Idle speed control device for a vehicle

Abstract

An idle control device (40) for a subject vehicle (1) that terminates an idle operation of an engine (2) to automatically stop the engine (2) when a predetermined condition is met, the subject vehicle (1) comprising: a front environment detection device (20) comprising a front environment detection unit and an obstacle detection unit, wherein the front environment detection unit receives environmental information in front of the subject vehicle (1) and the obstacle detection unit detects an obstacle in front of the subject vehicle (1) based on the environmental information in front of the subject vehicle (1); characterized in that the idle control device (40) comprises: a stop-to-avoid-a-danger determination unit that determines whether or not the subject vehicle (1) has stopped in front of the obstacle based on at least one of environmental information in front of the subject vehicle (1), obstacle information from the obstacle detection unit, and a traveling state of the subject vehicle (1) before the vehicle was stopped; and an idle reduction prevention unit that prevents automatic shutdown of the engine (2) when the stop-to-avoid-a-danger determination unit determines that the subject vehicle (1) has stopped in front of the obstacle to avert a danger and allows automatic shutdown of the engine when the stop-to-avoid-a-danger determination unit determines that the subject vehicle (1) has not stopped in front of the obstacle to avert a danger and the idle control device (40) is configured to: perform a first determination (S208) to determine whether or not a narrow road ahead of the subject vehicle (1) is detected by the obstacle detection unit when the subject vehicle (1) is stopped at the obstacle and the obstacle detected by the obstacle detection unit is an oncoming vehicle; perform a second determination (S209) to determine whether or not the time before the subject vehicle (1) is passed by the oncoming vehicle is within a predetermined period of time when the narrow road was detected in the first determination (208); to determine to allow automatic engine shutdown if a narrow road was not detected in the first determination (S208) or the time is longer than the predetermined time period in the second determination (S209); and to determine not to allow automatic engine shutdown if the time is equal to or shorter than a predetermined period of time.

Description

[0001] The present invention relates to an idle control device for a vehicle having an idle reduction function for stopping an idling operation of an engine to automatically stop the engine when a predetermined traveling condition is satisfied.

[0002] Various idle reduction technologies for vehicles have been proposed and implemented to reduce fuel consumption and emissions. These idle reduction technologies automatically stop an engine when engine operation is not required, such as while waiting at a traffic light, waiting for a train to pass, or waiting for a person to arrive, and restart the engine when engine operation is required again. For example, JP 2004-232538 A discloses a technology for a vehicle with an idle control function that automatically stops an engine based on the operation of a brake pedal when the vehicle is stopped and restarts the engine when the brake pedal is released or an accelerator pedal is depressed. According to this technology, an obstacle detection sensor is provided for detecting an obstacle in front of the vehicle.If the sensor detects that an obstacle is approaching in front of the vehicle before the engine is automatically stopped, the automatic engine stop based on the operation of the brake pedal is prevented.

[0003] The idle reduction function explained above is not very effective in reducing exhaust gas consumption, or even increases it, when a vehicle is stopped for only a very short time. The technology for an idle control device disclosed in JP 2004-232538 A may be effective in addressing this problem. However, this technology prevents idle reduction when approaching an obstacle in front of the vehicle. Therefore, when the vehicle stops due to a traffic jam, for example, idle reduction is not performed. As a result, the number of executions of idle reduction decreases significantly, preventing the benefits of idle reduction from being fully realized.

[0004] In addition to JP 2004-232 538 A, DE 10 2008 031 340 A1, DE 101 39 595 A1 and DE 10 2006 009 654 A1 also disclose an idle control device for switching a vehicle engine on and off depending on the traffic situation.

[0005] The present invention has been made in view of the above and aims to provide an idle control device for a vehicle which appropriately prevents only unnecessary idle reductions based on a current driving situation, so that the advantages of idle reduction such as reduction of fuel consumption and emissions are fully achieved.

[0006] This object is achieved by an idle control device according to claim 1. Advantageous embodiments of the invention are specified in the subclaims.

