JP4380465B2 - Control device for hydrogen fuel engine - Google Patents

Description

  The present invention relates to a control device for a hydrogen fuel engine that operates using at least one of hydrogen and fossil fuels such as gasoline, light oil, and natural gas as a fuel, and more specifically, a hydrogen fuel engine including a NOx storage catalyst in an exhaust passage. Belongs to the technical field related to the control device.

  In general, in a vehicle engine or the like, a three-way catalyst is used as an apparatus for removing harmful components such as CO (carbon monoxide), HC (hydrocarbon), and NOx (nitrogen oxide) contained in exhaust gas. However, in the case of an engine that employs a lean combustion method or the like for the purpose of improving fuel efficiency in recent years, the oxygen concentration in the exhaust gas becomes high, so in the conventional three-way catalyst in which the window is in a narrow range near the theoretical air-fuel ratio, There arises a problem that NOx cannot be sufficiently removed.

  To cope with this, NOx in the exhaust gas is absorbed when the air-fuel ratio is lean (oxygen-excess state) in the exhaust passage, and NOx that is absorbed is released when the air-fuel ratio becomes rich (oxygen-deficient state). It is known to arrange a storage catalyst. According to this, by appropriately controlling the air-fuel ratio, in the lean state, NOx is absorbed by the NOx storage catalyst, and in the rich state, NOx is released from the NOx storage catalyst and exists in a large amount. , Reacts with HC, and the emission of harmful components to the outside is also suppressed. As a result, it is possible to effectively reduce the NOx emission amount of the engine that employs the lean combustion system.

  By the way, the NOx storage catalyst has a problem of sulfur poisoning. That is, the sulfur component contained in the fuel becomes SOx or the like, adheres to the NOx storage catalyst, obstructs the NOx absorption of the catalyst, and reduces the NOx purification rate. Therefore, it is necessary to periodically release and remove sulfur from the NOx storage catalyst. For example, as sulfur release control described in Patent Document 1, the amount of sulfur adhering to the NOx storage catalyst is estimated based on the fuel flow rate, exhaust gas temperature, and the like. In some cases, when the estimated amount exceeds a predetermined amount, the air-fuel ratio is enriched, and the exhaust gas is heated to release and remove sulfur from the NOx storage catalyst in order to raise the temperature of the catalyst.

  On the other hand, in recent years, in response to environmental protection, hydrogen fuel engines that use hydrogen instead of fossil fuels such as gasoline, light oil, and natural gas, or hybrid hydrogen fuels that operate using both fossil fuel and hydrogen An engine has been proposed. There exists an engine of patent document 2 as an example of such a hydrogen fuel engine. According to this, the engine is provided with a fuel injection valve for supplying gasoline and a hydrogen injection valve for supplying hydrogen into the combustion chamber, and is configured to be able to switch which fuel to use depending on the operating conditions. .

JP-A-11-44211 JP-A-7-97906

Incidentally, as described above, in an engine that can use hydrogen fuel as the fuel, when the NOx storage catalyst is disposed in the exhaust passage, the air-fuel ratio of the mixed gas supplied to the combustion chamber for sulfur removal is rich. When the hydrogen injection amount is increased, the hydrogen injection amount increases. However, when the hydrogen injection amount increases, the tendency of harmful H ₂ S to be generated due to the strong reducing power of hydrogen or incomplete combustion increases, and knocking occurs. There is a problem that vibration and noise similar to those are likely to occur.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a control device for a hydrogen fuel engine that can suppress the generation of H ₂ S and the generation of vibration and noise when sulfur is released from a NOx storage catalyst. And

  In order to solve the above problems, the present invention is configured as follows.

That is , according to the first aspect of the present invention, the NOx storage catalyst that stores NOx when the air-fuel ratio is lean and releases NOx that is stored when the air-fuel ratio is the stoichiometric air-fuel ratio or rich is provided in the exhaust passage. A first fuel supply means for supplying fossil fuel into the combustion chamber, a second fuel supply means for supplying hydrogen into the combustion chamber, an operating condition detecting means for detecting the operating condition of the engine, and the operating condition of the engine And a fuel ratio changing means for changing the ratio of fossil fuel and hydrogen in the fuel supplied to the combustion chamber in accordance with the parameter, the parameter relating to the degree of sulfur poisoning of the NOx storage catalyst. a sulfur poisoning degree detecting means for detecting, as well as the air-fuel ratio to the rich when more sulfur poisoning degree predetermined is detected by the detecting means, fuel the degree of the air-fuel ratio to the rich Ratio changing means is provided with a air-fuel ratio control means so large that when the ratio of fossil fuel to total fuel which is set in accordance with the operating state is large, the above fuel ratio changing means is emptied by the air-fuel ratio control means When the fuel ratio is made rich, the ratio of fossil fuel is increased.

