KR102383370B1 - Control method for engine start of hybrid electric vehicle - Google Patents

Abstract

The present invention relates to a control method for starting an engine of a hybrid vehicle, and a control method for starting an engine using a motor in a one-motor two-clutch TMED hybrid system using an automatic transmission equipped with an HSG and torque converter. Its main purpose is to provide In order to achieve the above object, in a control method for starting an engine using a drive motor in a TMED hybrid system using an automatic transmission equipped with a torque converter, the lockup clutch of the transmission is operated while the drive motor is being driven. releasing; starting engine clutch engagement control for engagement of the engine clutch; controlling an engine speed increase slope by the engine clutch engagement control while the engine speed increases after starting the engine clutch engagement control; controlling the torque output of the motor to compensate for the torque generated due to the fluctuation of the engine speed while the engine speed is increased; and engaging the lock-up clutch when fuel injection control is started and torque is output from the engine.

Description

BACKGROUND ART Control method for engine start of hybrid electric vehicle

The present invention relates to a method for controlling engine starting of a hybrid vehicle, and more particularly, control for starting an engine using a motor (drive motor) in a one-motor two-clutch TMED hybrid system using an automatic transmission equipped with a torque converter it's about how

A hybrid electric vehicle (HEV) refers to a vehicle that uses two or more different driving sources, but in general, an engine (Internal Combustion Engine, ICE) that obtains rotational power by burning fuel (fossil fuel such as gasoline) and battery power It means a vehicle driven by using a motor that obtains rotational force.

A hybrid vehicle can output optimum torque and maximize vehicle fuel efficiency depending on how the engine and motor are harmoniously operated in the process of driving with two types of driving sources consisting of an engine and a motor.

A hybrid vehicle can configure a drive system in various structures using an engine and a motor. A TMED (Transmission Mounted Electric Device) type in which the engine and the motor are connected through an engine clutch and a transmission is connected to the output side of the motor is known.

Looking at the configuration in detail, as shown in FIG. 1, the TMED hybrid system includes an engine 1 and a motor 3 that are driving sources for vehicle driving, and an engine clutch interposed between the engine 1 and the motor 3 ( 2), a transmission 4 connected to the output side of the motor 3, an inverter 5 for driving the motor 3, and a battery 6 connected to the motor 3 through the inverter 5 to be charged and discharged ) is included.

In addition to this, the TMED hybrid system may include a motor that is connected to the engine 1 to transmit power to start the engine or generate power with rotational force transmitted from the engine, that is, a Hybrid Starter and Generator (HSG) 7 . .

The HSG 7 operates as a motor 3 or as a generator, and is connected to the engine 1 through a power transmission device such as a belt and pulley so that power can be transmitted at all times, so it is also used to control the engine speed.

The engine clutch 2 operates to close or open by hydraulic pressure to connect or block power transmission between the engine 1 and the motor 3 .

In addition, the inverter 5 converts the DC current of the battery 7 into a three-phase AC current for driving the motor and applies it to the motors 3 and 7 .

The transmission 4 shifts the power of the motor 3 or the combined power of the engine 1 and the motor 3 and transmits it to the drive wheel through a drive shaft, and an automatic transmission (AT) or a double clutch transmission (DCT) ) can be used.

FIG. 1 shows an example in which an automatic transmission is mounted. The automatic transmission 4 includes a torque converter 4a, and a clutch and brake not shown, a planetary gear device, a hydraulic control device, and the like.

A vehicle equipped with the hybrid system as described above, that is, a hybrid vehicle such as HEV or PHEV (Plug-in HEV), uses only the power of the motor (drive motor) in the EV (Electric Vehicle) mode, which is a pure electric vehicle mode, or the power of the engine and It can be driven in HEV (Hybrid Electric Vehicle) mode that uses the power of the motor in combination.

In addition, during braking of the vehicle or during coasting due to inertia, a regenerative mode in which the kinetic energy of the vehicle is recovered through the motor to charge the battery 6 is performed.

