Abstract:
An electric continuously variable transmission includes first and second planetary gear sets each having a corresponding electric motor/generator. Both planetary gear sets are integrally linked to an input shaft that transfers torque from an engine. The electric motor/generators switch between driving and retarding rotation of the corresponding planetary gear set to generate various ranges, providing variable transmission speed ratios. A brake may be selectively engaged producing an overdrive range for cruising speeds. The electric continuously variable transmission drives a first driveline for driving a first pair of wheels. A controller and battery are also provided for respectively controlling the various electric motor/generators and either storing or providing energy.

Description:
[0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 09/643,238 filed on Aug. 22, 2000. The disclosure of which is incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to hybrid vehicles and more particularly to an electric hybrid four-wheel drive vehicle.  
         BACKGROUND OF THE INVENTION  
         [0003]    The powertrains of conventional vehicles are designed to provide more power than required for the vehicle at cruising speeds. Specifically, the engine of conventional vehicles is larger than required to provide power for acceleration and hill climbs. This extra power is not required once the vehicle is at cruising speed. As a result, conventional vehicle powertrains are inefficient.  
           [0004]    Therefore, it is desirable to have an improved vehicle powertrain for implementation in a vehicle, such as a hybrid vehicle, which overcomes inefficiencies inherent in a conventional powertrain.  
           [0005]    Additionally, various types of continuously variable transmissions (CVTs) have been developed throughout the years. The object of a CVT is to provide a continuously variable drive ratio from a transmission enabling an engine to run at an optimum point on a brake specific fuel consumption curve. Essentially, CVTs aim at improving engine efficiency by enabling the engine to continuously run at its most efficient point. Due to the significant complexity, traditional CVTs have posed problems in both implementation and application. Traditional belt drive-type CVTs are also inefficient in that significant parasitic losses occur in achieving continuously variable transmission ratios. Moreover, such devices are power limited.  
           [0006]    Therefore, it is desirable in the industry to provide an improved CVT for implementation in a vehicle, such as a hybrid vehicle, which overcomes the deficiencies of traditional CVTs.  
         SUMMARY OF THE INVENTION  
         [0007]    In achieving the above identified objectives, the present invention provides a continuously variable transmission comprising a first planetary gear set, a second planetary gear set operably coupled to said first planetary gear set, an input shaft rotatably coupled to each of the first and second planetary gear sets for selectively providing a drive torque, an output shaft rotatably coupled to the second planetary gear set, a first electric motor operably coupled to the first planetary gear set for selectively functioning to one of either rotatably drive the first planetary gear set and retard rotation of the first planetary gear set, and a second electric motor operably coupled to the second planetary gear set for selectively functioning to one of either rotatably drive the second planetary gear set and retard rotation of the second planetary gear set. The first and second electric motors cooperate to selectively manipulate rotation of the first and second planetary gear sets for varying a drive ratio between the input shaft and the output shaft.  
           [0008]    The present invention further provides a hybrid vehicle comprising an engine, the above-described transmission operably attached to the engine, and a first driveline operably interconnected with the output shaft for driving a first wheel. The hybrid vehicle may further comprise a second driveline operably interconnected with the output shaft for driving a second wheel, thereby providing a multi-wheel drive vehicle.  
           [0009]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a schematic view of an electric continuously variable transmission according to the principles of the present invention;  
         [0011]    [0011]FIG. 2 is a schematic view of a hybrid vehicle implementing the electric continuously variable transmission of FIG. 1;  
         [0012]    [0012]FIG. 3 is a schematic view of an alternative embodiment of an electric continuously variable transmission according to the principles of the present invention; and  
         [0013]    [0013]FIG. 4 is a schematic view of an alternative embodiment of a hybrid vehicle implementing the electric continuously variable transmission of FIG. 3. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]    At the outset, it is important to note that the herein described embodiment is a preferred embodiment and merely exemplary in nature. Being exemplary, the preferred embodiment is in no way intended to limit the invention or its application.  
         [0015]    With reference to FIG. 1, a schematic view of a first exemplary embodiment of an electric continuously variable transmission (CVT)  10  is shown. The electric CVT  10  comprises a first planetary gear set  12 , a second planetary gear set  14 , a first electric motor/generator  16  operably coupled to the first planetary gear set  12  and a second motor/generator  18  operably coupled to the second planetary gear set  14 . An input shaft  20  is externally driven by an engine  22  (see FIG. 2) through a connection  24  and an output shaft  46  provides output drive torque to an external system. The connection  24  is preferably a conventional flywheel and vibration damper. The first and second planetary gear sets  12 ,  14  are selectively manipulated by the first and second electric motor generators  16 ,  18 , respectively, for providing continuously variable drive ratios between the input shaft  20  and the output shaft  46 .  
