Abstract:
A speed-limiting accessory drive system is provided that limits the speed range over which an engine-driven accessory operates while maintaining the operating speed range of the engine. A torque-transmitting mechanism is selectively engagable to operatively connect the engine and the accessory. A controller is configured to maintain the torque-transmitting mechanism in an engaged state only when monitored engine speed is within a predetermined speed range and to control a drive motor to drive the driven accessory when the monitored engine speed is not within the predetermined range. A method of controlling the speed of at least one driven accessory, which may be carried out using the speed-limiting accessory drive system, is also provided.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a vehicle accessory drive system having a torque-transmitting mechanism to selectively connect an engine to an accessory. The invention also relates to a method of controlling the speed of a driven accessory. 
       BACKGROUND OF THE INVENTION 
       [0002]    Vehicle accessories such as air conditioning systems, power steering systems and water pumps are typically driven directly by the engine crankshaft through, for example, a belt and pulley system. Therefore, the accessories must be capable of operating over the entire speed range of the engine, as the operating speeds of the accessories in a conventional drive system are directly proportional to the speed of the engine. The accessories are therefore typically designed to provide full capacity when the engine is operating at the low end of the engine speed range, because the accessories must be designed to give sufficient performance at low speeds, such as during engine idle, as well as being capable of running at high speeds during engine maximum speed operation. At higher engine speeds, excess energy is transferred to the accessories that may be lost. 
       SUMMARY OF THE INVENTION 
       [0003]    A speed-limiting accessory drive system is provided that limits the speed range over which one or more engine-driven accessories operate while maintaining the operating speed range of the engine. A speed-limiting accessory drive system includes an engine and a battery as well as a drive motor operatively connected with the battery. At least one driven accessory is operatively connected with the drive motor. A torque-transmitting mechanism is selectively engageable to operatively connect the engine with the accessory. An engine speed sensor is operable to monitor the speed of the engine. A controller is operatively connected to the torque-transmitting mechanism, to the engine speed sensor and to the drive motor. The controller is configured to maintain the torque-transmitting mechanism in an engaged state only when the monitored engine speed is within a predetermined speed range and to control the drive motor to drive the driven accessory when the monitored engine speed is not within the predetermined range. Preferably, the predetermined speed range at which the controller maintains the torque-transmitting mechanism in an engaged state is calculated based upon the optimal speed range of the driven accessory. When the controller disengages the torque-transmitting mechanism, the controller can control the drive motor to supply torque such that the accessory is driven at a speed by the motor within an optimal speed range for the accessory. Preferably, the speed-limiting accessory drive system is part of a powertrain that includes the engine and an electromechanical transmission. 
         [0004]    The speed-limiting accessory drive system may drive multiple driven accessories, in which case selective engagement of the torque-transmitting mechanism operatively connects the engine and the multiple accessories, potentially at different relative speeds. This may be accomplished by a belt and pulley torque transfer arrangement wherein different size pulleys are operatively connected with the different accessories. Alternatively, a chain and sprocket torque transfer arrangement may be used. 
         [0005]    Preferably, the torque-transmitting mechanism is configured for operation as both an overrunning clutch and an underrunning clutch. Thus, if the engine output member (e.g., an engine crankshaft) is running at a speed below the predetermined speed range, the torque-transmitting mechanism is overrunning, i.e., the portion of the torque-transmitting mechanism operatively connected with the driven accessory is rotating faster than the portion of the torque-transmitting mechanism operatively connected with the engine. Preferably, the torque-transmitting mechanism may also operate as an underrunning clutch when the engine is running at a speed above the predetermined speed range. In this case, the portion of the clutch operatively connected with the engine is rotating faster than the portion of the clutch operatively connected with the accessories. 
         [0006]    A method of controlling the speed of at least one driven accessory, which may be carried out using the speed-limiting accessory drive system, includes providing a drive motor adapted for driving the driven accessory as well as a torque-transmitting mechanism that is selectively engageable to operatively connect the engine with the driven accessory. The method further includes monitoring whether the torque-transmitting mechanism is in an engaged state or a disengaged state. The method includes monitoring speed of the engine and comparing monitored engine speed to a predetermined range of speeds. Finally, the method includes controlling the drive motor as well as engagement of the torque-transmitting mechanism such that the driven accessory is driven by the engine if monitored speed is within the predetermined range and is driven by the drive motor if monitored engine speed is not within the predetermined range. 
