JP7533258B2 - Vehicle control device - Google Patents

Description

The present invention relates to a vehicle control device.

In recent years, there have been bi-fuel vehicles, such as automobiles, equipped with engines that use gaseous fuels, such as compressed natural gas (CNG), and liquid fuels, such as gasoline. A conventional vehicle of this type is described in Patent Document 1.

Patent Document 1 describes a technology for starting the engine by setting the target air-fuel ratio of the engine to be leaner than the theoretical air-fuel ratio when a start request is generated to start the engine using gaseous fuel and it is determined that the engine is in a warm-up completed state. Patent Document 1 also describes that the technology is applied to an internal combustion engine having an idle stop function 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.

JP 2014-234791 A

However, the technology described in Patent Document 1 does not ensure sufficient restartability of the internal combustion engine when gaseous fuel is used. By using gaseous fuel such as compressed natural gas, the engine of a bi-fuel vehicle can improve fuel efficiency compared to when using liquid fuel such as gasoline. However, because the path from the injector for gaseous fuel to the combustion chamber is longer than the path of the injector for liquid fuel, when starting the internal combustion engine using gaseous fuel, it has the characteristic that it takes a long time from when the gaseous fuel is injected to start the internal combustion engine until the starting torque required to start the vehicle is generated.

As a result, when restarting an internal combustion engine from an automatic stop state due to idle stop using gaseous fuel, the time from start-up until the generation of starting torque is longer than when liquid fuel is used, and there is a risk that the vehicle will not start as intended by the driver.

The present invention was made in response to the above-mentioned problems, and aims to provide a vehicle control device that can improve fuel efficiency while ensuring the vehicle's starting performance.

The present invention is a control device for a vehicle equipped with an internal combustion engine that switches between gaseous fuel and liquid fuel, and is equipped with 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 during the automatic stop of the internal combustion engine , and a slope detection unit that detects a road surface slope , wherein the restart condition includes a brake operation amount becoming smaller than a predetermined restart threshold, and when the slope detection unit detects that the road surface slope is an uphill slope and the internal combustion engine is restarted using the gaseous fuel, the control unit sets the restart threshold to a larger value than when the internal combustion engine is restarted using the liquid fuel.

In this way, the present invention provides a vehicle control device that can improve fuel efficiency while ensuring the vehicle's starting performance.

FIG. 1 is a block diagram of a vehicle equipped with a control device according to a first or second embodiment of the present invention. FIG. 2 is a flowchart illustrating the operation of the vehicle control device according to the first embodiment of the present invention. FIG. 3 is a flow chart for explaining the operation of the vehicle control device according to the second embodiment of the present invention.

A vehicle control device according to one embodiment of the present invention is a control device for a vehicle equipped with an internal combustion engine that switches between gaseous fuel and liquid fuel, and includes 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 restart condition including a brake operation amount becoming smaller than a predetermined restart threshold, and the control unit is characterized in that when restarting the internal combustion engine using gaseous fuel, the control unit sets the restart threshold to a larger value compared to when restarting the internal combustion engine using liquid fuel. As a result, the vehicle control device according to one embodiment of the present invention can improve fuel efficiency while ensuring the starting performance of the vehicle.

The vehicle control device according to the first embodiment of the present invention will be described below with reference to the drawings. Figures 1 and 2 are diagrams for explaining the vehicle control device according to the first embodiment of the present invention. As shown in Figure 1, a vehicle 1 equipped with a vehicle control device according to one embodiment of the present invention includes an internal combustion engine 2 (referred to as "engine" in the drawing) as a drive source, a transmission 4 to which power is transmitted from the internal combustion engine 2, a clutch 3 provided between the internal combustion engine 2 and the transmission 4, and drive wheels 5 to which power is transmitted from the transmission 4.

The vehicle 1 also includes an accelerator pedal sensor 12A, a brake pedal sensor 13A, a clutch pedal sensor 14A, a vehicle speed sensor 15, an acceleration sensor 16, and an ECU (Electronic Control Unit) 11 that controls the internal combustion engine 2 and the transmission 4.