[0007] One aspect of the present invention provides an idle control device for a vehicle that stops an idle operation of an engine to automatically stop the engine when a predetermined condition is satisfied.The idle control device for a vehicle includes: a front environment detection unit that acquires environment information in front of a subject vehicle; an obstacle detection unit that detects an obstacle for the subject vehicle based on environment information in front of the subject vehicle; a stop-to-avoid-a-danger determination unit that determines whether the subject vehicle has stopped because of the obstacle based on at least one of environment information in front of the subject vehicle, obstacle information from the obstacle detection unit, and a traveling state of the subject vehicle before the vehicle was stopped; and an idle reduction prevention unit that prevents automatic stop of the engine when the stop-to-avoid-a-danger determination unit determines that the subject vehicle has stopped in front of the obstacle to avoid a danger.

[0008] The invention will be further explained below using an embodiment with reference to the drawings, in which Fig. 1 is a schematic configuration view of a vehicle including an idle control device for a vehicle according to an embodiment of the present invention, Fig. 2 is a flowchart of an idle control program according to the embodiment of the present invention, Fig. 3 is a flowchart of a subroutine for automatic engine stop permission determination according to the embodiment of the present invention, Fig. 4 is a graph showing a relationship between a relative speed and an overlap degree between the vehicle and a target object and a brake intervention distance for collision prevention control according to the embodiment of the present invention, Fig. 5 is an explanatory view showing brake intervention distances set between the vehicle and a target object according to the embodiment of the present invention, and Fig. 6 is an exemplary view of a relationship between the vehicle and an oncoming vehicle according to the embodiment of the present invention.

[0009] An embodiment of the present invention will be described below with reference to the drawings.

[0010] In Fig. In FIG. 1, reference numeral 1 denotes a subject vehicle. An engine 2 is disposed in a front portion of the subject vehicle 1. Driving force generated by the engine 2 is transmitted from an automatic transmission (shown as including a torque converter and other components) 3 to a center differential device 4 through a transmission output shaft 3a.

[0011] The driving force is transmitted from the center differential device 4 via a rear drive shaft 5, a propeller shaft 6 and a drive bevel gear 7 to a rear wheel final reduction gear 8 and also from the center differential device 4 via a front drive shaft 9 to a front wheel final reduction gear 10. The automatic transmission 3, the center differential device 4, the front wheel final reduction gear 10 and the like are housed together in a case 11.

[0012] The drive force introduced into the rear wheel final reduction gear 8 is transmitted via a left rear wheel drive shaft 12rl to a left rear wheel 13rl and via a right rear wheel drive shaft 12rr to a right rear wheel 13rr. The drive force introduced into the front wheel final reduction gear 10 is transmitted via a left front wheel drive shaft 12fl to a left front wheel 13fl and via a right front wheel drive shaft 12fr to a right front wheel 13fr.

[0013] A braking force unit 15 of the subject vehicle is connected to a master cylinder 17, which is connected to a brake pedal operated by a driver. When a driver operates (depresses) the brake pedal, braking pressure is applied by the master cylinder 17 via the braking force unit 15 to each wheel cylinder (a left front wheel wheel cylinder 18fl, a right front wheel wheel cylinder 18fr, a left rear wheel wheel cylinder 18rl, and a right rear wheel wheel cylinder 18rr) of each of the four wheels 13fl, 13fr, 13rl, and 13rr, thereby stopping the four wheels.

[0014] The braking force unit 15 is a hydraulic unit including components such as a pressure application source, a pressure reduction valve, and a pressure increase valve. The braking force unit 15 is configured to independently apply braking pressure to each of the wheel cylinders 18fl, 18fr, 18rl, and 18rr according to input signals.

[0015] The subject vehicle 1 includes a stereo camera 21, a front environment recognition device 20, a collision prevention control device 30, and an idle control device 40.

[0016] The stereo camera 21 is part of a front environment detection unit that captures environmental information in front of a subject vehicle 1. It consists of a left and right pair of cameras using, for example, solid-state image sensors. The pair of cameras are arranged on a front portion of a ceiling of a passenger compartment at a predetermined distance from each other, capture images of external objects in stereo from different viewpoints, and output image data to the front environment detection device 20.

