JP2007198308A - Start control device for internal combustion engine - Google Patents

Abstract

A start control device for an internal combustion engine capable of stably burning alcohol-mixed fuel when starting the engine and quickly starting the internal combustion engine.
In a start control device applied to an internal combustion engine 1 capable of using an alcohol-mixed fuel containing alcohol, a variable valve mechanism 20 capable of changing a valve closing timing of an intake valve 11 of the internal combustion engine 1, an alcohol And an alcohol concentration sensor 32 that acquires the alcohol concentration of the mixed fuel, and the ECU 50 controls the operation of the variable valve mechanism 20 as the alcohol concentration acquired by the alcohol concentration sensor 32 increases, so that the internal combustion engine 1 is started. Is closed to the intake bottom dead center BDC of the cylinder 2 in which the intake valve 11 is provided.
[Selection] Figure 1

Description

  The present invention relates to a start control device for an internal combustion engine capable of using an alcohol mixed fuel containing alcohol.

  In a fuel heating apparatus applied to an internal combustion engine using an alcohol-mixed fuel containing alcohol, a reserve of the alcohol-mixed fuel according to the alcohol concentration of the alcohol-mixed fuel in order to improve the fuel combustibility at the time of starting the engine or the like A fuel heating device that performs heating is known (see Patent Document 1).

Japanese Patent Laid-Open No. 5-209579

  When the fuel is heated by a heater or the like as described above, a time for preheating the fuel is required, so that the start time is increased and the startability is deteriorated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a start control device for an internal combustion engine that can surely burn alcohol-mixed fuel when the engine is started and that can quickly start the internal combustion engine.

  The start control device for an internal combustion engine according to the present invention is a start control device applied to an internal combustion engine that can use alcohol-mixed fuel containing alcohol, and a variable valve that can change the closing timing of the intake valve of the internal combustion engine. A mechanism, alcohol concentration acquisition means for acquiring the alcohol concentration of the alcohol-mixed fuel, and control of the operation of the variable valve mechanism as the alcohol concentration acquired by the alcohol concentration acquisition means increases to start the internal combustion engine The above-described problem is solved by providing an operation control means for bringing the closing timing of the intake valve close to the intake bottom dead center of the cylinder provided with the intake valve (Claim 1).

  Since the compression ratio increases as the closing timing of the intake valve approaches the intake bottom dead center, the in-cylinder temperature at the end of the compression stroke, that is, the in-cylinder temperature at the compression end can be increased. According to the start control device of the present invention, the higher the alcohol concentration of the alcohol-mixed fuel, the closer the intake valve closing timing at the start of the internal combustion engine is to the intake bottom dead center, so that the in-cylinder temperature at the compression end is increased. The vaporization of the alcohol mixed fuel in the cylinder can be promoted. Therefore, it is possible to reliably start the internal combustion engine by reliably burning the alcohol-mixed fuel when starting the engine. In addition, since the preheating time of the alcohol mixed fuel can be shortened or eliminated, the internal combustion engine can be started quickly.

  In one aspect of the present invention, intake air temperature acquisition means for acquiring the intake air temperature of the internal combustion engine, and closing of the intake valve at the start of the internal combustion engine as the intake air temperature acquired by the intake air temperature acquisition means is lower It may further comprise valve closing timing correction means for correcting the valve closing timing of the intake valve so that the timing approaches the intake bottom dead center (Claim 2). Since the in-cylinder temperature at the compression end decreases as the intake air temperature decreases, the in-cylinder temperature at the compression end is appropriately adjusted to a temperature at which vaporization of the alcohol-mixed fuel is promoted by correcting the valve closing timing of the intake valve in this way. Can be adjusted. For this reason, the alcohol-mixed fuel can be more reliably burned when the engine is started.

  In one aspect of the present invention, the fuel supply system of the internal combustion engine further includes a heating unit capable of heating the alcohol mixed fuel and changing a heat amount supplied to the alcohol mixed fuel, and the operation control unit includes: The operation of the heating means may be controlled such that the higher the alcohol concentration acquired by the alcohol concentration acquisition means, the greater the amount of heat supplied to the alcohol-mixed fuel when the internal combustion engine is started. ). In this case, since the fuel before being supplied to the cylinder can be heated by the heating means, the alcohol-mixed fuel can be quickly vaporized in the cylinder. Therefore, the internal combustion engine can be started more quickly.

