Engine System

Abstract

To provide an engine system capable of preventing oxidation deterioration of a catalyst in a reforming section.SOLUTION: An engine system 1 includes: an intake passage 4 in which air to be supplied to an ammonia engine 3 flows; a main throttle valve 7 controlling a flow rate of air to be supplied to the ammonia engine 3; a reforming section 21 having a reforming catalyst 21a decomposing the ammonia gas to hydrogen; an air flow passage 13 that is connected to the intake passage 4 and in which air to be supplied to the reforming section 21 flows; a sub throttle valve 14 controlling a flow rate of air to be supplied to the reforming section 21; an accelerator opening sensor 24 and an accelerator off determination section 26 detecting a state of an accelerator 24a; and an air flow control section 28 controlling the main throttle valve 7 and the sub throttle valve 14 so that air flows in the intake passage 4 in preference to the air flow passage 13 when switching of the accelerator 24a from the off state to the on state is detected.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an engine system. [Background technology]

[0002] Known conventional engine systems include, for example, the technology described in Patent Document 1. The engine system described in Patent Document 1 includes an engine block, an intake pipe connected to a combustion chamber of the engine block via a surge tank, an electronic throttle installed midway through the intake pipe, a bypass pipe branched off from the intake pipe, a reformer having a reforming catalyst and connected to the tip of the bypass pipe, a flow control valve installed midway through the bypass pipe, a connecting pipe connecting the reformer and the surge tank, and a fuel supply device that supplies fuel to the combustion chamber and the reformer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-251273 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, when a vehicle is traveling with the accelerator off, such as on a steep downhill slope, the supply of fuel to the combustion chamber is stopped and the electronic throttle and the flow control valve are closed, but the engine piston continues to reciprocate. If a butterfly valve or the like that is not completely sealed when fully closed is used as the electronic throttle and the flow control valve, a small amount of air leaks from the gap of the electronic throttle and the flow control valve, and a small amount of air flows into the engine and the reformer. At this time, the engine piston reciprocates, sucking air into the combustion chamber. Meanwhile, since the reformer operates in a reducing atmosphere, the reforming catalyst is in a reduced state. Therefore, when a small amount of air flows into the reforming catalyst, an oxidation reaction occurs between the reforming catalyst and the air. As a result, the reforming catalyst may become hot and deteriorate.

[0005] An object of the present invention is to provide an engine system capable of preventing oxidative deterioration of the catalyst in the reforming section. [Means for solving the problem]

[0006] One aspect of the present invention is an engine system mounted on a vehicle, the engine comprising: an intake passage through which air supplied to the engine flows; a first throttle valve disposed in the intake passage and configured to control the flow rate of air supplied to the engine; a first fuel supply valve configured to supply fuel to the engine; a reforming unit having a catalyst that decomposes fuel into hydrogen and that reforms the fuel to produce a reformed gas containing hydrogen; an air flow path connected to the intake passage through which air supplied to the reforming unit flows; a second throttle valve disposed in the air flow path and configured to control the flow rate of air supplied to the reforming unit; the second fuel supply valve configured to supply fuel to the reforming unit; a reformed gas flow path through which the reformed gas produced by the reforming unit flows towards the engine; an accelerator state detection unit that detects the state of the vehicle's accelerator; and an air flow control unit that controls controlled objects including the first throttle valve and the second throttle valve so that air flows preferentially into the intake passage over the air flow path when the accelerator state detection unit detects that the accelerator has changed from an on state to an off state.

[0007] In such an engine system, when it is detected that the accelerator of the vehicle has been changed from on to off, the control objects including the first throttle valve and the second throttle valve are controlled so that air flows preferentially to the intake passage rather than the air flow path. This makes it difficult for air to flow toward the reforming section. Therefore, even if a butterfly valve or the like that does not completely seal when fully closed is used as the second throttle valve, it is difficult for air to flow into the catalyst of the reforming section. This prevents oxidation deterioration of the catalyst of the reforming section.

[0008] The controlled objects are the first throttle valve and the second throttle valve, and the airflow control unit may control the second throttle valve to close and the first throttle valve to open when the accelerator state detection unit detects that the accelerator has changed from on to off. In this configuration, air flows through the intake passage toward the engine even when the accelerator changes from on to off. Therefore, air flows preferentially through the intake passage rather than the air flow path, without the need to add a new valve.

[0009] The engine system may further include a storage unit that stores opening data of the first throttle valve when the accelerator pedal changes from an on state to an off state, and the airflow control unit may control the opening of the first throttle valve according to the opening data of the first throttle valve stored in the storage unit. In such a configuration, since the opening data of the first throttle valve when the accelerator pedal changes from an on state to an off state is acquired in advance and stored in the storage unit, it is not necessary to use a sensor in controlling the opening of the first throttle valve, and the control process can be simplified.

[0010] The engine system may further include a first flow rate detector that detects the flow rate of air downstream of the first throttle valve in the intake passage and a second flow rate detector that detects the flow rate of air downstream of the second throttle valve in the air passage, and the air flow control unit may control the opening of the first throttle valve so that the flow rate of air downstream of the first throttle valve in the intake passage is greater than the flow rate of air downstream of the second throttle valve in the air passage. In this configuration, the flow rate of air supplied to the reforming unit can be brought close to zero while easily controlling the opening of the first throttle valve.