The internal combustion engine 2 is a four-stroke engine that performs a series of four strokes consisting of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke, and generates driving force for the vehicle 1 by igniting between the compression stroke and the expansion stroke. In addition to the internal combustion engine 2, the vehicle 1 may also be equipped with a motor as a driving source. The vehicle 1 is equipped with a starter 6 that starts the internal combustion engine 2.

The transmission 4 is configured as a parallel shaft gear type speed change mechanism that is generally used in manual transmissions. The clutch 3 is configured as a dry single plate friction clutch, and has a flywheel 3A connected to the output shaft 2A of the internal combustion engine 2 and a clutch disc 3B connected to the transmission 4.

The clutch 3 transmits power between the internal combustion engine 2 and the transmission 4 when the clutch disc 3B is switched to an engaged (connected) state relative to the flywheel 3A, and cuts off the power transmission between the internal combustion engine 2 and the transmission 4 when the clutch disc 3B is switched to an open (disconnected) state.

In a vehicle 1 configured in this manner, the rotation output from the internal combustion engine 2 is changed in speed at a gear ratio corresponding to the gear stage established in the transmission 4, and is transmitted to the drive wheels 5 via a differential device and a drive shaft (not shown).

The accelerator pedal sensor 12A is provided on the accelerator pedal 12 and detects the amount of operation of the accelerator pedal 12. The brake pedal sensor 13A is provided on the brake pedal 13 and detects the amount of operation of the brake pedal 13. The clutch pedal sensor 14A is provided on the clutch pedal 14 and detects the amount of operation of the clutch pedal 14. Here, the amount of operation of each pedal refers to the amount of depression by the driver, and the greater the amount of depression, the greater the amount of operation. Note that the brake pedal sensor 13A may be configured to detect the hydraulic pressure (master cylinder pressure) of a master cylinder connected to the brake pedal 13 instead of the amount of depression of the brake pedal 13. Hereinafter, the amount of depression of the brake pedal 13 or the master cylinder pressure will be referred to as the brake operation amount.

The vehicle speed sensor 15 is provided on the drive wheel 5 and detects the vehicle speed based on the rotational speed of the drive wheel 5. The acceleration sensor 16 detects the acceleration of the vehicle 1 and the attitude of the vehicle 1.

The internal combustion engine 2 is a bi-fuel internal combustion engine that can use liquid fuel and gaseous fuel. Therefore, the vehicle 1 is a bi-fuel automobile. The internal combustion engine 2 can use gasoline or diesel fuel as the liquid fuel, and compressed natural gas (CNG) as the gaseous fuel.

The vehicle 1 is equipped with a first fuel storage section 8 that stores liquid fuel and a second fuel storage section 9 that stores gaseous fuel. The liquid fuel is injected into the intake path or the combustion chamber by an injector (not shown) for liquid fuel. The gaseous fuel is injected into the intake path by an injector (not shown) for gaseous fuel.

The vehicle 1 is equipped with a fuel switching device 7 that switches the fuel supplied to the internal combustion engine 2 between liquid fuel and gas fuel, and a fuel selection switch 18 operated by the driver. Either the liquid fuel or the gas fuel selected by the fuel selection switch 18 is supplied to the internal combustion engine 2 via the fuel switching device 7.

The vehicle 1 is equipped with a brake pressure holding unit 17. The brake pressure holding unit 17 increases, holds, and reduces the braking force applied to the wheel cylinders (not shown) of the drive wheels 5. The brake pressure holding unit 17 realizes a so-called hill hold function, and when the amount of brake operation becomes smaller than the restart threshold, the brake pressure corresponding to the road surface inclination is held for a predetermined holding time and then reduced. As a result, when the vehicle 1 is stopped on an uphill slope and the driver switches from the brake pedal 13 to the accelerator pedal 12 to start moving, the brake pressure is held for the predetermined holding time by the brake pressure holding unit 17 even after the driver releases his/her foot from the brake pedal 13, and the vehicle 1 can be prevented from rolling down when starting.