  As described above, according to the present invention, the higher the alcohol concentration of the alcohol-mixed fuel, the closer the intake valve closes to the intake bottom dead center and raises the in-cylinder temperature at the compression end. The alcohol mixed fuel can be surely vaporized. For this reason, the alcohol-mixed fuel can be reliably burned when the engine is started. Moreover, since it is not necessary to preheat the alcohol mixed fuel, the internal combustion engine can be started quickly.

  FIG. 1 shows an embodiment of an internal combustion engine in which a start control device is incorporated in the present invention. An internal combustion engine (hereinafter also referred to as an engine) 1 is a four-cycle engine mounted on a vehicle as a driving power source, and a plurality of cylinders 2 (only one is shown in FIG. 1) are formed. A cylinder block 3 and a cylinder head 4 attached to the upper part of the cylinder block 3 are provided. A piston 5 is inserted into each cylinder 2 so as to be able to reciprocate. A combustion chamber 6 is formed in each cylinder 2 by the piston 5, the wall surface of the cylinder 2, and the cylinder head 4. The piston 5 is connected to the crankshaft 8 via a connecting rod 7. An intake passage 9 and an exhaust passage 10 are connected to each cylinder 2, and an intake valve 11 and an exhaust valve 12 for opening and closing the intake passage 9 and the exhaust passage 10 with respect to the combustion chamber 6. Spark plugs 13 are provided for igniting the fuel mixture. The intake passage 9 is provided with an air cleaner 14 for filtering the intake air, a throttle valve 15 for controlling the intake air amount, and an intake air temperature sensor 16 as an intake air temperature acquisition means for outputting a signal corresponding to the intake air temperature. An exhaust purification catalyst 17 is provided in the exhaust passage 10.

  The engine 1 also includes a variable valve mechanism 20, a fuel supply device 30 as a fuel supply system, and a starter motor 40. The starter motor 40 may be the same as a known starter motor that drives the crankshaft 8 to start the engine 1, and thus detailed description thereof is omitted. The variable valve mechanism 20 includes an intake valve opening / closing drive actuator 21 for opening / closing the intake valve 11 and an exhaust valve opening / closing drive actuator 22 for opening / closing the exhaust valve 12. The valve operating characteristics such as the valve opening timing, the valve closing timing, the operating angle, and the lift amount of the exhaust valve 12 can be changed.

  The fuel supply device 30 is a fuel tank 31 in which alcohol mixed fuel containing alcohol (hereinafter abbreviated as mixed fuel) is stored, and alcohol concentration acquisition means for outputting a signal corresponding to the alcohol concentration of the alcohol mixed fuel. The alcohol concentration sensor 32 and the injector 33 provided for each cylinder 2 are provided. That is, the engine 1 can be operated using the mixed fuel. In this embodiment, a fuel obtained by mixing ethanol and gasoline is used as the mixed fuel. Therefore, hereinafter, the alcohol concentration may be referred to as ethanol concentration. The ethanol concentration in the mixed fuel varies from 0%, that is, only gasoline, to 100%, that is, only ethanol. The mixed fuel stored in the fuel tank 31 is sent to each injector 33 via a fuel supply line 34 by a fuel pump (not shown), and then injected from each injector 33 and supplied to each cylinder 2. As shown in FIG. 1, the fuel supply line 34 is provided with an electric heater 35 as a heating means. The electric heater 35 can adjust the energization time and output from a power source (not shown), and the amount of heat supplied to the mixed fuel flowing through the fuel supply line 34 can be changed by changing these parameters. As the alcohol concentration sensor 32, for example, a known sensor that detects the ethanol concentration by utilizing the difference between the electric resistance value of gasoline and the electric resistance value of ethanol is used.

  The operations of the variable valve mechanism 20 and the electric heater 35 are controlled by an engine control unit (ECU) 50, respectively. The ECU 50 is configured as a computer including a microprocessor and peripheral devices such as RAM and ROM necessary for its operation, and controls the operation state of the engine 1 by controlling the operation of the spark plug 13, the injector 33, the starting motor 40, and the like. It is a well-known computer unit. A plurality of sensors such as an intake air temperature sensor 16, an alcohol concentration sensor 32, and a cooling water temperature sensor 51 that outputs a signal corresponding to the temperature of the cooling water of the engine 1 are connected to the ECU 50, and the ECU 50 outputs signals from these sensors. To control the operating state of the engine.

