CN113548051B

CN113548051B - Method for adjusting output torque between driving axles of vehicle, system and control equipment thereof

Info

Publication number: CN113548051B
Application number: CN202010305753.9A
Authority: CN
Inventors: 张进; 梅兴泰; 周伟
Original assignee: Guangzhou Automobile Group Co Ltd
Current assignee: Guangzhou Automobile Group Co Ltd
Priority date: 2020-04-17
Filing date: 2020-04-17
Publication date: 2024-07-12
Anticipated expiration: 2040-04-17
Also published as: CN113548051A

Abstract

The invention relates to a method for adjusting output torque between driving shafts of a vehicle, a system and control equipment thereof, wherein the method comprises the following steps: periodically obtaining the driving style of the vehicle according to the speed and the longitudinal acceleration of the vehicle, wherein the driving style is represented by numerical values; periodically calculating front and rear axle tire forces of the current period of the vehicle according to a preset vehicle model and the relation between the longitudinal force of the front axle tire and the longitudinal force of the rear axle tire when the vehicle starts four-wheel drive control, and determining the safety boundaries of the front and rear axle tire forces according to the front and rear axle tire forces; and determining a corresponding safety boundary threshold according to the driving style of the current period, comparing the safety boundaries of the front axle tire and the rear axle tire of the current period with the safety boundary threshold respectively, and determining whether to start a four-wheel drive control system to carry out drive control according to a comparison result so as to adjust the output torque between the driving axles. By implementing the invention, the output torque between the driving shafts can be adjusted according to the driving style of the driver.

Description

Method for adjusting output torque between driving axles of vehicle, system and control equipment thereof

Technical Field

The invention relates to the technical field of vehicle engine control, in particular to a method for adjusting output torque between driving shafts of a vehicle, a system and control equipment thereof.

Background

The existing non-full-time four-wheel drive control system has certain limitation, and is mainly characterized in that a control mode is single (for example, a fixed inter-axle torque distribution is adopted) or manual adjustment is required by a driver (for example, multiple driving modes correspond to multiple inter-axle torque distribution, but the driver is required to manually adjust by setting the driving modes).

Different drivers have different demands on insufficient or excessive steering characteristics of the vehicle under different working conditions, and one fixed or multiple steering characteristic adjustment modes which need manual selection often have difficulty in coping with the use demands under different road conditions. While a professional driver can adjust the center of mass by acceleration and deceleration control, changing the vertical load of each drive wheel adjusts the lateral stiffness of each wheel, and thus adjusts the steering characteristics of the vehicle, this requires familiarity with the dynamics of the vehicle and sufficient experience and operational skill, which is not so severe for a typical driver.

The four-wheel drive control system of the vehicle almost simultaneously generates the steering characteristic of the vehicle and the adjustment of the lateral safety boundary of the vehicle by adjusting the output torque between driving shafts, but the conventional four-wheel drive control system of the vehicle is usually calibrated for meeting the requirement of the lateral safety boundary of the vehicle. Therefore, the lateral boundary of the vehicle is met, and when the vehicle has the steering characteristic adjustment requirement, the four-wheel drive control system of the vehicle cannot be intervened, so that the control requirement of a driver in driving a curve cannot be fully met; further, the steering characteristic of the vehicle is not adjusted according to the style of the driver, thereby reducing the driving pleasure and improving the operation load.

Disclosure of Invention

The invention aims to provide a method and a system for adjusting output torque between driving shafts of a vehicle, control equipment and the vehicle, so as to adjust the output torque between the driving shafts according to the driving style of a driver.

An embodiment of the present invention provides a method for adjusting an output torque between driving axles of a vehicle, the method including:

periodically obtaining the driving style of the vehicle according to the speed and the longitudinal acceleration of the vehicle, wherein the driving style is represented by numerical values;

periodically calculating front and rear axle tire forces of the current period of the vehicle according to a preset vehicle model and the relation between the longitudinal force of the front axle tire and the longitudinal force of the rear axle tire when the vehicle starts four-wheel drive control, and determining the safety boundaries of the front and rear axle tire forces according to the front and rear axle tire forces;

And determining a corresponding safety boundary threshold according to the driving style of the current period, comparing the safety boundaries of the front axle tire and the rear axle tire of the current period with the safety boundary threshold respectively, and determining whether to start a four-wheel drive control system to carry out drive control according to a comparison result so as to adjust the output torque between the driving axles.

An embodiment of the present invention further provides a system for adjusting output torque between driving axles of a vehicle, the system including:

a driving style determination unit for periodically obtaining a driving style of the vehicle according to a speed and a longitudinal acceleration of the vehicle, the driving style being represented by a numerical value;

The safety boundary calculating unit is used for periodically calculating the front axle tire force and the rear axle tire force of the current period of the vehicle according to a preset vehicle model and the relation between the longitudinal force of the front axle tire and the longitudinal force of the rear axle tire when the vehicle starts four-wheel drive control, and determining the safety boundary of the front axle tire force and the rear axle tire force according to the front axle tire force and the rear axle tire force; and

And the driving moment adjusting unit is used for determining a corresponding safety boundary threshold according to the driving style of the current period, comparing the safety boundaries of the front axle tire and the rear axle tire of the current period with the safety boundary threshold respectively, and determining whether to start the four-wheel drive control system to carry out driving control according to the comparison result so as to adjust the output moment between the driving axles.

An embodiment of the present invention further provides a control device, which is a system for adjusting output torque between driving axles of a vehicle according to the above embodiment; or a memory and a processor, the memory having stored therein computer readable instructions that, when executed by the processor, cause the processor to perform the steps of the method for adjusting output torque between vehicle drive axles according to the above-described embodiments.

