JP7841469B2 - Fuel injection control device for an internal combustion engine using hydrogen fuel - Google Patents

Description

This invention relates to a fuel injection control device for an internal combustion engine using hydrogen fuel.

In internal combustion engines using gasoline or diesel fuel, post-injection may be performed during the expansion stroke, where fuel is injected from the in-cylinder injector. Post-injection raises the exhaust temperature, accelerating catalyst warm-up and increasing boost pressure (see, for example, Patent Document 1).

Japanese Patent Publication No. 2000-045828

Hydrogen fuel is sometimes used as fuel for internal combustion engines. Hydrogen fuel has superior ignition properties compared to gasoline and diesel. Therefore, when using hydrogen fuel, there is room to improve the exhaust gas temperature rise compared to when gasoline or diesel is used.

Therefore, the present invention aims to provide a fuel injection control device for an internal combustion engine using hydrogen fuel with improved exhaust gas temperature rise.

The above objective can be achieved by a fuel injection control device for a hydrogen fuel-based internal combustion engine that performs post-injection, injecting hydrogen fuel from an in-cylinder injection valve during the expansion stroke. This device comprises: a calculation unit that calculates the in-cylinder temperature during the opening of the exhaust valve of the internal combustion engine during the expansion stroke; and an injection control unit that, based on the opening temperature, starts the post-injection before the exhaust valve opens and continues it while the exhaust valve is open.

The injection control unit may continue the post-injection even while the exhaust valve is open if the temperature during valve opening is above the lower limit that ensures the ignition of the mixture of hydrogen fuel and gas in the cylinder.

A turbocharger turbine is positioned in the exhaust passage connected to the internal combustion engine. The calculation unit may calculate the valve-open temperature based on a reference cylinder temperature and reference cylinder volume at a predetermined timing during the expansion stroke before the exhaust valve opens, and the valve-open volume, which is the sum of the cylinder volume at the valve-open timing (when the exhaust valve opens) and the passage volume of the exhaust passage from the exhaust valve to the turbine.

A catalyst is positioned in the exhaust passage connected to the internal combustion engine, and the calculation unit may calculate the temperature during valve opening based on a reference cylinder temperature and reference cylinder volume at a predetermined timing during the expansion stroke before the exhaust valve opens, and the volume during valve opening, which is the sum of the cylinder volume at the valve opening timing and the passage volume of the exhaust passage from the exhaust valve to the catalyst.

The reference cylinder temperature is the peak temperature, which is the maximum value of the cylinder temperature during the expansion stroke, and the reference cylinder volume is the cylinder volume when the cylinder temperature reaches the peak temperature. The calculation unit may calculate the reference cylinder temperature and the reference cylinder volume based on the rotational speed, torque, and ignition timing of the internal combustion engine.

According to the present invention, a fuel injection control device for an internal combustion engine using hydrogen fuel with improved exhaust gas temperature rise can be provided.

Figure 1 is a schematic diagram of the engine system. Figure 2 is a timing chart illustrating the change in in-cylinder temperature during post-injection control. Figure 3 is a flowchart illustrating the post-injection control performed by the ECU. Figures 4A and 4B are maps for calculating the peak temperature, and Figures 4C and 4D are maps for calculating the peak CA, which is the crank angle at the peak temperature. Figure 5 is a map for calculating the specific heat ratio k. Figure 6A is an explanatory diagram for calculating the start CA and end CA of continuous post-injection, and Figure 6B is an explanatory diagram for calculating the start CA and end CA of normal post-injection.

Figure 1 is a schematic diagram of the engine system 1. The engine system 1 includes an engine 10, an ECU (Electronic Control Unit) 40, and other components. The engine 10 uses hydrogen fuel. The engine 10 has multiple cylinders 11 (only one is shown in Figure 1) in a cylinder block. A piston 12 located within each cylinder 11 is connected to a crankshaft 13 via a connecting rod 14. The connecting rod 14 converts the reciprocating motion of the piston 12 into the rotational motion of the crankshaft 13. A cylinder head is mounted on the upper part of the cylinder block. A combustion chamber 15, where a spark plug 16 is located, is formed between the cylinder head and the upper end of the piston 12. An intake port 17 and an exhaust port 18, corresponding to the combustion chamber 15, are connected to an intake passage 19 and an exhaust passage 20, respectively.

