Abstract:
A method of converting an existing vehicle powertrain including a manual transmission to a hybrid powertrain system with an automated powertrain transmission. The first step in the method of attaching a gear train housing to a housing of said manual transmission, said gear train housing receiving as end of drive shaft of said transmission and rotatably supporting a gear train assembly. Secondly, mounting an electric motor/generator to said gear train housing and attaching a motor/generator drive shaft of said electric motor/generator to said gear train assembly. Lastly, connecting an electro-mechanical clutch actuator to a friction clutch mechanism of said manual transmission.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of pending application Ser. No. 09/302,719 entitled “Powertrain System for a Hybrid Electric Vehicle” filed Apr. 30, 1999 by the same inventors as in the present application which is now abandoned. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The government of the United States of America has rights in this invention pursuant to Subcontract No. ZAN-6-16334-01 awarded by the U.S. Department of Energy. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates generally to a powertrain system for hybrid electric vehicles and, more particularly, to an automated manual transmission powertrain system for a hybrid electric vehicle having input shaft synchronization using an electric motor. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Since the invention of power vehicles, many different powertrain systems have been attempted, including a steam engine with a boiler or an electric motor with a storage battery. It was, however, the discovery of petroleum in 1856 and the four-stroke internal combustion engine invented by Otto in 1876, that provided the impetus for the modern motor vehicle industry. 
     Although fossil fuel emerged as the fuel of choice for motor vehicles, recent concerns regarding fuel availability and increasingly stringent federal and state emission regulations have renewed interest in alternative fuel powered vehicles. For example, alternative fuel vehicles may be powered by methanol, ethanol, natural gas, electricity, or a combination of these fuels. 
     A dedicated electric powered vehicle offers several advantages: electricity is readily available, an electric power distribution systems is already in place, and an electric powered vehicle produces virtually no emissions. There are, however, several technological disadvantages that must be overcome before electric powered vehicles gain acceptance in the marketplace. For instance, the range of an electric powered vehicle is limited to approximately 100 miles, compared to approximately 300 miles for a similar fossil fuel powered vehicle. Further, the acceleration is significantly less than that of a comparable fossil fuel powered vehicle. 
     A hybrid powered vehicle, powered by both a renewable and non-renewable energy source, overcomes the technical disadvantages of a dedicated electric vehicle while still offering an environmental benefit. The performance and range characteristics of the hybrid powered vehicle is comparable to a conventional fossil fuel powered vehicle. Thus, there is a need in the art for a hybrid powertrain system for a motor vehicle that is energy efficient, has low emissions, and offers the performance of a conventional fossil fuel powered vehicle. In particular, there is a need for a transmission system to complement the combined electric and gas power plants. 
     There are presently two typical powertrains for use on the conventional automobile. The first, and oldest, type of powertrain is the manually operated powertrain. These powertrains are typically characterized in that vehicles having manually transmissions include a clutch pedal to the left of a brake pedal and a gear shift lever which is usually mounted at the center of the vehicle just behind the dash board. To operate the manual transmission, the driver must coordinate depression of the clutch and acceleration pedals with the position of the shift lever in order to select the desired gear. Proper operation of a manual transmission is well known to those skilled in the art, and will not be described further herein. 
     In a vehicle having an automatic transmission, no clutch pedal is necessary, and the standard H configuration of the shift lever is replaced by a shift lever which typically moves back and forth. The driver need only select between park, reverse, neutral, drive, and 1 or 2 low gears. As it is commonly known in the art, the shift lever is placed in one of several positions having the designator P, R, N, D, 2, AND MAYBE 1, which corresponds to park, reverse, neutral, drive, and 1 or 2 low gears, respectively. Vehicle operation when the gear shift lever is placed in one of these positions is well know in the art. In particular, when in drive mode, the transmission automatically selects between the available forward gears. As is well known, older systems typically included first, second, and third gears, while newer systems include first through third gears as well as a fourth and possibly a fifth overdrive gear. The over drive gears provide an improved fuel economy at higher speeds. 
     As is well known, early transmissions were almost exclusively manually operated transmissions. With a steady development of automatic transmissions, drivers increasingly gravitated toward the easy operation of automatic transmissions. However, in the mid 1970&#39;s, rising concerns about present and future fossil fuel shortages resulted in implementation of corporation average fuel economy regulations prorogated in several countries. These fuel economy requirements necessitated the investigation of increasing the fuel economy of motor vehicles in order to meet government regulations. These government regulations prompted a gradual return to manual transmissions which are typically more efficient than automatic transmissions. 
     In the ensuing years, many mechanically operated vehicle systems were replaced or at least controlled by electronic control systems. These electronic control systems greatly increase the fuel efficiency of vehicle engines and enabled a gradual return to the convenience of automatic transmissions. In addition, electronic controls placed on automatic transmissions, greatly improved the shift schedule and shift feel of automatic transmissions and also enabled implementation of fourth and fifth overdrive gears, thereby increasing fuel economy. Thus, automatic transmissions have once again become increasingly popular. 
     Automatic and manual transmissions offer various competing advantages and disadvantages. As mentioned previously, a primary advantage of a manual transmission is improved fuel economy. Conversely, automatic transmissions first and foremost offer easy operation, so that the driver need not burden both hands, one for the steering wheel and one for the gear shifter, and both feet one for the clutch and one for the gas and break while driving. When operating a manual transmission, the driver has both one hand and one foot free. In addition, an automatic transmission provides extreme convenience in stop and go situations, as the driver need not worry about continuously shifting gears to adjust to the ever changing speed of traffic. 