The embodiment scheme has the following beneficial effects:

Aiming at the limitation of a driving axle torque distribution adjustment mode of the existing vehicle four-wheel drive control system, the technical scheme for adjusting the output torque between the driving axles of the vehicle based on driving style identification is provided, the driving style of the identified driver can be periodically utilized, the safety boundary of the front axle tire longitudinal force and the rear axle tire longitudinal force obtained by calculating the relation between the front axle tire longitudinal force and the rear axle tire longitudinal force when the vehicle starts four-wheel drive control according to a preset vehicle model is combined, and the driving style-corresponding driving axle torque adjustment strategy is adopted, so that different types of drivers can obtain better driving experience under respective styles, the vehicle can be kept in a stable state range, the requirements of different types of drivers can be further met, the driving interest of curve driving is improved, and the operation load is reduced.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a flow chart of a method for adjusting output torque between driving axles of a vehicle according to an embodiment of the invention.

FIG. 2 is a block diagram of a system for adjusting output torque between drive axles of a vehicle in accordance with another embodiment of the present invention.

Detailed Description

Various exemplary embodiments, features and aspects of the disclosure will be described in detail below with reference to the drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Although various aspects of the embodiments are illustrated in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

In addition, numerous specific details are set forth in the following examples in order to provide a better illustration of the invention. It will be understood by those skilled in the art that the present invention may be practiced without some of these specific details. In some instances, well known means have not been described in detail in order to not obscure the present invention.

An embodiment of the invention provides a method for adjusting output torque between driving shafts of a vehicle, which is suitable for a non-full-time four-wheel-drive vehicle, wherein the non-full-time four-wheel-drive vehicle generally adopts front shaft driving (a main driving shaft is a front shaft), and when a four-wheel-drive control system is needed to be interposed due to poor road surface passing performance or vehicle stability change, the vehicle adopts front and rear shafts to drive simultaneously (a secondary driving shaft is a rear shaft).

Referring to fig. 1, the method includes the following steps S101 to S103:

S101, periodically obtaining the driving style of the vehicle according to the speed and the longitudinal acceleration of the vehicle, wherein the driving style is represented by numerical values;

Specifically, the real-time identification of the driving style is a precondition for the adjustment of the dynamic response of the vehicle, and various methods for acquiring the driving style in real time exist at present. In general, the more robust the style of driver, the more consistent it is to control the dynamics of the vehicle. For example, when driving in a straight line, the vehicle speed controlled by a steady driver changes slowly, the acceleration change is smaller, and the posture of the vehicle body caused by the acceleration change is smaller. And the more aggressive the style of driver, the more discrete it tends to control the dynamics of the vehicle. For example, when driving in a straight line, the speed of the vehicle controlled by the aggressive driver changes rapidly, and the vehicle is usually driven at a high speed, but is limited by road conditions, such as speed limit, other traffic participants and the like, frequent acceleration and deceleration are often required, so that the acceleration change is large, and the vehicle body posture is also large in shaking. Therefore, the acceleration change can be obtained according to the speed and the longitudinal acceleration in the running process of the vehicle, and the current driving style is determined to be in a biased state or in a biased state according to the acceleration change.

In this embodiment, any driving style method may be used for recognition, and therefore, the driving style recognition means is not specifically limited in this embodiment.

It can be understood that the step of identifying the driving style is periodically performed, that is, the driving style is continuously updated according to the driving condition of the driver in the whole driving process, so as to more truly and accurately represent the driving style of the driver.

Step S102, periodically calculating the front axle tire force and the rear axle tire force of the current period of the vehicle according to a preset vehicle model and the relation between the longitudinal force of the front axle tire and the longitudinal force of the rear axle tire when the vehicle starts four-wheel drive control, and determining the safety boundaries of the front axle tire force and the rear axle tire force according to the front axle tire force and the rear axle tire force;

Specifically, according to a preset vehicle model, a corresponding vehicle motion differential equation can be determined, the vehicle motion differential equation represents the relationship among parameters such as front axle tire force, rear axle tire force, front wheel rotation angle, vehicle acceleration, yaw acceleration, vehicle mass, vehicle moment of inertia and the like of the vehicle, so that based on the relationship between the front axle tire longitudinal force and the rear axle tire longitudinal force when the vehicle starts four-wheel drive control, the front axle tire force and the rear axle tire force of the vehicle can be calculated by acquiring other dynamic parameters such as the front wheel rotation angle and the like of the vehicle in real time, and further, the safety boundaries of the corresponding front axle tire force and the corresponding rear axle tire force can be determined according to the front axle tire force and the rear axle tire force.

Step S103, determining a corresponding safety boundary threshold according to the driving style of the current period, comparing the safety boundaries of the front axle tire and the rear axle tire of the current period with the safety boundary threshold respectively, and determining whether to start a four-wheel drive control system to carry out drive control according to the comparison result so as to adjust the output torque between the driving axles.

Specifically, the safety boundary threshold corresponds to a driving style, and can be calibrated in advance through a real vehicle test.

Aiming at the limitation of a driving axle torque distribution adjustment mode of the existing vehicle four-wheel drive control system, the embodiment provides a vehicle driving axle output torque adjustment technical scheme based on driving style identification, can periodically meet the requirements of different types of drivers according to the driving style of the identified drivers, combines the safety boundaries of the front axle tire longitudinal force and the rear axle tire longitudinal force calculated according to the preset vehicle model and the relation between the front axle tire longitudinal force and the rear axle tire longitudinal force when the vehicle starts four-wheel drive control, adopts a driving axle torque adjustment strategy corresponding to the driving style, ensures that different types of drivers can obtain better driving experience under respective styles, can keep the vehicles in a stable state range, can further meet the requirements of different types of drivers, improves the driving interest of curve driving and reduces the operation load

In one embodiment, the step S101 specifically includes:

Step S201, acquiring the speed and the longitudinal acceleration of the vehicle every other preset time, and acquiring the dispersion of the acceleration change in the current time period according to all the speed and the longitudinal acceleration acquired in the current time period; the current time period is a time period from the current acquisition time to the current acquisition time, and the length delta of the time period is preset;

Specifically, the time period length delta for identifying the driving style is taken as a statistical sliding window length, the statistical sliding window slides forwards on a time axis, which is equivalent to the step of sliding the sliding window forwards for a preset time t ₀, the speed and the longitudinal acceleration of the vehicle once are collected, and the acceleration change of the vehicle can be determined according to the speed and the longitudinal acceleration, so that the vehicle acceleration change in the statistical sliding window is counted, and the dispersion of the acceleration change in the current time period can be obtained by carrying out dispersion calculation.

