JP4711233B2 - Exhaust gas purification system for hydrogen engine - Google Patents

Description

  The present invention relates to an exhaust gas purification system for a hydrogen engine, and more particularly to an exhaust gas purification system for a hydrogen engine that uses hydrogen gas to purify specific components of the exhaust gas after combustion in the hydrogen engine.

At present, as an automobile power source, an electric vehicle using a fuel cell is considered to be promising, but a hydrogen engine that obtains power by directly burning hydrogen as a fuel in the engine is also considered promising.
The hydrogen engine is equipped with a hydrogen storage tank that stores hydrogen in a high pressure state in a vehicle, and burns hydrogen supplied from the hydrogen storage tank to obtain a driving force of the vehicle.
At this time, the hydrogen engine supplies fuel by directly injecting the hydrogen into the combustion chamber of the hydrogen engine using the pressure when hydrogen is stored in the hydrogen storage tank in a high pressure state.

Japanese Patent No. 3661555 JP-A-2-86915 JP-A-2-149714 JP 2002-13412 A Japanese Patent Laid-Open No. 2005-240656 No. 5-13937 No. 6-10129

By the way, in the conventional exhaust gas purification system of a hydrogen engine, when the excess air ratio of the air-fuel mixture (also referred to as “air-fuel ratio”) λ is “λ <1” during the operation of the hydrogen engine, During combustion, nitrogen in the air is reduced under an excess of hydrogen (also referred to as “rich”), and harmful ammonia (also referred to as “NH3”) is generated.
In other words, if you write a simple chemical formula,
H2 + O2 + N2 → H2O + NH3
It becomes.

Further, when the air-fuel ratio λ of the air-fuel mixture is “λ ≧ 1,” there is a disadvantage that a large amount of nitrogen oxide (also referred to as “NOx”) is exhausted as a harmful exhaust gas component in the exhaust gas. is there.
In other words, if you write a simple chemical formula,
H2 + O2 + N2 → H2O + NOx
It becomes.
In the above-described λ control of the exhaust gas purification system, when the air-fuel ratio λ of the air-fuel mixture is the stoichiometric air-fuel ratio, “λ = 1”. When hydrogen gas is used as fuel, the theoretical air-fuel ratio (A / F) when “λ = 1” is “A / F = 34.3”.

Further, in the case of a combustion gas that does not contain carbon monoxide (also referred to as “CO”) or hydrocarbon (also referred to as “HC”) as a reducing agent in the exhaust gas, a catalyst that is widely used in automobiles is used. There is an inconvenience that the processing apparatus cannot be used.
Moreover, as a NOx purification system in such a case, a lean NOx catalyst or the like has been put into practical use, but there are disadvantages in its purification performance and heat resistance.
Furthermore, the urea-filled NOx reduction system used in large diesel vehicles also has the disadvantage that it is necessary to add a device for supplying urea to the exhaust system.

An object of the present invention is to realize an exhaust gas purification system of a hydrogen engine that improves the purification of exhaust gas components by burning stored hydrogen gas in a hydrogen engine as fuel and also supplying it to exhaust gas after combustion. There is.
If it adds, it will be set as the combustion which suppresses discharge | emission of ammonia when hydrogen gas is primarily supplied to a hydrogen engine and burned.
Further, the purification of a specific component (also referred to as “nitrogen oxide” or “NOx”) of the exhaust gas that is secondarily supplied into the exhaust gas and increases with the suppression control is improved.
Furthermore, the consumption of hydrogen gas for maintaining the purification performance is reduced.
Through the above, the object is to improve fuel efficiency.

Therefore, in order to eliminate the above disadvantages, the present invention provides a hydrogen storage tank for storing hydrogen in a high pressure state, a hydrogen engine for burning hydrogen supplied from the hydrogen storage tank, and a catalyst provided in an exhaust pipe of the hydrogen engine. In an exhaust gas purification system for a hydrogen engine provided so that hydrogen gas can be supplied into the exhaust pipe during operation of the hydrogen engine, an upstream exhaust gas sensor for detecting an exhaust gas component is provided in the exhaust pipe upstream of the catalyst. An exhaust side hydrogen gas injection device for injecting hydrogen gas into the exhaust pipe is provided upstream of the upstream exhaust gas sensor, and a downstream side exhaust gas sensor for detecting exhaust gas components is provided in the exhaust pipe downstream of the catalyst. , the supply amount of hydrogen gas supplied to the hydrogen engine so that the exhaust gas based on the detection of the upstream exhaust gas sensor becomes a predetermined air-fuel ratio leaner While the feedback control, a control means for supplying a small amount of hydrogen gas than a hydrogen gas supplied to the hydrogen engine from the exhaust side hydrogen gas injection device is provided, the control means, the detection of the downstream exhaust gas sensor Based on the feedback correction control so as to correct the increase or decrease of the supplied hydrogen gas while monitoring the reduction rate of the hydrogen gas supplied from the exhaust-side hydrogen gas injection device to the exhaust gas after passing through the catalyst based on To do.