[0011] The engine system may further include a first pressure detector that detects the pressure downstream of the first throttle valve in the intake passage and a second pressure detector that detects the pressure downstream of the second throttle valve in the air passage, and the airflow control unit may control the opening of the first throttle valve so that the pressure downstream of the second throttle valve in the air passage is higher than the pressure downstream of the first throttle valve in the intake passage. In this configuration, air flows from the air passage side to the intake passage side, making it difficult for air to flow toward the reforming unit.

[0012] The engine system may further include a temperature detection unit that detects the temperature of the reforming unit, and the airflow control unit may control the opening of the first throttle valve so that the temperature of the reforming unit does not reach the deterioration temperature of the catalyst within a predetermined time. In this configuration, the temperature of the reforming unit does not reach the deterioration temperature of the catalyst within the predetermined time, thereby preventing oxidative deterioration of the catalyst.

[0013] The airflow control unit determines the gradient of the temperature rise of the reforming unit based on the temperatures of the reforming unit detected over time by the temperature detection unit, and controls the opening of the first throttle valve so that the gradient of the temperature rise of the reforming unit is equal to or less than a threshold value, and the threshold value may be a gradient value such that the temperature of the reforming unit does not reach the degradation temperature of the catalyst within a predetermined time. In this configuration, by determining the gradient of the temperature rise of the reforming unit, it is possible to easily realize control of the opening of the first throttle valve so that the temperature of the reforming unit does not reach the degradation temperature of the catalyst within a predetermined time.

[0014] The engine system may further include an on-off valve disposed in the air flow path, and the control targets are the first throttle valve, the second throttle valve, and the on-off valve, and the airflow control unit may control the first throttle valve and the second throttle valve to close and also control the on-off valve to close when the accelerator state detection unit detects that the accelerator has changed from an on state to an off state. In this configuration, when the accelerator changes from an on state to an off state, the on-off valve closes, making it difficult for air to flow through the air flow path toward the reforming unit, so that air flows preferentially into the intake passage rather than the air flow path. Effect of the Invention

[0015] According to the present invention, it is possible to prevent the catalyst in the reforming section from being deteriorated by oxidation. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic configuration diagram showing an engine system according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a vehicle traveling uphill and downhill; [Diagram 3] 4 is a graph showing an example of the relationship between the accelerator opening and the main throttle valve opening. [Figure 4] 4 is a flowchart showing the procedure of an airflow control process executed by the airflow control unit shown in FIG. [Diagram 5] FIG. 4 is a schematic configuration diagram showing an engine system according to a second embodiment of the present invention. [Figure 6] 6 is a flowchart showing the procedure of an airflow control process executed by the airflow control unit shown in FIG. 5. [Figure 7] FIG. 5 is a schematic configuration diagram showing an engine system according to a third embodiment of the present invention. [Figure 8] 8 is a flowchart showing the procedure of an airflow control process executed by the airflow control unit shown in FIG. [Figure 9] FIG. 11 is a schematic configuration diagram showing an engine system according to a fourth embodiment of the present invention. [Figure 10] 10 is a flowchart showing the procedure of an airflow control process executed by the airflow control unit shown in FIG. [Figure 11] 4 is a graph showing an example of the slope of the temperature rise of a reforming catalyst for comparison. [Figure 12] FIG. 11 is a schematic configuration diagram showing an engine system according to a fifth embodiment of the present invention. [Figure 13] 13 is a flowchart showing the procedure of an airflow control process executed by the airflow control unit shown in FIG. 12. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0018] Fig. 1 is a schematic diagram showing an engine system according to a first embodiment of the present invention. In Fig. 1, an engine system 1 of this embodiment is mounted on a vehicle 2 (see Fig. 2). The engine system 1 includes an ammonia engine 3, an intake passage 4, an exhaust passage 5, a main injector 6, and a main throttle valve 7.

[0019] The ammonia engine 3 is an engine that uses ammonia gas (NH3 gas) as fuel. In the ammonia engine 3, hydrogen (H2) is mixed with the ammonia gas as a combustion improver to facilitate combustion of the flame-retardant ammonia gas. The ammonia engine 3 has a combustion chamber (not shown) in which the ammonia gas is burned together with the hydrogen to generate exhaust gas.

[0020] The intake passage 4 and the exhaust passage 5 are connected to the combustion chamber of the ammonia engine 3. The intake passage 4 is a passage through which air supplied to the ammonia engine 3 flows. The exhaust passage 5 is a passage through which exhaust gas generated by the ammonia engine 3 flows.

[0021] The main injector 6 is an electromagnetic fuel injection valve that injects ammonia gas toward the ammonia engine 3. The main injector 6 constitutes a first fuel supply valve that supplies ammonia gas to the ammonia engine 3.

