Engine auto-stop vehicle and control method therefor

A controller actuates an electrical oil pump when an idle stop condition or a coast stop condition holds and causes the actuation of the electrical oil pump to continue without being stopped until an accelerated state of a vehicle or a driver's intention to accelerate is determined even if the idle stop condition and the coast stop condition no longer holds thereafter.

FIELD OF THE INVENTION

The present invention relates to an engine auto-stop vehicle in which an engine is automatically stopped and restarted.

BACKGROUND OF THE INVENTION

An engine stop control is known which automatically temporarily stops an engine when a predetermined engine stop condition holds and automatically restarts the engine when a restart condition holds. For example, an idle stop control and a coast stop control are known as the engine stop control.

The idle stop control stops an engine when a vehicle stops and an idle stop condition holds and restarts the engine when a brake is off and the idle stop condition no longer holds.

The coast stop control stops an engine when an accelerator is off and a brake is on to set a coast state and a vehicle speed is equal to or below a predetermined vehicle speed while a vehicle is running, and restarts the engine when the accelerator is on or the brake is off and the coast stop condition no longer holds.

When the engine is stopped by the above engine stop control, a mechanical oil pump driven by the engine also simultaneously stops. Accordingly, it is disclosed in JP2007-247910A that an electrical oil pump which is operated by power stored in a battery is provided separately from a mechanical oil pump and a working pressure of a transmission is ensured by driving the electrical oil pump during an engine stop control.

SUMMARY OF THE INVENTION

Here, when the electrical oil pump is switched from an OFF state to an ON state, a motor driver which controls a motor for driving and rotating the pump generates heat. Accordingly, to prevent the overheating of the motor driver, the electrical oil pump is so controlled that the restart thereof is prohibited for a predetermined time after the stop.

However, the restart of the electrical oil pump is still prohibited in such a state where the engine stop condition immediately holds again after the engine stop condition no longer holds during the engine stop control and the engine restarts and the electrical oil pump stops. Thus, the actuation of the mechanical oil pump needs to be continued to ensure a hydraulic pressure, wherefore the engine cannot be stopped before the elapse of a restart prohibition time.

That is, even in a situation where the engine stop control is possible, the engine stop control cannot be executed until the restart prohibition of the electrical oil pump is lifted. Thus, the start of the engine stop control is delayed and a time during which the engine is stopped is shortened by that much, wherefore a fuel economy improvement effect by the engine stop control is reduced.

The present invention aims to promote a fuel economy improvement effect by an engine stop control.

An engine auto-stop vehicle according to an aspect of this invention includes an engine which automatically stops when a stop condition holds and restarts when a restart condition holds, a first oil pump which is driven by the engine, a second oil pump which operates during the automatic stop of the engine, an acceleration determining unit that performs one or more of acceleration condition determinations as to whether or not the vehicle is in an accelerating state, whether or not there is an acceleration request and whether or not an acceleration request is predicted, and an oil pump control unit that actuates the second oil pump when the stop condition holds and causes the actuation of the second oil pump to continue during a period until the determination is performed by the acceleration determining unit after the restart condition holds.

A control method according to another aspect of this invention is a control method for an engine auto-stop vehicle including an engine which automatically stops when a stop condition holds and restarts when a restart condition holds, a first oil pump which is driven by the engine and a second oil pump which operates during the automatic stop of the engine. The control method includes a determining step of performing one or more of acceleration condition determinations as to whether or not the vehicle is in an accelerating state, whether or not there is an acceleration request and whether or not an acceleration request is predicted, and a continuing step of actuating the second oil pump when the stop condition holds and causing the actuation of the second oil pump to continue during a period until the determination is performed in the determining step after the restart condition holds.

According to these aspects, since stopping of the second oil pump can be avoided in a situation where the automatic stop of the engine is temporarily interrupted, the engine can be quickly automatically stopped without being restricted by the second oil pump when the engine stop condition holds again. Therefore, a fuel economy improvement effect by the automatic stop of the engine can be promoted.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention are described with reference to the accompanying drawings. In the following description, a “speed ratio” of a certain transmission is a value obtained by dividing an input rotation speed of this transmission by an output rotation speed thereof.

