JP2004316747A - Stop and start control system for internal combustion engine - Google Patents

Abstract

The present invention provides a technique for preventing a creep torque from being set low due to an engine stop in a stop and start control system for an internal combustion engine.
A stop and start control system for an internal combustion engine, comprising: a transmission in which a clutch operation is automatically performed during a gear shift; and automatic stop / start means for automatically stopping and starting the internal combustion engine. Transmission control means for changing the creep torque while operating the clutch of the transmission, wherein the transmission control means reduces the creep torque when the engine speed becomes equal to or lower than a predetermined speed. The setting conditions of the creep torque are changed based on the amount of decrease in the creep torque of the above, and the setting conditions are not changed when the automatic stop / start means stops and starts the engine.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a stop and start control system for an internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art In a hybrid vehicle including a stepped transmission capable of automatic shifting and a motor generator, a technique for avoiding the occurrence of a sense of deceleration due to clutch disengagement during shifting is known (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-11-69509 (pages 3-5)
[0004]
[Problems to be solved by the invention]
By the way, when a transmission that automatically performs a clutch operation is provided, learning control of creep torque is performed. This is to suppress the stop of the internal combustion engine by maintaining the engine speed at or above a predetermined speed, and reduce the creep torque and reduce the engine speed when the engine speed is at or below the predetermined speed. To increase the number. When the creep torque is changed by a predetermined value or more, learning control for changing the reference value of the creep torque is performed, and feedback control of the engine speed is performed based on the changed reference value.
[0005]
On the other hand, in order to improve fuel efficiency, the internal combustion engine may be stopped when the vehicle stops, or the wheels may be driven by the motor generator while the internal combustion engine is stopped when the vehicle is running at low speed.
[0006]
However, when the learning control of the creep torque is performed, the feedback control of the engine speed is performed when the engine speed is lower than a predetermined value while the engine is stopped, and as a result, the creep torque is reduced. Therefore, the reference value of the creep torque is set to a low value. Then, after the engine is started, the engine speed is maintained at a predetermined value or more, so that the feedback control of the engine speed by the creep torque is not performed, and the creep torque of the low reference value set when the engine is stopped is applied. The Rukoto.
[0007]
The present invention has been made in view of the above-described problems, and has an object to provide a technique for preventing a creep torque from being set low due to an engine stop in a stop and start control system for an internal combustion engine. And
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a stop and start control system for an internal combustion engine according to the present invention employs the following means. That is,
A transmission in which clutch operation is automatically performed during gear shifting;
Automatic stop / start means for automatically stopping and starting the internal combustion engine,
A stop and start control system for an internal combustion engine comprising:
Transmission control means for changing the creep torque while performing the clutch operation of the transmission, wherein the transmission control means reduces the creep torque when the engine speed becomes equal to or lower than a predetermined speed, The setting conditions of the creep torque are changed based on the amount of decrease in the creep torque, and the setting conditions are not changed when the automatic stop / start means stops and starts the engine.
[0009]
The most significant feature of the present invention is that the change of the creep torque control condition is stopped when the engine is stopped and started by the automatic stop / start means, and the creep torque is prevented from lowering.
[0010]
Here, the creep torque is a torque at which the output of the internal combustion engine is transmitted to the transmission via the clutch when the vehicle is stopped or running at low speed, and the output can be adjusted by the pressing force of the clutch. That is, the creep torque increases as the pressing force of the clutch increases.
[0011]
In the stop and start control system for an internal combustion engine configured as described above, when the engine speed becomes equal to or lower than a predetermined speed, the creep torque is reduced to increase the engine speed. Then, learning control for changing the reference value of the creep torque is performed based on the amount of decrease in the creep torque at that time. However, in the case where an automatic stop / start means for automatically stopping and starting the internal combustion engine is provided, if the engine speed decreases at the time of engine stop or start, the creep torque is reduced to reduce the creep torque of the internal combustion engine. Control for increasing the rotation speed is performed. In this case, as the engine speed decreases, the creep torque decreases, and when the internal combustion engine is completely stopped, the creep torque becomes very small. Then, when the engine is started, the creep torque having the low value is applied. Therefore, in the present invention, the creep torque learning control is stopped when the automatic stop / start means stops and starts the engine. This makes it possible to suppress the creep torque from being set to a very small value.