In the regenerative mode, the motor that receives the kinetic energy of the vehicle operates as a generator to charge the battery 6 connected through the inverter 5 .

Meanwhile, efforts are being made to delete the HSG 7 from the TMED hybrid system for cost reduction and engine room package improvement.

However, since the mechanism for starting the engine disappears when the HSG is deleted, it is necessary to install an engine starting mechanism that can replace it or to implement the engine starting with control technology.

Some automobile companies are implementing engine starting by installing a 12V starter instead of HSG, or implementing engine starting through engine clutch and DCT clutch control.

Among them, a DCT must be used as a transmission in a specific TMED hybrid system, more specifically, in a known one-motor two-clutch TMED hybrid system.

Although DCT has the advantage of fast shifting speed, it has a disadvantage in terms of ride comfort, and therefore, the use of DCT is limited in luxury sedans where ride comfort is important.

This means that a one-motor two-clutch TMED hybrid system cannot be used in luxury sedans and the like.

Therefore, it is necessary to develop a one-motor two-clutch system to which an automatic transmission equipped with a torque converter is applied instead of the DCT.

However, it is difficult to utilize the engine start control technology of a one-motor two-clutch system equipped with DCT due to the characteristics of the torque converter.

Accordingly, as shown in FIG. 1 , a control technology capable of starting the engine in a one-motor two-clutch TMED hybrid system using an automatic transmission 4 equipped with a torque converter 4a, in particular, a system in which the HSG 7 is eliminated. There is a demand for a control technology capable of starting the engine 1 using the driving motor 3 without affecting the drivability of the vehicle.

Accordingly, the present invention was created in consideration of the above points, and a control method capable of starting an engine using a motor in a one-motor two-clutch TMED hybrid system using an automatic transmission equipped with an HSG and a torque converter. Its purpose is to provide

In order to achieve the above object, according to an embodiment of the present invention, in a control method for starting an engine using a driving motor in a TMED hybrid system using an automatic transmission equipped with a torque converter, the driving motor drives and releasing the lock-up clutch of the transmission in the present state; starting engine clutch engagement control for engagement of the engine clutch; controlling an engine speed increase slope by the engine clutch engagement control while the engine speed increases after starting the engine clutch engagement control; controlling the torque output of the motor to compensate for the torque generated due to the fluctuation of the engine speed while the engine speed is increased; and engaging the lock-up clutch when fuel injection control is started and torque is output from the engine.

Accordingly, according to the engine start control method according to the present invention, the engine using a motor (drive motor) without affecting drivability in a one-motor two-clutch TMED hybrid system using an automatic transmission equipped with an HSG and a torque converter can be started.

1 is a configuration diagram illustrating a TMED hybrid system using an automatic transmission equipped with a torque converter.
2 is a diagram illustrating a motor speed (rpm) and an engine speed (rpm) during control for engine starting in a TMED hybrid system employing DCT.
3 is a view showing the configuration of a conventional torque converter.
4 is a diagram illustrating a timing chart of a control process for starting an engine according to the present invention.
5 is a flowchart of a control process for starting an engine according to the present invention.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the embodiments of the present invention. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms.

Throughout the specification, when a part "includes" a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated.

In the following description, the configuration of the TMED hybrid system will be described with reference to FIG. 1 , but the one-motor two-clutch TMED hybrid system to which the present invention is applied uses an automatic transmission 4 equipped with a torque converter 4a. As a hybrid system, the HSG 7 may be deleted from the configuration of FIG. 1 .

Also, the engine starting control method according to the present invention is a control method capable of starting the engine using the driving motor 3 instead of the HSG 7 .

First, in order to help the understanding of the present invention, a control method for starting an engine in a one-motor two-clutch TMED hybrid system equipped with a DCT (Double Clutch Transmission) will be described.

