CN111071237B

CN111071237B - Seamless downshift control method for hybrid system

Info

Publication number: CN111071237B
Application number: CN201911386242.8A
Authority: CN
Inventors: 司文; 梁志海; 惠无垠
Original assignee: Getec Vehicle Technology Suzhou Co ltd
Current assignee: Getec Vehicle Technology Suzhou Co ltd
Priority date: 2019-12-29
Filing date: 2019-12-29
Publication date: 2021-10-12
Anticipated expiration: 2039-12-29
Also published as: CN111071237A

Abstract

The invention discloses a seamless downshift control method for a hybrid system, which comprises the steps of grading according to the working process of a clutch and controlling the torque of a front-end motor and an engine so as to adjust the rotating speed of the engine to match the target rotating speed. The invention solves or weakens the power interruption in the gear shifting process, and weakens the feeling of a driver on the power interruption; the rotating speed of the engine is adjusted through torque control, and the impact feeling when the gear shifting starts or ends is solved; in the gear shifting process, part or all of the energy used by the rear end motor is provided by the power generation of the front end motor, so that the discharge requirement of the battery under the working condition is reduced or eliminated, the dependence on the battery is reduced, and the efficiency loss caused by the battery is reduced; the rotating speed of the engine is adjusted through torque control, so that when the clutch is locked, the speed difference between the rotating speed of the engine and the rotating speed of the input shaft is reduced, the service life of the clutch can be greatly prolonged, or the clutch with lower cost can be adopted.

Description

Seamless downshift control method for hybrid system

Technical Field

The invention relates to the technical field of automobiles, in particular to a torque and speed control method for a downshift process in a hybrid system.

Background

At present, hybrid electric vehicles in new energy vehicles in China develop most rapidly. A hybrid vehicle is a vehicle that uses multiple energy sources, typically a conventional engine that uses liquid fuel and an electric machine that uses electric energy to drive the vehicle simultaneously or separately.

In a hybrid powertrain of a new energy vehicle, a plurality of motors may be present. The motor directly connected with the engine at the front end of the clutch and sharing the rotating speed is called a front end motor, and is commonly called as a P0 motor and a P1 motor. The motor at the rear end of the clutch and fixedly connected with the transmission/speed reducer system is called a rear end motor, and is commonly called P2, P2.5 and P3 motors.

Hybrid transmissions, if there are multiple engine gears, still face the power performance issues during engine shifts and gear shifts during direct engine drive. Because the current engine electric control generally does not accept target rotating speed control, in the gear shifting process, the speed changer can limit the torque of the engine according to the rotating speed required by the next gear, and the speed is regulated by reducing the torque of the engine. Due to the excessive magnitude of the engine torque modulation (especially during the clutch torque transfer recovery phase), common problems during shifting are: the power response is slow, and the gear shifting time is long; and power interruption occurs in the gear shifting process, and acceleration impact of the whole vehicle occurs when the gear shifting is started and finished, and the like. In addition, in the gear shifting process, the rotating speed of the engine is controlled in a closed loop mode through torque limitation, so that sudden driving intention changes of a driver cannot be reasonably coped with, and the safety is also improved.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a seamless downshift control method for a hybrid system, in particular to a torque and vehicle speed control method for a downshift process in the hybrid system.

The purpose of the invention is realized by the following technical scheme:

a seamless downshift control method for a hybrid system comprises the following steps:

s1, dividing the downshift process into five time periods according to the working process of the clutch, namely a clutch high gear locking stage L0, a clutch transmission torque disappearance stage L1, a stage L2 in which the clutch is completely opened and does not transmit power, a clutch transmission torque recovery stage L3 and a clutch low gear locking stage L4;

s2, in the stages L1, L2 and L3, the front end motor is controlled to output a reverse torque which changes in real time and is opposite to the engine torque according to the difference between the low gear target rotating speed and the actual rotating speed of the engine after the downshift, when the engine torque is controlled to be reduced to the low gear target torque at the end of the stage L3, the difference value of the reverse torque and the engine torque is increased until the low gear target rotating speed is reached at the beginning of the stage L3, and the absolute value of the limit torque of the front end motor is larger than the high gear torque of the engine.

Preferably, in the phase L1, the front end motor is controlled to provide the reverse torque, the absolute value of which has a course that increases linearly until the end of the phase L1, the absolute value of which is equal to the absolute value of the engine torque.

Preferably, in the stage L2, the absolute value of the reverse torque of the front-end motor is controlled to decrease rapidly and increase slowly again.

Preferably, the engine torque is controlled to decrease from the high gear torque to the low gear target torque during the combination period of the stages L2 and L3, and the torque variation process is a linear variation process.