The intake passage 19 is equipped with an air flow meter 21, a throttle valve 22, and the compressor 23A of the supercharger 23, from its upstream side. The throttle valve 22's opening degree is changed by a throttle actuator 24, thereby regulating the amount of air drawn into the combustion chamber 15. The intake passage 19 is branched at the intake manifold located downstream of the throttle valve 22, and this branched section is connected to each combustion chamber 15. Furthermore, an in-cylinder injection valve 25 for injecting hydrogen fuel into the cylinder 11 is also provided.

The turbine 23B of the supercharger 23 is located in the exhaust passage 20. Exhaust gas generated from combustion in the combustion chamber 15 of each cylinder is introduced to the turbine 23B of the supercharger 23 through the exhaust manifold. When the turbine 23B is activated by the introduced exhaust gas, the compressor 23A on the intake passage 19 side is activated in conjunction, compressing the air in the intake passage 19. This compression increases the pressure in the intake passage 19, i.e., the intake pressure, and this pressure efficiently fills the combustion chamber 15 with air.

The exhaust passage 20 is provided with a bypass passage 33 that bypasses the turbine 23B. A wastegate valve 34 is provided in the bypass passage 33. The wastegate valve 34 regulates the boost pressure of the supercharger 23. Downstream of the wastegate valve 34, a catalyst 29 for purifying the exhaust gas is provided.

The engine 10 is equipped with intake valves 26 and exhaust valves 27, which open and close intake ports 17 and exhaust ports 18, respectively, connected to the intake passage 19 and exhaust passage 20. The intake valves 26 and exhaust valves 27 open and close in conjunction with the rotation of the intake and exhaust camshafts, which are driven and connected to the crankshaft 13. As a result, the intake valves 26 and exhaust valves 27 are driven to open and close at predetermined timings, synchronized with the rotation of the crankshaft 13, that is, corresponding to the reciprocating movement of each piston 12.

The engine system 1 is equipped with various sensors. Specifically, these include a crank angle sensor 30, an accelerator pedal position sensor 31c, an air flow meter 21, a throttle position sensor 32, and so on.

The ECU 40 comprises a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and a storage device. The ECU 40 controls the engine 10 by executing programs stored in the ROM and storage device. The ECU 40 is an example of a fuel injection control device and performs post-injection control, which is described later. Post-injection control is performed by a calculation unit and an injection control unit, which are functionally realized by the CPU, ROM, RAM, and storage device.

Post-injection refers to fuel injection performed by the in-cylinder injection valve 25 during the expansion stroke after the main injection. Main injection, for example, is fuel injection performed during the intake stroke, and is used to output the desired torque to the engine 10. Post-injection is fuel injection aimed at raising the exhaust gas temperature. In this embodiment, post-injection includes continuous post-injection and normal post-injection. In this specification, the term "post-injection" simply includes both continuous and normal post-injection. Continuous post-injection is post-injection that begins before the exhaust valve 27 opens and continues while the valve is open. Normal post-injection is post-injection that begins before the exhaust valve 27 opens and ends before the exhaust valve 27 opens. Further details will be described later.

The ECU 40 performs predetermined calculations based on the detection signals from the various sensors described above. For example, based on the detection signal from the crank angle sensor 30, the rotational phase of the crankshaft 13, i.e., the crank angle, is calculated, and furthermore, the rotational speed of the engine 10 is calculated. Based on the detection signal from the accelerator pedal position sensor 31c, the opening degree of the accelerator pedal operated by the driver is calculated. Based on the detection signal from the air flow meter 21, the intake air volume is calculated.

[Post-injection control]
Figure 2 is a timing chart illustrating the change in cylinder temperature during post-injection control. The vertical axis represents cylinder temperature, and the horizontal axis represents crank angle. Figure 2 also shows the change in cylinder temperature when post-injection is not performed and when continuous post-injection is performed. Here, the crank angle at which the maximum value of the cylinder temperature, the peak temperature, is reached is called the peak CA. The crank angle at the timing when the exhaust valve 27 opens is called the opening CA. The crank angle at the timing when continuous post-injection starts is called the start CA. The crank angle at the timing when continuous post-injection ends is called the end CA. The permitted CA and limit CA will be described later.

