Bi-fuel vehicle

Abstract

To provide a bi-fuel vehicle capable of improving startability when restarting an internal combustion engine from an automatic stop even when using fuel with poor startability.SOLUTION: Startability of an internal combustion engine when using first fuel is inferior to the startability of the same when using second fuel. When restarting using the first fuel (CNG) with a restart condition met (Yes in Step S1 and Yes in Step S2), an ECU injects the second fuel (gasoline) a predetermined number of times (Step S6) at the start of a restart and, then, continues the restart by injecting the first fuel (Step S7). The ECU acquires a cranking speed during the restart and sets the predetermined number of times according to the cranking speed (Step S5). The ECU injects the second fuel the predetermined number of times at the start of the restart (Step S7) under a condition that the cranking speed is less than a predetermined value (Yes in Step S4).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a bi-fuel vehicle. [Background technology]

[0002] Patent Document 1 describes a bi-fuel vehicle with an internal combustion engine that can switch between two types of fuel. This bi-fuel vehicle is equipped with a liquid fuel injector that injects gasoline and a gas fuel injector that injects CNG (compressed natural gas). The liquid fuel injector is located in an intake port just before the combustion chamber in the intake path, and the gas fuel injector is located in an intake manifold upstream of the liquid fuel injector in the intake path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-138275 Summary of the Invention [Problem to be solved by the invention]

[0004] In the bi-fuel vehicle described in Patent Document 1, the distance from the gas fuel injector to the combustion chamber is longer than that of a liquid fuel injector, and the time it takes for the gas fuel to reach the combustion chamber is longer than that for the liquid fuel.

[0005] In general, gaseous fuels have a smaller mass than liquid fuels, so their flow rate decreases when the inertial force of the intake air weakens.Furthermore, gaseous fuels made from CNG have a higher ignition point than liquid fuels made from gasoline.

[0006] Therefore, in the bi-fuel vehicle described in Patent Document 1, due to the placement of the fuel injector (distance to the combustion chamber) and the fuel characteristics (ignition point), when restarting the internal combustion engine using CNG from an idle stop, it takes a long time from the start of cranking to the start of independent rotation, and since the starting performance of the internal combustion engine is poor, there is a possibility that the vehicle will not be able to start at the time intended by the driver.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a bi-fuel vehicle that can improve the startability when restarting an internal combustion engine after automatic shutdown, even when using a fuel with poor startability. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the present invention provides a bi-fuel vehicle comprising an internal combustion engine operated by injecting either a first fuel or a second fuel of different types, and a control unit that automatically stops the internal combustion engine when a predetermined automatic stop condition is met and restarts the internal combustion engine when a predetermined restart condition is met while the internal combustion engine is automatically stopped, wherein the startability of the internal combustion engine when using the first fuel is inferior to the startability of the internal combustion engine when using the second fuel, and when the restart is performed using the first fuel due to the restart condition being met, the control unit injects the second fuel a predetermined number of times at the start of the restart, and then continues the restart by injecting the first fuel. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a bi-fuel vehicle that can improve the startability when restarting an internal combustion engine after an automatic stop, even when using a fuel that is poor in startability. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the configuration of a bi-fuel vehicle according to an embodiment of the present invention. [Figure 2]FIG. 2 is a flowchart illustrating the operation of the ECU when restarting the internal combustion engine in the bi-fuel vehicle according to one embodiment of the present invention. [Figure 3] FIG. 3 is a timing chart showing the transition of the vehicle state when the internal combustion engine in the bi-fuel vehicle according to one embodiment of the present invention is restarted. [Figure 4] FIG. 4 is a timing chart showing the transition of the vehicle state when the cranking rotation speed is high when restarting the internal combustion engine in a bi-fuel vehicle according to one embodiment of the present invention. [Figure 5] FIG. 5 is a timing chart showing the transition of the vehicle state when the cranking rotation speed is low when restarting the internal combustion engine in a bi-fuel vehicle according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] A bi-fuel vehicle according to one embodiment of the present invention is a bi-fuel vehicle including an internal combustion engine operated by injecting either a first fuel or a second fuel, which are different from each other, and a control unit that automatically stops the internal combustion engine when a predetermined automatic stop condition is met and restarts the internal combustion engine when a predetermined restart condition is met while the internal combustion engine is automatically stopped, wherein the startability of the internal combustion engine when using the first fuel is inferior to the startability of the internal combustion engine when using the second fuel, and when restarting using the first fuel due to the restart condition being met, the control unit injects the second fuel a predetermined number of times at the start of the restart and then continues the restart by injecting the first fuel. This allows the bi-fuel vehicle according to one embodiment of the present invention to improve the startability of the internal combustion engine when restarting from automatic stop, even when using a fuel with inferior startability. [Example]