     With respect to a hybrid vehicle, however, manual transmissions prove to be particularly advantageous to increasing efficiency, thereby improving fuel economy. The primary reason for the superior efficiency of the manual transmission for the hybrid vehicle lies in the basic operation of the automatic transmission. In most automatic transmissions, the output of the engine connects to the input of the transmission through a torque converter. Most torque converters have an input turbine that is connected to the output shaft of the engine and an input impeller that is connected to the input shaft of the transmission. Movement of the turbine at the input side results in a hydraulic fluid flow which causes a corresponding movement of the hydraulic impeller connected to the input shaft of the transmission. While torque converters provide a smooth coupling between the engine and the transmission, the hydraulic fluid results in a parasitic loss, thereby decreasing efficiency of the powertrain. Further, the shift operation in an automatic transmission also requires hydraulic fluid pressure, thereby introducing additional parasitic losses of efficiency in the powertrain. 
     Even with the more efficient manual transmissions, there are substantial losses of kinetic energy due to the friction losses that occur during engagement of the synchronization mechanisms typically used in a manual transmission. 
     Before a shift between the gear ratios of a manual transmission can occur, it is necessary to synchronize the rotational speed of the drive shaft with the rotational speed of the driven shaft. Typically, synchronization is obtained in a manual transmission by way of a synchronizing mechanism such as a mechanical synchronizer which is well known in the art. The mechanical synchronizer varies the speed of drive shaft to match the speed of the driven shaft to enable smooth engagement of the selected gear set. For example, during an upshift, the mechanical synchronizer utilizes frictional forces to decrease the rate of rotation of the drive shaft so that the desired gear on the drive shaft is engaged smoothly to drive the desired gear of the driven shaft. Conversely, during a downshift, the mechanical synchronizer increases the rate of rotation of the drive shaft so that the desired gear is engaged smoothly to drive the desired gear on the driven shaft. 
     Thus, there is a need in the art for a powertrain system having an efficient transmission which limits kinetic losses due to mechanical synchronizers as well as parasitic losses due to hydraulic control. 
     Further, in a typical hybrid powertrain system, the electric motor is connected to the drive wheels downstream of the transmission output shaft. Accordingly, at low vehicle speeds the electric motor is driven relatively slowly when operating in the regenerative mode. However, the efficiency of the electric motor is greatly reduced at these relatively low speeds. In addition, typical hybrid powertrain systems have utilized large electric motors which are capable of providing all of the drive torque necessary for driving the vehicle. These large electric motors are typically 75-100 Kw motors which are extremely expensive and heavy. The system of the present invention provides a mild hybrid powertrain system which uses a smaller electric motor (approximately 15 kW) connected to the input/drive shaft of an automated manual-type transmission. The electric motor is used in limited situations for providing driving torque for propelling the vehicle. The electric motor also operates as a generator and because it is drivingly connected to the input shaft of the transmission, the electric motor is still driven at relatively high speeds even when the vehicle speed is low in order to provide more efficient regeneration. 
     The present invention also provides a hybrid powertrain system that utilizes an electric motor/generator to synchronize a speed of a transmission drive shaft with a speed of a transmission driven shaft. The present invention also provides a transmission for a hybrid powertrain system which is electro-mechanically controlled to substantially operate as an automated manual transmission, thereby eliminating parasitic loses due to hydraulic fluid flow. Also, a method of retrofitting an existing manual transmission to become an automated manual transmission and/or a method of converting a powertrain system having an engine and a manual transmission into a hybrid electric powertrain system, is also provided. 
     To achieve the foregoing objects, the present invention provides a hybrid powertrain system, including an internal combustion engine having an engine output shaft; a transmission including a transmission drive shaft coupled to the internal combustion engine by a friction clutch mechanism, the transmission further including a transmission driven shaft selectively driven at a plurality of gear ratios relative to the transmission drive shaft; an electric motor/generator drivingly engaged with the transmission drive shaft; wherein the electric motor/generator is utilized to synchronize rotation of the transmission drive shaft with the driven shaft. 
