Abstract:
A motor torque management method of hybrid vehicles. The method includes torque synthesis and limitation in electric driving mode, torque synthesis and limitation in electricity generating mode, and torque arbitrating management. Wherein, the torque arbitrating management arbitrates torque according to its priority, and sends the torque request with the highest priority to a motor controller ( 5 ).

Description:
[0001]    This application claims the benefit of Chinese Patent Application No. 200710164139.x, titled “Motor torque management method for hybrid vehicle”, filed with the China Patent Office on Sep. 30, 2007, which is incorporated herein by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of hybrid vehicle control, and in particular, to a motor torque management method for hybrid vehicles. 
       BACKGROUND OF THE INVENTION 
       [0003]    Energy crisis and environmental pollution have become great bottlenecks to global economy development. Energy-saving and environment friendly vehicles provide a good way to release energy pressure and reduce environmental pollution. Hybrid vehicles have the advantages of both internal-combustion engine vehicles and pure electric vehicles, such as low gasoline consumption, less emissions and long mileage, and therefore would be a feasible solution to energy crisis and environmental pollution. 
         [0004]    Parallel hybrid vehicles have two power sources, an engine and a motor. A Hybrid Control Unit (HCU) determines a working mode based on a current operation state of the vehicle, and sends a power request and a mode request to the engine and the motor, respectively. Control units of the engine and the motor control respective power sources according to an instruction of the HCU, to meet requirements of the whole vehicle. 
         [0005]    When the hybrid vehicle sends a torque request for auxiliary driving, electricity generating or regenerative braking, the HCU limits the torque request according to the status of the motor, battery and engine. If more than two of the torque requests above are present, the HCU is to arbitrate the torque requests, then send a torque request to the motor. Therefore, how to limit the torque requests and whether torque arbitration mechanism is suitable will affect performance of the hybrid vehicle. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention proposes a priority based motor torque management method, especially suitable for coaxial parallel moderate hybrid vehicles, thereby realizing the management of a plurality of torque request sources. 
         [0007]    The invention includes: electric mode torque synthesis and limitation, electricity generating mode torque synthesis and limitation, torque arbitration management, etc. 
         [0008]    1. An electric mode torque request is a toque request for the motor to work in an electric mode, and in the present invention, this type of torque requests include auxiliary driving torque requests and battery warming-up torque (Bw_MotTq) requests. Auxiliary driving torque requests include driving torque requests aiming for fulfilling vehicle power performance (Mp) and driving torque requests aiming for improving vehicle efficiency (Me). Both the battery warming-up torque request and the driving torque request aiming for efficiency are to improve vehicle efficiency, and therefore the larger one of these two is selected to be an efficiency electric torque request (Me_Merge). 
         [0009]    If one or more of the torque requests above are present, in order to prevent the motor from being damaged by a requested torque that is too large or too small, the HCU limits the electric toque requests within a proper range according to conditions such as peak torque allowed by the motor and maximum allowed torque in continuous operation, thereby getting an efficiency electric torque limit (Me_Limit) and a performance electric torque limit (Mp_Limit). 
         [0010]    2. An electricity generating mode torque request is a torque request for the motor to work in an electricity generating mode, and in this invention, this type of torque requests include electricity generating requests in the event that the State of Charge (SOC) of the battery is low, regenerative braking torque requests (Regen), battery warming-up torque requests (Bw_GenTq) and engine warming-up torque requests (Ew_GenTq). 
         [0011]    When the battery or the engine needs to be warmed up, or the battery requires charging, the engine may have to provide all or part of the electricity generating torque, therefore the smallest one of Gen, Bw_GenTq and Ew_GenTq is selected to be a synthesized electricity generating torque Gen_Syn. 
         [0012]    When the torque requests above are present, the motor have to work in an electricity generating state, and the requested torque has a negative value. In order to limit the motor electricity generating torque in a proper range, the HCU limits the electricity generating torque according to the minimum continuous torque allowed by the motor, thereby getting a regenerative braking toque limit (Regen_Limit) and an electricity generating torque limit (Gen_Limit). 
         [0013]    3. Torque arbitration management: when a plurality of torque requests are present, the HCU arbitrates according to priorities of the torque requests, and makes a torque having the highest priority a current torque request. Torques in the order of their priorities from highest to lowest are: Mp_Limit, Regen_Limit, Gen_Limit and Me_Limit. As can be seen from the priorities, auxiliary driving aiming for fulfilling vehicle power performance has the highest priority, the regenerative braking torque request is lower, then goes the electricity generating torque request, and finally auxiliary driving aiming for efficiency. 