[0012] An embodiment of the present invention will be described below with reference to Figures 1 to 5. As shown in Figure 1, a vehicle 1 equipped with a bi-fuel vehicle according to an embodiment of the present invention includes an internal combustion engine 10, a fuel supply device 20 that supplies fuel to the internal combustion engine 10, and an ECU 100 as a control unit.

[0013] In this embodiment, the vehicle 1 is a bi-fuel vehicle, and the internal combustion engine 10 is a bi-fuel engine that can selectively use a gas fuel as a second fuel or a liquid fuel as a first fuel. The vehicle 1 uses CNG (compressed natural gas) as the gas fuel and gasoline as the liquid fuel.

[0014] The internal combustion engine 10 includes, in order from upstream to downstream in the air flow direction, an air cleaner (not shown), a throttle valve 11, a surge tank 12, an intake manifold 14, and an intake port 19. The interior of the intake manifold 14 and the intake port 19 constitute an intake path 21.

[0015] The air that has flowed into the surge tank 12 is divided into intake manifolds 14 that individually correspond to a plurality of cylinders 13 (four in this embodiment) provided in the internal combustion engine 10.

[0016] Four strokes are performed in sequence in each cylinder 13. More specifically, when the piston 15 moves downward in FIG. 1 from top dead center, the mixed fuel is supplied into the cylinder 13 via the intake valve 16 (intake stroke). Then, in the cylinder 13 to which the mixed fuel has been supplied, the mixed fuel is compressed as the piston 15 moves upward in FIG. 1 (compression stroke).

[0017] Thereafter, when the piston 15 reaches the top dead center and starts to move downward again in FIG. 1, the fuel mixture is burned in the cylinder 13 by ignition of a plug (not shown), and the thrust generated by this combustion is transmitted to the crankshaft 17 via the piston 15 (combustion stroke).

[0018] Then, the crankshaft 17 rotates in a specified direction due to the transmitted thrust, and the piston 15 reaches bottom dead center and moves upward in FIG. 1, and the exhaust gas, which is the burned mixed fuel, is exhausted out of the cylinder 13 through the exhaust valve 18 (exhaust stroke).

[0019] Next, the fuel supply device 20 will be described. The fuel supply device 20 includes a liquid fuel supply system 30 and a gaseous fuel supply system 40. The liquid fuel supply system 30 supplies liquid fuel stored in a liquid fuel tank 31 to each cylinder 13 of the internal combustion engine 10. The gaseous fuel supply system 40 supplies gaseous fuel stored at high pressure in a gaseous fuel tank 41 to each cylinder 13 of the internal combustion engine 10.

[0020] The liquid fuel supply system 30 includes a fuel pump 32 that draws liquid fuel from inside a liquid fuel tank 31, a liquid fuel delivery pipe 33 through which the fuel discharged from the fuel pump 32 is pumped, and a liquid fuel injector 34 connected to the liquid fuel delivery pipe 33.

[0021] The liquid fuel injector 34 injects liquid fuel into each intake port 19 that individually corresponds to each cylinder 13 of the internal combustion engine 10. The injection timing, number of injections, and length of injection time of the liquid fuel are controlled by the ECU 100. In this way, the liquid fuel injector 34 injects liquid fuel (gasoline) as a second fuel into the intake path 21 of the internal combustion engine 10, and constitutes a second injector in the present invention.

