JP2012082789A - Engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine control device which achieves both of the improvement of certainty of securing brake assisting force by booster negative pressure and the improvement of fuel consumption by prolonging of an idle stop period.SOLUTION: The engine control device is applied to a vehicle provided with a booster device for introducing the intake negative pressure of an engine as a booster negative pressure to assist the brake pedal stepping force of a driver and an idle stop system for permitting automatic stopping of the engine without waiting for time when the vehicle speed becomes zero, and is provided with a brake restart means for recovering the brake assistant force by automatically restarting the engine when the booster negative pressure becomes lower than a predetermined threshold value TH1 in the automatic stopping of the engine and an idle stop prohibition determination means S23 for determining whether the automatic stop prohibition of engine is right or not on the basis of the lowering amount Δpave of the booster negative pressure (history that the brake assistant force becomes lower) during the engine operation.

Description

  The present invention relates to an engine (engine) control device applied to a vehicle including an idle stop system.

  In the conventional idle stop system, when the driver's intention to stop is detected, for example, by depressing the brake pedal, the fuel injection is cut off on condition that the vehicle speed is zero. The engine (internal combustion engine) is automatically stopped (idle stop) to improve fuel efficiency. In recent years, there is a technique in which the fuel injection is cut and idle stop is performed without waiting for the vehicle speed to become zero, thereby extending the idle stop period and further improving fuel efficiency (see Patent Document 1).

JP-A-11-257115

  By the way, in a vehicle equipped with a booster device that introduces the intake negative pressure of the engine as a booster negative pressure and assists the brake pedal depression force by the driver with the booster negative pressure, the intake negative pressure cannot be supplied when the engine is stopped. Negative pressure decreases (booster negative pressure approaches atmospheric pressure). As a result, the force required to depress the brake pedal increases, so that the brake pedal feels hard for the driver, and the brake operability deteriorates. Therefore, when the booster negative pressure becomes less than a predetermined threshold value TH1 (see FIG. 2) during idle stop, it is common to restart the engine to ensure the booster negative pressure. In particular, when the idling stop is performed without waiting for the vehicle speed to become zero as described above, it is required to ensure a positive booster negative pressure.

  However, even if the engine is restarted when the booster negative pressure becomes less than the threshold value TH1, there is a time lag (for example, 0.5 seconds to 1.5 seconds) before the booster negative pressure starts to increase. For this reason, the threshold value TH1 is set higher in consideration of the fact that the booster negative pressure decreases during the time lag.

  Also, because of the structure of the booster device, the booster negative pressure is greatly reduced when the brake pedal that is depressed is loosened. Therefore, if the driver performs a pumping operation (pumping brake) that repeatedly depresses the brake pedal, the booster negative pressure is reduced in a short time. Decreases rapidly. Therefore, in order to ensure a sufficient booster negative pressure even if the booster negative pressure is greatly reduced immediately after the engine is restarted, the threshold value TH1 needs to be set high.

  In this way, the higher the threshold TH1 is set in consideration of the possibility of a pumping operation, the more certainty of securing the booster negative pressure can be improved. However, as the threshold TH1 is set to be higher, restarting is required immediately after idling stop, so that it is not possible to sufficiently improve fuel efficiency by extending the idling stop period.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the certainty of securing brake assisting force by booster negative pressure and improve fuel efficiency by expanding the idle stop period. It is to provide a control device.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  In the first aspect of the present invention, a booster device that introduces the intake negative pressure of the engine as a booster negative pressure and assists the brake pedal depression force by the driver with the booster negative pressure, and without waiting for the vehicle speed to become zero. It is assumed that the present invention is applied to a vehicle including an idle stop system that allows automatic stop of the engine.

  And a brake restarting means for automatically restarting the engine and recovering the brake assisting force due to the booster negative pressure when the booster negative pressure becomes less than a predetermined threshold at the time of the automatic engine stop. And an idle stop prohibition judging means for judging whether or not the engine is automatically stopped based on a history of a decrease in the brake assisting force during operation of the engine.

