CN111071242B

CN111071242B - Seamless downshift control method for hybrid system

Info

Publication number: CN111071242B
Application number: CN201911386247.0A
Authority: CN
Inventors: 惠无垠; 司文; 梁志海
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: 2021-08-31
Anticipated expiration: 2039-12-29
Also published as: CN111071242A

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 actively adjusting the torque of a front-end motor and the torque of an engine according to the characteristics of the front-end motor so as to change the rotating speed of the engine. 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 in fixed connection with the transmission/reducer system is called a rear end motor, commonly known as P2, P2.5 and P3 motors, for example, fig. 1 shows a hybrid system including a front end motor and a rear end motor.

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, controlling the front end motor to output a reverse torque in the direction opposite to the engine torque according to the difference between the target rotating speed and the actual rotating speed of the engine high gear after the downshift at the starting time of the stage L1;

s3, comparing and judging the absolute value of the limit torque of the front end motor with the high gear torque and the low gear target torque after downshift of the engine;

s4, controlling the engine torque and the reverse torque respectively according to the result of the step S3, and ensuring that the real-time difference torque between the reverse torque and the engine torque can increase the engine speed until reaching the low gear target speed at the beginning of the stage L3.

Preferably, in step S3, when the absolute value of the limit torque of the front end motor is greater than the high range torque of the engine, the engine torque is controlled to decrease to the low range target torque until the end of the phase L3.

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 L2, the "controlling the absolute value of the reverse torque of the front end motor to decrease rapidly and increase slowly again" includes the specific steps of,

calculating the actual rotating speed of the engine before gear shifting, wherein the actual rotating speed is equal to the product of the wheel speed and the total speed ratio of the front end of the high gear,

calculating the target low gear speed of the engine after gear shifting, which is equal to the product of the wheel speed and the total low gear front end speed ratio,

calculating a target angular acceleration of the engine during the gear shifting process, wherein the target angular acceleration is equal to a quotient obtained by dividing an absolute value of a difference between a low-gear target rotating speed of the engine after the gear shifting and an actual rotating speed of the engine before the gear shifting by a target speed regulating time;

calculating a difference torque C, wherein the difference torque C is larger than or equal to the algebraic sum of the engine torque and the negative limit torque of the front end motor, and the absolute value of the difference torque C divided by the inertia of the front end is always larger than the target angular acceleration of the engine in the gear shifting process and is required to be larger than a safety value designed by a hybrid power transmission system;

ensuring that the absolute value of the limit torque of the front-end motor is greater than the sum of the quotient of the required torque at the wheel end divided by the total speed ratio at the front end in the high gear and the absolute value of the differential torque C, the absolute value of the reverse torque of the front-end motor is equal to the absolute value of the difference between the negative value of the target torque of the engine and the differential torque C, the target torque of the engine being the torque value at each time point in the torque variation line between the high gear torque and the target torque in the low gear of the engine after downshift.

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, the absolute value of which 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.

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 remaining torque and the low range 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 invention discloses a seamless downshift control method for a hybrid system, which specifically comprises the following steps:

s11, 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;

s12, in the stage L0, the engine outputs the high gear torque, and the front end motor does not output the torque at the moment;

s13, 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;

s14, 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;

s15, 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;

s16, 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.

Preferably, in step S3, when the absolute value of the limit torque of the front end motor is smaller than the high range torque of the engine and larger than the low range target torque after the downshift, the engine torque is controlled to decrease from the high range torque to the low range target torque after the downshift in the phase L1, and the reverse torque is controlled to increase until the absolute value of the reverse torque is equal to the absolute value of the engine torque at the end of the phase L1; the reverse torque is controlled to be small in the stage L2 so that the difference torque between the reverse torque and the engine torque is enough to raise the engine speed in the stage L2 until the low gear target speed is reached at the start of the stage L3, and the engine torque is controlled to maintain the low gear target torque and continue to be output in the stages L2, L3, and L4.

Preferably, the phase L1 is divided into two parts L11 and L12 in time sequence, the time point between the two parts is a time point a, the duration of the phase L11 is the time when the reverse torque is linearly increased from the starting time of the phase L1 to the negative value of the low gear target torque after the engine downshift, and the time point a is the starting point of controlling the engine torque to be decreased from the high gear torque to the low gear target torque after the downshift.