FIG. 1is a schematic construction diagram of an engine auto-stop vehicle according to a first embodiment of the present invention. This vehicle includes an engine1as a driving source. Output rotation of the engine1is transmitted to drive wheels7via a torque converter2with a lock-up clutch, a first gear train3, a continuously variable transmission (hereinafter, merely referred to as a “transmission4”), a second gear train5and a final speed reducer6. The second gear train5includes a parking mechanism8for mechanically locking an output shaft of the transmission4in a parked state so as not to be able to rotate.

The transmission4includes a mechanical oil pump10mto which the rotation of the engine1is input and which is driven by utilizing a part of power of the engine1and an electrical oil pump10ewhich is driven upon receiving the supply of power from a battery13. The electrical oil pump10eis composed of an oil pump main body, an electric motor for driving and rotating the oil pump main body and a motor driver, and can control an operating load to an arbitrary load or in multiple steps. Further, the transmission4includes a hydraulic control circuit11for adjusting a hydraulic pressure (hereinafter, referred to as a “line pressure PL”) from the mechanical oil pump10mor the electrical oil pump10eand supplying the adjusted hydraulic pressure to the respective components of the transmission4.

The transmission4includes a V-belt continuously variable transmission mechanism (hereinafter, referred to as a “variator20”) and a sub-transmission mechanism30provided in series with the variator20. “To be provided in series” means that the variator20and the sub-transmission mechanism30are provided in series in a power transmission path from the engine1to the drive wheels7. The sub-transmission mechanism30may be directly connected to an output shaft of the variator20as in this example or may be connected via another transmission or power transmission mechanism (e.g. gear train). Alternatively, the sub-transmission mechanism30may be connected before (input shaft side) the variator20.

The variator20includes a primary pulley21, a secondary pulley22and a V-belt23mounted between the pulleys21and22. Each of the pulleys21,22includes a fixed conical plate, a movable conical plate arranged with a sheave surface faced toward the fixed conical plate and forming a V-groove between the movable conical plate and the fixed conical plate, and a hydraulic cylinder23a,23bprovided on the back surface of the movable conical plate for displacing the movable conical plate in an axial direction. When hydraulic pressures supplied to the hydraulic cylinders23a,23bare adjusted, the widths of the V-grooves change to change contact radii of the V-belt23and the respective pulleys21,22, whereby a speed ratio of the variator20continuously changes.

The sub-transmission mechanism30is a transmission mechanism with two forward speeds and one reverse speed. The sub-transmission mechanism30includes a Ravigneaux-type planetary gear mechanism31in which carriers of two planetary gears are coupled, and a plurality of frictional engagement elements (low brake32, high clutch33, reverse brake34) which are connected to a plurality of rotation elements constituting the Ravigneaux-type planetary gear mechanism31to change coupled states of these rotation elements. If the supply of hydraulic pressures to the respective frictional engagement elements32to34are adjusted to change engaged and released states of the respective frictional engagement elements32to34, a gear position of the sub-transmission mechanism30is changed.

For example, the sub-transmission mechanism30is set to a first gear position if the low brake32is engaged and the high clutch33and the reverse brake34are released. The transmission mechanism30is set to a second gear position with a gear ratio smaller than in the first gear position if the high clutch33is engaged and the low brake32and the reverse brake34are released. The sub-transmission mechanism30is set to a reverse gear position if the reverse brake34is engaged and the low brake32and the high clutch33are released. In the following description, a case where the sub-transmission mechanism30is in the first gear position is expressed by that “the transmission4is in a low-speed mode” and a case where the sub-transmission mechanism30is in the second gear position is expressed by that “the transmission4is in a high-speed mode”.

A controller12is for controlling the engine1and the transmission4in a comprehensive manner and includes a CPU121, a memory device122composed of a RAM/ROM, an input interface123, an output interface124and a bus125which connects these components to each other as shown inFIG. 2.

To the input interface123are input an output signal of an accelerator pedal opening sensor41for detecting an accelerator pedal opening APO which is an operated amount of an accelerator pedal, an output signal of a rotation speed sensor42for detecting an input rotation speed of the transmission4(=rotation speed of the primary pulley21, hereinafter, referred to as a “primary rotation speed Npri”), an output signal of a vehicle speed sensor43for detecting a vehicle speed VSP, an output signal of a line pressure sensor44for detecting the line pressure PL, an output signal of an inhibitor switch45for detecting the position of a select lever, an output signal of a brake fluid pressure sensor46for detecting a brake fluid pressure, an output signal of an acceleration sensor47for detecting an acceleration of the vehicle and like output signals.

