Abstract:
A single motor clutchless, torque converter-less buffer system is provided for linking an engine ( 101 ) to a transmission ( 111 ). Within this context of this system, the drive train comprises an engine ( 101 ), an electric motor ( 103 ), and a lossless buffer ( 109 )receiving the engine output ( 106 ) and the motor output ( 107 ), and having a buffer output ( 113 ), such that the lossless buffer ( 109 ) provides a range of transmission ratios including a zero transmission ratio. The term “lossless” denotes the absence of intentional frictional losses/slippage such as may be present in clutches and torque converters. In an embodiment, the lossless buffer ( 109 ) includes a planetary system between the engine ( 101 ) and the transmission ( 111 ), wherein the single electric motor ( 103 ) functions to vary the transmission ratio of the buffer ( 109 ).

Description:
TECHNICAL FIELD 
       [0001]    This patent disclosure relates generally to continuously variable transmissions and, more particularly to continuously variable transmission having a clutchless input that does not require a torque converter. 
       BACKGROUND 
       [0002]    When a powered machine is accelerated, i.e., “launched,” from a standstill to a forward or reverse speed, the primary mover, e.g., the engine, of the machine transitions from a disengaged state to an engaged state. Whenever the engine is in the engaged state, its speed is generally related to the speed of the machine by a transmission ratio. However, this relationship is approximate in that a clutch or torque converter is generally employed to smooth the transition from the disengaged to the engaged state. Without the clutch or torque converter, the engine could stall or, at best, lug severely. 
         [0003]    Although a number of types of transmissions are usable in such machines, a continuously variable transmission (“CVT”) is often used for its ability to provide a wide range of ratios and to smoothly vary the transmission ratio. One traditional CVT type is a split path transmission which includes an input for the primary mover as well as for two motors. The two motors, working in cooperation, set the ratio of the transmission. However, while providing smooth operation and a wide range of transmission ratios, the motors also contribute size, weight, and expense to the final transmission assembly. 
         [0004]    Although single motor CVTs have been attempted, none has been of a design and configuration sufficient to substantially ameliorate the foregoing problems. 
       SUMMARY 
       [0005]    In one aspect, the disclosed principles pertain to a single motor drive train system for propelling a host machine, the drive train system comprising an engine, a motor, and a lossless buffer receiving the engine output and the motor output, and having a buffer output, such that the lossless buffer provides a range of transmission ratios between the rotational engine output and the rotational buffer output, wherein the range of transmission ratios includes a zero transmission ratio. It should be noted that in the context of this disclosure, the term “lossless” does not mean that the entity in question experiences, or has imposed upon it, no loss of energy whatsoever. Rather, the term “lossless” denotes the absence of intentional frictional losses/slippage such as may be present in clutches and torque converters. 
         [0006]    Continuing with this aspect of the disclosure, the transmission input is linked directly to the rotational buffer output, and has a rotational transmission output linked to a propulsion means to propel the host machine. Thus, rotation of the transmission input rotates the transmission output, causing the propulsion means to propel the host machine. 
         [0007]    In another aspect, a machine is provided for rendering clutchless engagement of a transmission without the use of a torque converter. The machine comprises an engine for propelling the machine, a transmission having a transmission input and a transmission output, and a lossless buffer between the engine and the transmission, wherein the lossless buffer employs a single electric motor to provide ratios in a range including zero between the engine output and the transmission input. 
         [0008]    In yet another aspect of the disclosure, a buffer system is provided for managing the transmission of power between an engine and a transmission in the absence of a torque converter or clutch between the engine and the transmission. The buffer system comprises a mechanical buffer receiving as input an output of the engine and providing as output an input to the transmission, and a single electric motor controlling the input-to-output transmission ratio of the mechanical buffer to allow the mechanical buffer to provide such ratios in a range including zero. The system also includes a controller for controlling the single electric motor to modify the transmission ratio of the mechanical buffer. 
