Fuel injection control device for an internal combustion engine using hydrogen fuel

Abstract

To provide a fuel injection control device of an internal combustion engine using hydrogen fuel improved in temperature rise performance of exhaust gas.SOLUTION: A fuel injection control device of an internal combustion engine using hydrogen fuel in which post injection for injecting hydrogen fuel from an in-cylinder injection valve is executed in an expansion stroke, includes a calculating section for calculating a valve open time temperature which is an in-cylinder temperature at opening of an exhaust valve of the internal combustion engine in the expansion stroke, and an injection control section for starting the post injection before the exhaust valve is opened and continuing the post injection even while the exhaust valve is opened on the basis of the valve open time temperature.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a fuel injection control device for an internal combustion engine using hydrogen fuel.

Background Art

[0002] In an internal combustion engine using gasoline or light oil, post injection may be performed to inject fuel from an in-cylinder injection valve during the expansion stroke. By performing post injection, the exhaust gas temperature can be raised, and the warm-up of the catalyst can be promoted and the supercharging pressure can be increased (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Hydrogen fuel may be used as the fuel for an internal combustion engine. Hydrogen fuel has better ignition properties compared to gasoline and light oil. Therefore, when using hydrogen fuel, there is room to improve the exhaust gas temperature increase compared to when using gasoline or light oil.

[0005] Therefore, an object of the present invention is to provide a fuel injection control device for an internal combustion engine using hydrogen fuel with improved exhaust gas temperature increase.

Means for Solving the Problems

[0006] The above objective can be achieved by a fuel injection control device for an internal combustion engine using hydrogen fuel, which performs post-injection, injecting hydrogen fuel from an in-cylinder injection valve during the expansion stroke, comprising: a calculation unit that calculates the in-cylinder temperature, which is the temperature inside the cylinder while the exhaust valve of the internal combustion engine is open during the expansion stroke; and an injection control unit that, based on the in-cylinder temperature, starts the post-injection before the exhaust valve opens and continues it while the exhaust valve is open.

[0007] The injection control unit may continue the post-injection even while the exhaust valve is open if the temperature during valve opening is above a lower limit that ensures the ignition of the mixture of hydrogen fuel and gas in the cylinder.

[0008] A turbocharger turbine is located 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 a volume during valve opening 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.

[0009] A catalyst is placed 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 a volume during valve opening 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.

[0010] 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. [Effects of the Invention]

[0011] 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. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram of the engine system. [Figure 2] Figure 2 is a timing chart illustrating the change in in-cylinder temperature during post-injection control. [Figure 3] Figure 3 is a flowchart illustrating the post-injection control performed by the ECU. [Figure 4] 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] Figure 5 is a map for calculating the specific heat ratio k. [Figure 6] Figure 6A is an explanatory diagram for calculating the start and end CA of continuous post-injection, and Figure 6B is an explanatory diagram for calculating the start and end CA of normal post-injection. [Modes for carrying out the invention]

[0013] 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, etc. 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 in the cylinder 11 is connected to the 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 top of the cylinder block. A combustion chamber 15 is formed between the cylinder head and the upper end of the piston 12, where a spark plug 16 is located. 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.

[0014] The intake passage 19 is equipped with an air flow meter 21, a throttle valve 22, and a 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 an intake manifold located downstream of the throttle valve 22, and this branched section is connected to each combustion chamber 15. In addition, an in-cylinder injection valve 25 for injecting hydrogen fuel into the cylinder 11 is provided.

[0015] The turbine 23B of the supercharger 23 is located in the exhaust passage 20. The exhaust gas generated by 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 operated by the introduced exhaust gas, the compressor 23A on the intake passage 19 side is activated in conjunction, and the air in the intake passage 19 is compressed. The compression of the air increases the pressure in the intake passage 19, i.e., the intake pressure, and this pressure efficiently fills the combustion chamber 15 with air.

[0016] 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 adjusts the boost pressure of the supercharger 23. Downstream of the wastegate valve 34 is a catalyst 29 that purifies the exhaust gas.

[0017] The engine 10 is equipped with intake valves 26 and exhaust valves 27 that open and close intake ports 17 and exhaust ports 18, respectively, which are connected to intake passage 19 and exhaust passage 20. The intake valves 26 and exhaust valves 27 open and close in accordance with the rotation of the intake-side camshaft and exhaust-side camshaft, 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 in synchronization with the rotation of the crankshaft 13, that is, in accordance with the reciprocating movement of each piston 12.

[0018] The engine system 1 includes various sensors. Specifically, they are the crank angle sensor 30, the accelerator opening sensor 31c, the air flow meter 21, the throttle opening sensor 32, etc.

[0019] The ECU 40 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and a storage device. The ECU 40 controls the engine 10 by executing programs stored in the ROM or the storage device. The ECU 40 is an example of a fuel injection control device and executes post-injection control described later. The post-injection control is functionally realized by the CPU, the ROM, the RAM, and the storage device, and is executed by a calculation unit and an injection control unit.

[0020] Post-injection is a fuel injection executed by the in-cylinder injection valve 25 during the expansion stroke after the main injection. The main injection is, for example, a fuel injection performed during the intake stroke and is a fuel injection for outputting a desired torque to the engine 10. Post-injection is a fuel injection aimed at raising the temperature of the exhaust. The post-injection in this embodiment includes continuous post-injection and normal post-injection. Note that when simply referred to as post-injection in this specification, both continuous post-injection and normal post-injection are included. Continuous post-injection is a post-injection that starts injection before the opening of the exhaust valve 27 and continues injection during the valve opening. Normal post-injection is a post-injection that injects from before the opening of the exhaust valve 27 and ends injection before the opening of the exhaust valve 27. Details will be described later.