  Here, if the booster negative pressure suddenly drops due to pumping brakes or the like during engine operation and the brake assisting force is reduced, the brake re-use will be resumed even if the engine is subsequently idle stopped (automatic stop). There is a high possibility that the engine will be restarted immediately by the starting means.In addition, even after restarting, the booster negative pressure will continue to drop sharply immediately thereafter, and the brake operability may deteriorate beyond tolerance. high.

  In the above-described invention in view of this point, it is determined whether to prohibit the idle stop (automatic stop) based on the history of the decrease in the brake assisting force during engine operation. For this reason, when the pumping brake is applied during engine operation and the booster negative pressure (brake assist force) suddenly decreases, the engine is automatically stopped regardless of whether the brake assist force is below a predetermined threshold. It can be prohibited. Therefore, even if the engine is restarted immediately after the idle stop, the abrupt decrease in the booster negative pressure will continue immediately thereafter, and the brake operability will deteriorate beyond tolerance. However, it is possible to ensure the booster negative pressure.

  Since the above-mentioned concern due to the pumping brake is eliminated by providing such an idle stop prohibition determining means, “threshold TH1 used by the brake restarting means in consideration of the possibility of a pumping operation (see FIG. 2). It is possible to eliminate the need to set “high”. Therefore, since the threshold TH1 is set to a low value and the opportunity for restarting by the brake restarting means can be reduced, the idle stop period can be extended and fuel efficiency can be improved.

  As described above, according to the present invention, it is possible to improve the certainty of securing the brake assisting force by providing the idle stop prohibition determining means. Therefore, the threshold TH1 used in the brake restarting means is set low and the idle stop period is set. The fuel consumption can be improved by expanding the fuel consumption.

  The invention according to claim 2 is characterized in that the idle stop prohibition determining means determines whether or not automatic stop prohibition is based on the vehicle speed at that time in addition to the history of the brake assist force decreasing.

  Here, even if the brake assisting force decreases and the brake operability deteriorates, if the vehicle speed at that time is very low (for example, several kilometers per hour) just before stopping, a large braking force is not necessary, Permissible. On the other hand, if the vehicle speed is not sufficiently low, even if the brake operability is slightly deteriorated, it is not acceptable for the driver. Therefore, even if the brake assist force decrease history during engine operation is the same, it is desirable to prohibit idle stop if the vehicle speed at that time is not sufficiently low, and permit idle stop if the vehicle speed is extremely low.

  In view of this point, in the above invention, in addition to the brake assist force decrease history, whether to stop the idle stop is determined based on the vehicle speed at that time, the determination according to the allowance of the brake operability deterioration that changes with the vehicle speed is realized. it can. Therefore, since the brake assisting force by the booster negative pressure can be ensured without prohibiting the idle stop unnecessarily, both the securing of the brake assisting force and the extension of the idle stop period can be promoted.

  According to a third aspect of the present invention, a negative pressure sensor for detecting the booster negative pressure is provided, and the idle stop prohibition determining means is a booster negative pressure decreasing rate calculated from a detection value of the negative pressure sensor or a predetermined period. The total decrease amount of the booster negative pressure is calculated as a decrease history of the brake assist force. According to a fourth aspect of the present invention, a hydraulic pressure sensor that detects the pressure of the brake oil (brake hydraulic pressure) is provided, and the idle stop prohibition determination unit is configured to reduce the pressure decrease rate calculated from the detection value of the hydraulic pressure sensor or a predetermined value. The total pressure decrease amount during the period is calculated as the brake assist force decrease history.

  Here, the change in the brake assisting force has a correlation with the change in the depression force of the brake pedal, the change in the depression amount, the change in the vehicle braking force, etc. Therefore, if these depression force, depression amount, and braking force are detected, the brake It is possible to estimate the history of the reduction in assist power. However, since it is the booster negative pressure or brake oil pressure (brake hydraulic pressure) that directly determines the brake auxiliary force, the booster negative pressure or the brake hydraulic pressure has a higher correlation with the brake auxiliary force.