After the main injection, ignition of the fuel-air mixture occurs in the latter half of the compression stroke, causing combustion and an increase in cylinder temperature. The cylinder temperature reaches its peak in the first half of the expansion stroke after top dead center. Due to adiabatic changes caused by the increase in cylinder volume during the expansion stroke, the cylinder temperature decreases from the peak. When the crank angle reaches the start CA, continuous post-injection begins. This results in a higher cylinder temperature than if post-injection were not performed. Continuous post-injection continues even after the valve opens CA. When the crank angle reaches the end CA, continuous post-injection ends.

Here, after valve opening CA, the cylinder interior and the exhaust passage 20 are connected, causing the cylinder interior temperature to decrease. When gasoline or diesel fuel is used, the ignition properties of the fuel mixture deteriorate at the cylinder interior temperature after valve opening CA. However, in this embodiment, hydrogen fuel, which has superior ignition properties than gasoline or diesel fuel, is used. Therefore, under predetermined conditions, continuous post-injection continues even after valve opening CA.

This section explains the exhaust gas heating properties of continuous post-injection and normal post-injection. In normal post-injection, as described above, injection begins before valve opening CA and ends before valve opening CA. Valve opening CA is the crank angle near bottom dead center, close to the end of the expansion stroke. Therefore, normal post-injection is performed during a period when the rate of increase in cylinder volume is fast and the rate of decrease in cylinder temperature is fast, just before bottom dead center. In contrast, continuous post-injection is performed before and after valve opening CA near bottom dead center. Near bottom dead center, the rate of increase in cylinder volume is slow. That is, continuous post-injection is performed during a period when the rate of decrease in cylinder temperature is slow. Therefore, continuous post-injection has less impact on the exhaust gas heating properties due to the decrease in cylinder temperature accompanying the increase in cylinder volume compared to normal post-injection. Furthermore, while the exhaust valve 27 is open, oxygen is supplied from the exhaust passage 20 to the area around the tip of the in-cylinder injection valve 25. This improves combustibility in continuous post-injection compared to normal post-injection. Thus, continuous post-injection improves the exhaust gas heating properties.

Figure 3 is a flowchart illustrating the post-injection control performed by the ECU 40. The ECU 40 determines whether or not there is a request for exhaust gas temperature increase (step S1). For example, exhaust gas temperature increase is requested when there is a request for catalyst 29 temperature increase or when there is a request for operation in the supercharging region. If the answer in step S1 is No, this control terminates. If the answer in step S1 is Yes, the ECU 40 calculates the peak temperature during the expansion stroke and the volume at peak temperature, which is the internal volume of the cylinder at the peak temperature (step S2). The peak temperature is an example of a reference cylinder temperature. The volume at peak temperature is an example of a reference cylinder volume.

Figures 4A and 4B are maps for calculating peak temperature. Figure 4A is a map that defines the peak temperature according to the torque [Nm] and rotational speed [rpm] of engine 10. Figure 4A shows the case where the peak temperature [K] is between temperatures T1 and T3, and the higher the torque and rotational speed, the higher the calculated peak temperature. Figure 4B is a map that defines the relationship between the ignition timing difference [deg] and the peak temperature deviation [K]. The ignition timing difference is the difference obtained by subtracting the optimal ignition timing from the actual ignition timing. The peak temperature deviation is the amount subtracted from the peak temperature when ignition occurs at the optimal ignition timing. The larger the difference, the greater the negative value of the peak temperature deviation. That is, the more the actual ignition timing is retarded compared to the optimal ignition timing, the lower the calculated peak temperature will be.

Figures 4C and 4D are maps for calculating peak CA, which is the crank angle at peak temperature. Figure 4C is a map that defines peak CA according to the torque and rotational speed of engine 10. Figure 4C shows the case where peak CA is at angles A1 to A3, and the higher the torque and rotational speed, the larger the calculated peak CA value. Figure 4D is a map that defines the relationship between the ignition timing difference and the deviation amount of peak CA. The deviation amount of peak CA is the amount added to peak CA when ignition occurs at the optimal ignition timing. The larger the difference, the greater the positive value of the deviation amount of peak CA. That is, the more the actual ignition timing is retarded compared to the optimal ignition timing, the larger the calculated peak CA value will be.

