Idle stop control method and apparatus for an internal combustion engine

Abstract

In an internal combustion engine that performs idle stop when the vehicle is stopped, the combustion operation can be restarted without cranking when the brake pedal is released immediately after stopping. [Solution] When the vehicle stops at time t1 and the idle stop permission condition is met, at time t3 the (e) fuel cut permission determination flag is turned on, and fuel injection and ignition stop. When the driver releases the brake pedal immediately after stopping, when the brake fluid pressure falls below the threshold Ps (time t4), it is determined that the brake pedal has been released, and provided that the rotational speed of the internal combustion engine 1 is above a predetermined rotational speed, fuel injection and ignition are restarted at time t6. This restarts combustion operation without cranking. The threshold Ps is set according to the gradient of the road surface.

Description

Technical Field

[0004] , , ,

[0001] The present invention relates to an idle stop control method and apparatus for an internal combustion engine that automatically stops the internal combustion engine when a predetermined idle stop permission condition including depressing the brake pedal is satisfied when the vehicle stops, and then restarts the internal combustion engine when a predetermined idle stop release condition including releasing the brake pedal is satisfied.

Background Art

[0002] For example, in order to avoid unnecessary fuel consumption during vehicle stop at an intersection, a so-called idle stop technology that automatically stops the internal combustion engine when the vehicle stops and then automatically restarts the internal combustion engine when the vehicle starts has been conventionally known.

[0003] [[ID=1⑤]]<000001②>Patent Document 1 discloses an invention in which after the internal combustion engine is stopped by idle stop, the crank stop position during stop is detected, a restart permission brake hydraulic pressure is set based on this crank stop position, and when the brake hydraulic pressure becomes less than or equal to the restart permission brake hydraulic pressure, the internal combustion engine is restarted as if the brake pedal has been released.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Automatic restart in idle stop is generally performed with cranking by a starter motor. However, if combustion operation can be restarted without cranking when there is a brake release operation immediately after vehicle stop, it is preferable in terms of the response of restarting and the like.

[0006] In order to restart combustion without cranking, fuel injection and ignition must be restarted before the internal combustion engine comes to a complete stop.

[0007] In typical brake switch-based brake release detection systems, the detection delay often prevents the engine from slowing down in time, necessitating cranking.

[0008] Patent Document 1 describes a configuration that waits for the rotation of the crankshaft of an internal combustion engine to come to a complete stop in order to detect the crank stop position, and it is not possible to restart combustion operation by restarting fuel injection and ignition before the rotation comes to a complete stop. [Means for solving the problem]

[0009] This invention relates to an idle stop control method for an internal combustion engine, which automatically stops the internal combustion engine when predetermined idle stop permission conditions, including pressing the brake pedal, are met when the vehicle stops, and then restarts the internal combustion engine when predetermined idle stop release conditions, including releasing the brake pedal, are met. In the process of automatically stopping the internal combustion engine when the above idle stop permission conditions are met, if the brake pedal is released while the internal combustion engine's rotational speed is above a predetermined rotational speed, the combustion operation of the internal combustion engine will be restarted by restarting fuel injection and ignition without cranking by the starter motor. At this point, it is determined that the brake pedal release operation has occurred because the brake fluid pressure falls below a predetermined threshold.

[0010] For example, if the driver releases the brake pedal immediately after the vehicle comes to a stop, the brake pedal release operation is detected promptly based on the brake fluid pressure. If the internal combustion engine's rotational speed is still above a predetermined speed at this time, the combustion operation of the internal combustion engine is restarted by restarting fuel injection and ignition. [Effects of the Invention]

[0011] According to this invention, for example, in situations where a vehicle restarts immediately after coming to a stop, the probability of restarting combustion operation without cranking is increased, improving the responsiveness of restarting, and suppressing power consumption and discomfort caused by cranking. [Brief explanation of the drawing]

[0012] [Figure 1] A diagram illustrating the system configuration of one embodiment. [Figure 2] A time chart showing the operation of one embodiment. [Figure 3] A characteristic diagram showing the relationship between road surface gradient and brake fluid pressure threshold. [Modes for carrying out the invention]

[0013] Figure 1 is a diagram illustrating the system configuration of one embodiment of the idle stop control device according to the present invention. The internal combustion engine 1 mounted on the vehicle is, for example, a four-stroke cycle spark-ignition internal combustion engine, a so-called gasoline engine, and is configured to drive the drive wheels 3 via a stepped automatic transmission 2. The internal combustion engine 1 is equipped with a starter motor 4 for cranking during startup.

