Abstract:
A vehicle includes an engine and a fraction motor. A clutch is configured to selectively mechanically couple the engine to the traction motor. A controller or controllers are provided that are configured to command a change in magnitude of an electric current supplied to the electric machine. The command is made in response to initiation of the clutch engaging the traction motor to the engine. The change in magnitude of the electric current ensures the speed of the traction motor remains generally constant during clutch engagement while a speed of the engine is less than that of the traction motor.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to the control of torque in a traction motor of a hybrid electric vehicle at times in which the engine is being pulled-up. 
       BACKGROUND 
       [0002]    Hybrid electric vehicles (HEV&#39;s) include an internal combustion engine and an electric traction motor to provide power to propel the vehicle. One method of increasing fuel economy in an HEV is to shut down the engine when the overall power demands are low. However, if the overall power demands increase such that the traction motor cannot provide enough power to meet the demand, or if the fraction battery state of charge (SOC) is below a certain threshold, the engine must be activated to supplement the power output of the traction motor. 
       SUMMARY 
       [0003]    According to one embodiment of the present disclosure, a vehicle includes an engine, and electric machine, and a clutch configured to couple the engine and the electric machine. At least one controller is configured to command a change in magnitude of a current supplied to the electric machine in response to initiation of clutch engagement. The speed of the electric machine remains generally constant during clutch engagement. A speed of the engine is less than the speed of the electric machine during clutch engagement and while the speed of the electric machine is generally constant. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a schematic illustration of a powertrain of a hybrid electric vehicle; 
           [0005]      FIG. 2  is a graphical representation of motor speed and engine speed while the engine is being pulled-up; 
           [0006]      FIG. 3  is a graphical representation of motor torque and engine torque as the engine is pulled-up; and 
           [0007]      FIG. 4  is a flow chart of an algorithm for controlling a vehicle. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
         [0009]    Referring to  FIG. 1 , a schematic diagram of a vehicle  10  is illustrated according to one embodiment of the present disclosure. The vehicle  10  is an HEV. The powertrain or driveline of the vehicle  10  includes an engine  12 , an electric machine or motor/generator (M/G)  14 , and a transmission  16  disposed between the M/G  14  and wheels  18 . A torque converter  19  can optionally be provided between the M/G  14  and the transmission  16 . The torque converter  19  transfers rotating power from the M/G  14  to the transmission  16 . It should be understood that instead of a torque converter  19 , one or more clutches can be provided to selectively transfer torque from the M/G  14  to the transmission  16 . Other configurations are also possible. 
         [0010]    The M/G  14  can operate as a generator by receiving torque from the engine  12  and supplying AC voltage to an inverter  20 , whereby the inverter  20  converts the voltage into DC voltage to charge a traction battery, or battery  22 . The M/G  14  can operate as a generator by utilizing regenerative braking to convert the braking energy of the vehicle  10  into electric energy to be stored in the battery  22 . Alternatively, the M/G  14  can operate as a motor. The M/G  14  receives power from the inverter  20  and battery  22  and provides torque through the torque converter  19  (or clutch), through the transmission  16  and ultimately to the wheels  18 . A differential  24  can be provided to distribute torque from the output of the transmission  16  to the wheels  18 . 
         [0011]    A first clutch, or disconnect clutch  26 , is located between the engine  12  and the M/G  14 . The disconnect clutch  26  can be fully open, partially engaged, or fully engaged (locked). In order to start the engine  12 , the M/G  14  rotates the engine  12  when the disconnect clutch  26  is at least partially engaged. Once the engine  12  is rotated by the M/G  14  to a certain speed (e.g., ˜100-200 rpm), fuel entry and ignition can commence. This enables the engine  12  to “start” and to provide torque back to the M/G  14 ; the M/G  14  can charge the battery  22  and/or distribute torque from the engine  12  to the torque converter  19 , through the transmission  16  and ultimately to the wheels  18 . In another embodiment, a separate engine starter motor (not shown) can be provided. 
         [0012]    The vehicle  10  also includes a control system, shown in the embodiment of  FIG. 1  as three separate controllers: an engine control module (ECM)  28 , a transmission control module (TCM)  30 , and a vehicle system controller (VSC)  32 . The ECM  28  is directly connected to the engine  12 , and the TCM  30  can be connected to the M/G  14  and the transmission  16 . The three controllers  28 ,  30 ,  32  are connected to each other via a controller area network (CAN)  34 . The VSC  32  commands the ECM  28  to control the engine  12  and the TCM  30  to control the M/G  14  and the transmission  16 . Although the control system of the vehicle  10  includes three separate controllers, such a control system can include more or less than three controllers as desired. For example, a separate motor control module can be directly connected to the M/G  14  and to the other controllers in the CAN  34 . 