[0012]
In the present invention, the apparatus further comprises communication means for exchanging information between the transmission control means and the automatic stop / start means, and when the automatic stop / start means stops or starts the engine, the creep torque setting condition is The stop or start of the internal combustion engine can be performed after the change is transmitted from the transmission control unit to the automatic stop / start unit.
[0013]
By not stopping or starting the internal combustion engine unless the stop of the change of the control condition of the creep torque is transmitted by the communication means, it is possible to suppress the creep torque from being set to a very small value. It becomes.
[0014]
In the present invention, the automatic stop / start means can stop or start the internal combustion engine after the clutch is disengaged by the transmission control means.
[0015]
When the vehicle is stopped or running at low speed, the internal combustion engine is stopped. If the clutch is not disengaged at this time, the load on the internal combustion engine increases and the internal combustion engine stops with a sharp decrease in the number of revolutions. . On the other hand, if the stop and start of the internal combustion engine are performed after confirming that the clutch has been disengaged, it is possible to suppress the stop of the internal combustion engine accompanying a sharp decrease in the rotational speed.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
<First embodiment>
Hereinafter, specific embodiments of a stop and start control system for an internal combustion engine according to the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a diagram showing a schematic configuration of a stop and start control system for an internal combustion engine according to the present embodiment.
[0018]
The stop and start control system for an internal combustion engine according to the present embodiment includes a diesel engine 1, a transmission 30, a power split device 31, a motor generator 32, a battery 33, an inverter 34, an axle 35, a speed reducer 36, and wheels 37. Have been. Power split device 31 splits the power generated from engine 1 into motor generator 32 and axle 35. The motor generator 32 rotates at a rotational speed proportional to the axle 35 via a speed reducer 36. The motor generator 32 assists the output of the engine 1 as needed during normal operation, and functions as a generator during braking to recover energy. Further, motor generator 32 obtains power from engine 1 to generate power and charge battery 33.
[0019]
A joint between the transmission 30 and the engine 1 is provided with a clutch 30a. At the time of shifting, the clutch 30a is operated by a shift control unit 3 described later. As described above, in the present embodiment, a transmission in which the operation of the clutch 30a is automatically performed is employed. The transmission 30 has a plurality of gears, and a gear that matches the engine speed and the vehicle speed is selected.
[0020]
The engine 1 is provided with an electronic control unit (ECU: Electronic Control Unit) 2 for controlling the engine 1. The ECU 2 is a unit that controls the operating state of the engine 1 according to the operating conditions of the engine 1 and the driver's requirements.
[0021]
The ECU 2 is connected with various sensors via an electric wiring, in addition to an accelerator opening sensor 4 for outputting an electric signal corresponding to the amount of depression of the accelerator by the driver, and the output signals of the various sensors are input to the ECU 2. It is supposed to be. The ECU 2 stores various application programs and various control maps.
[0022]
On the other hand, the transmission 30 is provided with a shift control unit 3 for controlling the transmission 30 including the clutch 30a. The transmission control unit 3 for controlling the transmission 30 is also connected to the ECU 2 via wiring, and data transmission and reception are performed between the ECU 2 and the transmission control unit 3. When the driver performs a shift operation, the shift control unit 3 disengages the clutch 30a, and after the gear is changed, the clutch 30a is engaged by the shift control unit 3. The clutch is operated by, for example, an electric motor, and the clutch operation is performed by controlling the shift control unit 3 of the electric motor.
[0023]
In the hybrid system thus configured, the wheels 37 are driven by the output of the engine 1 or the output of the motor generator 32 during normal traveling. On the other hand, at the time of deceleration, the kinetic energy can be converted to electric energy and collected by the battery 33 while the motor generator 32 is operated as a generator by the rotational force of the wheels 37 to reduce the speed. As described above, the kinetic energy is converted into the electric energy when the vehicle is decelerated, so that the vehicle can be decelerated.
[0024]
Further, the transmission control unit 3 adjusts the creep torque. If the creep torque is larger than the required value, the engine load may be large and the engine speed may decrease, and the engine may stop. On the other hand, when the creep torque is smaller than the required value, the engine speed increases due to a small engine load, and the engine may be damaged.