  As is well known, alcohol such as ethanol is less likely to vaporize than gasoline. Therefore, the ECU 50 controls the operation of the variable valve mechanism 20 and the electric heater 35 in accordance with the alcohol concentration in the mixed fuel so that the mixed fuel is appropriately combusted in the cylinder 2 when the engine 1 is started. FIG. 2 shows a start control routine executed by the ECU 50 to start the engine 1 by controlling the operations of the variable valve mechanism 20 and the electric heater 35 at the start of the engine 1 and controlling the operation of the start motor 40. Yes. The control routine of FIG. 2 is executed when the ECU 50 is started, and after the ECU 50 is started, it is repeatedly executed at a predetermined cycle until a predetermined end condition is satisfied.

  In the control routine of FIG. 2, the ECU 50 first determines whether or not there is a request for starting the engine 1 in step S11. It is determined that the start request of the engine 1 is present when a predetermined start condition is satisfied, for example, the ignition switch is switched on. Also, in a so-called eco-run vehicle that stops the engine 1 when a predetermined engine stop condition is satisfied during operation of the engine 1, the engine 1 is operated when the predetermined engine stop condition is satisfied and the engine 1 is stopped. It is determined that the engine 1 has been requested to start even when the accelerator pedal or the shift gear is operated by a person. If it is determined that there is no request for starting the engine 1, the current control routine is terminated. On the other hand, if it is determined that there has been a request for starting the engine 1, the process proceeds to step S12, and the ECU 50 refers to the output signals of the intake air temperature sensor 16, the alcohol concentration sensor 32, and the cooling water temperature sensor 51 to determine the ethanol concentration and the cooling water temperature. , And intake air temperature, respectively.

  In the next step S13, the ECU 50 determines whether or not the ethanol concentration is equal to or higher than a predetermined concentration. When the ethanol concentration in the mixed fuel is low, the engine 1 can be started under the same conditions as in the case of gasoline alone. Therefore, as the predetermined concentration, an ethanol concentration capable of starting the engine 1 under the same conditions as in the case of gasoline only is set. When it is determined that the ethanol concentration is less than the predetermined concentration, the process proceeds to step S14, where the ECU 50 sets the closing timing of the intake valve 11 to the reference closing timing θb. In this process, the ECU 50 prohibits the operation of the electric heater 35. That is, when the electric heater 35 is operating, the electric heater 35 is stopped (OFF), and when the electric heater 35 is stopped, the stopped (OFF) state is maintained. Further, in this process, the set values such as the ignition timing and the fuel injection timing are set to values when the gasoline 1 is supplied to the engine 1 and the engine 1 is started (gasoline start time set value). Thereafter, steps S15 to S20 are skipped and the process proceeds to step S21.

  The closing timing of the intake valve 11 when the engine 1 is started will be described with reference to FIG. FIG. 3 shows an example of the lift curve L1 of the intake valve 11 when the engine 1 is started. In general, the closing timing of the intake valve 11 when starting the engine 1 is shown in FIG. 3 in order to reduce the in-cylinder pressure in the compression stroke to reduce the load on the starting motor 40 and to reduce power consumption. As described above, it is set closer to the top dead center (TDC) of the compression stroke. In the present invention, this position is called the normal valve closing timing θb.

  On the other hand, if it is determined that the ethanol concentration is equal to or higher than the predetermined concentration, the process proceeds to step S15, and the ECU 50 determines whether or not the cooling water temperature of the engine 1 is equal to or lower than the predetermined temperature. When the temperature of the engine 1 is high, the mixed fuel can be vaporized by the heat of the engine 1. Therefore, it is determined whether or not it is necessary to execute the process for promoting the vaporization of the mixed fuel with reference to the coolant temperature correlated with the temperature of the engine 1. The predetermined temperature is set to a temperature at which ethanol can be sufficiently vaporized by the heat of the engine 1. For example, 20 ° C. is set as the predetermined temperature. When it is determined that the coolant temperature of the engine 1 is higher than the predetermined temperature, the process proceeds to step S16, where the ECU 50 sets the closing timing of the intake valve 11 to the reference closing timing θb and stops (turns off) the electric heater 35. . In this process, the set values such as the ignition timing and the fuel injection timing are set to values (ethanol start time set values) when only ethanol is supplied to the engine 1 and the engine 1 is started. Thereafter, steps S17 to S20 are skipped and the process proceeds to step S21.