[0017] The front environment recognition device 20 includes an image processing processor that processes at high speed an image captured by the stereo camera 21 and serves as a processing unit that performs a recognition process based on an output result of the image processing processor and travel information of the subject vehicle 1 such as a subject vehicle speed Vo. The front environment recognition device 20 processes the image captured by the stereo camera 21, for example, in the following manner.

[0018] First, the front environment recognition device 20 generates distance information for a pair of stereo images in the traveling direction of the subject vehicle 1 captured by the stereo camera 21 based on the amount of alignment deviation between corresponding positions in the images. Then, the distance information is subjected to a known grouping process, and the processed information is compared with frames (windows) of previously stored data such as three-dimensional road shape data, stone wall data, and three-dimensional object data. As a result of the comparison, lane line data and sidewall data such as a guardrail and a curb extending along the road are extracted.

[0019] In addition, three-dimensional data is extracted and categorized into a vehicle, a crossing pedestrian, a red light (detected based on the height of a red light-emitting part, for example), and other three-dimensional objects such as a utility pole. The obtained data is subjected to calculation in a coordinate system whose origin is the subject vehicle 1 and whose X-axis and Y-axis extend in the front-backward direction and the lateral direction of the subject vehicle 1, respectively. The lane line data, the sidewall data such as a guardrail or a curb extending along the road, the types of the three-dimensional objects, the distances of the objects from the subject vehicle 1, the center positions, speeds, and the like of the obtained data are output to the collision prevention control device 30 and the idle control device 40.For each obtained road shape, its width is calculated. Roads with a width of a predetermined value (for example, two meters) or less are categorized as a narrow road. This categorization result is also output to the idle control device 40. Furthermore, objects categorized as a vehicle with a speed different from the speed direction of the subject vehicle 1 are detected as an oncoming vehicle. This categorization result is also output to the idle control device 40.

[0020] In this embodiment, the stereo camera 21 is used as a detection sensor. Alternatively, however, another system such as a molecular camera, a millimeter-wave radar, an inter-vehicle communication system, and the like may be used as a detection sensor. As previously noted, the front environment detection device 20 serves as a front environment detection unit and an obstacle detection unit.

[0021] The collision prevention control device 30 serves as a collision prevention control unit. When a target object such as a three-dimensional object is detected in front of the subject vehicle 1, the collision prevention control device 30 executes control for preventing a collision between the subject vehicle 1 and the target object based on the obstacle information from the front environment detection device 20 according to, for example, a method disclosed in Japanese Patent Application JP 2009-262701 A. More specifically, in this collision prevention control, for example, the collision prevention control device 30 sets a first braking intervention distance D1 and a second braking intervention distance D2 as braking intervention distances with respect to the target object (see Fig. 5).

[0022] The first braking intervention distance D1 is a distance limit (collision avoidance distance limit) at which it is difficult to avoid a collision with the target object by either braking or steering. The first braking intervention distance D1 is set in advance based on an experiment, simulation, or the like. The collision avoidance distance limit changes according to, for example, a relative speed Vrel between the subject vehicle 1 and the target object, and further changes according to an overlap ratio R1 between the subject vehicle 1 and the target object. A map showing a relationship between the relative speed Vrel and the overlap ratio R1 between the subject vehicle 1 and the target object and the first braking intervention distance D1 is shown in Fig. 4, is set in advance and stored in the collision prevention control device 30. The collision prevention control device 30 selects the first braking intervention distance D1 with reference to the map.

[0023] The second braking intervention distance D2 is set to be longer than the first braking intervention distance D1 by a predetermined distance. More specifically, the second braking intervention distance D2 is set in advance, for example, based on an experiment, a simulation, or the like, and is set to be longer than the collision avoidance distance limit by a predetermined distance from the subject vehicle according to the relative speed Vrel. A map showing a relationship between the relative speed Vrel and the overlap ratio R1 between the subject vehicle 1 and the target object and the second braking intervention distance D2, as exemplified in Fig. 4, is preset and stored in the collision prevention control device 30. The collision prevention control device 30 selects the second braking intervention distance D2 with reference to the map.

