Patent Description:
A type of internal combustion engine using hydrogen as fuel is known. In such an internal combustion engine, hydrogen gas accumulates in the crankcase. It is thus desirable that the hydrogen concentration in the crankcase be below the lower limit of the combustible range. Therefore, for example, an internal combustion engine disclosed in <CIT> includes a ventilation fan that discharges hydrogen gas from the inside of the crankcase to the outside.

However, if a ventilation fan is provided, for example, a space for mounting the ventilation fan is required. In addition, for example, mounting an internal combustion engine equipped with a ventilation fan on a vehicle increases spatial constraint. Therefore, it is desired to reduce the hydrogen concentration in the crankcase without providing such a ventilation fan. Besides, <CIT> discloses a working gas circulation engine, <CIT> discloses a controller for internal combustion engine, and <CIT> discloses an internal combustion engine with casing ventilation.

In one general aspect, a controller for an internal combustion engine is provided, as defined in claim <NUM>. The internal combustion engine uses hydrogen as fuel and includes a coupling passage that connects a crankcase and an intake passage to each other. The controller is configured to execute a control of causing an air-fuel ratio of an air-fuel mixture to be lower when a target output of the internal combustion engine is relatively high than when the target output is relatively low, and a pressure reduction process of reducing a pressure in the intake passage when the target output is less than a specific value. The pressure reduction process is a process of reducing the pressure in the intake passage to be lower than that before an execution of the pressure reduction process.

In another general aspect, a control method for an internal combustion engine is provided, as defined in claim <NUM>. The internal combustion engine uses hydrogen as fuel and includes a coupling passage that connects a crankcase and an intake passage to each other. The control method includes: executing a control of causing an air-fuel ratio of an air-fuel mixture to be lower when a target output of the internal combustion engine is relatively high than when the target output is relatively low; and executing a pressure reduction process of reducing a pressure in the intake passage when the target output is less than a specific value. The pressure reduction process is a process of reducing the pressure in the intake passage to be lower than that before an execution of the pressure reduction process.

Modifications of the methods, apparatuses, and/or systems described are apparent to one of ordinary skill in the art. Sequences of operations are exemplary, and may be changed as apparent to one of ordinary skill in the art, except for operations necessarily occurring in a certain order.

A controller <NUM> for an internal combustion engine <NUM> mounted on vehicle <NUM> according to one embodiment will now be described.

As shown in <FIG>, the internal combustion engine <NUM> mounted on the vehicle <NUM> includes a cylinder block <NUM>, a cylinder head <NUM>, a head cover <NUM>, and an oil pan <NUM>. The cylinder block <NUM> includes a cylinder <NUM> in which a piston <NUM> is disposed to reciprocate.

The cylinder head <NUM> includes an intake port <NUM> that conducts intake air into a combustion chamber <NUM> of the internal combustion engine <NUM> and an exhaust port <NUM> that discharges exhaust gas from the combustion chamber <NUM>. The intake port <NUM> is provided with an intake valve <NUM>. The drive system of the intake valve <NUM> is provided with an intake-side variable valve timing mechanism <NUM>, which is a variable valve actuation mechanism that changes valve timing (opening/closing timing) of the intake valve <NUM>. The exhaust port <NUM> is provided with an exhaust valve <NUM>. The drive system of the exhaust valve <NUM> is provided with an exhaust-side variable valve timing mechanism <NUM>, which is a variable valve actuation mechanism that changes valve timing (opening/closing timing) of the exhaust valve <NUM>.

The cylinder head <NUM> also includes a port injection valve <NUM> that injects hydrogen as fuel into the intake port <NUM>, a direct injection valve <NUM> that directly injects hydrogen into the combustion chamber <NUM>, and an ignition plug (not shown).

A crankcase <NUM> is provided below the cylinder block <NUM>. The crankcase <NUM> accommodates a crankshaft <NUM>, which is an output shaft of the internal combustion engine <NUM>. An oil pan <NUM> that stores lubricant is provided in a lower portion of the crankcase <NUM>.