According to the invention described in claim 1, sulfur when poisoning degree is equal to or greater than a predetermined causes the activation of combustion by enriching the air-fuel ratio, the sulfur that has been absorbed to the NOx storage catalyst at elevated exhaust gas temperatures emitted However, since the air-fuel ratio is enriched by increasing the ratio of fossil fuel to the fuel at this time, it is possible to avoid the increase in reducing power and the occurrence of incomplete combustion by increasing the supply amount of hydrogen. Thus, generation of H ₂ S and generation of vibration and noise can be suppressed. Furthermore, the ratio of fossil fuel to the fuel when sulfur is released is not set to 100%, the reduction power is not excessive, and hydrogen is included in the fuel at a rate that does not cause incomplete combustion, thereby raising the temperature of the exhaust gas. Therefore, it is possible to improve the efficiency of sulfur release.

On the other hand, if the ratio of fossil fuel in the fuel is increased when the air-fuel ratio is enriched, the effect of raising the temperature of exhaust gas more efficiently by hydrogen combustion is reduced, and it takes a long time to raise the catalyst temperature. The substantial start of sulfur release may be delayed. On the other hand, according to the invention described in claim 1 , since the richness of the air-fuel ratio is controlled to increase as the proportion of fossil fuel in the fuel increases, the temperature of exhaust gas is raised by active combustion. Thus, the efficiency of sulfur release from the NOx storage catalyst can be improved.

  Embodiments according to the present invention will be described below.

  First, FIG. 1 shows the overall configuration of the engine 1. The engine 1 is a hydrogen fuel engine that uses both hydrogen and gasoline as fuel, and includes a cylinder block 3 in which a plurality of cylinders 2... 2 (only one is shown) are provided in series, and a cylinder block 3 disposed on the cylinder block 3. A cylinder head 4 is provided, and a piston 5 is fitted into each cylinder 2 so as to be able to reciprocate. A combustion chamber 6 is placed in the cylinder 2 between the crown surface of the piston 5 and the lower surface of the cylinder head 4. Is defined. The reciprocating motion of the piston 5 is converted into a rotational motion of the crankshaft 8 via the connecting rod 7. The cylinder block 3 includes an electromagnetic crank angle sensor 9 for detecting the rotation angle of the crankshaft 8, a knock sensor 10 for detecting knocking based on fluctuations in combustion pressure for each cylinder 2, and An engine water temperature sensor 11 that detects the temperature of the cooling water (engine water temperature) is disposed facing the interior of a water jacket (not shown).

  On the other hand, two intake ports 20 and two exhaust ports 21 are opened in the cylinder head 4 so that each cylinder 2 faces the ceiling surface of the combustion chamber 6, and the combustion chamber 6 of each port 20, 21 is opened. An intake valve 22 and an exhaust valve 23 are arranged in the opening on the side. The intake valve 22 and the exhaust valve 23 are opened and closed in synchronization with the rotation of the crankshaft 8 by an intake side and an exhaust side camshaft (not shown) pivotally supported in the cylinder head 4. The intake cam shaft is provided with an electromagnetic cam angle sensor 24 for detecting the rotation angle. An ignition plug 25 is disposed for each cylinder 2 so as to penetrate the cylinder head 4 in the vertical direction and be surrounded by the intake and exhaust valves 22 and 23. The electrode at the tip of the spark plug 25 protrudes downward from the ceiling surface of the combustion chamber 6 by a predetermined distance. The base end portion of the spark plug 25 is connected to an ignition circuit (igniter) 27 disposed so as to penetrate the head cover 26.