A control program of the engine1, a transmission control program of the transmission4, and various maps and tables used in these programs are stored in the memory device122. The CPU121reads the transmission control program stored in the memory device122and implements it, performs various computations on various signals input via the input interface123to generate a fuel injection amount signal, an ignition timing signal, a throttle opening signal, a transmission control signal and a drive signal for the electrical oil pump10e, and outputs the generated signals to the engine1, the hydraulic control circuit11and the motor driver of the electrical oil pump10evia the output interface124. Various values used in the computations by the CPU121and the results of these computations are appropriately stored in the memory device122.

The hydraulic control circuit11includes a plurality of flow passages and a plurality of hydraulic control valves. In accordance with the transmission control signal from the controller12, the hydraulic control circuit11controls the plurality of hydraulic control valves to switch supply passages of the hydraulic pressure, prepares a necessary hydraulic pressure from a hydraulic pressure produced by the mechanical oil pump10mor the electrical oil pump10e, and supplies this hydraulic pressure to the respective components of the transmission4. In this way, the speed ratio of the variator20and the gear position of the sub-transmission mechanism30are changed to shift the transmission4.

Here, the actuations of the mechanical oil pump10mand the electrical oil pump10eare described.

Since the mechanical oil pump10mis driven utilizing a part of power of the engine1, the hydraulic pressure cannot be supplied to the hydraulic control circuit11while the engine1is in a stopped state. Accordingly, to ensure the hydraulic pressure during the stop of the engine, the electrical oil pump10eis driven while the engine1is in the stopped state.

Note that “while the engine1is in the stopped state” mentioned here does not include a parked state of the vehicle (key-off state) and means that the vehicle is in an operating state (after the start of the engine and a key-on state) (including a state where the vehicle speed=0) and the engine1is in the stopped state. Further, the “stop of the engine1” does not necessarily require that the rotation of the engine1is completely stopped and includes very low speed rotation at which a necessary hydraulic pressure cannot be ensured only by the mechanical oil pump10m.

That is, the electrical oil pump10eoperates when the engine1is stopped by an idle stop control or a coast stop control, i.e. when the engine1is in an idle stop state or a coast stop state. The idle stop control and the coast stop control are described below.

The idle stop control is a control for suppressing a fuel consumption amount by automatically stopping the engine1(idle stop) during the stop of the vehicle.

Upon performing an idle stop, the controller12determines conditions a1 to a6 listed below.a1: vehicle is in a stopped state (VSP=0)a2: brake pedal is depressed (brake fluid pressure is equal to or higher than a predetermined value)a3: accelerator pedal is completely released (accelerator pedal opening APO=0)a4: water temperature of the engine1is in a predetermined range Xea5: oil temperature of the transmission4is in a predetermined range Xta6: inclination of a vehicle body (≈road surface gradient) is equal to or smaller than a predetermined value

Then, the controller12determines that an idle stop condition holds and permits an idle stop to cancel fuel injection and stop the engine1when all of these conditions a1 to a6 hold.

A lower limit value of the predetermined range Xe of the water temperature of the engine1is set at a temperature at which warm-up of the engine1is judged to be already finished, and an upper limit value thereof is set at the lower limit of a high temperature region where after idle of the engine1is necessary.

During the idle stop, a time required up to a state where the frictional engagement element can transmit power is shortened by engaging the frictional engagement element of the transmission4or changing a position of a piston toward engage side by the hydraulic pressure produced by the electrical oil pump10e. Accordingly, the predetermined range Xt of the oil temperature of the transmission4is set at a temperature range where the electrical oil pump10ecan normally rotate in view of the viscosity of hydraulic oil.

Further, the controller12determines whether or not the above conditions a1 to a6 respectively continue to hold even during the idle stop, and determines that the idle stop condition does not hold and ends the idle stop, i.e. restarts the engine1if even one of them no longer holds.

