Patent Publication Number: US-9903448-B2

Title: Accessory devices drive system

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a divisional patent application filed under 35 U.S.C. §§ 120 and 121 based on U.S. patent application Ser. No. 14/049,532, filed Oct. 9, 2013, and claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 61/805,356, filed Mar. 26, 2013, which applications are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a system for driving accessory devices for a vehicle, in particular, a system driving the accessory devices using an output of a crankshaft, a transmission shaft, or an electric machine. 
     BACKGROUND 
     It is known to drive accessory devices for a vehicle, such as an alternator, water pump, or oil pump, using belts and pulleys driven by the crankshaft of the engine for the vehicle. Thus, the rotational speeds for the accessory devices have fixed ratios with respect to the rotational speed of the crankshaft. The accessory devices are normally sized to deliver full output at engine idle speed in order to allow full functionality at idle speed. As a result, during normal operation of the vehicle, when the crankshaft is rotating at speeds greater than the idle speed rotation, the accessory devices are being rotated much faster than required. Further, when the engine is turned off, the accessories come to a stop, which creates problems for stop-start and hybrid capable vehicles. 
     SUMMARY 
     According to aspects illustrated herein, there is provided an accessories drive system, including: a clutch assembly with a drive shaft; and at least one accessory device connected to the drive shaft. In a first position for the clutch assembly: the clutch assembly is arranged to transmit a first torque from a shaft for the transmission to the drive shaft to drive the at least one accessory device and rotation of the drive shaft is isolated from rotation of a crankshaft for the vehicle. In a second position for the clutch assembly: the clutch assembly is arranged to transmit a second torque from the crankshaft to the drive shaft to drive the at least one accessory device and the rotation of the drive shaft is isolated from rotation of the shaft for the transmission. 
     According to aspects illustrated herein, there is provided an accessories drive system, including: an electric machine; a clutch assembly connectable to a shaft for the transmission and a crankshaft for the vehicle and including a drive shaft; and at least one accessory device connected to the drive shaft. In a first position for the clutch assembly, the clutch assembly is arranged to transmit a first torque from the shaft for the transmission to the drive shaft to drive the at least one accessory device. In a second position for the clutch assembly, the clutch assembly is arranged to transmit a second torque from the crankshaft to the drive shaft to drive the at least one accessory device. In a third position for the clutch assembly, the electric machine is arranged rotate the drive shaft to drive the at least one accessory device. 
     According to aspects illustrated herein, there is provided an accessories drive system, including: an electric machine; and a clutch assembly including: a drive shaft; a first drive element connectable to a shaft for the transmission; a second drive element connectable to a crankshaft for the vehicle; and a drive hub non-rotatably connected to the drive shaft. The drive system includes at least one accessory device connected to the drive shaft. In a first position for the clutch assembly: the first drive element is arranged to transmit a first torque from the shaft for the transmission to the drive shaft to drive the at least one accessory device; and the drive shaft is rotatable with respect to the second drive element. In a second position for the clutch assembly: the second drive element is arranged to transmit a second torque from the crankshaft to the drive shaft to drive the at least one accessory device; and the drive shaft is rotatable with respect to the first drive element. In a third position for the clutch assembly: the drive shaft is rotatable with respect to the first and second drive elements; and the electric machine is arranged to rotate the drive shaft to drive the at least one accessory device. 