As described in detail above, according to the present invention, the combustion state is averaged and maintained on the lean side, so that the emission of NH3 among the exhaust gas components can be suppressed to a very low level.
Further, the increased NOx can be selectively reduced on the catalyst by the secondary supply of hydrogen gas, so that the purification efficiency by the catalyst can be maintained high in total.
Furthermore, the consumption of hydrogen gas to be secondarily supplied can be reduced.

As a result of the invention as described above, the control means feedback-controls the amount of hydrogen gas supplied to the hydrogen engine based on the detection of the upstream side exhaust gas sensor so that the exhaust gas has a predetermined lean air-fuel ratio.
Further, the control means controls to supply a smaller amount of hydrogen gas than the hydrogen gas supplied from the exhaust-side hydrogen gas injection device to the hydrogen engine.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

1 to 6 show an embodiment of the present invention.
In FIG. 2, reference numeral 1 denotes an exhaust gas purification system for a hydrogen engine.
The exhaust gas purification system 1 includes a hydrogen storage tank 2 that stores hydrogen in a high-pressure state (about several tens of MPa, for example, about 35 to 70 MPa), and a hydrogen engine 3 that combusts hydrogen supplied from the hydrogen storage tank 2. A catalyst provided in the exhaust pipe 4 of the hydrogen engine 3, such as a catalyst 5, is provided so that a trace amount of hydrogen gas can be supplied into the exhaust pipe 4 during operation of the hydrogen engine 3.
At this time, the hydrogen engine 3 employs in-cylinder direct injection fuel supply and is a four-cycle engine with a supercharger (also referred to as “turbocharger”) 23 described later.

As shown in FIGS. 2 and 3, the hydrogen engine 3 of the exhaust gas purification system 1 includes a cylinder block 6, a cylinder head 7, and a cylinder head cover 8 that are integrally formed.
A piston 9 is slidably provided on the cylinder block 6.
A combustion chamber 10 that cooperates with the cylinder head 7 is formed.
Further, the cylinder head 7 is provided with an intake camshaft 11 and an intake valve 12 driven by the intake camshaft 11 in an intake system.
Further, the cylinder head 7 is provided with an exhaust cam shaft 13 and an exhaust valve 14 driven by the exhaust cam shaft 13 in an exhaust system.

In the intake system of the hydrogen engine 3, an air cleaner 15, an intake pipe 16 that guides intake air from the air cleaner 15 to the hydrogen engine 3, a throttle body 18 having a throttle valve 17, and a surge tank 19 are integrated into a cylinder. An intake manifold 20 attached to the head 7 is sequentially connected.
On the other hand, in the exhaust system of the hydrogen engine 3, an exhaust manifold 21 attached to the cylinder head 7 so as to guide the exhaust from the hydrogen engine 3 is connected to the upstream side of the exhaust manifold 21. The exhaust pipe 4 in which the catalytic converter 22 to be accommodated is disposed is sequentially connected.

The hydrogen engine 3 is provided with a supercharger (also referred to as “turbocharger”) 23.
The supercharger 23 supercharges intake air from the air cleaner 15 side and supplies the supercharged air to the hydrogen engine 3 side.
The supercharger 23 is disposed in the supercharger case 24 in the exhaust pipe 4 between the compressor 25 disposed in the middle of the intake pipe 16 and the exhaust manifold 21 and the catalytic converter 22. And a turbine 26 rotating at the same time.
The exhaust flow to the turbine 26 is adjusted by a wastegate mechanism 28 having a wastegate valve (also referred to as “waistgate control VSV”) 27.
The intake pipe 16 between the compressor 25 and the throttle body 18 is provided with an intercooler 29 for cooling the intake air supercharged by the supercharger 23.

The hydrogen engine 3 is provided with a hydrogen gas injection system 30 that injects hydrogen gas.
The hydrogen gas injection system 30 includes an intake side hydrogen gas injection device 31 and an exhaust side hydrogen gas injection device 32.
At this time, the intake-side hydrogen gas injection device 31 employs in-cylinder direct injection fuel supply that directly injects hydrogen gas into the combustion chamber 10 in the intake system of the hydrogen engine 3.
The exhaust-side hydrogen gas injection device 32 injects hydrogen gas into the exhaust pipe 4.