Preferably, in the stage L12, the front end motor is controlled to provide the reverse torque of a stable magnitude, which is equal in absolute value to the magnitude of the low range target torque after the engine downshift.

Preferably, in the stage L12, the engine torque is controlled to linearly decrease from the high gear torque to the low gear target torque after the downshift.

Preferably, the "controlling the absolute value of the reverse torque of the front end motor to decrease rapidly and increase slowly again" includes the specific steps of:

Preferably, in the phase L3, the front end motor is controlled to provide the reverse torque, the absolute value of which has a course of linear decrease, until the end of the phase L3 the reverse torque is zero.

The invention discloses another seamless downshift control method for a hybrid system, which specifically comprises the following steps:

s21, 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;

s22, in the stage L0, the engine outputs the high gear torque, and the front end motor does not output the torque at the moment;

s23, in a stage L1, 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;

in a phase L11 before the time point a, the absolute value of the reverse torque has a linearly increasing course, and the reverse torque is equal to the negative value of the engine low range target torque by the time point a; the engine torque maintains the high gear torque unchanged;

controlling the engine torque to linearly decrease from the high gear torque to the low gear target torque after the downshift in a stage L12 from the time point a until the end of the stage L1, the reverse torque being kept stably output and having an absolute value equal to the magnitude of the low gear target torque after the engine downshift;

controlling the rear end motor to output a forward torque, an absolute value of which has a process of linearly increasing;

s24, in a stage L2, controlling the engine torque to maintain a low gear target torque after the downshift, controlling the absolute value of the limit torque of the front end motor to be smaller than the high gear torque of the engine and larger than the low gear target torque after the downshift, and controlling the reverse torque of the front end motor to be small so that the difference torque between the reverse torque and the low gear target torque is enough to increase the engine speed in the stage L2 until reaching the low gear target speed at the start time of the stage L3; the absolute value of the reverse torque is always smaller than the absolute value of the engine torque during 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;

s25, in phase L3, controlling the front end motor to provide a linearly decreasing counter torque equal to zero by the end of phase L3; controlling the engine torque to keep a low gear target torque and continuously outputting the low gear target torque; controlling the absolute value of the forward torque of the rear end motor to linearly decrease;

s26, 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.

Preferably, in the step S3, when the absolute value of the limit torque of the front end motor is smaller than the low range target torque of the engine, the engine torque is controlled to decrease from the high range torque to the transitional torque in the phase L1 so that the difference torque between the reverse torque and the transitional torque is enough to increase the engine speed in the phase L2 until the low range target speed is reached at the beginning of the phase L3, and the engine torque is controlled to increase from the transitional torque to the low range target torque in the phase L3

Preferably, the phase L1 is divided into two parts L11 and L12 in time sequence, the time point between the two parts is a time point a, the duration of the phase L11 is the time when the reverse torque increases linearly from the starting time of the phase 1 to the negative value of the transition torque, and the time point a is the starting point of controlling the engine torque to decrease from the high gear torque to the transition torque.

Preferably, the phase L3 is divided into two parts L31 and L32 in time sequence, the time point between the two parts is a time point b, the duration of the phase L31 is the time point when the reverse torque is linearly reduced from the starting time of the phase L3 to zero, and the time point b is the starting point for controlling the engine torque to increase from the transitional torque to the low gear target torque.

Preferably, in the stage L1, the front end motor is controlled to provide the reverse torque, the absolute value of which has a linearly increasing course in the stage L11, and which is equal to the negative value of the transition torque up to the time point a; in a phase L12 from the time point a until the end of the phase L1, the engine torque is controlled to linearly decrease from the high gear torque to a transient torque, and the reverse torque is kept in a stable output with an absolute value equal to that of the transient 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, and the engine torque is controlled to maintain the transient torque and stabilize the output.

