Abstract:
A method for controlling a drive system includes driveably connecting an engine to a variator, using a pulley to transmit rotating power from an electric machine through a gearset that increases speed of an input of the variator relative to a speed of the pulley, controlling a speed ratio of the variator, and transmitting power through the gearset and variator to the engine.

Description:
This is a divisional application of pending U.S. application Ser. No. 12/840,353, filed Jul. 21, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to transmitting rotating power between an electric machine and engine in a motor vehicle, and through a transmission having a stepless speed ratio range. 
     2. Description of the Prior Art 
     On vehicles equipped with assisted direct start (ADS), the engine is stopped when the vehicle comes to a stop with the brake pedal depressed and the accelerator pedal released. While the engine is stopped in this way, the electric machine should drive the vehicle accessories and to restart the engine when the driver signals that the vehicle is to move again by releasing the brake pedal and depressing the accelerator pedal. The electric machine replaces the alternator that is conventionally used. 
     A transmission located in a power path between the electric machine and the engine will allow the engine to remain at zero rotational speed while the electric machine is driving the accessories through the transmission, permit the electric machine to rotate the engine up to start speed when the engine restart is required, and allow the engine to drive the electric machine and accessories under normal driving conditions. 
     A need exists in the industry for a drive connection between the engine and electric machine, particularly on vehicles equipped with ADS that will provide the desired and necessary functions. 
     SUMMARY OF THE INVENTION 
     A method for controlling a drive system includes driveably connecting an engine to a variator, using a pulley to transmit rotating power from an electric machine through a gearset that increases speed of an input of the variator relative to a speed of the pulley, controlling a speed ratio of the variator, and transmitting power through the gearset and variator to the engine. 
     The pulley is part of a pulley and belt system that provides a driveable connection to an electric machine and other components of the front end accessory drive. 
     The drive system provides a variable speed drive between the engine and the pulley when the engine is driving the electric machine and the front end accessory drive (FEAD). 
     The system provides a variable engine to pulley speed ratio from 0.0 to about 1:1, so that the engine can be smoothly restarted by the electric machine by varying the IVT speed ratio while the electric machine continues running. 
     The engine is driven through a substantial torque multiplication when the IVT speed ratio is about 0.0. 
     Since no clutches are required, only the variator speed ratio requires control. 
     The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a drive system for restarting an engine and driving an electric machine at a variable speed ratio; 
         FIG. 2  is a chart showing the number of teeth on the sun gear, ring gear and planet pinions of the gearsets; 
         FIG. 3  is a chart showing the variation of the speed ratios of system components as the variator speed ratio changes; and 
         FIG. 4  is a schematic diagram of the drive system of  FIG. 1  with a one-way clutch in the system. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings,  FIG. 1  illustrates a drive system  10  that includes a Milner ball variator  12 , and two planetary gearsets  14 ,  16 . An engine  18  is connected to the gearset  16 . A pulley  20  is connected to gearset  16 . The Milner ball variator  12 , two planetary gearsets  14  and  16 , and the pulley  20  are concentric with the engine crankshaft centerline  33 . A pulley  22  is driveably connected to an electric machine  24 . A drive belt  23  driveably connects pulleys  20  and  22  and other vehicle accessories of the FEAD. The pulleys  20  and  22  and drive belt  23  provide a fixed speed relationship between the electric machine  24  and pulley  20 . The electric machine is an electromagnetic device that converts mechanical energy to electrical energy to charge the battery and power the vehicle&#39;s electric system when its engine is running. In this mode, it replaces the alternator that is more conventionally used. It also converts electrical energy to mechanical energy to drive the vehicle accessories of the FEAD when the engine is stopped as well as to restart the engine when required. 
     The Milner ball variator  12  includes spherical balls  26  and is a type of variable geometry, 4-point contact ball bearing. The inner race is divided in two parts  28 ,  29 , and the outer race is divided in two parts  30 ,  31 . By varying the axial distance between the parts of the outer race  30 ,  31  the distance between the parts of the inner race  28 ,  29  changes and the balls  26  are displaced radially between the inner and outer races. As the position of the balls change relative to the races, the location of the contact between the balls  26  and the races varies, thereby changing the speed ratio of the variator. 
     As used in this description, the inner race  28 ,  29  is the input to the variator  12 , the outer race  30 ,  31  is grounded at  32  against rotation preferably on a case or chassis, and the ball carrier  34 , which rotates about axis  33 , is the variator output. The output speed of variator  12  is always less than the speed of its input  28 ,  29 . 
