WO2012063389A1

WO2012063389A1 - Engine automatic stop and start control apparatus

Info

Publication number: WO2012063389A1
Application number: PCT/JP2011/005008
Authority: WO
Inventors: Masatomo Yoshihara; Koji Okamura; Shinichi Sugiura
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2010-11-12
Filing date: 2011-09-07
Publication date: 2012-05-18
Also published as: JP2012102694A; JP5563958B2

Abstract

In an automatic stop and start control apparatus of an engine provided with a variable valve mechanism, when an automatic stop request is triggered during engine operation, fuel cutoff is tripped after the variable valve mechanism is moved from an operation position to a start position (or a position near the start position). When a restart request is triggered while an engine rotation speed is dropping due to the fuel cutoff, whether or not starterless start is possible is determined based upon whether or not the engine rotation speed is not less than a determination threshold equivalent to a lower limit value in a rotation speed region where the starterless start is possible, and if the starterlss start is determined to be possible, the engine is restarted by only resuming fuel injection without using the starter.

Description

ENGINE AUTOMATIC STOP AND START CONTROL APPARATUS

The present invention relates to an engine automatic stop and start control apparatus which is equipped with a variable valve mechanism for changing a valve opening/closing characteristic of an engine and with an idling stop system.

An idling stop system and a variable valve mechanism have been widely known as a technique for reduction in fuel consumption or emission of an engine. There are variable types of valve mechanisms, such as a variable valve timing mechanism for adjusting a valve timing, a variable valve lift mechanism for adjusting a lift amount, and a mechanism for adjusting an angle of action, any of which is installed on an engine alone or in combination with others.

On the other hand, the idling stop system is configured so that, when an automatic stop request of stopping an engine automatically during an idling operation (which is generally called "idling stop request") is triggered, the engine is automatically stopped by tripping fuel cutoff, and thereafter, when a driver conducts an operation for starting a vehicle, such as a brake releasing operation, an accelerator stepping operation, a restart request is triggered to automatically energize a starter and restart the engine.

In recent years, vehicles equipped with both the idling stop system and the variable valve mechanism have been increasingly available to achieve much higher fuel efficiency or other objects (see PTL 1 and 2). In general, in the variable valve mechanism, a start position suitable for starting of an engine is located at a different position from an operation position located during an engine operation, and therefore it is desirable that, when the engine is automatically stopped in response to an automatic stop request, the variable valve mechanism is moved from the operation position to a predetermined start position in preparation for the next restart, and is locked thereat by a locking pin or the like.

Japanese Patent Application No. 2010-163070 Japanese Patent Application No. 2010-163994

Now, in many systems, the automatic stop request is triggered after a vehicle stops. However, there are recently some systems configured such that, while a vehicle is running, the automatic stop request is triggered in a deceleration region where the vehicle may stop, in order to expand a fuel cutoff region for controlling an idling stop up to the deceleration region before vehicle stop. In such idling stop systems, the restart request may be triggered while the automatic stop request is triggered in the deceleration region to trip fuel cutoff and an engine rotation speed is dropping, in which case it is necessary to immediately resume fuel injection and restart the engine.

As described above, it is desirable that when the engine is automatically stopped, the variable valve mechanism is moved from an operation position to a predetermined start position in preparation for the next restart. However, in such a case that a restart request is triggered during an engine rotation drop, the period from the tripping of fuel cutoff in response to the automatic stop request to the triggering of the restart request is so short that there is almost no time to spare for moving the variable valve mechanism from the operation position to the start position. Accordingly, when a restart request is triggered during an engine rotation drop, there is a high possibility that restart may be performed before the variable valve mechanism is not completely moved from the operation position to its original start position, and that consequently restart performance may degrade, or , since the variable valve mechanism is not locked at the start position, the variable valve mechanism may flap and produce noise at the restart time or deteriorate in durability.