[0022] The main throttle valve 7 is disposed in the intake passage 4. The main throttle valve 7 is an electromagnetic first throttle valve that controls the flow rate of air supplied to the ammonia engine 3. The main throttle valve 7 is configured as a butterfly valve. An air cleaner 8 that removes foreign matter such as dust and dirt contained in the air is disposed upstream of the main throttle valve 7 in the intake passage 4.

[0023] The engine system 1 also includes an ammonia cylinder 10, a vaporizer 11, a reformer 12, an air passage 13, a sub-throttle valve 14, a sub-injector 15, a reformed gas passage 16, and a cooler 17.

[0024] The ammonia cylinder 10 is a container for storing ammonia in a liquid state. That is, the ammonia cylinder 10 stores liquid ammonia.

[0025] The vaporizer 11 vaporizes the liquid ammonia stored in the ammonia cylinder 10 to generate ammonia gas. The ammonia gas generated in the vaporizer 11 flows through an ammonia flow path 18 and is supplied to the main injector 6, and also flows through an ammonia flow path 19 and is supplied to the sub-injector 15.

[0026] The reformer 12 has a cylindrical housing 20, and a reforming section 21 and an electric heater 22 housed in the housing 20. The housing 20 is made of a metal material such as stainless steel that is resistant to corrosion by ammonia gas.

[0027] The reforming section 21 generates reformed gas containing hydrogen by reforming ammonia gas using heat generated by burning the ammonia gas. The reforming section 21 has a reforming catalyst 21a having, for example, a honeycomb structure. The reforming catalyst 21a is a catalyst that burns ammonia gas and decomposes the ammonia gas into hydrogen. The reforming catalyst 21a is, for example, an ATR (Autothermal Reformer) type ammonia reforming catalyst. As the reforming catalyst 21a, for example, a cobalt-based catalyst, a rhodium-based catalyst, a ruthenium-based catalyst, a palladium-based catalyst, or the like is used.

[0028] The electric heater 22 is disposed upstream of the reforming section 21 inside the housing 20. When power is applied to the electric heater 22, the electric heater 22 generates heat, and uses the heat to heat the reforming section 21. Specifically, the heat generated by the electric heater 22 is transmitted to the reforming section 21 through the housing 20 itself, and is also transmitted to the reforming section 21 through the ammonia gas and air flowing inside the housing 20.

[0029] The air flow path 13 connects the intake passage 4 and the reformer 12. One end of the air flow path 13 is connected to a position in the intake passage 4 between the air cleaner 8 and the main throttle valve 7. The other end of the air flow path 13 is connected to an inlet portion 20a of a housing 20 of the reformer 12. The air flow path 13 is a flow path through which air supplied to the reformer section 21 flows.

[0030] The sub-throttle valve 14 is disposed in the air flow path 13. The sub-throttle valve 14 is an electromagnetic second throttle valve that controls the flow rate of air supplied to the reforming section 21. Like the main throttle valve 7, the sub-throttle valve 14 is also configured as a butterfly valve.

[0031] The sub-injector 15 is an electromagnetic fuel injection valve that injects ammonia gas into the air flow path 13. The sub-injector 15 injects ammonia gas between the sub-throttle valve 14 and the reformer 12 in the air flow path 13. The sub-injector 15 constitutes a second fuel supply valve that supplies ammonia gas to the reforming section 21.

[0032] The reformed gas flow passage 16 connects the reformer 12 and the intake passage 4. One end of the reformed gas flow passage 16 is connected to an outlet portion 20b of a housing 20 of the reformer 12. The other end of the reformed gas flow passage 16 is connected to a portion of the intake passage 4 between the main throttle valve 7 and the ammonia engine 3. The reformed gas flow passage 16 is a flow passage through which the reformed gas generated by the reforming section 21 flows toward the ammonia engine 3.

[0033] The cooler 17 is disposed in the reformed gas passage 16. The cooler 17 cools the reformed gas flowing through the reformed gas passage 16, for example, by using engine cooling water that cools the ammonia engine 3.

[0034] The engine system 1 also includes an accelerator opening sensor 24 and a controller 25.

[0035] The accelerator opening sensor 24 is a sensor that detects the opening of an accelerator 24a of the vehicle 2 (see FIG. 2). The opening of the accelerator 24a corresponds to the depression amount of the accelerator pedal. The accelerator opening sensor 24 detects the opening of the accelerator 24a as the state of the accelerator 24a.

[0036] The controller 25 is configured with a CPU, a RAM, a ROM, an input / output interface, etc. The controller 25 has an accelerator-off determination unit 26, a storage unit 27, and an airflow control unit .

[0037] Accelerator off determination unit 26 determines whether accelerator 24a has changed from an on state to an off state, based on the opening of accelerator 24a detected by accelerator opening sensor 24. When accelerator 24a is on (hereinafter sometimes referred to as accelerator on), the accelerator pedal is depressed. When accelerator 24a is off (hereinafter sometimes referred to as accelerator off), the accelerator pedal is not depressed. Accelerator off determination unit 26 cooperates with accelerator opening sensor 24 to constitute an accelerator state detection unit that detects whether accelerator 24a has changed from an on state to an off state.

