JP4506366B2 - Engine alcohol concentration estimation device - Google Patents

Description

  The present invention relates to an alcohol concentration estimation device for estimating an alcohol concentration in fuel in an engine using an alcohol-containing fuel in which alcohol is mixed in gasoline.

Patent Document 1 discloses a fuel injection control that corrects a fuel injection amount based on an alcohol concentration in a fuel in an engine using an alcohol-containing fuel. An air-fuel ratio sensor for detecting the air-fuel ratio based on the oxygen concentration of the air-fuel ratio, the deviation between the air-fuel ratio feedback correction coefficient calculated based on the air-fuel ratio detected by the air-fuel ratio sensor and the reference value, that is, air-fuel ratio feedback A method for estimating the alcohol concentration in the fuel based on the amount of deviation of the base air-fuel ratio obtained without correction from the target air-fuel ratio is disclosed.
Japanese Patent Laid-Open No. 05-163992

By the way, in the alcohol-containing fuel, the higher the alcohol concentration, the worse the volatility at a low temperature than the fuel of 100% gasoline.
For this reason, in the cold state immediately after start-up, it is necessary to increase the injection amount to compensate for the deterioration in volatility, and the amount of unburned components increases, thereby correctly determining the air-fuel ratio from the oxygen concentration in the exhaust gas. As a result, the alcohol concentration may be erroneously estimated, and the fuel injection amount may be corrected based on an alcohol concentration that is greatly different from the actual alcohol concentration.

  The present invention has been made in view of the above problems, and prevents the alcohol concentration from being erroneously estimated due to a decrease in the volatility of the alcohol-containing fuel, and the fuel injection amount is corrected based on an alcohol concentration that is greatly different from the actual one. An object of the present invention is to provide an engine alcohol concentration estimation device that can avoid this situation.

Therefore, in the present invention, an air-fuel ratio sensor is used in an engine that uses alcohol-containing fuel in which alcohol is mixed in gasoline and injects the alcohol-containing fuel from a fuel injection valve provided in an intake port toward the intake valve. An alcohol concentration estimation device that estimates the alcohol concentration in the fuel based on the actual air-fuel ratio detected by the engine, and configured to prohibit the estimation of the alcohol concentration based on the actual air-fuel ratio in a cold state of the engine . More specifically, the estimation of the alcohol concentration based on the actual air-fuel ratio is prohibited until a predetermined time has elapsed from the start of the engine, and the predetermined time is made variable according to the engine coolant temperature at the time of engine start. I set it.

  According to the above configuration, estimation of alcohol concentration is prohibited when the accuracy of estimation of alcohol concentration based on the detection result of the air-fuel ratio sensor deteriorates due to a decrease in volatility of the alcohol-containing fuel in a cold state of the engine. Therefore, it is possible to prevent the alcohol concentration from being updated to a value that is significantly different from the actual value, and to prevent the operability (exhaust properties, output characteristics) of the engine from being greatly impaired.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of a vehicle engine using an alcohol-containing fuel.
In FIG. 1, air is sucked into each cylinder of an engine (internal combustion engine) 1 through an intake duct 2, an intake manifold 3, and an intake valve 4.
The intake duct 2 is provided with an electrically controlled throttle valve 6 that is driven to open and close by a motor 5, and the opening degree of the electrically controlled throttle valve 6 is controlled by drive control of the motor 5. The amount is adjusted.

The intake port upstream of the intake valve 4 is provided with a fuel injection valve 7 for each cylinder. The fuel injection valve 7 injects alcohol-containing fuel in which ethanol (alcohol) is mixed into gasoline into each cylinder.
The fuel injection valve 7 injects alcohol-containing fuel toward the back of the umbrella of the intake valve 4.

The air-fuel mixture in the combustion chamber of each cylinder is ignited and burned by spark ignition by the spark plug 8, and the combustion gas is discharged into the atmosphere via the exhaust valve 9, the exhaust manifold 10, and the exhaust duct 11.
Each ignition plug 8 is provided with an ignition coil 12 incorporating a power transistor.

A catalytic converter 13 and a muffler 14 are interposed in the exhaust duct 11.
The motor 5, the fuel injection valve 7, and the power transistor of the electric throttle valve 6 are controlled by an engine control unit (ECU) 21 incorporating a microcomputer.
Detection signals from various sensors are input to the engine control unit 21.

  The various sensors include an air flow meter 22 that measures the intake air amount Qa of the engine 1 on the upstream side of the electric throttle valve 6, a crank angle sensor 23 that detects the crank angle of the engine 1, and the coolant temperature Tw of the engine 1. A water temperature sensor 24 that detects the air-fuel ratio, an air-fuel ratio sensor 25 that is provided in the exhaust duct 11 upstream of the catalytic converter 13 and detects the air-fuel ratio based on the oxygen concentration in the exhaust, and an accelerator that detects the amount of depression of the accelerator pedal (accelerator opening) An opening sensor 26, a throttle opening sensor 27 for detecting the opening of the throttle valve 6, and the like are provided.

