 will be described.

  The supercharger 6 is a positive displacement supercharger, and is driven by a motor 7 connected via a shaft 6a when a large torque is required, such as when acceleration is requested or when climbing. A shaft rotation speed sensor 11 that detects the rotation speed of the shaft 6a is provided in the vicinity of the shaft 6a.

  By using a motor 7 having a power generation function, the turbocharger 6 is rotated by the suction negative pressure of the engine 1 during coasting, for example, and this rotation is transmitted to the motor 7 via the shaft 6a. Power generation can be performed. The generated power is stored in the battery 8 and used to drive the in-vehicle device and the supercharger 6.

  Next, opening and closing of the bypass valve 14 will be described.

  When a large torque is required due to an acceleration request or the like, the supercharger 6 is driven and the bypass valve 14 is closed. As a result, the entire amount of intake air introduced from the air duct passes through the supercharger 6 and can be supercharged efficiently. Note that when the supercharger 6 is started and stopped, the transient characteristics are improved by controlling the bypass valve 14 and the motor 7 in association with each other. Further, when the motor 7 has a power generation function as described above, the bypass valve 14 is closed during coasting or the like so that the intake air passes through the supercharger 6. Thereby, the supercharger 6 becomes easy to rotate, and can generate electric power efficiently.

  When there is no need for supercharging as when traveling at a constant speed, the supercharger 6 is stopped and the bypass valve 14 is opened. As a result, the intake air flows through the bypass passage 5 having a low ventilation resistance, so that the mechanical loss can be kept small.

  The control of the bypass valve 14 and the supercharger 6 when the engine is started will be described.

  Since the engine 1 is a Miller cycle engine as described above, the substantial compression ratio is lower than the structural compression ratio determined by the cylinder volume and the combustion chamber volume. For this reason, an expansion ratio becomes large compared with a compression ratio, and this improves a fuel consumption. However, since the output decreases as the compression ratio decreases, it is necessary to increase the substantial compression ratio by setting the structural compression ratio high in order to satisfy the output requirement.

  However, when the structural compression ratio is increased, the volume of the combustion chamber is reduced, so that the friction is large as in cold start, and the torque required to maintain idle rotation after ignition by the spark plug is higher than in normal operation. If it is large, there is a possibility that idle rotation cannot be maintained due to insufficient intake air amount.

  For this reason, even if an attempt is made to delay the intake valve closing timing in order to improve fuel efficiency, it is limited to ensure startability.

  Not only the mirror cycle but also an engine having a large friction ratio with respect to the engine output, such as a small displacement engine, there is a restriction on the closing timing of the intake valve in order to ensure startability.

  Therefore, when the engine is started, the bypass valve 14 and the supercharger 6 are controlled as shown in the flowchart of FIG. 2 in order to secure an intake amount sufficient to maintain idle rotation after ignition by the spark plug.

  Hereinafter, it demonstrates according to each step.

  In step S1, it is determined whether or not the ignition switch is ON.

  When it is ON, the process proceeds to step S2, and when it is OFF, the process is terminated.

  In step S2, it is determined whether or not the starter switch is ON.

  In step S3, it is determined whether or not the cooling water temperature detected by the water temperature sensor 12 is lower than a preset water temperature Tw1. The water temperature Tw1 is set by obtaining in advance an experiment or the like the cooling water temperature when the engine friction increases to such an extent that it is difficult to start the engine. The engine friction is greatly affected by the viscosity of the engine oil, and the viscosity of the engine oil depends on the temperature. Therefore, the temperature of the engine oil may be detected. Here, the relationship between the engine friction and the engine oil viscosity, temperature, and cooling water temperature is obtained, and based on this, the cooling water temperature Tw1 at which the engine friction is at a level that does not hinder engine start is set.

  As a result, the water temperature sensor 12 can be used for both the detection of the cooling water temperature and the determination of the magnitude of the engine friction, and it is not necessary to provide a separate sensor for detecting the temperature of the engine oil, thereby suppressing an increase in cost. it can.

  When the cooling water temperature is lower than Tw1 in step S3, the process proceeds to step S4, and supercharging by the supercharger 6 described later is performed.

  If it is higher than Tw1, the engine torque required for maintaining idle rotation is not large, and there is no need to increase the intake air amount, so the routine proceeds to step S14. In step S14, the starter motor is started as usual and the engine is started. This determination eliminates unnecessary driving of the supercharger 6.

  In step S4, the bypass valve 14 is closed. Thereby, all the intake air supplied to the engine passes through the supercharger 6.

  In step S5, engine friction is estimated.

  The engine friction and the cooling water temperature used when setting the water temperature Tw1 described above have a relationship in which the friction increases as the temperature decreases, as shown in FIG. Based on this relationship, the engine friction at the current cooling water temperature can be estimated.

  In step S6, the rotational speed (required supercharger rotational speed) of the supercharger 6 for supplying the intake air amount necessary for starting the engine is obtained by the following procedure.

  First, an intake air amount necessary for starting the engine is obtained with respect to the engine friction obtained in step S5. Since the amount of intake air necessary for starting the engine is substantially proportional to the magnitude of engine friction, it can be obtained from equation (1) using the engine friction obtained in step S5.

Qeng = k1 × F (1)
Qeng: required intake air amount F: engine friction k1: coefficient Further, the intake air amount supplied from the supercharger 6 to the engine 1 is proportional to the rotational speed of the supercharger 6, and therefore can be obtained from the equation (2).

Qcomp = k2 × Neq (2)
Qcomp: intake air amount supplied from the supercharger to the engine Neq: rotational speed of the supercharger k2: coefficient In order to obtain the required supercharger rotational speed, a rotational speed satisfying Qeng = Qcomp may be obtained. Therefore, it can obtain | require by Formula (3).