  The crown surface of the piston 5 serving as the bottom of the combustion chamber 6 has an outer peripheral portion substantially parallel to the ceiling surface of the combustion chamber 6, while the piston 5 has a substantially central portion of the crown surface in plan view. A generally lemon-shaped recess is provided. Further, a hydrogen injector 28 for injecting hydrogen fuel into the combustion chamber 6 is disposed at a peripheral portion on the intake side of the combustion chamber 6 so as to face the inlet. On the other hand, a gasoline injector 29 is provided for injecting gasoline (light oil, natural gas or other fossil fuels) into the intake port 20 with the inlet port 20 faced.

  The base end side of the hydrogen injector 28 is connected to a hydrogen fuel distribution pipe 30 common to all the cylinders 2, and hydrogen fuel discharged from the high-pressure hydrogen fuel pump 31 through the hydrogen fuel distribution pipe 30 is supplied to each cylinder 2. The hydrogen injector 28 is distributed. Then, when hydrogen is injected in the compression stroke by the hydrogen injector 28, the hydrogen fuel spray is decelerated by the intake air flow in the combustion chamber 6 to form an air-fuel mixture in an appropriate concentration state around the spark plug 25. . The hydrogen fuel distribution pipe 30 is provided with a hydrogen fuel pressure sensor 32 for measuring the pressure state (fuel injection pressure) of the hydrogen fuel injected from the hydrogen injector 28.

  On the other hand, the base end side of the gasoline injector 29 is connected to a gasoline fuel distribution pipe 33 common to all the cylinders 2, and fuel discharged from the high-pressure fuel pump 34 through the gasoline fuel distribution pipe 33 is supplied to each cylinder 2. The fuel is distributed by the gasoline injector 29 for each intake port 20 that faces. When gasoline is injected by the gasoline injector 29 in the intake stroke, the gasoline is sucked into the combustion chamber 2 by the intake air flow. The gasoline fuel distribution pipe 33 is provided with a gasoline fuel pressure sensor 35 for measuring the pressure state (fuel injection pressure) of gasoline injected from the gasoline injector 29.

  Here, the hydrogen injector 28 is configured to be directly injected into the combustion chamber 6, and the gasoline injector 29 is configured to be injected into the intake port 20. However, the hydrogen injector 28 is connected to the intake port 20. The gasoline injector 29 is configured to be an injection and direct injection into the combustion chamber 6, both the hydrogen and gasoline injectors 28 and 29 are directly injected into the combustion chamber 6, or both are intake ports 20. You may comprise so that it may inject. If the hydrogen injector 28 is configured to be injected into the intake port 20, hydrogen may be combusted before being introduced into the combustion chamber 6, that is, in the intake port 20 due to high flammability of hydrogen.

  An intake passage 40 is connected to one side surface of the engine 1 (the right side surface in FIG. 1) so as to communicate with the intake port 20 of each cylinder 2. The intake passage 40 supplies the intake air filtered by the air cleaner 41 to the combustion chamber 6 of the engine 1, and the air flow for detecting the intake air amount to the engine 1 in order from the upstream side to the downstream side. A sensor 42, an electric throttle valve 43 that changes the sectional area of the intake passage 40, a throttle sensor 44 that detects the position thereof, and a surge tank 45 are disposed. The throttle valve 43 is not mechanically connected to an accelerator pedal (not shown), and is opened and closed by an electric motor (not shown). The surge tank 45 is provided with a boost sensor 46 that detects the pressure in the intake passage 40 downstream of the throttle valve 43.

  Further, the intake passage 40 on the downstream side of the surge tank 45 is an independent passage branched for each cylinder 2, and the downstream end portion of each independent passage is further divided into two and individually connected to the intake port 20. It is a branch road that communicates with Between this branch path and the independent path, a throttle valve (Table Swirl Valve: hereinafter referred to as TSCV) 47 for adjusting the strength of the intake air flow in the combustion chamber 6 is disposed. It is opened and closed by a motor or the like. The valve body of the TSCV 47 has a notch in a part thereof. In the fully closed state, the intake air flowing downstream only from the notch generates a strong in-cylinder flow in the combustion chamber 6. On the other hand, as the TSCV 47 is opened, the intake air circulates from other than the notch, and the strength of in-cylinder flow gradually decreases.