The hydrogen gas injection system 30 includes the hydrogen storage tank 2, a hydrogen gas supply passage 33 connected to one end side of the hydrogen storage tank 2, and a pressure regulator 34 connected to the other end side of the hydrogen gas supply passage 33. .
At this time, the pressure regulator 34 has a switching function of two systems, and several hundred kPa of hydrogen gas stored in the hydrogen storage tank 2 in a high pressure state (about several tens of MPa, for example, about 35 to 70 MPa). It has a function of depressurizing (for example, about several atmospheres).
The intake side hydrogen gas injection device 31 includes a primary supply side passage 35 connected to the pressure regulator 34 at one end side, and a delivery pipe 36 attached to the cylinder head 7 connected to the other end side of the primary supply side passage 35. The primary supply side injector (also referred to as “in-cylinder injector”) 37 connected to the delivery pipe 36.
The exhaust-side hydrogen gas injection device 32 has a secondary supply side passage 38 connected at one end side to the pressure regulator 34 and the other end side of the secondary supply side passage 38 connected thereto. It comprises a secondary supply side injector 39 for injecting gas.

The hydrogen engine 3 is provided with an idle speed control device 40.
In this idle speed control device 40, a bypass passage 41 is provided so as to bypass the throttle valve 17 and communicate the inside of the throttle body 18 and the surge tank 19, and to the hydrogen engine 3 in the middle of the bypass passage 41. An ISC valve (also referred to as an “idle air amount control valve”) 42 for adjusting the amount of idle air is provided.

Further, an ignition coil 43 and a PCV valve 44 are attached to the cylinder head cover 8 of the hydrogen engine 3.
A tank side blowby gas passage 45 communicating with the inside of the surge tank 19 is connected to the PCV valve 44.
The cylinder head cover 8 is connected to a cleaner-side blow-by gas passage 46 communicating with the air cleaner 15.

A fuel pressure sensor 47 and an engine water temperature sensor 49 are attached to the hydrogen engine 3.
The fuel pressure sensor 47 is attached to the delivery pipe 36 and detects the fuel pressure to the primary supply side injector 37.
The engine water temperature sensor 49 detects the cooling water temperature in the cooling water passage 48 formed in a part of the hydrogen engine 3.

The throttle body 18 is provided with a throttle sensor 50 for detecting the throttle opening of the throttle valve 17, and one end side of the pressure guiding passage 51 is connected to the downstream side of the throttle valve 17.
An intake pressure sensor 52 that detects an intake pipe pressure on the downstream side of the throttle valve 17 is provided on the other end side of the pressure guide passage 51.
An intake temperature sensor 53 for detecting the temperature of intake air is attached to the surge tank 19.
An upstream exhaust gas sensor (also referred to as “air-fuel ratio sensor” or “λ sensor”) 54 that detects an exhaust gas component is disposed upstream of the catalytic converter 22, that is, on the exhaust pipe 4 upstream of the catalyst 5. The exhaust side hydrogen gas injection device 32 that injects hydrogen gas into the exhaust pipe 4 is provided upstream of the upstream side exhaust gas sensor 54.
Further, a downstream exhaust gas sensor (also referred to as “hydrogen (H2) sensor” or “NOx sensor”) 55 for detecting an exhaust gas component is provided in the exhaust pipe 4 on the downstream side of the catalyst 5.
At this time, on the exhaust side of the hydrogen engine 3, as shown in FIG. 2, the exhaust manifold 21, the turbine 26 of the supercharger 23, the upstream exhaust gas sensor 54, the catalytic converter 22, and the downstream exhaust sequentially from the upstream side. A gas sensor 55 is provided, and in order to inject hydrogen gas into the exhaust pipe 4 by the exhaust side hydrogen gas injection device 32, the secondary supply side injector 39 of the exhaust side hydrogen gas injection device 32 is supercharged. 23 at the downstream end of the exhaust manifold 21 upstream of the turbine 26.

The wastegate valve 27, the pressure regulator 34, the primary supply side injector 37 of the intake side hydrogen gas injection device 31, the secondary supply side injector 39 of the exhaust side hydrogen gas injection device 32, the ISC valve 42, the ignition coil 43, and the fuel. The pressure sensor 47, engine water temperature sensor 49, throttle sensor 50, intake pressure sensor 52, intake temperature sensor 53, upstream side exhaust gas sensor 54, and downstream side exhaust gas sensor 55 communicate with control means (also referred to as “ECM”) 56. is doing.
The control means 56 is in communication with a crank angle sensor 57 and a battery 60 via a main switch 58 and a fuse 59.
At this time, the crank angle sensor 57 detects the crank angle, and the control means 56 determines the fuel injection start timing.