The ECU 11 is composed of a computer unit equipped with a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), flash memory, input ports, and output ports, and electrically controls the controlled objects.

The ROM of the ECU 11 stores various control constants, various maps, and the like, as well as a program for causing the computer unit to function as the ECU 11. In the ECU 11, the CPU executes the program stored in the ROM, causing the computer unit to function as the ECU 11.

The input port of the ECU 11 is electrically connected to the internal combustion engine 2, various sensors such as an accelerator pedal sensor 12A, a brake pedal sensor 13A, a clutch pedal sensor 14A, a vehicle speed sensor 15, an acceleration sensor 16, and a fuel selection switch 18.

The output port of the ECU 11 is connected to control objects such as the internal combustion engine 2, the starter 6, the fuel switching device 7, and the brake pressure holding unit 17. The ECU 11 controls the control objects connected to the output port based on detection signals from sensors and the like input to the input port.

In this embodiment, the ECU 11 includes a control unit 11A, which automatically stops the internal combustion engine 2 when a predetermined automatic stop condition is met, and restarts the internal combustion engine 2 when a predetermined restart condition is met while the internal combustion engine 2 is automatically stopped. In this way, the control unit 11A performs so-called idle stop control.

Here, the restart condition includes that the brake operation amount becomes smaller than a predetermined restart threshold. The restart threshold is a threshold of the brake operation amount at which restart of the internal combustion engine 2 is initiated. As a result, the automatic stop of the internal combustion engine 2 is maintained while the brake operation amount by the driver is equal to or greater than the restart threshold, and when the brake operation amount by the driver becomes smaller than the restart threshold, the restart condition is met and the internal combustion engine 2 is restarted. The ECU 11 also includes an inclination detection unit 11B, which detects the inclination of the road surface based on the attitude of the vehicle 1 detected by the acceleration sensor 16.

Here, in an internal combustion engine 2 that switches between liquid fuel and gas fuel, the path from the gas fuel injector to the combustion chamber is longer than in a liquid fuel injector, and the time it takes for the injected gas fuel to reach the combustion chamber is longer than in the case of liquid fuel, so it has the characteristic that the time from the start of starting the internal combustion engine 2 until the start-up torque required to start the vehicle is generated is longer. Therefore, when the driver removes his foot from the brake pedal 13 and the internal combustion engine 2 restarts from the automatic stop state due to idle stop, the time until the start-up torque required to start the vehicle 1 is generated is longer in the case of restart using gas fuel than in the case of restart using liquid fuel.

Therefore, in this embodiment, when the internal combustion engine 2 is restarted using gaseous fuel, the control unit 11A sets the restart threshold to a larger value compared to when the internal combustion engine 2 is restarted using liquid fuel. Therefore, when the internal combustion engine 2 is restarted using gaseous fuel, the restart of the internal combustion engine 2 is initiated in a state where the brake operation amount is larger compared to when the internal combustion engine 2 is restarted using liquid fuel. In other words, when gaseous fuel is used, the start timing of the restart of the internal combustion engine 2 is brought forward compared to when liquid fuel is used.

In addition, in this embodiment, the automatic stop condition includes the brake operation amount becoming larger than a predetermined automatic stop threshold. When automatically stopping the internal combustion engine 2 while gas fuel is being used, the control unit 11A sets the automatic stop threshold to a larger value compared to when automatically stopping the internal combustion engine 2 while liquid fuel is being used. Therefore, when gas fuel is used, both the restart threshold and the automatic stop threshold of the idle stop control are set to larger values compared to when liquid fuel is used.

Note that the restart of the internal combustion engine 2 by idle stop control is performed while the internal combustion engine 2 is stopped by automatic stop, so the automatic stop threshold is set to a value greater than the restart threshold regardless of whether liquid fuel or gas fuel is used.