         [0007]    The predetermined range of speeds may be from a predetermined minimum speed to a predetermined maximum speed, including both the predetermined minimum and predetermined maximum speeds. Preferably, the predetermined minimum speed and the predetermined maximum speed are calculated based on an optimal speed range for operation of the driven accessory. In this case, any speed multiplier or speed reduction in the torque transfer arrangement (e.g., the belt and pulley or chain and sprocket system) between the engine and the driven accessory is accounted for in determining the minimum and the maximum speeds. 
         [0008]    There are four different possible modes determined under the monitoring steps. In a first mode, the monitored engine speed is not less than the predetermined minimum speed and not greater than the predetermined maximum speed and the torque-transmitting mechanism is in the engaged state. In this first mode, the torque-transmitting mechanism is maintained in the engaged state so that the driven accessory is driven by the engine. 
         [0009]    In a second mode, the monitored engine speed is not less than the predetermined minimum speed and not greater than the predetermined maximum speed and the torque-transmitting mechanism is in the disengaged state. In this second mode, the controlling step includes engaging the torque-transmitting mechanism so that the driven accessory is driven by the engine. 
         [0010]    In a third mode, monitored engine speed is less than the predetermined minimum speed or is greater than the predetermined maximum speed and the torque-transmitting mechanism is in the engaged state. In this third mode, the controlling step includes disengaging the torque-transmitting mechanism and controlling the motor so that the driven accessory is driven by the motor at a speed that is not less than the predetermined minimum speed and not greater the predetermined maximum speed. 
         [0011]    Finally, in a fourth mode, the monitored engine speed is less than the predetermined minimum speed or greater than the predetermined maximum speed and the torque-transmitting mechanism is in the disengaged state. In this fourth mode, the disengaged state of the torque-transmitting mechanism is maintained and the motor is controlled so that the driven accessory is driven by the motor at a speed not less than the predetermined minimum speed and not greater than the predetermined maximum speed. 
         [0012]    Accordingly, the speed-limiting accessory drive system and the method of control described herein limit the minimum and maximum drive speed of the accessory without limiting the operating speed range of the engine. Thus, the accessory design and size can be based upon the smaller operating speed range (the range between and including the predetermined minimum and maximum speeds) rather than the operating speed range of the engine, which is likely to be a much broader range. 
         [0013]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic illustration of a vehicle having a speed-limiting accessory drive system within the scope of the invention; and 
           [0015]      FIG. 2  is a flow chart illustrating a method of controlling the speed of at least one driven accessory. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Referring to the drawings wherein like reference numerals refer to like components, in  FIG. 1  a vehicle  10  is shown schematically. The vehicle  10  has a powertrain  12  to drive the wheels (not shown) of the vehicle  10 . The powertrain  12  includes an engine  14  which is operatively connected to a transmission input member  16  of a transmission  18 . The transmission  18  provides power at various speed ratios to the output member  19 . In this embodiment, the transmission  18  is a hybrid electromechanical transmission having first and second motor/generators  20 ,  22 , respectively, that may function as either motors or generators. The first motor/generator  20  is in an input-split arrangement with the engine  14  as both are connected to different elements of the first gearing arrangement  24 . The second motor/generator  22  is in an output-split arrangement in that it is connected to an element of a second gearing arrangement  26 . The motor/generators  20 ,  22  function as motors by receiving power from an electrical power source  30 , such as a battery. A controller  32  is operatively connected to the battery  30  through a power inverter module  34 . The power inverter module  34  includes separate power inverters, one operatively connected to the motor/generator  20 , one operatively connected to the motor/generator  22 , as well as one operatively connected to a drive motor  70  (discussed below). The controller  32  causes the power inverter module  34  to provide power received from the battery  30  to either or both of the motor/generators  20 ,  22  so that the motor/generators  20 ,  22  may provide torque through the respective gearing arrangements  24 ,  26 . If the motor/generators  20 ,  22  are to function as generators, the controller  32  controls them to receive power from the respective gearing arrangements  24 ,  26 . Those skilled in the art will readily understand the functional operation of a hybrid transmission. It should be appreciated that, although a hybrid electrically variable transmission is illustrated, a non-hybrid manual or automatic transmission may be used within the scope of the invention. 