Here, the hydrogen engine 3 adopting in-cylinder direct injection fuel supply will be additionally described.
The in-cylinder direct injection method is a preferable measure in the case of gaseous fuel (hydrogen gas or the like) in order to prevent atmospheric release at the time of stoppage or icing of the injector.
The direct injection type in-cylinder achieves high output, low fuel consumption, and low exhaust gas by directly injecting high-pressure fuel, that is, hydrogen gas, into the combustion chamber 10.
Further, as shown in FIG. 3, a tumble flow is generated by straightening the intake port 61 of the hydrogen engine 3 and the shape of the top of the piston 9, and the fuel injection timing is precisely controlled, so that the vicinity of the spark plug 62 is obtained. It is a weak stratified combustion system that forms a dense air-fuel mixture layer and enables stable combustion regardless of cooling and warming up.
As shown in FIG. 3, this weakly stratified combustion system employs a straight port upright up to the intake valve 12 in the shape of the intake port 61 to increase the flow rate of the intake air and to form an elliptical concave portion offset at the top of the piston 9. 63 generates a tumble flow (vertical swirl flow).
The fuel injection at this time has a penetrating force due to high pressure and an appropriate injection angle, and is performed directly in the combustion chamber 10 during the intake stroke.
The fuel injected into the combustion chamber 10 during the intake stroke is guided to a tumble flow, and as shown in FIG. 4, forms a mixture distribution in which the periphery of the spark plug 62 is a rich air-fuel ratio and the outer peripheral portion is a thin air-fuel ratio. The combustion chamber 10 as a whole is controlled to the stoichiometric air-fuel ratio, enabling stable combustion.

Further, in the fuel injection control of the hydrogen engine 3 adopting in-cylinder direct injection fuel supply, the injection timing and the injection time (in other words, “amount”) of the fuel injected from the primary supply side injector 37 are controlled. Then, an optimal amount of fuel is injected at an optimal time.
The fuel injection timing and the fuel injection time are determined by start-up injection control that is executed when the engine is started and post-start-up injection control that is executed during normal operation.
In addition, fuel cut control is performed according to the driving state in order to protect the engine and improve fuel efficiency.

The start-up injection control will be described.
The fuel injection timing in the start-up injection control is sequential injection at the injection timing (see the part A in FIG. 5) based on the crank angle sensor signal as shown in FIG. 5 when the engine speed is below a predetermined rotation speed. I do.
However, when the crank angle sensor signal rises at an extremely low temperature, divided injection is performed several times at regular intervals.
The fuel injection time in the start-up injection control is determined by adding various corrections such as engine speed correction and voltage correction to the start-up basic injection time determined by the coolant temperature.
Note that the basic injection time at start-up improves the startability by extending the injection time as the cooling water temperature is lower.

The post-startup injection control will be described.
The fuel injection timing in the post-startup injection control includes synchronous injection and asynchronous injection.
As shown in FIG. 6, in the synchronous injection, the sequential injection is performed at the injection timing (refer to the part A in FIG. 6) based on the crank angle sensor signal.
In addition, the asynchronous injection is not synchronized with the crank angle sensor signal at the time of deceleration fuel cut recovery or sudden acceleration, but temporarily performs simultaneous injection of all cylinders as shown by the thick shaded line B in FIG.
Further, the fuel injection time in the post-start injection control is determined by the intake pipe pressure and the engine speed, and the basic injection time is corrected by a signal from each sensor to obtain an optimum value according to the operating state. Determine the fuel injection time.
There are the following corrections.
(1) Voltage correction
In order to correct the delay in the injection timing due to the decrease in the battery voltage, the energization time to the injector is lengthened in accordance with the decrease in the battery voltage.
(2) Engine speed correction
The fuel injection time is corrected according to the engine speed.
(3) Intake air temperature correction
Correct the difference in air density due to changes in intake air temperature.
(4) A / F correction
The deviation from the target air-fuel ratio in each operating range is corrected.
(5) Feedback correction
Correction is made so as to keep the air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio from the oxygen level in the exhaust gas.
(6) Learning correction
Correction is made so that the base air-fuel ratio that shifts due to secular change or the like is maintained near the theoretical air-fuel ratio.
(7) Warm-up correction
The fuel injection amount is increased according to the cooling water temperature at the time of cooling, and the correction amount is gradually decreased as the warming-up proceeds.
(8) Atmospheric pressure correction
The deviation of the air-fuel ratio caused by the change in atmospheric pressure is corrected. The atmospheric pressure is an estimated value calculated from the intake pipe pressure and the engine speed.
(9) Throttle opening correction
The fuel injection time is corrected according to the change in the throttle opening.
(10) Purge concentration correction
The change in the air-fuel ratio when the fuel evaporative gas is introduced or cut is corrected.
(11) Acceleration increase / decrease decrease correction
The acceleration / deceleration state is detected, the correction amount is increased during acceleration to improve the acceleration performance, and the deceleration amount is decreased during deceleration to suppress exhaust gas and improve fuel efficiency.
(12) Increase correction immediately after starting
By increasing the amount immediately after starting and then gradually decreasing the correction amount, the drivability becomes smooth.