  When it is determined that the coolant temperature of the engine 1 is equal to or lower than the predetermined temperature, the process proceeds to step S17, and the ECU 50 calculates the valve closing timing θ of the intake valve 11. The valve closing timing θ of the intake valve 11 is calculated by subtracting the first advance angle amount θ1 and the second advance angle amount θ2 from the reference valve closing timing θb. An example of the lift curve of the intake valve 11 when the valve closing timing is advanced to the intake bottom dead center BDC side is shown by a line L2 in FIG. FIG. 4 shows an example of the relationship between the ethanol concentration of the mixed fuel and the first advance amount θ1. The valve closing timing of the intake valve 11 is advanced to approach the intake bottom dead center BDC shown in FIG. 3, thereby increasing the amount of air compressed during the compression stroke and increasing the temperature in the cylinder 2 at the compression end. The vaporization of the mixed fuel in the cylinder 2 can be promoted. On the other hand, the higher the ethanol concentration, the harder the vaporized fuel becomes. Therefore, as shown in FIG. 4, the higher the ethanol concentration is, the closer the closing timing of the intake valve 11 is to the intake bottom dead center BDC, and the first advance amount θ1 is set to increase the temperature in the cylinder 2 at the compression end. It is set large. FIG. 5 shows an example of the relationship between the intake air temperature and the second advance angle amount θ2. Since the temperature in the cylinder 2 at the compression end decreases as the intake air temperature decreases, it is necessary to increase the temperature in the cylinder 2 at the compression end. Therefore, the second advance angle amount θ2 is set larger as the intake air temperature is lower. In subsequent step S18, the ECU 50 changes the valve closing timing θ of the intake valve 11 to the calculated valve closing timing θ.

  In the next step S19, the ECU 50 calculates the amount of heat Q to be supplied from the electric heater 35 to the mixed fuel. The supplied heat amount Q is calculated by adding the first heating amount Q1 set based on the ethanol concentration of the mixed fuel and the second heating amount Q2 set based on the cooling water temperature of the engine 1. FIG. 6 shows an example of the relationship between the ethanol concentration of the mixed fuel and the first heating amount Q1. As described above, the higher the ethanol concentration, the more difficult it is to vaporize, so the higher the ethanol concentration, the larger the first heating amount Q1 is set. FIG. 7 shows an example of the relationship between the cooling water temperature of the engine 1 and the second heating amount Q2. When the temperature of the engine 1 is high, the mixed fuel can be vaporized by the heat of the engine 1, so the second heating amount Q2 is set smaller as the cooling water temperature of the engine 1 is higher. In the following step S20, the ECU 50 starts (ON) the electric heater 35 to heat the mixed fuel, and outputs and energizes the electric heater 35 so that the calculated heat Q is supplied from the electric heater 35 to the mixed fuel. Control the time.

  In the next step S21, the ECU 50 starts the starter motor 50 and starts cranking of the engine 1. Further, the ECU 50 controls the operation of the intake valve opening / closing drive actuator 21 so that the intake valve 11 is closed at the valve closing timing set in step S14, S16 or S18 during the cranking. In subsequent step S22, the ECU 50 determines whether or not the engine 1 has been started. Whether or not the engine 1 has been started is determined based on, for example, the number of revolutions of the engine 1, and the number of revolutions of the engine 1 is equal to or greater than the number of revolutions when a complete explosion state in which the engine 1 can continue to burn is obtained. In this case, it is determined that the engine 1 has started. If it is determined that the engine 1 has not been started, this process is repeated. On the other hand, if it is determined that the engine 1 has been started, the current control routine is terminated.

  In the control routine of FIG. 2, the higher the ethanol concentration, the closer the intake valve 11 closes to the intake bottom dead center BDC when the engine 1 is started. Therefore, the temperature in the cylinder 2 at the compression end is increased to increase the cylinder 2 It is possible to promote the vaporization of the mixed fuel inside. Therefore, the internal combustion engine can be reliably started by stably burning the mixed fuel in the cylinder 2 at the time of starting. Further, by increasing the in-cylinder temperature and promoting the vaporization of the mixed fuel in the cylinder 2, the time for heating the mixed fuel in the fuel supply device 30 can be shortened or eliminated. Can be started quickly, and fuel efficiency can be improved by saving energy. Furthermore, since the amount of heat supplied from the electric heater 35 to the mixed fuel increases as the alcohol concentration increases, the mixed fuel can be quickly vaporized in the cylinder 2 even if the alcohol concentration is high.

  Note that the ECU 50 functions as an operation control means and a valve closing timing correction means of the present invention by executing the processing of steps S17 and S18 in FIG. 2 and changing the valve closing timing of the intake valve 11.

  After the engine 1 is started, the closing timing of the intake valve 11 is appropriately adjusted according to the warm-up state of the engine 1 so that the combustion of the alcohol-mixed fuel does not become unstable. For example, the closing timing of the intake valve 11 that has been advanced according to the rate of increase in the coolant temperature of the engine 1 is gradually retarded. When the temperature of the engine 1 rises and a complete warm-up state in which heat dissipation from the radiator is started, the closing timing of the intake valve 11 is, for example, the closing timing of the intake valve 11 during normal operation of the engine 1. It adjusts suitably based on the map which showed the relationship with the alcohol concentration of mixed fuel.