On the other hand, the coast stop control is a control for stopping the engine1when the vehicle is in a coast state and, for example, the lock-up clutch is released.

In the coast state, fuel injection is canceled for the purpose of suppressing the fuel consumption amount. Since the engine1is rotated as the drive wheels rotate, the mechanical oil pump10mis driven and a necessary hydraulic pressure can be ensured. However, when the vehicle speed decreases to a certain extent, the lock-up clutch of the torque converter2is released, whereby the rotation speed of the engine1decreases. Thus, fuel injection is restarted to avoid an engine stall. A control for canceling the fuel injection and stopping the engine1in a region where the fuel injection has been originally restarted in this way is the coast stop control.

Since the fuel injection is canceled and the lock-up clutch is released during the coast stop control, the rotation speed of the engine1is very low, whereby the rotation of the mechanical oil pump10mis almost stopped. Accordingly, the electrical oil pump10eis driven at the time of the coast stop control to ensure a necessary hydraulic pressure.

To determine the coast stop state, the controller12determines, for example, conditions b1 to b4 listed below:b1: vehicle is running (VSP≠0)b2: vehicle speed is equal to or lower than a predetermined vehicle speed VSP1(VSP≦VSP1)b3: accelerator pedal is completely released (accelerator pedal opening APO=0)b4: brake pedal is depressed (brake fluid pressure is equal to or higher than a predetermined value)

Note that the predetermined vehicle speed VSP1is set a value equal to or below a vehicle speed, at which the lock-up clutch is released in the coast state, and larger than zero.

The controller12determines that a coast stop condition holds, permits the coast stop, cancels the fuel injection and stops the engine1when all of these conditions b1 to b4 hold.

The controller12determines whether or not the above conditions b1 to b4respectively continue to hold even during the coast stop, and determines that the coast stop condition does not hold and ends the coast stop, i.e. restarts the engine1if even one of them no longer holds. Note that the conditions based on which the coast stop is ended are not limited to the above conditions b1 to b4.

The idle stop control and the coast stop control are executed as described above, and the engine1is judged to be in the stopped state and the electrical oil pump10eis driven when either one of the controls is executed. Note that, as is clear from the above conditions, a transition is directly made to the idle stop state if the vehicle stops in the coast stop state. In this case, a transition is made from the coast stop control to the idle stop control with the engine1stilled stopped, i.e. with the electrical oil pump10estill in a driven state.

Here, how to prevent the overheating of the electrical oil pump10eis described.

The electrical oil pump10eis composed of the oil pump main body, the electric motor for driving and rotating the oil pump main body and the motor driver as described above. Since the motor driver generates heat when the electrical oil pump10eis switched from the OFF state to the ON state, damage and reduced lives of components caused by the overheating of the motor driver need to be prevented. Thus, the electrical oil pump10eis so controlled that the restart thereof is prohibited for a predetermined time after the actuation, and prohibited from being turned on again before the predetermined time elapses.

Accordingly, the restart of the electrical oil pump10eis prohibited and, as a result, the engine1cannot be stopped since the above predetermined time has not yet elapsed when the conditions of the idle stop control and the coast stop control temporarily no longer hold and, immediately thereafter, hold again.

For example, when a driver completely releases the brake pedal in the idle stop state and, thereby, the idle stop condition no longer holds and the engine1restarts, the electrical oil pump10ecannot be driven until a start prohibition timer (EOP start prohibition timer) of the electrical oil pump10efinishes even if the brake pedal is depressed immediately thereafter and the idle stop condition holds again. During this time, the engine1cannot be stopped. Thus, the fuel consumption amount increases by as much as a delay in the stop of the engine1, thereby deteriorating fuel economy.

Accordingly, in this embodiment, the electrical oil pump10eis controlled as follows.FIG. 3is a flow chart showing the content of the control of the electrical oil pump10eexecuted by the controller12. Note that this flow chart is repeatedly performed at every interval of a specified time (e.g. every 10 msec).

In Step S11, the controller12determines whether or not the electrical oil pump10eis in the stopped state. The process proceeds to Step S12when the electrical oil pump10eis in the stopped state while proceeding to Step S15when the electrical oil pump10eis in the operating state.