  In view of this point, the above-described invention includes a negative pressure sensor that detects the booster negative pressure or a hydraulic pressure sensor that detects the pressure of the brake oil, and a booster negative pressure and a decrease rate of the brake hydraulic pressure calculated from the detection values of these sensors. Since (the amount of change per unit time) is calculated as the brake assist force decrease history, the calculation accuracy can be increased.

  In addition, as the total amount of decrease in the booster negative pressure and brake hydraulic pressure during the specified period (the integrated value of the amount of change) increases, the brake assist force should decrease, and the correlation between these total decrease amount and brake assist force Since it is high, according to the above-described invention that calculates the total decrease amount of the booster negative pressure and the brake hydraulic pressure in a predetermined period as the brake assist force decrease history, the calculation accuracy can be increased.

  The invention according to claim 5 is characterized in that the rate of decrease is calculated from a moving average value of the detected values.

  Here, because of the structure of the booster device, as described above, the booster negative pressure greatly decreases when the depressed brake pedal is loosened. Therefore, the booster negative pressure during the pumping brake implementation period decreases stepwise. For this reason, if the instantaneous decrease speed is calculated, it becomes a decrease speed that is significantly different from the average decrease speed during the pumping brake period. Damaged. Specifically, if it is determined based on the decrease speed when the brake pedal is loosened, idle stop is prohibited more than necessary, and if it is determined based on the decrease speed when the brake pedal is depressed, it is more than necessary. Idle stop will be allowed.

  In the above-mentioned invention in view of this point, the speed of decrease is calculated from the moving average value of the detection values of the negative pressure sensor or the hydraulic pressure sensor (the average value of the latest n detection values). Can be suppressed, and the optimality of the determination can be improved.

  According to a sixth aspect of the present invention, when it is determined by the idle stop prohibition determining means that the automatic stop of the engine is prohibited, after the prohibition determination, a period until the brake auxiliary force increases and reaches a predetermined value is automatically It is characterized by continuing the prohibition of the stop.

  Here, even if it is determined that the idling stop prohibition is caused due to a sudden decrease in the brake assisting force, if the speed of the brake assisting force decreases thereafter, the process shifts to the idling stop permitting determination. There is a concern that the brake assisting force may become less than the threshold value and be restarted immediately after the operation is performed. In response to this concern, according to the above-described invention, after the idle stop prohibition determination, the automatic stop prohibition is continued during the period until the brake assist force increases and reaches a predetermined value. Thus, it is possible to avoid a situation where the brake is restarted immediately by the brake restarting means.

1 is an overall view of an engine and a booster device to which an engine control device according to an embodiment of the present invention is applied. The time chart which shows changes, such as a booster negative pressure, when idle stop is made in the middle of decelerating driving | running | working with a pumping brake. 6 is a flowchart showing a control procedure for automatically restarting the engine when the booster negative pressure is insufficient during the idle stop period in the embodiment of the present invention. The flowchart which shows the procedure of the control which determines the propriety of idle stop prohibition based on the variation | change_quantity of the booster negative pressure at the time of engine driving | operation in embodiment of this invention.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings. The vehicle according to the present embodiment includes an idle stop system that automatically stops and restarts the engine 10 (internal combustion engine), and also includes a braking device that includes a booster device 30 described below.

  First, the master cylinder 20 and the booster device 30 constituting the braking device mounted on the vehicle will be described with reference to FIG.

  The master cylinder 20 is operated by the depression force (brake depression force) of the brake pedal 11 by the driver to generate brake oil pressure (brake oil pressure). When the brake pedal 11 is depressed by the driver, the brake depression force is transmitted to the piston 22 via the rod 21, and the brake oil filled in the cylinder 23 is compressed by the compression operation of the piston 22, and the brake hydraulic pressure is increased. Will rise. The brake hydraulic pressure boosted in this way is transmitted to a front wheel cylinder and a rear wheel cylinder (not shown), and each wheel cylinder is operated by the brake hydraulic pressure to exert a braking force.

