Abstract:
A hybrid-electric vehicle powertrain including a first prime mover and an electric traction motor/generator provides for electric operation of a power take off. A sensor indicates electric fraction motor/generator speed. A control system provides for limiting engagement of the power take off to the electric traction motor/generator through a transmission to periods when the electric traction motor/generator is turning a less than a predefined maximum speed.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The field relates power take off from hybrid electric vehicles and more particularly to use of the vehicle&#39;s powertrain control system to control engagement and disengagement of the power take off 
         [0003]    2. Description of the Technical Field 
         [0004]    Some hybrid electric vehicles transmit mechanical torque and angular velocity to a power take off (PTO) output shaft through a use a manual or automated manual type transmission. In these circumstances the PTO conventionally includes an intermediary coupling and decoupling mechanism (hereafter PTO coupler) between the transmission and the loads attached to a PTO output shaft. A problem can occur during either the initial engagement or re-engagement of the intermediary mechanism if the transmission&#39;s internal drive gearing is not fully stopped. Engagement combined with the inertia cost down of the traction motor/generator and transmission gearing can create a condition within the intermediary mechanism where coupling gears and shift collar teeth clash due to a difference in speeds (angular velocities) of the two active members. This produces gear grinding problems. 
       SUMMARY 
       [0005]    A hybrid-electric vehicle powertrain including a first prime mover and an electric traction motor/generator provides for electric operation of a power take off A sensor indicates electric traction motor/generator speed. A control system provides for limiting engagement of the power take off to the electric traction motor/generator through a transmission to periods when the electric traction motor/generator is turning a less than a predefined maximum speed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic of a hybrid-electric vehicle drive train and associated control system. 
           [0007]      FIG. 2  is a block diagram of a state machine for the hybrid-electric vehicle drive train of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    In the following detailed description, like reference numerals and characters may be used to designate identical, corresponding, or similar components in differing drawing figures. Furthermore, example sizes/models/values/ranges may be given with respect to specific embodiments but are not to be considered generally limiting. 
         [0009]    Referring to  FIG. 1  a hybrid-electric powertrain  10  comprises an internal combustion (IC) engine  12 , an electric traction motor/generator  14 , a clutch  16  by which the electric traction motor/generator  14  and IC engine  12  may be mechanically coupled to one another, a manual or automated manual transmission  18  by which torque and angular velocity may be applied to an output shaft/driveshaft  20 . That hybrid-electric powertrain  10  incorporates an IC engine  12  is illustrative only, as the engine could be selected from any number of sources of mechanical energy, such as a gas turbine or steam engine and the like. 
         [0010]    Depending from the transmission  18  is a power take off (PTO)  26  through which torque and angular velocity can be transferred from the transmission  18  to a PTO output shaft  32 . PTO output shaft  32  is attached to PTO integrated equipment  34  such as a hydraulic or pneumatic pump, an electrical generator, and the like. PTO  26  includes a PTO coupler  28  which allows engagement and disengagement of the PTO output shaft  32  to the transmission  18 . Translation of the PTO coupler  28  between engaged and disengaged positions is effected using a PTO actuator  30 . 
         [0011]    PTO actuator  30  is depicted as a spring biased pneumatic piston in cylinder device however, PTO actuator  30  can be realized in a number of different ways. The apparatus for engaging and disengaging the mechanical PTO coupler  28  can include without limitation: an electromechanical solenoid and linkage, electromechanical solenoid pneumatic valve with piston, mechanized ball screw and nut, a pneumatic piston and clutch, a hydraulic piston and clutch, linear motors, worm gears, and the like. For a spring biased pneumatic piston in cylinder device a source of compressed air is used (compressed air tank  36 ) to urge the spring biased piston against the direction of bias to engage the PTO coupler  28 . The application of compressed air occurs through a solenoid controlled valve  38  with the valve controlled in turn by an electrical signal from RPM  40 . RPM  40  is also connected to receive an engagement indication signal from the PTO actuator  30 . While present the engagement signal is not needed for operation of the presently described control arrangement. 
         [0012]    Hybrid-electric powertrain  10  is instrumented and the instrumentation includes two angular velocity sensors. The first is an output shaft angular velocity sensor  22  which provides a voltage signal proportional to the angular velocity at which the output shaft  20  is turning. The second is a motor angular velocity sensor  24  which provides a signal which is proportional to the angular velocity of electric traction motor/generator  14 . These signals are routed by wire connections to nodes of a powertrain/vehicle control system  11 , in particular the angular velocity signal for the output shaft/driveshaft  20  is transmitted to either (or both) the engine controller  46  or the transmission controller  48 , which report the value over the twisted pair datalink  42 . The body controller  44  accesses the messages carrying the angular velocity signal from the datalink  42 . The output of the motor angular velocity sensor  22  is applied to the body controller  44 . 
         [0013]    The powertrain control system  11  is based on a controller area network (CAN) architecture which includes a twisted wire pair datalink  42  to transmit data between a plurality of nodes. The architecture of  FIG. 1  is a simplified representation with only four nodes shown, a body controller  44 , an engine controller  46 , a transmission/traction motor controller  48  and a remote power module (RPM)  40 . The RPM  40  operates essentially as a slave of the body controller  44  to provide the function of a PTO coupler engagement/disengagement controller. The body controller  44  has control over PTO  26  operation and receives various chassis inputs through which requests for PTO  26  operation occur. The chassis inputs can include operator requests for PTO  26  operation (which result in engagement or disengagement) and requests relating to PTO output shaft  32  angular velocity and torque (which are communicated to the engine controller  46  or to the transmission controller  48  in its function as motor controller). 