  An exhaust passage 50 for discharging burned gas (exhaust gas) from the combustion chamber 6 in the cylinder 2 is connected to the other side surface (the left side surface in FIG. 1) of the engine 1. The upstream side of these exhaust passages 50 is constituted by an exhaust manifold connected to the intake port 20 for each cylinder 2, and the exhaust passage 50 downstream of the exhaust manifold has HC (carbonization) that is a harmful component in the exhaust gas. Two catalytic converters 51 and 52 for purifying hydrogen), CO (carbon monoxide), and NOx (nitrogen oxide) are arranged in series.

  Although not shown in detail, the upstream catalytic converter 51 contains a honeycomb-structured carrier in a casing, and a catalyst layer of a so-called three-way catalyst 53 is formed on the wall surface of each through hole of the carrier. As is well known in the art, this three-way catalyst 53 can purify HC, CO, and NOx almost completely when the air-fuel ratio of the exhaust gas is in a predetermined state that substantially includes the stoichiometric air-fuel ratio.

  Further, the downstream catalytic converter 52 accommodates two carriers in series in one casing, and forms a so-called NOx occlusion type catalyst layer on each through-hole wall surface of the upstream carrier, so that the upstream side In addition to the NOx storage catalyst 54, a downstream NOx storage catalyst 55 is configured by forming a NOx storage type catalyst layer on the downstream carrier in the same manner. The NOx storage catalysts 54 and 55 are composed of barium as a main component, alkali metals such as potassium, magnesium, strontium and lanthanum, alkaline earth metals or rare earths, and precious metals having a catalytic reaction action such as platinum. NOx in the exhaust gas is occluded when the air-fuel ratio of the exhaust gas is leaner than the state corresponding to the stoichiometric air-fuel ratio, while the NOx occluded in this way is used to enrich the air-fuel ratio. In response to this, it has a function of releasing and reducing and purifying (NOx release control).

  Further, since the NOx storage catalysts 54 and 55 contain barium, there is a problem of sulfur poisoning in which sulfur components (SOx) in the fuel adhere to the catalyst. Sulfur cannot be released by NOx release control, and if this is left as it is, the NOx purification ability is reduced. Therefore, the treatment for releasing the attached sulfur and restoring the purification ability of the catalyst (SOx release control), that is, sulfur poisoning The temperature of the NOx storage catalysts 54 and 55 is increased for elimination.

  The temperature increase of the NOx storage catalysts 54 and 55 is achieved by increasing the exhaust gas temperature by enriching the air-fuel ratio and activating combustion, as well as by dividing the fuel and retarding the ignition timing (ignition retard). You can also Sulfur poisoning is more likely to proceed as the air-fuel ratio is leaner. Therefore, in the SOx release control, the air-fuel ratio is enriched and the NOx storage catalysts 54 and 55 are heated to promote the release of sulfur. Is done.

Here, the mechanism by which NOx in the exhaust gas is occluded or released by the NOx occlusion catalysts 54 and 55 is as follows. First, as schematically shown in FIG. 2 (a), when the air-fuel ratio is in a lean state, NOx and SOx in the exhaust gas in an oxygen-excess atmosphere react with oxygen O ₂ on the catalyst metal, and a part thereof While combined with barium, it is stored as NOx and SOx. On the other hand, as shown in FIG. 2 (b), when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the reaction proceeds in the opposite direction to that in the lean state, and NOx separated from barium is contained in the exhaust gas. It reacts with HC and CO (reduction reaction) and is decomposed into nitrogen N ₂ and oxygen O ₂ . At this time, SOx is not released and remains bonded to barium.

  In the operation for performing the NOx release control, the state of FIG. 2 (a) and FIG. 2 (b) is repeated. As shown in FIG. 2 (c), a large amount of SOx is combined with barium. When remaining on the surface, NOx cannot be occluded in the lean state of FIG. 2A, and NOx is released into the atmosphere as it is without being decomposed into harmless substances.

  On the other hand, as shown in FIG. 2D, the temperature of the catalysts 54 and 55 is raised to 600 to 650 ° C. at the timing when the surfaces of the NOx storage catalysts 54 and 55 are covered with SOx and the NOx cannot be stored. At the same time, by enriching the air-fuel ratio, SOx bonded to the barium surface is released, and a region where NOx can be adsorbed on the barium surface is secured.