  The booster device 30 introduces the intake negative pressure of the engine 10 as a booster negative pressure, and assists the brake pedal force with this booster negative pressure. The booster device 30 includes a housing 31 that forms a pressure chamber therein, and a diaphragm 32 that partitions the pressure chamber inside the housing 31 into a constant pressure chamber 31a and a variable pressure chamber 31b. The constant pressure chamber 31 a communicates with the intake pipe 12 of the engine 10 via the check valve 33. For this reason, a negative pressure is introduced into the constant pressure chamber 31a during operation of the engine 10. The pressure in the constant pressure chamber 31a corresponds to “booster negative pressure”. The variable pressure chamber 31 b is configured to be able to communicate with the atmosphere via the atmosphere valve 34. Further, the constant pressure chamber 31 a and the variable pressure chamber 31 b are configured to communicate with each other via the vacuum valve 35.

  When the brake pedal 11 is not depressed, the atmospheric valve 34 is closed and the vacuum valve 35 is opened. Therefore, the constant pressure chamber 31a and the variable pressure chamber 31b are in a communication state and the same negative pressure is generated. On the other hand, when the brake pedal 11 is depressed, the vacuum valve 35 is first closed, and the constant pressure chamber 31a and the variable pressure chamber 31b are in a non-communication state. Thereafter, when the brake pedal 11 is further depressed, the atmospheric valve 34 is opened, and the atmosphere is introduced into the variable pressure chamber 31b. Thereby, the variable pressure chamber 31b becomes atmospheric pressure, while the constant pressure chamber 31a becomes negative pressure. Therefore, a pressure difference is generated between the constant pressure chamber 31a and the variable pressure chamber 31b, and this differential pressure acts on the diaphragm 32 to become an assist force (brake assist force) that assists the brake pedal force.

  Next, a method for controlling the operation of the engine 10 by the ECU 40 and an idle stop system will be described. An engine 10 shown in FIG. 1 is an ignition type gasoline engine (internal combustion engine), and is a port injection type engine that injects fuel from a fuel injection valve 13 into an intake pipe 12. The ECU 40 mainly controls the fuel injection amount, the injection timing, the intake amount, and the ignition timing by controlling the operations of the fuel injection valve 13, the throttle valve 14, and the ignition device 15. Thereby, the operation of the engine 10 is controlled so that the exhaust emission and the output torque are in a desired state.

  The idle stop system automatically detects the driver's intention to stop while the vehicle is running and automatically injects fuel from the fuel injection valve 13 without waiting for the vehicle speed to reach zero when a predetermined idle stop condition is satisfied. Is stopped (fuel injection cut) and the operation of the ignition device 15 is stopped to automatically stop the engine 10.

  Specific examples of the detection of the stop intention described above include that the amount of depression of the brake pedal 11 detected by the brake pedal sensor 11a is equal to or greater than a predetermined amount, and that the accelerator pedal is not depressed. Specific examples of the idle stop condition include that the vehicle speed is decreasing, that the vehicle speed is less than a predetermined vehicle speed THa (see FIG. 2A), that the charge amount of the in-vehicle battery is greater than or equal to a predetermined amount, engine The power transmission from 10 to the vehicle drive wheel is cut off. As a specific example of the idle stop cancellation condition, the charge amount of the on-vehicle battery is less than a predetermined amount, the brake pedal 11 is not depressed (or the depression amount is less than the predetermined amount), and the accelerator pedal is depressed. And the like.

  Thus, when the engine 10 is automatically stopped without waiting for the vehicle speed to become zero, the pressure in the constant pressure chamber 31a increases and approaches the atmospheric pressure (the negative pressure in the constant pressure chamber 31a decreases). As a result, the assist force (brake assist force) decreases, and as a result, the force required to step on the brake pedal 11 increases, so that the driver feels the brake pedal 11 hard, There is concern about the deterioration of brake operability.