An intake manifold <NUM>, which includes a surge tank <NUM>, is connected to the upstream side of intake port <NUM>. An intake pipe <NUM> is connected to the upstream side of the surge tank <NUM>. The intake pipe <NUM>, the surge tank <NUM>, and the intake manifold <NUM> form an intake passage of the internal combustion engine <NUM>.

The intake pipe <NUM> is provided with an air cleaner <NUM>, an air flow meter <NUM>, a compressor wheel 24C of a forced-induction device <NUM>, an intercooler <NUM>, a boost pressure sensor <NUM>, and a throttle valve <NUM> arranged in that order from the upstream side to the downstream side of the intake pipe <NUM>. The forced-induction device <NUM> is driven using exhaust gas discharged from the combustion chamber <NUM>. The surge tank <NUM> is provided with an intake pressure sensor <NUM>. The opening degree of the throttle valve <NUM> is changed by an electric motor.

The air cleaner <NUM> filters intake air taken into the intake pipe <NUM>. The forced-induction device <NUM> compresses air in the intake pipe <NUM>. The intercooler <NUM> cools the air that has passed through the compressor wheel 24C. The throttle valve <NUM> regulates the amount of intake air by adjusting the opening degree.

The air flow meter <NUM> detects an intake air amount GA. The boost pressure sensor <NUM> detects a boost pressure PTC at a downstream side of the compressor wheel 24C in the intake pipe <NUM>. The intake pressure sensor <NUM> detects an intake pressure PIM, which is a pressure in the surge tank <NUM>.

An exhaust passage <NUM> is connected to the downstream side of the exhaust port <NUM>. A housing that accommodates a turbine wheel 24T of the forced-induction device <NUM> is connected to an intermediate portion of the exhaust passage <NUM>. A bypass passage <NUM> connects a section of the exhaust passage <NUM> on the upstream side of the turbine wheel 24T to a section of the exhaust passage <NUM> on the downstream side of the turbine wheel 24T. A wastegate valve (hereinafter, referred to as WGV) <NUM> is provided in the bypass passage <NUM>. The opening degree of the WGV <NUM> is adjusted by an actuator. The WGV <NUM> is a valve that adjusts the amount of exhaust gas flowing through the bypass passage <NUM>. As the opening degree of the WGV <NUM> increases, the amount of exhaust gas that bypasses the turbine wheel 24T and passes through the bypass passage <NUM> increases. Accordingly, the boost pressure of the intake air, which is increased by the forced-induction device <NUM>, decreases.

The internal combustion engine <NUM> is provided with a blow-by gas treating device, which treats gas leaking from the combustion chamber <NUM> into the crankcase <NUM> during a compression stroke or a combustion stroke, that is, so-called blow-by gas. The blow-by gas treating device includes a suction passage <NUM> configured to conduct the blow-by gas in the crankcase <NUM> to a main separator <NUM>, which is an oil separator installed in the head cover <NUM>. The end of the suction passage <NUM> connected to the main separator <NUM> opens in the crankcase <NUM>.

The main separator <NUM> is connected to the surge tank <NUM> via a positive crankcase ventilation (PCV) valve <NUM>, which is a differential pressure regulating valve, and a PCV passage <NUM>. The PCV valve <NUM> opens when the pressure in the surge tank <NUM> becomes lower than the pressure in the main separator <NUM>, thereby allowing the blow-by gas to flow from the main separator <NUM> to the surge tank <NUM>. The suction passage <NUM>, the main separator <NUM>, the PCV valve <NUM>, and the PCV passage <NUM> form a coupling passage that connects the surge tank <NUM>, which forms part of the intake passage, to the crankcase <NUM>.

For example, when the boost pressure of the forced-induction device <NUM> is relatively low, the pressure in the surge tank <NUM> is lower than the pressure in the main separator <NUM>. Accordingly, the blow-by gas in the crankcase <NUM> is drawn into the surge tank <NUM> via the suction passage <NUM>, the main separator <NUM>, the PCV valve <NUM>, and the PCV passage <NUM>. The drawn-in blow-by gas is delivered to the combustion chamber <NUM> together with the intake air and burned therein.