Next, the flow of operations of the vehicle control device according to this embodiment will be described with reference to the flowchart shown in FIG. 2. FIG. 2 shows the operations of the control unit 11A when the internal combustion engine 2 is restarted due to a reduction in the brake stroke during automatic stopping of the internal combustion engine 2 by idle stop control, and the vehicle 1 starts moving.

In FIG. 2, the control unit 11A acquires the engine state (step S1) and determines whether the engine is in an automatic engine stop state (step S2). Here, the engine state refers to the operating state of the internal combustion engine 2. The automatic engine stop state refers to a state in which the internal combustion engine 2 is stopped by idle stop control.

If the control unit 11A determines in step S2 that the engine is not in the automatic engine stop state, it returns to step S1. If the control unit 11A determines in step S2 that the engine is in the automatic engine stop state, it determines whether gas fuel has been selected (step S3).

If the determination in step S3 is NO, i.e., liquid fuel is selected, the control unit 11A obtains the brake stroke amount as the brake operation amount (step S4) and determines whether the brake stroke amount is less than threshold value 2 (step S5).

If the control unit 11A determines in step S5 that the brake stroke amount is not less than threshold value 2, it returns to step S4, and if it determines that the brake stroke amount is less than threshold value 2, it starts the internal combustion engine 2 using liquid fuel (step S6).

On the other hand, if the determination in step S3 is YES, that is, if gas fuel is selected, the control unit 11A obtains the brake stroke amount (step S7) and determines whether the brake stroke amount is less than threshold value 1 (step S8). Here, threshold value 1 and threshold value 2 are restart threshold values in the present invention. The control unit 11A sets threshold value 1 to a value larger than threshold value 2 (large brake stroke amount threshold value).

If the control unit 11A determines in step S8 that the brake stroke amount is not less than threshold value 1, it returns to step S7, and if it determines that the brake stroke amount is less than threshold value 1, it starts the internal combustion engine 2 using gaseous fuel (step S9).

Then, after the internal combustion engine 2 is started in step S6 or step S9, the vehicle 1 starts moving when the brake stroke amount is further reduced (step S10).

As described above, the vehicle control device of this embodiment includes a control unit 11A that automatically stops the internal combustion engine 2 when a predetermined automatic stop condition is met, and restarts the internal combustion engine 2 when a predetermined restart condition is met while the internal combustion engine 2 is automatically stopped. The restart condition also includes the brake operation amount becoming smaller than a predetermined restart threshold. When restarting the internal combustion engine 2 using gaseous fuel, the control unit 11A sets the restart threshold to a larger value compared to when restarting the internal combustion engine 2 using liquid fuel.

As a result, the internal combustion engine 2 is automatically stopped when a predetermined automatic stop condition is met, thereby improving fuel efficiency.

In addition, when starting the internal combustion engine 2 using gaseous fuel, the restart threshold for the brake operation amount is increased compared to when liquid fuel is used, so the restart of the internal combustion engine 2 can be initiated at an earlier timing. Therefore, a starting torque can be generated at the same timing as when starting the internal combustion engine 2 using liquid fuel.

As a result, fuel efficiency can be improved while maintaining vehicle 1's starting performance.

In addition, in this embodiment, the automatic stop condition includes the brake operation amount becoming larger than a predetermined automatic stop threshold. When automatically stopping the internal combustion engine 2 while gas fuel is being used, the control unit 11A sets the automatic stop threshold to a larger value compared to when automatically stopping the internal combustion engine 2 while liquid fuel is being used.

This prevents the difference between the automatic stop threshold and the restart threshold when gas fuel is used from becoming small, and therefore prevents the internal combustion engine 2 from restarting simply by the driver slightly reducing the amount of depression of the brake pedal 13 during automatic stop. This makes it possible to prevent the internal combustion engine 2 from restarting unintentionally by the driver.