     According to aspects illustrated herein, there is provided a vehicle, including: an engine; a crankshaft connected to the engine; a torque converter including a cover and an output; a connection element non-rotatably connecting the crankshaft and the cover; a transmission including an output shaft and an input shaft non-rotatably connected to the output of the torque converter; and at least one accessory device. In a first mode of operation for the vehicle, the at least one accessory device is driven by the transmission at a rotational speed of the output shaft and rotation of the drive shaft is isolated from rotation of the crankshaft. In a second mode of operation for the vehicle, the at least one accessory device is driven by the engine at a rotational speed for the crankshaft; and rotation of the drive shaft is isolated from rotation of the output shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments are disclosed, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, in which: 
         FIG. 1A  is a perspective view of a cylindrical coordinate system demonstrating spatial terminology used in the present application; 
         FIG. 1B  is a perspective view of an object in the cylindrical coordinate system of  FIG. 1A  demonstrating spatial terminology used in the present application; 
         FIG. 2  is a cross-sectional view of an accessories drive system; 
         FIG. 3  is an enlarged view of area  3  in  FIG. 2 ; 
         FIG. 4  is a schematic block diagram of a vehicle with an accessories drive system; 
         FIG. 5  is a schematic block diagram of a vehicle with an accessories drive system; 
         FIG. 6  is a cross-sectional view of a connection to an input shaft of a transmission for an accessories drive system; and, 
         FIG. 7  is a schematic block diagram of a vehicle with an accessories drive system. 
     
    
    
     DETAILED DESCRIPTION 
     At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the disclosure. It is to be understood that the disclosure as claimed is not limited to the disclosed aspects. 
     Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present disclosure. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure. 
       FIG. 1A  is a perspective view of cylindrical coordinate system  80  demonstrating spatial terminology used in the present application. The present invention is at least partially described within the context of a cylindrical coordinate system. System  80  has a longitudinal axis  81 , used as the reference for the directional and spatial terms that follow. The adjectives “axial,” “radial,” and “circumferential” are with respect to an orientation parallel to axis  81 , radius  82  (which is orthogonal to axis  81 ), and circumference  83 , respectively. The adjectives “axial,” “radial” and “circumferential” also are regarding orientation parallel to respective planes. To clarify the disposition of the various planes, objects  84 ,  85 , and  86  are used. Surface  87  of object  84  forms an axial plane. That is, axis  81  forms a line along the surface. Surface  88  of object  85  forms a radial plane. That is, radius  82  forms a line along the surface. Surface  89  of object  86  forms a circumferential plane. That is, circumference  83  forms a line along the surface. As a further example, axial movement or disposition is parallel to axis  81 , radial movement or disposition is parallel to radius  82 , and circumferential movement or disposition is parallel to circumference  83 . Rotation is with respect to axis  81 . 
     The adverbs “axially,” “radially,” and “circumferentially” are with respect to an orientation parallel to axis  81 , radius  82 , or circumference  83 , respectively. The adverbs “axially,” “radially,” and “circumferentially” also are regarding orientation parallel to respective planes. 
       FIG. 1B  is a perspective view of object  90  in cylindrical coordinate system  80  of  FIG. 1A  demonstrating spatial terminology used in the present application. Cylindrical object  90  is representative of a cylindrical object in a cylindrical coordinate system and is not intended to limit the present invention in any manner. Object  90  includes axial surface  91 , radial surface  92 , and circumferential surface  93 . Surface  91  is part of an axial plane, surface  92  is part of a radial plane, and surface  93  is a circumferential surface. 
       FIG. 2  is a cross-sectional view of transmission accessories drive system  100 . 
       FIG. 3  is an enlarged view of area  3  in  FIG. 2 . 
       FIG. 4  is a schematic block diagram of a vehicle with transmission accessories drive system  100 . The following should be viewed in light of  FIGS. 2 through 4 . In an example embodiment, vehicle  101  includes engine  103 , crankshaft  105 , and transmission  115  with input shaft  117 , output shaft  121  to drive wheels  123 , and optional counter shafts, layshafts or concentric shafts. By “transmission” we mean a device for transmitting torque with an input shaft, an output shaft, and gearing for converting a rotational speed of the input shaft to a different speed at the output shaft. Transmission  115  may be a multi-speed planetary automatic transmission, a multi-speed manual gearbox, or a continuously variable transmission, for example. Vehicle  101  includes at least one accessory device  106 . In a first mode of operation for the vehicle, the at least one accessory device is driven by the engine at a rotational speed for the crankshaft. In a second mode of operation for the vehicle, the at least one accessory device is driven by the transmission at a rotational speed of one of the shafts of transmission  115 . 