         [0013]    As previously described, the M/G  14  is utilized to start the engine  12 . This is referred to as engine pull-up. It can be advantageous to pull-up the engine  12  in order to spin the M/G  14  and charge the battery  22 , for example. It can also be advantageous to pull-up the engine  12  to satisfy acceleration demands. During engine pull-up, the disconnect clutch  26  is at least partially engaged, and torque from the M/G  14  is applied through the disconnect clutch  26  and to the engine  12 . Once the engine  12  is pulled-up, a boost of torque can be provided through the powertrain due to, for example, sudden ignition in the engine  12 . The increase in speed of the engine after engine pull-up can be translated into increased rotational speed of the M/G  14 . Increased rotational speed of the M/G  14  causes the battery  22  to be charged and/or more torque to be applied to the torque converter  19 , as previously described. Once the battery  22  is sufficiently charged and the vehicle  10  does not require engine power for propulsion, the engine  12  can be disabled or pulled-down. 
         [0014]    According to one embodiment of the present disclosure, the M/G  14  is controlled to combat the torque boost provided from the engine  12  during engine pull-up. Once the engine  12  is pulled-up and activated and the disconnect clutch  26  is partially engaged or locked, the M/G  14  provides torque back towards the engine  12  in an opposite direction as the engine torque to counteract the engine torque. 
         [0015]    During this torque transfer between the M/G  14  and the engine  12 , the VSC  32  can control the powertrain such that torque noise is not felt at the wheels  18 . Changes in rotational speed of the M/G  14  necessarily change the input of the torque converter  19 , which in turn can alter the rotational speed in the input of the transmission  16 . If the transmission input speed increases, speed at the wheels  18  increase. Therefore during engine pull-up and pull-down, the M/G  14  can be controlled to increase torque to counteract the engine torque while remaining at a generally constant speed such that speed fluctuations are not transferred to the wheels  18 , as will be further described below. A clutch downstream of the torque converter  19  (e.g., in the transmission  16 ) may also be slipped during engine pull-up to assure that the speed of the M/G  14  remains generally constant during engagement of the disconnect clutch  26 . 
         [0016]    Referring to  FIGS. 1 and 2  the speed of the M/G  14  (“motor speed”) and the speed of the engine  12  (“engine speed”) are illustrated. Up until time T 1 , the motor speed is generally constant such that the torque at the wheels  18  is generally constant. At time T 1 , conditions as described above cause the VSC  32  to command the disconnect clutch  26  to partially engage. Because the speed of the M/G  14  is greater than the speed of the engine  12 , the engine speed begins to rise. As will be discussed with reference to  FIG. 3 , however, the motor speed remains generally constant throughout the engagement of the disconnect clutch  26  (between times T 1 -T 3 ) such that the torque input into the torque converter  19  remains generally constant. 
         [0017]    At time T 2 , ignition occurs. Ignition can occur anywhere between T 1  and T 3 , and the amount of time between T 1 -T 2  and T 2 -T 3  can alter ( FIG. 2  illustrates but one example). Ignition causes the engine speed to continue to increase. At a point where the motor speed and the engine speed are generally equivalent (e.g., within 20 rpms), the VSC  32  can command the disconnect clutch  26  to lock as will be discussed with reference to time T 3 .  FIG. 2  also includes a dotted line that represents an example of the engine speed continuing to rise beyond the motor speed. This line represents what can happen if too much torque boost occurs after ignition, and the motor torque does not alter to combat the boost in speed and torque from the engine  12 . The altering of the motor torque can inhibits the engine speed from increasing to a level above that of the motor speed. 
         [0018]    At time T 3 , the disconnect clutch  26  is locked, and the motor speed and the engine speed are equivalent. At any time after T 3  as driver torque demands increase or decrease, both the engine speed and the motor speed increase or decrease accordingly, due to the power increases in the engine. 
         [0019]    Referring to  FIG. 3 , various torques, speeds, and pressures are illustrated and will now be described. Times T 1 , T 2  and T 3  represent the points of partial engagement of the disconnect clutch  26 , ignition, and locking of the disconnect clutch  26 , respectively, as in  FIG. 2 . 
         [0020]    Before time T 1 , the motor speed is generally constant, and the torque of the M/G  14  (“motor torque”) is also generally constant. The pressure of the arrangement of the disconnect clutch  26  (“clutch pressure”) is at or about  0 , as the disconnect clutch is open such that the M/G  14  and the engine  12  are not coupled. The torque of the engine  12  (“engine torque”) is therefore also at or about 0, as the engine is disabled. The total torque felt at the wheels  18  of the vehicle also remains generally constant, consistent with the motor speed. 