Next, the flow of operation of the vehicle control device according to the second embodiment will be described with reference to the flowchart shown in FIG. 3. In this embodiment, the operation of the control unit 11A of the ECU 11 is different in the vehicle 1 having the configuration shown in FIG. 1. The operation of the control unit 11A of the ECU 11 will be described below. FIG. 3 shows the operation of the control unit 11A when the internal combustion engine 2 is restarted due to a reduction in the brake stroke while the internal combustion engine 2 is automatically stopped by idle stop control, and the vehicle 1 starts moving.

In FIG. 3, the control unit 11A obtains the road surface inclination from the inclination detection unit 11B (step S11), obtains the engine state (step S12), and determines whether the engine is in an automatic stop state (step S13).

If the control unit 11A determines in step S13 that the engine is not in the automatic engine stop state, it returns to step S12, and if it determines in step S13 that the engine is in the automatic engine stop state, it determines whether gas fuel has been selected (step S14).

If the determination in step S14 is NO, i.e., liquid fuel is selected, the control unit 11A obtains the brake stroke amount as the brake operation amount (step S15) and determines whether the brake stroke amount is less than threshold value 2 (step S16).

If the control unit 11A determines in step S16 that the brake stroke amount is not less than threshold value 2, the process returns to step S15. If the control unit 11A determines that the brake stroke amount is less than threshold value 2, the control unit 11A starts the internal combustion engine 2 using liquid fuel (step S17). Thereafter, the control unit 11A quickly reduces the brake holding pressure (step S18). Here, the control unit 11A holds the brake pressure for a predetermined holding time before reducing it. The holding time in step S18 is shorter than the holding time in step S22, which will be described later. Therefore, the brake holding pressure is reduced relatively quickly.

On the other hand, if the determination in step S14 is YES, i.e., gas fuel is selected, the control unit 11A acquires the brake stroke amount (step S19) and determines whether the brake stroke amount is less than threshold value 1 (step S20).

Here, threshold value 1 and threshold value 2 are restart threshold values in the present invention. Furthermore, when the slope detection unit 11B detects that the road surface slope is an upward gradient and the internal combustion engine 2 is restarted using gaseous fuel, the control unit 11A sets the restart threshold value to a larger value compared to when the internal combustion engine 2 is restarted using liquid fuel. In other words, when the slope detection unit 11B detects that the road surface slope is an upward gradient, the control unit 11A sets threshold value 1, which is the restart threshold value when the internal combustion engine 2 is restarted using gaseous fuel, to a larger value (larger brake stroke amount threshold) than threshold value 2, which is the restart threshold value when the internal combustion engine 2 is restarted using liquid fuel.

If the control unit 11A determines in step S20 that the brake stroke amount is not less than threshold value 1, the process returns to step S19. If the control unit 11A determines that the brake stroke amount is less than threshold value 1, the control unit 11A starts the internal combustion engine 2 using gas fuel (step S21). Thereafter, the control unit 11A gradually reduces the brake holding pressure (step S22). Here, the control unit 11A holds the brake pressure for a predetermined holding time before reducing it. The holding time in step S22 is longer than the holding time in step S18. Therefore, the brake holding pressure is reduced relatively gradually.

Then, when the predetermined holding time has elapsed and the brake holding pressure has decreased due to step S18 or step S22, the vehicle 1 starts moving (step S23).

When the slope detection unit 11B detects that the road surface slope is an upward gradient, the control unit 11A may not only set threshold 1 larger than threshold 2, but may also set both threshold 1 and threshold 2 larger than when the slope detection unit 11B does not detect that the road surface slope is an upward gradient.

As described above, this embodiment includes a control unit 11A that automatically stops the internal combustion engine 2 when a predetermined automatic stop condition is met, and restarts the internal combustion engine 2 when a predetermined restart condition is met while the internal combustion engine 2 is automatically stopped, and an inclination detection unit 11B that detects the inclination of the road surface. In addition, the restart condition includes the brake operation amount becoming smaller than a predetermined restart threshold value.