[0014] The internal combustion engine 1 is controlled by the engine controller 6. The engine controller 6 is connected to other controllers, such as the AT controller 5 that controls the automatic transmission 2, via an in-vehicle network 7 (e.g., CAN communication), and transmits and receives necessary signals. The engine controller 6 receives detection signals from sensors such as a crank angle sensor 11 for detecting engine rotational speed, an air flow meter 12 for detecting the amount of intake air corresponding to the load, a water temperature sensor 13 for detecting the coolant temperature, an accelerator position sensor 14 for detecting the opening of the accelerator pedal operated by the driver, and an air-fuel ratio sensor 15 for detecting the exhaust air-fuel ratio, either directly or via other controllers. Based on these detection signals, the engine controller 6 optimally controls the fuel injection amount and timing by the fuel injector, the ignition timing by the spark plug, the throttle valve opening, etc.

[0015] Furthermore, the vehicle is equipped with a brake switch 22 that detects the driver's pressing of the brake pedal 21, and a brake fluid pressure sensor 23 that detects the brake fluid pressure generated as a result of the brake operation. These detection signals are also input directly or indirectly to the engine controller 6. In addition, the vehicle is equipped with a gravity sensor 24 to detect the gradient of the road surface.

[0016] Next, the idle stop function, which is the core of the present invention, will be described. When the vehicle decelerates from a moving state and comes to a stop, if predetermined idle stop permission conditions, including pressing the brake pedal 21, are met, the internal combustion engine 1 is automatically stopped (fuel injection and ignition are stopped). The idle stop permission conditions are an AND condition of many conditions, including, for example, the automatic transmission 2 being in the D range position, the brake fluid pressure being higher than a predetermined threshold, not steering, and the coolant temperature being above a predetermined temperature (i.e., not being in a cold state). After the internal combustion engine 1 has automatically stopped, the internal combustion engine is restarted when predetermined idle stop release conditions, including releasing the brake pedal 21, are met. Basically, when any of the individual conditions of the idle stop permission conditions are not met, the idle stop release conditions are assumed to be met, and the internal combustion engine 1 is restarted using cranking by the starter motor 4.

[0017] On the other hand, after fuel injection and ignition are stopped as part of idle stop, it takes a certain amount of time for the rotation of the crankshaft of the internal combustion engine 1 to completely stop. In other words, even after fuel injection and ignition are stopped, the crankshaft continues to rotate due to inertia. As long as the internal combustion engine 1 is rotating in this way, it is possible to restart combustion operation by restarting fuel injection and ignition without cranking. Therefore, if the brake pedal 21 is released immediately after the vehicle has stopped, it is preferable to restart combustion operation by restarting fuel injection and ignition without cranking, provided that the rotational speed of the internal combustion engine 1 is above a predetermined rotational speed.

[0018] In this invention, it is determined that the brake pedal release operation has occurred when the brake fluid pressure falls below a predetermined threshold. In particular, in one preferred embodiment, it is determined that the brake pedal release operation has occurred when either the brake fluid pressure falls below a predetermined threshold or the brake switch 22 is turned off. In other words, the two conditions, brake fluid pressure falling below a predetermined threshold and brake switch 22 being turned off, are OR conditions. Depending on the driver's operation of the brake pedal 21 and the setting of the threshold, in many cases the brake fluid pressure may drop below the threshold before the driver releases the brake pedal 21 and the brake switch 22 is turned off. By detecting the brake pedal release operation based on the brake fluid pressure, the delay is shortened, and the probability of achieving a restart of combustion operation without cranking is increased.

[0019] Figure 2 is a time chart showing the operation of one embodiment. From top to bottom, the figures show (a) vehicle speed, (b) on / off of brake switch 22, (c) brake fluid pressure, (d) rotational speed of internal combustion engine 1, (e) on / off of fuel cut permission judgment flag, (f) idle stop state transition, and (g) fuel injection on / off. Note that the idle stop state transition in column (f) represents multiple stages of control states related to idle stop.

[0020] Figure 2 corresponds to a situation where a moving vehicle approaches an intersection, the driver steps on the brake pedal 21, temporarily stops the vehicle, and then immediately after that, the driver releases the brake pedal 21 and starts moving again. At the first point in Figure 2, the brake pedal 21 has already been stepped on, and the vehicle speed gradually decreases until the vehicle stops at time t1. As a result, the basic idle stop permission condition is satisfied at time t1. However, after the engine controller 6 inquires other controllers such as the AT controller 5 about the presence or absence of the idle stop prohibition condition, the final idle stop permission condition is satisfied. Therefore, at time t3, which is delayed from time t1, the fuel cut permission determination flag in column (e) turns on. When this fuel cut permission determination flag turns on, as shown in column (g), the fuel injection stops. At the same time, the ignition also stops. Therefore, the rotational speed of the internal combustion engine 1 gradually decreases.