  Therefore, in the present embodiment, the negative pressure sensor 30a that detects the negative pressure in the constant pressure chamber 31a is attached to the housing 31 to detect the booster negative pressure. The ECU 40 permits idling stop under the condition that the booster negative pressure detected by the negative pressure sensor 30a during engine operation is equal to or higher than a predetermined threshold value TH1 (see FIG. 2C). Further, when the booster negative pressure detected during the idling stop control is reduced to less than the threshold value TH1, the engine 10 is automatically restarted.

  When the booster negative pressure is reduced to the lower limit threshold TH2 (see FIG. 2C) set to a value lower than the threshold TH1, the engine control is switched to fail-safe control. In the fail-safe control, for example, the fuel injection amount and the intake air amount are limited, and the engine output and the vehicle speed are limited so that the engine rotation speed and the vehicle speed are less than a predetermined value.

  A solid line in FIG. 2 is a time chart showing a change in booster negative pressure or the like when an idle stop is made while the vehicle is decelerating while performing a pumping brake. Will be described.

  First, at time t1, the vehicle speed starts to decrease as the vehicle driver depresses the brake pedal 11 (see FIGS. 2D and 2A). Thereafter, the brake pedal force is once relaxed at time t2, and thereafter, a pumping operation (pumping brake) is performed in which the brake pedal 11 is repeatedly depressed and loosened. Then, with this pumping operation, the booster negative pressure rapidly decreases (see FIG. 2C). After that, when the vehicle speed decreases to the predetermined vehicle speed THa at the time point t3 and the idle stop condition is satisfied, the idle stop that automatically stops the engine is executed, and the engine rotation speed decreases to zero as the engine stops. (See FIGS. 2A and 2B). In the example of FIG. 2, the pumping operation is started from time t2 before the engine is automatically stopped, and the pumping operation is continued until the vehicle speed becomes zero even after the automatic stop.

  Here, the reason why the booster negative pressure decreases when the pumping operation is performed will be described below. After the engine 10 is automatically stopped, if the brake pedal 11 is depressed and the depression amount is reduced to such an extent that the idle stop condition is satisfied, the vacuum valve 35 is opened and the negative pressure in the constant pressure chamber 31a is changed to the variable pressure chamber. It flows into 31b. Thereafter, when the brake pedal 11 is depressed, the atmospheric valve 34 opens and the negative pressure in the variable pressure chamber 31b escapes to the atmosphere. Therefore, when the driver performs a pumping operation on the brake pedal 11 when the engine is stopped, the negative pressure supply from the intake pipe 12 to the constant pressure chamber 31a is interrupted, and the negative pressure in the constant pressure chamber 31a is changed every time the pumping operation is performed. To exit from the atmospheric valve 34. Therefore, while the brake pedal 11 is kept depressed, the booster negative pressure hardly decreases, but every time the brake pedal 11 is loosened, the booster negative pressure decreases stepwise (FIGS. 2C and 2D). )reference).

  In the example of FIG. 2, the booster negative pressure is reduced by the pumping operation during the period from t2 to t3 when the engine is operated. Since there is a time lag, the period from t2 to t3 corresponds to the time lag. Therefore, if the engine is not stopped at time t3, the booster negative pressure starts to increase and recovers after time t3 even if the pumping operation is continued. However, in the example of FIG. 2, since the engine is stopped at time t3, the booster negative pressure continues to decrease, and at time t4 when it has decreased to the threshold value TH1, continuation of idle stop is stopped and the engine 10 is automatically restarted. I am letting.

  With this restart, the engine rotation speed starts to increase, but the booster negative pressure does not start increasing immediately due to the time lag described above, and the booster negative pressure continues to decrease even after the engine 10 is restarted. . Then, the booster negative pressure starts increasing at time t5. In the example of FIG. 2, the booster negative pressure starts to increase at time t5 without reaching the lower threshold TH2, and thus the above-described fail-safe control is not performed.