s31, dividing the downshift process into five time periods according to the working process of the clutch, namely a clutch low 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 high gear locking stage L4;

s32, in the stage L0, the engine outputs the low gear torque, and the front end motor does not output the torque at the moment;

s33, in a stage L1, controlling the front end motor to output a reverse torque in the direction opposite to the engine torque according to the difference between the target rotating speed and the actual rotating speed of the engine in the high gear after the downshift;

setting a transition torque to ensure that a difference torque between the reverse torque and the transition torque is sufficient to reduce the engine speed until reaching a high gear target speed,

in a phase L11 preceding the time point a, the absolute value of the reverse torque has a course of linear increase, the reverse torque being equal to the negative value of the transition torque by the time point a; the engine torque maintains the low gear torque unchanged;

controlling the engine torque to linearly decrease from the low range torque to the transition torque in a phase L12 from the time point a until an end of a phase L1, the reverse torque maintaining a stable output with an absolute value equal to an absolute value of the transition torque;

s34, in the stage L2, controlling the engine torque to maintain a transition torque, the absolute value of the limit torque of the front end motor is smaller than the low gear torque of the engine, the reverse torque of the front end motor is controlled to continuously increase, the engine speed is reduced until reaching the high gear target speed at the beginning of the stage L3, the absolute value of the reverse torque is always larger than the absolute value of the engine torque, and the increase of the reverse torque is a nonlinear increasing 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;

s35, in phase L3, controlling the front end motor to provide the reverse torque, the absolute value of which has a linearly decreasing course, the reverse torque being equal to zero by a time point b in phase L3;

controlling the engine torque to be continuously output at a transition torque before the time point b, and to be increased to a high-gear target torque and continuously output after the time point b, wherein the torque increasing process is a linear increasing process; controlling the absolute value of the forward torque of the rear end motor to linearly decrease;

and S36, in the stage L4, the engine outputs the high gear torque, and the front end motor and the rear end motor do not output the torque at the moment.

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 sudden driving intention change of the driver is reasonably and effectively coped with, and the safety is greatly improved;

6. the intelligent control system is highly intelligent, provides different control strategies according to the limit torque of the front-end motor, and is safe and reliable.

Drawings

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

FIG. 1: a schematic diagram of an embodiment of a prior art blending system;

FIG. 2: a control method of the present invention is a flowchart;

FIG. 3: a control schematic of a first embodiment of the invention;

FIG. 4: a control schematic of a second embodiment of the invention;

FIG. 5: a control schematic of a third embodiment of the 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 actively adjusting the torque of a front-end motor and the torque of an engine according to the characteristics of the front-end motor so as to change 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. 2, a seamless downshift control method for a hybrid system includes the following steps:

Referring to fig. 3-5, the present invention divides the downshift into five time periods, namely, a clutch high lock-out period L0 (before time 1 in the figure), a clutch off-torque transmission period L1 (between time 1 and time 2 in the figure), a clutch full open and no-power transmission period L2 (between time 2 and time 3 in the figure), a clutch on-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. Wherein, the partial embodiment also comprises a time point a and a time point b, the time point a is positioned between the phases L1, the time point a is preceded by the phase L11 and followed by the phase L12; time b lies between phases L3, preceded by phase L31 and followed by phase L32.

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 phase L1, the clutch is in the transmission torque disappearance phase, 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 is in the torque recovery stage, and its torque is increased (linearly increased in the present 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.

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, in the first embodiment of the invention shown in fig. 3, the engine continues to output the torque in the high gear at the stage L1; 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; controlling the reverse direction of the front end motorThe absolute value of the torque TFM decreases rapidly and increases again slowly, which in combination with the engine torque controls the engine speed nE until the low gear target speed is reached at the beginning of the phase L3, during which the absolute value of the counter torque is always smaller than the absolute value of the engine torque.