[0038] For example, as shown in Fig. 2, when the vehicle 2 travels on a steep uphill slope Ra, the accelerator pedal is depressed and the vehicle is in an accelerator-on state. After that, when the vehicle 2 travels on a steep downhill slope Rb after reaching the top of the uphill slope Ra, the accelerator pedal is not depressed and the vehicle is in an accelerator-off state.

[0039] 3, the memory unit 27 stores opening degree data of the main throttle valve 7 corresponding to the opening degree of the accelerator 24a. In other words, the memory unit 27 stores opening degree data of the main throttle valve 7 when the accelerator 24a changes from an on state to an off state.

[0040] In the opening data shown in Fig. 3, when the opening of the accelerator 24a is equal to or greater than a specified value, the opening of the main throttle valve 7 increases in proportion to the opening of the accelerator 24a. When the opening of the accelerator 24a is equal to or less than a specified value, the opening of the main throttle valve 7 is a constant value A regardless of the opening of the accelerator 24a. Therefore, the opening of the main throttle valve 7 is set so that the main throttle valve 7 opens slightly even when the opening of the accelerator 24a is 0 (accelerator off). Such opening data is determined in advance by experiment, etc.

[0041] When the accelerator-off determination unit 26 detects that the accelerator 24a has changed from an on state to an off state, the air flow control unit 28 controls the main throttle valve 7 and the sub-throttle valve 14 so that air flows preferentially into the intake passage 4 rather than into the air flow path 13. The main throttle valve 7 and the sub-throttle valve 14 are objects to be controlled.

[0042] When accelerator off determination unit 26 detects that accelerator 24a has changed from an on state to an off state, air flow control unit 28 controls sub throttle valve 14 to close and also controls main throttle valve 7 to open. At this time, air flow control unit 28 controls the opening of main throttle valve 7 in accordance with the opening data of main throttle valve 7 stored in memory unit 27.

[0043] 4 is a flowchart showing the procedure of the air flow control process executed by the air flow control unit 28. This process is executed when an ignition switch (not shown) of the vehicle 2 is turned ON.

[0044] 4, the air flow control unit 28 first judges whether the accelerator-off judgment unit 26 judges that the accelerator has changed from an accelerator-on state to an accelerator-off state (step S101). When it is judged that the accelerator has changed from an accelerator-on state to an accelerator-off state, the air flow control unit 28 reads the opening degree data of the main throttle valve 7 stored in the memory unit 27 (step S102).

[0045] Then, the air flow control unit 28 controls the opening of the main throttle valve 7 in accordance with the read opening data, and also controls the sub-throttle valve 14 to be fully closed (step S103).

[0046] In the engine system 1 as described above, when an ignition switch (not shown) of the vehicle 2 is turned on, the electric heater 22 is energized to heat the reforming section 21, so that the temperature of the reforming section 21 rises.

[0047] Then, when the main throttle valve 7 opens, air is supplied to the ammonia engine 3. In addition, when the sub-injector 15 and the sub-throttle valve 14 open, ammonia gas and air are supplied to the reforming section 21.

[0048] When the temperature of the reforming section 21 reaches the activation temperature, the ammonia gas is burned by the reforming catalyst 21a. Specifically, as shown in the following formula, ammonia and oxygen in the air undergo a chemical reaction (exothermic reaction). NH3+3 / 4O2→1 / 2N2+3 / 2H2O …(A)

[0049] Then, the temperature of the reforming section 21 further increases due to the heat of combustion of the ammonia gas. Then, when the temperature of the reforming section 21 reaches the reaction temperature, the ammonia gas is reformed by the reforming catalyst 21a. Specifically, as shown in the following formula, a decomposition reaction of ammonia occurs (endothermic reaction), and a reformed gas containing hydrogen is generated. NH3→3 / 2H2+1 / 2N2…(B)

[0050] The reformed gas flows through the reformed gas flow passage 16 and the intake passage 4 and is supplied to the ammonia engine 3. Furthermore, the main injector 6 opens, so that ammonia gas is supplied to the ammonia engine 3. Then, in the ammonia engine 3, the state transitions to a steady state in which the ammonia gas is combusted together with the hydrogen in the reformed gas.

[0051] In a steady state, the openings of the main injector 6 and the sub-injector 15 are controlled according to the rotation speed and load of the ammonia engine 3, and the openings of the main throttle valve 7 and the sub-throttle valve 14 are also controlled.

[0052] 2, when the vehicle 2 travels on a steep uphill slope Ra, the accelerator pedal is depressed to a large extent, and the accelerator is in an on state. As a result, the openings of the main injector 6 and the sub-injector 15 become larger, increasing the amount of ammonia gas supplied to the ammonia engine 3 and the reforming section 21, while the openings of the main throttle valve 7 and the sub-throttle valve 14 become larger, increasing the amount of air supplied to the ammonia engine 3 and the reforming section 21.

[0053] Thereafter, when the vehicle 2 travels on a steep downhill slope Rb, the accelerator pedal is not depressed and the accelerator is off. At this time, the main injector 6 and the sub injector 15 are fully closed, and ammonia gas is not supplied to the ammonia engine 3 and the reforming section 21. In addition, the sub throttle valve 14 is fully closed, but the main throttle valve 7 opens slightly.