         [0017]    A speed-limiting accessory drive system  40  allows the engine  14  to selectively drive multiple accessories, accessory  42 , accessory  44 , and accessory  46 . The accessories may include but are not limited to a power steering pump, a water pump and an air conditioning compressor. The first accessory  42  is a power steering pump, the second accessory  44  is a water pump, and the third accessory is an air conditioning compressor, for purposes of illustration. 
         [0018]    The speed-limiting accessory drive system  40  includes a torque-transmitting mechanism  48  which is preferably a rotating friction clutch. The torque-transmitting mechanism  48  is selectively engageable under the control of controller  32  through hydraulic, electric or other communication means to connect a crankshaft  50  of engine  14  with an accessory drive shaft  52 . A rotatable member  54  is connected for common rotation with the accessory drive shaft  52 . A torque-transmitting arrangement  53  connects the rotatable member  54  such that rotation of the rotatable member  54  drives the accessories,  42 ,  44  and  46 . The torque-transmitting arrangement  53  includes rotatable members  56 ,  58  and  60  connected for common rotation with drive shafts  62 ,  64  and  66 , respectively, of the accessories  42 ,  44  and  46 . An endless rotation transferring device  68  connects the rotatable member  54  with the rotatable members  56 ,  58  and  60  such that the rotation of the rotatable member  54  may cause rotation of the other rotatable members  56 ,  58  and  60  via the endless rotation transferring device  68 . Within the scope of the invention, the rotatable members  54 ,  56 ,  58  and  60  may be pulleys and the rotation transferring device  68  may be an endless belt. Alternatively, within the scope of the invention, the rotatable members  54 ,  56 ,  58  and  60  may be sprockets and the rotation transfer device  68  may be a chain. It should be appreciated, that the rotatable members  54 ,  56 ,  58  and  60  may have different radial dimensions so that the rotation transfer device causes rotation of the respective drive shaft  62 ,  64 ,  66  at different relative speeds. 
         [0019]    The speed-limiting accessory drive system  40  also includes an electric drive motor  70  operatively connected with the accessories  42 ,  44  and  46  via an electric drive motor shaft  72  and rotatable member  74  that is also operatively connected to the rotatable members  56 ,  58  and  60  through the rotation transfer device  68 . The controller  32  controls operation of the electric drive motor  70  through another power inverter included in the power inverter module  34 , commanding it to spin freely with rotation of the rotatable member  74  or commanding it to provide torque to drive the rotatable member  74 . Specifically, the controller  32  is configured with a stored algorithm that controls the engagement of the torque-transmitting mechanism  48  between an engaged state in which the engine  14  may drive the accessories  42 ,  44 ,  46  via the torque-transmitting arrangement  53  and a disengaged state in which the controller drives the accessories  42 ,  44 ,  46  via the electric drive motor  70  so that the electric drive motor  70 , acts as a motor providing torque through the torque-transmitting arrangement  53 . 
         [0020]    The speed-limiting accessory drive system  40  includes a sensor  78  operatively connected to the engine crankshaft  50  and to the controller  32  (transfer conductors connecting the sensor  78  with the controller  32  not shown for purposes of simplicity in the drawing). The sensor  78  senses speed of the crankshaft  50  and provides this information to the controller  32 . The speed-limiting accessory drive system  40  also includes a sensor  80  operatively connected to the controller  32  and to the accessory drive shaft  52  that enables the controller  32  to determine whether the torque-transmitting mechanism  48  is in an engaged state or a disengaged state. For example, the sensor  80  may be a strain gauge connected with the accessory drive shaft  52 . 
         [0021]    Referring to  FIG. 2 , an algorithm within the controller controls the speed-limiting accessory drive system  40  according to the method  100  illustrated in the flow chart of  FIG. 2 . The method  100  includes step  102 , providing a drive motor adapted for driving at least one accessory. Method  100  also includes step  104 , providing a torque-transmitting mechanism that is selectively engageable to operatively connect an engine with the accessory. The method  100  further includes step  106 , monitoring speed of the engine. After step  106 , the method  100  includes step  108 , comparing the monitored engine speed with a predetermined range of speeds. This preferably includes determining whether the engine speed is greater than or equal to a predetermined minimum speed and also whether the engine speed is less than or equal to a predetermined maximum speed. The predetermined minimum speed and the predetermined maximum speed may be based upon the optimal operating speed of the accessory or accessories. For example, the optimal operating speed ranges of the first, second and third accessories,  42 ,  44  and  46  can be stored within the controller  32 . The accessory having the greatest lower minimum speed is used by the controller  32  to determine minimum speed. The accessory having the lowest upper maximum speed may be used by the controller  32  to determine the maximum speed. Based on the determination of step  108 , under step  109 , the controller  32  controls power to the drive motor  72  and engagement of the torque-transmitting mechanism  48  so that the accessories  42 ,  44  and  46  are driven by the engine  14  if the engine speed is within the predetermined range of speeds and is driven by the drive motor  70  if monitored engine speed is not within the predetermined range of speeds. 