         [0009]    Other aspects and features will be apparent from the detailed description, taken in conjunction with the drawings, of which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration showing a power train system and an associated environment within which embodiments of the disclosed principles may be employed; 
           [0011]      FIG. 2  is a schematic illustration of a lossless buffer system according to an embodiment of the disclosed principles; 
           [0012]      FIG. 3  is a power flow diagram illustrating power flow during an idle mode from an engine to a motor via a lossless buffer according to an embodiment of the disclosed principles; 
           [0013]      FIG. 4  is a power flow diagram illustrating power flow from an engine and motor to machine propulsion via a lossless buffer during propelled motion of the host machine according to an embodiment of the disclosed principles; 
           [0014]      FIG. 5  is a power flow diagram illustrating power flow from the host machine to the motor via the lossless buffer during braking of the host machine according to an embodiment of the disclosed principles; and 
           [0015]      FIG. 6  is a flow chart illustrating a process of regulating and coordinating a lossless buffer, engine and motor according to an embodiment of the disclosed principles. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    This disclosure relates to machines requiring a transmission to link a power source to a final ground-engaging mechanism, e.g., wheels, tracts, etc. Examples of such machines include machines used for mining, construction, farming, transportation, and other industries and endeavors known in the art. For example, the machine may be an earth-moving machine, such as a wheel loader, excavator, dump truck, backhoe, motor grader, material handler or the like. Moreover, an implement may be connected to the machine. Such implements may be utilized for a variety of tasks, including, for example, loading, compacting, lifting, brushing, and may include, for example, buckets, compactors, forked lifting devices, brushes, grapples, cutters, shears, blades, breakers/hammers, augers, and others. 
         [0017]      FIG. 1  is a diagrammatic illustration showing a power train system  100  and the associated environment within which embodiments of the disclosed principles may be used. The illustrated power train system  100  includes an engine  101 , which is an example of a primary mover, having an engine output  106 . It will be appreciated that the operation of the engine  101  is executed based on one or more inputs, including, for example, an input from a user interface (not shown), e.g., a pedal or lever, as well as an input from a controller  105 , e.g., for purposes of torque control, traction control, etc. 
         [0018]    A motor  103 , e.g., an electric motor is provided having a motor output  107 . It will be appreciated that the motor  103  may consume electrical energy to provide a torque or may be driven while providing a reactive force, thus generating electricity for storage in a battery (not shown) or other storage element. A lossless buffer  109  is interposed between the motor  103  and engine  101 , and a transmission  111 . For driving a load, the lossless buffer  109  provides at a buffer output  113  to the transmission  111  a weighted combination of the rotation of the engine  101  and the rotation of the motor  103 . 
         [0019]    The details of the lossless buffer  109  will be discussed in detail below with reference to  FIG. 2 , however, before proceeding, the characteristics and operation of the power train system  100  will be described in overview via continued reference to  FIG. 1 . As can be seen, the power train system  100  operates to provide rotational power to the remainder of the machine drive train  115 , which may comprise one or both of wheels, tracks, or other propulsion means. The power required to propel the drive train  115  originates in the primary mover, e.g., the engine  101 . Additional power may be supplied via a battery which may be charged by one or both of an off-board system and the motor  103 . 
         [0020]    The power train system  100  exhibits three primary states. The first occurs when the engine  101  is running, but the machine is not moving. In this state, the torque provided to the transmission  111  by the engine  101  via the engine output  106  is essentially reflected to the motor  103  via the motor output  107 , whereupon the energy is either stored, e.g., via a battery, or dissipated, e.g., via a resistive grid. In the second state, usually occurring when the machine is being launched from the first state, the engine  101  provides torque to the lossless buffer  109  via the engine output  106 , the machine is moving at least slightly, and the motor  103  is being driven by the lossless buffer  109  via the motor output  107 , but is providing a reactive torque to accelerate or move the machine. 
         [0021]    In other words, in this second stage, the motor  103  resists movement, and as such, the buffer output  113  of the lossless buffer  109  moves or accelerates under the force of the engine  101 . In the third stage, the engine  101  provides torque to the lossless buffer  109  via the engine output  106  and the motor  103  provides proactive torque to the lossless buffer  109  via the motor output  107 . In this state, the rotational speed of the buffer output  113  is a weighted average of the rotational speed of the engine  101  and the motor  103 . The effective transmission ratio of the lossless buffer  109  relative to the engine output  106  is controlled by the rotational speed of the motor output  107 , i.e., the rotational speed of the motor  103 . Thus, for example, if the engine speed and motor speed are of equal magnitudes but opposite directions, the transmission ratio of the lossless buffer  109  is zero. Moreover, fractional or overdrive ratios between the engine output  106  and the buffer output  113  can be provided by varying the speed of rotation of the motor output shaft  107 . 