The control means 56 in this embodiment feedback-controls the supply amount of hydrogen gas supplied to the hydrogen engine 3 based on the detection of the upstream side exhaust gas sensor 54 so that the exhaust gas has a predetermined lean air-fuel ratio. The configuration is such that a smaller amount of hydrogen gas is supplied than the hydrogen gas supplied from the exhaust-side hydrogen gas injection device 32 to the hydrogen engine 3.
That is, the control means 56 determines the supply amount of hydrogen gas from the primary supply side injector 37 of the intake side hydrogen gas injector 31 to the hydrogen engine 3 and a predetermined air / fuel ratio on the lean side of the exhaust gas (for example, λ≈ 1.05), feedback control is performed based on the detection signal from the upstream side exhaust gas sensor 54.
The control means 56 supplies hydrogen gas supplied from the secondary supply side injector 39 of the exhaust side hydrogen gas injector 32 into the exhaust pipe 4 from the primary supply side injector 37 of the intake side hydrogen gas injector 31. The amount is smaller than the hydrogen gas supplied to the engine 3.
In basic hydrogen gas supply control, there is a relationship of primary supply amount >> secondary supply amount, and the secondary supply amount is very small compared to the primary supply amount. However, when the target of λ control by the feedback on the primary side is lean, the secondary supply amount increases depending on the degree of lean, so the secondary supply amount is relatively small compared to the primary supply amount. Sometimes.

  Further, the control means 56 monitors the reduction rate of the hydrogen gas supplied from the exhaust-side hydrogen gas injection device 32 to the exhaust gas after passing through the catalyst based on the detection of the downstream-side exhaust gas sensor 55, and supplies the supplied hydrogen gas. Feedback correction control is performed so as to correct the increase or decrease.

More specifically, the hydrogen engine 3 is an in-cylinder direct injection fuel supply.
Accordingly, the supply pressure (injection pressure) from the primary supply side injector 37 of the hydrogen gas that is the fuel must overcome the internal pressure of the combustion chamber (cylinder) when the fuel is injected over the compression stroke.
For this reason, when pressure is reduced by the pressure regulator 34, for example, it is necessary to make the pressure higher to some extent as compared to atmospheric pressure or supercharging pressure.
When fuel is injected without being proud of the compression stroke, the output may be relatively small and the supply pressure (injection pressure) may be small during lean combustion.
At this time, the supply pressure (injection pressure) from the secondary supply side injector 39 for secondary supply of hydrogen gas into the exhaust pipe 4 is also set to a certain level in consideration of the pressure of the exhaust gas of the supercharged engine. There is a need.
If the supply pressure is high, it is preferable to diffuse or penetrate the exhaust pipe 4, and the driving time of the secondary supply side injector 39 that is originally shorter than the primary supply side injector 37 can be further shortened.
In addition, since excess oxygen (O2) gas is partially converted to water vapor by hydrogen (H2) gas in the catalyst 5, it can be kept low so that the catalyst temperature does not increase excessively.
Thereby, it can manage so that the catalyst 5 may be stored in the temperature range which becomes an active state.
Further, even if the hydrogen engine 3 is a multi-cylinder engine, the supply frequency of the hydrogen gas to be supplied secondarily may be less than the number of cylinders per crank rotation, and may be about the injection timing matched to a specific cylinder.
It is sufficient that diffusion mixing proceeds while flowing down the exhaust pipe 4 and the exhaust gas component after passing through the catalyst is further purified in cooperation with the exhaust gas component holding capacity of the catalyst 5.
Furthermore, fine correction by the downstream exhaust gas sensor 55 becomes effective by performing highly accurate feedback control by the upstream exhaust gas sensor 54.

In the exhaust gas purification system 1 described above, hydrogen gas as fuel is stored in the hydrogen storage tank 2 in a high pressure state (about several tens of MPa, for example, about 35 to 70 MPa).
The high-pressure hydrogen gas in the hydrogen storage tank 2 reaches the pressure regulator 34 through the hydrogen gas supply passage 33 of the hydrogen gas injection system 30 as indicated by an arrow in FIG. The hydrogen gas is depressurized from a high pressure state (about several tens of MPa, for example, about 35 to 70 MPa) to several hundred kPa (for example, about several atmospheric pressures).
The decompressed hydrogen gas is sent to a delivery pipe 36 attached to the cylinder head 7 by a primary supply side passage 35 of the intake side hydrogen gas injection device 31 as indicated by an arrow in FIG. The hydrogen engine 3 is driven by being directly injected into the combustion chamber 10 through the connected primary supply side injector 37 and burned.