     One advantage of the present invention is that the automated manual-style transmission provides a more efficient transmission system by eliminating parasitic losses due to hydraulic fluid flow. Another advantage of the present system is that an electronic controller automatically controls the manual-style transmission so that the transmission operates as a functional equivalent to an automatic transmission to the driver. Another advantage of the present invention is that during a shift, the electric motor substantially synchronizes the speed of the input shaft with the speed of the output shaft of the transmission. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however 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 from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a cross-sectional view of a hybrid powertrain system for a motor vehicle according to the principles of the present invention; 
     FIG. 2 is a schematic diagram of the hybrid powertrain system including the electrical connections according to the principles of the present invention; 
     FIG. 3 is a plan view of the gear train connecting the electric motor to the transmission drive shaft; 
     FIG. 4 is a top view of a cross over shift actuator used in accordance with the principles of the present invention; 
     FIG. 5 is a side view of the cross over shift actuator of FIG. 4; 
     FIG. 6 is a top view of a select shift actuator used in accordance with the principles of the present invention; 
     FIG. 7 is a side view of the cross over shift actuator of FIG. 6; 
     FIG. 8 is a detailed view of a parking sprag assembly in a disengaged position, according to the principles of the present invention; 
     FIG. 9 is a detailed view similar to FIG. 8 with the parking sprag engaging a top portion of a tooth of a parking gear; 
     FIG. 10 is a detailed view similar to FIG. 8 with the parking sprag engaged with the parking gear; 
     FIG. 11 is an exploded view of the sprag mechanism which is utilized with the present invention; 
     FIG. 12 illustrates the cam linkage drive assembly according to the principles of the present invention; 
     FIG. 13 is a cross-sectional view taken along line  13 — 13  of FIG. 12 illustrating the second cam and corresponding switch; 
     FIG. 14 is a cross-sectional view taken along line  14 — 14  of FIG. 12 illustrating the third cam and corresponding switch; 
     FIG. 15 illustrates the circuitry for controlling the electric parking sprag according to the principles of the present invention; 
     FIG. 16 is cross-sectional view of an electro-mechanical clutch actuator according to the principles of the present invention; 
     FIG. 17 is a cross-sectional view taken along line  17 — 17  of FIG. 20 of the electro-mechanical clutch actuator according to the principles of the present invention; 
     FIG. 18 is an end view of the electro-mechanical clutch actuator according to the present invention with the gear train housing removed; 
     FIG. 19 is a schematic diagram illustrating the relative positioning of the actuator housing, the electric motor and the linear potentiometer; 
     FIG. 20 is an end view of the gear train cover; 
     FIG. 21 is a cross-sectional view taken along line  21 — 21  of FIG. 16, illustrating the assist cam assembly according to the principles of the present invention; 
     FIG. 22 is a side view of an assist lever of the assist cam assembly according to the principles of the present invention; 
     FIGS. 23 a - 23   f  illustrate the relative position of the assist lever of the assist cam assembly during various ranges of travel during actuation of the clutch actuator; 
     FIGS. 24 a - 24   d  schematically illustrate the operation of the wear compensator according to the principles of the present invention; 
     FIG. 25 is a graph illustrating the amount of release load force required for disengaging a clutch as well as the calculated amount of release load assistance provided by the assist spring assembly during various intervals of cable travel; and 
     FIG. 26 is a detailed cross-sectional view of the one-way friction clutch utilized in the system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, a hybrid powertrain system  10 , according to the present invention, is illustrated for a motor vehicle, generally shown at  8 . The hybrid powertrain system  10  includes a heat engine  14  operating on a hydrocarbon based or fossil fuel. In this example, the engine  14  is a compression-ignited engine fueled by a diesel fuel. Preferably, the engine  14  is sized comparable to a diesel engine for a non-hybrid motor vehicle. 
     The hybrid powertrain system  10  includes a clutch mechanism  16 , as is known in the art, for operably interconnecting engine  14  and transmission  18 . The Clutch mechanism  16  compensates for the difference in rotational speed of engine  14  and transmission  18 , to smooth engagement between the engine  14  and the transmission  18 . 
     Transmission  18  includes a drive or input shaft  20  (hereinafter referred to as “drive shaft  20 ”) which connects to an engine output shaft  22  through clutch  16  and transmits engine rotation and power at various ratios to the drive wheels of the motor vehicle. Thus, transmission  18  enables the motor vehicle to accelerate through predetermined gear ratios, while engine  14  functions within a predetermined operating range. Examples of known transmission types include an automatic transmission, a manual transmission, and a continuously variable transmission. It should be appreciated that in a preferred embodiment of the present invention as shown, transmission  18  is a five-speed manual transmission as is well known in the art. 
     The drive shaft  20  of the transmission  18  is operatively connected to clutch mechanism  16 . Drive shaft  20  supports a plurality of drive gears  28   a-f  which are engaged with a plurality of driven gears  30   a-f  supported on an output or driven shaft  32  (hereinafter referred to as “driven shaft  32 ”). Driven shaft  32  includes an output gear  34  which meshingly engages with an input gear  36  of a differential unit  38 . The differential unit  38  engages a pair of axle shafts  40  which are operably connected to the drive wheels  26 , and selectively provide power to the drive wheels  26  in accordance with the operation of a differential unit as is known to those skilled in the art. 
     The operation of engine  14  produces a torque output which, through clutch mechanism  16 , causes the drive shaft  20  to rotate at a first rate. Concurrently, driven shaft  32  rotates at a second rate related to a rate of rotation of the drive shaft  20  and the particular engaged gear set of drive shaft  20  and driven shaft  32 . Similarly, the driven shaft  32  drives the differential unit  38  for driving axle shafts  40  and wheels  26 . 
     The hybrid powertrain system  10  also includes an electric motor/generator  42  (hereinafter referred to as “electric motor  42 ”) operably connected to transmission  18  at the opposite end of drive shaft  20  from clutch  16 . Electric motor  42  is connected to input shaft  20  opposite from clutch  16  by a gear train  44 . The electric motor  42  is able to provide both positive and regenerative torque, by functioning as a motor and a generator, respectively. An example of an electric motor  42  is an induction motor or a permanent magnet motor, which is available from Delphi Corporation. 
