Abstract:
The present invention includes an apparatus and a method for controlling the idle speed of a powertrain. The possible idle speed control operating modes detailed are (1) engine-torque-control/motor-speed-control, (2) engine-off/motor-speed-control, and (3) engine-speed-control/motor-torque-control. The engine-off/motor-speed-control mode is used when all conditions to turn the engine off are met. The motor is run at a speed that is determined by the ancillary demands—subject to motor or engine constraints. The engine-torque-control/motor-speed-control operating mode is used when the engine is required to be on to provide torque to various mechanically driven ancillary loads, or to charge the batteries. The engine-speed-control/motor-torque-control operating mode is used when the engine is required to be on because of conditions not related to providing torque to other components.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of powertrain control systems for hybrid powertrain configurations. In particular, the present invention includes a system and method for controlling the idle speed of a hybrid powertrain utilizing the torque from one or both of an internal combustion engine and an electric motor-generator. 
     2. Description of the Related Art 
     Hybrid vehicles generally consist of series hybrid vehicles, powersplit hybrid vehicles, and parallel hybrid vehicles. Parallel hybrid vehicles usually include at least a internal combustion engine and a motor-generator disposed along a vehicle powertrain such that the torques produced by each drive means are effectively summed together to drive ,the vehicle. A typical hybrid vehicle is usually driven directly by the mechanical output of the internal combustion engine. However, when the vehicle must be accelerated or decelerated at a rate that cannot be accomplished by the internal combustion engine alone or if the drive efficiency of the engine would be degraded if only the internal combustion engine were used, the motor-generator, which is mechanically connected to the powertrain, operates as an electric motor (during acceleration) or as an electric generator (during deceleration) to compensate for the limitations or inefficiencies of the internal combustion engine. 
     In a hybrid vehicle the motor-generator can provide rapid acceleration or deceleration. Fluctuation in the internal combustion engine&#39;s speed can be suppressed, and thus the hybrid vehicle provides the advantages of reduced fuel consumption and reduced emissions. Since the consumption of the internal combustion engine can be regulated as desired, the hybrid vehicle can be low-noise, low-emission and low-fuel consumption vehicle. For example, the hybrid vehicle can be driven by only the motor-generator even if the internal combustion engine is stopped, since both the internal combustion engine and the motor-generator are selectively mechanically connected to the driving wheels. The motor can also quickly start and stop the internal combustion engine, further increasing fuel economy. 
     A problem that arises in a typical hybrid vehicle occurs when the vehicle is in an idle state, i.e. the torque provided by the respective powertrain components is not being transferred to the drive wheels. Nevertheless, any hybrid powertrain must operate in a neutral, speed control mode for various purposes including powering accessories, recharging batteries, or warming up the internal combustion engine and exhaust aftertreatment system, or meeting other requirements. A specific control system for controlling the idle speed of a hybrid powertrain is therefore desirable. 
     Generic drive control systems exist for hybrid vehicles. For example, one drive control system discloses an apparatus and method for limiting the usage of the internal combustion engine such that the necessary torque is generated, the fuel consumption of the vehicle is maximized, and the undesirable emissions from the vehicle are minimized. The aforementioned system, however, does not disclose a control system for specifically controlling the performance of the hybrid powertrain when the powertrain is in an idle model 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an apparatus and a method for controlling the idle speed .of a powertrain. The present invention receives information about the state of the Starting/Lighting/ignition (SLI) 12 V battery and the High Voltage (HV) battery, and demands from accessories like air conditioning to determine which of several idle speed control modes the powertrain should operate within, and then executes that control strategy. 
     The possible idle speed control operating modes detailed are (1) engine-torque-control/motor-speed-control, (2) engine-off/motor-speed-control, and (3) engine-speed-control/motor-torque-control. Note that the mode engine-speed-control/motor-off is assumed to be a special case of (3) above wherein the desired motor torque is zero, meaning that the motor is switched off. 