[0054] Generally, when the opening of the accelerator 24a becomes 0, the opening of the main throttle valve 7 also becomes 0 (see the dashed line in FIG. 3), so that the main throttle valve 7 as well as the sub-throttle valve 14 are fully closed.

[0055] However, the main throttle valve 7 and the sub-throttle valve 14 are configured as inexpensive butterfly valves, and are not completely sealed even when fully closed, so air gradually leaks out. For this reason, even when the sub-throttle valve 14 is fully closed, a small amount of air flows into the reforming section 21. Since the reforming section 21 operates in a reducing atmosphere, the reforming catalyst 21a is in a reducing state. When a small amount of air flows into such a reforming catalyst 21a, an oxidation reaction occurs between the reforming catalyst 21a and the air, and the temperature of the reforming catalyst 21a rises. This leads to oxidation deterioration of the reforming catalyst 21a.

[0056] To address this issue, in this embodiment, as shown in FIG. 3, even when the opening of the accelerator 24a becomes 0 (accelerator off), the opening of the main throttle valve 7 is controlled so that a small amount of air flows through the intake passage 4 toward the ammonia engine 3, so that air is less likely to flow to the reforming section 21.

[0057] As described above, according to this embodiment, when it is detected that the accelerator 24a of the vehicle 2 has changed from an on state to an off state, the main throttle valve 7 and the sub-throttle valve 14 are controlled so that air flows preferentially into the intake passage 4 rather than into the air flow path 13. This makes it difficult for air to flow toward the reforming section 21. Therefore, even if a butterfly valve that is not completely sealed when fully closed is used as the sub-throttle valve 14, it is difficult for air to flow into the reforming catalyst 21a of the reforming section 21. This prevents oxidative deterioration of the reforming catalyst 21a.

[0058] Furthermore, in this embodiment, when it is detected that the accelerator 24a has changed from an on state to an off state, the sub throttle valve 14 is controlled to close and the main throttle valve 7 is controlled to open. Therefore, even when the accelerator 24a changes from an on state to an off state, air flows through the intake passage 4 toward the ammonia engine 3. Therefore, even without adding a new valve, air flows preferentially through the intake passage 4 rather than the air flow path 13.

[0059] Furthermore, in this embodiment, since it is sufficient to obtain in advance and store in the memory unit 27 the opening data of the main throttle valve 7 when the accelerator 24a changes from the on state to the off state, there is no need to use a sensor in controlling the opening of the main throttle valve 7, and the control process can be simplified.

[0060] 5 is a schematic diagram showing an engine system according to a second embodiment of the present invention. In FIG. 5, an engine system 1A of this embodiment includes flow rate sensors 31 and 32 in addition to the configuration of the first embodiment.

[0061] The flow rate sensor 31 is connected between the main throttle valve 7 in the intake passage 4 and the ammonia engine 3. The flow rate sensor 31 is a sensor (first flow rate detection unit) that detects the flow rate of air downstream of the main throttle valve 7 in the intake passage 4.

[0062] The flow rate sensor 32 is connected in the air flow path 13 between the sub-throttle valve 14 and the reformer 12. The flow rate sensor 32 is a sensor (second flow rate detection unit) that detects the flow rate of air downstream of the sub-throttle valve 14 in the air flow path 13.

[0063] Moreover, the engine system 1A includes a controller 25A instead of the controller 25 in the first embodiment. The controller 25A includes the accelerator-off determination unit 26 and an airflow control unit 28A.

[0064] When the accelerator off determination unit 26 detects that the accelerator 24a has changed from an on state to an off state, the air flow control unit 28A controls the sub throttle valve 14 to close, and also controls the main throttle valve 7 to open based on the detection values ​​of the flow sensors 31, 32.

[0065] At this time, the air flow control unit 28A controls the opening degree of the main throttle valve 7 so that the flow rate of air downstream of the main throttle valve 7 in the intake passage 4 is greater than the flow rate of air downstream of the sub-throttle valve 14 in the air flow path 13.

[0066] FIG. 6 is a flowchart showing the procedure of the air flow control process executed by air flow control unit 28A, and corresponds to FIG.

[0067] In FIG. 6, when it is determined in step S101 that the accelerator state has changed from the accelerator on state to the accelerator off state, the air flow control unit 28A acquires the detection values ​​of the flow rate sensors 31 and 32 (step S112).

[0068] Then, the air flow control unit 28A sets the opening degree of the main throttle valve 7 so that the flow rate of air downstream of the main throttle valve 7 in the intake passage 4 (main side air flow rate) is greater than the flow rate of air downstream of the sub-throttle valve 14 in the air flow path 13 (sub side air flow rate) (step S113). At this time, the opening degree of the main throttle valve 7 is set so that a desired amount of air flows toward the ammonia engine 3, thereby making the flow rate of air toward the reforming unit 21 approximately zero.

[0069] Next, the air flow control section 28A controls the opening of the main throttle valve 7 in accordance with the opening set in step S113, and also controls the sub-throttle valve 14 to be fully closed (step S114).

[0070] In the present embodiment as described above, when it is detected that the accelerator 24a has changed from an on state to an off state, the opening of the main throttle valve 7 is controlled so that the flow rate of air downstream of the main throttle valve 7 in the intake passage 4 is greater than the flow rate of air downstream of the sub-throttle valve 14 in the air flow path 13. Therefore, the flow rate of air supplied to the reforming section 21 can be brought close to zero while easily controlling the opening of the main throttle valve 7.

[0071] 7 is a schematic diagram showing an engine system according to a third embodiment of the present invention. In FIG. 7, an engine system 1B of this embodiment includes pressure sensors 35 and 36 in addition to the configuration in the first embodiment.

[0072] The pressure sensor 35 is connected in the intake passage 4 between the main throttle valve 7 and the ammonia engine 3. The pressure sensor 35 is a first pressure detection unit that detects the pressure in the intake passage 4 downstream of the main throttle valve 7.

[0073] The pressure sensor 36 is connected in the air flow path 13 between the sub-throttle valve 14 and the reformer 12. The pressure sensor 36 is a second pressure detection unit that detects the pressure in the air flow path 13 downstream of the sub-throttle valve 14.

[0074] Moreover, the engine system 1B includes a controller 25B instead of the controller 25 in the above-described first embodiment. The controller 25B includes the above-described accelerator-off determination unit 26 and an airflow control unit 28B.

[0075] When the accelerator off determination unit 26 detects that the accelerator 24a has changed from an on state to an off state, the air flow control unit 28B controls the sub throttle valve 14 to close, and also controls the main throttle valve 7 to open based on the detection values ​​of the pressure sensors 35, 36.

[0076] At this time, the air flow control unit 28B controls the opening degree of the main throttle valve 7 so that the pressure downstream of the sub-throttle valve 14 in the air flow path 13 is higher than the pressure downstream of the main throttle valve 7 in the intake passage 4.

[0077] FIG. 8 is a flowchart showing the procedure of the air flow control process executed by air flow control unit 28B, and corresponds to FIG.

[0078] In FIG. 8, when it is determined in step S101 that the accelerator-on state has changed to the accelerator-off state, the airflow control unit 28B acquires the detection values ​​of the pressure sensors 35 and 36 (step S122).

[0079] Then, the air flow control unit 28B sets the opening degree of the main throttle valve 7 so that the pressure downstream of the sub-throttle valve 14 in the air flow path 13 (sub-side pressure) is higher than the pressure downstream of the main throttle valve 7 in the intake passage 4 (main-side pressure) (step S123).

[0080] Next, the air flow control section 28B controls the opening of the main throttle valve 7 in accordance with the opening set in step S123, and also controls the sub-throttle valve 14 to be fully closed (step S124).

[0081] In the present embodiment as described above, when it is detected that the accelerator 24a has changed from an on state to an off state, the opening degree of the main throttle valve 7 is controlled so that the pressure downstream of the sub-throttle valve 14 in the air passage 13 becomes higher than the pressure downstream of the main throttle valve 7 in the intake passage 4. Therefore, air flows from the air passage 13 side to the intake passage 4 side, making it difficult for air to flow toward the reforming section 21.

[0082] 9 is a schematic diagram showing an engine system according to a fourth embodiment of the present invention. In FIG. 9, an engine system 1C of this embodiment includes a temperature sensor 38 in addition to the components in the first embodiment.

[0083] The temperature sensor 38 is connected to the reforming section 21. The temperature sensor 38 is a temperature detection section that detects the temperature of the reforming section 21. The temperature sensor 38 detects, for example, the temperature of the reforming catalyst 21a.

[0084] Moreover, the engine system 1C includes a controller 25C in place of the controller 25 in the above-described first embodiment. The controller 25C includes the above-described accelerator-off determination unit 26 and an airflow control unit 28C.

[0085] When the accelerator off determination unit 26 detects that the accelerator 24a has changed from an on state to an off state, the air flow control unit 28C controls the sub throttle valve 14 to close, and also controls the main throttle valve 7 to open based on the detection value of the temperature sensor 38.

[0086] At this time, the airflow control unit 28C controls the opening of the main throttle valve 7 so that the temperature of the reforming unit 21 does not reach the degradation temperature of the reforming catalyst 21a within a predetermined time. Specifically, the airflow control unit 28C determines the gradient of the temperature rise of the reforming unit 21 based on the temperature of the reforming unit 21 detected over time by the temperature sensor 38, and controls the opening of the main throttle valve 7 so that the gradient of the temperature rise of the reforming unit 21 is equal to or less than a threshold value.

[0087] FIG. 10 is a flowchart showing the procedure of the air flow control process executed by air flow control unit 28C, and corresponds to FIG.

[0088] In FIG. 10, when it is determined in step S101 that the accelerator-on state has changed to an accelerator-off state, the airflow control unit 28C acquires the detection values ​​of the temperature sensor 38 in chronological order (step S132).