[0021] In the example of Figure 2, after the vehicle stops once, at time t2 immediately after that, the driver starts to loosen the stepping on the brake pedal 21, and the brake hydraulic pressure decreases. This brake hydraulic pressure is compared with the predetermined threshold value Ps as described above. At time t4, the brake hydraulic pressure becomes less than or equal to the threshold value Ps, and thereby the release operation of the brake pedal 21 is detected. In the illustrated example, at this stage, the brake switch 22 remains on.

[0022] When it is determined that the brake pedal 21 has been released based on the brake hydraulic pressure (at time t4), in the illustrated example, the rotational speed of the internal combustion engine 1 is above the predetermined rotational speed. Therefore, the engine controller 6 determines that combustion operation restart without cranking is possible, and restarts fuel injection and ignition without performing cranking. In the illustrated example, due to the time required for the process, the fuel cut permission determination flag in column (e) turns off at time t6, and fuel injection (and ignition) is restarted as shown in column (g). The brake switch 22 turns off at time t5.

[0023] Therefore, in the example in Figure 2, by determining that the brake pedal 21 has been released based on the brake fluid pressure, the combustion operation restarts earlier, and the combustion operation restarts at the same timing as when the brake switch 22 is turned off. As a result, discomfort and power consumption due to cranking can be suppressed, and the responsiveness of restarting is improved.

[0024] Furthermore, if the brake switch 22 is turned off before the brake fluid pressure falls below the threshold Ps, the release operation of the brake pedal 21 is detected by the turning off of the brake switch 22, thus ensuring that combustion operation can be reliably restarted.

[0025] In a preferred embodiment, the brake fluid pressure threshold Ps is set according to the road surface gradient detected by the gravity sensor 24, and more specifically, the steeper the gradient, the higher the value. Figure 3 shows the relationship between the road surface gradient and the threshold Ps. The road surface gradient (%) on the horizontal axis exists in both positive and negative values, for example, when the front of the vehicle is raised, but the characteristics of the threshold Ps are generally symmetrical between positive and negative values. In other words, the larger the absolute value of the gradient, the higher the threshold Ps, and the lowest value is obtained on a flat road.

[0026] Generally, on steep road surfaces, the driver presses the brake pedal 21 firmly, resulting in high brake fluid pressure. When the driver releases the pedal to restart, the brake fluid pressure decreases from this high level. On the other hand, on flat roads, the brake fluid pressure while stopped is relatively low. When the driver releases the pedal to restart, the brake fluid pressure decreases from this relatively low level. Therefore, by setting a threshold Ps according to the road surface gradient as shown in Figure 3, the brake pedal release operation can be detected early and accurately without causing misjudgments.

[0027] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications are possible. For example, the present invention is not limited to a configuration in which an internal combustion engine 1 is combined with a stepped automatic transmission 2, but can also be applied to configurations in which it is combined with a continuously variable transmission or a manual transmission. [Explanation of Symbols]

[0028] 1…Internal combustion engine 2…Automatic transmission 4… Starter motor 6…Engine controller 21...Brake pedal 22...Brake switch 23...Brake fluid pressure sensor 24… Gravity sensor

Claims

1. An internal combustion engine idle stop control method that automatically stops the internal combustion engine when predetermined idle stop permission conditions, including pressing the brake pedal, are met when the vehicle stops, and then restarts the internal combustion engine when predetermined idle stop release conditions, including releasing the brake pedal, are met, In the process of automatically stopping the internal combustion engine when the above idle stop permission conditions are met, if the brake pedal is released while the internal combustion engine's rotational speed is above a predetermined rotational speed, the combustion operation of the internal combustion engine will be restarted by restarting fuel injection and ignition without cranking by the starter motor. Here, it is determined that the brake pedal release operation has occurred when the brake fluid pressure falls below a predetermined threshold. A method for controlling the idle stop function of an internal combustion engine.

2. It is equipped with a brake switch that detects when the brake pedal is in the depressed position, The brake release operation is determined to have occurred when either the brake fluid pressure falls below a predetermined threshold, or the brake switch is turned off. The idle stop control method for an internal combustion engine according to claim 1.

3. The above threshold is set to a higher value the steeper the road surface gradient. The idle stop control method for an internal combustion engine according to claim 1.

4. In an internal combustion engine idle stop control device that automatically stops the internal combustion engine when predetermined idle stop permission conditions, including pressing the brake pedal, are met when the vehicle comes to a stop, and then restarts the internal combustion engine when predetermined idle stop release conditions, including releasing the brake pedal, In the process of automatically stopping the internal combustion engine when the above idle stop permission conditions are met, if the brake pedal is released while the internal combustion engine's rotational speed is above a predetermined rotational speed, the combustion operation of the internal combustion engine will be restarted by restarting fuel injection and ignition without cranking by the starter motor. Here, it is determined that the brake pedal release operation has occurred when the brake fluid pressure falls below a predetermined threshold. An idle stop control device for internal combustion engines.

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