[0022] The gas fuel supply system 40 includes a high-pressure fuel pipe 42 connected to a gas fuel tank 41, a gas fuel delivery pipe 43 connected to the downstream end (the right end in FIG. 1) of the high-pressure fuel pipe 42, and a gas fuel injector 47 connected to the gas fuel delivery pipe 43.

[0023] The gas fuel tank 41 is connected to the high-pressure fuel pipe 42 via a main valve 44 equipped with a normally closed solenoid valve. The main valve 44 is opened and closed by the ECU 100. When the main valve 44 is in a closed state, the inside of the gas fuel tank 41 is sealed.

[0024] In addition, a shutoff valve 45 is provided in the high-pressure fuel pipe 42 downstream of the main valve 44 (to the right in FIG. 1 ). The shutoff valve 45 is opened and closed by the ECU 100. When both the main valve 44 and the shutoff valve 45 are open, the gaseous fuel in the gaseous fuel tank 41 is supplied to the gaseous fuel delivery pipe 43 via the high-pressure fuel pipe 42. When the shutoff valve 45 is closed, the gaseous fuel is no longer supplied to the gaseous fuel delivery pipe 43.

[0025] In addition, a regulator 46 is provided in the high-pressure fuel pipe 42 downstream of the shutoff valve 45. The regulator 46 reduces the pressure of the gaseous fuel supplied from the gaseous fuel tank 41 (i.e., on the upstream side), i.e., the fuel pressure, so that gaseous fuel at a specified fuel pressure is supplied to the gaseous fuel delivery pipe 43.

[0026] The gaseous fuel injector 47 injects gaseous fuel into each intake manifold 14 that individually corresponds to each cylinder 13 of the internal combustion engine 10. In this embodiment, the injection timing, number of injections, and length of injection time of the gaseous fuel are controlled by the ECU 100. As described above, the gaseous fuel injector 47 injects gaseous fuel (CNG) as a first fuel into the intake path 21 of the internal combustion engine 10, and constitutes a first injector in the present invention. The gaseous fuel injector 47 is disposed upstream of the liquid fuel injector 34 in the intake path 21.

[0027] The internal combustion engine 10 is provided with a starter 52, which starts the internal combustion engine 10 by rotating a flywheel 53 connected to the crankshaft 17 of the internal combustion engine 10 (hereinafter also referred to as cranking).

[0028] The vehicle 1 is provided with a fuel selection switch 51, and the driver uses the fuel selection switch 51 to select whether gas fuel or liquid fuel is to be used as fuel for the internal combustion engine 10.

[0029] The vehicle 1 is provided with an intake air temperature sensor 54 that detects the temperature of the air passing through the intake path 21 and a coolant temperature sensor 55 that detects the temperature of the coolant flowing through the internal combustion engine 10.

[0030] The vehicle 1 is equipped with a gaseous fuel temperature sensor 56. The gaseous fuel temperature sensor 56 is provided in the gaseous fuel delivery pipe 43 and detects the temperature of the gaseous fuel in the gaseous fuel delivery pipe 43. Detection signals from the intake air temperature sensor 54, the coolant temperature sensor 55, and the gaseous fuel temperature sensor 56 are input to the ECU 100.

[0031] Next, we will explain the ECU 100. The ECU 100 is configured by a computer unit that includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), flash memory, input ports, and output ports.

[0032] The ROM of the ECU 100 stores various control constants, various maps, and the like, as well as a program for causing the computer unit to function as the ECU 100. That is, in the ECU 100, the CPU executes the program stored in the ROM, causing the computer unit to function as the ECU 100.

[0033] An input port of the ECU 100 is connected to an intake air temperature sensor 54, a coolant temperature sensor 55, and a gas fuel temperature sensor 56. Various sensors, such as a crank angle sensor and an accelerator position sensor (not shown), are also connected to the input port of the ECU 100.

[0034] The output port of the ECU 100 is connected to various control objects including the gas fuel injector 47, the liquid fuel injector 34, and the starter 52. The ECU 100 controls each control object based on detection signals from each sensor.