In the DCT-equipped 1-motor 2-clutch TMED hybrid system, first, slip control of the clutch of the DCT input shaft is performed, and while the slip control of the clutch of the DCT input shaft is performed, the driving motor (reference numeral in FIG. 1) 3), a speed control is performed to increase the speed (rpm) to the target speed.

As described above, while the motor driving and speed control for the motor are performed, the engine 1 is started by the power of the motor 2 by attaching the engine clutch (reference numeral 2 in FIG. 1 ).

Then, after starting the engine, the slip control for the clutch of the DCT input shaft is terminated.

The target speed of the motor while performing the above control may be determined based on the following equation.

(1)

(One)

Here, I _eng represents the engine moment of inertia, I _mot represents the motor moment of inertia, and I _clutch represents the engine clutch moment of inertia.

In addition, ω _after represents the engine and motor rotation speeds after engine clutch engagement, and ω _mot represents the motor rotation speeds before engine clutch engagement, respectively.

The above formula is a relational expression for the kinetic energy of the rotating body, and is based on the energy conservation law, which states that the kinetic energy before joining is the same as the kinetic energy after joining based on the engine clutch joining time.

2 is a graph showing the motor speed (rpm) and the engine speed (rpm) during control for engine starting in a TMED hybrid system employing DCT, and the motor speed and engine speed during the aforementioned control process are graphed .

On the other hand, when the aforementioned DCT-based 1-motor 2-clutch system engine start control method is applied to a 1-motor 2-clutch system equipped with a torque converter (the engine is started using a driving motor in the starting control process), the torque The vehicle driving torque fluctuates due to the characteristics of the converter.

More specifically, the torque converter 4a has a structure as shown in FIG. 3 , and includes an impeller 11 , a drive hub 12 , a stator 13 , a turbine runner 14 , a damper clutch 15 , and a front cover. (16).

The torque converter 4a has a characteristic that is transmitted to the output shaft by multiplying the torque of the input shaft when the speed of the input shaft is higher than the speed of the output shaft by the impeller 11, the stator 13, and the turbine runner 14.

Due to these characteristics, when a control to increase the rotation speed (motor speed) of the motor is applied, the driving torque of the motor is multiplied by the torque converter and transmitted to the transmission input shaft.

Since a driving force greater than the driving force required by the driver is generated, such a situation should be avoided, and therefore, a method for starting the engine while limiting the torque multiplication caused by the torque converter is required.

Hereinafter, a control method for starting an engine according to the present invention will be described with reference to FIGS. 4 and 5 .

First, the control unit (not shown) determines whether a predetermined HEV mode entry condition is satisfied in the EV mode (S11), and if the condition is satisfied, the control unit (not shown) determines that there is a request for switching to the HEV mode to switch from the EV mode to the HEV mode Start the engine start control process of the present invention for

At this time, if the lock-up clutch in the torque converter 4a of the transmission 4 or the transmission input stage is engaged while the drive motor is being driven, it is released (in the 'Lock Up' state in FIG. 4 ). transition to 'Slip' state).

When the engine 1 is started by attaching the engine clutch 2 while the lock-up clutch is engaged, the torque fluctuation and vibration generated when the engine clutch 2 is engaged are transmitted to the transmission 4, impairs drivability.

To prevent this, the lock-up clutch is first released so that the torque converter 4a can act as a damper, so that part of the vibration generated when the engine clutch 2 is engaged can be absorbed by the torque converter 4a. let it be

Then, the control unit increases the motor speed (rpm) at a predetermined slope while maintaining the motor torque constant during the initial period before torque compensation to be described later, and starts joint control of the engine clutch 2 to start the engine (S14).

As described above, after the bonding control for the engine clutch 2 is started, the rotational force of the motor is transmitted to the engine through the engine clutch, and the rotational speed of the engine, that is, the engine speed (engine rotational speed) (rpm) is increased.

At this time, according to the state in which the engine clutch is jointly controlled, the speed at which the engine is started, that is, the slope (= engine rotation acceleration) at which the engine speed (engine speed) rises is determined and controlled, and the rising slope of the engine speed is determined by the engine speed. It becomes an important element of starting control.