Next, the ECU 40 calculates the volume at the permitted temperature, which is the internal volume of the cylinder when the internal temperature reaches the permitted temperature, using the following formula (1) (step S3).
Allowable temperature / Peak temperature = (Volume at peak temperature / Volume at allowable temperature) ^k-1 ... (1)
k [J/g·K] is the specific heat ratio of the gas inside the cylinder. Equation (1) is valid when it is assumed that the gas inside the cylinder undergoes an adiabatic change from the volume at peak temperature [cc] to the volume at the permitted temperature [cc]. The permitted temperature [K] is the upper limit of the cylinder temperature at which the heating of the exhaust gas by post-injection becomes effective. This is because if post-injection is started when the cylinder temperature is too high, the cylinder temperature will drop significantly as the cylinder volume decreases, reducing the heating effect of the exhaust gas by post-injection. Note that a spark plug 16 may or may not be used to ignite the fuel mixture. If a spark plug 16 is used, the permitted temperature may be set to a lower value than when it is not used.

Figure 5 is a map for calculating the specific heat ratio k. In Figure 5, the specific heat ratio k is defined according to the peak temperature. The higher the peak temperature, the smaller the calculated specific heat ratio k. Furthermore, the calculated specific heat ratio k is greater than 1.

Next, the ECU 40 calculates the permitted CA based on the volume at the permitted temperature (step S4). The permitted CA is the crank angle at the point when the cylinder temperature reaches the permitted temperature. The ECU 40 calculates the permitted CA based on the volume at the permitted temperature by referring to a map that defines the relationship between the cylinder volume and the crank angle.

Next, the ECU 40 determines whether the permitted CA is less than or equal to the limit CA (step S5). The limit CA is the upper limit of the crank angle at which post-injection can be initiated. If the answer in step S5 is No, this control process ends.

If the answer in step S5 is Yes, the ECU 40 calculates the in-cylinder temperature [K], which is the temperature inside the exhaust valve 27 while it is open, based on the following formula (2) (step S6).
Open valve temperature / Peak temperature = (Volume at peak temperature / Volume during open valve) ^k-1 …(2)

Equation (2) is valid when it is assumed that the gas inside the cylinder undergoes an adiabatic change from the volume at peak temperature to the volume during valve opening [cc]. Here, the volume during valve opening is the sum of the internal volume of the cylinder at the time the exhaust valve 27 opens and the volume of the passage from the exhaust valve 27 to a predetermined position in the exhaust passage 20. That is, the temperature during valve opening calculated by equation (2) is the steady-state gas temperature when the gas inside the cylinder increases from the volume at peak temperature to the volume during valve opening due to the adiabatic change. Therefore, the temperature during valve opening calculated by equation (2) is calculated to be lower than the actual internal cylinder temperature at the time the exhaust valve 27 opens.

Here, the volume during valve opening is calculated to a different value depending on the purpose of the exhaust gas temperature increase request. If the exhaust gas temperature increase request is for increasing boost pressure, the volume during valve opening is the sum of the internal volume of the exhaust valve 27 at the valve opening timing and the passage volume of the exhaust passage 20 from the exhaust valve 27 to the turbine 23B. This is because the increase in boost pressure is achieved by supplying high-temperature exhaust gas to the turbine 23B. If the exhaust gas temperature increase request is for increasing the temperature of the catalyst 29, the volume during valve opening is the sum of the internal volume of the exhaust valve 27 at the valve opening timing and the passage volume of the exhaust passage 20 from the exhaust valve 27 to the catalyst 29. This is because the temperature of the catalyst 29 is achieved by supplying high-temperature exhaust gas to the catalyst 29. Thus, the volume during valve opening is calculated according to the purpose of the exhaust gas temperature increase request. Therefore, the temperature during valve opening is calculated according to the purpose of the exhaust gas temperature increase request.

Next, the ECU 40 determines whether the calculated valve-open temperature is above the sustainable temperature (step S7). The sustainable temperature is the lower limit of the temperature at which the ignition of the hydrogen fuel-gas mixture can be ensured. As mentioned above, hydrogen fuel has superior ignition properties compared to gasoline or diesel fuel. Therefore, the sustainable temperature is set lower than when using gasoline or diesel fuel. Furthermore, when using a spark plug 16 for ignition of the mixture, the sustainable temperature is set lower than when not using a spark plug.

If the answer in step S7 is Yes, the ECU 40 performs the continuous post-injection described above (step S8). As mentioned above, the calculated valve-open temperature is lower than the actual in-cylinder temperature at the valve-opening timing of the exhaust valve 27. If the calculated valve-open temperature, which is lower than the actual in-cylinder temperature at the valve-opening timing, is above the sustainable temperature, then the actual in-cylinder temperature at the valve-opening timing is considered to be sufficiently higher than the sustainable temperature. Therefore, it is assumed that the ignition of the air-fuel mixture at the valve-opening timing is ensured, and continuous post-injection is performed.