Here, the engine control unit 21 controls the motor 5 (throttle valve opening) based on the accelerator opening or the like, and calculates the engine rotation speed Ne based on the detection signal of the crank angle sensor 23.
Further, the ignition timing is calculated based on the engine load, the engine rotational speed Ne, and the like, and the ON period of the power transistor is controlled so that ignition is performed at the ignition timing.

Further, the engine control unit 21 calculates a fuel injection amount (fuel injection pulse width) Ti by the fuel injection valve 7 as described below.
Ti = Tp × CO × HOSETHA × α + Ts
Tp is a basic fuel injection amount (basic fuel injection pulse width), and a stoichiometric air-fuel mixture can be formed from the intake air amount Qa and the engine rotational speed Ne when 100% gasoline fuel is injected. Calculated as a possible value.

The CO is various correction coefficients, and is adapted to increase the fuel injection amount Ti during cold operation or acceleration operation in conformity with the state in which 100% gasoline fuel is injected.
Α is an air-fuel ratio feedback correction coefficient so that when a predetermined air-fuel ratio feedback control condition is satisfied, the actual air-fuel ratio detected by the air-fuel ratio sensor 25 matches the theoretical air-fuel ratio which is the target air-fuel ratio. For example, proportional / integral / derivative control is performed.

The Ts is a correction amount set according to the voltage of the battery that is the driving power source of the fuel injection valve 7.
Further, the HOSETHA is an ethanol concentration correction coefficient set according to the estimation result of the ethanol concentration (alcohol concentration) in the alcohol-containing fuel injected by the fuel injection valve 7, and the theoretical air-fuel ratio due to the change in ethanol concentration The fuel injection amount is corrected to cope with the change.

The initial values of the air-fuel ratio feedback correction coefficient α and the ethanol concentration correction coefficient HOSETHA are 1.0.
Here, the estimation process of the ethanol concentration by the engine control unit 21 will be described according to the flowchart of FIG.
In step S1, it is determined whether or not the coolant temperature Tw is equal to or lower than a reference temperature (for example, 80 ° C.).

  In the present embodiment, as will be described later, the ethanol concentration (alcohol concentration) is estimated based on the exhaust air-fuel ratio detected by the air-fuel ratio sensor 25. However, under conditions where the cooling water temperature Tw is equal to or lower than the reference temperature, the alcohol-containing fuel is When a large amount of ethanol (alcohol) is contained, the volatility of the alcohol-containing fuel is greatly reduced, the combustibility is lowered, and a large amount of unburned components are discharged. Therefore, the exhaust air-fuel ratio detected by the air-fuel ratio sensor 25 is reduced. The ethanol concentration (alcohol concentration) is not correctly reflected.

Therefore, under the condition where the cooling water temperature Tw is equal to or lower than the reference temperature, the estimation accuracy of the ethanol concentration (alcohol concentration) is greatly reduced.
Therefore, when the cooling water temperature Tw is equal to or lower than the reference temperature, the process proceeds to step S2, prohibiting the ethanol concentration estimation process, and ending this routine without updating the ethanol concentration.
As a result, an ethanol concentration greatly different from the actual one is estimated, and it is avoided that the fuel injection amount Ti is corrected based on an erroneous ethanol concentration correction coefficient HOSETHA, and deterioration of engine operability due to an air-fuel ratio shift can be prevented.

Instead of judging the cold state of the engine 1 in which the volatility of the alcohol-containing fuel is reduced based on the coolant temperature Tw, it is based on the temperature of the lubricating oil, the temperature of the cylinder block, the fuel temperature, the temperature of the intake port wall surface, etc. Can be judged.
By the way, since the volatility of the alcohol-containing fuel depends on the temperature in the vicinity of the intake valve 4 particularly in the case of the intake port injection, the temperature of the intake valve 4 is estimated based on the cooling water temperature Tw or the like, or When the temperature of the intake valve 4 is directly detected by a sensor and the temperature of the intake valve 4 is equal to or lower than a reference temperature (for example, 70 ° C.), the ethanol concentration estimation process can be prohibited.

Further, since the temperature of the engine 1 changes with the passage of time from the start, the ethanol concentration estimation process can be prohibited until a predetermined time has passed after the start.
Furthermore, since the time during which the cold state continues continues depending on the temperature condition at the time of starting, it is preferable to variably set the time for prohibiting the estimation process of ethanol concentration from the starting according to the cooling water temperature at the time of starting.

When it is determined in step S1 that the cooling water temperature Tw (intake valve temperature) exceeds the reference temperature (or when it is determined that a predetermined time has elapsed since the start), the ethanol concentration is estimated. Proceed to step S3 and subsequent steps to perform this.
In step S3, it is determined whether or not an air-fuel ratio feedback condition is satisfied.
Note that the air-fuel ratio feedback control is stopped (clamped) at the time of starting, at the time of low water temperature, at the time of high engine load, and at the time of deceleration.

If the air-fuel ratio feedback condition is satisfied, the process proceeds to step S4.
In step S4, the maximum value αmax and the minimum value αmin of the air-fuel ratio feedback correction coefficient α are read. In the next step S5, the average value of the maximum value αmax and the minimum value αmin, that is, the average value of the air-fuel ratio feedback correction coefficient α. αave is calculated.
αave = (αmax + αmin) / 2
In step S6, a deviation ΔM between the average value αave and the reference value 1.0 at which correction by the air-fuel ratio feedback correction coefficient α is not substantially performed is calculated.

