Abstract:
A two-mode, compound-split, electromechanical transmission utilizes an input member for receiving power from an engine, and an output member for delivering power from the transmission. First and second motor/generators are operatively connected to an energy storage device through a control for interchanging electrical power among the storage device. The transmission employs three planetary gear sets that cooperate with a plurality of torque transmitting devices to provide two distinct gear trains or power paths corresponding to two modes of electrically variable operation in which the speed ratio between the input member and the output member varies with the speed of at least one of the motor/generators. The torque transmitting devices are selectively engageable to provide six discrete, fixed speed ratios.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a two-mode, compound-split, hybrid electromechanical vehicular transmission that utilizes three interactive planetary gear arrangements that are operatively connected to an engine and two motor/generators. The planetary gear arrangements provide two modes, or gear trains, that are selectively available to transmit power from the engine and/or the motor/generators to the output member of the transmission. The transmission also provides six available fixed ratios.  
       BACKGROUND OF THE INVENTION  
       [0002]     The purpose of a vehicular transmission is to provide a neutral, at least one reverse and one or more forward driving ranges that impart power from an engine, and/or other power sources, to the drive members which deliver the tractive effort from the vehicle to the terrain over which the vehicle is being driven. As such, the drive members may be front wheels, rear wheels or a track, as required to provide the desired performance.  
         [0003]     A series propulsion system is a system in which energy follows a path from an engine to a first motor/generator, then to an optional electric storage device, and then to a second motor/generator which applies power to rotate the drive members. There is no direct mechanical connection between the engine and the drive members in a series propulsion system.  
         [0004]     Transmissions adapted to receive the output power from either an engine-driven generator or an energy storage device, or both, have heretofore relied largely on what has been designated as series, hybrid propulsion systems. Such systems are designed with auxiliary power units (APUs) of relatively low power for minimum emissions and best fuel economy. However, such combinations of small APUs and even large energy storage devices do not accommodate high-average power vehicles or address duty cycles that demand continuous, constant speed operation. Steep grades and sustained high-average cruising speeds at desired high efficiencies are not achievable with a typical, series, hybrid transmission configuration.  
         [0005]     The challenge, therefore, is to provide a power system that will operate at high efficiencies over a wide variety of operating conditions. Desirable electric variable transmissions should leverage the benefits of a series, hybrid transmission for desirable low-average power duty cycles—i.e., low speed start/stop duty cycles—as well as the benefits of a parallel hybrid transmission for high-average output power, high speed duty cycles. In a parallel arrangement, the power supplied by the engine and the power supplied by the source of electrical energy are independently connected to the drive members to ensure maximum efficiency in both low and high average power duty cycles.  
         [0006]     Moreover, perfecting a concept wherein two modes, or two integrated power split gear trains, with either mode available by synchronous selection of internal clutching by the on-board computer to transmit power from the engine and/or the motor/generator to the output shaft, results in a hybrid transmission having an extremely wide range of applications.  
         [0007]     The desired beneficial results may be accomplished by the use of a variable, two-mode, input and compound split, parallel hybrid electro-mechanical transmission. Such a transmission utilizes an input member to receive power from the vehicle engine and a power output member to deliver power to drive the vehicle. First and second motor/generator power controllers are connected to an energy storage device, such as a battery pack, so that the energy storage device can accept power from, and supply power to, the first and second motor/generators. A control unit regulates power flow among the energy storage devices and the motor/generators as well as between the first and second motor/generators.  
         [0008]     A variable, two-mode, input-split, parallel, hybrid electro-mechanical transmission also employs at least one planetary gear set. The planetary gear set has an inner gear member and an outer gear member, each of which meshingly engages a plurality of planet gear members. The input member is operatively connected to one of the gear members in the planetary gear set, and means are provided operatively to connect the power output member to another of the gear members in the planetary gear set. One of the motor/generators is connected to the remaining gear member in the planetary gear set, and means are provided operatively to connect the other motor/generator to the output shaft.  
         [0009]     Operation in the first or second mode may be selectively achieved by using torque transfer devices. Heretofore, in one mode the output speed of the transmission is generally proportional to the speed of one motor/generator, and in the second mode the output speed of the transmission is generally proportional to the speed of both motor/generators.  
         [0010]     In some embodiments of the variable, two-mode, input-split, parallel, hybrid electromechanical transmission, a second planetary gear set is employed. In addition, some embodiments may utilize three torque transfer devices—two to select the operational mode desired of the transmission and the third selectively to disconnect the transmission from the engine. In other embodiments, all three torque transfer devices may be utilized to select the desired operational mode of the transmission.  