     As a generator, electric motor  42  is driven by the drive shaft  20  and produces a regenerative torque, preferably as an alternating current (A/C), which is transferred to a control mechanism, such as motor controller  46 . Motor controller  46  changes the alternating current into a direct current (D/C), as is well known in the art. The direct current may then be transmitted to an energy storage apparatus  48 , such as a battery. Alternatively, as a motor, the electric motor  42  produces a positive torque that is applied to the drive shaft  20  of the transmission  18  and ultimately provides torque to drive wheels  26 . The system of the present invention provides a mild hybrid powertrain system which uses a small electric motor  42  (less than 50 Kw and preferably approximately 15 kW) connected to the drive shaft  20 . Typically, hybrid powertrain systems utilize much larger motors such as 75 and 100 Kw motors. The electric motor  42  is used in limited situations for providing driving torque for propelling the vehicle. The electric motor  42  also operates as a generator and because it is drivingly connected to the drive shaft  20  of the transmission  18 , the electric motor  42  is still driven at high speeds even when the vehicle speed is low in order to provide more efficient regeneration. 
     Hybrid powertrain system  10  also includes a transmission controller  50 , such as an electronic control unit. Transmission controller  50  enables electronic control of transmission  18  to enable the transmission  18  to be configured as a manual-style transmission, but to be operated from a drivers standpoint as an automatic transmission. To effect such operation, transmission  18  has a pair of electro-mechanical shift actuators  52 ,  54  which simulate positioning of the stick shift actuators as in a conventional manual transmission. Further, an electro-mechanical clutch actuator  56  enables operation of clutch  16  in replacement of a clutch pedal as on a conventional manual transmission. In order to generate such control signals, transmission controller  50  receives input signals from engine  14  or an engine controller  58 . Examples of such information received from engine  14  or engine controller  58  include vehicle speed, RPM, and the like. Similarly, transmission controller  50  generates output signals to control actuators  52 ,  54 , and  56  and also outputs diagnostic and other communication signals to engine  14  and/or engine controller  58 . Transmission controller  50  may also receive other vehicle condition signals, depending on a particular configuration of the transmission controller  50 . 
     In this example, the electric motor  42  is positioned to rotate drive shaft  20 , although other configurations are possible. By configuring electric motor  42  to rotate drive shaft  20 , electric motor  42  eliminates the need for the mechanical synchronizers as required by standard manual transmissions. In particular, rotation sensors  59   a ,  59   b  are used to sense the rotational speed of drive shaft  20  and driven shaft  32 , respectively. Transion controller  50  generates control signals to electric motor  42  through motor controller  46 , to effect activation and deactivation of electric motor  42 . Activation and deactivation of electric motor  42  enables varying the speed of the drive shaft  20  through gear train  44  so that synchronization of drive shaft  20  and driven shaft  22  may be achieved (taking into consideration the gear ratio of the selected gear) to engage the desired gears. During an upshift, the electric motor  42  is operated as a generator to apply torque to the drive shaft  20  to slow down the drive shaft  20  for synchronizing the drive shaft  20  with the drive shaft  32 . The regenerative torque is applied by the electric motor  42 . The regenerative mode produces potential energy which is stored in the battery. During a downshift, the electric motor is driven to increase the rotational speed of the drive shaft  32  to synchronize the rotation with the driven shaft  32 . Via this process, electric motor  42  is able to synchronize the inertia of drive shaft  20  of the transmission  18  with the driven shaft  32 , thereby eliminating the need for the mechanical synchronizer which is typically employed in a manual transmission. 
     Another example of a capability of the electric motor  42  is to start the engine  14 . Electric motor  42 , while functioning as a motor, may initiate the torque and rotational speed necessary to rotate drive shaft  20 , and through engagement of clutch mechanism  16 , start engine  14 . Therefore, a starter motor, as is known in the art, is unnecessary. 
     The hybrid powertrain system  10  also includes a braking system (not shown) operably connected to the wheels. An example of a known braking system is a driver assisted hydraulic braking system, known in the art. The driver operates a brake pedal (not shown) to mechanically apply a braking force to slow down the spinning of drive wheels  26  or maintain drive wheels  26  in a stationary position. However, with a hydraulic braking system, the momentum of the motor vehicle, in the form of kinetic energy, is usually lost. 
     A preferred type of braking system for use with the present invention also includes a regenerative braking system, capable of capturing kinetic energy from the momentum of the motor vehicle as it is slowing down and storing this energy as potential energy in the energy storage apparatus  48 . Electric motor  42  slows the motor vehicle down by applying a braking force that slows down the rotation of drive axles  40 . During the regenerative braking, electric motor  42  functions as a generator and captures the reverse energy flow as potential energy in the form of electricity. 
     In operation, as will be described in greater detail herein, transmission controller  50  receives input signals from engine  14 , engine controller  58 , clutch  16 , clutch actuator  56 , transmission  18 , and through additional sensors. With reference to clutch actuator  56 , this actuator is preferably a rotary actuator which causes linear movement to effect engagement and disengagement of clutch  16 . 
     Transmission controller  50  causes shifting of gears through shift actuators  52  and  54 . With respect to actuators  52  and  54 , these actuators combine to mimic movement of the shift lever in a conventional manual transmission. That is, in visioning the typical “H” shift configuration, shift actuator  52  may operate as the cross over actuator, i.e., determining what leg of the “H” the shifter is in. Similarly, shift actuator  54  operates as a select actuator which mimics an upward or downward movement of the shifter within the leg of the “H”. The actuators  52 ,  54 , and  56  receive control signals from transmission controller  50  to operate the shifting portion of transmission  18  as in a conventional manual transmission. 
     Hybrid powertrain system  10  includes an energy storage apparatus  48 , such as a battery, to store potential energy for later use by the motor vehicle. For example, the potential energy stored in the battery may be transferred, as DC current, to operate an accessory component  60 . 