[0089] Then, the airflow control unit 28C calculates the gradient of the temperature rise in the reforming unit 21 based on the time-series detection values ​​of the temperature sensor 38 (step S133). Next, the airflow control unit 28C sets the opening degree of the main throttle valve 7 so that the gradient of the temperature rise in the reforming unit 21 is equal to or smaller than a threshold value (step S134).

[0090] 11(a), when the vehicle 2 is running in a steady state and the accelerator is switched from an on state to an off state, the temperature of the reforming catalyst 21a rises from the steady operating temperature T0 (for example, about 600°C) and may exceed the deterioration temperature Tx. The deterioration temperature Tx is the temperature at which the reforming catalyst 21a is oxidized and deteriorated.

[0091] The threshold value is a gradient value S at which the temperature of the reforming catalyst 21a does not reach the degradation temperature Tx in a predetermined time assumed when the vehicle 2 travels downhill Rb (see FIG. 2), as shown in FIG. 11(b).

[0092] Next, the air flow control section 28C controls the opening of the main throttle valve 7 in accordance with the opening set in step S134, and also controls the sub-throttle valve 14 to be fully closed (step S135).

[0093] In the present embodiment as described above, when it is detected that the accelerator 24a has changed from an on state to an off state, the opening degree of the main throttle valve 7 is controlled so that the temperature of the reforming section 21 does not reach the deterioration temperature of the reforming catalyst 21a within a predetermined time. Therefore, since the temperature of the reforming section 21 does not reach the deterioration temperature of the reforming catalyst 21a within the predetermined time, oxidation deterioration of the reforming catalyst 21a is prevented.

[0094] Furthermore, in this embodiment, the gradient of the temperature rise of the reforming section 21 is obtained based on the temperatures of the reforming section 21 detected over time, and the opening of the main throttle valve 7 is controlled so that the gradient of the temperature rise of the reforming section 21 is equal to or less than a threshold value. By obtaining the gradient of the temperature rise of the reforming section 21 in this manner, it is possible to easily realize control of the opening of the main throttle valve 7 so that the temperature of the reforming section 21 does not reach the deterioration temperature of the reforming catalyst 21a within a predetermined time.

[0095] Fig. 12 is a schematic diagram showing an engine system according to a fifth embodiment of the present invention. In Fig. 12, an engine system 1D of this embodiment includes an on-off valve 40 disposed in the air flow path 13 in addition to the configuration in the first embodiment.

[0096] The on-off valve 40 is disposed upstream of the sub-throttle valve 14 in the air flow path 13. The on-off valve 40 is an electromagnetic ON / OFF valve that allows or blocks the flow of air in the air flow path 13. The on-off valve 40 is less susceptible to air leakage in the closed state than the sub-throttle valve 14. The on-off valve 40 may be disposed downstream of the sub-throttle valve 14 in the air flow path 13.

[0097] Moreover, the engine system 1D includes a controller 25D instead of the controller 25 in the first embodiment. The controller 25D includes the accelerator-off determination unit 26 and an airflow control unit 28D.

[0098] When the accelerator off determination unit 26 detects that the accelerator 24a has changed from an on state to an off state, the air flow control unit 28D controls the main throttle valve 7, the sub-throttle valve 14, and the opening / closing valve 40 so that air flows preferentially into the intake passage 4 rather than into the air flow path 13. The opening / closing valve 40 is one of the objects to be controlled, together with the main throttle valve 7 and the sub-throttle valve 14.

[0099] The air flow control unit 28D normally controls the on-off valve 40 to be open. When the accelerator off determination unit 26 detects that the accelerator 24a has changed from the on state to the off state, the air flow control unit 28D controls the main throttle valve 7 and the sub throttle valve 14 to be closed, and also controls the on-off valve 40 to be closed.

[0100] FIG. 13 is a flowchart showing the procedure of the air flow control process executed by air flow control unit 28D, and corresponds to FIG.

[0101] 13, when it is determined in step S101 that the accelerator has been released from the accelerator on state, the airflow control unit 28D controls the main throttle valve 7 and the sub throttle valve 14 to be fully closed (step S142). The airflow control unit 28D also controls the opening / closing valve 40 to be closed (step S143).

[0102] In the present embodiment as described above, when it is detected that the accelerator 24a has changed from an on state to an off state, the main throttle valve 7 and the sub throttle valve 14 are controlled to close, and the on-off valve 40 is also controlled to close. Therefore, when the accelerator 24a changes from an on state to an off state, the on-off valve 40 closes, making it difficult for air to flow through the air flow path 13 toward the reforming section 21, so that air flows preferentially into the intake passage 4 rather than into the air flow path 13.

[0103] The present invention is not limited to the above embodiment. For example, in the above embodiment, the accelerator opening sensor 24 detects the opening of the accelerator 24a (the depression amount of the accelerator pedal) as the state of the accelerator 24a, but the present invention is not limited to this form, and the depression position of the accelerator pedal, etc. may be detected as the state of the accelerator 24a.

[0104] In the above embodiment, the reforming unit 21 has the reforming catalyst 21a that has both the function of burning ammonia gas and the function of decomposing the ammonia gas into hydrogen, but is not particularly limited to such a form. The reforming unit 21 may have a combustion catalyst that burns ammonia gas and a reforming catalyst that decomposes the ammonia gas into hydrogen separately.