In Step S12, the controller12determines whether or not the idle stop condition or the coast stop condition holds. The process proceeds to Step S13when the idle stop condition or the coast stop condition holds while ending when neither of the conditions holds. Here, the idle stop condition and the coast stop condition consist of the conditions a1 to a6 and b1 to b4 based on which the execution of the above idle stop control and coast stop control is determined.

In Step S13, the controller12determines whether or not the EOP start prohibition timer has finished. The process proceeds to Step S14when it is determined that the EOP start prohibition timer has finished while ending when this timer is greater than zero. The EOP start prohibition timer is a timer provided to count a period during which the restart of the electrical oil pump10eis prohibited, and is so set that the value thereof gradually decreases from a predetermined value to zero when the electrical oil pump10eis stopped after being started. When the EOP start prohibition timer has not finished yet, the process ends since the electrical oil pump10ecannot be started even if the idle stop condition or the coast stop condition holds.

In Step S14, the controller12starts the electrical oil pump10e. That is, the controller12stops the engine1and starts the electrical oil pump10ewhen the idle stop condition or the coast stop condition holds and the restart prohibition period has elapsed after the last stop of the electrical oil pump10e.

On the other hand, when it is determined in Step S11that the electrical oil pump10eis in the operating state, the controller12determines in Step S15whether or not neither the idle stop condition nor the coast stop condition holds. The process proceeds to Step S16when neither of the conditions holds while ending when either of the conditions holds. The idle stop condition and the coast stop condition are the same as those in Step S12described above. Note that the engine1is restarted regardless of the driven state of the electrical oil pump10ewhen neither the idle stop condition nor the coast stop condition holds.

In Step S16, the controller12determines whether or not the vehicle is in an accelerating state. The process proceeds to Step S18when the vehicle is determined to be in the accelerating state while proceeding to Step S17when the vehicle is determined not to be in the accelerating state. That the vehicle is in the accelerating state is determined when one or more of the following conditions c1 to c4 are satisfied.c1: acceleration of the vehicle has changed from a negative value (decelerating state) to a positive value (accelerating state)c2: accelerating state has continued for a predetermined time T1or longerc3: vehicle speed is higher than the vehicle speed when it was determined that neither the idle stop condition nor the coast stop condition heldc4: state where the vehicle speed is higher than the vehicle speed when it was determined that neither the idle stop condition nor the coast stop condition held has continued for a predetermined time T2or longer.

Note that the predetermined time T1in the condition c2 is set at a time sufficient to allow an accurate determination that the vehicle is in the accelerating state. The vehicle speed when it was determined that neither condition held in the conditions c3 and c4 is the vehicle speed when it was determined that neither the idle stop condition nor the coast stop condition held in Step S15described above. The predetermined time T2in the condition c4 is set at a time sufficient to allow an accurate determination that the vehicle speed is higher than the one when it was determined that neither the idle stop condition nor the coast stop condition held.

In Step S17, the controller12determines whether or not there is an acceleration request given to the vehicle or an acceleration request is predicted. The process proceeds to Step S18when there is the acceleration request given to the vehicle or the acceleration request is predicted while ending when it is determined that no acceleration request is given and no acceleration request is predicted. That there is an acceleration request given to the vehicle or an acceleration request is predicted is determined when one or more of the following conditions are satisfied.d1: accelerator pedal is depressed (accelerator pedal opening APO≠0)d2: depressed state of the accelerator pedal has continued for a predetermined time T3or longerd3: depressed amount of the accelerator pedal is equal to or more than an acceleration determining depressed amountd4: state where the depressed amount of the accelerator pedal is equal to or more than the acceleration determining depressed amount has continued for a predetermined time T4or longerd5: depressing speed of the accelerator pedal is equal to or higher than an acceleration determining depressing speed (opening/sec)d6: releasing speed of the brake pedal is equal to or higher than an acceleration determining releasing speed (opening/sec) (reducing speed of the brake fluid pressure is equal to or higher than the acceleration determining releasing speed)d7: depression switching time from the complete release of the brake pedal to the depression of the accelerator pedal is equal to or shorter than an acceleration determining depression switching timed8: range or mode is switched (e.g. judgment is made based on a switch to an S-range or L-range in which a shift is made only in one or more gear positions at a low-speed side, a switch to an M-mode in which a manual shift is possible, a shift by a paddle switch, turn-on of a power mode switch to shift an entire shift map toward the low-speed side, a shift to an R-range which is a reverse range, and the like).d9: acceleration of the vehicle in forward and backward directions, that in a lateral direction or a resultant acceleration is equal to or higher than a predetermined acceleration