[0035] In this embodiment, the ECU 100 constitutes a control system for the vehicle 1, and starts its control operation when an ignition switch (not shown) is operated by the driver. The ignition switch is configured to be operable to any one of an OFF (system shutdown) position, an ON (system startup) position, and a START (engine startup) position.

[0036] The ECU 100 is activated and starts a control operation when an ignition switch is turned to an ON position, and ends the control operation when the ignition switch is turned to an OFF position.

[0037] When the driver activates the system, a driving cycle begins, and when the driver deactivates the system, the driving cycle ends.

[0038] Furthermore, when the driver performs a start operation, that is, when the ignition switch is turned to the START position, the ECU 100 drives the starter 52 in response to a detection signal from the ignition switch.

[0039] The ECU 100 operates the internal combustion engine 10 using either gas fuel or liquid fuel, whichever is selected by the driver through operation of the fuel selection switch 51. The ECU 100 drives the gas fuel injector 47 when gas fuel is selected by the fuel selection switch 51, and drives the liquid fuel injector 34 when liquid fuel is selected.

[0040] In the initial state when the ignition switch is turned from the OFF position to the ON position and the system is started, liquid fuel is set as the initial value, so the driver does not need to operate the fuel selection switch 51 if he or she intends to start the internal combustion engine 10 using liquid fuel.

[0041] When the starter 52 is driven by the driver's start operation, the ECU 100 cooperates with the starter 52 to drive the liquid fuel injector 34 or the gas fuel injector 47. The starter 52 may be driven directly by the driver's start operation without the intervention of the ECU 100. In this case, the ECU 100 monitors whether the starter 52 is being driven and whether the engine is rotating, thereby enabling the ECU 100 to cooperate with the starter 52 to drive the liquid fuel injector 34 or the gas fuel injector 47.

[0042] The ECU 100 automatically stops the internal combustion engine 10 when predetermined automatic stop conditions are met, and restarts the internal combustion engine 10 when predetermined restart conditions are met while the internal combustion engine 10 is automatically stopped. In this way, the ECU 100 controls the so-called idling stop function.

[0043] Here, the first fuel, which is CNG, has the property of being able to reduce emissions compared to the second fuel, which is gasoline, and therefore, in order to reduce emissions, it is preferable to use the first fuel as the fuel used by the internal combustion engine 10.

[0044] On the other hand, the first fuel, which is CNG, has a higher ignition point than the second fuel, which is gasoline. Therefore, the first fuel cannot ignite (start burning) unless it is at a higher temperature than the second fuel, and the startability of the internal combustion engine 10 is relatively inferior to when the second fuel is used. Therefore, when starting the internal combustion engine 10 using the first fuel, cranking must be performed for a long period of time.

[0045] Furthermore, in the internal combustion engine 10 that switches between using the first fuel, which is CNG, and the second fuel, which is gasoline, the path from the gas fuel injector 47 for the first fuel to the combustion chamber is longer than the path from the liquid fuel injector 34 for the second fuel to the combustion chamber, so the time required to start the internal combustion engine 10 when using the first fuel (start-up time) is longer than the start-up time when using the second fuel.

[0046] As described above, the first fuel and the second fuel differ in fuel characteristics, fuel supply structure, etc. As a result, the startability of the internal combustion engine 10 when using the first fuel is inferior to the startability of the internal combustion engine 10 when using the second fuel. Here, startability refers to the ease with which the internal combustion engine 10 can be started, and can be quantified, for example, by the elapsed time from when the internal combustion engine 10 starts cranking until it starts rotating independently, or the degree of increase in engine speed (engine rotational speed) or engine torque after the internal combustion engine 10 starts cranking.

[0047] When the internal combustion engine 10 is restarted using the first fuel due to the satisfaction of the restart conditions, the vehicle 1 may not be able to start at the timing intended by the driver due to poor startability of the internal combustion engine 10 when using the first fuel. To avoid this problem, it is possible to consider structural modifications such as moving the installation position of the gas fuel injector 47 further downstream or sharing the gas fuel injector 47 with the liquid fuel injector 34, but this is not easy in terms of layout constraints, technical difficulty, etc.