         [0011]     With reference, again, to a simple planetary gear set, the planet gear members are normally supported for rotation on a carrier that is itself rotatable. When the sun gear is held stationary and power is applied to the ring gear, the planet gear members rotate in response to the power applied to the ring gear and thus “walk” circumferentially about the fixed sun gear to effect rotation of the carrier in the same direction as the direction in which the ring gear is being rotated.  
         [0012]     When any two members of a simple planetary gear set rotate in the same direction and at the same speed, the third member is forced to turn at the same speed, and in the same direction. For example, when the sun gear and the ring gear rotate in the same direction, and at the same speed, the planet gears do not rotate about their own axes but rather act as wedges to lock the entire unit together to effect what is known as direct drive. That is, the carrier rotates with the sun and ring gears.  
         [0013]     However, when the two gear members rotate in the same direction, but at different speeds, the direction in which the third gear member rotates may often be determined simply by visual analysis, but in many situations the direction will not be obvious and can only be determined by knowing the number of teeth present in the gear members of the planetary gear set.  
         [0014]     Whenever the carrier is restrained from spinning freely, and power is applied to either the sun gear or the ring gear, the planet gear members act as idlers. In that way, the driven member is rotated in the opposite direction as the drive member. Thus, in many transmission arrangements when the reverse drive range is selected, a torque transfer device serving as a brake is actuated frictionally to engage the carrier and thereby restrain it against rotation so that power applied to the sun gear will turn the ring gear in the opposite direction. Thus, if the ring gear is operatively connected to the drive wheels of a vehicle, such an arrangement is capable of reversing the rotational direction of the drive wheels, and thereby reversing the direction of the vehicle itself.  
         [0015]     As those skilled in the art will appreciate, a transmission system using a power split arrangement will receive power from two sources. Utilization of one or more planetary gear sets permits two or more gear trains, or modes, by which to deliver power from the input member of the transmission to the output member thereof.  
         [0016]     U.S. Pat. No. 5,558,588 issued Sep. 24, 1996, to Schmidt, and which is hereby incorporated by reference in its entirety, teaches a variable, two-mode, input-split, parallel, hybrid electromechanical transmission wherein a “mechanical point” exists in the first mode and two mechanical points exist in the second mode. U.S. Pat. No. 5,931,757 issued Aug. 3, 1999 to Schmidt, and which is hereby incorporated by reference in its entirety, teaches a two-mode, compound-split, electromechanical transmission with one mechanical point in the first mode and two mechanical points in the second mode.  
         [0017]     A mechanical point occurs when either of the motor/generators is stationary at any time during operation of the transmission in either the first or second mode. The lack of a mechanical point is a drawback inasmuch as the maximum mechanical efficiency in the transfer of power from the engine to the output occurs when one of the motor/generators is at a mechanical point—i.e., stationary. In variable, two-mode, input-split, parallel, hybrid electro-mechanical transmissions, however, there is typically one point in the second mode at which one of the motor/generators is not rotating such that all the engine power is transferred mechanically to the output.  
         [0018]     The two-mode, compound-split, electromechanical transmission referenced above is an efficient option for commercial-duty vehicles, such as transient buses and the like, which regularly operate at close to their maximum capacity. In very light vehicles, however, losses generated in the motor-inverter system can influence fuel economy in some instances. Also, the power to weight factors of many light vehicles cannot always be reduced if, for instance, a towing requirement establishes engine sizing.  
       SUMMARY OF THE INVENTION  
       [0019]     The present invention provides an adaptation of a two-mode, compound-split, electro-mechanical transmission which is particularly useful in personal trucks, wherein the typical load is less than half of maximum capacity. The transmission provides two electrically variable modes of operation wherein the speed ratio between an input member and an output member varies with the speed of one or more electric motors. The transmission also provides six fixed-ratio modes of operation whereby six different discrete speed ratios between the input member and the output member are available. Discrete speed ratios provide a means to reduce electrical losses in some instances. The transmission enables maximum power to be reached more quickly for passing, towing and hauling, and enables the use of smaller electrical components with high power engines which may be cost-effectively implemented into personal trucks and other light vehicles.  
         [0020]     Thus, the transmission provides a means of operating in most instances as an electrically variable transmission (EVT) wherein the engine is operated at or near minimum brake specific fuel consumption (BSFC) and/or at minimum emissions, and also provides a means to operate in a fixed ratio mode, which is especially advantageous when a very high instantaneous power is demanded (such as when passing) or a very light power is demanded for an extended duration.  