         [0016]    The input shaft  20  is connected to a sun gear  26  of the second planetary gear set  14  and a carrier  28  of the first planetary gear set  12 . A plurality of planetary gears  30  are rotatably supported on the carrier  28 . A sun gear  32  of the first planetary gear set  12  is rotatably supported about the input shaft  20  and is connected to both the first electric motor/generator  16  by a gear  34  and a lock-up clutch or brake  36 . The brake  36  can be selectively engaged to prohibit rotation of the sun gear  32 . A ring gear  38  of the first planetary gear set  12  is connected to a carrier  40  of the second planetary gear set  14 . The ring gear  38  is meshingly engaged with the planetary gears  30  which are also meshingly engaged with the sun gear  32 . A plurality of planetary gears  42  are rotatably supported on carrier  40 . The second electric motor/generator  18  is connected to a ring gear  44  of the second planetary gear set  14 . The ring gear  44  is meshingly engaged with the planetary gears  42  which are also meshingly engaged with the sun gear  26 . The output shaft  46  is connected to the carrier  40  and includes a parking pawl  48  disposed thereon.  
         [0017]    Referencing FIG. 2, a hybrid vehicle powertrain  100  is shown having the electric CVT  10  implemented therein. The hybrid vehicle powertrain  100  includes the engine  22  operably interconnected with the electric CVT  10 , a rear axle assembly  102  operably interconnected to the electric CVT  10  by the output shaft  46  for driving a pair of real wheels  104 , a front axle assembly  106  operably interconnected to the electrical CVT  10  by a controller  108  for driving a pair of front wheels  110 . A battery  112  is also included and is in electrical communication with the controller  108 . Further, each of the first and second electric motor/generators  16 ,  18  are in electrical communication with the controller  108 . The controller  108  manages the driving and generating modes of the first and second electric motor/generators  16 ,  18 , as well as managing the charge and discharge of the battery  112 . In this manner, the first and second motor/generators may selectively manipulate the first and second planetary gear sets  12 ,  14  for continuously varying the drive ratio of the electric CVT  10 . Also included is an actuator  109  in operative communication between the brake  36  and the controller  108  for selectively engaging the brake  36 , as described in further detail herein.  
         [0018]    The output shaft  46  is connected to a rear differential  114  of the rear axle assembly  102  for driving rear differential  114 , in turn driving the rear wheels  104 . The front axle assembly  106  includes a front differential  116  that that is driven by a third electric motor/generator  118  through a third planetary gear set  120 . The third electric motor/generator  118  is in electrical communication with the controller  108 . The third planetary gear set  120  includes a sun gear  122  driven by the third motor/generator  118 . A ring gear  124  of the third planetary gear set  120  is fixed from rotating and a carrier  126  provides an input to the front differential  116 . A plurality of planetary gears  128  are rotatably mounted to the carrier  126 . The third electric motor/generator  118  is operated by the controller  108  and powered by the battery  112 .  
         [0019]    While the hybrid vehicle powertrain  100  is at rest with the engine  22  running, the ring gear  44  rotates opposite to the direction of rotation of input shaft  20 , at a reduced speed: The ring gear  44  drives the second electric motor/generator  18 , functioning in a generation mode. The electric energy that the second electric motor/generator  18  generates is fed to the first electric motor/generator  16 . This event is termed “power recirculation”. If enough electrical energy is generated, the second electric motor/generator  18  may also feed power to the third electric motor/generator  118  and/or the battery  112 . Once a predetermined level of power has been created, a reaction torque produced by the second electric motor/generator  18  will drive the hybrid vehicle powertrain  100  at low speed. This simulates the feel of a conventional automatic transmission without the power loss associated with automatic transmissions.  
         [0020]    As the second electric motor/generator  18  absorbs more power, the rotational speed of the ring gear  44  slows and the hybrid vehicle powertrain  100  accelerates. It is anticipated that an exemplary low speed ratio of 5.30:1 is achievable as the rotational speed of the ring gear  36  approaches zero. As the rotational speed of the ring gear  44  passes zero, the second electric motor  18  switches from a generator mode to a motor mode and the first electric motor/generator  16  switches to a generator mode. The first electric motor/generator  16  absorbs energy from the first planetary gear set  12  for feeding power to the second electric motor/generator  18 , helping to drive the hybrid vehicle powertrain  100  in a mid speed range operating mode. When the rotational speed of the sun gear  32  and the first electric motor/generator  40  approach zero, it is anticipated that an exemplary overdrive speed ratio of 0.77:1 is achievable. Upon achieving this speed ratio, the brake  36  is applied and all power from the engine  22  is transferred mechanically for providing maximum efficiency.  