[0024] When a relative distance d between the subject vehicle 1 and the target object becomes equal to or smaller than the first braking intervention distance D1, the collision prevention control device 30 executes braking control by automatic braking intervention (hereinafter also referred to as full braking control). In full braking control, for example, the collision prevention control device 30 selects a predetermined fixed value for the deceleration (target deceleration) to be generated by the braking control and a predetermined amount of change in the deceleration (deceleration change amount) in generating the target deceleration, and calculates a deceleration instruction value based thereon. Then, the collision prevention control device 30 outputs the calculated deceleration instruction value to the braking force unit 15, so that automatic braking is actuated (executed).

[0025] When the relative distance d is longer than the first braking intervention distance D1 and equal to or shorter than the second braking intervention distance D2, the collision prevention control device 30 executes braking control with automatic braking intervention (hereinafter also referred to as boosted braking control) before the full braking control. In the boosted braking control, for example, the collision prevention control device 30 variably sets the target deceleration and the deceleration change amount and calculates the deceleration instruction value based thereon. Then, the collision prevention control device 30 outputs the calculated deceleration instruction value to the braking force unit 15 to initiate (perform) automatic braking.

[0026] An actuation signal indicating the collision prevention control actuated by the collision prevention control device 30 is output to the idle control device 40.

[0027] The idle control device 40 receives the road information and obstacle information from the front environment recognition device 20, the operation signal of the collision prevention control from the collision prevention control device 30, the subject vehicle speed Vo from a vehicle speed sensor 51, a steering wheel angle θH from a steering wheel angle sensor 52, a longitudinal acceleration Gx from a longitudinal acceleration sensor 53, a position of the shift lever from a shift lever position sensor 54, and a depression amount of the accelerator pedal from an accelerator pedal depression amount sensor 56.

[0028] Normally, when a predetermined traveling condition (automatic engine stop condition: idle reduction execution condition) is satisfied, the idle control device 40 outputs a signal to an engine control device 50 so that idle reduction is executed to terminate the idling operation of the engine 2 to automatically stop the engine 2. When the automatic engine stop is not permitted (idle reduction is prohibited), the idle control device 40 prohibits or prevents the execution of the idle reduction.

[0029] The idle reduction execution condition refers to, for example, a state that satisfies all of the following conditions: the brake pedal is depressed, the accelerator pedal is not depressed, the shift lever is in any one of the positions “P”, “N”, “D”, “Third gear”, “Second gear” and “First gear”, the subject vehicle speed Vo is practically zero and a battery is still sufficiently charged.

[0030] The condition in which the execution of idle reduction is prohibited refers to a condition in which it is determined that the subject vehicle 1 has been stopped to avoid a danger. It is assumed that the subject vehicle 1 has been stopped to avoid a danger if any of the following conditions exist: (1) The subject vehicle 1 was stopped at an obstacle according to automatic braking initiated by the collision prevention control device 30, (2) the subject vehicle 1 was stopped at a crossing pedestrian, (3) the subject vehicle 1 has been stopped at an oncoming vehicle, a narrow road is detected in front of the subject vehicle 1, and a time period elapsed before the subject vehicle 1 is passed by the oncoming vehicle (time calculated by Df1 / Vf1 in a situation as shown in Fig. 6, where Df1 is a distance between the subject vehicle 1 and the oncoming vehicle and Vf1 is a speed of the oncoming vehicle) is equal to or shorter than a predetermined period of time, (4) when the subject vehicle 1 has been stopped at an obstacle, a braking operation for the stop is started within a predetermined period of time, (5) when the subject vehicle 1 has been stopped at an obstacle, the deceleration generated is equal to or greater than a predetermined value until the stop, and (6) when the subject vehicle 1 has been stopped at an obstacle, a steering wheel is operated at a steering speed (dΘH / dt) of a predetermined value or greater during braking until the stop.

[0031] Even if it is determined that the subject vehicle 1 has been stopped to avoid danger in the above-mentioned manner, when a red light is detected in front of the subject vehicle 1, a determination that the subject vehicle 1 has not been stopped to avoid danger is given priority, and idle reduction is permitted.