The conditions d1 to d5 are for determining whether or not there is an acceleration request and the conditions d6 to d9 are for determining whether or not an acceleration request is predicted. Accordingly, in this Step, whether or not there is a driver's intention to accelerate is determined by determining whether or not one or more of the conditions d1 to d9 are satisfied.

Note that the predetermined time T3in the condition d2 is set at a time sufficient to allow an accurate determination that the accelerator pedal is depressed. The acceleration determining depressed amount in the condition d3 is set at an opening sufficient to allow an accurate determination that the driver has depressed the accelerator pedal with an intention to accelerate. The predetermined time T4in the condition d4 is set at a time sufficient to allow an accurate determination that the driver has depressed the accelerator pedal with an intention to accelerate. The acceleration determining depressing speed in the condition d5 is set at a speed sufficient to allow an accurate determination that the driver has depressed the accelerator pedal with an intention to accelerate. The acceleration determining releasing speed in the condition d6 is set at a speed sufficient to allow an accurate determination that the driver has released the brake pedal with an intention to accelerate. The acceleration determining depression switching time in the condition d7 is set at a time sufficient to allow an accurate determination that the driver has switched from the depression of the brake pedal to that of the accelerator pedal with an intention to accelerate.

That is, in Steps S16and S17, the controller12determines whether or not there is a possibility that the idle stop condition or the coast stop condition holds and the idle stop control or the coast stop control is restarted immediately after the idle stop control or the coast stop control stops.

In Step S18, the controller12stops the electrical oil pump10e. That is, when it is determined that the vehicle is in the accelerating state or there is the driver's intention to accelerate in Step S16or S17, the controller12stops the electrical oil pump10e, judging a low possibility of restarting the idle stop control and the coast stop control immediately thereafter. Since the engine1is already started in this case, a necessary hydraulic pressure is ensured even if the electrical oil pump10eis stopped.

In Step S19, the controller12actuates the EOP start prohibition timer. By this, the restart of the electrical oil pump10eis prohibited until the EOP start prohibition timer finishes, i.e. until this timer becomes zero.

The above process is summarized as follows. Even if the idle stop condition and the coast stop condition no longer hold when the idle stop control or the coast stop control is executed and the electrical oil pump10eis operating, the actuation of the electrical oil pump10eis continued until it is determined that the vehicle is in the accelerating state or there is the driver's intention to accelerate.

Next, functions of this embodiment are described with reference toFIGS. 4 to 6.FIG. 4is a time chart showing an operating state of an electrical oil pump in a comparative example.

While the vehicle is running in a coast state where the vehicle speed is reduced by the driver depressing the brake pedal, the coast stop condition holds and the electrical oil pump10estarts at time ta.

Thereafter, at time tb, the driver completely releases the brake pedal and the coast stop condition no longer holds, whereby the engine1is started and the electrical oil pump10eis stopped. By this, the EOP start prohibition timer is actuated and the restart of the electrical oil pump10eis prohibited until the EOP start prohibition timer finishes.

Thereafter, at time tc, the driver depresses the brake pedal again and the coast stop condition holds again. However, since the EOP start prohibition timer has not finished yet, the restart of the electrical oil pump10eis prohibited and, hence, the coast stop control cannot be executed.

At time td, the EOP start prohibition timer finishes and, at this time point, the electrical oil pump10ecan be restarted. Thus, the electrical oil pump10eis started and the coast stop control is executed.

That is, the start of the coast stop control is delayed from time tc to time td and the stop of the engine1is delayed by that much. Therefore, a fuel consumption amount increases to deteriorate fuel economy.

FIGS. 5 and 6are time charts showing functions of the engine auto-stop vehicle in this embodiment.