ΔM = αave−1.0
In step S7, the ethanol concentration EthC is calculated based on a function having the deviation ΔM as a variable.
Here, the larger the ΔM (the leaner the base air-fuel ratio), the larger the ethanol concentration EthC is calculated.

On the other hand, when it is determined in step S3 that the air-fuel ratio feedback condition is not satisfied, that is, when the air-fuel ratio feedback control is in the clamping condition, the process proceeds to step S8, and the intake air amount Qa and the fuel injection amount Ti at that time From the above, an air-fuel ratio (hereinafter referred to as an assumed air-fuel ratio A) in setting the fuel injection amount Ti is calculated.
In the next step S9, the actual air-fuel ratio B detected by the air-fuel ratio sensor 25 is read.

In step S10, it is determined whether or not the actual air-fuel ratio B is greater than the predetermined air-fuel ratio A, in other words, the actual air-fuel ratio B is greater than the predetermined air-fuel ratio A. It is determined whether or not it is lean.
Since the theoretical air-fuel ratio decreases as the ethanol concentration of the fuel used increases, when the air-fuel ratio B as a result of injection with 100% gasoline applied is larger than the assumed air-fuel ratio A, the ethanol in the fuel used Contamination will be estimated.

Therefore, when the actual air-fuel ratio B is larger than the assumed air-fuel ratio A to a predetermined value e or more and it is estimated that ethanol is mixed in at a predetermined concentration or more, the process proceeds to step S11.
In step S11, a ratio C between the actual air-fuel ratio B and the assumed air-fuel ratio A is calculated.
C = B / A
In step S12, the ethanol concentration EthC is calculated based on the ratio C.

Here, the larger the ratio C, the larger the ethanol concentration EthC is calculated.
On the other hand, when it is determined in step S10 that the difference between the assumed air-fuel ratio A and the actual air-fuel ratio B is less than the predetermined value e, even if ethanol (alcohol) is mixed in the gasoline, the concentration is It is determined that the value is small enough to be ignored (for example, 10% or less), and the process proceeds to step S13.

In step S13, the ethanol concentration is set to 0%, and the ethanol concentration correction coefficient HOSETHA is set to an initial value of 1.0.
Here, the deviation of the air-fuel ratio due to the mixing of 10% or less of ethanol is compensated by the air-fuel ratio feedback correction based on the output of the air-fuel ratio sensor 25.
In the above embodiment, the fuel injection valve 7 is configured to inject fuel into the intake port. However, in an engine that directly injects fuel into the combustion chamber, the ethanol concentration (alcohol concentration) is estimated when the engine is cold as described above. Prohibiting the same effect can be achieved.

Moreover, the alcohol mixed into gasoline is not limited to ethanol, and a configuration in which other alcohol is mixed may be used.
Further, the method of estimating the ethanol concentration (alcohol concentration) based on the average value αave of the air-fuel ratio feedback correction coefficient α, the assumed air-fuel ratio A, and the actual air-fuel ratio B is limited to the method using the deviation ΔM and the ratio C. It is not something.

  Further, the present invention can be applied to the engine 1 in which the target air-fuel ratio of the engine 1 is variably set according to the engine load, the engine speed, and the like.

1 is a system diagram of an engine in an embodiment. The flowchart which shows the estimation process of the ethanol concentration (alcohol concentration) in embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Engine, 4 ... Intake valve, 6 ... Throttle valve, 7 ... Fuel injection valve, 8 ... Spark plug, 9 ... Exhaust valve, 21 ... Engine control unit, 22 ... Air flow meter, 23 ... Crank angle sensor, 24 ... Water temperature Sensor, 25 ... Air-fuel ratio sensor

Claims (3)

In an engine that uses an alcohol-containing fuel in which alcohol is mixed in gasoline and injects the alcohol-containing fuel from a fuel injection valve provided in an intake port toward the intake valve, an actual air-fuel ratio detected by an air-fuel ratio sensor is detected. An alcohol concentration estimation device for estimating an alcohol concentration in a fuel based on a fuel ratio,
The alcohol concentration is prohibited from being estimated based on the actual air-fuel ratio until a predetermined time elapses after the engine is started, and the predetermined time is variably set according to the engine coolant temperature at the time of starting the engine. An alcohol concentration estimation device for an engine characterized by the above. An air-fuel ratio feedback correction coefficient for correcting the fuel injection amount is calculated based on the air-fuel ratio detected by the air-fuel ratio sensor, and an alcohol concentration is estimated based on a deviation between the air-fuel ratio feedback correction coefficient and a reference value. The engine alcohol concentration estimating apparatus according to claim 1, wherein And air-fuel ratio obtained from the amount of intake air fuel injection amount, alcohol engine according to claim 1, characterized in that to estimate the alcohol concentration, based on the ratio of the air-fuel ratio detected by the air-fuel ratio sensor Concentration estimation device.

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