[0032] When the engine has been automatically stopped by idle reduction and a predetermined condition for restarting the engine 2 is met, the idle control device 40 outputs a signal to the engine control device 50 to restart the engine 2. The predetermined condition for restarting the engine 2 refers, for example, to a state in which the previously described idle reduction execution condition is not met. The idle control device 40 thus serves as a stop-to-avoid-danger determination unit and an idle reduction prevention unit.

[0033] Next, the idle control performed by the idle control device 40 will be described with reference to the Fig. The flowchart shown in Figure 2 is described.

[0034] First, in step (hereinafter abbreviated as "S") 101, necessary parameters are read such as the detected road information and obstacle information from the front environment detection device 20, the collision prevention control initiation signal from the collision prevention control device 30, the subject vehicle speed Vo from the vehicle speed sensor 51, the steering wheel angle θH from the steering wheel angle sensor 52, the longitudinal acceleration Gx from the longitudinal acceleration sensor 53, the position of the shift lever from a shift lever position sensor 54, and the amount of depression of the accelerator pedal from the accelerator pedal depression amount sensor 56.

[0035] In the following S102, it is determined whether the aforementioned automatic engine stop condition (idle reduction execution condition) is satisfied. If the idle reduction execution condition is satisfied, the program proceeds to S103, where an automatic engine stop permission determination process is executed (the automatic engine stop permission determination process will be described later with reference to the Fig. 3). Then, in S104, it is determined whether the automatic engine stop permission determination is permitted.

[0036] If it is determined in S104 that the automatic engine stop permission determination is enabled, the program proceeds to S105, where a signal is output to the engine control device 50 to execute idle reduction, which terminates the idle operation of the engine 2 to automatically stop the engine 2. Then, the program exits.

[0037] If the idle reduction execution condition in S102 is not met, the program proceeds to S106, where it is determined whether the engine has been automatically shut down (i.e., idle reduction has been performed). If idle reduction has not been performed, the program exits without any changes. If idle reduction has been performed, the program proceeds to S107, where a signal is output to the engine control device 50 to restart the engine 2. The program then exits.

[0038] Next, the automatic engine stop permission determination process executed in S103 will be described with reference to the Fig. The flowchart shown in Figure 3 is described.

[0039] First, in S201, it is determined whether or not a red traffic light is detected as a result of the detection performed by the front environment detection device 20.

[0040] If it is determined in S102 that a red traffic light is not detected, the process proceeds to S202. If a red traffic light is detected, the process proceeds to S203 to allow automatic engine stop and then exits the utility program.

[0041] In S202, it is determined whether or not an obstacle is detected as a result of the detection performed by the front environment detection device 20. If an obstacle is not detected, the process proceeds to S203 to determine that automatic engine stop is permitted and then exits the routine.

[0042] If an obstacle is detected, the process proceeds to S204. If the subject vehicle 1 has stopped in front of an obstacle, it is determined in step S204 whether or not the subject vehicle 1 has stopped in front of the obstacle according to automatic braking initiated by the collision prevention control device 30. If it is determined in S204 that the subject vehicle 1 has stopped according to the automatic braking initiated by the collision prevention control device 30, it is determined that the subject vehicle 1 has stopped to avert a danger (case (1)). The process then proceeds to S205 to determine that automatic engine stop is not permitted and then exits the routine.

[0043] If the vehicle has not been stopped as a result of automatic braking initiated by the collision prevention control device 30, the process proceeds to S206.

[0044] In S206, it is determined whether the obstacle detected by the front environment detection device 20 when the subject vehicle 1 is stopped is a crossing pedestrian. If the obstacle is a crossing pedestrian, it is determined that the subject vehicle 1 has been stopped to avoid a danger (case (2)). The process then proceeds to S205 to determine that automatic engine stop is not permitted and then exits the routine.

[0045] If it is determined in S206 that the obstacle is something other than a crossing pedestrian, the process proceeds to S207, where it is determined whether the obstacle detected by the front environment detection device 20 when the subject vehicle 1 is stopped is an oncoming vehicle. If the obstacle is an oncoming vehicle, the process proceeds to S208.

[0046] In S208, it is determined whether or not a narrow road is detected ahead of the subject vehicle 1. If a narrow road is detected, the process proceeds to S209.