In the stage L2, the "controlling the absolute value of the reverse torque TFM of the front end motor to decrease rapidly and increase slowly again" includes the following specific steps: calculating the actual engine speed before shifting, which is equal to the product of the wheel speed and the total speed ratio of the front end of the high gear, calculating the target low-gear speed of the engine after shifting, which is equal to the product of the wheel speed and the total speed ratio of the front end of the low gear, and calculating the target angular acceleration of the engine during shifting, which is equal to the quotient of the absolute value of the difference between the target low-gear speed of the engine after shifting and the actual engine speed before shifting divided by the target speed regulation time; calculating a difference torque C, wherein the difference torque C is larger than or equal to the algebraic sum of the engine torque and the negative limit torque of the front end motor, and the absolute value of the difference torque C divided by the inertia of the front end is always larger than the target angular acceleration of the engine in the gear shifting process and is required to be larger than a safety value designed by a hybrid power transmission system; ensuring that the absolute value of the limit torque of the front-end motor is greater than the sum of the quotient of the required torque at the wheel end divided by the total speed ratio at the front end in the high gear and the absolute value of the differential torque C, the absolute value of the reverse torque of the front-end motor is equal to the absolute value of the difference between the negative value of the target torque of the engine and the differential torque C, the target torque of the engine being the torque value at each time point in the torque variation line between the high gear torque and the target torque in the low gear of the engine after downshift.

The safety value in the present invention is a standard value set in the design of the hybrid transmission system, determined by testing and calibration, and is intended to be used to match the driver's temporary driving intention.

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, and controlling the rear end motor torque to be = (wheel required torque-front end net residual 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.

In the second embodiment of the present invention shown in fig. 4, the front end motor is controlled to output a reverse torque in the opposite direction to the engine torque in accordance with the difference between the low engine speed target after the downshift and the actual engine speed at stage L1.

In a phase L11 before the time point a, the absolute value of the reverse torque has a linearly increasing course, and the reverse torque is equal to the negative value of the engine low range target torque by the time point a; the engine torque TE maintains the high range torque unchanged.

And in a stage L12 from the time point a until the stage L1 is finished, the engine torque is controlled to linearly decrease from the high gear torque to the low gear target torque after the downshift, the reverse torque is kept in a stable output, and the absolute value of the reverse torque is equal to the magnitude of the low gear target torque after the engine downshift.

In the phase L2, it is assumed that,controlling the engine torque TE to maintain the low gear target torque after the downshift, the limit torque TFM of the front end motor_MAXIs smaller than the high range torque of the engine and larger than the low range target torque after downshift. Controlling the absolute value of the reverse torque TFM of the front end motor to rapidly decrease and slowly increase again, wherein the reverse torque and the engine torque jointly act to control the engine speed nE to increase in a stage L2 until reaching a low gear target speed at the starting moment of a stage L3; the absolute value of the reverse torque is always smaller than the absolute value of the engine torque during this process.

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

In phase L3, the front end motor is controlled to provide the counter torque, the absolute value of which has a course of linear decrease, equal to zero by the end of phase L3. Controlling the engine torque to keep a low gear target torque and continuously outputting the low gear target torque; 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, and controlling the rear end motor torque to be = (wheel required torque-front end net residual torque and low gear front end total speed ratio)/rear end total speed ratio.

In stage L4, the engine continues to output the low range target output torque, with no torque output from both the front end motor and the rear end motor.

In the third embodiment of the present invention shown in fig. 5, in the stage L1, the front end motor is controlled to output a reverse torque in the opposite direction to the engine torque according to the difference between the low engine speed target after downshift and the actual engine speed; a transition torque is set to ensure that the difference torque between the reverse torque and the transition torque is sufficient to increase the engine speed until a low gear target speed is reached.

The phase L1 is divided into two parts L11 and L12 in time sequence, the time point between the two parts is a time point a, the duration of the phase L11 is the time when the reverse torque increases linearly from the starting time of the phase 1 to the negative value of the transition torque, and the time point a is the starting point of controlling the engine torque to decrease from the high gear torque to the transition torque.

The invention has a linear increase in the absolute value of the counter torque in phase L11, which is equal to the negative value of the transition torque by the time point a; the engine torque remains unchanged during this period for high range torque.

The present invention controls the engine torque to linearly decrease from the high gear torque to the transient torque from the stage L12, during which the reverse torque keeps a stable output with an absolute value equal to that of the transient torque.

In stage L2, the engine torque TE is controlled to maintain the transition torque unchanged. Ultimate torque TFM of the front end motor_MAXIs less than the low range target torque of the engine. Controlling the absolute value of the reverse torque TFM of the front end motor to rapidly decrease and slowly increase again, wherein the reverse torque and the engine torque jointly act to control the engine speed nE to increase in a stage L2 until reaching a low gear target speed at the starting moment of a stage L3; the absolute value of the reverse torque is always smaller than the absolute value of the engine torque (transition torque at the present stage) in this process.