An ejector <NUM> is connected to the main separator <NUM> via a connection passage <NUM>. The ejector <NUM> is provided in the bypass passage <NUM>. The bypass passage <NUM> connects a section of the intake pipe <NUM> on the upstream side of the compressor wheel 24C to a section of the intake pipe <NUM> on the downstream side of the compressor wheel 24C. The ejector <NUM> includes a constriction for generating a negative pressure by the Venturi effect.

The blow-by gas treating device is provided with an atmosphere introducing passage <NUM> for drawing in intake air into the crankcase <NUM> for scavenging. One of the opposite ends the atmosphere introducing passage <NUM> is connected to a section of the intake pipe <NUM> between the air cleaner <NUM> and the compressor wheel 24C. The atmosphere introducing passage <NUM> extends through the head cover <NUM>, passes through the inside of the cylinder head <NUM> and the cylinder block <NUM>, and is connected to the crankcase <NUM>. An atmosphere-side separator <NUM>, which is an oil separator installed in the head cover <NUM>, is provided in the atmosphere introducing passage <NUM>.

When the boost pressure of the forced-induction device <NUM> is relatively high, air flows through the bypass passage <NUM> from the downstream side to the upstream side of the compressor wheel 24C, so that a negative pressure is generated in the ejector <NUM>. Due to the negative pressure generated in the ejector <NUM>, the blow-by gas in the crankcase <NUM> is drawn into the ejector <NUM> through the suction passage <NUM>, the main separator <NUM>, and the connection passage <NUM>. The blow-by gas drawn into the ejector <NUM> is conducted together with air into a section of the intake pipe <NUM> on the upstream side of the compressor wheel 24C via the bypass passage <NUM>. The blow-by gas drawn into the intake pipe <NUM> is delivered to the combustion chamber <NUM> together with the intake air and burned therein.

The controller <NUM> controls the internal combustion engine <NUM>. The controller <NUM> operates various devices to be operated, such as the throttle valve <NUM>, the port injection valve <NUM>, the direct injection valve <NUM>, the ignition plug, the intake-side variable valve timing mechanism <NUM>, the exhaust-side variable valve timing mechanism <NUM>, and the WGV <NUM>.

The controller <NUM> includes a central processing unit (hereinafter, referred to as a CPU) <NUM> and a memory <NUM>, which stores programs and data that are used in control operations. The controller <NUM> executes various types of control operations by causing the CPU <NUM> to execute programs stored in the memory <NUM>.

The controller <NUM> receives detection signals from the air flow meter <NUM>, the boost pressure sensor <NUM>, and the intake pressure sensor <NUM>. The controller <NUM> also receives detection signals from a crank angle sensor <NUM>, which detects the rotational angle of the crankshaft <NUM> (crank angle). The controller <NUM> calculates an engine rotation speed NE based on a detection signal of the crank angle sensor <NUM>. Furthermore, the controller <NUM> receives detection signals from a vehicle speed sensor <NUM>, which detects a vehicle speed SP of the vehicle <NUM> mounting the internal combustion engine <NUM>, and an accelerator operation amount sensor <NUM>, which detects an accelerator operation amount ACP of an accelerator pedal. The controller <NUM> calculates an engine load factor KL based on the engine rotation speed NE and the intake air amount GA. The engine load factor KL is a parameter that determines the amount of air filling the combustion chamber <NUM>, and is the ratio of the inflow air amount per combustion cycle in one cylinder to a reference inflow air amount. The reference inflow air amount may be varied in accordance with the engine rotation speed NE.

The controller <NUM> calculates a target output Pe, which is a target value of an output required to be produced by the internal combustion engine <NUM>, based on the accelerator operation amount ACP and the vehicle speed SP. The controller <NUM> executes a control of causing the air-fuel ratio of the air-fuel mixture to be lower when the target output Pe is relatively high than when the target output Pe is relatively low. For example, when the target output Pe is a first value, the controller <NUM> executes a control of causing the air-fuel ratio of the air-fuel mixture to be lower than that when the target output Pe is a second value, which is lower than the first value. More specifically, the controller <NUM> basically maintains the throttle valve <NUM> at an opening degree greater than or equal to a specified value, for example, at an opening degree close to the fully opened state, and sets a required injection amount Qd such that the required injection amount Qd increases as the target output Pe increases. The required injection amount Qd is a target value of the total amount of fuel injected from the port injection valve <NUM> and the direct injection valve <NUM>. Then, the controller <NUM> controls the port injection valve <NUM> and the direct injection valve <NUM> such that the required injection amount Qd is obtained. As described above, in the internal combustion engine <NUM>, basically, the output adjustment is performed by changing the air-fuel ratio of the air-fuel mixture through adjustment of not the intake air amount but the fuel injection amount.