Step S202, respectively comparing the dispersion of the acceleration change in the current time period with a plurality of preset thresholds, and taking the threshold corresponding to the minimum comparison deviation as a driving style recognition result at the current acquisition moment;

Specifically, the output value of the driving style recognition result in the step is a numerical value in the range of [ -1,1], and the closer the numerical value is to 1, the more the recognized driver style is excited; the closer the value is to-1, the more robust the identified driver style is explained. In the embodiment, a plurality of thresholds are preset, for example,: -1, -0.9, -0.8 … … are incremented to 1 all the time by increments of 0.1, i.e. there are 21 thresholds, and when the dispersion of the identified acceleration change is 0.71, its comparison deviation with the threshold value 0.7 is minimal, so that the driving style identification result is output as 0.7.

Step S203, driving style recognition results of all the acquisition moments in the current time period are obtained, and the current driving style is obtained according to the driving style recognition results of all the acquisition moments in the current time period.

Specifically, as can be seen from steps S201 to S202, the output value of the driving style recognition result is updated once every preset time t ₀, and then the current driving style of the driver is continuously recognized and updated, and the number of the output values of the driving style recognition result in the time period δ is n ₁,n₁＝δ/t₀; that is, in step S203, the current driving style may be obtained by performing statistical analysis according to the n ₁ driving style recognition results in the current time period.

In one embodiment, the step S203 specifically includes:

Step S301, obtaining a transient driving style recognition result and a steady driving style recognition result of the current time period according to driving style recognition results of all acquisition moments in the current time period;

Specifically, the transient driving style recognition result is used for indicating the transient driving style of the driver in a short time, and mainly reflects the current driving condition or scene change; the steady state driving style recognition results are used to indicate the driver's individual long-term driving style, i.e., the inherent driving tendencies.

Step S302, determining a current driving style m _driver according to a comparison result of a deviation absolute value of a steady driving style recognition result and a transient driving style recognition result in a current time period and a preset threshold; wherein, m _driver is represented by a numerical value, the larger m _driver is, the more aggressive the driving style is, and the smaller m _driver is, the more robust the driving style is.

In a specific embodiment, the transient driving style identification result includes a transient driving style average value m ₀, and the steady driving style identification result includes a steady driving style average value m ₁;

The calculation step of the transient driving style average value m ₀ is as follows:

Setting the current time period as a kth time period, calculating the average value of driving style identification results of all acquisition moments in the current time period, and taking the average value as a transient driving style average value m _1(k) in the current time period;

The calculation step of the steady driving style average value m ₀ is as follows:

Calculating a steady driving style accumulated value m _0(k) of the current time period according to the transient driving style average value m _1(k) of the current time period; where m _0(k)＝α₀×m_1(k)+(1-α₀)×m_0(k-1),m₀₍₀₎＝m₀₍₁₎＝0,α₀ is a weight coefficient, 0< α ₀ <1.

Specifically, the weight coefficient alpha ₀ is set according to the characteristics of the vehicle type and the target driving group, and if the vehicle type is in a partial motion style, alpha ₀ is larger; if the vehicle model itself is in a commercial style, α ₀ is smaller, and typically α ₀ =0.5.

In a specific embodiment, determining the current driving style m _driver according to a comparison result of a deviation absolute value of a steady driving style recognition result and a transient driving style recognition result in the current time period and a preset threshold value specifically includes:

If the absolute value of the deviation of the steady driving style accumulated value m ₀ of the current time period and the transient driving style average value m ₁ is smaller than the set threshold value m _th1, the current driving style m _driver is m ₀;

If the absolute value of the deviation between the steady driving style accumulated value m ₀ and the transient driving style average value m ₁ in the current time period is greater than the set threshold value m _th1 and less than the set threshold value m _th2, the current driving style m _driver is (m ₁+m₀)/2;

If the absolute value of the deviation of the steady driving style accumulated value m ₀ of the current time period and the transient driving style average value m ₁ is larger than the set threshold value m _th2, the current driving style m _driver is m ₁.

In a specific embodiment, the transient driving style identification result further includes a transient driving style standard deviation v ₁, and the steady driving style identification result further includes a steady driving style standard deviation v ₀;

the calculation steps of the transient driving style standard deviation v ₁ are as follows:

Setting the current time period as a kth time period, calculating standard deviation of driving style identification results of all acquisition moments in the current time period, and taking the standard deviation as transient driving style standard deviation v _1(k) of the current time period;

the calculation steps of the steady driving style standard deviation v ₀ are as follows:

Forming a numerical matrix [ m _0(k),m_0(k-1),…,m_0(k-n0) ] according to the current time period and the accumulated values of the steady driving styles of the previous n ₀ time periods, and obtaining the standard deviation of the numerical matrix as the steady driving style standard deviation v _0(k) of the current time period;

The step S302 further includes:

Judging whether the vehicle meets the following conditions (1) - (3) at the same time according to the transient driving style and the steady driving style in the current time period;

If the conditions (1) - (3) are satisfied at the same time, executing a step of determining the current driving style m _driver according to a comparison result of a deviation absolute value of a steady driving style recognition result and a transient driving style recognition result in the current time period and a preset threshold;

If the conditions (1) - (3) are not satisfied at the same time, the step of determining the current driving style m _driver according to the comparison result of the absolute value of the deviation of the steady driving style recognition result and the transient driving style recognition result in the current time period and the preset threshold value is not executed;

wherein the conditions (1) - (3) are specifically as follows:

Condition (1): the number of times of the identified transient or steady driving style meeting the preset typical working condition is accumulated to be more than or equal to n _t1;

Condition (2): the vector standard deviation formed by n _m1 steady driving style accumulated values m ₀ corresponding to n _m1 time periods is less than or equal to m _t1;

Condition (1): the 80 percentile value of a vector formed by n _v1 steady driving style standard deviations v ₀ corresponding to n _v1 time periods is less than or equal to v _t1;

Wherein n _t1、n_m1、m_t1、n_v1、v_t1 is a preset value.