  The present invention is not limited to the above-described form and can be implemented in various forms. For example, the present invention may be applied to a so-called direct injection internal combustion engine in which fuel is directly injected into a cylinder. When the present invention is applied to a direct injection internal combustion engine, the fuel injection timing at the time of cranking may be set in the latter half of the compression stroke. In this case, since the mixed fuel is supplied into the air whose temperature has increased due to the compression stroke, vaporization of the mixed fuel can be further promoted.

  The present invention may also be applied to an engine incorporated in a hybrid system. Since the cranking speed can be changed in such a system, the cranking speed may be increased during cranking. By increasing the cranking speed in this manner, the in-cylinder temperature can be increased before the fuel is supplied into the cylinder, so that the vaporization of the mixed fuel can be further promoted.

  The means for acquiring the alcohol concentration of the mixed fuel is not limited to the alcohol concentration sensor. Since the fuel injection amount and the engine output are affected by the alcohol concentration of the mixed fuel, the relationship between the fuel injection amount and the engine output at each alcohol concentration is stored as a map in the ECU, and this map is used for the engine. The alcohol concentration of the mixed fuel may be estimated. Further, since the air-fuel ratio of the exhaust gas is affected by the alcohol concentration of the mixed fuel, the approximate alcohol concentration may be calculated based on the measured air-fuel ratio of the exhaust gas. An injector provided with a heater capable of heating the fuel to be injected may be provided as a heating means for the mixed fuel. The variable valve mechanism of the internal combustion engine to which the present invention is applied may be any variable valve mechanism that can change at least the closing timing of the intake valve. As such a variable valve mechanism, in addition to the valve mechanism shown in the above embodiment, for example, a valve mechanism that opens and closes an intake valve and an exhaust valve by an electric motor, or an intake magnet and an exhaust valve that are opened and closed by an electromagnet. An electromagnetically driven valve mechanism or the like may be provided.

The figure which shows one form of the internal combustion engine in which the starting control apparatus was integrated in this invention. The flowchart which shows the starting control routine which ECU performs. The figure which shows an example of the lift curve of an intake valve at the time of engine starting. The figure which shows an example of the relationship between the ethanol concentration of mixed fuel, and the 1st advance amount. The figure which shows an example of the relationship between intake temperature and 2nd advance amount. The figure which shows an example of the relationship between the ethanol concentration of mixed fuel, and the 1st heating amount. The figure which shows an example of the relationship between the engine coolant temperature and the second heating amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 11 Intake valve 16 Intake temperature sensor (intake temperature acquisition means)
20 Variable valve mechanism 30 Fuel supply device (fuel supply system)
32 Alcohol concentration sensor (alcohol concentration acquisition means)
35 Electric heater (heating means)
50 Engine control unit (operation control means, valve closing timing correction means)
BDC Inspiratory bottom dead center

Claims (3)

In a start control device applied to an internal combustion engine capable of using an alcohol-mixed fuel containing alcohol,
A variable valve mechanism that can change the closing timing of the intake valve of the internal combustion engine, an alcohol concentration acquisition unit that acquires the alcohol concentration of the alcohol-mixed fuel, and a higher alcohol concentration acquired by the alcohol concentration acquisition unit Operation control means for controlling the operation of the variable valve mechanism to bring the closing timing of the intake valve at the time of starting the internal combustion engine closer to the intake bottom dead center of the cylinder provided with the intake valve. An internal combustion engine start control device.   An intake air temperature acquisition means for acquiring the intake air temperature of the internal combustion engine, and the lower the intake air temperature acquired by the intake air temperature acquisition means, the closer the closing timing of the intake valve at the start of the internal combustion engine is to the intake bottom dead center. 2. The start control device for an internal combustion engine according to claim 1, further comprising valve closing timing correction means for correcting the valve closing timing of the intake valve so as to approach. Provided with a fuel supply system of the internal combustion engine, further comprising a heating means for heating the alcohol mixed fuel and capable of changing the amount of heat supplied to the alcohol mixed fuel;
The operation control means controls the operation of the heating means such that the higher the alcohol concentration acquired by the alcohol concentration acquisition means, the greater the amount of heat supplied to the alcohol mixed fuel when the internal combustion engine is started. 3. The start control device for an internal combustion engine according to claim 1, wherein the start control device is an internal combustion engine.

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