Preferably, in the stage L3, the front end motor is controlled to provide the reverse torque, the absolute value of which has a linearly decreasing course.

Preferably, in the stages L1, L2, L3, the rear end motor is controlled to output a forward torque.

Preferably, the absolute value of the forward torque has a course of linear increase in the stage L1; a process in which the forward torque has a stable output in the stage L2; the absolute value of the forward torque has a linearly decreasing course in the stage L3.

Preferably, in the stage L2, the "process in which the forward torque has a stable output" specifically includes,

calculating a driver-end lost power value equal to the difference between the wheel-end demanded torque minus the product of the front-end net torque and the front-end total speed ratio in stage L2;

calculating the absolute value of the forward torque, which is equal to the quotient of the power value lost by the driving end divided by the total speed ratio at the rear end;

the output is continued in accordance with the absolute value of the forward torque.

The seamless downshift control method of the hybrid system specifically comprises the following steps:

s2, in the stage L0, the engine outputs the high gear torque, and the front end motor does not output the torque at the moment;

s3, in stage L1, the engine continues to output with high gear torque; controlling the front end motor to output a reverse torque in a direction opposite to the engine torque according to the difference between the low-gear target rotating speed and the actual rotating speed of the engine after the downshift, wherein the absolute value of the reverse torque has a linear increasing process until the stage L1 is finished, and the absolute value of the reverse torque is equal to the absolute value of the engine torque; controlling the rear end motor to output a forward torque, an absolute value of which has a process of linearly increasing;

s3, in the stage L2, controlling the engine torque to decrease from the high gear torque to the low gear target torque, wherein the torque change process is a linear change process, and the absolute value of the limit torque of the front end motor is larger than the high gear torque of the engine; controlling the absolute value of the reverse torque of the front end motor to rapidly decrease and slowly increase again, wherein the reverse torque and the engine torque act together to control the engine speed until reaching the low gear target speed at the starting moment of the stage L3, and the absolute value of the reverse torque is always smaller than the absolute value of the engine torque in the process; controlling the rear end motor to continuously and stably output the forward torque, wherein all or part of the electric power of the rear end motor is provided by the power generation of the front end motor;

s4, in the stage L3, the engine torque continues to decrease until the target output torque of the low gear after the downshift; controlling said front-end motor to provide said counter-torque having a linearly decreasing course in absolute value, said counter-torque being equal to zero by the end of phase L3; controlling the absolute value of the forward torque of the rear end motor to decrease linearly until the end of stage L3 when the reverse torque equals zero;

s5, in the stage L4, the engine continuously outputs the low-gear target output torque, and no torque is output from both the front end motor and the rear end motor.

The invention has the following beneficial effects:

1. the problem that power interruption in the gear shifting process is weakened, the feeling of a driver on the power interruption is weakened, and the problem that the waiting time in the gear shifting process is too long is solved or weakened;

2. the rotating speed of the engine is controlled and adjusted through the torque change of the front-end motor, so that the impact feeling when the gear shifting starts or ends is solved;

3. in the gear shifting process, part or all of the energy used by the rear end motor is provided by the power generation of the front end motor, so that the discharge requirement of the battery under the working condition is reduced or eliminated, the dependence on the battery is reduced, and the efficiency loss caused by the battery is reduced;

4. the rotating speed of the engine is controlled and adjusted through the torque change of the front-end motor, so that when the clutch is locked, the speed difference between the rotating speed of the engine and the rotating speed of the input shaft is reduced, the service life of the clutch can be greatly prolonged, or the clutch with lower cost (no sensor feedback and lower precision) can be adopted;

5. the driver's sudden driving intention changes are responded to reasonably and effectively, and the safety is greatly improved.

Drawings

The technical scheme of the invention is further explained by combining the accompanying drawings as follows:

FIG. 1: control schematic of the preferred embodiment of the present invention.

Detailed Description

The present invention will be described in detail below with reference to specific embodiments shown in the drawings. These embodiments are not intended to limit the present invention, and structural, methodical, or functional changes that may be made by one of ordinary skill in the art in light of these embodiments are intended to be within the scope of the present invention.

The invention discloses a seamless downshift control method for a hybrid system, which specifically comprises the steps of grading according to the working process of a clutch and controlling the torque of a front-end motor and an engine so as to adjust the rotating speed of the engine. At the start of the shift, the control objective of the inventive method is to reduce the front end output total torque to 0, while reducing the rear end output torque to: front end pre-shift torque low gear ratio/rear end total ratio. Therefore, the front end motor is adjusted to enter a torque control mode, and torque opposite to that of the engine is input.