At this time, lean combustion is controlled by measuring the oxygen ratio with the upstream side exhaust gas sensor 54 arranged upstream of the catalyst 5 so that it can be operated at a target lean lean air-fuel ratio (for example, λ≈1.05). Feedback control of the fuel injection amount.
Note that when combustion is simply performed with an air-fuel ratio of λ ≧ 1, nitrogen in the air-fuel mixture is oxidized by the following formula to generate NOx.
H2 + O2 + N2 → H2O + NOx + O2 + N2

Therefore, not only the primary supply of hydrogen gas by the primary supply side injector 37 of the intake side hydrogen gas injection device 31 but also the secondary supply of hydrogen gas by the secondary supply side injector 39 of the exhaust side hydrogen gas injection device 32 is performed. Is.
In other words, the secondary supply side injector 39 is provided in the exhaust pipe 4 upstream from the catalyst 5, and the pressure regulator 34 makes the pressure different from the combustion pressure to the primary supply side injector 37 (about several hundred kPa). Depressurize the hydrogen gas.
A part of the decompressed hydrogen gas is sent to the secondary supply side injector 39 by the secondary supply side passage 38 of the exhaust side hydrogen gas injection device 32 as shown by the arrow in FIG. It is injected into the exhaust pipe 4 by the side injector 39, and NOx produced in the exhaust gas using this hydrogen gas as a reducing agent is reduced on the catalyst 5 to prevent harmful NOx from being released into the atmosphere.
At the same time, excess O 2 is also oxidized on the catalyst 5 by hydrogen gas, and part of it becomes water vapor.
The above situation is disclosed by the following equation.
Pt, Rh
NOx + H2 → N2 + H2O
Pt, Rh
O2 + H2 → H2O
Pt: Platinum
Rh: Rhodium
At this time, the injection timing of the secondary supply side injector 39 may be set to a driving state in which an operation synchronized with one of the primary supply side injectors 37 is performed, for example.

  The amount of hydrogen gas injected into the exhaust pipe 4 by the secondary supply side injector 39 of the exhaust side hydrogen gas injection device 32 is monitored by the upstream side exhaust gas sensor 54 and the downstream side downstream from the catalyst 5. The excess hydrogen gas that has not been subjected to reduction is controlled by the side exhaust gas sensor 55, and the injection amount from the secondary supply side injector 39 is feedback controlled so that the hydrogen gas is not excessively injected from the secondary supply side injector 39.

In addition, the white arrow of FIG. 2 has shown the flow of the intake air.
That is, the intake air that has passed through the air cleaner 15 reaches the compressor 25 of the supercharger 23 through the intake pipe 16, and is supercharged by the compressor 25 and then reaches the intercooler 29.
The intake air cooled by the intercooler 29 passes through the throttle body 18, the surge tank 19, and the intake manifold 20 provided with the throttle valve 17 and then reaches the combustion chamber 10 of the hydrogen engine 3.
In the throttle body 18, when the ISC valve 42 of the idle speed control device 40 is open, the intake air flows into the surge tank 19 so as to bypass the throttle valve 17 by the bypass passage 41. Become.

Further, hatched arrows in FIG. 2 indicate the flow of exhaust gas.
That is, the exhaust gas discharged from the combustion chamber 10 of the hydrogen engine 3 reaches the exhaust pipe 4 through the exhaust manifold 21 and reaches the catalyst 5 of the catalytic converter 22 disposed in the middle of the exhaust pipe 4. .
The catalyst 5 purifies exhaust gas by simultaneously reducing HC (mainly due to blow-by gas), CO, and NOx, which are harmful components in the exhaust gas, and then exhausting it to the outside air. It will be.

  Next, the operation will be described along the control flowchart of the exhaust gas purification system 1 of the hydrogen engine 3 in FIG.

When the control program of the exhaust gas purification system 1 is started (102), it is judged (104) whether or not the λ feedback (also referred to as “F / B”) condition such as after engine warm-up is ON. Transition.
If this determination (104) is NO, the determination (104) is repeated until the λ feedback condition is turned ON.
If the determination (104) is YES, the process proceeds to the process (106) for starting the λ feedback operation.
In the process (106) for starting the λ feedback operation, normal PI control is performed by the primary supply side injector 37 and the upstream side exhaust gas sensor 54 which is a λ sensor.
Furthermore, PI control is a general term for proportional operation and integral operation, and indicates control in which integral operation is added to proportional operation.