     Hybrid powertrain system  10  also includes at least one accessory component  60 . An example of an accessory component may be a power steering pump, a water pump, a lighting system, a heating and cooling system, which are all conventional and well known in the art. Accessory components  60  are usually mechanically driven by the engine  14  or electrically powered with energy from battery  48 . For example, accessory component  60 , such as the power steering pump, is operably connected to engine  14  and mechanically driven by engine  14 . The lighting system relies on energy supplied by the energy storage apparatus  48 , as a source of power. However, according to the present invention, all of the accessory components  60  are electrically powered using energy from the energy storage apparatus  48 . 
     The present invention takes advantage of the kinetic energy available during braking of the motor vehicle and stores it as potential energy in battery  48 . In a first direction of power flow, if a braking force is applied to drive wheels  26 , the available kinetic energy is directed through drive axles  40  and transmission  18 , as the rotational speed of the axle shafts  40 , driven shaft  32  and drive shaft  20  decreases. The kinetic energy flows into the electric motor  42 , causing it to function as a generator, to produce a regenerative torque, preferably as an A/C current. The A/C current is transmitted to the motor controller  46  which converts it to a D/C current. The D/C current is transferred to the energy storage apparatus  48  for storage as potential energy. If the accessory component  60  requires energy, it is drawn from battery  48 , such as in the form of D/C current. This enhances the efficiency of engine  14 , since engine  14  is not expending power to operate accessory  60 . 
     In an opposite situation, energy storage apparatus  48  supplies potential energy, such as a D/C current, to motor controller  46 , which converts it into an A/C current. The A/C current is directed to the electric motor  42 , causing it to act as a motor and produce a positive torque. The positive torque is applied to the transmission  18 , which in turn induces the rotation of the axle shafts  40  and the rotation of the drive wheels  26  of the motor vehicle. 
     The hybrid powertrain system  10  according to one embodiment of the present invention, as shown, includes a standard five-speed manual transmission  18 . The manual transmission is retrofitted with an electro-mechanical clutch actuator  56  which will be described in detail hereinbelow for disengaging the clutch mechanism  16 . The cross over shift actuator  52  is shown in FIGS. 4 and 5 and includes a rotary electric motor  64  drivingly engaged with a potentiometer  66  via a coupling housing  67 . Electric gear motor  64  is coupled to a worm gear  68  which is rotatably supported within an actuator housing  70  by a pair of bearing assemblies  72 . A gear segment  74  engages worm gear  68  and is driven thereby. Gear segment  74  is mounted to an actuator shaft  76  which is rotatably driven. The actuator shaft  76  extends through the housing of the transmission  18  and engages the existing cross over shift mechanism (not shown) of the transmission  18 . The actuator housing  70  is mounted to an exterior surface of the transmission housing. The electric motor  64  is connected to the transmission controller  50  and is operably controlled in order to shift the transmission  18 . 
     The select shift actuator  54  is similar to the cross over shift actuator  52  in that the select shift actuator  54  includes an actuator housing  70  which supports a worm gear  68  via bearing assemblies  72 . The worm gear  68  engages a gear segment  74  which is attached to an actuator shaft  76  which is inserted through a transmission housing and engages the existing select shift mechanism (not shown) of the manual transmission  18 . The select shift actuator  54  (as shown) is different from the cross over shift actuator  52  in that the electric motor  64  is disposed on one side of the actuator housing  70  and is in driving engagement with the worm gear  68 . The potentiometer  66  is disposed on an opposite side of the actuator housing  70 . In the preferred embodiment as shown, the configurations of the shift actuators  52 ,  54  were selected in order to provide appropriate spacing for the shift actuators  52 ,  54  to be mounted to the transmission housing. As discussed above, shift actuators  52 ,  54  are controlled by the transmission controller  50  in order to mimic the movements of the shift linkage system of the manual transmission. 
     With reference to FIGS. 1 and 3, the gear train assembly  44  will now be described. The gear train assembly  44  includes a gear train housing  80  which is mounted to the transmission housing  82  via threaded fasteners (not shown). Electric motor  42  is mounted to the gear train housing  80  and includes a motor drive shaft  86 . A drive gear  88  is mounted to the motor drive shaft  86 . An idler gear  90  is in meshing engagement with drive gear  88  and is supported on an idler shaft  92  which is supported between gear train housing  80  and gear train cover  94 . A driven gear  96  is in meshing engagement with idler gear  90 . Driven gear  96  is mounted to drive shaft  20  of transmission  18 . It should be noted that according to the embodiment shown, the drive shaft  20  has been provided with a shaft extension  98  in order to extend the exiting drive shaft  20  through the transmission housing  84  and into the gear train housing  80 . Accordingly, the existing manual transmission  18  has been retrofitted into a hybrid powertrain system by providing an electric motor  42  in driving engagement with the drive shaft  20  via gear train  44 . 
     The members of the consuming public who have preferred automobiles with automatic transmissions have become accustomed to a standard shift lever system which includes a PRNDL shift arrangement. However, it is typical that a manual transmission does not include a park feature. Accordingly, manual transmission vehicles are typically provided with a parking brake which is activated by the driver of the vehicle. Typically, parking brake systems for manual transmission vehicles provide a dual function as an emergency brake which frictionally engages the vehicle wheels to inhibit rotation. In addition, manual transmissions are often placed in gear by the operator after the vehicle engine is turned off in order to provide an effective brake for the vehicle in a parked condition. 