         [0014]    If a plurality of torque request sources are present, the HCU determines according to the priorities above, responds to the torque request with the highest priority, and then sends a torque request to the engine and motor control modules, respectively. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a mechanical connection diagram of the invention; 
           [0016]      FIG. 2  is a structural diagram of the control principle of the invention; 
           [0017]      FIG. 3A  is a flow chart A for electric mode torque synthesis and limitation; 
           [0018]      FIG. 3B  is a flow chart B for electric mode torque synthesis and limitation; 
           [0019]      FIG. 4  is a flow chart for electricity generating mode torque synthesis and limitation; and 
           [0020]      FIG. 5  is a flow chart for torque arbitration. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    As shown in  FIG. 1 , the hybrid vehicle is a uniaxial parallel hybrid vehicle, an engine  1  and a motor  2  are coaxially arranged, and the motor  2  is an ISG (Integrated Starter Generator) motor with integrated electricity generating and electric functions. The power system of the hybrid vehicle uses three control units: a Hybrid Control Unit (HCU)  3 , an Engine Management System (EMS)  4  and a Motor Control Unit (MCU)  5 . The three control units are responsible for controlling the vehicle, the engine and the motor, respectively. 
         [0022]    The ISG may work in a torque mode, a speed mode and a zero torque mode. The torque mode is a working mode aiming for fulfilling torque requests of the HCU. In the invention, when the motor works in the torque mode, the motor has the functions of: auxiliary driving (Mp, Me), electricity generating (Gen) and regenerative braking (Regen). 
         [0023]      FIG. 2  illustrates a structural diagram of torque management performed by the HCU according to the invention. The implementation method is described below. The HCU determines torque requests of the system based on e.g. a vehicle state, or a driver requirement, and identifies the torque requests as electric mode torque requests and electricity generating mode torque requests, then synthesizes and limits the requested torques, so as to make sure that each of the torque requests is within a proper range, next, arbitrates the torques based on set priorities, and sends a torque request with the highest priority to the motor control module after smoothing, thereby obtaining the required torque. 
         [0024]    1. Electric Mode Torque Synthesis and Limitation 
         [0025]    Electric mode torque requests are toque requests for the motor to work in an electric mode, and in the present invention, this type of torque requests include auxiliary driving torque requests and battery warming-up torque (Bw_MotTq) requests. Auxiliary driving torque requests include driving torque requests aiming for fulfilling vehicle power performance (Mp) and driving torque requests aiming for improving vehicle efficiency (Me). Both the battery warming-up torque request and the driving torque request aiming for efficiency are to improve vehicle efficiency, and therefore the larger one of these two is selected to be an efficiency electric torque request (Me_Merge). 
         [0026]    If one or more of the torque requests above are present, in order to prevent the motor from being damaged by a requested torque that is too large or too small, the HCU limits the electric toque requests within a proper range according to conditions such as peak torque allowed by the motor and maximum allowed torque in continuous operation, thereby getting an efficiency electric torque limit (Me_Limit) and a performance electric torque limit (Mp_Limit). 
         [0027]    The torque synthesis and limitation process in the electric mode is shown in  FIGS. 3A and 3B . Step  1  to step  4  illustrate the synthesis processes for Me and Bw_MotTq torques. If there is an Me request or the battery needs to be warmed up, the efficiency electric torque flag (me_flag) is set to be 1, and the larger one of the two torques is selected to be a synthesized efficiency electric torque me_merge. Step  5 -step  7  illustrate the process for determining whether there is an Mp request affecting synthesized torques mp_syn and me_syn. Step  8 -step  16  illustrate the process for limiting mp_syn and obtaining a performance torque limit mp_limit. The limitation process is described below. First, determine whether an initial value of the performance toque limit mp_init_limit is smaller than the maximum continuous torque (cont_max) that the motor can provide currently (S 10 ); and if it is not smaller than the maximum continuous torque of the motor, go to step  12 . In step  12 , determine whether mp_syn is smaller than the peak toque of the motor (peak_torque); and if so, set mp_limit to be mp_init_limit (step  15 ); if not, i.e., mp_syn is larger than the maximum torque that the motor can provide, then set the requested torque to be the peak torque of the motor (step  16 ). If it is true in step  10 , further determine whether mp_syn is larger than the maximum continuous torque of the motor (step  11 ); and if it is not larger than the maximum continuous torque of the motor, set mp_limit to be mp_syn (step  14 ); and if it is larger than the maximum continuous torque of the motor, limit mp_limit to be the maximum continuous torque of the motor (step  13 ). By the process above, the synthesized performance electric torque is limited within the range between the continuous torque and the peak torque of the motor. 