     The engine-off/motor-speed-control mode is used when all conditions to turn the engine off (such as catalytic converter temperature, engine temperature, battery state of charge, etc) are met. The motor is run at a speed that is determined by the ancillary demands—subject to motor or engine constraints. 
     The engine-torque-control/motor-speed-control operating mode is used when the engine is required to be on to provide torque to various mechanically driven ancillary loads, or to charge the batteries. The engine torque is set to meet the requirements and demands, and the fast response of the motor in speed-control mode is used to keep the engine at idle speed. Note that if the engine runs smoother under heavy load, then the engine idle speed may be lowered. This instance may occur, for example, if the motor is generating power into the battery. 
     The engine-speed-control/motor-torque-control operating mode is used when the engine is required to be on because of conditions not related to providing torque to other components. Using this scheme, the engine is set into idle-speed control mode, and the motor is used to provide fast transient responses to keep the idle speed smooth, and to keep the engine slightly under load for “opportunistic” charging and to allow the engine to operate at a lower idle speed and more smoothly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic block diagram of a typical hybrid vehicle powertrain showing the control system of the present invention. 
     FIG. 2 is a flow chart depicting the operation of the Powertrain System Controller of the present invention. 
     FIG. 3 is a flow chart, depicting the operation of the Engine Control Unit of the present invention. 
     FIG. 4 is a flow chart depicting the operation of the Motor Control Unit of the present invention. 
     FIG. 5 is a flow chart depicting an alternative torque control mode of the system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the present invention, FIG. 1 is a schematic block diagram of a hybrid vehicle powertrain incorporating an idle speed control system  10  further described herein. The idle speed control system  10  includes a Powertrain System Controller (PSC)  12  receiving a plurality of vehicle state inputs  11 . The PSC  12  is coupled to an Engine Control Unit (ECU)  14  and a Motor Control Unit (MCU)  16 . As shown, the PSC  12 , ECU  14 , and MCU  16  are distinct control systems. However, in a preferred embodiment, the PSC  12 , ECU  14 , and MCU  16  are integrated into a single control system (not shown) for controlling the idle speed of a hybrid vehicle powertrain. 
     In a preferred embodiment, the PSC  12  controls both the ECU  14  and MCU  16 , which are operatively coupled to an internal combustion engine  20  and an electric motor  18 , respectively. The internal combustion engine  20  and the electric motor  18  are coupled to the vehicle driveline  26 , which transmits the collective torque output of the internal combustion engine  20  and electric motor  18  to a transmission assembly  22 . The transmission assembly  22  transmits the drive torque to a pair of drive wheels  24  for driving the hybrid vehicle. In the configuration shown, the electric motor  18  is disposed between the internal combustion engine  20  and the transmission assembly  22 , a so-called in-line configuration. Alternatively, the powertrain may be constructed in a “belt-driven” configuration in which the internal combustion engine  20  is disposed between the electric motor  18  and the transmission assembly  22 . 
     The PSC  12  is adapted to receive drive state inputs  11  and control the ECU  14  and the MCU  16  in response thereto. Representative drive state inputs  11  include driver intent (i.e. torque demand from driver), vehicle state (transmission gearing, engine temperature, auxiliary loads), and battery health (state of charge of the battery). Given the respective drive state inputs  11 , the PSC  12  schedules idle speed control through powers, torques, and speeds from the internal combustion engine  20  and the electric motor  18 . The local control units, i.e. the ECU  14  and the MCU  16 , execute the delivery of the commands. The PSC  12  administers the idle speed control in accordance with the following control scheme. 
     FIG. 2 shows a flowchart corresponding to an initial control scheme implemented by the PSC  12 . In step S 100 , the PSC  12  calculates the power necessary to charge the low voltage batteries, LVBP. In step S 102 , the PSC calculates the power necessary to charge the high voltage batteries, HVBP. In step S 104 , the PSC  12  calculates the power necessary to drive an auxiliary power load, AUXP, such as an air conditioning system (not shown). In step S 106 , the PSC  12  inquires as to whether the hybrid powertrain is in an idle mode. This determination is made based upon the drive state inputs  11  received continuously by the PSC  12 . 