And after the process (106) which starts (lambda) feedback driving | operation, it transfers to the process (108) by a closed loop (subloop).
In the processing (108) by this closed loop (sub-loop), a detection signal from the downstream exhaust gas sensor 55, which is an H2 sensor, is taken in, and whether the H2 concentration is equal to or higher than a constant CH2 of the target H2 concentration, that is,
H2 concentration ≧ CH2
It is determined whether or not (110).
And this judgment (110) is YES, that is,
H2 concentration ≧ CH2
In this case, the process for controlling the valve opening time signal of the secondary supply side injector 39 so as to decrease it by the increase / decrease value of the injector driving time (also referred to as “the constant of the target concentration feedback control”) TH2 (112). Migrate to
In addition, the judgment (110) is NO, that is,
H2 concentration <CH2
In this case, the routine proceeds to a process (114) for controlling to increase the valve opening time signal of the secondary supply side injector 39 by the increase / decrease value TH2 of the injector driving time.
After these processes (112) and (114), whether the above-described H2 concentration is equal to or greater than the constant CH2 of the target H2 concentration, that is,
H2 concentration ≧ CH2
It returns to judgment (110) of whether it is.

Further, after the processing (108) by the above closed loop (sub-loop), it is determined (116) whether or not the λ feedback condition is OFF.
If this determination (116) is NO, the process returns to the determination (104) as to whether or not the above-mentioned λ feedback condition is ON.
If the determination (116) is YES, the process proceeds to the end (118).

Thus, a hydrogen storage tank 2 for storing hydrogen in a high pressure state, a hydrogen engine 3 for burning hydrogen supplied from the hydrogen storage tank 2, and a catalyst 5 provided in an exhaust pipe 4 of the hydrogen engine 3 are provided. In the exhaust gas purification system 1 of the hydrogen engine 3 provided so as to be able to supply hydrogen gas into the exhaust pipe 4 during the operation of 3, an upstream side exhaust gas sensor for detecting an exhaust gas component in the exhaust pipe 4 upstream of the catalyst 5 54 and an exhaust-side hydrogen gas injection device 32 that injects hydrogen gas into the exhaust pipe 4 is provided upstream of the upstream exhaust gas sensor 54, and the exhaust gas is on the lean side based on the detection of the upstream exhaust gas sensor 54. The exhaust gas is supplied from the exhaust-side hydrogen gas injection device 54 to the hydrogen engine 3 while feedback controlling the supply amount of the hydrogen gas supplied to the hydrogen engine 3 so that the predetermined air-fuel ratio is obtained. The control means 56 for controlling to supply a small amount of hydrogen gas than a hydrogen gas is provided to.
Therefore, by averaging the combustion state and maintaining it on the lean side, it is possible to keep NH3 emissions out of the exhaust gas components very low.
Further, the increased NOx can be selectively reduced by the hydrogen gas supplied secondarily, so that the purification efficiency by the catalyst 5 can be maintained high in total.
Furthermore, the consumption of hydrogen gas to be secondarily supplied can be reduced.

Further, a downstream side exhaust gas sensor 55 for detecting an exhaust gas component is provided in the exhaust pipe 4 on the downstream side of the catalyst 5, and the control means 56 is configured to detect the exhaust side hydrogen gas injection device based on the detection of the downstream side exhaust gas sensor 55. While monitoring the reduction rate of the hydrogen gas supplied from 32 to the exhaust gas after passing through the catalyst, feedback correction control is performed so that the supplied hydrogen gas is corrected to increase or decrease.
As a result, the amount of hydrogen gas supplied to the secondary supply can be remarkably reduced, and both the exhaust gas purification performance and the fuel consumption can be improved.

  The present invention is not limited to the above-described embodiments, and various application modifications are possible.

For example, in the embodiment of the present invention, the downstream exhaust gas sensor is a hydrogen (H2) sensor, the excess exhaust gas not supplied for reduction is controlled by this downstream exhaust gas sensor, and the hydrogen gas is excessively supplied from the secondary supply side injector. However, instead of the hydrogen (H2) sensor, the downstream exhaust gas sensor is replaced with an oxygen (O2) sensor, and O2 in the exhaust gas is used. It is possible to adopt a configuration in which the amount of hydrogen gas injected from the secondary supply side injector to the exhaust pipe is feedback-controlled by monitoring the amount, and a NOx sensor can also be used.
In addition, when using an oxygen (O2) sensor instead of a hydrogen (H2) sensor, if the reduction rate by the hydrogen gas in a catalyst is used empirically, it can handle equally.