  Incidentally, as shown by the dotted line L1 in FIG. 2D, if the pumping operation is stopped at the time t2a and the pedaling force is kept constant without loosening the brake pedal 11, the dotted line L2 in FIG. As shown in FIG. 3, the booster negative pressure is maintained even after the engine is stopped and does not drop rapidly.

  FIG. 3 is a flowchart showing the processing procedure when the microcomputer of the ECU 40 performs the engine control according to the detected value of the booster negative pressure as described above. The processing is repeatedly executed at a predetermined cycle (for example, a calculation cycle performed by the CPU of the microcomputer or every predetermined crank angle).

  First, in step S10 shown in FIG. 3, it is determined whether or not the booster negative pressure detected by the negative pressure sensor 30a is equal to or higher than the lower limit threshold TH2 shown in FIG. When it is determined that the booster negative pressure is less than TH2 (S10: NO), in the next step S11, the above-described fail-safe control of the engine 10 is executed. If it is determined that the booster negative pressure is greater than or equal to TH2 (S10: YES), in the next step S12, it is determined whether or not the booster negative pressure is greater than or equal to a threshold value TH1 (where TH1> TH2) shown in FIG. judge.

  If it is determined that booster negative pressure ≧ TH1 (S12: YES), idling stop is permitted in the next step S13. That is, during engine operation, the engine 10 is automatically stopped if an idle stop condition such as vehicle speed <THa is satisfied. Further, if the engine is in idle stop, the engine stop state is continued unless the idle stop cancellation condition is satisfied.

  On the other hand, if it is determined that the booster negative pressure is less than TH1 (S12: NO), it is determined in the next step S14 whether the engine is idling stopped or not (S14: NO). If so, fail safe control is executed in step S11. Note that, in the determination of step S14, if the state of TH2 ≦ booster negative pressure <TH1 (S10: YES, S12: NO) has elapsed for a predetermined time or more during engine operation, a negative determination is made and fail-safe control (S11) is performed. May be implemented. On the other hand, if it is determined that the engine is in idle stop (S14: YES), the engine is determined in the next step S15 (brake restarting means) regardless of whether or not the aforementioned idle stop release condition is satisfied. 10 is automatically restarted.

  Here, as the threshold TH1 is set higher, the booster negative pressure may become less than the lower threshold TH2 in the period from the time t4 when the engine is restarted to the time t5 until the booster negative pressure starts to increase. Can be reduced. However, as the threshold TH1 is set higher, restarting is immediately required even when the idling stop is performed at the time point t3, so that the fuel consumption cannot be sufficiently improved by extending the idling stop period.

  Therefore, in this embodiment, the presence or absence of a pumping operation is determined during engine operation, and when it is determined that the pumping operation has been performed, idle stop is prohibited. Specifically, if the booster negative pressure decreasing rate is equal to or higher than a predetermined value THb, it is determined that the pumping operation is performed, and the idle stop is prohibited regardless of whether the booster negative pressure is equal to or higher than the threshold value TH1.

  FIG. 4 is a flowchart showing a processing procedure for determining whether or not the idle stop is prohibited as described above. The microcomputer of the ECU 40 performs a predetermined cycle (for example, every calculation cycle performed by the CPU of the microcomputer or every predetermined crank angle). Repeatedly executed. Note that the process of FIG. 4 is executed during engine operation, and is not executed during an engine stop period such as an idle stop.

  First, in step S20 shown in FIG. 4, based on a plurality of sampling values (detection values) detected by the negative pressure sensor 30a, an average (moving average value Pave) of the n detection values nearest to the present time is calculated. For example, the average of n detection values in the period indicated by symbol i-2 in FIG. 2C is calculated as a moving average value Pave (i-2), and then n times in the period of i−1. The average of the detected values is calculated as the moving average value Pave (i−1), and then the average of the n detected values in the period i is calculated as the moving average value Pave (i). Repeat. In the next step S21, a change amount ΔPave of the moving average value Pave calculated in step S20 is calculated. Specifically, it is calculated by the equation: ΔPave = Pave (i) −Pave (i−1).