  Incidentally, an oxygen concentration sensor (first oxygen concentration sensor) 56 for detecting the oxygen concentration in the exhaust gas is disposed in the vicinity of the exhaust manifold manifold of the engine 1, and the signal from the sensor 56 is mainly used. Based on this, air-fuel ratio feedback control of the engine 1 is performed. Further, in the middle of the two catalytic converters 51 and 52, a second oxygen concentration detection sensor 57 for determining the deterioration state of the upstream side three-way catalyst 53 and the temperature of the exhaust gas flowing into the NOx storage catalyst 54 are detected. And a third oxygen concentration sensor 59 is disposed between the two NOx storage catalysts 54 and 55.

  The exhaust passage 50 downstream of the exhaust manifold communicates with the upstream end of an exhaust recirculation passage (hereinafter referred to as an EGR passage) 60 that recirculates a part of the exhaust gas to the intake passage 40 so as to diverge from the exhaust passage 50. is doing. The downstream end of the EGR passage 60 is open facing the inside of the surge tank 45, and an EGR valve 61 comprising a duty solenoid valve is disposed in the EGR passage 60 near the downstream end. The EGR valve 61 adjusts the recirculation amount of the exhaust gas in the EGR passage 60.

  The ignition circuit 27, the hydrogen and gasoline injectors 28 and 29, the high pressure fuel pumps 31 and 34 for hydrogen and gasoline, the throttle valve 43, the TSCV 47, the EGR valve 61, etc. are all engine control units (hereinafter referred to as ECU) 70. The operation is controlled by. On the other hand, the ECU 70 includes outputs from at least the crank angle sensor 9, the knock sensor 10, the water temperature sensor 11, the air flow sensor 41, the throttle sensor 44, the three oxygen concentration sensors 56, 57, 59, the exhaust temperature sensor 58, and the like. Each signal is input, and further, an output signal from an accelerator opening sensor 71 that detects an operation amount of an accelerator pedal (hereinafter referred to as an accelerator opening), a rotation speed sensor 72 that detects an engine speed, and a vehicle speed are detected. An output signal from the vehicle speed sensor 73 is input.

  The ECU 70 controls the intake air amount to the engine 1, the fuel injection amount for each cylinder 2, the injection timing and the ignition timing based on the signals input from the sensors, and further increases the intake flow in the cylinder 2. Control the exhaust gas recirculation ratio.

  On the other hand, FIG. 3 is a map showing regions set according to the operation mode during lean operation excluding NOx release control, SOx release control, and acceleration (air-fuel ratio A / F = 30). The hydrogen main mode is set on the low load and low rotation side, and the gasoline main mode is set on the high load and high rotation side. The hydrogen main mode is set so that the volume ratio of hydrogen injected into the combustion chamber 6 and gasoline becomes 200: 1. When this volume ratio is converted into an output contribution, it becomes 80:20, and hydrogen is larger. This mode contributes to combustion. On the other hand, the gasoline main mode is set so that the volume ratio is 12: 1. At this time, the output contribution is 20:80, and gasoline is more greatly contributed to combustion.

4 to 6 show specific control procedures for NOx release control and SOx release control by the ECU 70 of the hydrogen fuel engine 1. As the condition for starting the NOx release control, and when the NOx occlusion quantity Q calculated by the time integrated value of the lean operation from the previous NOx release becomes the first predetermined value Q ₁ or more, an acceleration of a predetermined amount or more Is set, and the start condition of the SOx release control is the lean operation time integrated value from the previous SOx release (5 to 10 times the time integrated value calculated in the NOx release control). It is set when the SOx sulfur-poisoning amount S該被poison amount S by calculating a becomes the second predetermined values S ₁ or more from.

  First, as shown in FIG. 4, in step S1, various signals from the water temperature sensor 11, the cam angle sensor 24, the air flow sensor 41, the oxygen concentration sensors 56, 57, 59, the accelerator opening sensor 71, the rotation speed sensor 52, and the like. And the data temporarily stored in the RAM of the ECU 70 are read. Subsequently, in step S2, the operation mode is determined based on the map shown in FIG. 3 using the engine load and the engine speed.