Specifically, the step S101 is divided into two stages, wherein the first stage includes transient acquisition of the driving style recognition result and steady driving style recognition result, and the end condition of the first stage is that the above 3 conditions are simultaneously satisfied. When the above 3 conditions are satisfied simultaneously, the corresponding current vehicle driving distance is a driving distance threshold L ₁, and when the vehicle driving distance L > the driving distance threshold L ₁, the second stage of step S101 is entered, that is, the current driving style m _driver is determined according to the comparison result of the deviation absolute value of the steady driving style recognition result and the transient driving style recognition result in the current time period and the preset threshold.

More specifically, the first stage of step S101 is mainly set in consideration of that in a shorter driving range, less judgment event triggers for driving style recognition are generated, a stable and significant statistical characteristic cannot be formed by a driving style recognition sample, more sporadic factors can cause more jump of a steady driving style recognition result, and at this time, if the vehicle acceleration is directly adjusted according to the steady driving style recognition result, frequent changes of steering characteristics and stability of the vehicle are caused by the jump of the acceleration, so that discomfort of drivers and passengers is caused. The second stage of step S101 is entered after the recognition samples of the driving style are sufficiently large and tend to stabilize. The condition (1) is used for judging whether the number of samples meets the requirement of statistical calculation; the condition (2) is used for judging whether the statistical result is stable; and (3) the condition is used for judging the credibility requirement of the statistical result. In the first stage of step S101, the current driving style m _driver is 0.

The style of the driver in the second stage of step S101 has tended to be stable, i.e. the larger m ₀ is, the driver is the driver who is inherently biased toward aggressive driving style, and the smaller m ₀ is, the driver is the driver who is inherently biased toward robust driving style; if the average value m ₁ of the transient driving style recognition results deviates greatly from the accumulated value m ₀ of the steady driving style recognition results at this time, it is indicated that the driver is desirous of temporarily changing the driving style when deviating from the past relatively steady driving style, such as occasional aggressive driving or overtaking acceleration, or may be caused by working conditions, so that the driver needs to temporarily change the driving style, such as having to perform robust driving in a congestion state, and after the deviation is greater than a threshold value, the weight of the transient driving style recognition results is increased to correspond to the temporary driving style change situation of the driver.

In one embodiment, the step S102 specifically includes:

Step S401, periodically sampling and obtaining front wheel rotation angle, longitudinal acceleration, lateral acceleration and yaw acceleration of the vehicle;

Step S402, calculating longitudinal force and lateral force of the front and rear axle tires according to the front wheel corner, longitudinal acceleration, lateral acceleration, yaw acceleration, linear three-degree-of-freedom vehicle motion differential equation and the relation between the longitudinal force of the front axle tire and the longitudinal force of the rear axle tire of the vehicle;

Specifically, the fineness and the complexity of the vehicle tire force estimation are comprehensively considered, and the vehicle front and rear axle tire force is estimated by adopting a linear three-degree-of-freedom vehicle model. The three degrees of freedom are longitudinal movement of the vehicle along the vehicle x-axis, lateral movement along the vehicle y-axis, and yaw movement about the vehicle z-axis, respectively.

Step S403, calculating the vertical forces of the front and rear axle tires according to the longitudinal forces and the lateral forces of the front and rear axle tires;

and step S404, calculating the safety boundaries of the front axle tire force and the rear axle tire force according to the vertical forces of the front axle tire and the rear axle tire.

Through the above steps S401 to S404, the safety margin of the corresponding front and rear axle tire forces can be obtained in each cycle.

In a specific embodiment, the linear three-degree-of-freedom vehicle motion differential equation is shown as follows:

Wherein F _{x_f}、F_{x_r}、F_{y_f}、F_{y_r} is the longitudinal force of the front axle tire, the longitudinal force of the rear axle tire, the lateral force of the front axle tire and the lateral force of the rear axle tire, l _f and l _r are the distance from the center of mass of the vehicle to the front axle and the distance from the center of mass of the vehicle to the rear axle, θ is the front wheel rotation angle, a _x is the acceleration along the x axis of the vehicle at the center of mass of the vehicle, a _y is the acceleration along the y axis of the vehicle at the center of mass of the vehicle, The yaw acceleration of the vehicle, m is the vehicle mass, and I _z is the moment of inertia of the vehicle around the z-axis;

the relation between the longitudinal force of the front axle tire and the longitudinal force of the rear axle tire of the vehicle is shown in the following expression:

F_{x_f}·i_{d_r}-F_{x_r}·i_{d_f}＝0 (2)

wherein i _{d_f} and i _{d_r} are the percentages of the front axle and rear axle drive torque to the total drive torque, respectively; for example, when the front-rear drive torque distribution of the vehicle is 70:30, i _{d_f}＝70％、i_{d_r} =30%.

In a specific embodiment, the calculation process of step S403 is specifically shown as the following expression:

Wherein, For the vertical force of the front axle tire, F _{x_f} is the longitudinal force of the front and rear axle tire, F _{y_f} is the lateral force of the rear axle tire,For the vertical force of the rear axle tire, F _{x_r} is the longitudinal force of the rear axle tire, F _{y_r} is the lateral force of the rear axle tire, and a and b are preset constants.

Specifically, from the formulas (1) and (2), the following equation set can be obtained:

AX＝Y (4)

Wherein,

The longitudinal force and the lateral force of the tire of the front axle and the rear axle can be obtained by solving and calculating the equation set (3).

According to the longitudinal vehicle front and rear wheel grounding point moment balance, an equation set can be obtained:

Wherein F _{z_f} and F _{z_r} are the vertical loads of the front axle and the rear axle, respectively, and h is the height of the mass center of the vehicle.

The tire vertical forces of the front axle and the rear axle of the vehicle can be calculated from equation set (4).

The longitudinal force, the lateral force and the vertical force of the front and rear axle tires can be calculated by the equation set (3) and the equation set (4).