This is because the rising slope of the engine speed determines the torque generated by the engine, and this torque is transmitted to the input stage of the engine clutch.

The motor must compensate for the torque generated by the engine speed change. However, if the engine speed rises too steeply, the torque generated due to the engine speed change increases, which is the amount of torque that the motor can compensate. There is a possibility that the limit will be exceeded.

Accordingly, the controller performs the engine clutch engagement control in consideration of the degree of surplus of torque that can be compensated for by the motor, and determines a rising slope of the engine rotation speed through the engine clutch engagement control.

That is, after the lock-up clutch of the transmission (lock-up clutch of the torque converter) is released, the excess torque of the motor is checked (S13), the engine clutch engagement control is performed (S14), and at this time, the rising slope of the engine speed through the engine clutch engagement control is determined, and thereafter, motor torque compensation control is performed in consideration of the surplus torque of the motor while the engine speed increases (S15, S16).

Here, the control unit may check the motor surplus torque that can be additionally output for the compensation from the maximum motor output possible torque (T _{mot _max} ) and the motor demand torque (T _{mot _demand} ) for driving the vehicle.

In this case, the motor spare torque may be calculated as a difference value between the maximum output possible torque of the motor and the motor required torque for driving the vehicle (refer to Equation (2) below).

In addition, the engine clutch engagement control is performed based on the motor spare torque, and at this time, the engine clutch engagement control is performed so that the engine rotation speed can be controlled according to a rising slope of the engine rotation speed corresponding to the motor spare torque.

In the control unit, the excess torque of the motor may be confirmed based on the following equation, and the slope of the increase of the engine rotation speed corresponding to the excess torque of the motor may be determined from the following equation.

(2)

(2)

는 엔진 회전수 상승 기울기(= 엔진 회전 가속도)를 나타낸다.Here, I _eng represents the engine moment of inertia, I _clutch represents the engine-side engine clutch moment of inertia,

denotes an engine speed increase slope (= engine rotation acceleration).

In addition, T _{mot _max} represents the maximum possible output torque of the motor, and T _{mot _demand} represents the motor required torque for driving the vehicle requested by the driver, respectively.

In the above equation, the engine moment of inertia I _eng , and the engine clutch moment of inertia I _clutch on the engine side are determined during design, and are known values that are input and stored in the control unit in advance and set.

In addition, T _{mot _max} , which is the maximum motor output torque value at the current rotation speed, is also a value known by the control unit (eg, motor controller (MCU)), and T _{mot _demand} , which is the motor demand torque for driving the vehicle, is also known by the control unit (eg, For example, it is a known value because it is determined by the hybrid controller (HCU).

That is, since it is a known value that is known to all of the controller except for the slope of the increase in engine rotation speed, the control unit can determine the slope of the increase in engine rotation speed satisfying Equation (2) from the known values.

Then, when the engine speed reaches a certain value (that is, when the engine determines that the cylinder for fuel injection is first performed), the control unit checks whether the fuel injection is possible (S17), and if the fuel injection is possible, the fuel injection Control for (fuel injection) is performed (S18), whereby the engine outputs torque.

At this time, when fuel injection is started, the control unit observes and estimates the torque transmitted to the engine clutch, that is, the engine clutch transmission torque, and outputs a compensation torque (torque corresponding to a negative value of the transmission torque) corresponding to the estimated transmission torque. The motor is controlled to do so (S18), so that only the vehicle driving torque of the motor can be transmitted to the input shaft of the torque converter.

Various methods are known for a method of observing, estimating, and calculating the engine clutch transmission torque, and since the engine clutch transmission torque estimation technique is a known technique, a detailed description thereof will be omitted herein.