In step S3 and step S4, the NOx occlusion amount Q and the SOx poisoning amount S are calculated from the lean operation time integrated value and the like, and the stored data stored in the RAM of the ECU 70 are updated. Then, in step S5, the flag F ₁ is to determine whether it is set to 1, when the flag F ₁ = 0, the process proceeds to step S6. In step S6 it determines whether the calculated NOx storage amount Q at step S3 is larger than the predetermined value Q ₁ that is set in advance. When the NOx occlusion quantity Q is smaller than a predetermined amount _{Q 1} is the flow proceeds to step S21 in FIG. 5, when the NOx storage amount Q is larger than the predetermined value _{Q 1} is initiating the NOx release control proceeds to step S7.

NOx release control, first, set the timer _{C 1} in step S7, sets the flag _{F 1} to 1 in step S8. Next, in step S9, it is determined whether the currently used fuel is only hydrogen or a mixture of hydrogen and gasoline or only gasoline. If the currently used fuel is only hydrogen or a mixture of hydrogen and gasoline, step S9 is performed. After proceeding to S10 and switching the fuel to only gasoline, the routine proceeds to step S11 where the target air-fuel ratio A / F is set to be rich (A / F = 14.7). If the only fuel currently used is gasoline in step S9, the process proceeds to step S11 as it is and the target air-fuel ratio A / F is similarly enriched. Next, in step S12, the target gasoline injection amount is calculated based on the target air-fuel ratio A / F and the intake air amount set in step S11. Then, 1 is added to the count T ₁ at step S13, based on the target gasoline injection amount calculated in step S12 to perform the fuel injection at step S14, the process returns. In this NOx release control, the fuel is completely switched to gasoline to enrich the air-fuel ratio A / F, thereby releasing NOx.

Further, when the flag _{F 1} is 1 in step S5, the count _{T 1} is determined whether equal timer _{C 1} at step S15, when the count _{T 1} is not equal to _{C 1} proceeds to step S9 use The fuel is switched to gasoline only to enrich the air-fuel ratio. On the other hand, if the count _{T 1} is equal to _{C 1} terminates the NOx release control. In other words, the flag _{F 1} proceeds to step S16 is reset to 0, the NOx occlusion quantity Q calculated in step S4 is reset to 0 in step S17, resets the count _{T 1} to 0 in step S18. In step S19, the target air-fuel ratio A / F is set to a normal lean state (A / F = 30), and in step S20, the target air-fuel ratio A / F, the hydrogen / gasoline ratio corresponding to the operation mode, and the suction are set. Based on the air amount, a target gasoline injection amount and a target hydrogen injection amount are calculated. Next, it progresses to step S14, performs fuel injection based on the calculated target gasoline injection amount and target hydrogen injection amount, and returns.

On the other hand, when the NOx occlusion quantity Q is the first predetermined value _{Q 1} or less in the step S6, the process proceeds to step S21 in FIG. 5, the flag _{F 2} is determined whether or not 1. When the flag _{F 2} is not 1, the routine proceeds to step S22, calculated in step S4 SOx sulfur-poisoning amount S is equal to or a predetermined amount _{S 1} or more, SOx sulfur-poisoning amount S is a predetermined amount S When it is ₁ or more, SOx release control is started.

SOx release control, first, set the timer _{C 2} in step S23. At this time, the timer C ₂ is higher exhaust gas temperature is set short. Then, it sets the flag _{F 2} to 1 at step S24, sets the SOx release target air-fuel ratio A / F in accordance with the gasoline a percentage of the fuel in step S25. That is, in setting the target air-fuel ratio A / F for SOx release, the target air-fuel ratio A / F is set to a value between 11 and 14.7, and the gasoline ratio is large within this range. It is set to be rich as time goes. In step S26, the target air-fuel ratio A / F before setting the target air-fuel ratio A / F for SOx release, that is, the target air-fuel ratio A / F at the time of normal lean operation = 30, and hydrogen / gasoline corresponding to the operation mode. A target hydrogen injection amount is calculated based on the ratio and the intake air amount. Next, in step S27, the hydrogen injection amount calculated in step S26 to realize the SOx release target air-fuel ratio A / F based on the SOx release target air-fuel ratio A / F and the intake air amount. The target gasoline injection amount is calculated as the fuel to be added to the engine. At this time, since the hydrogen injection amount calculated in step S26 is for a normal lean operation, in the rich state set in step S25, the proportion of gasoline in the fuel becomes larger than in the normal lean operation. .