In the stage L2, the "controlling the absolute value of the reverse torque TFM of the front end motor to decrease rapidly and increase slowly again" includes the following specific steps:

calculating the actual rotating speed of the engine before gear shifting, wherein the actual rotating speed is equal to the product of the wheel speed and the total speed ratio of the front end of the high gear; calculating a target low gear speed of the engine after gear shifting, wherein the target low gear speed is equal to the product of the wheel speed and the total low gear front end speed ratio; calculating a target angular acceleration of the engine during the gear shifting process, wherein the target angular acceleration is equal to a quotient obtained by dividing an absolute value of a difference between a low-gear target rotating speed of the engine after the gear shifting and an actual rotating speed of the engine before the gear shifting by a target speed regulating time; calculating a difference torque C, wherein the difference torque C is larger than or equal to the algebraic sum of the engine torque and the negative limit torque of the front end motor, and the absolute value of the difference torque C divided by the inertia of the front end is always larger than the target angular acceleration of the engine in the gear shifting process and is required to be larger than a safety value designed by a hybrid power transmission system; ensuring that the absolute value of the limit torque of the front-end motor is greater than the sum of the quotient of the required torque at the wheel end divided by the total speed ratio at the front end in the high gear and the absolute value of the differential torque C, the absolute value of the reverse torque of the front-end motor is equal to the absolute value of the difference between the negative value of the target torque of the engine and the differential torque C, the target torque of the engine being the torque value at each time point in the torque variation line between the high gear torque and the target torque in the low gear of the engine after downshift.

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

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, the reverse torque being equal to zero by the time point b in the stage L3. The phase L3 is divided into two parts L31 and L32 in time sequence, the time point between the two parts is the time point b, the duration of the phase L31 is the time point when the reverse torque is linearly reduced from the starting time of the phase L3 to zero, and the time point b is the starting point for controlling the engine torque to rise to the low gear target torque. And controlling the engine torque to be continuously output at a transition torque before the time point b, and to be increased to a low gear target torque and continuously output after the time point b, wherein the torque increasing process is a linear increasing process.

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, and controlling the rear end motor torque to be = (wheel required torque-front end net residual torque and high gear front end total speed ratio)/rear end total speed ratio.

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

The invention is highly intelligent, provides different control strategies according to the limit torque of the front-end motor, and is safe and reliable; and good driving experience is provided, the sudden driving intention change of a driver can be responded in time due to the existence of the difference torque, the safety of the vehicle is greatly improved, and the method is worthy of being widely popularized.

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. A seamless downshift control method for a hybrid system is characterized by comprising the following steps: the method comprises the following steps:

s4, respectively controlling the engine torque and the reverse torque according to the result of the step S3, and ensuring that the real-time difference torque between the reverse torque and the engine torque can increase the engine speed until reaching the low gear target speed at the starting moment of the stage L3;

controlling the rear end motor to output a forward torque in the stages L1, L2, L3, the absolute value of which has a course of linearly increasing 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 a hybrid system according to claim 1, characterized in that: in step S3, when the absolute value of the limit torque of the front end motor is larger than the high range torque of the engine, the engine torque is controlled to be decreased to the low range target torque until the end of the stage L3.

3. The seamless downshift control method of a hybrid system according to claim 2, 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.

4. The seamless downshift control method of a hybrid system according to claim 3, 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.

5. The seamless downshift control method of a hybrid system according to claim 4, 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.

6. The seamless downshift control method of a hybrid system according to claim 2, 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.

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

8. The seamless downshift control method of a hybrid system according to claim 2, characterized in that: the method specifically comprises the following steps:

9. The seamless downshift control method of a hybrid system according to claim 1, characterized in that: in step S3, when the absolute value of the limit torque of the front end motor is smaller than the high range torque of the engine and larger than the low range target torque after the downshift, the engine torque is controlled to decrease from the high range torque to the low range target torque after the downshift in the stage L1, and the reverse torque is controlled to increase until the absolute value of the reverse torque is equal to the absolute value of the engine torque at the end of the stage L1; the reverse torque is controlled to be small in the stage L2 so that the difference torque between the reverse torque and the engine torque is enough to raise the engine speed in the stage L2 until the low gear target speed is reached at the start of the stage L3, and the engine torque is controlled to maintain the low gear target torque and continue to be output in the stages L2, L3, and L4.