[0047] In S209, it is determined whether the time elapsed before the subject vehicle 1 is passed by the oncoming vehicle (Df1 / Vf1 in Fig. 6) is equal to or shorter than a predetermined time period. If the time is equal to or shorter than the predetermined time period, it is determined that the subject vehicle 1 has been stopped to avert danger (case (3)). The process then proceeds to S205 to determine that automatic engine stop is not permitted and then exits the routine.

[0048] If a narrow road is not detected in S208 or if the time is longer than the predetermined time period in S209, the process proceeds to S203 to determine that the automatic engine stop is permitted and then exits the assistance program.

[0049] If it is not determined in S207 that the obstacle detected by the front environment detection device 20 is an oncoming vehicle, the process proceeds to S210.

[0050] In S210, it is determined whether or not a braking operation for stopping the subject vehicle 1 in front of an obstacle is initiated within a predetermined period of time. Specifically, it is determined whether a braking operation for the stop has been initiated while an expected time to collision TTC is equal to or less than a predetermined period of time.

[0051] If it is determined in S210 that braking to stop is initiated while the expected time to collision TTC is equal to or shorter than the predetermined time period, it is determined that the subject vehicle 1 has been stopped to avert danger (case (4)). The process then proceeds to S205 to determine that automatic engine stop is not permitted and exits the routine.

[0052] If a braking operation for stopping has been started while the expected time to collision TTC is longer than the predetermined time period, the process proceeds to S211.

[0053] If the subject vehicle 1 has stopped in front of an obstacle, it is determined in S211 whether the longitudinal acceleration Gx from the longitudinal acceleration sensor 53 is equal to or greater than a predetermined deceleration to the stop. If the generated deceleration is equal to or greater than the predetermined value to the stop, it is determined that the subject vehicle 1 has stopped to avoid danger (case (5)). The process then proceeds to S205 to determine that automatic engine stop is not permitted and exits the routine.

[0054] If the generated deceleration does not become equal to or greater than the predetermined value until the stop, the process proceeds to S212.

[0055] When the subject vehicle 1 has stopped in front of an obstacle, it is determined in S212 whether or not a steering wheel is operated at a steering speed (dΘH / dt) of a predetermined value or greater during braking until the stop. If it is determined that the steering wheel is operated at a steering speed (dΘH / dt) of the predetermined value or greater during braking until the stop, it is determined that the subject vehicle 1 has stopped to avoid danger (case (6)). The process then proceeds to S205 to determine that automatic engine stop is not permitted, and then exits the routine.

[0056] If the steering wheel is not operated at a steering speed (dΘH / dt) of the predetermined value or greater during the braking operation until the stop, the process goes to S203 to determine that automatic engine stop is permitted and then exits the assistance program.

[0057] Therefore, according to the above-described embodiment of the present invention, normally, when the predetermined idle reduction execution condition is satisfied, a signal is output to the engine control device 50 to execute idle reduction to stop the idling operation of the engine 2 to automatically stop the engine 2. Further, it is determined whether or not the subject vehicle 1 has stopped in front of an obstacle to avoid danger based on at least one of environmental information in front of the subject vehicle 1, obstacle information, and a traveling state of the subject vehicle 1 before it was stopped. If it is determined that the subject vehicle 1 has stopped in front of the obstacle to avoid danger, automatic engine stop is not permitted.As a result, only unnecessary idle reduction is appropriately recognized as impermissible by determining with high accuracy whether or not the subject vehicle 1 has stopped before the obstacle to avoid danger based on actual driving situations, so that the benefits of idle reduction such as reduction of fuel consumption and emissions are fully realized. SUMMARY OF REVELATION

[0058] In an idle control device for a vehicle, normally, when a predetermined idle reduction application condition is satisfied, a signal is output to the engine control device 50 to execute idle reduction to stop the idling operation of an engine 2 to automatically stop the engine 2. Further, it is determined whether or not a subject vehicle 1 has stopped in front of an obstacle to avoid a danger based on at least one of environmental information in front of the subject vehicle 1, obstacle information, and a traveling state of the subject vehicle 1 before it was stopped. If it is determined that the subject vehicle 1 has stopped in front of the obstacle to avoid a danger, automatic engine shutdown is not permitted.