Therefore, it is a problem to be solved by the invention to provide an engine automatic stop and start control apparatus which ensures that an engine can be restarted with a variable valve mechanism in its original start position even when there is a short time the tripping of fuel cutoff in response to an automatic stop request to the triggering of a restart request.

In order to solve the above-mentioned problem, the present invention is configured to comprise a variable valve mechanism for changing a valve opening and closing characteristic of at least one of an intake valve and an exhaust valve of an engine, and an idling stop control means for tripping fuel cutoff to stop operation of the engine when an automatic stop request is triggered during engine operation and thereafter resuming fuel injection to restart the engine when a restart request is triggered, wherein the idling stop control means trips fuel cutoff after moving the variable valve mechanism from an operation position to a predetermined start position or a position near the start position, which is set within a predetermined range from the start position, when the automatic stop request is triggered.

By tripping fuel cutoff after moving the variable valve mechanism from the operation position to the start position or the position near the start position when the automatic stop request is triggered, as according to the present invention, such control is made possible that the variable valve mechanism can be moved from the operation position to the start position and then fuel injection is resumed to perform restart in response to the restart request, even within a short time the tripping of fuel cutoff in response to an automatic stop request to the triggering of a restart request; thereby the engine can be securely restated. In addition, the variable valve mechanism with a locking mechanism can be locked at the start position before restart, thereby preventing itself from flapping at a restart time, and eliminating the problems of noise and deterioration in durability, which would be otherwise caused by the flapping of the variable valve mechanism.

Further, the present invention is preferably configured such that, when the variable valve mechanism is moved from the operation position to the start position or the position near the start position when the automatic stop request is triggered, at least one of a throttle opening degree and an ignition timing is controlled so as to suppress engine rotation fluctuation. Briefly, if the variable valve mechanism is moved from the operation position to the start position without changing the throttle opening degree or the ignition timing when the automatic stop request is triggered, the output of the engine will change and the engine rotation speed will fluctuate, which may give a driver a feeling of discomfort. As a countermeasure against this problem, at least one of the throttle opening degree and the ignition timing is controlled so as to suppress the engine rotation fluctuation, so that the driver's feeling of discomfort due to the engine rotation fluctuation can be eliminated.

Furthermore, the present invention may be configured to comprise a manual stop control means for immediately tripping fuel cutoff to stop operation of the engine regardless of the operation position of the variable valve mechanism, when a manual stop request is triggered by a driver's off operation of an ignition switch. When the driver turns off the ignition switch to stop operation of the engine, no restart request is triggered during an engine rotation drop, and there is time to spare for moving the variable valve mechanism from the operation position to the start position. Therefore, the driver is saved from feeling a delay in engine stop, by immediately tripping fuel cutoff to stop operation of the engine when the manual stop request is triggered.

The variable valve mechanism used in the present invention may be any of a variable valve mechanism for adjusting a valve timing, a variable valve lift mechanism for adjusting a lift amount, and a mechanism for adjusting an angle of action, or may be a combination of at least two of these mechanisms.

For example, when a variable valve mechanism is used which is configured such that both the valve timing and the lift amount can be adjusted, an operation position during an idling time and a start position are separated far from each other as shown in Fig. 2, and therefore it takes relatively long time to move the variable valve mechanism from the operation position to the start position when an automatic stop request is triggered. However, if the present invention is applied to this configuration, the variable valve mechanism can be moved from the operation position to the start position before a restart request is triggered, and the engine can be securely restarted with the variable valve mechanism in its original start position, so that a bigger effect of application of the present invention can be achieved.

Fig. 1 is a schematic diagram of the whole engine control system according to an embodiment of the present invention. Fig. 2 is a diagram showing one example of the operation characteristics of a variable valve mechanism of an intake valve. Fig. 3 is a time chart for explaining one example of starterless start in the case where a restart request is triggered during fuel cutoff/engine rotation drop for controlling an idling stop. Fig. 4 is a flowchart showing a flow of processing an engine stop control program.