     However, in converting a manual transmission to an automated manual transmission, it is desirable to provide a shift lever which simulates that of a standard automatic transmission including a parking position. Therefore, the present invention provides a parking gear  100  mounted to the driven shaft  32  within the gear train housing  80 . The driven shaft  32  includes a shaft extension  102  which extends the driven shaft  32  through the transmission housing  82  and into the gear train housing  80 . The parking gear  100  is selectively engaged by a parking sprag assembly  104  which will be described in greater detail hereinbelow. According to a preferred embodiment, the parking sprag assembly  104  is operated electrically. The sprag mechanism  106 , as shown in FIG. 11, is known in the prior art. The sprag mechanism  106  includes an activation rod  108  provided with a pivot on one end for attachment to an actuation lever (not shown) and a cam roller assembly  112  is attached to an opposite end of activation rod  108  and includes a housing  114  which rotatably supports a pair of cam rollers  116 . A pressure release spring  118  is provided between a detent portion  108   a  on activation rod  108  and pivot member  110 . 
     A sprag member  120  is attached to a guide bracket  122  via a pivot pin  124 . A sleeve  126  is provided on the pivot pin  124  and supports the sprag  120  thereon. A pair of end fittings  128  and a bushing  130  are provided for maintaining the spacing of the sprag member  120  relative to the guide bracket  122 . A return spring  132  is provided for biasing the sprag member  120  toward the guide bracket  122 . A blocker pin  134  is provided for limiting movement of the guide bracket  122 . 
     As best shown in FIGS. 8-10, the guide bracket  122  includes a cam surface  136  and sprag member  120  includes an opposing cam surface  138 . The cam rollers  116  of cam roller assembly  112  are received between cam surfaces  136 ,  138  of guide bracket  122  and sprag member  120 , respectively. 
     According to the present invention, the activation rod  108  is attached to an actuation lever  140  which is pivotably attached to the gear train housing  80  via pivot pin  142 . Lever  140  includes a first arm portion  144  attached to the activation rod  108  and secured thereto by a C-clip  145 . Lever  140  includes a second arm portion  146  supporting a cam roller  148  at an end thereof. Cam roller  148  engages a linkage cam member  150  which is rotatably mounted about pivot point  152 . A spring  154  is connected between the first arm portion  144  of lever  140  and guide bracket  122 . Spring  154  biases lever  140  to rotate in a counter clockwise direction as shown in FIGS. 8-10 so as to maintain cam roller  148  in contact with cam  150 . Spring  118  is weaker than spring  154  so that spring  118  does not prevent cam roller  148  from maintaining contact with cam  150  when the spring  118  is in a compressed state. 
     During engagement of the parking sprag assembly, linkage cam  150  is rotated from the position shown in FIG. 8, wherein the parking sprag is in the disengaged position, to the position as shown in FIG.  9 . As linkage cam  150  rotates, lever  140  pivots in a counter clockwise direction causing the cam rollers  116  of roller cam assembly  112  to engage cam surfaces  136 ,  138  of guide bracket  122  and sprag member  120 , respectively. As roller cam assembly  112  is pressed into engagement with cam surfaces  136 ,  138 , sprag member  120  is pressed against the biasing force of return spring  132  toward engagement with parking gear  100 . 
     As shown in FIG. 9, the sprag member  120  may come in contact with a top portion of a tooth  158  of parking gear  100  and will not be allowed to engage the parking gear  100 . During continued rotation of linkage cam  150  and corresponding rotation of lever  140 , activation rod  108  will continue to place force against roller cam assembly  112  which is pressed against cam surfaces  136 ,  138  for separating sprag member  120  from guide member  122 . The biasing force of spring  154  and pressure release spring  118  will build up as linkage cam  150  rotates while sprag member  120  abuts tooth  158  of parking gear  100 . The spring force is such that any rotation of the vehicle wheels  26  which causes rotation of the driven shaft  32  of transmission  18  will cause parking gear  100  to rotate slightly thereby allowing sprag member  120  to engage the teeth  158  of parking gear  100  and affirmatively lock the driven shaft  32  in a parked position. 
     With reference to FIGS. 12-14, motor  160  is provided for driving a speed reducer  162  which is connected to linkage cam  150  via a coupling shaft  164 . A second cam  166  is installed on the coupling shaft  164  between the gear motor  160 / 162  and the linkage cam  150 . The second cam  166  throws a single pole double throw (SPDT) micro switch  168 . The second cam  166  is designed to close one pole of the switch  168  for the first 180 degrees of rotation and close the second pole for the next 180 degrees of rotation. FIG. 15 illustrates a control circuit that uses the switch  168  driven by the second cam  166  and a similar SPDT switch  170  mounted to the shifter lever in the passenger compartment. The shifter-mounted switch  170  is thrown when the shift lever is moved into the park position. This closes the first circuit  172 . Power is then supplied to a relay  176  that drives the electric gear motor  160 / 162  until the second cam  166  throws switch  168 , opening the first circuit  172 . The rotation of the parking linkage cam  150  is then stopped and the sprag member  120  locks the parking gear  100 . 
     When the shift lever is moved from park, the second circuit  174  is closed. Power is then supplied to the relay  176  that drives the electric gear motor  160 / 162  until the second cam  166  throws its switch  168 , opening the second circuit  174 . The rotation of the parking linkage cam  150  is then stopped and sprag member  120  unlocks the parking gear  100 . 