Then, when the synchronization of the engine speed and the motor speed is completed (S19), the engine start is completed and the engine can output the driving torque, the control unit checks whether the lock-up clutch of the torque converter can be connected, and lock-up If it is a condition that the clutch can be joined, the control for joining the lock-up clutch is performed (switching from the 'Slip' state to the 'Lock Up' state in FIG. 4) (S20).

Here, since it is a well-known process known to those skilled in the art to check whether the lock-up clutch of the torque converter can be connected, a detailed description thereof will be omitted herein.

However, in brief, as an example of a method of determining whether the lock-up clutch can be joined, it can be determined that the lock-up clutch can be joined if the speed difference between the turbine and the impeller is checked and the speed difference is less than or equal to a certain value. .

Alternatively, when the speed ratio of the turbine and the impeller (= turbine speed/impeller speed) is equal to or greater than a predetermined value, it may be determined that the lock-up clutch can be joined.

At the same time, the control unit performs control of blending torques of the engine and the motor (S21), and performs normal hybrid mode control so that the vehicle can be driven in the hybrid mode.

In this way, according to the control method of the present invention, it is possible to start the engine without affecting drivability in the one-motor two-clutch TMED hybrid system using the automatic transmission equipped with the torque converter.

In the present invention, the EV area may be reduced because the torque of the motor is required for starting the engine due to the characteristics of the 1 motor 2 clutch.

In addition, since the motor outputs torque in a positive direction only in a section in which the engine is cranked during a section in which the engine speed is increased when the engine is started, responsiveness of vehicle behavior can be improved.

Although the embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention as defined in the following claims Also included in the scope of the present invention.

1: engine 2: engine clutch
3: Motor 4: Transmission
4a: torque converter 5: inverter
6: Battery 7: HSG
11: impeller 12: drive hub
13: stator 14: turbine runner
15: damper clutch 16: front cover

Claims (6)

A control method for starting an engine using a drive motor in a TMED (Transmission Mounted Electric Device) hybrid system using an automatic transmission equipped with a torque converter, the control method comprising:
releasing the lock-up clutch of the transmission while the drive motor is being driven;
starting engine clutch engagement control for engagement of the engine clutch;
controlling an engine speed increase slope by the engine clutch engagement control while the engine speed increases after starting the engine clutch engagement control;
controlling the torque output of the motor to compensate for the torque generated due to the fluctuation of the engine speed while the engine speed is increased; and
engaging the lock-up clutch when fuel injection control is started and torque is output from the engine;
After the step of releasing the lock-up clutch of the transmission, further comprising the step of confirming the drive motor surplus torque that can be additionally output for the compensation from the maximum output possible torque of the drive motor and the torque required for driving the vehicle;
The control method for starting an engine of a hybrid vehicle, characterized in that the engine clutch engagement control is performed so that the engine speed can be controlled with a rising slope of the engine speed corresponding to the surplus torque of the driving motor.
The method according to claim 1,
A control method for starting an engine of a hybrid vehicle, characterized in that while performing the engine clutch engagement control, a motor speed (rpm) is increased at a predetermined slope.
delete The method according to claim 1,
The drive motor spare torque may be calculated as a difference value between the maximum output possible torque of the drive motor and the required torque of the drive motor, and the engine rotation speed increase slope corresponding to the drive motor spare torque is determined from the following equation A control method for starting the engine of a vehicle.
ceremony :

where I _eng is the engine moment of inertia, I _clutch is the engine clutch moment of inertia,

is the engine speed rising slope, T _{mot_max} is the maximum output torque of the motor, and T _{mot_demand} is the motor required torque for driving the vehicle.
The method according to claim 1,
When fuel injection is started by the fuel injection control, the engine clutch transmission torque is estimated, and the driving motor is controlled to output a compensation torque corresponding to the estimated engine clutch transmission torque during fuel injection. Control method for starting the engine.
The method according to claim 1,
After the fuel injection control is started, it is checked whether the engine speed and the motor speed are synchronized, and when the synchronization is completed, a control for coupling the lock-up clutch is performed. .

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