An embodiment where a mode for carrying out the present invention is embodied will be described below.
A schematic configuration of the whole engine control system will be first described with reference to Fig. 1.
Provided at the most upstream section of an intake pipe 12 of an engine 11 is an air cleaner 13, downstream of which an airflow meter 14 for detecting an intake air amount is provided. Provided downstream of the airflow meter 14 are a throttle valve 16 whose opening degree is adjusted by a motor 15 and a throttle valve opening degree sensor 17 for detecting an opening degree (throttle opening degree) of the throttle valve 16.

Further, provided downstream of the throttle valve 16 is a serge tank 18, which is equipped with an intake pipe pressure sensor 19 for detecting an intake pipe pressure. The surge tank 18 is also equipped with an intake manifold 20 for introducing air into each cylinder of the engine 11, and near an intake port of the intake manifold 20 for each cylinder, a fuel injection valve 21 for injecting fuel toward the intake port is attached. Further, a cylinder head of the engine 11 has an ignition plug 22 for each cylinder attached thereto, and spark discharge of each ignition plug 22 ignites an air-fuel mixture in each cylinder.

On the other hand, provided in an exhaust pipe 23 of the engine 11 is an exhaust gas sensor 24 for detecting an air-fuel ratio, reach/lean, or the like of exhaust gas (such as air-fuel ratio sensor or oxygen sensor), downstream of which a catalyst 25 is provided, such as a three-way catalyst for cleaning up exhaust gas.

Further, a cooling water temperature sensor 26 for detecting a cooling water temperature is attached to a cylinder block of the engine 11. Attached to an outer periphery side of the crank shaft 27 of the engine 11 is a crank angle sensor 28 for outputting a pulse signal each time when a crank shaft 27 rotates by a predetermined crank angle, so that an engine rotation speed is detected based upon an interval (cycle) of output pulses of the crank angle sensor 28, and detection of a crank angle and discrimination between a cylinder for an intake stroke and a cylinder for a compression stroke (namely, an ignition cylinder) are made by counting the output pulses of the crank angle sensor 28 based upon an output signal of a cam angle sensor (not shown).

Also attached to the engine 11 is a starter 30 for rotationally driving the crank shaft 27 at a normal start other than a starterless start as described later. As the starter 30, an always-meshing type starter where a pinion is always caused to mesh with a ring gear coupled to the crank shaft 27 of the engine 11 may be used, or a starter configured such that a pinion is caused to be protruded to mesh with a ring gear at a normal start other than a starterless start may be used. In a hybrid electric automobile, a motor for vehicle driving may double as a starter.

In addition, hydraulic-driven

variable valve mechanisms

37 and 38 are provided on an intake valve 35 and an exhaust valve 36 of the engine 11, respectively. Each of the

variable valve mechanisms

37 and 38 is configured to have a combination of a variable valve timing mechanism for adjusting a valve timing and a variable valve lift mechanism for adjusting a lift amount and an angle of action.

A control apparatus 31 for controlling operation of the engine 11 is composed of one or more of ECUs (electronic control units). When the control apparatus 31 is composed of a plurality of ECUs, it may be composed of an ECU for an engine, an ECU for idling stop, and the like. The control apparatus 31 is inputted with signals from various sensors for detecting operation states, such as a brake switch 32 for detecting operation (ON)/non-operation (OFF) of a brake, an accelerator sensor 33 for detecting an accelerator opening degree, and a vehicle speed sensor 34 for detecting a vehicle speed, in addition to the airflow meter 14, the throttle opening degree sensor 17, the intake pipe pressure sensor 19, the exhaust gas sensor 24, and the cooling water temperature sensor 26 as described above.