     In an example embodiment, the vehicle includes accessories drive system  100  connected to crankshaft  105  and one of the shafts of the transmission, and including drive shaft  104 . The at least one accessory device  106  is connected to the drive shaft. In the first mode of operation for the vehicle, the accessories drive system is arranged to transmit a first torque from one of the shafts of the transmission to the drive shaft to drive the at least one accessory device while rotation of the drive shaft is isolated from rotation of a crankshaft. In the second mode of operation, the accessories drive system is arranged to transmit a second torque from crankshaft  105  to the drive shaft to drive the at least one accessory device while the rotation of the drive shaft is isolated from rotation of the shaft for the transmission. 
     In an example embodiment, vehicle  101  includes launch device  107  and connection element  109  non-rotatably connecting engine  103  and cover  111  of the launch device. In an example embodiment, launch device  107  is a wet or dry launch clutch or double clutch. In an example embodiment, launch device  107  is a torque converter. The discussion that follows is directed to torque converter  107 ; however, it should be understood that the discussion is applicable to a launch device in general. Connection element  109  can include a flexplate. In an example embodiment, cover  111  in non-rotatably connected to pump  113  of the torque converter. Input shaft  117  is non-rotatably connected to an input of the torque converter, for example cover  111 , and output shaft  121  drives wheels  123 . In a first mode of operation for the vehicle, the at least one accessory device is driven by the engine at a rotational speed for the crankshaft. In a second mode of operation for the vehicle, the at least one accessory device is driven by the transmission at a rotational speed of output shaft  121  or one of the transmission counter shafts, layshafts or concentric shafts. 
     In an example embodiment, the vehicle includes accessories drive system  100  connected to the cover and output shaft  121  and including drive shaft  104 . The at least one accessory device  106  is connected to the drive shaft. In the first mode of operation for the vehicle, the accessories drive system is arranged to transmit a first torque from output shaft  121  to the drive shaft to drive the at least one accessory device. In the second mode of operation, the accessories drive system is arranged to transmit a second torque from cover  111  to the drive shaft to drive the at least one accessory device. In general, the portion of the launch device connected to system  100  rotates at the same speed as the crankshaft. 
     In an example embodiment, accessories drive system  100  includes clutch assembly  102 . As further described below, in a first position for the clutch assembly, the clutch assembly is arranged to transmit torque from output shaft  121  for transmission  115  to the drive shaft to drive the accessory device(s). As further described below, in a second position for the clutch assembly, the clutch assembly is arranged to transmit torque from cover  111  of torque converter  107 , for example, pump hub  110  of the torque converter, to the drive shaft to drive the accessory device(s). The pump hub is non-rotatably connected to pump  113 . 
     In an example embodiment, assembly  100  includes electric machine  112 . In a third position for the clutch assembly, the drive shaft is rotatable with respect to shaft  121  and cover  111  and the electric machine rotates the drive shaft to drive the at least one accessory device. By “electric machine” we mean an electrical device capable of generating electrical current, for example, to charge a battery and/or capable of producing torque, for example an electric motor. 
     In an example embodiment, the clutch assembly includes drive element  114  arranged to transmit torque from the output shaft. Drive element  114  is connectable to the output shaft, for example via chain or belt  119 . In an example embodiment, the clutch assembly includes drive element  116  arranged to transmit torque from cover  111 . Drive element  116  is connectable to cover  111 , for example via chain or belt  125 . In the first position, drive element  114  is arranged to transmit torque from the output shaft to the drive shaft. In the second position, drive element  116  is arranged to transmit torque from the output of the torque converter to the drive shaft. 