         [0014]    In addition to the chassis inputs relating to requests relating to PTO  26  operation various interlock conditions may be programmed into the system which must be satisfied before the powertrain  10  enters an PTO operational state. Some of the interlock conditions may be values for chassis inputs and signals relating to other interlocks may be communicated to body controller  44  over twisted wire pair datalink  42 . Examples of values relating to interlocks communicated over twisted wire pair datalink  42  include vehicle speed and current gear achieved from the transmission controller  48 . Values which may be received as chassis inputs include park brake status. 
         [0015]    The powertrain control system  11  leverages a controller area network (CAN) based control architecture to control engagement and disengagement of the PTO coupler  28  mechanism. In relation to this the hybrid-electric powertrain  10  can source angular velocity and torque during the operation of the PTO integrated equipment  34  from two sources, those being the IC engine  12  or the electric traction motor/generator  14 . A hybrid-electric powertrain which can support PTO operation by use of its traction motor without operation of its engine is said to be in an electrified PTO state or “ePTO mode.” The ePTO mode usually occurs outside of an operator&#39;s specific request during PTO operation on a hybrid-electric vehicle when its rechargeable energy storage system (RESS) has an adequate state of charge. 
         [0016]    In the ePTO mode for hybrid-electric powertrain  10  it remains possible for the IC engine  12  to produce angular velocity, however, the clutch  16  positioned between the IC engine  12  and the electric traction motor/generator  14  is either partially or completely open and energy is not transmitted from IC engine to the PTO output shaft  32 . Body controller  44  with its subordinate RPM  40  use the traction motor/generator  14  angular velocity data from motor angular velocity sensor  24  to intelligently control engagement and disengagement of the PTO actuator/shift mechanism  30  to avoid clashing of PTO coupler  28  gearing or excessive clutch slippage due to significant speed differentials between active coupling members. 
         [0017]    In ePTO mode it is possible for the PTO coupler  28  to disengage while the electric traction motor/generator  14  is turning. In ePTO modes of interest here the current gear achieved by the transmission  18  is always neutral (meaning torque is not transmitted to transmission output shaft  20 ). Upon disengagement of the PTO coupler  28  there will be no load on the electric traction motor/generator  14  and the electric traction motor/generator will begin to coast down unless some provision is made for regenerative braking of the motor/generator. This is not usual as the available energy for recapture is usually small. The PTO integrated equipment  34  is usually under load and will decelerate much more quickly than the electric traction motor/generator  14 . A speed difference will open between the components that only begins closing about the time the PTO integrated equipment  34  comes to a stop and disappears only when the electric traction motor/generator  14  itself comes to a stop. The speed difference between electric traction motor/generator  14  and the PTO integrated equipment  34  when the PTO coupler  28  is disengaged is usually substantially equal to the angular velocity measurement of the motor angular velocity sensor  24 . 
         [0018]    The body controller  44  does not engage the PTO actuator  30  (or more precisely, cause the RPM  40  to apply an activation signal to solenoid  38 ) until the angular velocity speed of the PTO coupler  28  matches, or is within a predetermined speed range, of the traction motor/generator  14 . It is possible to customize the speeds at which PTO coupler  28  engages and disengages based on rate of angular velocity of the traction motor/generator  14 . This ability is accomplished through software adjustment parameters built into the body controller  44  software. 
         [0019]    Referring to  FIG. 2  a state machine is used to further explain the present system. State  60  represents a state in which ePTO mode is active, the electric traction motor/generator  60  is turning (note that “turning” does not imply that the motor is receiving electrical energization), the PTO coupler  28  is engaged and the ePTO primary interlock conditions have been met. The primary interlock conditions vary from vehicle to vehicle. A representative set for PTO integrated equipment  34  that includes a manned basket for overhead power line work could be: 1) park brake set; 2) vehicle speed (which may be obtained from the angular velocity of the output shaft  20 ) of less than 5 kph; and 3) the current gear achieved is neutral. If any of these three conditions fail the state will transition to state  62  where, while ePTO mode remains active the PTO coupler  28  is disengaged. State  62  remains current as long as the electric traction motor/generator  14  is turning at greater than a maximum limit, which can be on the order of 4 to 5 RPM. No transition from state  62  to state  60  occurs until motor angular velocity falls below the maximum limit (assuming the other conditions for state  60  have been established or restored). In other words the conditions for transitions between states  60  and  62  are not symmetric. 
         [0020]    It is possible for ePTO mode to initially be in either state  60  or state  62 . In addition, it is also possible to establish that the motor be turning at some minimal rate, say at least 1 RPM, before a transition from state  62  to state  60  occurs. If traction motor/generator  14  is motionless upon ePTO mode becoming active than a minimal application of power to the motor/generator may occur to initiate turning. This is done to ease meshing of the gears within the PTO coupler  28  without giving rise to grinding. 
         [0021]    A state  64  is illustrated indicated disengagement of PTO coupler  28  where motor angular velocity of the electric traction motor/generator  14  has exceeded a limit for the PTO integrated equipment  34 . For example, motor angular velocity may reach a speed which would produce cavitation in a hydraulic pump which was part of the PTO integrated equipment  34 . In this case the PTO coupler  28  may be reengaged upon lapse of the over speed condition. 
         [0022]    The state machine of  FIG. 2  is not comprehensive with respect all possible vehicle states. For example, it will be clear to those skilled in the art that should ePTO mode becomes inactive upon closure of clutch  16  to connect the electric traction motor/generator  14  to IC engine  12 , which may occur if the state of charge of a vehicle RESS (not shown) decline to a level that initiates operation of the IC engine to back drive the electric traction motor/generator  14  to generate electricity. In this case the powertrain  10  may remain in a PTO mode, however it will not be an ePTO mode.