[0021] The ECU 40 performs predetermined calculations based on the detection signals of the various sensors described above. For example, based on the detection signal of the crank angle sensor 30, the rotational phase of the crankshaft 13, that is, the crank angle, is calculated, and further, the rotational speed of the engine 10 is calculated. Based on the detection signal of the accelerator opening sensor 31c, the opening of the accelerator pedal operated by the driver is calculated. Based on the detection signal of the air flow meter 21, the intake air amount is calculated.

[0022] [Post-injection Control] Figure 2 is a timing chart illustrating the change in in-cylinder temperature during post-injection control. The vertical axis represents in-cylinder temperature, and the horizontal axis represents crank angle. Figure 2 also shows the change in in-cylinder temperature when post-injection is not performed and when continuous post-injection is performed. Here, the crank angle at which the maximum in-cylinder temperature, the peak temperature, occurs is called the peak CA. The crank angle at the timing of the exhaust valve 27 opening 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.

[0023] When the fuel-air mixture is ignited in the latter half of the compression stroke after the main injection, the mixture burns and the in-cylinder temperature rises. The in-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 the internal volume of the cylinder during the expansion stroke, the in-cylinder temperature decreases from the peak temperature. When the crank angle reaches the starting CA, continuous post-injection begins. This causes the in-cylinder temperature to rise more than if post-injection had not been performed. Continuous post-injection continues even after the valve opens CA. When the crank angle reaches the ending CA, continuous post-injection ends.

[0024] Here, after valve opening CA, the cylinder and exhaust passage 20 are in communication, causing the cylinder temperature to decrease. When gasoline or diesel fuel is used, the ignition of the fuel mixture deteriorates at the cylinder temperature after valve opening CA. However, in this embodiment, hydrogen fuel, which has better ignition properties than gasoline or diesel fuel, is used. For this reason, continuous post-injection is continued even after valve opening CA under predetermined conditions.

[0025] The exhaust gas heating properties of continuous post-injection and normal post-injection will be explained. In normal post-injection, as described above, injection starts 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 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 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 than normal post-injection. In addition, while the exhaust valve 27 is open, oxygen is supplied from the exhaust passage 20 side to the area around the tip of the in-cylinder injection valve 25. As a result, combustion is improved with continuous post-injection compared to normal post-injection. Thus, the exhaust gas heating properties are improved with continuous post-injection.

[0026] 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 heating (step S1). For example, exhaust gas heating is requested when there is a request for heating of the catalyst 29 or when there is a request for operation in the supercharging region. If the answer in step S1 is No, this control is terminated. 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 internal cylinder temperature. The volume at peak temperature is an example of a reference internal volume of the cylinder.

[0027] 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 the higher the 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. In other words, the more the actual ignition timing is retarded compared to the optimal ignition timing, the lower the calculated peak temperature will be.

[0028] 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 the higher the rotational speed, the larger the value of peak CA calculated. Figure 4D is a map that defines the relationship between the ignition timing difference and the amount of deviation of peak CA. The amount of deviation 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 of peak CA. That is, the more the actual ignition timing is retarded compared to the optimal ignition timing, the larger the value of peak CA calculated.

[0029] Next, the ECU40 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.

[0030] 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.

[0031] Next, the ECU40 calculates the permitted CA based on the volume at the permitted temperature (step S4). The permitted CA is the crank angle at which the cylinder temperature reaches the permitted temperature. The ECU40 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.

[0032] Next, the ECU40 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 started. If the answer in step S5 is No, this control is terminated.

[0033] 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)

[0034] 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. In other words, the temperature during valve opening calculated by equation (2) is the steady-state gas temperature when the gas inside the cylinder has increased 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.

[0035] 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 purpose of the exhaust gas temperature increase request is to increase the boost pressure, the volume during valve opening is the sum of the internal volume of the exhaust valve 27 at the 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 purpose of the exhaust gas temperature increase request is to raise 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 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. In this way, the volume during valve opening is calculated according to the purpose of the exhaust gas temperature increase request. Consequently, the temperature during valve opening is calculated according to the purpose of the exhaust gas temperature increase request.

[0036] 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 mixture of hydrogen fuel and gas in the cylinder can be ensured. As mentioned above, hydrogen fuel has better ignition properties than gasoline or diesel fuel. For this reason, the sustainable temperature is set lower than when gasoline or diesel fuel is used. Furthermore, when a spark plug 16 is used to ignite the mixture, the sustainable temperature is set lower than when it is not used.

[0037] 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. For this reason, it is assumed that the ignition of the air-fuel mixture at the valve-opening timing is ensured, and continuous post-injection is performed.

[0038] 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.

[0039] Next, we will explain how to calculate the start CA [deg] and end CA [deg] of continuous post-injection. Figure 6A is an explanatory diagram for calculating 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 about 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]. Duration a is the duration of post-injection from the opening timing of the exhaust valve 27. 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.

[0040] 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 post-injection is stopped before the exhaust valve 27 opens, so that combustion in the cylinder ends before the valve opens. The margin period c is calculated to be a larger value the higher the rotational speed of the engine 10. This is because if post-injection is not stopped earlier at a higher rotational speed of the engine 10, there is a risk that combustion will continue even at the valve opening timing. The start CA is calculated by adding the injection period b to the end CA.

[0041] 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 present invention as described in the claims. [Explanation of Symbols]

[0042] 1. Engine System 10. Engine (internal combustion engine) 11 cylinders 40 ECU (Fuel Injection Control Unit, Calculation Unit, Injection Control Unit)

Claims

1. 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.

2. 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.

3. 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.

4. 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 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, as a fuel injection control device for an internal combustion engine using hydrogen fuel according to claim 2.

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