     In order to prevent the gear motor inertia from carrying the cam a full 180 degrees past the required stopping point, the relay  176  is designed to short the motor  160  to ground when it is not being driven electrically. This effectively provides an electric braking action which is provided for stopping the gear motor  160 / 162  as required. In order to help a vehicle control identify whether the parking gear is unlocked and prevents it from trying to launch the vehicle while still in park, a third cam  180  and switch  182  are provided next to second cam  166 . The third cam  180  has a lobe  184  which is aligned to indicate when the parking gear is unlocked. 
     With reference to FIGS. 16-26, the electro-mechanical clutch actuator  56  according to the present invention will be described. The clutch actuator  56  includes an electric motor  212  which provides a rotary drive member which is drivingly engaged with a ball screw assembly  214  via a drive gear  216  mounted on a drive shaft  218  of the electric motor  212 . An idler gear  220  is driven by the drive gear  216 . Idler gear  220  drives a driven gear  222  which is mounted to a ball screw shaft  224  of ball screw assembly  214 . A ball screw nut  226  is disposed on the ball screw shaft  224 . 
     A self-adjuster housing  228  is attached to the ball screw nut  226  via an adapter plate  229 . The self-adjuster housing  228  serves as a first member of a wear compensator assembly  230 . The self-adjuster housing  228  supports a pair of pivot pawls  232  (as seen in FIG. 17) which serve as an engagement mechanism for engaging the self-adjuster housing  228  with a rack  234  having a toothed surface thereon. Rack  234  serves as a second member of the wear adjustment assembly  230 . Rack  234  is formed as a generally cylindrical cup-shaped member which is received in a central opening portion  236  of self-adjuster housing  228 . Pivot pawls  232  are pivotably mounted to the self-adjuster housing  228  by pivot pins  240 . Pivot pawls  232  each include a ramp portion  242  which is engagable with a pair of adjustment retractor members  244  which extend radially inward from an actuator housing  246 . 
     As the self-adjuster housing  228  is moved in the direction of arrow “A” toward the left-most position, as shown in FIGS. 16 and 17, thereby providing slack in the clutch cable  248 , the ramp portion  242  of pivot pawls  232  engage the adjuster retractor members  244  causing pivot pawls  232  to pivot about pivot pins  240  and thereby disengage the rack  234 . At this time, a preload spring  250  which is disposed between the self-adjuster housing  228  and rack  234  is allowed to extend generally to its relaxed position, thereby pressing the rack  234  relative to the self-adjuster housing  228  and thereby taking out any slack in the clutch cable  248 . Accordingly, the wear compensator assembly  230  automatically adjusts the position of the release linkage in order to maintain the same clamp load as the clutch disk wears down over its useful life. 
     As the electric motor  212  is operated to drive the ball screw assembly  214  and thereby the self-adjuster housing  228  in the direction of arrow B, the ramp portion  242  of locking pawls  232  disengage from the adjustment retractor members  244  and are biased by leaf springs  252  back into engagement with rack  234 . 
     The clutch cable  248  of the present invention is designed to be attached to a clutch disengagement linkage system. For example, FIGS. 24 a - 24   d  illustrate a typical clutch linkage system including a release lever  254  which is pivotably mounted to a transmission case. The release lever  254  is attached to a constant contact release bearing  256  which engages a diaphragm spring  258 . The diaphragm spring  258  normally biases a clutch disk  260  into an engaged position. 
     In order to disengage the clutch disk  260 , the electric motor  212  is driven and causes rotation of drive gear  216  which in turn drives the idler gear  220  and driven gear  22 . Driven gear  222  causes rotation of the ball screw shaft  224  of ball screw assembly  214 . Rotation of the ball screw shaft  224  causes axial movement of the ball screw nut  226  in the direction of arrow B. Movement of the ball screw nut  226  causes the self-adjuster housing  228  to move therewith. The self-adjuster housing  228 , via engagement with the locking pawls  232 , causes the rack  234  to move therewith along with the clutch cable  248 . The clutch cable  248 , which is attached to release lever  254 , causes disengagement of the clutch disk  260 . 
     As a clutch disk  260  wears down over its useful life, the position of the release linkage must be adjusted to maintain the same clamp load. Adjustment is also important because the assist spring force curve should preferably match the clutch disk during the entire wear cycle. Accordingly, the clutch actuator  56  of the present invention is provided with an automatic wear adjustment feature whereby the self-adjuster housing is driven in the direction of arrow A to a predetermined position whereby the ramp portion  242  of locking pawls  232  engage the adjustment retractor members  244  then cause the pivot pawls  232  to pivot about pivot pins  242  and disengage from rack  234 . At this point, the pre-load spring  250  presses against the rack  234 , so that rack  234  may be moved relative to the self-adjuster housing  228  in the instance that clutch disk wear is sufficient enough to require adjustment. In order to reengage the locking pawls  232  with the rack  234 , the electric motor  212  is driven in order to drive the ball screw nut  226  in the direction of arrow B which causes the self-adjuster housing  228  to move therewith thereby causing the locking pawls  232  to disengage from the adjustment retractor members  244 . At this time, the leaf springs  252  bias the locking pawls  232  back into engagement with the rack  234 , and the actuator is automatically adjusted to compensate for wear of the clutch disk. 