         [0028]    Step  16  and step  17  illustrates the processes for limiting the torque Me, by which the requested value of Me is limited between a set minimum value and the maximum continuous operating torque of the motor. 
         [0029]    2. Electricity Generating Mode Torque Synthesis and Limitation 
         [0030]    Electricity generating mode torque requests are torque requests for the motor to work in an electricity generating mode, and in this invention, this type of torque requests include electricity generating requests in the event that the State of Charge (SOC) of the battery is low, regenerative braking torque requests (Regen), battery warming-up torque requests (Bw_GenTq) and engine warming-up torque requests (Ew_GenTq). 
         [0031]    When the battery or the engine needs to be warmed up, or the battery requires charging, the engine may have to provide all or part of the electricity generating torque, therefore the smallest one of Gen, Bw_GenTq and Ew_GenTq is selected to be a synthesized electricity generating torque Gen_Syn. 
         [0032]    When the torque requests above are present, the motor have to work in an electricity generating state, and the requested torque has a negative value. In order to limit the motor electricity generating torque in a proper range, the HCU limits the electricity generating torque according to the minimum continuous torque allowed by the motor, thereby getting a regenerative braking toque limit (Regen_Limit) and an electricity generating torque limit (Gen_Limit). 
         [0033]      FIG. 4  shows the torque synthesis and limitation process in the electricity generating mode. Step  18 -step  21  illustrate the processing of a regenerative braking torque, and when there is a regenerative braking torque request, a corresponding flag (regen_flag) is set to be 1 (true), and the requested braking torque can not be smaller than the minimum continuous operating torque of the motor (step  21 ). 
         [0034]    Step  22 -step  35  illustrates the processing of the electricity generating torque. The process is described below. When one of the conditions for battery warming-up electricity generating requests, engine warming-up requests and battery charging requests is met, set the synthesized electricity generating request flag to be 1 (step  26 ), and select the smallest one the three toques to be the electricity generating torque request (step  27 ). Step  29  shows that the electricity generating torque can not be smaller than the minimum continuous operating torque of the motor. In step  30 , an acceptable electricity generating torque for the engine is obtained by looking up a rotation speed table of the current motor. Step  31  shows that the electricity generating torque can not exceed the acceptable range for the engine under the current rotation speed. The electricity generating request is that, the torque that the engine has to provide equals the total electricity generating requested torque minus the torque that regenerative brake provides. Step  33 -step  35  show that if the electricity generating requested torque is larger than a set minimum value (note that electricity generating torques have a negative value), the electricity generating torque is set to be zero. 
         [0035]    3. Torque Arbitration Management 
         [0036]    When a plurality of torque requests are present, the HCU arbitrates according to priorities of the torque requests, and makes a torque with the highest priority a current torque request. Torques in the order of their priorities from highest to lowest are: Mp_Limit, Regen_Limit, Gen_Limit and Me_Limit. As can be seen from the priorities, auxiliary driving aiming for fulfilling vehicle power performance has the highest priority, the regenerative braking torque request is lower, then goes the electricity generating torque request, and finally auxiliary driving aiming for efficiency. 
         [0037]    If a plurality of torque request sources are present, the HCU determines according to the priorities above, responds to the torque request with the highest priority, and then sends a torque request to the engine and motor control modules, respectively. 
         [0038]      FIG. 5  illustrates the arbitration process of the torques after synthesis and limitation. First, determine the request Mp having the highest priority; and if Mp_flag is 1 (true), set the torque request value of the motor (ISG_reqTqSyn) to be mp_limit (step  41 ); if there is no Mp request, determine whether there is a regenerative braking torque request (regen_flag), and if there is and the requested torque is smaller than the electricity generating requested torque, set the torque request sent to the motor to be regen_limit (step  42 ); if there is no regenerative braking torque request, determine whether there is a electricity generating request (gen_flag), and if so, set ISG_reqTqSyn to be gen_limit (step  43 ); if there is no electricity generating torque request, determine whether there is an Me request, and if so, set ISG_reqTqSyn to be me_limit (step  44 ); if there is no Me request, set ISG_reqTqSyn to be zero. After the torque request to be sent to the ISG is calculated, smoothing of the torque is performed (S 45 ). 
         [0039]    The torque request after torque arbitration and smoothing is sent to the ISG in the end, to fulfill torque requirements of the HCU, and thereby realizing various torque working modes of the hybrid vehicle in the invention.