     Planetary speed change gearset  14  includes a sun gear  36 , secured to the inner races  28 ,  29 ; a grounded ring gear  38 , a carrier  40 , and a set of planet pinions  42  supported for rotation on the carrier  40  and in meshing engagement with the sun gear  36  and ring gear  38 . 
     Planetary mixing gearset  16  includes a sun gear  44 , secured to the ball carrier  34 ; a ring gear  46 , driveably connected to the shaft  48  of the engine  18 ; a carrier  50 ; and a set of planet pinions  52  supported for rotation on the carrier  50  and in meshing engagement with the sun gear  44  and ring gear  46 . Carriers  40  and  50  are secured mutually and are, driveably connected to pulley  20 . 
     The variator  12  in combination with two planetary gearsets  14 ,  16  comprise a transmission that produces an infinitely variable speed ratio. 
     Beta, the ratio of the ring gear pitch diameter and the sun gear pitch diameter of a planetary gearset, is chosen for planetary gearsets  14  and  16  so that, when used with the available speed ratio range of the variator  12 , the overall speed ratio of the engine  18  to the pulley  20  can be varied between  0  and  1 , or slightly more than  1 .  FIG. 2  shows the betas of gearsets  14 ,  16 . 
     The engine  18  can be smoothly restarted by the electric machine  24  by changing the speed ratio of the drive system  10  from  0  to about  1 : 1 , which is accomplished by changing the speed ratio of the variator  12  from 0.625 towards 0.24479. The speed ratio of the variator  12  is defined as the speed of ball carrier  34  divided by the speed of the variator&#39;s inner race  28 ,  29  and sun gear  36 . When the engine  18  is driving the electric machine  24 , the speed ratio of variator  12  is preferably 0.24479. In this condition, inner race  28 ,  29  and sun gear  36  rotate 4.0851 times faster than carriers  40 ,  50  and pulley  20  rotate. 
     The electric machine  24  can drive the vehicle accessories, such as the air conditioning system compressor and power steering pump, through the FEAD when the engine  18  is stopped. As  FIG. 3  shows, when the variator speed ratio is 0.62500 and the electric machine is driven in rotation by the vehicle&#39;s battery, engine speed is zero. When axial positions of the inner race  28 ,  29  and outer race  30 ,  31  of the variator are controlled such the variator&#39;s speed ratio decreases to 0.43490, the engine speed increases to one-half the speed of pulley  20 . When the variator&#39;s speed ratio decreases to 0.24479, the engine speed is equal to the speed of pulley  20 . When the variator speed ratio decreases to 0.15625, the engine is overdriven at a speed that is 1.2329 time the speed of pulley  20 . 
     Also the engine  18  can drive the pulley  20  at a variable speed ratio, from about 1:1 to an overdrive speed at which the pulley  20  rotates faster than engine  18 . 
     As  FIG. 3  shows, when the variator speed ratio is 0.35885 and the engine is driving, the pulley  20  is overdriven relative to the engine at a speed that is 1.4286 times engine speed, and the speed of the sun gear  36  and the inner race  28 ,  29  is 5.8359 times the speed of the engine  18 . When the variator speed ratio increases to 0.47292 and the engine is driving, the pulley  20  is overdriven relative to the engine at a speed that is  2 . 500  times engine speed, and the speed of the sun gear  36  and the inner race  28 ,  29  is 10.2128 times the speed of engine  18 . 
       FIG. 4  shows the system  10  with a one-way clutch  60  producing a one-way drive connection between the carrier  40  of speed change gearset  14 , which is driveably connected to the pulley  20 , and the engine shaft  48 . In this case, when the engine  18  is running, pulley  20  is driven directly through the one-way clutch  60  at a 1:1 ratio, thereby eliminating variator and gearing efficiency losses when the electric machine only needs to be driven by the engine at engine speed. The pulley  20  could still be overdriven relative to the engine as necessary. 
     If a one-way clutch  60  is used, the alternate driving O/D operation shown in  FIG. 3 , in which engine  18  is being driven by the pulley  20  at a speed greater than that of the electric machine is not available, and the variator speed ratio cannot be lower than 0.24479 for the preferred beta ratios of the planetary gearsets  14 ,  16 . 
     The drive system allows engine  18  to remain at zero speed while electric machine  24  is driving the vehicle accessories, permits the electric machine to drive the engine up to its starting speed when an engine restart is required, and allows the engine to drive both the electric machine and accessories under normal driving conditions. 
     In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.