As shown in fig. 1, the present invention divides the downshift process into five periods, namely, a clutch high lock-out period L0 (before time 1 in the figure), a clutch torque off-transmission period L1 (between time 1 and time 2 in the figure), a clutch fully open and no-power-transmission period L2 (between time 2 and time 3 in the figure), a clutch torque-transmission recovery period L3 (between time 3 and time 4 in the figure), and a clutch low lock-out period L4 (after time 4 in the figure), according to the operation of the clutch.

In the stage L0, since the clutch is in the lockup stage, the torque TC is the same as the engine torque TE, and the high-range torque is output; in the stage L1, the clutch transmission is in the transmission torque disappearance stage, and the torque thereof is reduced (linearly reduced in the present preferred embodiment); in the stage L2, the clutch is in the fully open and power-off stage, and the torque is zero; in the stage L3, the clutch transmission is in the torque recovery stage, and the torque thereof is increased (linearly increased in the preferred embodiment); in the stage L4, the clutch is in the lockup stage, and the same torque as the engine is output at the low gear torque.

In stage L0, the engine is outputting high range torque, while the front end motor is outputting no torque.

The torque change is required when the gears are engaged, and the speed change is required when the gears are not engaged. Therefore, torque and speed changes need to be adjusted separately, and thus there is a shift interruption in the prior art. During gear shifting, if the clutch is disengaged and the front end rotating speed needs to be adjusted, the algebraic sum of the engine torque and the front end motor torque determines the speed of the change of the engine rotating speed, and the positive and negative of the algebraic sum of the engine torque and the front end motor torque determines the direction of the change of the engine rotating speed.

When the speed is changed from the high gear to the low gear, in order to ensure that the speed regulation process is completed smoothly and timely, the absolute value of the algebraic sum of the maximum capacities of the engine torque and the front-end motor torque is required to be ensured to be divided by the inertia of the front end, and the absolute value is greater than (wheel speed, total speed ratio of the front end of the low gear, wheel speed, total speed ratio of the front end of the high gear) |/target speed regulation time. Meanwhile, the positive and negative of the algebraic sum of the maximum capacities of the engine torque and the front-end motor torque are consistent with the positive and negative of (wheel speed: low gear front total speed ratio-wheel speed: high gear front total speed ratio). This algebraic sum is referred to hereinafter as the differential torque C. If the absolute value of the motor limit torque is greater than the engine torque + torque C, the front end motor reverse torque is used directly to offset the engine torque at the front end.

The front end total speed ratio is the total speed ratio from the engine and the front end motor to the wheel end; the rear end total speed ratio is the total speed ratio from the rear end motor to the wheel end. Because the speed ratios are all stepped, the front end refers to the engine and the front end electric machine, rather than a certain speed ratio.

Based on this, the invention is that in stage L1, the engine continues to output with high gear torque; and controlling the front-end motor to output a reverse torque in the direction opposite to the engine torque according to the difference between the low-gear target rotating speed and the actual rotating speed of the engine after the downshift, wherein the absolute value of the reverse torque has a linear increasing process until the stage L1 is finished, and the absolute value of the reverse torque is equal to the absolute value of the engine torque.

The rear end motor is controlled to output forward torque, the absolute value of the forward torque has a linear increasing process, and the difference value of the wheel demand torque and the difference value (front end net residual torque and low gear front end total speed ratio) is compensated by synchronously using the torque increasing mode of the rear end motor in the front end torque gradually disappearing process.

If the torque capacity limit of the rear end motor is greater than the difference between the wheel torque demand and (front net torque left — low gear front total speed ratio), then the rear end motor torque target is: (wheel demand torque-front net residual torque-low gear front total speed ratio)/rear total speed ratio.

The torque target of the rear end motor is the torque limit capability of the rear end motor if the torque capacity limit of the rear end motor is not greater than the difference between the wheel torque demand and (front end net torque left — low gear front end total speed ratio).

In the stage L2, the engine torque TE is controlled to decrease from the high gear torque to the low gear target torque, and the torque variation process is a linear variation process, and the limit torque TFM of the front end motor_MAXIs greater than the high range torque of the engine; the absolute value of the reverse torque TFM of the front-end electric machine, which is controlled to decrease rapidly and to increase slowly again, co-acts with the engine torque to control the engine speed nE until the low gear target speed is reached at the start of phase L3, during which the absolute value of the reverse torque of the front-end electric machine is always smaller than the absolute value of the engine torque.