     If the powertrain is not in an idle mode, then the PSC  12  enters a torque control mode corresponding to step S 108 . The details of the torque control mode are discussed further herein. If the powertrain is in an idle mode, then the PSC  12  selects one of the ECU  14  or the MCU  16  to perform engine-preferred speed control or motor-preferred speed control, respectively, in accordance with step S 110 . 
     The engine-preferred speed control scheme is detailed in FIG.  3 . Upon selecting the ECU  14  to execute the control scheme, the PSC  12  delegates the task of engine speed control to the ECU  14  such that the speed of the internal combustion engine  20  is controlled locally to the reference speed determined by the PSC. 
     In step S 112 , the PSC  12  calculates reference speeds for the respective loads on the powertrain: a high-voltage battery, a low-voltage battery, and an auxiliary load, for example an air-conditioning system. The required revolutions per minute (RPM) of the loads are denoted DSDRPM — 12 V, DSDRPM — 300 V, and DSDRPM_AC respectively. After calculating the reference speeds, the PSC  12  progresses to step S 114 . 
     In step S 114 , the PSC  12  inquires as to whether the internal combustion engine  20  is operating. If the internal combustion engine  20  is operational, then the PSC  12  progresses from step S 114  to step S 116  in which the engine speed control mode is initialized. In step S 118 , the PSC  12  terminates the operation of the electric motor  18 , such that the reference speed for the electric motor  18 , DSDRPM_MOT, is set to zero. 
     In step S 120 , the PSC  12  sets the reference speed of the ECU  12 , DSDRPM_ENG, to a value. This value is based of the load requirements, DSDRPM — 12 V, DSDRPM — 300 V, and DSDRPM_AC, as well as the minimum allowable engine speed, MIN_ENG_RPM. The internal combustion engine  20  is thereby directed to operate at a rotational speed as determined by the PSC  12 . In step S 122 , the PSC  12  sets the motor reference speed to zero. 
     Returning to step S 114 , if the internal combustion engine  20  is not operating, as indicated in step S 126 , then the PSC  12  sets MCU  16  to speed control mode as shown in step S 128 . If the internal combustion engine  20  is not operating, then the reference engine speed, DSDPRPM_ENG, is set to zero. 
     Accordingly, in step S 130 , the PSC  12  determines a reference speed for the MCU  16 . The reference speed, DSDRMP_MOT, is calculated based upon the maximum of the load requirements, DSDRPM — 12 V, DSDRPM — 300 V, including and DSDRPM_AC, as well as the minimum allowable motor speed, MIN_MOT_RPM. The MCU  16  is thereby directed to control the motor at the required rotational speed. . 
     FIG. 4 is a block diagram showing the control scheme for the motor-preferred speed control of the idle speed of the hybrid powertrain. Upon selecting the PSC  12  to execute the control scheme, the PSC  12  delegates the task of motor speed control to the MCU  16  such, that the speed of the electric motor  18  is controlled locally. 
     In step S 136 , the PSC  12  calculates reference speeds for the respective loads on the powertrain: a high-voltage battery, a low-voltage battery, and an auxiliary load, for example an air-conditioning system. The required revolutions per minute (RPM) of the loads are denoted DSDRPM — 12 V, DSDRPM — 300 V, and DSDRPM_AC respectively. After calculating the reference speeds, the PSC  12  progresses to step S 138 . 