     The clutch assembly includes one-way clutch functionality (for example, clutch  168  described below) and bi-directional clutch functionality (for example, clutch  170  described below). In an example embodiment, in the first position, the clutch assembly and drive element  114  are arranged to prevent rotation of the drive shaft in direction RD 1  and direction RD 2 , opposite direction RD 1 . In an example embodiment, in the second position, the drive shaft is rotatable in direction RD 1  and the clutch assembly and drive element  116  are arranged to prevent rotation of the drive shaft in a direction RD 2 . Note that directions RD 1  and RD 2  as shown in the figures can be reversed. 
     In general, only one of the first or second drive elements or the electric machine drives the drive shaft at any one time. For example, in the first position, drive element  114  is transmitting torque to the drive shaft, the drive shaft is rotatable with respect to drive element  116 , and the electric machine is being driven by the drive shaft. For example, in the second position, drive element  116  is transmitting torque to the drive shaft, the drive shaft is rotatable with respect to drive element  114 , and the electric machine is being driven by the drive shaft. For example, in the third position, the drive shaft is rotatable with respect to both drive element  114  and drive element  116  and is driven by the electric machine. 
     In an example embodiment, the clutch assembly includes hub  118 , wedge plate pairs  122  and  124 , and engagement system  125 . In an example embodiment, system  125  includes keys  126  and  128 . In an example embodiment, the clutch assembly includes actuator  130  including solenoid  132 , selection element  134 , and spring  136 . In an example embodiment, the spring and portions of the selection element are located radially inside of the drive shaft. Wedge plates pair  122  includes wedge plates  122 A and  122 B with respective outer circumferences  138 A and  138 B, respectively, engaged with drive element  114 . For example, circumferences  138 A and  138 B are disposed in groove  142 , to restrain wedge plates  122 A and  122 B in an axial direction, while enabling at least some radial movement as described below. Wedge plates pair  124  includes wedge plates  124 A and  124 B with respective outer circumferences  140 A and  140 B, respectively, engaged with drive element  116 . For example, circumferences  140 A and  140 B are disposed in groove  144 , to restrain wedge plates  124 A and  124 B in an axial direction, while enabling at least some radial movement as described below. 
     In  FIGS. 2 and 3 , the clutch assembly is in the third clutch position. The selection element is displacing the keys radially outward with respect to the hub such that wedge plate pairs  122  and  124  are non-rotatably connected to the hub. As a result, the wedge plate pairs are rotatable with respect to the drive elements and the drive shaft is rotatable with respect to the drive elements. In an example embodiment, hub  118  includes an outer circumferential surface with a plurality of circumferentially spaced ramps and wedge plate pairs  122  and  124  include respective inner circumferential surfaces with respective pluralities of circumferentially spaced ramps engageable with the ramps of hub  118 . When wedge plate pairs  122  and  124  do not rotate with respect to the drive hub, the ramps of hub  118  and the respective ramps of wedge plate pairs  122  and  124  do not rotate with respect to each other and the ramps of hub  118  do not engage with the respective ramps of wedge plate pairs  122  and  124  to radially outwardly expand wedge plate pairs  122  and  124 . Thus, wedge plate pairs  122  and  124  rotate with respect to drive elements  114  and  116 , respectively. 
     To attain the first clutch position, the selector element is displaced in direction D 1  such that key  126  disengages with wedge plate pair  122 , and contact between drive element  112  and wedge plate pair  122  rotates wedge plate pair  122  with respect to the hub to non-rotatably lock drive element  112  and with the hub. That is, the ramps for hub  118  and wedge plate pair  122  slide across each other, pushing wedge plate pair  122  radially outward to non-rotatably connect to drive element  114 . Key  128  non-rotatably connects wedge plate  124  and the hub such that the drive shaft is rotatable with respect to drive element  116 . That is, as described above, the ramps for hub  118  and wedge plate pair  124  do not rotate with respect to each other and wedge plate pair  124  is not expanded radially outward. 