Neq = k3 × F (3)
k3: coefficient Note that an atmospheric pressure sensor may be provided to detect the atmospheric pressure, and the required intake air amount may be corrected according to the atmospheric pressure. Thereby, a request | requirement supercharger rotational speed can be set more accurately. In this case, if the atmospheric pressure is low, the required intake air amount increases, so that the required supercharger rotation speed also increases.

  In steps S4 to S6 described above, the required rotational speed of the supercharger 6 is set according to the engine friction, so that it is possible to supply an intake air amount for starting the engine reliably and to consume the motor 7 by driving it. Electric power can be minimized.

  In step S7, the motor 7 is driven and supercharging by the supercharger 6 is started.

  In step S8, it is determined whether or not the rotational speed of the supercharger 6 has reached the required supercharger rotational speed. If not, the process returns to step S7, and the determination is repeated until it reaches.

  If it has reached, the process proceeds to step S9 and the starter motor 17 is started. Thereby, when the starter motor 17 is started, intake air necessary for starting the engine can be supplied into the cylinder.

  In step S10, it is determined whether or not the engine speed has reached a preset specified speed. If not, the process returns to step S9, and the determination is repeated until the specified rotational speed is reached.

  The specified rotation speed is set to a peak rotation speed that is reached when the engine starts and the self-sustaining operation is started when the engine is started (rotation speed at t1 in FIG. 4).

  If the specified rotational speed has been reached in step S10, that is, if the engine 1 has started a self-sustaining operation, the engine rotational speed can be controlled by controlling the opening of the throttle valve 10 as in normal operation. Thus, there is no need for supercharging by the supercharger 6. Therefore, the starter motor 17 (not shown) is stopped in step S11, the bypass valve 14 is opened in step S12, the motor 7 is stopped in step S13, and supercharging by the supercharger 6 is stopped.

  As a result, the intake air is supplied to the engine 1 through the bypass passage 5.

  In steps S9 to S13, after the starter motor 17 is started, when the engine starts a self-sustaining operation, the supercharging by the supercharger 6 is immediately stopped, so that the motor 7 is not driven wastefully and the power consumption is reduced. can do.

  By performing the control as described above, the shortage of intake air at the time of starting the engine is resolved, and it becomes possible to start stably. That is, the intake air amount required at the time of starting the engine is supplied by the supercharger 6 regardless of the closing timing of the intake valve, so that the closing timing of the intake valve is delayed in accordance with the fuel consumption requirement and the output requirement during normal driving. Is possible.

  Further, since it is possible to prevent an excessive intake air amount from being supplied, it is possible to prevent the engine from rising after the engine is started.

  As described above, in the present embodiment, supercharging is performed by the supercharger 6 when the engine is started, so that it is possible to secure an intake air amount necessary for starting the engine. Further, since the intake amount necessary for starting the engine can be ensured regardless of the intake valve closing timing, the intake valve closing timing can be set according to the output request, the fuel consumption request, and the like.

  Since the rotation speed of the supercharger 6 at the time of starting the engine is set according to the engine friction calculated based on the coolant temperature, the oil temperature, etc., the power consumption by driving the supercharger 6 can be reduced. .

  When a predetermined engine rotation speed is reached after ignition by the spark plug, it is determined that the explosion is complete, and the supercharger 6 is stopped. Therefore, it is possible to prevent the engine rotation speed from rising after starting. Moreover, the supercharger 6 is not driven uselessly, and the power consumption by driving the supercharger 6 can be reduced.

  Since the intake air amount required at the time of starting the engine is corrected according to the atmospheric pressure and the rotational speed of the supercharger 6 is determined based on the correction, the intake air amount required for starting the engine can be supplied regardless of the environment.

  Although the Miller cycle engine is used in this embodiment, the present invention can be applied to a normal gasoline engine that closes the intake valve after bottom dead center in order to actively use the inertia supercharging effect.

  The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims.

  The present invention is applicable to a gasoline engine that closes an intake valve after bottom dead center.

It is a figure showing the structure of the system of this embodiment. It is a control flowchart of this embodiment. It is a figure showing the relationship between engine friction and cooling water temperature. It is a figure for demonstrating the engine speed at the time of a start.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Intake manifold 3 Exhaust manifold 4 Intake passage 5 Bypass passage 6 Supercharger 7 Motor 8 Battery 9 Engine control unit (ECU)
DESCRIPTION OF SYMBOLS 10 Throttle valve 11 Shaft rotational speed sensor 12 Water temperature sensor 13 Rotational speed sensor 14 Bypass valve 15 Branch part 16 Merge part 17 Starter motor

Claims (7)

In the gasoline engine starting device in which the closing timing of the intake valve is near the middle position between the bottom dead center and the top dead center of the compression stroke,
A turbocharger having a motor as a drive source in the intake passage of the gasoline engine;
A gasoline engine starter characterized in that when the engine is started, the supercharger is driven to perform supercharging. Set the amount of intake air required when starting the engine according to the parameters representing the engine state,
The engine starter according to claim 1, wherein a rotation speed of the supercharger is set according to the intake air amount.   The engine starter according to claim 2, wherein engine friction is used as a parameter representing the state of the engine.   The engine starting device according to claim 3, wherein the engine friction is calculated based on a temperature of engine cooling water at the time of starting.   The engine starter according to claim 3, wherein the engine friction is calculated based on a temperature of engine oil at the time of start. An atmospheric pressure detection means for detecting atmospheric pressure is provided,
The engine starting device according to any one of claims 2 to 5, wherein an intake air amount required at the time of starting the engine is corrected according to an atmospheric pressure.   The engine starter according to any one of claims 1 to 6, wherein the supercharger is stopped when a predetermined engine rotation speed is reached when the engine is started.

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