According to the theory of the friction ellipse of the tire force, the maximum longitudinal force F _{x_max} and the maximum lateral force F _{y_max} which can be provided by the vehicle tire have the following relationship with the current vertical force of the tire within a certain range:

wherein a and b are proportional coefficients of friction ellipses of tire force, and are obtained by testing and calibrating according to different types of tires, patterns, inflation pressure and the like.

The vertical force used by the front and rear axle tires at the current moment is calculated by utilizing the longitudinal and lateral forces of the front axle and the longitudinal and lateral forces of the rear axle respectivelyEquation set (3) can be obtained.

In a specific embodiment, the step S404 includes:

calculating the utilization coefficients of the tire forces of the front axle and the rear axle according to the following expression:

Wherein, For the vertical force of the front axle tire,Η _f is the utilization coefficient of the tire force of the front axle, η _r is the utilization coefficient of the tire force of the rear axle;

And obtaining the safety boundaries of the front and rear axle tire forces according to the calculated utilization coefficients of the front and rear axle tire forces.

In order to ensure a certain tire force allowance to cope with emergency working conditions, the tire force utilization coefficient facing the common consumer is smaller than a set safety threshold value eta _t, and the difference eta _{t_f}、η_{t_r} between the current moment safety threshold value eta _t and the tire force utilization coefficient eta _f、η_r of the front axle and the rear axle is the safety boundary of the tire force of the front axle and the rear axle in the current vehicle state.

The greater the safety margin is, the more stable the vehicle state tends to be, the more the tire force has enough margin to cope with operation in emergency conditions; the smaller the safety margin value is, the more unstable the vehicle state tends to be, and if an emergency condition occurs at this time, the tire force has no margin available for coping with. The four-wheel drive control system of the vehicle can control the longitudinal force of the front and rear axle tires by controlling the driving moment of the front and rear axles, further adjust the vertical force utilized by the front and rear axle tires, further adjust the utilization coefficient of the tire force and further adjust the safety boundary of the front and rear axle tires.

In addition, at the time of wheel driving, as the tire driving force increases, the tire side force at the same slip angle will decrease. Therefore, when the front wheel driving force is increased, the slip angle of the front wheels must be increased in order to provide the required lateral force, which would cause the vehicle to have a tendency to increase understeer; when the rear wheel driving force increases, the slip angle of the rear wheel must increase in order to provide the required slip force, which will cause the vehicle to have a tendency to increase in oversteer.

Thus, the steering characteristics of the vehicle and the vehicle lateral safety margin can be adjusted by controlling the drive torque ratio of the front and rear drive shafts (adjusting the vehicle four-wheel drive control system). The safety threshold η _t and the adjustment amount of the vehicle steering characteristic can be adjusted according to different driving styles.

In one embodiment, the step S103 specifically includes:

step S501, determining a safety boundary threshold corresponding to the driving style according to the driving style of the current period;

Step S502, comparing the front and rear axle tire safety boundaries of the current period and the front and rear axle tire safety boundaries of the previous period with the safety boundary threshold values respectively, and determining a state value Af_flag of the front axle tire safety boundary and a state value Ar_flag of the rear axle tire safety boundary according to the comparison result; the state values af_flag and ar_flag are 0 or 1, when the state values af_flag and ar_flag are 1, the corresponding safety boundaries are lower, and when the state values af_flag and ar_flag are 0, the corresponding safety boundaries are higher;

and step S503, determining a corresponding moment adjustment strategy according to the state values Af_flag and Ar_flag, and adjusting the output moment between the driving shafts according to the moment adjustment strategy.

In a specific embodiment, the safety boundary threshold comprises Af_th1、Af_th2、Ar_th1、Ar_th2,Af_th1<0<Af_th2,Ar_th1<0<Ar_th2;

In this embodiment, the step S502 specifically includes:

The initial value of Af_flag is 0; if the safety boundary eta _{t_f} of the previous cycle front axle tire is smaller than the threshold value Af _th2 and the safety boundary eta _{t_f} of the current cycle front axle tire is larger than the threshold value Af _th2, setting Af_flag to 0; if the safety boundary eta _{t_f} of the previous cycle front axle tire is larger than the threshold value Af _th1 and the safety boundary eta _{t_f} of the current cycle front axle tire is smaller than the threshold value Af _th1, setting Af_flag to 1; otherwise, the value of the Af_flag in the last period is kept unchanged;

The initial value of Ar_flag is 0; if the previous cycle front axle tire safety boundary eta _{t_r} is smaller than the threshold Ar _th2 and the current cycle front axle tire safety boundary eta _{t_r} is larger than the threshold Ar _th2, setting Ar_flag to 0; if the previous cycle front axle tire safety boundary eta _{t_r} is greater than the threshold Ar _th1 and the current cycle front axle tire safety boundary eta _{t_r} is less than the threshold Ar _th1, setting Ar_flag to 1; otherwise, ar_flag keeps the value of the previous cycle unchanged.

In a specific embodiment, the step S501 specifically includes:

Af_th1＝-x1×m_driver–x2

Ar_th1＝-x1×m_driver–x2

Wherein m _driver is driving style, and x1, x2, and Af _th2、Ar_th2 are preset constant values.

Specifically, the value of Af _th2 can be calibrated to be 5%, the value of Af _th1 is calibrated according to different driving styles, and in general, the more aggressive the driving style is, the smaller the value of Afth1 is, so as to allow an aggressive driver to fully squeeze the adhesive force potential of the tire; the more robust the driving style, the greater the value of Af _th1, enabling the four-wheel drive control system to intervene as soon as possible to guarantee vehicle stability.

Taking a certain vehicle model as an example, the safety threshold η _t of the front axle tire force utilization coefficient is set to be 60%, and according to the recognition result of the driving style, m _driver, x1 and x2 are preferably but not limited to 0.1, and the following formula is calculated as Af _th1:

Af_th1＝-0.1m_driver-0.1 (8)

for example, the recognition result of the driving style is output m _driver＝1,Af_th1 = -20% (the utilization coefficient η _f =80% of the tire force corresponding to the front axle); if the driving style is recognized, m _driver＝-1,Af_th1 =0 (the utilization coefficient η _f =60% of the tire force corresponding to the front axle) is outputted.

The value of Ar _th2 can be calibrated to be 5%, the value of Ar _th1 is respectively calibrated according to different driving styles, and similar to the calibration method of Af _th1, x1 and x2 are preferably but not limited to 0.1, and are not repeated.

In a specific embodiment, the step S503 specifically includes:

If af_flag=0 and ar_flag=0, the safety boundaries of the front and rear axle tires are high, and the control purpose of the four-wheel drive control system is mainly to change the steering characteristics of the vehicle, so that the vehicle meets the driving requirements of drivers in different styles. Since the transfer of the driving torque from the front wheels to the rear wheels will increase the excessive steering tendency of the vehicle, in this case a first adjustment strategy is adopted, namely: detecting the yaw rate of the vehicle and the steering wheel turning speed in real time, starting a four-wheel drive control system to intervene and continuously control when the ratio of the yaw rate to the steering wheel turning speed is detected to be lower than a threshold kappa _th1 at a certain speed, increasing the excessive steering trend of the vehicle (namely, increasing the ratio of the yaw rate to the steering wheel turning speed of the vehicle) until the ratio of the yaw rate to the steering wheel turning speed of the vehicle is higher than a threshold kappa _th2 at a certain speed, and exiting the four-wheel drive control system; or when the values of the Af_flag and the Ar_flag are changed, adjusting according to a strategy corresponding to the change of the values of the Af_flag and the Ar_flag.

If af_flag=1 and ar_flag=0, the safety margin of the front axle tire is lower and the safety margin of the rear axle tire is higher, at this time, the control purpose of the four-wheel drive control system is mainly to change the safety margin of the front and rear axles of the vehicle, and transfer the driving torque of the front axle to the rear axle according to a fixed proportion, so as to reduce the longitudinal force of the front axle tire and further reduce the tire utilization coefficient of the front axle. The driving torque adjustment of the four-wheel drive control system in the situation does not consider the steering characteristic change of the vehicle, such as the steering characteristic change of the vehicle to an abnormal condition, and the dynamic control system of the vehicle such as ESC intervenes to perform forced intervention. Thus, in this case, a second adjustment strategy is employed, namely: the four-wheel drive control system continuously controls to adjust the driving torque of the front and rear shafts until the af_flag=0 or ar_flag=1 four-wheel drive control system exits.

If af_flag=0 and ar_flag=1, the safety margin of the front axle tire is higher and the safety margin of the rear axle tire is lower, which usually occurs in dangerous working conditions such as tail flick of the vehicle, the four-wheel drive control system should be immediately turned off, and the driving torque of the rear axle should be returned to the front axle, so as to improve the tire force safety margin of the rear axle, in which case a third adjustment strategy is adopted, namely: and immediately closing the four-wheel drive control system, and stopping adjusting the driving moment of the front shaft and the rear shaft.

If af_flag=1 and ar_flag=1, the safety margin of the front and rear axle tires is low, which is generally the case for lateral movements of the vehicle on low adhesion roadways, a fourth adjustment strategy is adopted, namely: the control strategy of the four-wheel drive control system of the last sampling period is kept unchanged, and the vehicle is prevented from being out of control due to sudden changes of tire force. For example, if the four-wheel drive control system has been involved at the last time, the intervention is maintained until af_flag=0, i.e. the front wheel has a sufficient safety margin and exits the four-wheel drive control; and if the four-wheel drive control system of the previous sampling period is not intervened, the four-wheel drive control system is kept not intervened until the values of the Af_flag and the Ar_flag are changed, and the adjustment is carried out according to a strategy corresponding to the values of the Af_flag and the Ar_flag.

In particular, the method of the embodiment is suitable for the situation that the vehicle has lateral movement and the four-wheel drive system is needed to intervene to change the steering characteristic or stability of the vehicle. The torque distribution between the shafts is fixed, the ratio of the driving torque output by the four-wheel drive control system to the rear shaft and the driving torque of the front shaft is fixed, and when the rear shaft is required to be driven, part of the driving torque is output to the rear shaft from the front shaft by the combination of the clutch through the combination or disconnection of the clutch; when rear axle drive is not required, the clutch is disengaged so that the rear axle becomes a non-drive axle. In a non-full-time four-wheel drive vehicle with variable-proportion adjustment of torque distribution among shafts, the proportion of the driving torque output by a four-wheel drive control system to the driving torque of a rear shaft and the driving torque of a front shaft is variable, and the proportion of the driving torque is adjusted through the slip ratio of a clutch, but the temperature of the clutch of the four-wheel drive control system is quickly increased by the adjustment mode to cause overheat protection, and more clutches are adopted to output torque in a combined and disconnected mode. Therefore, the present embodiment adjusts the duration of the output torque of the four-wheel drive control system by controlling the duration of the clutch engagement, specifically according to the above step S503.

In a specific embodiment, the step S503 specifically further includes:

Determining corresponding thresholds kappa _th1 and kappa _th2 according to the driving style of the current period; wherein, the more aggressive the driving style, the lower the values of the thresholds κ _th1 and κ _th2, the more robust the driving style, and the higher the values of the thresholds κ _th1 and κ _th2.

As shown in fig. 2, an embodiment of the present invention further proposes a system for adjusting output torque between driving axles of a vehicle, for performing the steps of the method of the above embodiment, the system comprising:

a driving style determination unit 1 for periodically obtaining a driving style of the vehicle based on a speed and a longitudinal acceleration of the vehicle, the driving style being represented by a numerical value;

A safety boundary calculating unit 2, configured to calculate the front axle tire force and the rear axle tire force of the current cycle of the vehicle periodically according to a preset vehicle model, and a relationship between the front axle tire longitudinal force and the rear axle tire longitudinal force when the vehicle starts four-wheel drive control, and determine the safety boundaries of the front axle tire force and the rear axle tire force according to the front axle tire force and the rear axle tire force; and

And the driving moment adjusting unit 3 is used for determining a corresponding safety boundary threshold according to the driving style of the current period, comparing the safety boundaries of the front axle tire and the rear axle tire of the current period with the safety boundary threshold respectively, and determining whether to start a four-wheel drive control system to carry out driving control according to the comparison result so as to adjust the output moment between the driving axles.

The system embodiments described above are merely illustrative, wherein the elements illustrated as separate elements may or may not be physically separate, and the elements shown as elements may or may not be physical elements, may be located in one place, or may be distributed over a plurality of network elements. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

It should be noted that, the system in the foregoing embodiment corresponds to the method in the foregoing embodiment, and therefore, a portion of the system in the foregoing embodiment that is not described in detail may be obtained by referring to the content of the method in the foregoing embodiment, which is not described herein. It will be understood that the content of the steps of the method described in the foregoing embodiment is the function of the system of this embodiment.

Also, the inter-vehicle drive axle output torque adjustment system of the above-described embodiment may be stored in a computer-readable storage medium if implemented in the form of a software functional unit and sold or used as a separate product.

In a further embodiment of the present invention, a control apparatus is provided for controlling the system for adjusting the output torque between driving axles of a vehicle according to the above embodiment; or a memory and a processor, the memory having stored therein computer readable instructions that, when executed by the processor, cause the processor to perform the steps of the method for adjusting output torque between vehicle drive axles according to the above-described embodiments.

Of course, the control device may also have a wired or wireless network interface, a keyboard, an input/output interface, and other components for implementing the functions of the device, which are not described herein.

The computer program may be divided into one or more units, which are stored in the memory and executed by the processor to accomplish the present invention, for example. The one or more units may be a series of computer program instruction segments capable of performing the specified functions, which instruction segments are used for describing the execution of the computer program in the control device.

The Processor may be a central processing unit (Central Processing Unit, CPU), but may also be other general purpose processors, digital processors (DIGITAL SIGNAL Processor, DSP), application SPECIFIC INTEGRATED Circuit (ASIC), off-the-shelf Programmable gate array (Field-Programmable GATE ARRAY, FPGA) or other Programmable logic device, discrete gate or transistor logic device, discrete hardware components, or the like. The general purpose processor may be a microprocessor or the processor may be any conventional processor or the like, which is a control center of the control device, connecting various parts of the entire control device using various interfaces and lines.

The memory may be used to store the computer program and/or the unit, and the processor may implement various functions of the control device by running or executing the computer program and/or the unit stored in the memory, and invoking data stored in the memory. In addition, the memory may include high-speed random access memory, and may also include non-volatile memory, such as a hard disk, memory, plug-in hard disk, smart memory card (SMART MEDIA CARD, SMC), secure Digital (SD) card, flash memory card (FLASH CARD), at least one disk storage device, flash memory device, or other volatile solid-state storage device.

The foregoing description of embodiments of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the various embodiments described. The terminology used herein was chosen in order to best explain the principles of the embodiments, the practical application, or the technical improvements in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method of adjusting an output torque between drive axles of a vehicle, the method comprising:

2. The method for adjusting the output torque between the drive shafts of the vehicle according to claim 1, wherein the driving style of the vehicle is obtained periodically from the vehicle speed and the longitudinal acceleration of the vehicle, specifically comprising:

Acquiring the speed and the longitudinal acceleration of the vehicle every other preset time, and acquiring the dispersion of the acceleration change in the current time period according to all the speed and the longitudinal acceleration acquired in the current time period; the current time period is a time period from the current acquisition time to the current acquisition time, and the length of the time period is preset;

comparing the dispersion of the acceleration change in the current time period with a plurality of preset thresholds respectively, and taking the threshold corresponding to the minimum comparison deviation as a driving style recognition result at the current acquisition moment;

and obtaining driving style identification results of all the acquisition moments in the current time period, and obtaining the current driving style according to the driving style identification results of all the acquisition moments in the current time period.

3. The method for adjusting the output torque between driving axles of the vehicle according to claim 2, wherein the current driving style is obtained according to the driving style recognition results of all the collection moments in the current time period, specifically comprising:

obtaining a transient driving style recognition result and a steady driving style recognition result of the current time period according to driving style recognition results of all the acquisition moments in the current time period;

Determining a current driving style m _driver according to a comparison result of a deviation absolute value of a steady driving style recognition result and a transient driving style recognition result in a current time period and a preset threshold; wherein, m _driver is represented by a numerical value, the larger m _driver is, the more aggressive the driving style is, and the smaller m _driver is, the more robust the driving style is.

4. A vehicle inter-drive shaft output torque adjustment method according to claim 3, characterized in that the transient driving style identification result includes a transient driving style average value m ₀, and the steady driving style identification result includes a steady driving style average value m ₁;

Wherein:

Setting the current time period as a kth time period, calculating the average value and standard deviation of driving style identification results of all acquisition moments in the current time period, and taking the average value as a transient driving style average value m _1(k) of the current time period;

Calculating a steady driving style accumulated value m _0(k) of the current time period according to the transient driving style average value m _1(k) of the current time period;

where m _0(k)＝α₀×m_1(k)+(1-α₀)×m_0(k-1),m₀₍₀₎＝0,α₀ is a weight coefficient, 0< α ₀ <1.

5. The method for adjusting the output torque between driving axles of a vehicle according to claim 4, wherein determining the current driving style m _driver according to the comparison result between the absolute value of the deviation of the steady driving style recognition result and the transient driving style recognition result in the current time period and the preset threshold value, specifically comprises:

6. The method for adjusting the output torque between the driving axles of the vehicle according to claim 4, wherein the transient driving style recognition result further includes a transient driving style standard deviation v ₁, and the steady driving style recognition result further includes a steady driving style standard deviation v ₀;

Wherein:

The step of obtaining the current driving style according to the driving style recognition results of all the acquisition moments in the current time period specifically further comprises the following steps:

If the transient driving style and the steady driving style in the current time period meet the following conditions (1) - (3) at the same time, determining the current driving style m _driver according to a comparison result of a deviation absolute value of a steady driving style recognition result and a transient driving style recognition result in the current time period and a preset threshold;

Wherein n _t1、n_m1、m_t1、n_v1、v_t1 is a preset value.

7. The method for adjusting the output torque between the driving axles of the vehicle according to claim 1, wherein the front axle tire force and the rear axle tire force of the current cycle of the vehicle are periodically calculated according to a preset vehicle model, the relation between the front axle tire longitudinal force and the rear axle tire longitudinal force when the vehicle is started to drive and control by four-wheel drive, and the safety boundaries of the front axle tire force and the rear axle tire force are determined according to the front axle tire force and the rear axle tire force, specifically comprising:

periodically sampling to obtain front wheel rotation angle, longitudinal acceleration, lateral acceleration and yaw acceleration of the vehicle;

Calculating front and rear axle tires according to the front wheel corner, the longitudinal acceleration, the lateral acceleration, the yaw angular acceleration, the linear three-degree-of-freedom vehicle motion differential equation and the relation between the longitudinal force of the front axle tire and the longitudinal force of the rear axle tire of the vehicle, so as to obtain the longitudinal force and the lateral force of the front and rear axle tires;

calculating vertical forces of the front and rear axle tires according to the longitudinal forces and the lateral forces of the front and rear axle tires;

and calculating the safety boundaries of the tire forces of the front axle and the rear axle according to the vertical forces of the front axle and the rear axle.

8. The method for adjusting the output torque between the vehicle drive shafts according to claim 7, wherein the linear three-degree-of-freedom vehicle motion differential equation is expressed as follows:

F_{x_f}·i_{d_r}-F_{x_r}·i_{d_f}＝0

Wherein i _{d_f} and i _{d_r} are the front and rear axle drive torques as a percentage of the total drive torque, respectively.

9. The method for adjusting the output torque between the drive axles of a vehicle according to claim 7, wherein the vertical forces of the front and rear axle tires are calculated based on the longitudinal forces and the lateral forces of the front and rear axle tires, as shown in the following expression:

10. The method of adjusting the output torque between the drive axles of a vehicle according to claim 7, wherein said calculating the safety margin of the tire forces of the front and rear axles from the vertical forces of the tires of the front and rear axles comprises:

11. The method for adjusting the output torque between the drive axles of the vehicle according to claim 1, wherein the method for adjusting the output torque between the drive axles of the vehicle is characterized by determining a corresponding safety boundary threshold according to the driving style of the current period, comparing the safety boundary of the front and rear axle tires of the current period with the safety boundary threshold respectively, and determining whether to enable the four-wheel drive control system to perform the drive control according to the comparison result, and specifically comprises the following steps:

determining a safety boundary threshold corresponding to the driving style according to the driving style of the current period;

comparing the front and rear axle tire safety boundaries of the current period and the front and rear axle tire safety boundaries of the previous period with the safety boundary threshold values respectively, and determining a state value Af_flag of the front axle tire safety boundary and a state value Ar_flag of the rear axle tire safety boundary according to the comparison result; the state values af_flag and ar_flag are 0 or 1, when the state values af_flag and ar_flag are 1, the corresponding safety boundaries are lower, and when the state values af_flag and ar_flag are 0, the corresponding safety boundaries are higher;

And determining a corresponding moment adjustment strategy according to the state values Af_flag and Ar_flag, and adjusting the output moment between driving shafts according to the moment adjustment strategy.

12. The method of adjusting an output torque between vehicle drive axles according to claim 11, wherein the safety margin threshold comprises Af_th1、Af_th2、Ar_th1、Ar_th2,Af_th1<0<Af_th2,Ar_th1<0<Ar_th2;

The method for determining the state value Af_flag of the front axle tire safety boundary and the state value Ar_flag of the rear axle tire safety boundary according to the comparison result specifically comprises the following steps:

13. The method for adjusting the output torque between the drive shafts of the vehicle according to claim 12, wherein the determination of the safety margin threshold corresponding to the driving style according to the driving style of the current cycle specifically includes:

Af_th1＝-x1×m_driver–x2

Ar_th1＝-x1×m_driver–x2

14. The method for adjusting the output torque between driving axles of the vehicle according to claim 12, wherein the corresponding torque adjustment strategy is determined according to the state values af_flag and ar_flag, and the output torque between driving axles is adjusted according to the torque adjustment strategy, specifically comprising:

if af_flag=0 and ar_flag=0, detecting the yaw rate of the vehicle and the steering wheel turning angle vehicle speed in real time, and when the ratio of the yaw rate to the steering wheel turning angle is lower than a threshold value kappa _th1 at a certain vehicle speed, starting the four-wheel drive control system to intervene and continuously control until the ratio of the yaw rate to the steering wheel turning angle of the vehicle is higher than a threshold value kappa _th2 at a certain vehicle speed, and exiting the four-wheel drive control system;

If Af_flag=1 and Ar_flag=0, the four-wheel drive control system continuously controls to adjust the driving torque of the front and rear shafts until the Af_flag=0 or Ar_flag=1 four-wheel drive control system exits;

If Af_flag=0 and Ar_flag=1, immediately closing the four-wheel drive control system, and stopping adjusting the driving torque of the front shaft and the rear shaft;

If af_flag=1 and ar_flag=1, the control strategy of the four-wheel drive control system in the previous period is kept unchanged.

15. The method for adjusting the output torque between driving axles of a vehicle according to claim 14, wherein a corresponding torque adjustment strategy is determined according to the state values af_flag and ar_flag, and the output torque between driving axles is adjusted according to the torque adjustment strategy, specifically further comprising:

Determining corresponding thresholds kappa _th1 and kappa _th2 according to the driving style of the current period; wherein the more aggressive the driving style, the lower the values of the thresholds κ _th1 and κ _th2, and the more robust the driving style, the higher the values of the thresholds κ _th1 and κ _th2.

16. A vehicle inter-drive-shaft output torque adjustment system for implementing the vehicle inter-drive-shaft output torque adjustment method according to any one of claims 1 to 15, characterized by comprising:

17. A control apparatus, characterized in that the vehicle inter-drive-shaft output torque adjustment system according to claim 16; or a memory and a processor, the memory having stored therein computer readable instructions that, when executed by the processor, cause the processor to perform the steps of the method of adjusting an output torque between drive axles of a vehicle according to any one of claims 1-15.