     To attain the second clutch position, the selector element is displaced in direction D 2  such that key  128  disengages with wedge plate pair  124 , and contact between drive element  114  and wedge plate pair  124  rotates wedge plate pair  124  with respect to the hub to non-rotatably lock drive element  114  and with the hub. That is, the ramps for hub  118  and wedge plate pair  124  slide across each other, pushing wedge plate pair  124  radially outward to non-rotatably connect to drive element  116 . Key  126  non-rotatably connects wedge plate  122  and the hub such that the drive shaft is rotatable with respect to drive element  114 . That is, as described above, the ramps for hub  118  and wedge plate pair  122  do not rotate with respect to each other and wedge plate pair  122  is not expanded radially outward. 
     It should be understood that the clutch assembly is not limited to the particular components described above, in particular with respect to one-way clutch functionality. For example, components different from the drive elements, keys, wedge plate pairs, and key actuator described above can be used to implement the one-way clutch functionality. 
     The position of the clutch assembly can be selected to provide a desired drive arrangement for the accessory devices. For example, a particular rotational speed is desired for the drive shaft. The desired speed could be related to minimum power requirements or efficiency of operation of the accessory devices. Drive elements  114  and  116  are rotating at respective speeds. Drive system  100  is configured such that the first or second position for the clutch assembly is selected according to which position best meets the conditions associated with the desired rotational speed for the drive shaft. For example, the rotational speed of drive element  114  is closer to the desired rotational speed than the rotational speed of drive element  116  and the first clutch position is selected, or the rotational speed of drive element  116  is closer to the desired rotational speed than the rotational speed of drive element  114  and the second clutch position is selected. 
     As another example, the rotational speed of drive element  114  is less than the desired rotational speed, the rotational speed of drive element  116  is greater than the desired speed, and the second clutch position is selected, or the rotational speed of drive element  116  is less than the desired rotational speed, the rotational speed of drive element  114  is greater than the desired speed, and the first clutch position is selected. As a further example, the clutch position associated with the lower of the rotational speeds for drive elements  114  or  116  can be selected. For example, if the rotational speed for element  114  is lower than the rotational speed for element  116 , the first clutch position is selected. Note that other criteria can be applied to selecting the first and second clutch positions. 
     In an example embodiment, drive element  114  is bi-directional. For example, torque can be transmitted from drive element  114  to the drive shaft, as when the vehicle is operating in a steady state mode (for example, cruising at highway speed and not accelerating or decelerating) or a deceleration mode (for example, when wheels are transmitting torque to the transmission). During some operating conditions (for example, launching from a stop light or pulling a trailer up a hill), torque from the electric machine may be transmitted from the drive shaft to drive element  114  to help propel the vehicle. 
     In an example embodiment, the torque converter includes a turbine, a pump, and a pump hub non-rotatably connected to the pump (not shown) and the torque converter output includes the pump hub. 
     In an example embodiment, the at least one accessory device includes a plurality of accessory devices. In an example embodiment, the at least one accessory device includes one or more of fuel pump  148 , engine oil pump  150 , vacuum pump  152 , air conditioning compressor  154 , water pump  156 , or transmission oil pump  158 . 
     The following provides further detail regarding system  100 . System  100  includes three-position selectable one-way clutch assembly  102  that connects, for example, a torque converter pump hub and a transmission output shaft to accessory devices  106 . For example, the clutch assembly includes respective one-way clutch functionality associated with torque input from the pump hub and from the output shaft. Thus, in the first clutch position, the accessory devices, are driven the speed of engine  103  (connected to the torque converter by crankshaft  105  and connection  109 ) by cover  111  and in the second clutch position, the accessory devices are driven by output shaft  121 , for example when decelerating or when a vehicle housing system  100  is operating at highway speed. In the third clutch position, the accessory devices are disconnected from the drive shaft and are driven by the electric machine, for example, when the vehicle is accelerating or when the engine is shut off. 
     In an example embodiment, torque converter clutch  166  is connected to cover  111 . Drive element  114 , wedge plate pair  122 , key  126 , and hub  118  form one-way clutch  168 . Drive element  116 , wedge plate pair  124 , key  128 , and hub  118  form one-way clutch  170 . In an example embodiment, drive pulley  172  is non-rotatably connected to drive shaft  104  to drive accessory devices  106 . For example, pulley  172  drives one of devices  106  via belt  174 . Belts  174 A-G are shown in  FIG. 4 . Alternatively, pulley  172  may drive two or more of devices  106  via a serpentine belt, as is known in the art. 