         [0021]    Reverse operation is achieved by the second electric motor/generator  18  driving the ring gear  44  faster in a reverse direction than the engine  22  normally drives it. In other words, since the engine  22  typically drives the ring gear  44  in a direction opposite its own rotational direction, the second electric motor/generator  18  must drive the ring gear  44  in the same rotational direction as the engine  22  to achieve reverse. It is anticipated that an exemplary reverse speed ratio of 6.37:1 is achievable.  
         [0022]    With particular reference to FIG. 3, an alternative exemplary embodiment of an electric CVT  10 ′ is shown. The following description of the electric CVT  10 ′ will include like reference numerals to the electric CVT  10 , followed by prime (′), for referencing like components. The electric CVT  10 ′ includes a first planetary gear set  12 ′, a second planetary gear set  14 ′ and first and second electric motor/generators  16 ′,  18 ′ in operative communication with the first and second planetary gear sets  12 ′,  14 ′, respectively. An input shaft  20 ′ is externally driven by an engine  22 ′ (see FIG. 4) through a connection  24 ′. The connection  24 ′ is preferably a conventional vibration damper. An output shaft  46 ′ is operably interconnected with the second planetary gear set  14 ′. The first and second planetary gear sets  12 ′,  14 ′ are selectively manipulated by the first and second electric motor generators  16 ′,  18 ′, respectively, for providing continuously variable drive ratios between the input shaft  20 ′ and the output shaft  46 ′.  
         [0023]    A sun gear  26 ′ is fixedly attached to an end of the input shaft  20 ′ and a carrier  28 ′ of the first planetary gear set  12 ′ is fixedly attached intermediate the length of the input shaft  20 ′. A brake  50  is also included and is disposed intermediate the length of the input shaft  20 ′ and is selectively activated for braking rotation of the input shaft  20 ′, thereby braking rotation of the sun gear  26 ′ and the carrier  28 ′. A sun gear  32 ′ of the first planetary gear set  12 ′ is rotatably supported about the input shaft  20 ′ and operably attached to both the first electric motor/generator  16 ′ by a gear  34 ′ and a brake  36 ′. The brake  36 ′ is selectively engageable to prohibit rotation of the sun gear  32 ′. A ring gear  38 ′ of the first planetary gear set  12 ′ is operably interconnected with a carrier  40 ′ of the second planetary gear set  14 ′. The second electric motor/generator  18 ′ is operably attached to a ring gear  38 ′ and the carrier  40 ′. The carrier  40 ′ is fixed for rotation with an output shaft  46 ′. A first transfer gear  52  is fixedly attached to the output shaft  46 ′ for transferring drive torque, as discussed in further detail hereinbelow.  
         [0024]    Referencing FIG. 4, an alternative hybrid vehicle powertrain  200  is shown having the electric CVT  10 ′ implemented therein. The hybrid vehicle powertrain  200  includes the engine  22 ′ operably interconnected with the electric CVT  10 ′, a rear axle assembly  202  operably interconnected with the electric CVT  10 ′ by a propshaft assembly  204  for driving a pair of rear wheels  206 , and a front axle assembly  208  operably interconnected with the electric CVT  10 ′ by a propshaft assembly  210  and a transfer mechanism  212  for driving a pair of front wheels (not shown). A controller  213  is in electric communication with the first and second electric motor/generators  16 ′,  18 ′, a first actuator  215  and a second actuator  217 . The first and second actuators are in operative communication with the brakes  36 ′,  50 , respectively, for selectively actuating the brakes  36 ′,  50 . The controller  213  controls actuation of the first and second actuators  36 ′,  50 , the first and second electric motor/generators  16 ′,  18 ′ and interconnects the electric CVT  10 ′ with a battery  219 .  
         [0025]    As described previously, the input shaft  20 ′ of the electric CVT  10 ′ is connected to the engine  22 ′ via the connection  24 ′. The propshaft assembly  204  interconnects the output shaft  46 ′ to a differential  214  of the rear axle assembly  202 . A pair of drive axles  216  interconnects the rear wheels  206  with the differential  214 . Thus, the electric CVT  10 ′ drives the rear wheels  206  by transmitting torque from the output shaft  46 ′, through the propshaft assembly  204 , to the differential  214  and out to the rear wheels  206 .  