The controller <NUM> calculates respective target valve timings of the intake valve <NUM> and the exhaust valve <NUM> based on the engine rotation speed NE, the engine load factor KL, and the like. The controller <NUM> performs drive control of the intake-side variable valve timing mechanism <NUM> and the exhaust-side variable valve timing mechanism <NUM> based on the respective target valve timings and the like.

The controller <NUM> calculates a target boost pressure PTCp based on the engine rotation speed NE, the engine load factor KL, and the like. The controller <NUM> performs a boost pressure control of the forced-induction device <NUM> by adjusting the opening degree of the WGV <NUM> based on the target boost pressure PTCp and the like.

As described above, during operation of the internal combustion engine <NUM>, the throttle valve <NUM> is basically maintained at an opening degree close to the fully opened state. Therefore, the state in which the pressure in the intake passage decreases is limited, and the discharge of blow-by gas from the crankcase <NUM> to the surge tank <NUM> via the PCV passage <NUM> and the like is unlikely to proceed. Hydrogen gas contained in the blow-by gas is likely to be accumulated in the crankcase <NUM>. If hydrogen gas is accumulated in the crankcase <NUM>, the hydrogen gas may leak to the atmosphere during maintenance of the internal combustion engine <NUM>. For example, such leakage of hydrogen gas is likely to occur when the amount of the lubricant stored in the oil pan <NUM> is checked by an oil level gauge or when the ignition plug is removed for inspection.

Therefore, in order to reduce the hydrogen concentration in the crankcase <NUM>, the controller <NUM> executes a pressure reduction process. The pressure reduction process is a process of reducing the pressure in the intake passage when the target output Pe is relatively low and is less than a predetermined specific value. When the internal combustion engine <NUM> is in an idling state or immediately before the vehicle <NUM> stops, the target output Pe is relatively low. Therefore, in the present embodiment, it is determined that the target output Pe is less than the specific value when the internal combustion engine <NUM> is in an idling state or immediately before the vehicle <NUM> stops.

<FIG> shows a processing procedure for executing the pressure reduction process. The processes shown in <FIG> are implemented by the CPU <NUM> repeatedly executing programs stored in the memory <NUM> at specific intervals. In the following description, the number of each step is represented by the letter S followed by a numeral.

In the series of processes shown in <FIG>, the CPU <NUM> first determines whether the current engine operating state is an idling state (S100). In the process of the S100, the CPU <NUM> acquires the accelerator operation amount ACP, for example, and determines that the engine operating state is an idling state if the acquired accelerator operation amount ACP is <NUM>.

When it is determined that the engine operating state is an idling state (S100: YES), the CPU <NUM> determines whether the vehicle <NUM> is in a stopped state (S110). In the process of S110, the CPU <NUM> determines that the vehicle <NUM> is in a stopped state if a state in which the vehicle speed SP is <NUM> has continued for a specified time, for example.

When it is determined that the vehicle <NUM> is in a stopped state (S110: YES), the CPU <NUM> executes the pressure reduction process (S160). As the pressure reduction process, the CPU <NUM> executes an opening degree changing process of reducing the current opening degree of the throttle valve <NUM> by an amount corresponding to a specified value α. The specified value α is a predetermined value that is required to reduce the pressure in the surge tank <NUM> to a pressure required to discharge blow-by gas through the PCV passage <NUM>. The CPU <NUM> executes the opening degree changing process by controlling the opening degree of the throttle valve <NUM>.

When a negative determination is made in the process of S100 or when a negative determination is made in the process of S110, the CPU <NUM> executes the process of S120 and the subsequent processes.