[0025]
Here, the magnitude of the creep torque can be adjusted by the pressing force of the clutch 30a. This pressing force is adjusted by the position of the clutch 30a. That is, when the creep torque is larger than the target, the clutch 30a is moved in the direction of disconnection, and the pressing force of the clutch 30a is reduced. On the other hand, when the creep torque is smaller than the target, the clutch 30a is moved in the connecting direction, and the pressing force of the clutch 30a is increased.
[0026]
In the present embodiment, a region where the wheels 37 are driven by the engine 1 and a region where the wheels 37 are driven by the motor generator 32 are determined based on the vehicle state determined by the vehicle speed and the accelerator opening. .
[0027]
Here, FIG. 2 is a diagram showing the relationship between the use area of the engine and the motor generator, the vehicle speed, and the accelerator opening. As described above, when the engine is running at a low speed and the accelerator opening is small, the wheels 37 are driven by the motor generator 32. Then, at this time, the engine 1 is stopped.
[0028]
By the way, as described above, it is important to set the creep torque to an appropriate value, and therefore, the creep torque is subjected to learning control. This learning control is performed when the engine speed becomes equal to or lower than the speed required for maintaining the engine rotation. In this case, the creep torque is reduced. As a result, the engine load can be reduced, the engine speed can be increased, and the stop of the engine can be suppressed. In addition, the setting condition of the creep torque is changed based on the value of the creep torque at this time. That is, the reference value of the creep torque is lowered and reset, and from the next time, the creep torque is output based on the reset reference value.
[0029]
Next, FIG. 3 is a diagram showing various states at the time of the conventional creep torque learning control.
[0030]
The “creep torque correction value” is a value that determines a reference value of a “target creep torque” described later, and the larger the “creep torque correction value”, the larger the reference value of the “target creep torque” is set. Then, the “creep torque correction value” is changed based on the creep torque necessary for the engine 1 not to stop. Here, when the creep torque is changed by a predetermined value or more to maintain the operation of the engine, the “creep torque correction value” is reduced, and the reference value of the “target creep torque” is set to a low value. As described above, the learning control for changing the “creep torque correction value” is performed based on the creep torque. When the engine is started, the "creep torque correction value" at the time of the previous engine operation is applied.
[0031]
"Target creep torque" is a target value of creep torque. A reference value of the “target creep torque” is determined based on the “creep torque correction value”. When the engine speed becomes lower than the engine speed (for example, idling speed) required to maintain the operation of the engine, the "target creep torque" is reduced to reduce the creep torque. Is performed.
[0032]
The “engine speed” is the speed of the output shaft of the engine 1.
[0033]
The “transmission input side rotation speed” is the rotation speed of the input shaft of the transmission 30. Here, the clutch 30a is interposed between the engine 1 and the transmission 30, and the rotation speed is adjusted by the clutch 30a. Therefore, the transmission input side rotation speed and the engine rotation speed are not always equal.
[0034]
“G” indicates the acceleration of the vehicle in the front-rear direction.
[0035]
The "brake signal" is a signal that is output when the driver is stepping on the brake, and the brake is stepped on in an upwardly convex state.
[0036]
Here, the conventional creep torque learning control does not consider the case where the drive source of the wheels 37 is changed from the engine 1 to the motor generator 32. Therefore, when feedback control of the engine speed is performed to maintain the engine speed at or above the predetermined value, the creep torque is reduced even during the stop of the engine.
[0037]
That is, when the engine speed decreases during the stop of the engine, the “target creep torque” is reduced in an attempt to increase the engine speed. Normally, the engine load can be increased because the engine load decreases due to the decrease in the "target creep torque", but the engine speed increases because the fuel supply is stopped while the engine is stopped. It stops without doing. As a result, the "target creep torque" becomes very low. Further, since the “target creep torque” becomes very low, the “creep torque correction value” is set to a low value.
[0038]
Next, when the engine 1 is started, the engine speed increases. However, since the “creep torque correction value” is set to a low value, the “target creep torque” is set to a lower value than when the engine was last operated. Is reset to As a result, the torque transmitted to the transmission 30 decreases, and the “transmission input side rotation speed” becomes a small value. Then, since the engine speed increases to a speed required for maintaining the operation of the engine, feedback control of the engine speed is not performed, and the "target creep torque" is maintained in a low state. As a result, the creep torque decreases, and the “transmission input side rotation speed” becomes a small value, and the torque for driving the wheels 37 becomes insufficient.