  In the subsequent step S22, the determination value THb used in the determination in the next step S23 is calculated according to the vehicle speed at that time. Note that the determination value THb is set to a higher value as the vehicle speed increases. For example, a map indicated by reference numeral M1 in FIG. 4 is previously stored in the memory, and the determination value THb is calculated based on the vehicle speed with reference to the map M1. In subsequent step S23 (idle stop prohibition determining means), it is determined whether or not the amount of change ΔPave (decrease amount) of the booster negative pressure to the minus side calculated in step S21 is equal to or larger than a determination value THb.

  When it is determined that −ΔPave ≧ THb (S23: YES), it is considered that the booster negative pressure (assist force) is drastically decreased due to the pumping operation or the like, and the idle stop is prohibited in the subsequent step S24. On the other hand, if -ΔPave <THb is determined (S23: NO), it is determined in the next step S25 whether the booster negative pressure has increased to a predetermined value TH3 (see FIG. 2) and has recovered. To do. The predetermined value TH3 is set to a value higher than the threshold value TH1.

  When it is determined that it has not recovered to the predetermined value TH3 (S25: NO), the prohibition of idling stop in step S24 is continued, and when it is determined that it has recovered to the predetermined value TH3 (S25: YES) In the subsequent step S26, the idle stop prohibition in step S24 is canceled and the idle stop is permitted.

  If the process of FIG. 4 demonstrated above is implemented, as shown by the continuous line in FIG.2 (c), when booster negative pressure falls rapidly resulting from pumping operation, it will determine with-(DELTA) Pave> = THb (S23) : YES), the idle stop is prohibited regardless of whether the booster negative pressure is equal to or higher than the threshold value TH1 (S24). Therefore, the necessity of “setting the threshold value TH1 higher in consideration of the possibility of a pumping operation” can be eliminated. Therefore, since the threshold TH1 is set to a low value and the opportunity for restarting by the brake restarting means can be reduced, the idle stop period can be extended and fuel efficiency can be improved.

  That is, by performing the process of FIG. 4 (idle stop prohibition judging means), it is possible to eliminate the concern that the pumping operation results in a situation where the support force of the brake is insufficient. Therefore, the process of FIG. By setting the threshold value TH1 used in (means) low, fuel efficiency can be improved by extending the idle stop period.

  In short, it is assumed that the engine is automatically stopped when the vehicle speed drops to THa. In this case, the booster negative pressure remains at the lower threshold TH2 even if the booster negative pressure is reduced below the threshold value TH1. It is estimated based on the brake assist force decrease history. If it is estimated that the lower limit threshold TH2 is reached, it can be said that the idle stop is prohibited (S24).

  Furthermore, according to the present embodiment, the determination value THb used for determining whether or not the idle stop is prohibited in step S23 is variably set according to the vehicle speed. Therefore, the idle stop according to the allowance for the deterioration of the brake operability that changes with the vehicle speed. It is possible to determine whether or not to prohibit.

  Furthermore, according to the present embodiment, after the idle stop is prohibited in step S24, the idle stop prohibition is continued until the booster negative pressure is restored to the predetermined value TH3. Then, it is possible to avoid a situation in which the booster negative pressure <TH1 (S12: NO) is immediately restarted.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be modified as follows. Moreover, you may make it combine the characteristic structure of each embodiment arbitrarily, respectively.

  In the above embodiment, the amount of change ΔPave per predetermined time of the booster negative pressure is calculated using the moving average value Pave of a plurality of sampling values detected by the negative pressure sensor 30a, and the idle stop is based on the amount of change ΔPave. Although the prohibition is determined, it is also possible to sequentially calculate the instantaneous change amount of the sampling value and determine whether the idle stop is prohibited based on the instantaneous change amount. For example, the difference between the current value and the previous value of the sampling value may be calculated as a change amount (instantaneous change amount) per unit time.

