JP4010210B2 - Idle stop vehicle control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for an idle stop vehicle capable of automatically stopping and restarting an engine, and more particularly to a technique for increasing the frequency and time for performing an engine automatic stop.
[0002]
[Prior art]
In recent years, in order to improve exhaust performance and fuel consumption performance, there has been proposed an idle stop vehicle that automatically stops the engine while the vehicle is temporarily stopped, such as waiting for an intersection. By the way, in an engine having a throttle in an intake passage such as a gasoline engine, generally, a booster negative pressure of a brake booster that boosts a braking force is obtained by using an intake negative pressure downstream of the throttle. It has become. However, during the automatic stop of the engine, the intake negative pressure greatly decreases to near atmospheric pressure, so it is not possible to compensate for the decrease in the booster negative pressure of the brake booster, and the brake performance may decrease. Ensuring braking force during idle stop is an important issue.
[0003]
Therefore, in Patent Document 1, when the booster negative pressure of the brake booster (brake booster) falls below a predetermined value during the idle stop, the engine is automatically restarted in order to ensure the negative pressure necessary for the brake. The technique to be performed is described. In Patent Document 2, an electromagnetic valve having a function capable of maintaining booster negative pressure regardless of supply of intake negative pressure from the engine is incorporated in a brake booster, and the engine is automatically stopped using this electromagnetic valve. Even if the intake negative pressure is reduced, the braking force is maintained.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-310133
[Patent Document 2]
Japanese Patent Laid-Open No. 2000-203415 [0006]
[Problems to be solved by the invention]
In the above Patent Document 1, if the intake negative pressure decreases during the engine automatic stop, even if the brake pedal is depressed deeply and the brake fluid pressure is sufficiently high, the engine automatically restarts, When the engine is running at low speed during slow traffic congestion, the engine will not stop automatically even if the brake pedal is depressed deeply and the brake fluid pressure is high enough. Nonetheless, further improvements are desired. In Patent Document 2, it is necessary to use an expensive brake booster with a built-in electromagnetic valve, which causes an increase in cost.
[0007]
The present invention has been made in view of such a problem, and is a novel device capable of effectively increasing the frequency and time of idling stop while ensuring the braking force at the time of automatic stop / restart of the engine. The main object is to provide a control device for an idle stop vehicle.
[0008]
[Means for Solving the Problems]
The control apparatus for an idle stop vehicle according to the present invention includes a hydraulic pressure detecting means for detecting a brake hydraulic pressure, and indicates that the vehicle is stopped and that the brake hydraulic pressure is higher than a hydraulic pressure lower limit threshold. The engine is automatically stopped when the idle stop condition including it is satisfied. The booster negative pressure of the brake booster that increases the braking force by using the intake negative pressure of the engine is detected, and this hydraulic pressure lower limit is set so that the lower the booster negative pressure, the higher the lower hydraulic pressure threshold. Correct the threshold value.
[0009]
【The invention's effect】
According to the present invention, the brake required at the time of engine automatic stop / automatic restart is corrected by correcting the hydraulic pressure lower limit threshold of the brake hydraulic pressure used for the determination of the automatic restart of the engine according to the booster negative pressure. While ensuring the power (this braking force largely depends on the brake fluid pressure and the booster negative pressure), the frequency and time of the automatic engine stop can be effectively increased. Improvements can be made.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic configuration diagram illustrating an idle stop vehicle control device according to an embodiment of the present invention. The intake passage 3 connected to the combustion chamber 2 of the engine 1 is provided with a throttle valve 5 for restricting the intake passage 3, and an intake manifold 4 having a predetermined volume is formed on the downstream side of the throttle valve 5. Has been.