During engine operation, the control apparatus 31 controls a fuel injection amount, an intake air amount (throttle opening degree) and an ignition timing of the engine 11, and operation positions (variable valve amounts) of the respective

variable valve mechanisms

37 and 38, according to the operation states detected by the above-described various sensors. The control apparatus 31 also functions as an idling stop control means, to monitor whether or not an automatic stop request (an idling stop request) is triggered during engine operation, and to stop fuel injection (trip fuel cutoff) to automatically stop combustion of the engine 11 after moving the

variable valve mechanisms

37 and 38 from the operation position to a predetermined start position or a position near the start position when the automatic stop request is triggered. Here, the term "a position near the start position" means "a position relatively close to the start position," which is set within a predetermined range from the start position (hereinafter, the same shall apply). On the other hand, when a manual stop request is triggered by a driver's off operation of the ignition switch 39, fuel cutoff is immediately tripped to stop operation of the engine 11 regardless of the operation positions of the

variable valve mechanisms

37 and 38.

The automatic stop request may be triggered only during vehicle stop, but in this embodiment, the automatic stop request is configured to be triggered even in a deceleration region at a low speed where a running vehicle may stop, in order to expand a fuel cutoff region for controlling an idling stop up to the deceleration region. Specifically, the following conditions are used to determine whether or not the vehicle has reached a predetermined deceleration state where a running vehicle may stop (whether or not the automatic stop request is triggered) is determined based upon the following conditions. For example, determination is made of: (1) whether or not the accelerator is off (the throttle is fully closed); (2) whether or not the brake is on; and (3) whether or not the vehicle speed is in a low speed region which is equal to or less than a predetermined vehicle speed. When these conditions (1) to (3) have been all continuously satisfied for a predetermined time period or longer, it is determined that the vehicle is put in the predetermined deceleration state where the vehicle may stop. Incidentally, it goes without saying that the method for determining the predetermined deceleration state where the vehicle may stop may be modified as appropriate.

Once it has been determined that the vehicle is put in the predetermined deceleration state where the running vehicle may stop, the automatic stop request is triggered to trip fuel cutoff to automatically stop combustion of the engine 11 and stop the vehicle idling after moving the

variable valve mechanisms

37 and 38 from the operation position to a predetermined start position (or the position near the start position). Thereafter, when a driver conducts an operation for re-accelerating or restarting the vehicle, such as a brake releasing operation, an accelerator stepping operation, an operation of shifting a shift lever to a drive range, during an idling stop period (specifically, during engine rotation drop due to fuel cutoff or after engine rotation stop), a restart request is triggered to restart the engine 11. In other systems, the restart request is triggered to restart the engine 11 by a control system for vehicle-mounted equipment such as a battery charging control system or an air conditioner.

Here, the reason for tripping fuel cutoff after moving the

variable valve mechanisms

37 and 38 from the operation position to the start position (the position near the start position) when the automatic stop request is triggered will be described with reference to Figs. 2 and 3.

Fig. 2 is a diagram showing the operation characteristics of the variable valve mechanism 37 of the intake valve 35. The operation characteristics of the variable valve mechanism 38 of the exhaust valve 36 are the same as those of the variable valve mechanism 37 of the intake valve 35, except in that advance and retard angles of a valve timing are reversed.

The

variable valve mechanisms

37 and 38 according to this embodiment are configured to adjust valve timings, lift amounts, and angles of action, and are controlled such that a valve timing on the intake side is at the most advance angle position, a valve timing on the exhaust side is at the most retard angle position, and the lift amounts and the angles of action on both the intake and exhaust sides are minimum during an idling time. On the other hand, when being at the start position suitable for starting of the engine 11, the

variable valve mechanisms

37 and 38 are controlled such that the valve timing on the intake side is at the most retard angle position, the valve timing on the exhaust side is at the most advance angle position, and the lift amounts and the angles of action on both the intake and exhaust sides are intermediate values, and are locked at the start position by a locking pin (not shown).

Since the operation position during the idling time and the start position are separated far from each other as shown in Fig. 2, it takes a relatively long time to move the

variable valve mechanisms

37 and 38 from the operation position to the start position when the automatic stop request is triggered. Therefore, in such a case that fuel cutoff is tripped immediately after an automatic stop request is triggered during engine operation (for example, during idling), and thereafter the restart request is triggered during an engine rotation drop, the period from the tripping of fuel cutoff in response to the automatic stop request to the triggering of the restart request is so short that there is almost no time to spare for moving the

variable valve mechanisms

37 and 38 from the operation position to the start position. Accordingly, when the restart request is triggered during an engine rotation drop, there is a high possibility that restart may be performed before the

variable valve mechanisms

37 and 38 are not completely moved from the operation position to their original start position, and that consequently restart performance may degrade, or, since the

variable valve mechanisms

37 and 38 are not locked at the start position, the

variable valve mechanisms

37 and 38 may flap and produce noise at the restart time or deteriorate in durability.

In view of these circumstances, according to this embodiment, fuel cutoff is tripped after the

variable valve mechanisms

37 and 38 are moved from the operation position to the start position (or the position near the start position), when the automatic stop request is triggered during engine operation, as shown in Fig. 3. When the restart request is triggered while the engine rotation speed is dropping due to the fuel cutoff, whether or not starterless start is possible is determined based upon whether or not the engine rotation speed is not less than a determination threshold equivalent to a lower limit value in a rotation speed region where the starterless start is possible, and if the starterlss start is determined to be possible, the engine 11 is restarted by only resuming fuel injection without using the starter 30. Conventionally, there is a high possibility that restart may be performed before the

variable valve mechanisms

37 and 38 are not completely moved from the operation position to their original start position, and that consequently the starterless start may fail even in the rotation speed region where the starterless start is possible. Note that, when the engine rotation speed at the time of triggering of the restart request is lower than the lower limit value (determination threshold) in the rotation speed region where the starterless start is possible, the starter 30 is energized to restart the engine 11.

The above-described idling stop control according to this embodiment is performed by the control apparatus 31 according to an engine stop control program shown in Fig. 4. This program is executed repeatedly at a predetermined cycle while power supply is on (the ignition switch 39 is on), and functions as an idling stop control means.

When this program is started, whether or not an automatic or manual stop request is triggered is first determined at Step 100, and unless either request is triggered, this program will be terminated as it is.

If it is determined at the above Step 100 that the automatic or manual stop request is triggered, the program proceeds to Step 101, where it is determined whether or not the triggered stop request is an automatic stop request, and if it is determined that the triggered stop request is not the automatic stop request (that is, it is the manual stop request), the program proceeds to Step 106, where a manual stop process is performed: fuel cutoff is tripped immediately regardless of the operation positions of the

variable valve mechanisms

37 and 38, to stop operation of the engine 11. When the operation of the engine 11 is stopped according to a manual stop request triggered by a driver's off operation of the ignition switch 39, no restart request is triggered during an engine rotation drop, and there is time to spare for moving the

variable valve mechanisms

37 and 38 from the operation position to the start position. Therefore, the driver is saved from feeling a delay in engine stop, by immediately tripping fuel cutoff to stop operation of the engine 11 when the manual stop request is triggered. This process at Step 106 serves as a manual stop control means.

On the other hand, if it is determined at the above Step 101 that the triggered stop request is the automatic stop request, the program proceeds to Step 102, where the

variable valve mechanisms

37 and 38 are moved from the operation position to the start position (or the position near the start position), and, at the next Step 103, engine rotation fluctuation suppressing control is performed to maintain the engine rotation speed at a target rotation speed. At this Step, at least one of a throttle opening degree and an ignition timing is controlled so as to suppress engine rotation fluctuation. Briefly, if the

variable valve mechanisms

37 and 38 are moved from the operation position to the start position without changing the throttle opening degree or the ignition timing when the automatic stop request is triggered, the output of the engine 11 will change and the engine rotation speed will fluctuate, which may give a driver a feeling of discomfort. As a countermeasure against this problem, at least one of the throttle opening degree and the ignition timing is controlled so as to suppress the engine rotation fluctuation, so that the driver's feeling of discomfort due to the engine rotation fluctuation can be eliminated.

At the next Step 104, it is determined whether or not the

variable valve mechanisms

37 and 38 have reached from the operation position to the start position (or the position near the start position), and if it is determined that the variable valve mechanisms have not yet reach to the start position (or the position near the start position), the processes at the above-described

Steps

102 and 103 are repeated. Thereafter, once it is determined at the above Step 104 that the

variable valve mechanisms

37 and 38 have reached from the operation position to the start position (or the position near the start position), the program proceeds to Step 105, where fuel cutoff is tripped.

According to the embodiment described above, fuel cutoff is tripped after the

variable valve mechanisms

37 and 38 are moved from the operation position to the start position (or the position near the start position) when the automatic stop request is triggered during engine operation, such control is made possible that the

variable valve mechanisms

37 and 38 can be moved from the operation position to the start position and then fuel injection is resumed to perform restart in response to the restart request, even within a short time the tripping of fuel cutoff in response to an automatic stop request to the triggering of a restart request; thereby the engine can be securely restated. In addition, the

variable valve mechanisms

37 and 38 can be locked at the start position before restart, thereby preventing themselves from flapping at a restart time, and eliminating the problems of noise and deterioration in durability, which would be otherwise caused by the flapping of the

variable valve mechanisms

37 and 38.

According to this embodiment, the

variable valve mechanisms

37 and 38 are provided on the intake valve 35 and the exhaust valve 36, respectively, but such a configuration may be adopted that a variable valve mechanism is provided only on either of the intake valve 35 and the exhaust valve 36. Further, the

variable valve mechanisms

37 and 38 according to this embodiment are configured such that all of their valve timings, lift amounts and angles of action can be adjusted, but such a configuration may be also adopted that variable valve mechanisms for adjusting only two or one thereof are used.

Besides, it goes without saying that the present invention can be variously modified and implemented within a scope which does not deviate from the gist; for example, it can be applied to and implemented in a hybrid electric vehicle where a motor for vehicle driving is doubled as a starter.

11: Engine, 12: Intake pipe, 16: Throttle valve, 21: Fuel injection valve, 22: Ignition plug, 23: Exhaust pipe, 30: Starter, 31: Control apparatus (idling stop control means, manual stop control means), 32: Brake switch, 33: Accelerator sensor, 34: Vehicle speed sensor, 35: Intake valve, 36: Exhaust valve, 37, 38: Variable valve mechanism, and 39: Ignition switch

Claims

An engine automatic stop and start control apparatus, comprising:
a variable valve mechanism for changing a valve opening and closing characteristic of at least one of an intake valve and an exhaust valve of an engine; and
an idling stop control means for tripping fuel cutoff to stop operation of the engine when an automatic stop request is triggered during engine operation and thereafter resuming fuel injection to restart the engine when a restart request is triggered, wherein
the idling stop control means trips fuel cutoff after moving the variable valve mechanism from an operation position to a predetermined start position or a position near the start position, which is set within a predetermined range from the start position, when the automatic stop request is triggered.
The engine automatic stop and start control apparatus according to claim 1, wherein, when the variable valve mechanism is moved from the operation position to the start position or the position near the start position when the automatic stop request is triggered, at least one of a throttle opening degree and an ignition timing is controlled so as to suppress engine rotation fluctuation.
The engine automatic stop and start control apparatus according to claim 1, further comprising a manual stop control means for immediately tripping fuel cutoff to stop operation of the engine regardless of the operation position of the variable valve mechanism, when a manual stop request is triggered by a driver's off operation of an ignition switch.
The engine automatic stop and start control apparatus according to claim 1, wherein the variable valve mechanism is configured such that both a valve timing and a lift amount can be adjusted.