     In an example embodiment, drive element  114  is connected to the transmission output shaft by chain or belt  119 , creating a ratio of 0.65. In an example embodiment, drive element  116  is connected to cover  111  by chain or belt  125  creating a ratio of 1:1. It should be understood that other ratios are possible. 
       FIG. 5  is a schematic block diagram of a vehicle with accessories drive system  200 . In an example embodiment, vehicle  202  includes accessories drive system  200 , engine  204 , starter  206 , crankshaft  208 , transmission  210 , and differential/wheels  212 . System  200  includes clutches  214 ,  216 , and  218 , at least one accessory device  220 , electric machine  222 , and drive shaft  224 . Clutch  218  is a friction clutch. Clutches  214  and  216  can be dog clutches, friction clutches, or switchable one-way clutches. In an example embodiment, the descriptions of clutches  168  and  170  are applicable to clutches  216  and  214  when clutches  216  and  214  are switchable one-way clutches. The discussion regarding devices  106  is applicable to device(s)  220 . Example ratios of 2.5:1 and 1:2 are shown between the electric machine and drive shaft  224  and between clutch  214  and drive shaft  224 , respectively; however, it should be understood that other ratios are possible. 
     The discussion regarding vehicle  101  and system  100  is generally applicable to vehicle  202  and system  200 . For example, in the first mode of operation for the vehicle, the at least one accessory device is driven by the engine at a rotational speed for the crankshaft. In a second mode of operation for the vehicle, the at least one accessory device is driven by the transmission at a rotational speed of one of the shafts of transmission  210 . 
     In an example embodiment, accessories drive system  200  is connected to crankshaft  208  and one of the shafts of the transmission, such as input shaft  226 , output shaft  228 , or counter shaft, layshaft or concentric shaft  230 , for example, within the transmission. The at least one accessory device  220  is connected to the drive shaft. In the first mode of operation for the vehicle, the accessories drive system is arranged to transmit a first torque from one of the shafts of the transmission to the drive shaft to drive the at least one accessory device while rotation of the drive shaft is isolated from rotation of a crankshaft. In the second mode of operation, the accessories drive system is arranged to transmit a second torque from crankshaft  208  to the drive shaft to drive the at least one accessory device while the rotation of the drive shaft is isolated from rotation of the shaft for the transmission. 
       FIG. 6  is a cross-sectional view of a connection to an input shaft of a transmission for an accessories drive system. 
       FIG. 7  is a schematic block diagram of a vehicle with accessories drive system  300 .  FIGS. 6 and 7  illustrate an arrangement to provide torque from input shaft  301  of a transmission. In  FIG. 6 , chain or belt  125  is connected to pump hub  302  for torque converter  304  (only partially depicted). Chain or belt  125  is contained in housing  306 . Passages  308  and  310  are apply and release pressure hydraulic passages for operation of the torque converter. Chain or belt  119  is connected to a sprocket on input shaft  300 . Housing  312  supports bearing  314  which supports gears in the transmission (not shown). 
     In an example embodiment, vehicle  316  includes accessories drive system  318 , engine  320 , starter  322 , crankshaft  324 , transmission  326 , and differential/wheels  328 . System  300  includes clutches  330 ,  332 , and  334 , at least one accessory device  336 , electric machine  338 , and drive shaft  340 . Clutch  334  is a friction clutch. Clutches  330  and  332  can be dog clutches, friction clutches, or switchable one-way clutches. In an example embodiment, the descriptions of clutches  168  and  170  are applicable to clutches  332  and  330  when clutches  332  and  330  are switchable one-way clutches. The discussion regarding devices  106  is applicable to device(s)  336 . 