[0011]
A brake booster (also referred to as a vacuum servo or a brake booster) 20 uses the intake negative pressure in the intake manifold 4 to boost the brake force. As is well known, the brake booster 20 applies a pressure difference between the negative pressure chamber and the atmospheric chamber defined inside to the diaphragm, and assists the pedaling force of the brake pedal 21 to be transmitted to the master cylinder 22. To do. The negative pressure chamber is connected to the intake manifold 4 via the communication passage 8, and intake negative pressure in the intake manifold 4 is introduced. A check valve 11 is disposed in the communication path 8. A stroke sensor 23 for detecting the stroke of the brake pedal 21, a first negative pressure sensor 24 for detecting the pressure in the intake manifold 4, and a second negative pressure for detecting the pressure in the negative pressure chamber of the brake booster 20, that is, the negative pressure of the booster. A sensor (negative pressure detection means) 25 and a hydraulic pressure sensor (hydraulic pressure detection means) 26 for detecting the brake hydraulic pressure of the master cylinder 22 are connected to an engine control unit (engine control unit; ECU) 13. A detection signal is output to the engine control unit 13.
[0012]
The engine control unit 13 includes a CPU, a memory, and the like, and performs general engine control such as fuel injection control and intake air amount control. Start. Further, the engine control unit 13 outputs a control signal to the throttle valve 5 and a hydraulic actuator unit 30 described later, and controls its operation.
[0013]
FIG. 2 shows a brake hydraulic circuit diagram of an ABS (anti-lock brake system). As is well known, the ABS has a function of preventing the wheels 31 from being locked during sudden braking or braking on a slippery road surface such as a snowy road and improving the stability of the vehicle. Specifically, the hydraulic actuator unit 30 determines whether the wheel 31 is in a slip state based on a signal from the rotation sensor 32 of each wheel 31, and increases the brake fluid pressure of the master cylinder 22 based on the determination.・ Hold and depressurize. In the present embodiment, this ABS functions as a slope retreat suppressing device that holds brake fluid pressure during idle stop (to be described later) (hill hold means) and suppresses the vehicle from retreating unexpectedly on a steep slope. To do.
[0014]
FIG. 3 is a flowchart showing a control flow of the present embodiment. In this idle stop vehicle, when a predetermined idle stop condition is satisfied, the routine proceeds to S (step) 3 where fuel injection is prohibited and the engine 1 is automatically stopped, that is, idle stop is executed. The idle stop condition is that the vehicle is stopped, that is, the vehicle speed is almost zero (S1), the brake fluid pressure is higher than the fluid pressure lower limit threshold, and the brake booster 20 The booster negative pressure is greater than the negative pressure lower limit threshold (S2).
[0015]
FIG. 4 shows a control map used for the determination of S2. In a conventional general idle stop vehicle, as shown by a broken line L1, the hydraulic pressure lower limit threshold is fixed to a predetermined hydraulic pressure lower limit fixed value Pa1, and the negative pressure lower limit threshold is a predetermined negative pressure lower limit fixed value. It is fixed to Pb1. On the other hand, in the present embodiment, as indicated by the solid line L2, in the region where the booster negative pressure is smaller than the negative pressure lower limit fixed value Pb1, the hydraulic pressure lower limit threshold increases as the booster negative pressure decreases. The hydraulic pressure lower limit threshold value is corrected (correcting means). In other words, in the region where the booster negative pressure is smaller than the negative pressure lower limit fixed value Pb1, the negative pressure lower limit threshold is corrected so that the negative pressure lower limit threshold decreases as the brake fluid pressure increases. As a result, the idling stop region used for the determination of the automatic engine stop is enlarged by the substantially V-shaped enlarged idling stop region R1 sandwiched between the broken line L1 and the solid line L2 in FIG.
[0016]
Referring to FIG. 3 again, in S4, it is determined based on the brake fluid pressure and the brake negative pressure whether the above-mentioned extended idle stop region R1 is reached. In the idle stop region other than the enlarged idle stop region R1, normal idle stop processing such as engine automatic restart is performed (S11), but the description is omitted here. Note that the determination of S4 may be omitted, and the processing after S5 may be always performed in the idle stop region.
[0017]
If it is in the extended idle stop region R1, that is, if the booster negative pressure is smaller than the negative pressure lower limit fixed value Pb1 and the idle stop is performed, when the brake pedal 21 is turned off, that is, the brake hydraulic pressure is reduced, S5 From S6, the ABS hydraulic actuator unit 30 immediately starts holding brake fluid pressure, that is, hill hold (hill hold means). Note that the hill hold may be started when the brake fluid pressure is reduced to a predetermined value.