  The moving average value Pave calculated in step S20 is not limited to a simple moving average that is a simple average without weighting of the latest n sampling values, but is a weight for calculating an average by assigning different weights to individual sampling values. It may be a moving average, or a known exponential moving average or triangular moving average.

  In determining whether or not the idle stop is prohibited based on the “brake assist force decrease history”, in the above embodiment, the amount of change in the booster negative pressure detected by the negative pressure sensor 30a is calculated as the brake assist force decrease history. However, the brake oil pressure in the cylinder 23 may be detected by the oil pressure sensor 20a, and the detected change amount of the brake oil pressure may be calculated as the brake assist force decrease history. Further, the braking force of the vehicle by the brake pedal depression force, the brake pedal depression amount, and the brake hydraulic pressure may be detected, and the change amount of the detected value may be calculated as the brake assist force decrease history.

  In the above embodiment, the amount of change in booster negative pressure is calculated as the brake assist force decrease history, but the total amount of booster negative pressure decrease in a predetermined period may be calculated as the brake assist force decrease history. . For example, in the example of the booster negative pressure shown in FIG. 2C, the integrated value of the booster negative pressure in the period from the time point t2 to the time point t3 may be calculated as the total decrease amount.

  ・ The transition waveform of changes in the booster negative pressure, brake hydraulic pressure, brake pedal depression force, brake pedal depression amount, braking force, etc. described above is calculated as the brake assist force decrease history, and the presence or absence of pumping operation is determined based on this transition waveform. Then, it may be determined whether or not the idle stop is prohibited.

  20a ... Hydraulic pressure sensor, 30 ... Booster device, 30a ... Negative pressure sensor, Pave ... Moving average value, [Delta] pave ... Decrease amount of booster negative pressure (history of brake assist force decreasing), S15 ... Brake restarting means, S23 ... idle stop prohibition judging means, TH1 ... predetermined threshold.

Claims (6)

A booster device that introduces the intake negative pressure of the engine as a booster negative pressure, and assists the brake pedal depression force by the driver with the booster negative pressure;
An idle stop system that allows the engine to automatically stop without waiting for the vehicle speed to reach zero;
Applied to vehicles with
When the engine is automatically stopped, when the booster negative pressure becomes less than a predetermined threshold, the engine is automatically restarted and the brake restarting means for recovering the brake assisting force due to the booster negative pressure;
Idle stop prohibition determining means for determining whether or not to automatically stop the engine based on a history of the brake assist force decreasing during operation of the engine;
An engine control device comprising:   2. The engine control apparatus according to claim 1, wherein the idle stop prohibition determination unit determines whether to automatically stop prohibition based on a vehicle speed at that time in addition to a history of the brake assist force decreasing. A negative pressure sensor for detecting the booster negative pressure;
The idle stop prohibition determining means calculates a booster negative pressure decrease rate calculated from a detection value of the negative pressure sensor or a total decrease amount of the booster negative pressure in a predetermined period as the brake assist force decrease history. The engine control device according to claim 1 or 2, wherein It has a hydraulic sensor that detects the pressure of brake oil,
The idle stop prohibition determining means calculates a pressure decrease speed calculated from a detection value of the hydraulic sensor or a total pressure decrease amount in a predetermined period as a decrease history of the brake assist force. Item 4. The engine control device according to any one of Items 1 to 3.   The engine control apparatus according to claim 3 or 4, wherein the rate of decrease is calculated from a moving average value of the detected values.   If it is determined by the idle stop prohibition determining means that the automatic stop of the engine is prohibited, the prohibition of the automatic stop is continued after the prohibition determination until the brake assist force increases and reaches a predetermined value. The engine control device according to any one of claims 1 to 5, wherein

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