     In step S 138 , the PSC  12  determines whether the internal combustion engine  20  is operating. If the internal combustion engine  20  is operational, then it progresses from step S 138  to step S 140  in which the PSC  12  learns the steady state motor speed control compensation torque, TQ_SS_ADJ. The adaptive torque adjustment term, TQ_ADJ_SS, is calculated. This represents the steady state torque offset required to drive the motor to a particular steady state operating point. For example, if the motor is operating at a steady state torque operating point of 10 Nm (Newton-meters) and the required operating point is 10 Nm, then TQ_SS_ADJ will take the value of 10 Nm. This will drive the motor to operate around 10Nm as the engine is providing the required torque offset. The motor may be required to operate at a non-zero mean operating point, for example, based on motor efficiency considerations. The PSC  12  continually calculates the adaptive torque adjustment term and commands the ECU  14  to operate the engine at the required torque. In step S 142  the PSC  12  sets the ECU  14  to torque control mode. In step S 144  sets the MCU  16  to speed control mode. 
     In step S 146 , the PSC  12  sets the reference speed of the MCU  16 , DSDRPM_MOT, to a value. The value of DSDRMP_MOT is calculated based upon the maximum of the load requirements, DSDRPM — 12 V, DSDRPM — 300 V, and including DSDRPM_AC, as well as the minimum allowable motor speed, MIN_MOT_RPM. The ECU  14  is accordingly directed to control the engine at a rotational speed of zero as determined by the PSC  12  in step S 148 . 
     In step S 150 , the PSC  12  commands to the ECU the feedforward torque request based on the power requirements of the various powertrain loads, the required idle speed and the torque adjustment factor, TQ_SS_ADJ. 
     Returning to step S 138 , if the internal combustion engine  20  is not operating, as indicated in step S 152 , then the PSC  12  sets the ECU  12  speed control mode as shown in step S 154 . If the internal combustion engine  20  is not operating, then the reference engine speed, DSDRPM_ENG, is set to zero. 
     Accordingly, in step S 156 , the PSC  12  determines a reference speed for the electric motor  18 . The value of DSDRMP_MOT is calculated based upon the load requirements, DSDRPM — 12 V, DSDRPM — 300 V, and including DSDRPM_AC, as well as the minimum allowable motor speed, MIN_MOT_RPM. The ECU  16  thereby directed to control the motor, at a rotational speed as determined by the MCU  16 . In step S 158 , the PSC  12  commands to the MCU the feedforward torque request based on the power requirements of the various powertrain loads and the required idle speed. In step S 106 , if the PSC; 12  does not detect an idle mode, then the PSC  12  progresses to step S 108 , the torque control mode. The torque control mode is detailed in FIG.  5 . 
     Returning to step S 106 , if the PSC  12  does not detect an idle mode, then the PSC  12  progresses to step S 108 , the torque control mode. The torque control mode is detailed in FIG.  5 . 
     The PSC  12  executes the torque control mode by initializing the torque control mode in the MCU  16  and the ECU  14  shown in steps S 160  and S 162  respectively. In step S 164 , the reference motor speed, DSDRPM_MOT, is set to zero. In step S 166 , the reference engine speed, DSDRPM_ENG, is also set to zero. 
     In step S 188 , the PSCL  12  monitors the torque output of the electric motor  18  and the internal combustion engine  20  and requests an feedforward torque adjustment term based upon the power requirement and the final idle speed of the powertrain. The feedforward torque adjustment term, TQ, may be selectively applied to either the electric motor  18  or the internal combustion engine  20 . The torque adjustment term is calculated as the sum of the power requirements of the powertrain divided by the actual rotational speed of the electric motor  18  and internal combustion engine when rotating as one. That is, 
     
       
           TQ={LVBC+HVBC+AUXP }/ENG_&amp;_MOT_RPM. 
       
     
     The PSC  12  continually calculates the feedforward torque adjustment term and controls both the electric motor  18  and the internal combustion engine  20  to supply the additional torque needed. 
     It should be apparent to those skilled in the art that the above-described embodiments are merely illustrative of but a few of the many possible specific embodiments of the present invention. Numerous and various other arrangements can be readily devised by those skilled in the art without departing from the spirit and scope of the invention as defined in the following claims.