Then, 1 is added to the count T ₂ in step S28, in step S29, by performing the fuel injection based on the target hydrogen injection quantity and the target gasoline injection amount calculated at step S27 calculated at step S26 return To do.

On the other hand, when the flag _{F 2} is 1 in step S21, the count _{T 2} it is determined whether or not equal to the timer _{C 2} proceeds to step S30, the process proceeds to step S25 when not equal. On the other hand, when they are equal, the process proceeds to step S31, and the SOx release control is terminated. That resets the flag _{F 2} to 0 in step S31, the SOx sulfur-poisoning amount S at the step S32 0, respectively resets the count _{T 2} to 0 in step S33. In step S34, the target air-fuel ratio A / F is set to a lean state of 30. In step S35, the target air-fuel ratio A / F, the hydrogen / gasoline ratio corresponding to the operation mode, and the intake air amount are set. A gasoline injection amount and a target hydrogen injection amount are calculated. Next, it progresses to step S29, performs fuel injection based on the target gasoline injection quantity and target hydrogen injection quantity which were calculated by said step S35, and returns.

On the other hand, when the SOx sulfur-poisoning amount S is equal to or less than the predetermined amount _{S 1} in step S20, determines whether or not the acceleration at step S36 in FIG. 6. When the vehicle is accelerating, the target air-fuel ratio A / F is set to a rich state of 14.7 in step S37. In step S38, the target gasoline injection amount and the target hydrogen injection amount are calculated based on the target air-fuel ratio A / F and the intake air amount. In step S39, fuel injection is executed based on the target gasoline injection amount and target hydrogen injection amount calculated in step S38, and the process returns.

  On the other hand, when the vehicle is not accelerating in step S36, the target air-fuel ratio A / F is set to a lean state of 30 in step S40. In step S41, the target gasoline injection amount and the target hydrogen injection amount are calculated based on the target air-fuel ratio A / F, the hydrogen / gasoline ratio corresponding to the operation mode, and the intake air amount. In step S39, the above-described step S41 is performed. The fuel injection is executed based on the target gasoline injection amount and the target hydrogen injection amount calculated in step 1, and the process returns.

  In steps 26 and 27, in order to realize the SOx releasing air-fuel ratio A / F, first, the target hydrogen injection amount when the target air-fuel ratio A / F is 30 is obtained, and the shortage of fuel is converted into gasoline. The hydrogen / gasoline ratio for SOx release control (the gasoline ratio is larger than normal) is set in advance, and the target gasoline injection amount and target hydrogen injection are based on this ratio. The amount may be determined.

Next, the above control will be described with reference to a time chart shown in FIG. According to this, when the operation is performed in a lean operation state where the air-fuel ratio A / F is 30 and the throttle opening is substantially constant in the hydrogen main mode, the NOx occlusion amount Q increases with time, and the constant amount when the NOx occlusion quantity Q is determined to be increased to Q _2, performs control enriching 14.7 air-fuel ratio a / F until time _{C 1} has elapsed, NOx from the NOx storing catalyst 54 and 55 To release. In this NOx release control, the fuel is completely switched to gasoline (gasoline ratio 100%, hydrogen ratio 0%).

On the other hand, slowly SOx poisoning amount of the NOx occlusion quantity Q S also increased, when the SOx sulfur-poisoning amount S to a certain amount S ₁ is is determined to have increased, until the time C ₂ elapses empty Control to enrich the fuel ratio A / F to 14.7 is performed, and SOx is released from the NOx storage catalysts 54 and 55. At this time, the target hydrogen injection amount is calculated based on the target air-fuel ratio A / F in the normal lean operation shown in FIG. 3, the hydrogen / gasoline ratio corresponding to the operation mode, and the intake air amount. That is, the hydrogen injection amount is calculated in the same way as normal without performing any special calculation for SOx release control, so the hydrogen ratio decreases when enriched, and at the same time, the target air-fuel ratio A / F for SOx release is realized. Therefore, the gasoline ratio increases because the gasoline injection amount is increased. At this time, since a slight amount of hydrogen is contained in the fuel, the temperature of the exhaust gas can be raised to some extent, but the ignition timing may be retarded to reliably raise the temperature of the exhaust gas.