Claims

[1] An idle control device (40) for a subject vehicle (1) that terminates an idling operation of an engine (2) to automatically stop the engine (2) when a predetermined condition is met, the subject vehicle (1) comprising: a front environment detection device (20) comprising a front environment detection unit and an obstacle detection unit, wherein the front environment detection unit receives environmental information in front of the subject vehicle (1) and the obstacle detection unit detects an obstacle in front of the subject vehicle (1) based on the environmental information in front of the subject vehicle (1); characterized by that the idle control device (40) comprises: a stop-to-avoid-a-danger determination unit that determines whether or not the subject vehicle (1) has stopped in front of the obstacle based on at least one of environmental information in front of the subject vehicle (1), obstacle information from the obstacle detection unit, and a traveling state of the subject vehicle (1) before the vehicle was stopped; and an idle reduction prevention unit that prevents automatic shutdown of the engine (2) when the stop-to-avoid-a-danger determination unit determines that the subject vehicle (1) has stopped in front of the obstacle to avert a danger and allows automatic shutdown of the engine when the stop-to-avoid-a-danger determination unit determines that the subject vehicle (1) has not stopped in front of the obstacle to avert a danger and the idle control device (40) is configured to: perform a first determination (S208) to determine whether or not a narrow road ahead of the subject vehicle (1) is detected by the obstacle detection unit when the subject vehicle (1) is stopped at the obstacle and the obstacle detected by the obstacle detection unit is an oncoming vehicle; perform a second determination (S209) to determine whether or not the time before the subject vehicle (1) is passed by the oncoming vehicle is within a predetermined period of time when the narrow road was detected in the first determination (208); to determine to allow automatic engine shutdown if a narrow road was not detected in the first determination (S208) or the time is longer than the predetermined time period in the second determination (S209); and to determine not to allow automatic engine shutdown if the time is equal to or shorter than a predetermined period of time. [2] The idle control device (40) for a vehicle according to claim 1, wherein the stop-to-avoid-a-danger determination unit determines that the subject vehicle (1) has been stopped in front of the obstacle to avert a danger when the subject vehicle (1) has been stopped and the obstacle in front of the subject vehicle (1) is a crossing pedestrian. [3] The idle control device (40) for a vehicle according to claim 1 or 2, wherein the stop-to-avoid-danger determination unit determines that the subject vehicle (1) has been stopped in front of the obstacle to avoid a danger when the subject vehicle (1) has been stopped and braking for the stop has been started while an expected time until collision TTC is equal to or shorter than a predetermined period of time. [4] The idle control device (40) for a vehicle according to any one of claims 1 to 3, wherein the stop-to-avoid-a-danger determination unit determines that the subject vehicle (1) has been stopped in front of the obstacle to avoid a danger when the subject vehicle (1) has been stopped in front of an obstacle and a generated deceleration becomes equal to or greater than a predetermined value until the stop. [5] The idle control device (40) for a vehicle according to any one of claims 1 to 4, wherein the stop-to-avoid-a-danger determination unit determines that the subject vehicle (1) has been stopped in front of the obstacle to avert a danger when the subject vehicle (1) has been stopped in front of an obstacle, and a steering wheel is operated at a steering speed of a predetermined value or greater during braking until the stop. [6] An idle control device (40) for a vehicle according to any one of claims 1 to 5, further comprising a collision prevention control unit (30) that prevents a collision between the obstacle and the subject vehicle (1) by initiating automatic braking, wherein the stop-to-avoid-a-danger determination unit determines that the subject vehicle (1) has stopped in front of the obstacle to avert a danger when the subject vehicle (1) has stopped in front of the obstacle according to the automatic braking initiated by the collision prevention control unit (30). [7] The idle control device (40) for a vehicle according to any one of claims 1 to 6, wherein when a red traffic light ahead of the subject vehicle (1) is detected by the front environment detection unit, the stop-to-avoid-danger determination unit gives priority to a determination that the subject vehicle (1) has not been stopped to avert a danger and idle reduction is permitted.

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