The control unit 11A sets the restart threshold to a larger value when the slope detection unit 11B detects that the road surface slope is an upward slope and the internal combustion engine 2 is restarted using gaseous fuel, compared to when the internal combustion engine 2 is restarted using liquid fuel.

As a result, when starting the internal combustion engine 2 using gas fuel on an uphill slope, the restart threshold for the brake operation amount is increased compared to when liquid fuel is used, so the internal combustion engine 2 can be restarted at an earlier timing. This makes it possible to generate a starting torque at the same timing as when starting the internal combustion engine 2 using liquid fuel. Therefore, even on an uphill slope that requires a larger starting torque than on a flat road, it is possible to make it less likely for the vehicle 1 to roll down the slope when starting the vehicle 1.

As a result, fuel efficiency can be improved while maintaining vehicle 1's starting performance.

In addition, this embodiment includes a brake pressure holding unit that holds the brake pressure according to the road surface inclination for a predetermined holding time and then reduces the pressure when the brake operation amount becomes smaller than the restart threshold. When restarting the internal combustion engine 2 using gas fuel, the control unit 11A sets the holding time to a longer value compared to when restarting the internal combustion engine 2 using liquid fuel.

As a result, when restarting the internal combustion engine 2 using gaseous fuel and starting on an uphill slope, a sufficient holding time is ensured for the driver to change pedal positions, thereby reliably preventing the vehicle 1 from rolling downhill.

In addition, in this embodiment, the automatic stop condition includes the brake operation amount becoming larger than a predetermined automatic stop threshold. When the internal combustion engine 2 is automatically stopped while gas fuel is being used, the automatic stop threshold is set to a larger value than when the internal combustion engine 2 is automatically stopped while liquid fuel is being used.

This prevents the difference between the automatic stop threshold and the restart threshold when gas fuel is used from becoming small, and therefore prevents the internal combustion engine 2 from restarting simply by the driver slightly reducing the amount of depression of the brake pedal 13 during automatic stop. This makes it possible to prevent the internal combustion engine 2 from restarting unintentionally by the driver.

Although an embodiment of the present invention has been disclosed, it is apparent that modifications may be made by one of ordinary skill in the art without departing from the scope of the present invention. All such modifications and equivalents are intended to be included in the following claims.

1 Vehicle 2 Internal combustion engine 11A Control unit 11B Inclination detection unit 17 Brake pressure holding unit

Claims (3)

A control device for a vehicle equipped with an internal combustion engine that switches between gas fuel and liquid fuel,
a control unit that automatically stops the internal combustion engine when a predetermined automatic stop condition is satisfied, and that restarts the internal combustion engine when a predetermined restart condition is satisfied during the automatic stop of the internal combustion engine ;
A slope detection unit that detects a road surface slope ,
The restart condition includes a brake operation amount becoming smaller than a predetermined restart threshold value,
The control unit is
A vehicle control device characterized in that, when the inclination detection unit detects that the road surface inclination is an upward gradient and the internal combustion engine is restarted using the gas fuel, the restart threshold is set to a larger value compared to when the internal combustion engine is restarted using the liquid fuel. a brake pressure holding unit that holds the brake pressure according to the road surface gradient for a predetermined holding time and then reduces the brake pressure when the brake operation amount becomes smaller than the restart threshold value,
The control unit is
2. The vehicle control device according to claim 1, wherein, when the internal combustion engine is restarted using the gas fuel, the hold time is set to a longer value compared to when the internal combustion engine is restarted using the liquid fuel. the automatic stop condition includes that the brake operation amount is greater than a predetermined automatic stop threshold value,
3. The vehicle control device according to claim 1, wherein the automatic stop threshold is set to a larger value when the internal combustion engine is automatically stopped while the gas fuel is being used, compared to when the internal combustion engine is automatically stopped while the liquid fuel is being used.

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