     Using chain or belt  119  and the connection to the input shaft of the transmission, when the vehicle is coasting to a stop, all the speeds of the transmission can be used to drive the accessories. For example, there is a fixed ratio between differential and wheels  328  and output shaft  342 . During coasting the rotational speed of the output shaft falls below minimum accessory drive speed very quickly as the wheels decelerate, such that accessory devices  336  cannot be driven by the output shaft. However, in coast, input shaft  344  rotates at a speed determined by gears engaged in transmission  326 . Therefore, all the gear ratios in transmission  326  are available to control the rotational speed of the input shaft. Thus, in coast, when the rotation of the output shaft is too low, the transmission can be shifted to increase the rotational speed of the input shaft such that the rotational speed of the input shaft is adequate to drive the accessory devices. 
     In an example embodiment (not shown), a one-way clutch is present between a turbine for torque converter  304  and input shaft  344 . The one-way clutch enables the turbine to drive the vehicle but not to back-drive the engine in coast. This would enable all kinetic energy to go into the accessory devices. 
     The following provides further detail regarding vehicles  101 / 202 / 302  and systems  100 / 200 / 300 . Although the following discussion is directed to vehicle  101  and system  100 , it should be understood that the discussion is applicable to vehicle  202 / 302  and system  200 / 300  as well. In an example embodiment, the accessory devices associated with operation of the engine, such as the water pump and air conditioner compressor, are located in an engine compartment. In an example embodiment, the accessory devices associated with operation of the engine, such as the water pump and air conditioner compressor, are located at or in the transmission. 
     In an example embodiment, transmission oil pump  158  is moved off-axis, for example, not directly driven by a torque converter pump hub, and connected through the clutch assembly, which advantageously enables use of a smaller pump providing full transmission pressure during sailing (engine off highway cruising). In an example embodiment, engine oil pump  150  is connected to system  100  to advantageously pressurize an oil system for the vehicle with the engine off, for example, to adjust a hydraulic vane-type variable cam timing (VCT) system for startup. 
     Thus, system  100  enables accessory devices to be driven at lower speeds during normal operation of the vehicle and to be driven while the engine is off. Further, system  100  enables accessory devices to be driven by the electric machine when the engine is off or when the vehicle is accelerating. System  100  also enables the vehicle to be hybridized by enabling use of a larger capacity electric machine and battery system in a conventional vehicle. Thus, system  100  enables multiple levels of hybridization by enabling increased sizing of the electric machine and battery. As a result, system  100  enables a modular hybrid strategy with one base power train. 
     System  100  provides several advantages for modern vehicle drivetrains. The system is an enabler for stop-start strategies in which the vehicle engine is turned off while approaching or waiting at a traffic light, for example. Because system  100  allows the electric machine to drive accessories with the engine off (i.e., the third clutch position), the cabin stays comfortable because the air conditioner is still functional, the engine oil pump can pressurize the variable cam timing system for optimum restart, and the engine will restart faster because the inertia of the accessory drive is removed. 
     The system also solves problems with turning the engine off when the vehicle is cruising on a highway, sometimes referred to as sailing. An output shaft driven transmission oil pump (i.e., the first clutch position) enables full hydraulic clutch control, including gear shifts, in the transmission, and a driven vacuum pump ensures vacuum boosted brakes remain operational for safety. In addition, downspeeding the accessories through chain or belt ratios and/or connection to the transmission output shaft reduces drag on the drivetrain. The same output shaft connection allows kinetic energy recovery to recharge the battery and drive the aforementioned accessories without using engine or battery power during deceleration. 
     The system also includes one-way clutch functionality when the engine is driving the accessories (i.e., the second clutch position). The one-way clutch decouples the accessory devices from engine vibration, since the one-way clutch function only transmits engine torque in one rotational direction. Thus, the slowing of the crankshaft between cylinder firings, which can create vibration and reduce operational efficiency, is not transmitted to the drive shaft. For example, in response to the slowing, drive element  116  free wheels rather than transmitting torque to the drive shaft. 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.