10. The seamless downshift control method of a hybrid system according to claim 9, characterized in that: the phase L1 is divided into two parts L11 and L12 in time sequence, the time point between the two parts is a time point a, the duration of the phase L11 is the time when the reverse torque is linearly increased from the starting time of the phase L1 to the negative value of the low gear target torque after the engine downshift, and the time point a is the starting point of controlling the engine torque to be decreased from the high gear torque to the low gear target torque after the downshift.

11. The seamless downshift control method of a hybrid system according to claim 9, characterized in that: in the stage L12, the front end motor is controlled to provide the reverse torque of a stable magnitude, which is equal in absolute value to the magnitude of the low range target torque after the engine downshift.

12. The seamless downshift control method of a hybrid system according to claim 11, 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.

13. The seamless downshift control method of a hybrid system according to claim 12, characterized in that: in the stage L12, the engine torque is controlled to linearly decrease from the high gear torque to the low gear target torque after the downshift.

14. The seamless downshift control method of a hybrid system according to claim 9, characterized in that: in the phase L3, the front end motor is controlled to provide the reverse torque, the absolute value of which has a linearly decreasing course, until the end of the phase L3 the reverse torque is zero.

15. The seamless downshift control method of a hybrid system according to claim 14, wherein: in the phase L2, the "process in which the forward torque has a stable output" specifically includes,

16. The seamless downshift control method of a hybrid system according to claim 9, characterized in that: the method specifically comprises the following steps:

17. The seamless downshift control method of a hybrid system according to claim 1, characterized in that: in step S3, when the absolute value of the limit torque of the front end motor is smaller than the target low-range torque of the engine, the engine torque is controlled to decrease from the high-range torque to the transitional torque in the stage L1 so that the difference torque between the reverse torque and the transitional torque is sufficient to increase the engine speed in the stage L2 until the target low-range speed is reached at the beginning of the stage L3, and the engine torque is controlled to increase from the transitional torque to the target low-range torque in the stage L3.

18. The seamless downshift control method of a hybrid system according to claim 17, wherein: the phase L1 is divided into two parts L11 and L12 in time sequence, the time point between the two parts is a time point a, the duration of the phase L11 is the time when the reverse torque increases linearly from the starting time of the phase 1 to the negative value of the transition torque, and the time point a is the starting point of controlling the engine torque to decrease from the high gear torque to the transition torque.

19. The seamless downshift control method of a hybrid system according to claim 18, wherein: the phase L3 is divided into two parts L31 and L32 in time sequence, the time point between the two parts is a time point b, the duration of the phase L31 is the time when the reverse torque is linearly reduced from the starting time of the phase L3 to zero, and the time point b is the starting point of controlling the engine torque to increase from the transitional torque to the low gear target torque.

20. The seamless downshift control method of a hybrid system according to claim 17 or 18, wherein: in the stage L1, the front end motor is controlled to provide the reverse torque, the absolute value of which has a course of linear increase in the stage L11, the reverse torque being equal to the negative value of the transition torque by the time point a; in a phase L12 from the time point a until the end of the phase L1, the engine torque is controlled to linearly decrease from the high gear torque to a transient torque, and the reverse torque is kept in a stable output with an absolute value equal to that of the transient torque.

21. The seamless downshift control method of a hybrid system according to claim 20, wherein: 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, and the engine torque is controlled to maintain the transient torque and stabilize the output.

22. The seamless downshift control method of a hybrid system according to claim 21, wherein: in the phase L2, the "process in which the forward torque has a stable output" specifically includes,

23. The seamless downshift control method of a hybrid system according to claim 17, wherein: the method specifically comprises the following steps:

s34, in a stage L2, controlling the engine torque to maintain a transition torque, controlling the absolute value of the limit torque of the front end motor to be smaller than the low 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, and reducing the engine speed until reaching the high gear target speed at the starting moment of the stage L3, wherein the absolute value of the reverse torque is always larger than the absolute value of the engine torque; 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;