[0039]
In this regard, in the present embodiment, the learning control of the creep torque is prohibited when the drive source of the wheel 37 is switched. As a result, it is possible to prevent the “creep torque correction value” and the “target creep torque” from decreasing, and to suppress the creep torque from becoming extremely low.
[0040]
Next, the flow of the creep torque learning control according to the present embodiment will be described.
[0041]
FIG. 4 is a flowchart illustrating a flow of the creep torque learning control when the engine is stopped according to the present embodiment.
[0042]
In step S101, it is determined whether an engine stop condition is satisfied.
[0043]
If both the vehicle speed and the accelerator opening are in the motor generator operation region shown in FIG. 2, it is determined that the engine stop condition is satisfied. The relationship shown in FIG. 2 is obtained in advance through experiments or the like and mapped. When the operation of the engine is stopped, the wheels 37 are driven by the motor generator 32.
[0044]
If an affirmative determination is made in step S101, the process proceeds to step S102, while if a negative determination is made, this routine ends.
[0045]
In step S102, it is determined whether or not the engine stop permission flag is "ON".
[0046]
Here, there are cases where the engine cannot be stopped due to other conditions even if it is determined in FIG. 2 that it is in the motor generator operation region. The engine stop permission flag is a flag for determining whether or not the engine 1 can be stopped. The engine can be stopped only when the engine stop permission flag is ON.
[0047]
For example, when the power required for starting the engine is secured, when the charge amount of the battery 33 is equal to or more than a predetermined amount, when the shift is not performed by the shift control unit 3, and when all of the conditions are satisfied. , The engine stop permission flag is turned ON.
[0048]
If the engine stop permission flag is not ON, the engine 1 is not stopped.
[0049]
When an affirmative determination is made in step S102, the process proceeds to step S103, and when a negative determination is made, the process proceeds to step S105.
[0050]
In step S103, a motor drive execution flag is transmitted.
[0051]
Here, the motor drive execution flag is a flag that is turned ON when all the conditions for stopping the engine are satisfied and the drive of the wheels 37 by the motor generator 32 becomes possible.
[0052]
Then, the motor drive execution flag is transmitted from the shift control unit 3 to the ECU 2. At this point, the engine 1 has not been stopped yet.
[0053]
In step S104, the learning control of the creep torque is stopped. Thereafter, engine 1 is stopped, and wheels 37 are driven by motor generator 32.
[0054]
In step S105, since the engine 1 is not stopped, the learning control of the creep torque is continuously performed.
[0055]
Thus, when the engine 1 is stopped, the learning control of the creep torque is stopped.
[0056]
Next, a flow of the creep torque learning control at the time of starting the engine according to the present embodiment will be described.
[0057]
FIG. 5 is a flowchart showing a flow of the creep torque learning control at the time of starting the engine according to the present embodiment.
[0058]
In step S201, it is determined whether an engine start condition is satisfied.
[0059]
The vehicle speed and the accelerator opening are substituted into the map shown in FIG. 2 to determine whether or not the vehicle is in the engine operating range.
[0060]
If an affirmative determination is made in step S201, the process proceeds to step S202, while if a negative determination is made, this routine ends.
[0061]
In step S202, it is determined whether the engine stop permission flag is ON. If it is not ON, the engine 1 is started. Here, the same determination as in step S102 is performed.
[0062]
If an affirmative determination is made in step S202, the process proceeds to step S203, while if a negative determination is made, the process proceeds to step S204.
[0063]
In step S203, the learning control of the creep torque is stopped.
[0064]
In step S204, a counter indicating the elapsed time from the start of the engine 1 is counted up.
[0065]
In step S205, it is determined whether or not the elapsed time from the start of the engine 1 has reached a time (for example, one second) required until the rotation speed of the engine 1 is stabilized.
[0066]
When an affirmative determination is made in step S205, the process proceeds to step S206. On the other hand, when a negative determination is made, the process proceeds to step S203 because learning control of creep torque is not performed.
[0067]
Thus, when the engine 1 is started, the learning control of the creep torque is stopped.
[0068]
In the present embodiment, an example of application to a hybrid vehicle has been described. However, the present invention is not limited to this, and any system having a system for stopping the engine while the vehicle is stopped can be applied.
[0069]
As described above, according to the present embodiment, when engine 1 is stopped and started to change the drive source of wheels 37, learning control of creep torque is stopped. Thereby, erroneous learning of the creep torque can be suppressed, and the creep torque after starting the engine can be set to an appropriate value.
<Second embodiment>
The present embodiment is different from the first embodiment in that the clutch 30a is disconnected and then the engine 1 is stopped when the vehicle speed is low. Note that, in the present embodiment, the basic configuration of the engine and other hardware to which the present invention is applied is the same as that of the first embodiment, and a description thereof will be omitted.
[0070]
Here, the longer the stopping time of the engine 1, that is, the longer the driving time of the wheels 37 by the motor generator 32, the more the fuel efficiency can be improved. Therefore, if the engine 1 is stopped when the vehicle is in a low-speed state before the vehicle stops, fuel efficiency can be improved.
[0071]
However, if the clutch is engaged in spite of the low speed state of the vehicle, the engine load increases, the engine speed decreases rapidly, and the engine stops earlier than expected. Further, when the engine is stopped in such a state, the learning control for lowering the reference value of the target creep torque is performed due to a sharp decrease in the creep torque, and the creep torque is reduced at the next engine start.
[0072]
When the drive source of the wheels 37 is switched from the engine 1 to the motor generator 32, the output of the motor generator is increased in accordance with a decrease in the output of the engine 1 so that the acceleration of the vehicle does not change rapidly. However, when the above-mentioned rapid decrease in the number of revolutions occurs, the output of the motor generator cannot catch up, and the vehicle rapidly decelerates, giving the driver discomfort.
[0073]
In this regard, in the present embodiment, the engine 1 is stopped after the clutch is disconnected.
[0074]
That is, the shift control unit 3 transmits the motor drive execution flag to the ECU 2 after disengaging the clutch 30a. This can be achieved by adding a case where the clutch 30a is disconnected as a determination condition for turning the engine stop permission flag ON in step S102 in FIG. 4 of the first embodiment.
[0075]
In this manner, when the vehicle is running at a low speed, the operation of the engine 1 can be stopped after the clutch 30a is disconnected. As a result, the stop of the engine 1 earlier than expected can be suppressed, and rapid deceleration of the vehicle can be suppressed.
[0076]
【The invention's effect】
In the stop and start control system for an internal combustion engine according to the present invention, when stopping and starting the internal combustion engine, the learning control of the creep torque can be stopped. Thereby, erroneous learning of the creep torque can be suppressed, and the creep torque after starting the engine can be suppressed from being set low.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a stop and start control system for an internal combustion engine according to an embodiment.
FIG. 2 is a diagram showing a relationship between a use area of an engine and a motor generator, an engine speed, and an accelerator opening.
FIG. 3 is a diagram showing various states during a conventional creep torque learning control.
FIG. 4 is a flowchart illustrating a flow of a creep torque learning control when the engine is stopped according to the first embodiment.
FIG. 5 is a flowchart showing a flow of a creep torque learning control at the time of engine start according to the first embodiment.
[Explanation of symbols]
1 engine 2 ECU
3 Transmission control unit 4 Accelerator opening sensor 30 Transmission 30a Clutch 31 Power split mechanism 32 Motor generator 33 Battery 34 Inverter 35 Axle 36 Reducer 37 Wheel

Claims (3)

A transmission in which clutch operation is automatically performed during gear shifting;
Automatic stop / start means for automatically stopping and starting the internal combustion engine,
A stop and start control system for an internal combustion engine comprising:
Transmission control means for changing the creep torque while performing the clutch operation of the transmission, wherein the transmission control means reduces the creep torque when the engine speed becomes equal to or lower than a predetermined speed, The setting conditions of the creep torque are changed based on the decrease amount of the creep torque of the internal combustion engine, and the setting conditions are not changed at the time of stopping and starting the engine by the automatic stop / start means. Start control system. A communication unit for exchanging information between the transmission control unit and the automatic stop / start unit is further provided, and when the engine is stopped or started by the automatic stop / start unit, the creep torque setting condition is not changed. The stop and start control system for an internal combustion engine according to claim 1, wherein the stop or start of the internal combustion engine is performed after the transmission of the internal combustion engine from the transmission control unit to the automatic stop / start unit. 3. The stop and start control system for an internal combustion engine according to claim 1, wherein the automatic stop / start means stops or starts the internal combustion engine after the clutch is disengaged by the transmission control means.

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