         [0021]    At time T 1 , the VSC  32  commands the disconnect clutch  26  to initiate engagement. This is seen as the clutch pressure increases (e.g., to about 100 lbs). The motor torque begins to rise to start pulling-up the engine  12 , while the disconnect clutch  26  is slipping and motor speed remains generally constant. The total torque felt at the wheels remains generally constant due to the slipping of the disconnect clutch  26 . The increase in torque to the M/G  14  is accomplished by increasing the electric current supplied to the M/G  14  from the inverter  20  and battery  22  while maintaining the speed of the M/G  14 . 
         [0022]    At time T 2 , ignition in the engine  12  occurs. Ignition can occur anywhere between T 1  and T 3 , and the amount of time between T 1 -T 2  and T 2 -T 3  can alter ( FIG. 2  illustrates but one example). The clutch pressure can remain generally constant between times T 2  and T 3 , or can change in magnitude to achieve a desired engine speed and torque. At some time immediately following ignition, the engine torque begins to rise rapidly. The motor torque correspondingly decreases due to a change in magnitude of the electric current supplied to the M/G  14 . The decrease in motor torque corresponds to the increase in engine torque so that the motor speed remains generally constant while quick engagement of the disconnect clutch  26  can occur. At some time between T 2  and T 3 , the motor torque is negative. This indicates a motor torque increase in a direction opposite to the engine torque. The motor torque can remain negative until a desired capacity in the disconnect clutch  26  is reached. The desired capacity is the capacity in the disconnect clutch  26  to carry the requested torque from the engine  12 , plus any safety factor. 
         [0023]    Once the desired capacity is reached, the motor torque can return in a positive direction, corresponding to time T 3  in which the disconnect clutch  26  is locked. Once the disconnect clutch  26  is locked, the motor speed and engine speed (not shown) are equal, and the disconnect clutch synchronizes the speeds of each of the M/G  14  and engine  12 . At any time after time T 3 , any changes in desired torque to the vehicle  10  results in a direct corresponding change in engine torque and motor torque, as well as engine speed and motor speed. Furthermore, the clutch pressure can continue to rise to maintain the synchronous state of the disconnect clutch  26 . 
         [0024]    The control system as illustrated in  FIGS. 1-3  can allow for a quick boost in engine torque. Furthermore, if a change in speed of the vehicle  10  is not desired during engine pull-up, the motor torque can be altered to maintain motor speed. Once an operator of the vehicle  10  desires an increase in speed, the control system allows for the engine  12  to engage quickly to efficiently provide torque to the wheels  18 . 
         [0025]    Referring to  FIGS. 1 and 4 , an algorithm for controlling the vehicle  10  is illustrated according to one embodiment of the present disclosure. The algorithm can be implemented by VSC  32 , for example. At operation  100 , the VSC  32  determines if an engine pull-up command is necessary. As previously described, this can be based on the SOC of the battery  22 , for example. If there is no engine pull-up command necessary, the algorithm ends at operation  102 . If circumstances exist that necessitate an engine pull-up command, the disconnect clutch  26  is partially engaged at operation  104 . This begins to rotate a shaft of the engine  12 . At operation  106 , the VSC  32  determines the torque of the engine  12  (τ eng ) and of the M/G  14  (τ mot ), as well as the speed of the engine  12  (ω eng ) and the M/G  14  (ω eng ). After the disconnect clutch  26  is partially engaged, ignition occurs in the engine  12  at operation  108 . 
         [0026]    At operation  110 , a determination is made as to whether the speed of the engine  12  is generally equivalent to the speed of the motor. During engine pull-up and shortly after ignition, if the speeds are generally equivalent, the disconnect clutch  26  is locked such that the speeds are locked together, and any speed increases in the engine  12  translate into speed increases in the M/G  14 . If the relative speeds at operation  110  are not generally equivalent, then at  114  the VSC  32  adjusts the torque of the M/G  14  while maintaining the speed of the M/G  14  to be relatively constant. The adjustment of the torque of the M/G  14  can continue until the relative speeds of the engine  12  and M/G  14  are generally equivalent, while maintaining the speed of the M/G  14 . 
         [0027]    The processes, methods, or algorithms disclosed herein can be deliverable to/implemented by a processing device, controller, or computer, which can include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, or algorithms can be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on non-writable storage media such as ROM devices and information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The processes, methods, or algorithms can also be implemented in a software executable object. Alternatively, the processes, methods, or algorithms can be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components. 
         [0028]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.