         [0021]     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  
       [0022]      FIG. 1  is a schematic representation of a two-mode, compound-split, electromechanical transmission embodying the concepts of the present invention; and  
         [0023]      FIG. 2  is a fixed ratio truth table for the transmission represented by  FIG. 1 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     Referring to  FIG. 1 , an electrically-variable transmission  10  is schematically depicted. The transmission  10  includes first, second, and third planetary gearsets  14 ,  18 ,  22 , each having respective first, second, and third members. More specifically, the first planetary gearset  14  includes a sun gear member  26 , a ring gear member  30 , and a planet carrier assembly  34 . The first planetary gearset  14  is compound, and thus planet carrier assembly  34  rotatably supports a first set of planet gears  38 A that mesh with sun gear member  26 . The planet carrier assembly  34  also rotatably supports a second set of planet gears  38 B that mesh with the first set of planet gears  38 A and with ring gear member  30 .  
         [0025]     The second planetary gearset  18  includes a sun gear member  40 , ring gear member  30 , and a planet carrier assembly  48 . It should be noted that the ring gear member  30  is common to both the first and second planetary gearsets  14 ,  18 . Accordingly, the ring gear of the first planetary gearset  14  and the ring gear of the second planetary gearset  18  are connected for unitary rotation. The planet carrier assembly  48  rotatably supports planet gears  52  that meshingly engage ring gear member  30  and sun gear member  40 . Planet carrier assembly  34  is operatively connected to planet carrier assembly  48  for unitary rotation therewith. Alternatively, and within the scope of the claimed invention, planetary gearsets  14 ,  18  may share a common carrier assembly that rotatably supports planet gears  38 A,  38 B, and  52 .  
         [0026]     The third planetary gearset  22  includes sun gear member  56 , ring gear member  60 , and planet carrier assembly  64 . The planet carrier assembly rotatably supports planet gears  68  that meshingly engage ring gear  60  and sun gear  56 . It should be noted that, where used in the claims, first, second, and third members of planetary gearsets do not necessarily refer to a member of a particular type; thus, for example, a first member may be any one of a ring gear member, sun gear member, or planet carrier assembly. Similarly, as used in the claims, the respective “first members” of two gearsets, for example, may or may not be the same type of member.  
         [0027]     The transmission  10  also includes a first electric motor/generator  72  and a second electric motor/generator  76 . An electrical storage device, such as battery  77 , is provided for supplying current to motor/generators  72 ,  76  when operating in a motoring mode, and receiving charging current from motor/generators  72 ,  76  when operating in a generating mode. An electronic control unit (ECU)  78 , including a microprocessor-based controller and suitable inverter circuitry, couples the battery  77  to motor/generators  72 ,  76 , and controls the same in response to various input signals, including the driver torque request signal (not shown) and the output shaft speed signal (not shown). In a preferred embodiment, the motor/generators  72 ,  76  are configured as induction machines, although other configurations are also possible. The first electric motor/generator  72  includes a stator  80  rigidly affixed to a stationary member such as transmission housing  84 . The first electric motor/generator  72  also includes a rotor  88 . The rotor  88  is connected to the sun gear member  40  of the second planetary gearset  18  for unitary rotation therewith via an interconnecting member such as sleeve  92 .  
         [0028]     The second electric motor/generator  76  includes a stator  96  that is affixed to the housing  84 , and a rotor  100 . The rotor  100  is connected to sun gear member  56  via an interconnecting member, such as sleeve  104 , for unitary rotation therewith. The transmission  10  also includes an input member, such as input shaft  108 . The input shaft  108  is operatively connected to an engine  110 , as understood by those skilled in the art. The input shaft  108  is also operatively connected to ring gear member  30  for rotation therewith.  
         [0029]     Planet carrier assembly  34  is operatively connected to main shaft  112  for rotation therewith. Sun gear member  26  is operatively connected to sleeve  116 . Planet carrier assembly  64  is operatively connected to an output member such as output shaft  120  for rotation therewith. Input shaft  108 , output shaft  120 , sleeves  92 ,  104 ,  116 , and shaft  112  are rotatable about a common axis A. The motor/generators  72 ,  76  and planetary gearsets  14 ,  18 ,  22  are coaxially aligned about the axis A.  
         [0030]     The transmission  10  further includes a plurality of selectively engageable torque transmitting devices or clutches C 1 -C 6 . More particularly, clutch C 1  is a brake configured to selectively couple ring gear member  60  to the housing  84 . Clutch C 2  selectively couples shaft  112  and the planet carrier assembly  34  of the first and second planetary gearsets  14 ,  18  to the planet carrier assembly  64  of the third planetary gearset, and, accordingly, to the output shaft  120 , for unitary rotation. Clutch C 3  is a brake configured to selectively couple sleeve  104 , and therefore the rotor  100  of the second electric motor/generator  76  and the sun gear member  56  of the third planetary gearset  22 , to the housing  84 . Clutch C 4  is configured to selectively couple sleeve  92 , and therefore rotor  88  and sun gear member  40 , to sleeve  116  and, correspondingly, to sun gear member  26  for unitary rotation. Clutch C 5  is configured to selectively couple sleeve  104 , and therefore rotor  100  and sun gear member  56 , to sleeve  116 , and, correspondingly, to sun gear member  26  for unitary rotation. Clutch C 6  is a brake configured to selectively couple sleeve  92 , and therefore the rotor  88  of the first electric motor/generator  72  and the sun gear member  40  of the second planetary gearset  18 , to the housing  84 .  