As shown inFIG. 5, this time chart is the same as the comparative example up to time tb. However, in this embodiment, the actuation of the electrical oil pump10eis continued even after the coast stop condition no longer holds at time tb. By this, when the coast stop condition holds again at time tc, the electrical oil pump10eis already started and the coast stop control can be executed independently of the EOP start prohibition timer.

Further, if it is determined at time to that the vehicle is in the accelerating state or there is the driver's intention to accelerate in a state where the electrical oil pump10econtinues to be actuated after the coast stop condition no longer holds at time tb as shown inFIG. 6, the actuation of the electrical oil pump10eis stopped. Thereafter, the EOP start prohibition timer is actuated.

That is, this embodiment provides for a case where the actuation of the electrical oil pump10eis continued until it is determined that the vehicle is in the accelerating state or there is the driver's intention to accelerate even after the coast stop condition and the idle stop condition no longer hold and, immediately thereafter, the coast stop condition and the idle stop condition hold again.

As described above, in this embodiment, if the idle stop condition and the coast stop condition no longer hold when the electrical oil pump10eis started because the idle stop condition or the coast stop condition holds, the actuation of the electrical oil pump10eis continued until it is, thereafter, determined that the vehicle is in the accelerating state or there is the driver's intention to accelerate. By this, stopping of the electrical oil pump10eand actuating of the EOP start prohibition timer can be avoided in such a situation where the idle stop control or the coast stop control is temporarily interrupted, and the engine1can be quickly automatically stopped when the idle stop condition or the coast stop condition holds again. Therefore, a fuel economy improvement effect by the automatic stop of the engine1can be promoted.

Further, the controller12determines that the vehicle is in the accelerating state when the acceleration of the vehicle has changed from a negative value (decelerating state) to a positive value (accelerating state) (condition c1), when the accelerating state has continued for the predetermined time T1or longer (condition c2), when the vehicle speed is higher than the vehicle speed when it was determined that the idle stop condition and the coast stop condition no longer held (condition c3) or when the state where the vehicle speed is higher than the vehicle speed when it was determined that the idle stop condition and the coast stop condition no longer held has continued for the predetermined time T2or longer (condition 4). Thus, the accelerating state of the vehicle can be easily and accurately determined.

Further, the controller12determines the driver's intention to accelerate when the accelerator pedal is depressed (condition d1), when the depressed state of the accelerator pedal has continued for the predetermined time T3or longer (condition d2), when the depressed amount of the accelerator pedal is equal to or more than the acceleration determining depressed amount (condition d3), when the state where the depressed amount of the accelerator pedal is equal to or more than the acceleration determining depressed amount has continued for the predetermined time T4or longer (condition d4), when the depressing speed of the accelerator pedal is equal to or higher than the acceleration determining depressing speed (opening/sec) (condition d5), when the releasing speed of the brake pedal is equal to or higher than the acceleration determining releasing speed (opening/sec) (condition d6) or when the depression switching time from the complete release of the brake pedal to the depression of the accelerator pedal is equal to or shorter than the acceleration determining depression switching time (condition d7). Thus, the driver's intention to accelerate can be easily and accurately determined.

In a second embodiment, a control described below is executed since an upper limit value is set for the drive duration of the electrical oil pump10e. Note that the overall construction of a vehicle is similar to that of the first embodiment.

FIG. 7is a flow chart showing the content of the control of the electrical oil pump10eexecuted by the controller12. Note that this flow chart is repeatedly performed at every interval of a specified time (e.g. every 10 msec).

Steps S31to S35are the same as Steps S11to S15of the first embodiment

In Step S36, the controller12actuates an electrical oil pump drive duration timer (EOP drive duration timer). The EOP drive duration timer is a timer set to avoid a long continuous operating time of the electrical oil pump10ewhen the actuation of the electrical oil pump10eis continued after the idle stop condition and the coast stop condition no longer hold. Since the motor driver generates heat due to the continuous actuation of the electrical oil pump10e, there is an upper limit to the continuous operating time to prevent overheating. Accordingly, the EOP drive duration timer is set at a predetermined timer value that enables the overheating of the motor driver to be prevented while the electrical oil pump10eis continuously operated in view of the operating time of the electrical oil pump10eat the time of the coast stop control and the idle stop control.