  Further, even in a general lean burn gasoline engine or diesel engine, if a hydrogen storage tank for reduction is provided and the hydrogen gas in the hydrogen storage tank is injected into the exhaust gas, NOx is reduced. It is possible.

  Further, for example, in a predetermined engine operating region based on the engine load, the supply amount of hydrogen gas from the secondary supply side injector that is secondary supplied is based on the supply amount from the primary supply side injector that is the primary supply, A guard may be applied so that the total injection amount falls on the lean side from the stoichiometry.

Furthermore, in the embodiment of the present invention, the pressure regulator regulates the hydrogen gas in the high pressure state (about several tens of MPa, for example, about 35 to 70 MPa) in the hydrogen storage tank to several hundred kPa (for example, about several atmospheric pressures). When the pressure is reduced, the pressure regulator is used to reduce the pressure at a time. However, it is also possible to adopt a multi-stage pressure reducing system in which pressure is reduced in two or more stages, such as primary pressure reduction, secondary pressure reduction, and so on.
In this case, by adopting the multistage depressurization method, it is possible to gradually and reliably depressurize the hydrogen gas.

  Furthermore, as a purification catalyst, a purification catalyst for FFV (flexible fuel vehicle) can be used as well as a purification catalyst for bi-fuel such as gaseous fuel-gasoline.

It is a flowchart for control of the exhaust-gas purification system of the hydrogen engine which shows the Example of this invention. 1 is a system configuration diagram of an exhaust gas purification system of a hydrogen engine. It is a general | schematic expanded sectional view of the hydrogen engine which shows weak stratified combustion. It is a figure which shows the air-fuel | gaseous mixture distribution at the time of seeing a combustion chamber from the piston side. It is a figure which shows the fuel injection timing of the injection control at the time of start-up of the exhaust gas purification system of a hydrogen engine. It is a figure which shows the fuel-injection time of the after-startup injection control of the exhaust gas purification system of a hydrogen engine.

Explanation of symbols

1 Exhaust gas purification system
2 Hydrogen storage tank
3 Hydrogen engine
4 Exhaust pipe
5 Catalyst
10 Combustion chamber
16 Intake pipe
20 Intake manifold
21 Exhaust manifold
22 Catalytic converter
23 Turbocharger (also called “turbocharger”)
29 Intercooler
30 Hydrogen gas injection system
31 Intake side hydrogen gas injection device
32 Exhaust-side hydrogen gas injection device
33 Hydrogen gas supply passage
34 Pressure regulator
35 Primary supply side passage
37 Primary supply side injector (also referred to as “in-cylinder injector”)
38 Secondary supply side passage
39 Secondary supply side injector
40 Idle rotation speed control device
42 ISC valve (also referred to as “idle air amount control valve”)
47 Fuel pressure sensor
49 Engine water temperature sensor
50 Throttle sensor
52 Intake pressure sensor
53 Intake air temperature sensor
54 Upstream exhaust gas sensor (also referred to as “air-fuel ratio sensor” or “λ sensor”)
55 Downstream exhaust gas sensor (also referred to as “hydrogen (H2) sensor”)
56 Control means (also referred to as “ECM”)
57 Crank angle sensor

Claims (1)

A hydrogen storage tank for storing hydrogen in a high-pressure state, a hydrogen engine for burning hydrogen supplied from the hydrogen storage tank, and a catalyst provided in an exhaust pipe of the hydrogen engine, and hydrogen in the exhaust pipe during operation of the hydrogen engine. In an exhaust gas purification system of a hydrogen engine provided so as to be able to supply gas, an exhaust gas sensor for detecting an exhaust gas component is provided in an exhaust pipe upstream of the catalyst, and an exhaust side for injecting hydrogen gas into the exhaust pipe A hydrogen gas injection device is provided upstream of the upstream exhaust gas sensor, a downstream exhaust gas sensor for detecting an exhaust gas component is provided in the exhaust pipe downstream of the catalyst, and the exhaust gas is detected based on the detection of the upstream exhaust gas sensor. While controlling the amount of hydrogen gas supplied to the hydrogen engine to achieve a predetermined lean air-fuel ratio, the exhaust-side hydrogen gas injector Control means for controlling so as to supply a small amount of hydrogen gas than a hydrogen gas supplied to the hydrogen engine from provided, the control means supplies the exhaust side hydrogen gas injection device based on the detection of the downstream exhaust gas sensor An exhaust gas purification system for a hydrogen engine, wherein feedback correction control is performed so as to correct the increase or decrease of the supplied hydrogen gas while monitoring the reduction rate of the hydrogen gas to the exhaust gas after passing through the catalyst .