         [0026]    The transfer mechanism  212  includes the first transfer gear  52  of the electric CVT  10 ′, a transfer chain  218 , a second transfer gear  220 , a clutch pack  222  and an output shaft  224 . The transfer chain  218  interconnects the first and second transfer gears  52 ,  220 , enabling the first transfer gear  52  to drive the second transfer gear  220 . The second transfer gear  220  is rotatably supported about the output shaft  224  and is fixed for rotation with a set of clutch plates  226  of the clutch pack  222 . The clutch pack  222  is fixed for rotation with the output shaft  224  and is in operative communication with an actuator  223  for selectively actuating the clutch pack  222 . The actuator  213  is further in operative communication with the controller  213 . The clutch plates  226  interact with the clutch pack  222  for selectively retarding rotational motion of the clutch plates  226  relative to the clutch pack  222 . In this manner, the amount of power transmitted from the first transfer gear  52 , through the second transfer gear  220 , through the clutch pack  222  and ultimately the output shaft  224 , may be manipulated as driving conditions require. The output shaft  224  is interconnected with the propshaft assembly  210  for driving the propshaft assembly  210 . The propshaft assembly  210  is further interconnected with a differential  228  of the front axle assembly  208  for driving the pair of front wheels (not shown).  
         [0027]    The hybrid vehicle powertrain  200  operates in one of either a hybrid mode, an electric mode or a power generation mode. In the hybrid mode, when the hybrid vehicle powertrain  200  is stationary, the ring gear  44 ′ of the second planetary gear set  14 ′ rotates opposite to the rotation of the engine  22 ′, at a reduced speed. The second motor/generator  18 ′, being fixed to the ring gear  44 ′, is in the generation mode generating power that is fed either to the first motor/generator  16 ′, or to the battery  219 . Upon the development of a small amount of electric power, a reaction torque produced by the second motor/generator  18 ′ will drive the hybrid vehicle powertrain  200  at low speeds, simulating the feel of an automatic transmission, without the power loss.  
         [0028]    As the second motor/generator  18 ′ absorbs more power, the ring gear  44 ′ slows and the hybrid vehicle powertrain  200  accelerates. Concurrently, the first motor/generator  16 ′ may drive the sun gear  32 ′ of the first planetary gear set  12 ′, thereby assisting the engine  22 ′. As the ring gear  44 ′ approaches and passes zero rotational speed, the second motor/generator  18 ′ switches to a drive mode and the first motor/generator  16 ′ switches to a generation mode. The first motor/generator  16 ′ absorbs power form the first planetary gear set  12 ′ to drive the second motor/generator  18 ′, thereby assisting the engine  22 ′ in driving the hybrid vehicle powertrain  200 . As the first motor/generator  16 ′ generates power, it retards rotation of the sun gear  32 ′ of the first planetary gear set  12 ′ until the sun gear  32 ′ stops rotating. At this point, the brake  36 ′ is applied and engine power is mechanically transferred through the electric CVT  10 ′ for maximum efficiency. Reverse operation is achieved, as detailed above, by the second electric motor/generator  18 ′ driving the ring gear  44 ′ faster in reverse than the engine  22 ′ would normally drive it.  
         [0029]    In the electric mode, power is selectively supplied by the battery  219 , through the controller  213 , to drive either or both the first and second electric motor/generators  16 ′,  18 ′, thereby driving the first and second planetary gear sets  12 ′,  14 ′. Because the engine  22 ′ is stopped, the brake  50  is actuated to hold a reaction torque that results from driving the first and second planetary gear sets  12 ′,  14 ′. It is anticipated that the electric mode may drive the hybrid vehicle powertrain  200  up to speeds of 40 mph, reducing fuel consumption to zero. In the power generation mode, with the hybrid vehicle powertrain  200  parked, the engine  22 ′ may drive the first electric motor/generator  16 ′ to provide auxiliary power or charge the battery  219 .  
         [0030]    It should also be noted that the exemplary embodiments of the electric CVT  10  should not be limited to application in hybrid vehicles. The electric CVT  10  is readily applicable in conventional combustion engine vehicles as well.  
         [0031]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention. Such variations or modifications, as would be obvious to one skilled in the art, are intended to be included within the scope of the following claims.