         [0031]     The transmission  10  is a two-mode, compound-split, electro-mechanical, vehicular transmission. In other words, the output member  120  receives power through two distinct gear trains within the transmission  10 . A first mode, or gear train, is selected when the torque transfer device C 1  is actuated in order to “ground” the outer gear member  60  of the third planetary gear set  22 . A second mode, or gear train, is selected when the torque transfer device C 1  is released and the torque transfer device C 2  is simultaneously actuated to connect the shaft  112  to the carrier  64  of the third planetary gear set  22 . The first and second modes are characterized by electrically variable operation wherein the speed ratio between the input shaft and the output shaft varies with the speed of rotor  88  and/or rotor  100 . The controller  78  is configured to control the speed and the torque of the rotors  88 ,  100  in the first and second modes in a manner similar to that described in commonly-assigned, copending U.S. Ser. No. 10/946,915 filed Sep. 22, 2004, entitled “Two-Mode, Compound-Split, Hybrid Electro-Mechanical Transmission Having Four Fixed Ratios,” and hereby incorporated by reference in its entirety.  
         [0032]     Referring to  FIGS. 1 and 2 , the controller  78  is configured to control the engagement of the torque transmitting devices C 1 -C 6  to provide, in addition to the first and second modes of electrically variable operation, six discrete, fixed speed ratios between the input shaft and the output shaft. More specifically, a first fixed speed ratio between the input shaft  108  and the output shaft  120  is obtained when clutches C 1 , C 4 , and C 5  are engaged, and clutches C 2 , C 3 , and C 6  are disengaged. A second fixed speed ratio is obtained when clutches C 1 , C 5 , and C 6  are engaged, and clutches C 2 -C 4  are disengaged. A third fixed speed ratio is obtained when clutches C 1 , C 2 , and C 5  are engaged, and clutches C 3 , C 4 , and C 6  are disengaged. A fourth fixed speed ratio is obtained when clutches C 2 , C 5 , and C 6  are engaged, and clutches C 1 , C 3 , and C 4  are disengaged. A fifth fixed speed ratio is obtained when clutches C 2 , C 4 , and C 5  are engaged, and clutches C 1 , C 3 , and C 6  are disengaged. A sixth fixed speed ratio is obtained when clutches C 2 , C 3 , and C 5  are engaged, and clutches C 1 , C 4 , and C 6  are disengaged.  
         [0033]     Further, engaging C 3  and C 5  when the engine  110  supplies torque to the input shaft provides a means to lock rotor  100 , thereby to prevent electrical losses when the reaction torque provided by motor  76  is sufficiently low. Clutch C 3  also provides a fixed overdrive ratio capability when applied simultaneously with the C 2  clutch. Optionally, clutch C 3  may be located on the C 5  drum connection to ground sun gear  26 , allowing reaction for starting the engine.  
         [0034]     Clutch C 4  provides a means of interlocking the motor/generators  72 ,  76  at the same speed. This results in a speed of the input shaft  108 , motor/generator  72 , and motor/generator  76  all operating at the same speed. Because they are locked, the input power to the transmission can be the sum of the engine  110 , motor/generator  72 , and motor/generator  76 , resulting in very high acceleration capability. The transmission  10  may be equipped with an input clutch (not shown) or other means to selectively disconnect the engine  10  and the input shaft  108 . When the engine is disconnected from the input shaft, clutches C 4  and C 5  may be applied to provide a means of using both motor/generators  72 ,  76  in an electric, i.e., or engine off, mode, and provides a mode for regeneration where both units equally share the power. This may be significant on long grades, where double the cooling area and a reduction in unit power is desired.  
         [0035]     The transmission may operate as a series transmission when clutch C 5  is open, with motor/generator  72  connected to the engine  110  through the planetary gearsets  14 ,  18 .  
         [0036]     An additional clutch, not shown, can hold planet carriers  34 ,  48  to ground. This is an alternate means of providing reaction during starting. A parking pawl  120  may be connected to planet carrier assembly  64 .  
         [0037]     Moreover, clutch C 4  could be applied, and the engine  110  started by motor/generator  72 . In this situation, the torque of motor/generator  72  is direct to the engine  110  without ratio mechanical advantage.  
         [0038]     In referring to the first, second and third gear sets, in this description and in the claims, these sets may be counted “first” to “third” in any order in the drawings (i.e., left to right, right to left, etc.)  
         [0039]     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.