If the answer in step S7 is No, the ECU 40 performs the normal post-injection described above (step S9). This is because if the temperature during valve opening is below the sustainable temperature, there is a risk that the fuel-air mixture will not ignite at the timing of the exhaust valve 27 opening.

Next, we will explain the calculation of the start CA [deg] and end CA [deg] of continuous post-injection. Figure 6A is an explanatory diagram for the calculation of the start CA and end CA of continuous post-injection. First, the amount of hydrogen fuel injected by continuous post-injection is calculated. The continuous post-injection amount [cc] is approximately a few percent to 10% of the main injection amount. Next, the injection time [s] is calculated by dividing the continuous post-injection amount by the post-injection flow rate [cc/s]. Next, the injection period b [deg] is calculated by converting the injection time into crank angle. The end CA is calculated by adding a predetermined duration a [deg] to the valve opening CA [deg]. The duration a is the duration of post-injection from the opening timing of the exhaust valve 27. The duration a is calculated to be a larger value the higher the engine rotation speed and the larger the intake air flow rate. The start CA is calculated by subtracting the above-mentioned injection period b from the end CA.

Figure 6B is an explanatory diagram for the calculation of the start CA and end CA of normal post-injection. The injection period b [deg] is calculated using the method described above. The end CA is calculated by subtracting a predetermined margin period c [deg] from the valve opening CA. The margin period c is the crank angle at which post-injection stops if it is stopped before the exhaust valve 27 opens, resulting in combustion in the cylinder ending before the valve opens. The margin period c is calculated as a larger value as the engine speed 10 increases. This is because, at higher engine speeds, if post-injection is not stopped earlier, combustion may continue even at the valve opening timing. The start CA is calculated by adding the injection period b to the end CA.

Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims.

1. Engine System 10. Engine (Internal Combustion Engine)
11 cylinders, 40 ECUs (fuel injection control unit, calculation unit, injection control unit)

Claims (4)

In a fuel injection control device for an internal combustion engine using hydrogen fuel, which performs post-injection by injecting hydrogen fuel from an in-cylinder injection valve during the expansion stroke,
A calculation unit that calculates the open temperature, which is the in-cylinder temperature of the exhaust valve of the internal combustion engine while it is open during the expansion stroke,
A fuel injection control device for an internal combustion engine using hydrogen fuel, comprising: an injection control unit that starts post-injection before the exhaust valve opens and continues it while the exhaust valve is open, when the crank angle at which the in-cylinder temperature reaches the upper limit of the in-cylinder temperature at which the heating of the exhaust by post-injection becomes effective is less than or equal to the upper limit of the crank angle at which post-injection can be started, and the temperature during valve opening is above the lower limit of the temperature at which the ignition of the mixture of hydrogen fuel and gas in the cylinder can be ensured. A turbocharger turbine is located in the exhaust passage connected to the internal combustion engine.
The calculation unit calculates the valve-opening temperature based on a reference cylinder temperature and reference cylinder volume at a predetermined timing during the expansion stroke before the exhaust valve opens, and a valve-opening volume which is the sum of the cylinder volume at the valve-opening timing when the exhaust valve opens and the passage volume of the exhaust passage from the exhaust valve to the turbine, according to claim 1 , a fuel injection control device for an internal combustion engine using hydrogen fuel. A catalyst is placed in the exhaust passage connected to the internal combustion engine.
The calculation unit calculates the valve-opening temperature based on a reference cylinder temperature and reference cylinder volume at a predetermined timing during the expansion stroke before the exhaust valve opens, and a valve-opening volume which is the sum of the cylinder volume at the valve-opening timing when the exhaust valve opens and the passage volume of the exhaust passage from the exhaust valve to the catalyst, according to claim 1 , a fuel injection control device for an internal combustion engine using hydrogen fuel. The aforementioned reference cylinder temperature is the peak temperature, which is the maximum value of the cylinder temperature during the expansion stroke.
The aforementioned standard cylinder volume is the cylinder volume when the internal temperature reaches the peak temperature.
The fuel injection control device for an internal combustion engine using hydrogen fuel according to claim 2 , wherein the calculation unit calculates the reference cylinder temperature and the reference cylinder volume based on the rotational speed, torque, and ignition timing of the internal combustion engine.