         [0022]    The illustrated configuration thus allows the machine to be launched from a stationary state to a moving state without clutches or torque converters between the engine  101  and the split torque transmission  103 , while also allowing a wide range of effective transmission ratios. This provides the benefits of allowing a compact and simple installation, while avoiding excess expenditures on equipment and maintenance. 
         [0023]      FIG. 2  illustrates in detail an example of a lossless buffer  109  according to the disclosed principles. In particular,  FIG. 2  is a schematic view of the lossless buffer  109 , showing exemplary configurations and internal connections and gearings of the lossless buffer  109 . As discussed above, the lossless buffer  109  links an engine output  106 , a motor output  107 , and a buffer output  113 . In the illustrated embodiment, the lossless buffer  109  includes a planetary gear set  200  including at least one sun gear  201 , at least one ring gear  203 , and at least one planet gear/planet gear carrier assembly  205 . 
         [0024]    As can be seen, the engine output  106  is connected to the at least one sun gear  201 , such that rotation of the engine  101  serves to rotate the at least one sun gear  201  at a like speed and in a like direction. Also shown, the motor output  107  is linked to the at least one ring gear  203 . In this way, the torque of the at least one ring gear  203  is transferred to second input  107  and hence to the motor  103 . Likewise, the torque of the motor  103  is transferred via the motor output  107  to the at least one ring gear  203 . Finally, in the illustrated embodiment, the at least one planet gear/planet gear carrier assembly  205  is linked to the buffer output  113 . In this way, the engine output  106 , motor output  107 , and buffer output  113  are interconnected and their rotational speeds are interrelated. 
         [0025]    It will be appreciated that the tooth counts used to reach these ratios are not critical, and that the ratios used in any particular implementation need not match the example given above to fall within the disclosed principles of operation. 
         [0026]      FIGS. 3-5  illustrate the power flow in the lossless buffer  109  according to the disclosed principles in various modes of operation including an idle state, a moving state, and a braking state. Referring specifically to  FIG. 3 , the power flow during the idle mode is from the engine  101  via the engine output  106  to the motor  103  via the motor output  107 . In this mode, the buffer output  113  is static because the host machine is stationary. 
         [0027]    Referring to  FIG. 4 , this power flow diagram illustrates the power flow through the lossless buffer  109  during propelled motion of the host machine. As can be seen, the power flow in this instance is from the engine  101  via the engine output  106 , and from the motor  103  via the motor output  107 , to the buffer output  113 . It will be appreciated that within this mode, the engine  101  provides a rotational torque in a given direction and the lossless buffer  109  imposes a rotational torque on the buffer output  113  in a given direction. However, the motor  103  may provide either active or reactive torque and thus will rotate in a direction that is dependent upon the desired speed of the machine in motion. 
         [0028]    Thus, for example, at the time of transition from the idle mode to forward or reverse motion of the machine, the motor  103  transitions from being a strictly driven element to providing an active or reactive torque at the second input  107 . The active or reactive torque can be generated by supplying a voltage input to the motor  103  in a direction the same as or opposite to (for reactive torque) the induced current, with the polarity of voltage determining the direction of the applied torque and the magnitude of the voltage determining the extent of the torque on the motor output  107 . 
         [0029]    It is also expected to use the illustrated configuration to provide a braking force to the buffer output  113 , e.g., to decelerate the host machine.  FIG. 5  illustrates the power flow in the split torque transmission  103  during braking. In particular, the engine  101 , which is no longer needed for acceleration, provides a resistive or reactive torque to the engine output  106 . At the same time, the motor  103  is switched from a powering mode to a generating mode, such that any electrical power is dissipated, e.g., via a resistive grid, or stored, e.g., via one or more batteries. Ordinary service brakes, e.g., friction brakes, may also be employed at this time. Moreover, it will be appreciated that, depending upon the degree of braking required, powered reactive braking through the motor  103  may also be employed. 