In the process of S120, the CPU <NUM> determines whether the current vehicle speed SP is less than a threshold SPref. The threshold SPref is a predetermined value. The value of the threshold SPref is set such that it can be determined that the vehicle speed SP is low enough to determine that the vehicle <NUM> is about to stop based on the fact that the vehicle speed SP is less than the threshold SPref.

When it is determined that the vehicle speed SP is less than the threshold SPref (S120: YES), the CPU <NUM> determines whether the accelerator operation amount ACP is less than a threshold ACPref (S130). The threshold ACPref is a predetermined value. The value of the threshold ACPref is set such that it can be determined that the accelerator operation amount ACP is small enough to determine that the vehicle <NUM> is about to stop based on the fact that the accelerator operation amount ACP is less than the threshold ACPref.

When it is determined that the accelerator operation amount ACP is less than the threshold ACPref (S130: YES), the CPU <NUM> determines whether an accelerator amount of change ACPH is less than a threshold ACPHref (S140). The accelerator amount of change ACPH is an amount of change of the accelerator operation amount ACP per unit time. The threshold ACPHref is a predetermined value. The value of the threshold ACPHref is set such that it can be determined that the accelerator amount of change ACPH is small enough to determine that the vehicle <NUM> is about to stop based on the fact that the accelerator amount of change ACPH is less than the threshold ACPHref.

When it is determined that the accelerator amount of change ACPH is less than the threshold ACPHref (S140: YES), the CPU <NUM> executes the process of S150. In the process of S150, the CPU <NUM> determines whether a duration time TP, which is time during which a state in which all of the determinations of S120, S130, and S140 are affirmative continues, is longer than or equal to a threshold TPref. The threshold TPref is a predetermined value. The value of the threshold TPref is set such that it can be determined that the affirmative determinations in the processes of S120, S130, and S140 are not temporary but stable based on the fact that the duration time TP is longer than or equal to the threshold TPref.

When it is determined that the duration TP is longer than or equal to the threshold TPref (S150: YES), the CPU <NUM> executes the process of S160 described above to execute the pressure reduction process.

When the process of the S160 is completed, or when a negative determination is made in the process of any of processes of S120, S130, S140, and S150, the CPU <NUM> temporarily suspends the series of processes shown in <FIG>.

Operation and advantages of the present embodiment will now be described.

The above-described embodiment may be modified as follows. The above-described embodiment and the following modifications can be combined as long as the combined modifications remain technically consistent with each other.

To determine whether the target output Pe is less than the specific value, the processes of S100 and S110 and the processes of S120, S130, S140, and S150 shown in <FIG> are executed. However, whether the target output Pe is less than the specific value may be determined based on other conditions.

It may be determined that the target output Pe is less than a predetermined specific value by comparing the target output Pe with the specific value.

Although the process of reducing the opening degree of the throttle valve <NUM> is executed as the pressure reduction process, another process may be executed.

The process of S200 shown in <FIG> may be executed as the pressure reduction process. That is, as the pressure reduction process, a valve timing changing process may be executed to advance the current valve timing of the intake valve <NUM> by an amount corresponding to a specified value β. The specified value β is a predetermined value of an advanced amount of the opening timing of the intake valve <NUM> that is required to reduce the pressure in the surge tank <NUM> to a pressure required to discharge blow-by gas through the PCV passage <NUM>. The CPU <NUM> executes the valve timing changing process through control of the intake-side variable valve timing mechanism <NUM>. When the opening timing of the intake valve <NUM> is advanced in this manner, the amount of air drawn into the cylinder from the surge tank <NUM> and the intake manifold <NUM> is increased in the intake stroke, so that the amount of air in the surge tank <NUM> decreases. When the amount of air in the surge tank <NUM> decreases, the pressure in the surge tank <NUM> decreases. Therefore, also in this modification, the pressure in the surge tank <NUM> is reduced. When this modification is employed, the variable valve actuation mechanism provided in the drive system of the intake valve <NUM> may include a mechanism capable of changing the valve opening timing of the intake valve <NUM>.