[0048] Therefore, when the restart condition is satisfied and the ECU 100 restarts the engine using the first fuel (CNG), the ECU 100 injects the second fuel (gasoline) a predetermined number of times at the start of the restart, and then continues the restart by injecting the first fuel. Here, the amount of fuel injected increases according to the number of injections. Therefore, injecting fuel a predetermined number of times means injecting a predetermined amount of fuel.

[0049] The ECU 100 acquires the cranking rotation speed at the time of restart and sets the predetermined number of times according to the cranking rotation speed. Here, the cranking rotation speed is the engine rotation speed when the internal combustion engine 10 is being cranked by the starter 52. The cranking rotation speed varies depending on the state of charge of the battery, the viscosity of the engine oil, etc., and the lower the cranking rotation speed, the more poorly the internal combustion engine 10 can be started. Therefore, the ECU 100 sets the predetermined number of times so that the lower the cranking rotation speed, the greater the number of times.

[0050] The ECU 100 injects the second fuel a predetermined number of times at the start of the restart, provided that the cranking rotation speed is less than a predetermined value. In other words, if the cranking rotation speed is sufficiently fast and equal to or greater than a predetermined value, the restart is completed quickly without injecting the second fuel, and restartability is ensured. In such cases, the restart is performed using only the first fuel.

[0051] The operation of the ECU 100 will be described with reference to the flowchart of FIG.

[0052] 2, the ECU 100 first determines whether or not CNG is being used (step S1). If it is determined in step S1 that CNG is not being used (NO in step S1), the ECU 100 injects gasoline to start the internal combustion engine 10 (step S8), and ends this operation.

[0053] If it is determined in step S1 that CNG is being used (YES in step S1), the ECU 100 determines whether the internal combustion engine 10 is restarting after being automatically stopped by the idling stop function (referred to as IS restart in the drawing) (step S2). If it is determined in step S2 that the internal combustion engine 10 is not restarting after being automatically stopped by the idling stop function (NO in step S2), the ECU 100 starts the internal combustion engine 10 by injecting CNG (step S7), and ends this operation.

[0054] If it is determined in step S2 that the internal combustion engine 10 is about to be restarted after being automatically stopped by the idling stop function (YES in step S2), the ECU 100 acquires the cranking rotation speed (step S3).

[0055] Next, the ECU 100 determines whether the cranking rotation speed is less than a predetermined value (step S4). If it is determined in step S4 that the cranking rotation speed is not less than the predetermined value (NO in step S4), the ECU 100 injects CNG to start the internal combustion engine 10 (step S7), and ends this operation.

[0056] If it is determined in step S4 that the cranking rotation speed is less than the predetermined value (YES in step S4), the ECU 100 sets the number of gasoline injections according to the cranking rotation speed (step S5). Here, the number of gasoline injections is set so that the lower the cranking rotation speed, the greater the number of gasoline injections.

[0057] Next, the ECU 100 injects gasoline for the number of injections set in step S5 (step S6).

[0058] Next, the ECU 100 injects CNG (step S7) and ends this operation.

[0059] With reference to the timing charts of FIGS. 3, 4 and 5, the transition of the vehicle state when the internal combustion engine 10 is restarted using CNG after automatic stop by the idling stop function will be described.

[0060] Fig. 3 shows a case where the internal combustion engine 10 is restarted when the cranking rotation speed is at a predetermined reference speed (a relatively medium speed). Fig. 4 shows a case where the internal combustion engine 10 is restarted when the cranking rotation speed is higher than the predetermined reference speed. Fig. 5 shows a case where the internal combustion engine 10 is restarted when the cranking rotation speed is lower than the predetermined reference speed.

[0061] 3, 4, and 5, the vertical axis represents engine speed, gasoline injection amount, CNG injection amount, cranking status (on or off), and post-start judgment (after starting or not after starting), and the horizontal axis represents time. The post-start judgment is a judgment of whether the engine speed has reached a self-sustaining rotation speed (complete combustion).