[0018]
If a predetermined engine automatic restart condition is satisfied during such an idle stop operation, the process proceeds to S8, and the engine is automatically restarted (automatic restart means). That is, the engine 1 is cranked by a motor, a starter, etc. (not shown), and fuel injection is resumed when the engine speed reaches a predetermined value. The engine automatic restart condition includes that the brake fluid pressure is lower than the fluid pressure upper limit threshold or that the brake booster negative pressure is smaller than the negative pressure upper threshold (S7).
[0019]
As shown in FIG. 4, in a conventional general idle stop vehicle, as indicated by a broken line L3, the hydraulic pressure upper limit threshold is fixed to a predetermined hydraulic pressure upper limit fixed value Pa2, and the negative pressure upper limit threshold is It is fixed to a predetermined negative pressure upper limit fixed value Pb2. The hydraulic pressure upper limit fixed value Pa2 is a value lower than the hydraulic pressure lower limit fixed value Pa1, and the negative pressure upper limit fixed value Pb2 is a value smaller than the negative pressure lower limit fixed value Pb1.
[0020]
On the other hand, in this embodiment, as indicated by the solid line L4, in the region where the booster negative pressure is smaller than the negative pressure upper limit fixed value Pb2, the hydraulic pressure upper limit threshold increases as the booster negative pressure decreases. The fluid pressure upper limit threshold value is corrected (second correction means). In other words, in the region where the booster negative pressure is smaller than the negative pressure upper limit fixed value Pb2, the negative pressure upper limit threshold is corrected so that the negative pressure upper limit threshold decreases as the brake fluid pressure increases. As a result, the idle stop region used for the determination of the automatic engine restart is enlarged by the substantially V-shaped enlarged idle stop region R2 sandwiched between the broken line L3 and the solid line L4 in FIG.
[0021]
As shown in the time chart of FIG. 5, when the booster negative pressure develops after the automatic restart of the engine and exceeds a predetermined release threshold value Pc, the hill hold by the hydraulic actuator unit 30 is released (S10, S10). S11). That is, the release of the hill hold is prohibited until the booster negative pressure exceeds the release threshold value Pc (release prohibiting means). In other words, the release of the hill hold is prohibited for a predetermined period ΔT from the engine automatic restart. The release threshold value Pc may be, for example, the negative pressure upper limit fixed value Pb2, or may be another fixed value. Alternatively, the release threshold value Pc may be adjusted according to the brake fluid pressure.
[0022]
The operation and effect of the present embodiment will be described. One of the reasons why booster negative pressure is used to determine whether the engine is automatically stopped and restarted is that the intake negative pressure becomes very small (close to atmospheric pressure) during automatic engine stop, so pumping Once the negative pressure in the booster is consumed due to the brake operation or the like, the booster negative pressure of the brake booster 20 cannot be increased again by the intake negative pressure, and there is a possibility that sufficient brake assisting force cannot be obtained. Because. For this reason, the engine is automatically stopped within the booster negative pressure range where the brake assist force equivalent to that during engine rotation can be obtained, that is, within the range where the booster negative pressure is equal to or greater than the negative pressure lower limit threshold value. When the negative pressure falls below the negative pressure upper limit threshold, the engine is automatically restarted.
[0023]
On the other hand, in consideration of the driver's intention to stop and start, the brake fluid pressure is used for the determination of the automatic stop and the automatic restart of the engine. The brake fluid pressure lower limit threshold used for determining whether to automatically stop the engine and the brake fluid pressure upper limit threshold used for determining whether to restart the engine automatically stop the vehicle stably even on hills. It is preferable to set the value as low as possible so as to improve the frequency and time of automatic engine stop (idle stop) as long as the state can be maintained.