[0105] Furthermore, in the above embodiment, ammonia is used as the fuel, but the present invention is also applicable to an engine system that uses a hydrocarbon or the like as the fuel.

[0106] Furthermore, in the above embodiment, it is detected that the accelerator 24a has changed from an on state to an off state as the vehicle 2 travels down a steep downhill slope Rb. However, the present invention is not limited to travel downhill, but can also be applied, for example, to a case where the engine brake is applied while traveling on a flat road, or where the engine crank rotates by inertia immediately after the engine is stopped. [Explanation of symbols]

[0107] 1, 1A, 1B, 1C, 1D... engine system, 2... vehicle, 3... ammonia engine (engine), 4... intake passage, 6... main injector (first fuel supply valve), 7... main throttle valve (first throttle valve, control object), 13... air flow path, 14... sub throttle valve (second throttle valve, control object), 15... sub injector (second fuel supply valve), 16... reformed gas flow path, 21... reforming section, 21a... reforming catalyst (catalyst), 24...accelerator opening sensor (accelerator state detection unit), 24a...accelerator, 26...accelerator off determination unit (accelerator state detection unit), 27...memory unit, 28, 28A, 28B, 28C, 28D...air flow control unit, 31...flow sensor (first flow rate detection unit), 32...flow sensor (second flow rate detection unit), 35...pressure sensor (first pressure detection unit), 36...pressure sensor (second pressure detection unit), 38...temperature sensor (temperature detection unit), 40...opening / closing valve (controlled object).

Claims

1. In an engine system installed in a vehicle, The engine, an intake passage through which air supplied to the engine flows; a first throttle valve disposed in the intake passage and configured to control a flow rate of air supplied to the engine; a first fuel supply valve for supplying fuel to the engine; a reforming unit that has a catalyst for decomposing fuel into hydrogen and reforms the fuel to generate a reformed gas containing hydrogen; an air flow path connected to the intake passage, through which air to be supplied to the reforming section flows; a second throttle valve disposed in the air flow passage and configured to control a flow rate of air supplied to the reforming section; a second fuel supply valve that supplies fuel to the reforming section; a reformed gas flow path through which the reformed gas generated by the reforming unit flows toward the engine; an accelerator state detection unit that detects a state of an accelerator of the vehicle; an air flow control unit that controls controlled objects including the first throttle valve and the second throttle valve so that air flows preferentially into the intake passage rather than the air flow path when the accelerator state detection unit detects that the accelerator has changed from an on state to an off state and the second fuel supply valve is fully closed.

2. the controlled object is the first throttle valve and the second throttle valve, 2. The engine system according to claim 1, wherein when the accelerator state detection unit detects that the accelerator has changed from an on state to an off state, the air flow control unit controls the second throttle valve to close and controls the first throttle valve to open in a state in which the second fuel supply valve is fully closed.

3. a storage unit configured to store opening data of the first throttle valve when the accelerator pedal is changed from an on state to an off state, 3. The engine system according to claim 2, wherein the airflow control unit controls the opening of the first throttle valve in accordance with the opening data of the first throttle valve stored in the memory unit.

4. a first flow rate detection unit that detects a flow rate of air downstream of the first throttle valve in the intake passage; a second flow rate detector configured to detect a flow rate of air downstream of the second throttle valve in the air flow path, 3. The engine system according to claim 2, wherein the air flow control unit controls the opening degree of the first throttle valve so that a flow rate of air downstream of the first throttle valve in the intake passage is greater than a flow rate of air downstream of the second throttle valve in the air flow passage.

5. a first pressure detection unit that detects a pressure in the intake passage downstream of the first throttle valve; a second pressure detection unit that detects a pressure downstream of the second throttle valve in the air flow path, 3. The engine system according to claim 2, wherein the airflow control unit controls the opening degree of the first throttle valve so that pressure downstream of the second throttle valve in the air flow passage is higher than pressure downstream of the first throttle valve in the intake passage.

6. Further comprising a temperature detector for detecting the temperature of the reforming unit, 3. The engine system according to claim 2, wherein the airflow control section controls the opening of the first throttle valve so that the temperature of the reforming section does not reach a deterioration temperature of the catalyst within a predetermined time.

7. the airflow control unit determines a gradient of a temperature rise in the reforming unit based on the temperature of the reforming unit detected over time by the temperature detection unit, and controls an opening degree of the first throttle valve so that the gradient of the temperature rise in the reforming unit is equal to or smaller than a threshold value; 7. The engine system according to claim 6, wherein the threshold value is a gradient value that prevents the temperature of the reforming section from reaching a deterioration temperature of the catalyst within the predetermined time.

8. An on-off valve is further provided in the air flow path, the controlled objects are the first throttle valve, the second throttle valve, and the on-off valve, 2. The engine system according to claim 1, wherein when the accelerator state detection unit detects that the accelerator has changed from an on state to an off state, the air flow control unit controls the first throttle valve and the second throttle valve to close and controls the opening / closing valve to close in a state in which the second fuel supply valve is fully closed.

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