[0062] 3, in the initial state at time t0, the internal combustion engine 10 is stopped (automatically stopped) by the idling stop function. At this time t0, the engine speed is 0, cranking is not performed, and the post-start determination is that the engine is not started.

[0063] After that, at time t1, predetermined restart conditions are met, so that cranking by the starter 52 is initiated, gasoline is injected, and the engine speed increases.

[0064] After that, at time t2, the predetermined number of gasoline injections is completed and injection of CNG is started. In other words, the predetermined number of gasoline injections is performed only at the beginning of starting the internal combustion engine 10, and thereafter, restarting is continued by injection of CNG.

[0065] After that, at time t3, the engine speed reaches the complete combustion determination threshold, and the post-start determination becomes "post-start." The timing of this time t3 is the same as when the internal combustion engine 10 is restarted by gasoline injection (step S8 in FIG. 2), and startability is improved.

[0066] Then, at time t4, cranking ends.

[0067] In FIG. 4, in the initial state at time t10, the internal combustion engine 10 is stopped (automatically stopped) by the idling stop function.

[0068] Then, at time t11, predetermined restart conditions are met, so cranking by the starter 52 begins, gasoline is injected, and the engine speed increases. Since the cranking speed at time t11 is higher than the cranking speed at time t1 in Figure 3, the engine speed increases more quickly than in Figure 3.

[0069] Thereafter, at time t12, the predetermined number of gasoline injections is completed and injection of CNG is started. In other words, the predetermined number of gasoline injections is performed only at the beginning of starting the internal combustion engine 10, and thereafter restarting is continued by injection of CNG.

[0070] After that, at time t13, the engine speed reaches the complete combustion determination threshold, and the post-start determination changes to "post-start." The timing of this time t13 is the same as when the internal combustion engine 10 is restarted by gasoline injection (step S8 in FIG. 2), and startability is improved.

[0071] Then, at time t14, cranking ends.

[0072] In FIG. 5, in the initial state at time t20, the internal combustion engine 10 is stopped (automatically stopped) by the idling stop function.

[0073] After that, at time t21, predetermined restart conditions are met, so that cranking by the starter 52 is initiated, gasoline is injected, and the engine speed increases.

[0074] The cranking rotation speed at time t21 is lower than the cranking rotation speed at time t1 in FIG. 3, so the engine rotation speed increases more slowly than in FIG.

[0075] Thereafter, at time t22, the predetermined number of gasoline injections is completed and injection of CNG is started. In other words, the predetermined number of gasoline injections is performed only at the beginning of starting the internal combustion engine 10, and thereafter restarting is continued by injection of CNG.

[0076] After that, at time t23, the engine speed reaches the complete combustion determination threshold, and the post-start determination changes to "post-start." The timing of this time t23 is the same as when the internal combustion engine 10 is restarted by gasoline injection (step S8 in FIG. 2), and startability is improved.

[0077] Then, at time t24, cranking ends.

[0078] As described above, in this embodiment, the startability of the internal combustion engine 10 when using the first fuel is inferior to the startability of the internal combustion engine 10 when using the second fuel, and when the restart condition is met and the ECU 100 restarts the engine using the first fuel (CNG), it injects the second fuel (gasoline) a predetermined number of times at the start of the restart, and then continues the restart by injecting the first fuel.

[0079] As a result, by injecting the second fuel, which has excellent startability, a predetermined number of times at the start of the restart, the engine speed of the internal combustion engine 10 can be quickly increased to a level at which the internal combustion engine 10 can rotate autonomously, compared to when the first fuel, which has poor startability, is injected from the start of the restart, thereby improving the startability of the internal combustion engine 10. As a result, even when using a fuel with poor startability, the startability of the internal combustion engine 10 when restarting from an automatic stop can be improved. In addition, the second fuel is injected a predetermined number of times (a predetermined amount) at the start of the restart, and thereafter the restart and operation of the internal combustion engine 10 are carried out by injecting the first fuel. Therefore, the use of the first fuel can ensure improved fuel economy and reduced emissions. Furthermore, the startability can be improved without changing the fuel injection position of the first fuel in the intake path 21, etc., thereby preventing increases in costs due to structural changes.