The invention controls the rear end motor to continuously and stably output the forward torque TRM, and the power of the rear end motor is wholly or partially provided by the power generation of the front end motor. Because the front end motor is reverse torque in this change process, then the front end motor is in negative torque electricity generation operating mode this moment, the negative torque of front end motor produces by the power generation braking completely this moment, the front end motor can be as the load and maintain the engine in high-efficient operating mode the time, directly turn into the electric energy with the kinetic energy of engine, the electric energy that the rear end motor needs this moment can be partly or whole by the electric energy compensation that the front end motor sent, reduce or eliminate the discharge demand of battery under this operating mode. Since the use of the battery is reduced or even eliminated, the efficiency loss of the system due to the battery will be reduced in this condition. The rear end motor continuously and stably outputs the forward torque TRM, the gear shifting power interruption is compensated, the rear end motor does not need to completely take power from the battery, and the participation degree of the battery is lowered at the moment. Because the battery loses energy every time it is charged and discharged, and the battery is less used, the loss caused by the battery is reduced.

At this time, torque control is applied to the rear end motor:

if the torque capacity limit of the rear end motor is greater than the wheel torque demand/rear end total speed ratio, the torque target of the rear end motor is the wheel torque demand/rear end total speed ratio.

The torque target of the rear end motor is the torque limit capability of the rear end motor if the torque capacity limit of the rear end motor is not greater than the wheel torque demand/rear end total speed ratio.

At this stage, since the clutch is in the state of being completely opened, the input shaft rotation speed nS is first decreased and then increased when the synchronizer is operated.

In stage L3, the engine torque continues to drop to the low range target torque after downshift and continues to be output; the front-end motor is controlled to provide said counter-torque, the absolute value of which has a course of linear decrease, equal to zero by the end of the phase L3. If the engine torque is not equal to the wheel torque demand/low range torque overall speed ratio at this time, the engine torque is restored to the wheel torque demand/low range torque overall speed ratio.

And controlling the absolute value of the forward torque of the rear end motor to linearly reduce, gradually reducing and removing the rear end motor torque in the torque recovery process, wherein the rear end motor torque = (wheel required torque-front end net winning torque and low gear front end total speed ratio)/rear end total speed ratio.

In stage L4, the engine is outputting the low range target torque, and there is no torque output from both the front end motor and the rear end motor.

The invention provides good driving experience, the existence of the difference torque can also timely cope with sudden driving intention changes of a driver, the safety of the vehicle is greatly improved, and the invention is worthy of great popularization.

It should be understood that although the present description refers to embodiments, not every embodiment contains only a single technical solution, and such description is for clarity only, and those skilled in the art should make the description as a whole, and the technical solutions in the embodiments can also be combined appropriately to form other embodiments understood by those skilled in the art.

The above-listed detailed description is only a specific description of a possible embodiment of the present invention, and they are not intended to limit the scope of the present invention, and equivalent embodiments or modifications made without departing from the technical spirit of the present invention should be included in the scope of the present invention.

Claims

1. The seamless downshift control method of the hybrid system is characterized by comprising the following steps: the method comprises the following steps:

s2, in the stages L1, L2 and L3, controlling the front end motor to output a reverse torque which changes in real time and is opposite to the engine torque according to the difference between the low gear target rotating speed and the actual rotating speed of the engine after the downshift, and increasing the engine rotating speed by the difference value of the reverse torque and the engine torque until the low gear target rotating speed is reached at the beginning of the stage L3 while controlling the engine torque to be reduced to the low gear target torque at the end of the stage L3, wherein the absolute value of the limit torque of the front end motor is larger than the high gear torque of the engine;

controlling the rear end motor to output a forward torque in the stages L1, L2 and L3; the absolute value of the forward torque has a linearly increasing course in the stage L1; a process in which the forward torque has a stable output in the stage L2; the absolute value of the forward torque has a linearly decreasing course in the stage L3.

2. The seamless downshift control method of the hybrid system according to claim 1, characterized in that: in the phase L1, the front end motor is controlled to provide the reverse torque, the absolute value of which has a course that increases linearly until the end of the phase L1, the absolute value of which is equal to the absolute value of the engine torque.

3. The seamless downshift control method of the hybrid system according to claim 2, characterized in that: in the stage L2, the absolute value of the reverse torque of the front-end motor is controlled to decrease rapidly and increase slowly again.

4. The seamless downshift control method of the hybrid system according to claim 3, characterized in that: during the combined period of the stages L2 and L3, the engine torque is controlled to decrease from the high gear torque to the low gear target torque, and the torque variation process is a linear variation process.

5. The seamless downshift control method of the hybrid system according to claim 1, characterized in that: in the stage L3, the front end motor is controlled to provide the reverse torque, the absolute value of which has a linearly decreasing course.

6. The seamless downshift control method of the hybrid system according to claim 1, characterized in that: in the phase L2, the "process in which the forward torque has a stable output" specifically includes,

7. The seamless downshift control method of the hybrid system is characterized by comprising the following steps: the method comprises the following steps: