Torque distribution method for engine and motor of energy-efficient hybrid electric vehicle

Abstract

A torque distribution method for an engine and a motor of an energy-efficient hybrid electric vehicle comprises the following steps: providing an offline specific fuel consumption map of the engine in all operating states; enabling the engine and motor to respond to the required torque T during travelling together, the motor and the engine working in cooperation at the same rotational speed so as to achieve the optimal working efficiency; acquiring a current state of charge (SOC) of the vehicle battery, and distributing the engine torque T and the motor torque T according to the following situation: if the SOC is greater than a first preset value, entering a first distribution mode; if the SOC is less than a second preset value, enter a second distribution mode; and otherwise, maintaining the current working state. The method can fully utilize the performance advantage of the engine and that of the motor, so that the system works at high efficiency all the time, thereby decreasing the energy consumption of the vehicle, greatly reducing harmful emission, and facilitating energy conservation and environmental protection.

Claims

1. A method for distributing torque between an engine and an electric motor for an energy efficiency improvement of hybrid electric vehicles, comprising: A. providing an offline Brake Specific Fuel Consumption (BSFC) map of the engine in all operating states, wherein the offline BSFC map illustrates contours of BSFC values of the engine with a horizontal axis thereof representing rotational speed of the engine and a vertical axis thereof representing torque of the engine, and the all operating states include operating states in which the rotational speed of the engine ranges from 0 to n.sub.Eng, and for each rotational speed the torque of the engine ranges from 0 to T.sub.Eng.sub._.sub.max, where n.sub.Eng represents a maximum rotational speed the engine can reach, and T.sub.Eng.sub._.sub.max represents a torque of external characteristic for each corresponding rotational speed, where the torque of external characteristic T.sub.Eng.sub._.sub.max is a net torque obtained by subtracting a frictional torque from an indicated torque of the engine; B. enabling the engine and the electric motor to collaboratively respond to a demanding torque T.sub.D during traveling, wherein the engine and the electric motor work in cooperation at a same rotational speed so as to achieve an improved working efficiency; and C. acquiring a current State Of Charge (SOC) of a power battery mounted on the vehicles, and distributing a torque generated by the engine T.sub.Eng.sub._.sub.pre and a torque generated by the electric motor T.sub.Mac.sub._.sub.pre as follows: c1. if the SOC is greater than a first preset value, entering a first distribution mode, which means: if T.sub.D<T.sub.Mac.sub._.sub.maxCAN, setting T.sub.Eng.sub._.sub.pre=0 and T.sub.Mac.sub._.sub.pre=T.sub.D, and if T.sub.D>T.sub.Mac.sub._.sub.maxCAN, setting T.sub.Mac.sub._.sub.pre=T.sub.Mac.sub._.sub.maxCAN and T.sub.Eng.sub._.sub.pre=T.sub.Mac.sub._.sub.maxCAN, where T.sub.Mac.sub._.sub.maxCAN is a maximum torque constraint value of the electric motor acquired in real time via an in-vehicle network; if the SOC is not greater than the first preset value, maintaining a current working state; or c2. if the SOC is less than a second preset value, entering a second distribution mode, which means: setting T.sub.Eng.sub._.sub.pre=T.sub.BSFC and T.sub.Mac.sub._.sub.pre=T.sub.DT.sub.BSFC, where T.sub.BSFC represents a torque of the engine corresponding to a lowest specific fuel consumption value in a current rotational speed of the engine, and T.sub.BSFC is acquired from the offline BSFC map; and if the SOC is not less than a second preset value, maintaining the current working state.

2. The method according to claim 1, wherein c2 further comprises acquiring a maximum torque constraint value of the engine T.sub.Eng.sub._.sub.maxCAN in real time via the in-vehicle network, and setting T.sub.Eng.sub._.sub.pre=T.sub.Eng.sub._.sub.Lim, wherein T.sub.Eng.sub._.sub.Lim is a smaller value of T.sub.BSFC and T.sub.Eng.sub._.sub.maxCAN, T.sub.Mac.sub._.sub.pre=T.sub.DT.sub.Eng.sub._.sub.Lim.

3. The method according to claim 2, wherein the maximum torque constraint value T.sub.Eng.sub._.sub.maxCAN is acquired from an engine sub-system in the hybrid electric vehicles via the in-vehicle network.

4. The method according to claim 3, wherein the first preset value is not equal to the second preset value.

5. The method according to claim 3, wherein the in-vehicle network is a Controller Area Network.

6. The method according to claim 2, wherein the first preset value is not equal to the second preset value.

7. The method according to claim 2, wherein the in-vehicle network is a Controller Area Network.

8. The method according to claim 1, wherein c2 further comprises: acquiring the maximum torque constraint value of the engine T.sub.Eng.sub._.sub.maxCAN in real time via the in-vehicle network, and wherein a smaller value of T.sub.BSFC and T.sub.Eng.sub._.sub.maxCAN is defined as T.sub.Eng.sub._.sub.Lim; implementing a filtering process to T.sub.Eng.sub._.sub.Lim to obtain a value of T.sub.Eng.sub._.sub.split, and setting T.sub.Eng.sub._.sub.pre=T.sub.Eng.sub._.sub.split, wherein the filtering process filters out values to prevent intense variation; and acquiring the maximum torque constraint value of the electric motor T.sub.Mac.sub._.sub.maxCAN and a minimum torque constraint value of the electric motor T.sub.Mac.sub._.sub.minCAN, computing an equation T.sub.DT.sub.BSFC+(T.sub.Eng.sub._.sub.LimT.sub.Eng.sub._.sub.split), wherein a smaller value of a result of the equation and T.sub.Mac.sub._.sub.maxCAN is defined as T.sub.Mac.sub._.sub.Lim, further a greater value of T.sub.Mac.sub._.sub.Lim and T.sub.Mac.sub._.sub.minCAN is defined as T.sub.Mac.sub._.sub.split, thereafter T.sub.Mac.sub._.sub.pre=T.sub.Mac.sub._.sub.split.

9. The method according to claim 8, wherein the filtering process constrains a variation rate of T.sub.Eng.sub._.sub.Lim greater than a torque variation rate of the engine.

10. The method according to claim 9, wherein the maximum torque constraint value T.sub.Eng.sub._.sub.maxCAN is acquired from an engine sub-system in the hybrid electric vehicles via the in-vehicle network.

11. The method according to claim 9, wherein the maximum torque constraint value T.sub.Mac.sub._.sub.maxCAN and minimum torque constraint value T.sub.Mac.sub._.sub.minCAN are acquired from an electric motor sub-system in the hybrid electric vehicles via the in-vehicle network.

12. The method according to claim 9, wherein the first preset value is not equal to the second preset value.

13. The method according to claim 9, wherein the in-vehicle network is a Controller Area Network.

14. The method according to claim 8, wherein the maximum torque constraint value T.sub.Eng.sub._.sub.maxCAN is acquired from an engine sub-system in the hybrid electric vehicles via the in-vehicle network.

15. The method according to claim 8, wherein the maximum torque constraint value T.sub.Mac.sub._.sub.maxCAN and minimum torque constraint value T.sub.Mac.sub._.sub.minCAN are acquired from an electric motor sub-system in the hybrid electric vehicles via the in-vehicle network.

16. The method according to claim 8, wherein the first preset value is not equal to the second preset value.

17. The method according to claim 8, wherein the in-vehicle network is a Controller Area Network.

18. The method according to claim 1, wherein the first preset value is not equal to the second preset value.

19. The method according to claim 1, wherein the in-vehicle network is a Controller Area Network.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Hereinafter, in conjunction with figures and embodiments, a detailed description of the present disclosure is provided.

(2) FIG. 1 schematically illustrates a diagram presenting a principle instruction of a method for distributing torque between an engine and an electric motor for an energy efficiency improvement of hybrid electric vehicles of the present disclosure;

(3) FIG. 2 schematically illustrates a flow diagram presenting a transfer logic between a first distribution mode and a second distribution mode for one embodiment of the method for distributing torque between the engine and the electric motor for an energy efficiency improvement of hybrid electric vehicles of the present disclosure;

(4) FIG. 3 schematically illustrates a diagram presenting a computational logic of T.sub.Eng.sub._.sub.split and T.sub.Mac.sub._.sub.split for embodiments of the method for distributing torque between the engine and the electric motor of an energy efficiency improvement of hybrid electric vehicles of the present disclosure.

(5) FIG. 4 schematically illustrates a diagram presenting a way of obtaining a torque generated by the engine T.sub.Eng.sub._.sub.pre for one embodiment of the method for distributing torque between the engine and the electric motor for an energy efficiency improvement of hybrid electric vehicles of the present disclosure; and

(6) FIG. 5 schematically illustrates a diagram presenting a way of obtaining a torque of the electric motor T.sub.Mac.sub._.sub.pre for one embodiment of the method for distributing torque between the engine and the electric motor for an energy efficiency improvement of hybrid electric vehicles of the present disclosure.

DETAILED DESCRIPTION

(7) It is noted that the preferred embodiments hereinafter are for specifically explaining principles, characteristics and advantages of a method for distributing torque between an engine and an electric motor for an energy efficiency improvement of hybrid electric vehicles of the present disclosure. However, all descriptions are used for explanation, but not posing any constraint to the present disclosure. In addition, any single characteristic described or implied in the following embodiments or figures of the present disclosure may continue being combined and removed arbitrarily among these characteristics (or equivalents) to acquire more other embodiments of the present disclosure, which may not be directly described in the present disclosure.

(8) In order to provide a better understanding of the present disclosure, further explanations and instructions are provided. First, for employing this method, an offline Brake Specific Fuel Consumption (BSFC) map of the engine in all operating states may be required (namely, contours of BSFC values of the engine (g/kWh) are drawn with a horizontal axis thereof representing rotational speed of the engine and a vertical axis thereof representing torque of the engine) as a fundamental reference. The phrase all operating states means all operating state points in a matrix consisting of a maximum working rotational speed range of the engine and an external characteristic of engine torque. For example, if a maximum rotational speed of the engine is n.sub.Eng, a torque of external characteristic for each rotational speed of the engine is T.sub.Eng.sub._.sub.max (namely, a frictional torque of the engine is subtracted from an indicated torque of the engine), and thus, the all operating states include operating states in which the rotational speed of the engine ranges from 0 to n.sub.Eng and the torque of the engine ranges from 0 to T.sub.Eng.sub._.sub.max.

(9) Second, the engine and the electric motor (may be single electric motor or multiple electric motors) may be enabled to collaboratively respond to a demanding torque T.sub.D require during travelling, and the electric motor and the engine may work in cooperation at a same rotational speed so as to achieve an improved working efficiency. As stated above, a working efficiency of the engine in the present disclosure may be simply understood as the BSFC values because the BSFC values of the engine may vary greatly under different rotational speeds and torques, which is a major factor affecting fuel consumption.

(10) Referring to FIG. 1, a computation of an improved working point of the engine is continuously described hereinafter. If in a certain operating state, the rotational speed is n.sub.0 and the demanding torque of a powerstain is T.sub.D, and a torque T.sub.BSFC of a lowest specific fuel consumption point corresponding to the rotational speed n.sub.0 may be found via the offline BSFC map. Thus, for the rotational speed n.sub.0, if a working torque of the engine T.sub.Eng.sub._.sub.pre is equal to T.sub.BSFC, a torque distributed to the electric motor T.sub.Mac.sub._.sub.pre is equal to T.sub.DT.sub.BSFC. When T.sub.DT.sub.BSFC>0, it means that the demanding torque of the powerstain is greater than the improved working point of the engine, so that the electric motor may be driven to provide a positive force to make up the torque of the engine. When T.sub.DT.sub.BSFC<0, it means that the demanding torque of the powerstrain is less than the improved working point of the engine, so that the torque of the engine has an extra torque after responding to the torque of dynamic source, and thereby, the electric motor is required to generate power, where the electric motor provides a negative torque to transfer the extra torque of the engine to electric energy and charging the battery.

(11) In the following, a method for distributing torque between an engine and an electric motor for an energy efficiency improvement of hybrid electric vehicles is provided.

(12) In general, the method may include:

(13) as stated before, providing the offline BSFC map;

(14) in addition, enabling the engine and the electric motor to collaboratively respond to a demanding torque T.sub.D during traveling, and the engine and the electric motor may work in cooperation at a same rotational speed so as to achieve an improved working efficiency;

(15) thereafter, acquiring a current State Of Charge (SOC) of a power battery, and distributing a torque of the engine T.sub.Eng.sub._.sub.pre and a torque of the electric motor T.sub.Mac.sub._.sub.pre according to the following situations:

(16) step a. if the SOC is greater than a first preset value, entering a first distribution mode, wherein if T.sub.D<T.sub.Mac.sub._.sub.maxCAN, setting T.sub.Eng.sub._.sub.pre=0 and T.sub.Mac.sub._.sub.pre=T.sub.D, and if T.sub.D>T.sub.Mac.sub._.sub.maxCAN, setting T.sub.Mac.sub._.sub.pre=T.sub.Mac.sub._.sub.maxCAN, T.sub.Eng.sub._.sub.pre=T.sub.DT.sub.Mac.sub._.sub.maxCAN, where T.sub.Mac.sub._.sub.maxCAN is a maximum torque constraint value of the electric motor acquired in real time via an in-vehicle network; otherwise, maintaining a current working state; or

(17) step b. if the SOC is less than a second preset value, entering a second distribution mode, wherein T.sub.Eng.sub._.sub.pre=T.sub.BSFC (T.sub.BSFC is a torque of the engine corresponding to a lowest BSFC value acquired from the offline specific fuel consumption map according to a current rotational speed of the engine), and T.sub.Mac.sub._.sub.pre=T.sub.DT.sub.BSFC; and otherwise, maintaining the current working state.

(18) In some embodiments, the first preset value may not be equal to the second preset value, which is to avoid frequent mode changes of the torque distribution between the engine and the electric motor in a hybrid system. Moreover, at a moment of the hybrid electric vehicles start, the condition whether the SOC is greater than a first preset value may be checked to determine either the first distribution mode or the second distribution mode is entered after the hybrid electric vehicles start, which is shown in FIG. 2.

(19) Besides, further changes may be made to the method for distributing torque between the engine and the electric motor of an energy efficiency improvement of hybrid electric vehicles.

(20) In some embodiments, referring to FIG. 4, the step b may further include: acquiring a maximum torque constraint value of the engine T.sub.Eng.sub._.sub.maxCAN in real time (e.g. the parameter may be acquired from an engine sub-system in the hybrid electric vehicles via the in-vehicle network, or other components, modules or devices in the hybrid electric vehicles), and a smaller value of T.sub.BSFC and is T.sub.Eng.sub._.sub.maxCAN assigned to T.sub.Eng.sub._.sub.Lim, which is the real split torque of the engine T.sub.Eng.sub._.sub.pre, and thereafter, according to the description stated hereinbefore, the torque of the electric motor T.sub.Mac.sub._.sub.pre is further determined by T.sub.Mac.sub._.sub.pre=T.sub.DT.sub.Eng.sub._.sub.Lim.

(21) In some embodiments, referring to FIG. 3 and FIG. 5, the step b may further include:

(22) acquiring a maximum torque constraint value of the engine T.sub.Eng.sub._.sub.maxCAN in real time (e.g. the parameter may be acquired from the engine sub-system in the hybrid electric vehicles via the in-vehicle network, or other components, modules or devices in the hybrid electric vehicles), and a smaller value of T.sub.BSFC and T.sub.Eng.sub._.sub.maxCAN, is assigned to T.sub.Eng.sub._.sub.Lim, which also is the real split torque distributed to the engine T.sub.Eng.sub._.sub.pre;

(23) and filtering T.sub.Eng.sub._.sub.Lim(e.g. it may be achieved via constraining a variation rate of T.sub.Eng.sub._.sub.Lim not greater than a torque variation rate of the engine or other proper values) for preventing a value of T.sub.Eng.sub._.sub.Lim from intense variation (namely, it may avoid the torque from intense variation under an operating state change) to acquire T.sub.Eng.sub._.sub.split, which also is the torque of the engine T.sub.Eng.sub._.sub.pre;

(24) thereafter, acquiring a maximum torque constraint value of the electric motor T.sub.Mac.sub._.sub.maxCAN in real time and a minimum torque constraint value of the electric motor T.sub.Mac.sub._.sub.minCAN (e.g. the parameters may be acquired from the electric motor sub-system in the hybrid electric vehicles via the in-vehicle network, or other components, modules or devices in the hybrid electric vehicles); since the torque of the engine is filtered, a deviation may be generated between T.sub.Eng.sub._.sub.split and T.sub.Eng.sub._.sub.Lim, and thereby, a corresponding compensation to the torque of the electric motor may be required by computing an equation T.sub.DT.sub.BSFC+(T.sub.Eng.sub._.sub.LimT.sub.Eng.sub._.sub.split), and a smaller value between a result of the equation and T.sub.Mac.sub._.sub.maxCAN is assigned to T.sub.Mac.sub._.sub.Lim and a greater value of T.sub.Mac.sub._.sub.Lim and T.sub.Mac.sub._.sub.minCAN is assigned to T.sub.Mac.sub._.sub.split, which also is the real split torque distributed to the electric motor T.sub.Mac.sub._.sub.pre.

(25) The above embodiments describe in detail about the method for distributing torque between the engine and the electric motor for an energy efficiency improvement of hybrid electric vehicles of the present disclosure, which are only used for explaining principles and implementations of the present disclosure but not for posing any constraint to the present disclosure, and those skilled in the art may modify and vary the embodiments without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure should not be limited by the embodiments disclosed herein.