As described above, when the SOx sulfur-poisoning amount S is ₁ or more predetermined value S, is activated combustion by enriching the air-fuel ratio, releases sulfur at elevated exhaust gas temperature has been absorbed in the NOx storage catalyst 54 and 55 However, since the enrichment of the air-fuel ratio is realized by increasing the gasoline injection amount at this time, the increase in reducing power and the occurrence of incomplete combustion due to the increase in the hydrogen injection amount are avoided, and the H ₂ S Generation and vibration / noise generation can be suppressed. Furthermore, it is possible to raise the temperature of the exhaust gas by not containing 100% of the gasoline in the fuel at the time of sulfur release, adding hydrogen to the fuel in such a ratio that the reducing power does not become excessive and incomplete combustion does not occur. As a result, the efficiency of sulfur release can be improved.

  7 indicates the operation in the gasoline main mode shown in FIG. 3. In the SOx release control, the target air-fuel ratio for SOx release is set to 11, and the degree of richness is increased as compared with the hydrogen main mode. ing. Also at this time, the hydrogen injection amount is calculated based on the target air-fuel ratio A / F during normal lean operation as in the hydrogen main mode, and the target air-fuel ratio A / F for SOx release is realized by supplementing with gasoline. To do. In this way, control is performed so that the richness of the air-fuel ratio increases as the proportion of gasoline in the fuel increases, so that even if the proportion of gasoline in the fuel increases and the temperature rise effect decreases, the richness increases. Exhaust gas can be raised in temperature satisfactorily by simple combustion, and the efficiency of sulfur release from the NOx storage catalysts 54 and 55 can be improved.

The present invention provides a control apparatus for a hydrogen fuel engine that can suppress the generation of H ₂ S and the generation of vibration and noise during the release of sulfur from a NOx storage catalyst. The present invention relates to a control device for a hydrogen fuel engine that operates using at least one of hydrogen and fossil fuels such as gasoline, light oil, and natural gas as a fuel, and more specifically, a hydrogen fuel engine including a NOx storage catalyst in an exhaust passage. It is widely suitable for the technical field regarding the control device.

1 is a system configuration diagram of an engine according to an embodiment of the present invention. It is explanatory drawing of NOx and SOx occlusion / release in a NOx occlusion catalyst. It is a map which shows the operation mode according to an engine load and an engine speed. It is a flowchart which shows a NOx release control and a SOx release control procedure. It is a flowchart which shows the control procedure. It is a flowchart which shows the control procedure. It is a time chart which shows the change of each parameter by the control.

Explanation of symbols

1 Engine (hydrogen fuel engine)
6 Combustion chamber 28 Hydrogen injector (second fuel supply means)
29 Gasoline injector (first fuel supply means)
50 Exhaust passages 54, 55 NOx storage catalyst 70 ECU (control device, operation state detection means, fuel ratio change means, sulfur poisoning degree detection means, air-fuel ratio control means)

Claims (1)

A NOx storage catalyst that stores NOx when the air-fuel ratio is lean and releases NOx that is stored when the air-fuel ratio is the stoichiometric air-fuel ratio or rich is disposed in the exhaust passage to supply fossil fuel into the combustion chamber. 1 fuel supply means, second fuel supply means for supplying hydrogen into the combustion chamber, operating state detection means for detecting the operating state of the engine, and fossil fuel in the fuel supplied to the combustion chamber according to the operating state of the engine A control device for a hydrogen fuel engine having a fuel ratio changing means for changing the ratio of hydrogen to hydrogen, a sulfur poisoning degree detecting means for detecting a parameter relating to the sulfur poisoning degree of the NOx storage catalyst, and the detecting means while the rich air-fuel ratio when more sulfur poisoning degree predetermined is detected by, according to the operating state by the fuel ratio changing means the degree to which the air-fuel ratio to the rich The ratio of the fossil fuel that occupies a constant fuel are provided with air-fuel ratio control means so large that is greater, the fuel ratio changing means, when the air-fuel ratio is made rich by the air-fuel ratio control means, A control apparatus for a hydrogen fuel engine, characterized in that the ratio of fossil fuel is increased.

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