[0024]
In a vehicle having a slope retreat suppression device such as the ABS hydraulic actuator unit 30 and having a function of holding the brake fluid pressure for a predetermined period, for example, even if the booster negative pressure is small, the brake fluid pressure corresponding to the driver's pedal operation is low. If sufficiently secured, it is possible to secure a braking force necessary for idling stop. Focusing on this point, in the present embodiment, as described above, the idle stop region is effectively expanded based on the brake fluid pressure and the booster negative pressure (R1, R2), thereby providing a sufficient braking force. The exhaust frequency and the fuel consumption performance can be improved by increasing the frequency and time at which the idling stop is performed while ensuring the above.
[0025]
However, when the engine is automatically stopped in the extended idle stop region R1, that is, when the engine is automatically stopped in a situation where the booster negative pressure is smaller than the negative pressure lower limit fixed value, the booster negative pressure is reduced immediately after the engine is automatically restarted. Since there is a possibility that the vehicle cannot be stably held on a slope due to a shortage, the release of the hill hold is prohibited until the booster negative pressure exceeds the negative pressure release threshold value Pc.
[Brief description of the drawings]
FIG. 1 is a configuration diagram schematically illustrating a control device for an idle stop vehicle according to an embodiment of the present invention.
FIG. 2 is a brake hydraulic circuit diagram of an ABS that also serves as a slope retreat suppressing device according to the present embodiment.
FIG. 3 is a flowchart showing a flow of control of automatic stop / automatic restart of the engine according to the present embodiment.
FIG. 4 is a control map used for determination of automatic stop / automatic restart of the engine according to the present embodiment.
FIG. 5 is a time chart showing hill hold release timing according to the present embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine 20 ... Brake booster 25 ... 2nd negative pressure sensor (negative pressure detection means)
26 ... Hydraulic pressure sensor (hydraulic pressure detecting means)
30 ... Hydraulic actuator unit (hill hold means)

Claims (5)

Fluid pressure detecting means for detecting brake fluid pressure;
Automatic stop means for automatically stopping the engine when an idle stop condition is satisfied including that the vehicle is stopped and the brake hydraulic pressure is higher than a hydraulic pressure lower limit threshold;
A brake booster that uses the intake negative pressure of the engine to increase the braking force;
Negative pressure detecting means for detecting the booster negative pressure of the brake booster;
A control device for an idle stop vehicle, comprising: correction means for correcting the hydraulic pressure lower limit threshold value such that the lower the booster negative pressure, the higher the hydraulic pressure lower limit threshold value. When the booster negative pressure is smaller than a predetermined negative pressure lower limit fixed value, correction is performed by the correction means. When the booster negative pressure is larger than the negative pressure lower limit fixed value, the hydraulic pressure lower limit threshold is set to a predetermined liquid pressure. The control device for an idle stop vehicle according to claim 1, wherein the control device is fixed to a pressure lower limit fixed value. A hill hold means for holding the brake fluid pressure according to a decrease in the brake fluid pressure when the engine is automatically stopped at least when the booster negative pressure is smaller than the negative pressure lower limit fixed value;
The control of the idle stop vehicle according to claim 2, further comprising: a release prohibiting means for prohibiting the release of the brake fluid pressure by the hill hold means until the booster negative pressure exceeds a predetermined negative pressure release threshold. apparatus. Automatic restarting means for automatically restarting the engine when the brake fluid pressure is lower than a fluid pressure upper limit threshold during automatic stop of the engine;
The second correction means for correcting the hydraulic pressure upper limit threshold so that the lower the booster negative pressure is, the higher the hydraulic pressure upper limit threshold is. Control device for idle stop vehicle. A brake booster that uses the intake negative pressure of the engine to increase the braking force;
Negative pressure detecting means for detecting the booster negative pressure of the brake booster;
Automatic stop means for automatically stopping the engine when an idle stop condition is satisfied including that the vehicle is stopped and the booster negative pressure is greater than a negative pressure lower limit threshold;
Fluid pressure detecting means for detecting brake fluid pressure;
A control device for an idle stop vehicle, comprising: correction means for correcting the negative pressure lower limit threshold value so that the negative pressure lower limit threshold value decreases as the brake fluid pressure increases.

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