[0080] In addition, this embodiment is provided with a gas fuel injector 47 that injects a first fuel into the intake path 21 of the internal combustion engine 10, and a liquid fuel injector 34 that injects a second fuel into the intake path 21, and the gas fuel injector 47 is positioned upstream of the liquid fuel injector 34 in the intake path 21.

[0081] As a result, even if the startability of the internal combustion engine 10 is poor when using the first fuel because the time required for the first fuel injected from the gas fuel injector 47 to reach the combustion chamber is longer than the time required for the second fuel injected from the liquid fuel injector 34 to reach the combustion chamber, by injecting the second fuel from the liquid fuel injector 34 which is closer to the combustion chamber at the start of restart, the engine speed of the internal combustion engine 10 can be quickly increased to a level at which it can rotate independently, thereby improving the startability of the internal combustion engine 10.

[0082] In addition, in this embodiment, the ECU 100 acquires the cranking rotation speed at the time of restarting, and sets the predetermined number of times according to the cranking rotation speed.

[0083] As a result, the cranking rotation speed changes depending on the battery voltage, etc., and the higher the cranking rotation speed, the more quickly the internal combustion engine 10 can transition to self-sustaining rotation and the better the startability. Therefore, by adjusting the number of injections (injection amount) of the second fuel according to the cranking rotation speed, the startability can be improved by increasing the number of injections of the second fuel when the cranking rotation speed is low. Also, when the cranking rotation speed is high, the number of injections of the second fuel can be reduced to ensure improved fuel efficiency and reduced emissions. Therefore, it is possible to ensure improved fuel efficiency and reduced emissions while improving startability.

[0084] In this embodiment, the ECU 100 injects the second fuel a predetermined number of times at the start of restarting, on condition that the cranking rotation speed is less than a predetermined value.

[0085] As a result, the second fuel is injected only when the cranking rotation speed is below a predetermined value and it takes time to restart the internal combustion engine 10. Therefore, when the cranking rotation speed is equal to or higher than a predetermined speed and it is unlikely that a restart delay will occur that would adversely affect drivability, the second fuel is not injected, thereby ensuring improved fuel efficiency and reduced emissions.

[0086] While one embodiment of this invention has been disclosed, it will be apparent to those skilled in the art that modifications may be made thereto without departing from the scope of the invention, and it is intended that all such modifications and equivalents be included within the scope of the following claims. [Explanation of symbols]

[0087] 1 vehicle (bi-fuel vehicle) 10 Internal combustion engine 21 Intake path 34 Liquid fuel injector (second injector) 47 Gaseous fuel injector (first injector) 100 ECU (control unit)

Claims

1. an internal combustion engine that is operated by injecting either a first fuel or a second fuel, the first fuel and the second fuel being different from each other; a control unit that automatically stops the internal combustion engine when a predetermined automatic stop condition is met, and restarts the internal combustion engine when a predetermined restart condition is met while the internal combustion engine is automatically stopped, the startability of the internal combustion engine when using the first fuel is inferior to the startability of the internal combustion engine when using the second fuel, When the restart condition is satisfied and the first fuel is used to restart the vehicle, the control unit injects the second fuel a predetermined number of times at the start of the restart, and then continues the restart by injecting the first fuel.

2. a first injector that injects the first fuel into an intake path of the internal combustion engine; a second injector that injects the second fuel into the intake path, 2. The bi-fuel vehicle according to claim 1, wherein the first injector is disposed upstream of the second injector in the intake path.

3. 3. The bi-fuel vehicle according to claim 1, wherein the control unit acquires a cranking rotation speed at the time of restarting, and sets the predetermined number of times in accordance with the cranking rotation speed.

4. 4. The bi-fuel vehicle according to claim 3, wherein the control unit injects the second fuel a predetermined number of times at the start of the restart, on condition that the cranking rotation speed is less than a predetermined value.

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