The process of S300 shown in <FIG> may be executed as the pressure reduction process. That is, as the pressure reduction process, a process of reducing the current boost pressure of the forced-induction device <NUM> by an amount corresponding to a specified value γ may be executed. The specified value γ is a predetermined value of a reduction amount of the boost pressure that is required to reduce the pressure in the surge tank <NUM> to a pressure required to discharge blow-by gas through the PCV passage <NUM>. The CPU <NUM> executes a process of reducing the boost pressure by the amount corresponding to the specified value γ by increasing the opening degree of the WGV <NUM> through the opening degree adjustment of the WGV <NUM> and increasing the amount of exhaust gas bypassing the turbine wheel 24T. When the boost pressure is reduced in this manner, the pressure in the intake passage downstream of the compressor wheel 24C is reduced, so that the pressure in the surge tank <NUM> is also reduced. Therefore, also in this modification, the pressure in the surge tank <NUM> is reduced.

The boost pressure may be reduced in a different manner. In a case in which the forced-induction device <NUM> is a variable displacement forced-induction device including a nozzle vane, the boost pressure may be reduced by an amount corresponding to the specified value γ through a change in the opening degree of the nozzle vane. Further, in a case in which the forced-induction device <NUM> is an electric forced-induction device in which the compressor wheel 24C is rotated by an electric motor, the boost pressure may be reduced by the specified value γ through a change in the rotation speed of the electric motor.

As the above-described pressure reduction process, at least one of the process of S160 shown in <FIG>, the process of S200 shown in <FIG>, and the process of S300 shown in <FIG> may be executed.

The expression "at least one" as used herein means "one or more" of desired options. As an example, the expression "at least one" as used herein means "only one option" or "both of two options" if the number of options is two. As another example, the expression "at least one" used herein means "only one option" or "a combination of any two or more options" if the number of options is three or more.

Although the PCV passage <NUM> is connected to the surge tank <NUM>, the PCV passage <NUM> may be connected to any section of the intake passage if the section is downstream of the throttle valve <NUM>.

The internal combustion engine <NUM> may include only one of the port injection valve <NUM> and the direct injection valve <NUM>.

If the process of S300 shown in <FIG> is not executed, the internal combustion engine <NUM> does not necessarily need to include the forced-induction device <NUM>.

If the process of S200 shown in <FIG> is not executed, the internal combustion engine <NUM> does not necessarily need to include the intake-side variable valve timing mechanism <NUM>.

The internal combustion engine <NUM> does not necessarily need to include the exhaust-side variable valve timing mechanism <NUM>.

The controller is not limited to a device that includes the CPU <NUM> and the memory <NUM>, and executes software processing. For example, the controller may include a dedicated hardware circuit (e.g. an application specific integrated circuit: ASIC) that executes at least part of the processes executed in the above-described embodiment. That is, the controller may be processing circuitry that has any one of the following configurations (a) to (c).

One or any desired number of software processing devices that each include a processor and a program storage device and one or any desired number of dedicated hardware circuits may be provided.

Claim 1:
A controller (<NUM>) for an internal combustion engine (<NUM>) mounted on a vehicle (<NUM>) and using hydrogen as fuel, wherein
the internal combustion engine (<NUM>) includes a coupling passage (<NUM>, <NUM>, <NUM>, <NUM>) that connects a crankcase (<NUM>) and an intake passage (<NUM>, <NUM>, <NUM>) to each other, the intake passage (<NUM>, <NUM>, <NUM>) includes a throttle valve (<NUM>)
the controller (<NUM>) is configured to execute
a control of causing the throttle valve (<NUM>) to maintain at an opening degree close to a fully opened state during operation of the internal combustion engine (<NUM>),
a control of causing an air-fuel ratio of an air-fuel mixture to be lower when a target output of the internal combustion engine (<NUM>) is relatively high than when the target output is relatively low, and
a pressure reduction process of reducing a pressure in the intake passage (<NUM>, <NUM>, <NUM>) in response to a determination that the internal combustion engine (<NUM>) is in an idling state and the vehicle (<NUM>) is in a stopped state or that the vehicle (<NUM>) is about to stop, and
the pressure reduction process is a process of reducing the pressure in the intake passage (<NUM>, <NUM>, <NUM>) to be lower than that before an execution of the pressure reduction process.