         [0030]    As shown in the example environment of  FIG. 1 , the operation of the lossless buffer  109  as well as the engine  101  and the motor  103  are monitored and controlled via a controller  105 . The controller  105  may be any computing device capable of sensing one or more conditions of the lossless buffer  109 , engine  101  and/or motor  103  and providing control outputs to one or more of the lossless buffer  109 , engine  101  and motor  103 . By way of example, the controller  105  may be integrated with an engine or machine control module, or may be a separate device. The controller  105  operates by reading computer-readable instructions from a computer-readable medium and executing the read instructions. The computer-readable medium may be a tangible medium such as a hard drive, optical disc, jump drive, thumb drive, flash memory, ROM, PROM, RAM, etc., or may be an intangible medium such as an electrical or optical wave form traveling in air, vacuum, or wire. 
         [0031]    The process executed by the controller  105  in regulating and coordinating the lossless buffer  109 , engine  101  and motor  103  is shown via the process  600  of  FIG. 6 . Although the process  600  proceeds from a stationary state, through a moving state, returning to a stationary state, it will be appreciated that the initial state may be other than stationary and that the control process in such a case would be executed from the appropriate step onward. 
         [0032]    The initial state of the host machine prior to execution of process  600  is idle, i.e., the engine  101  is running but the host machine is not moving. At stage  601  of the process  600 , the controller  105  receives an acceleration command, e.g., from a physical or electrical user interface element. Pursuant to the command received at stage  601 , the controller  105  first optionally connects the motor  103  to a motor controller at stage  603  if the motor  103  had been providing electrical power to a battery or the like during idling. At stage  605 , the controller  105  increases fuel flow to the engine  101  to increase its output power, while also increasing the reactive torque provided by the motor  103  via the motor controller. These actions have the net effect of increasing torque at the buffer output  113  to accelerate the host machine. 
         [0033]    Once a desired speed is attained, e.g., further acceleration is not requested, the controller  105  may continue to increase the speed of the motor  103  while decreasing the speed of the engine  101  at stage  607 . This increases the effective transmission ratio of the split torque transmission  103  to conserve fuel and allow the engine  101  to operate within an optimal operating range. 
         [0034]    At stage  609 , the controller  105  receives a retarding command, again optionally resulting from interaction of the user with a user interface element. At stage  611 , in response to the retarding command, the controller  105  idles the engine  101  and shunts the motor inputs so that the motor now supplies electrical energy to a battery or dissipater. This action tends to reduce the speed of the machine. If need be, the controller  105  may optionally apply the service brakes of the machine at stage  613 . 
       INDUSTRIAL APPLICABILITY 
       [0035]    The present disclosure is applicable to driven machines having transmissions for imparting motion to the machine. In particular, the disclosed principles provide a mechanism for omitting a clutch and torque converter from the machine drive train while maintaining the ability to start and stop the host machine without lugging or stalling the engine  101 . This system may be implemented in on-highway or off-highway machines, construction machines, industrial machines, etc. Although many machines that may benefit from the disclosed principles will be machines used at least occasionally for transport of goods, materials, or personnel, it will be appreciated that such transmissions are used in other contexts as well, and the disclosed teachings are likewise broadly applicable. 
         [0036]    Using the disclosed principles, a lossless buffer  109  is disposed in the machine drive train system  100  between driving elements, e.g., engine  101  and motor  103 , and a transmission. The buffer provides zero, fractional, and overdrive ratios between the engine  101  and the transmission to allow start up from full stop with the engine  101  running and to allow stopping from forward motion without stalling the engine  101 . It will be appreciated that this description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. Moreover, the references to examples herein are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to various features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated. Although the motor  103  has been referred to herein as an electric motor, it will be appreciated that the motor  103  may instead be a hydraulic motor or other non-electric motor without departing from the scope of the disclosed principles. 
         [0037]    Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order and from any suitable step unless otherwise indicated herein or otherwise clearly contradicted by context.