         [0022]    If it is determined in step  108  that the engine speed is within the predetermined range, then step  109  includes step  110 A in which the controller  32  determines whether the torque-transmitting mechanism  48  is engaged. If the torque-transmitting mechanism  48  is engaged, then it continues to be maintained in the engaged state, as this is the most optimal manner for driving the accessories  42 ,  44  and  46 . The method  100  then continues to monitor engine speed under step  108 . However, if it is determined in step  110 A that the torque-transmitting mechanism  48  is not engaged, then the method  100  moves to step  114 , engaging the torque-transmitting mechanism  48 . The engaging step  114 , thus occurs during a first mode of operating conditions in which the engine  14  is determined to be within a predetermined speed range so that the controller  32  allows the engine  14  to drive the accessories  42 ,  44  and  46 . The method  100  then continues to monitor the engine speed under step  108 . 
         [0023]    If in step  108  it is determined that the monitored engine speed is not within the predetermined range, then step  109  includes step  110 B (which is comparable with step  110 A), determining whether the torque-transmitting mechanism  48  is engaged. If the torque-transmitting mechanism  48  is determined to be engaged, method  100  then includes disengaging torque-transmitting mechanism  48  in step  116  and powering the motor  70  in step  118  so that the motor  70  drives the accessories  42 ,  44 ,  46  at a speed within an optimal range for the accessories  42 ,  44 ,  46 . If in step  108  it is instead determined that the monitored engine speed is not within the predetermined range and under step  110 B it is determined that the torque-transmitting mechanism  48  is not engaged, the method  100  goes directly to step  118  in which the controller  32  controls power to the motor  70  to drive the accessories within the optimal speed range. 
         [0024]    Thus, in a first mode of operating conditions in which engine speed is within the predetermined range, under step  108 , the controller  32  will determine that the engine speed is within the predetermined range (i.e., it is greater than or equal to the predetermined minimum speed and less than or equal to the predetermined maximum speed). In this instance, step  110 A will result in engaging the torque-transmitting mechanism  48  if it is disengaged via step  114  or maintaining it in the engaged state if it is already engaged so that the engine  14  drives the accessories  42 ,  44  and  46  via the torque-transmitting arrangement  53 . 
         [0025]    In a second mode of operating conditions in which the monitored speed of the engine is zero, such as when the engine is turned off and the vehicle  10  is being powered by the motor/generators  20 ,  22 , the method  100  determines in step  108  that the engine speed is less than the predetermined minimum speed. Under step  110 B, the method  100  determines whether the torque-transmitting mechanism is engaged and, if it is engaged, disengages the torque-transmitting mechanism in step  116 . The method  100  then controls power to the motor  70  under step  118  such that the motor  70  drives the accessories  42 ,  44  and  46 . 
         [0026]    In a third operating mode, the monitored engine speed of step  106  is a non-zero value but is less than the predetermined minimum speed. In this instance, after step  108  the controller will move to step  110 B and either disengage the torque-transmitting mechanism  48  in step  116  or move directly to step  118  (if the torque-transmitting mechanism  48  is not engaged) so that power is provided by the motor  70  to drive the accessories  42 ,  44  and  46  at a speed within the optimal range. 
         [0027]    Finally, in a fourth operating mode, the monitored engine speed of step  106  is greater than the predetermined maximum speed. Under step  108 , the method  100  will move to step  110 B and, if the torque-transmitting mechanism  48  is engaged, it will be disengaged under step  116  and, whether or not the torque-transmitting mechanism was determined to be engaged under step  110 B, under step  118  power will be provided by the motor  70  to drive the accessories  42 ,  44 ,  46  within the optimal range for the accessories  42 ,  44  and  46 . 
         [0028]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.