In this way, the drive duration upper limit time is set as the timer value in the EOP drive duration timer at the time of the first processing (when a determination result in Step S31changes from YES to NO) after the start of the electrical oil pump10e, and the timer value is counted during the succeeding processings.

Steps S37and S38are the same as Steps S16and S17of the first embodiment.

In Step S39, the controller12determines whether or not the EOP drive duration timer has finished. The process proceeds to Step S40when the EOP drive duration timer has finished while ending unless otherwise.

Steps S40and S41are the same as Steps S18and S19of the first embodiment.

The above process is summarized as follows. When it is not determined that the vehicle is in the accelerating state and there is the driver's intention to accelerate even if the actuation of the electrical oil pump10eis continued for the drive duration upper limit time after the idle stop condition and the coast stop condition no longer hold, the actuation of the electrical oil pump10eis stopped.

Next, functions of this embodiment are described with reference toFIG. 8.FIG. 8is a time chart showing functions of the engine auto-stop vehicle in this embodiment.

The process is similar to that of the first embodiment up to time tb as shown inFIG. 8. However, in this embodiment, the EOP drive duration timer is actuated when the coast stop condition no longer holds at time tb. After being increased in a stepwise manner up to the drive duration upper limit value at time tb, the EOP drive duration timer is gradually reduced with time.

Thereafter, the vehicle speed is substantially constant and neither the accelerating state of the vehicle nor the driver's intention to accelerate is detected for a period up to time tf. For example, in a situation where the vehicle is running downhill and a force in an accelerating direction subjected to the vehicle due to a gradient and a braking force subjected to the vehicle from engine braking and resistance are balanced, the vehicle speed may be held constant in a coast state where neither the accelerator pedal nor the brake pedal is depressed. If the EOP drive duration timer becomes zero at time tf in such a case, the actuation of the electrical oil pump10eis stopped even when neither the accelerating state of the vehicle nor the driver's intention to accelerate is determined.

As described above, in this embodiment, upon the elapse of the drive duration upper limit time after the coast stop condition and the idle stop condition no longer hold even if the actuation of the electrical oil pump10eis continued after the conditions no longer hold, the actuation of the electrical oil pump10eis stopped even when neither the accelerating state of the vehicle nor the driver's intention to accelerate is determined. Thus, continuous operation of the electrical oil pump10efor a long time can be avoided. This can suppress the shortening of a period, during which the electrical oil pump10ecan be continuously operated at the time of the next operation, due to the overheating of the motor driver caused by the continuous actuation of the electrical oil pump10e.

The embodiments of the present invention have been described above. The above embodiments are merely illustration of application examples of the present invention and not of the nature to limit the technical scope of the present invention to the specific constructions of the above embodiments. Various changes can be made without departing from the gist of the present invention.

For example, in the above first and second embodiments, the actuation of the electrical oil pump10eis continued until the accelerating state of the vehicle or the driver's intention to accelerate is determined or until the EOP drive duration timer finishes after the coast stop condition and the idle stop condition no longer hold. However, an instruction current to the electrical oil pump10ein this case may be set lower than that at the time of normal startup according to the operating state of the engine1.

That is, as shown in a time chart ofFIG. 9, a necessary hydraulic pressure is ensured by setting the instruction current to the electrical oil pump10eat a predetermined instruction current during the coast stop control or the idle stop control (time ta to tb), and the instruction current is set at a value lower than the predetermined instruction current (tb to tc) after the coast stop condition and the idle stop condition no longer hold. Since the engine1is restarted and the mechanical oil pump10mis operating during this time, the necessary hydraulic pressure can be sufficiently ensured even if the discharge pressure of the electrical oil pump10eis reduced. By returning the instruction current to the electrical oil pump10eto the predetermined instruction current in normal times when the coast stop condition or the idle stop condition holds again, the necessary hydraulic pressure can be ensured (tc and thereafter) even if the engine1stops.

Since the instruction current to the electrical oil pump10ecan be suppressed in this way while the mechanical oil pump10mis operating, fuel economy can be improved by suppressing power consumption of the electrical oil pump10eand suppressing the fuel consumption amount of the engine1necessary to charge the battery13anew.

This application claims priority from Japanese Patent Application No. 2010-197722, filed Sep. 3, 2010, which is incorporated herein by reference in its entirety.