     The clutch cable  248  is provided with an end fitting  262  which is received through an opening in rack  234 . The clutch cable  248  extends through an end piece  264  of actuator housing  246 . The self-adjuster housing  228  is provided with an axially extending guide portion  266  which is received within a central bore  268  in the end piece  264 . The clutch cable  248  extends through a central opening  270  in the axially extending guide portion  266  of the self-adjuster housing  228 . The clutch cable  248  is provided with an end fitting  272  which is connectable with the clutch release lever system described above. 
     An assist spring/cam assembly  274  is provided between the end piece  264  of the actuator housing  246  and the self-adjuster housing  228 . The assist spring/cam assembly  274  includes an assist spring  276  in the form of a coil spring which is seated against a spring seat portion  278  of the end piece  264 . A second end of the assist spring  276  is disposed against an assist washer  280  which is movably supported along the axially extending portion  266  of the self-adjuster housing  228 . A pair of assist cams  282  are disposed between assist washer  280  and a radially extending wall portion  284  of self adjuster housing  228 . 
     With reference to FIGS. 21 and 22, assist cams  282  each include an assist lever  286  pivotably attached to the actuator housing  246  by a pivot pin  288  and including a first roller  290  disposed against the assist washer  280  and a second roller  292  disposed against the radially extending wall portion  284  of self-adjuster housing  228 . The pivot pins  288  of the assist cam assembly  282  are supported by retainer members  294  which are attached to the actuator housing  246  via fasteners  296 , as shown in FIGS. 17 and 21. 
     As the clutch actuator  56  is operated for disengaging the clutch, the assist spring/cam assembly  274  helps to reduce the load on the electric motor. With reference to FIGS. 22 and 23 a - 23   f , the operation of the assist spring assembly will now be described. During normal engagement of the clutch disk  260 , the clutch actuator  56  is in a home position. In this state, the assist spring  276  presses against the assist washer  280  which presses against the assist levers  286  by acting on rollers  290 . In this position, a very short moment arm “x” exists between the center of the pivot pin  288  and the center of the roller  290 , while a maximum moment arm distance “y” is provided between the center of the pivot pin  288  and the center of roller  292 . During actuation of the clutch actuator  56 , movement of the self-adjuster housing  228  in the direction of arrow B allows the assist lever  286  to rotate about the pivot pin  288  causing an increase in the moment arm “x” and a corresponding decrease in the moment arm “y” during each increment of travel of the self-adjustor housing  228 . FIGS. 23 a - 23   f  illustrate the changes in the moment arm dimensions at 20% travel intervals during rotation of the assist lever  286 . FIG. 10 illustrates the amount of release load assist which is provided by the assist spring/cam assembly  274  in comparison with the amount of release load required for disengaging the clutch disk  260 . As can be readily understood by one of ordinary skill in the art, as the length of the moment arms “x” and “y” between each of the rollers  290 ,  292 , respectively, and the pivot pin  288  increase and decrease, respectively, during rotation of the assist levers  286 , the amount of release load assist that can be generated by the assist spring/cam assembly  274  also increases. This allows the spring assist force curve “s” to closely match the clutch load curve “c”. 
     Due to the low friction on the actuator system and the possible mismatch of the assist spring load to the clutch load, there is a possibility for the clutch actuator unit to back drive when the actuator is stopped during mid-stroke. To eliminate this possibility, a one-way friction device  300  is attached to the motor drive shaft  218 . With reference to FIG. 11, the one-way friction device  300  is shown. The one-way friction device  300  includes a housing base plate  302  which is attached to the electric motor  212 . A friction brake housing  304  is mounted to the housing base plate  302  and a spring housing  306  is attached to the friction brake housing  304  via a set screw  308 . A roller clutch  310  is disposed within the friction brake housing  304 . Roller clutch  310  includes a roller clutch shaft  312  which is attached to the motor drive shaft  218  via a set screw which is inserted through the socket head  314 . Anti-friction bushing  316  is disposed circumferentially around the roller clutch  310  and is sandwiched between first and second friction plates  318 , 320 . Friction plate  318  is disposed between the friction bushing  316  and the housing base plate  302 . Friction plate  320  is disposed between the friction bushing  316  and a spring bottom seat member  322 . The spring bottom seat member  322  is biased by a compression spring  324  which is seated against the spring bottom seat member  322  and a spring top seat member  326 . The spring top seat  326  is attached to a set screw  328  which is received through an opening in the spring housing  306 . A jam nut  330  is provided on the set screw  328  to adjustably support the set screw  328  in an axial position relative to the spring housing  306 . By adjustment of the jam nut  330 , the spring top seat  326  can be moved in an axial direction to increase or decrease the amount of compression force on compression spring  324  and can thereby alter the friction resistance provided by the one-way friction device  300 . 
     The electric motor  212  is attached to the actuator housing  246  by a motor mounting plate  334 . An end portion of the ball screw shaft  224  is supported by the motor mounting plate  334  by a bearing assembly  336 . A second end portion of the ball screw shaft  224  is supported via a bearing assembly  338  which is secured within adapter plate  229 . The self-adjuster housing  228  is slidably supported within the actuator housing  246  by an actuator bearing  340 . The end piece  264  is mounted to the actuator housing  246  by threaded fasteners  342 , as shown in FIG.  17 . The actuator housing  246  is also attached to the motor mounting plate  334  by fasteners  344 . A gear train housing  345  is attached to the motor mounting plate  334  for covering the drive gear  216 , the idler gear  220 , and the driven gear  222 . 
     A linear potentiometer  348  is provided to measure the travel of the actuator and give closed loop control of the actuator. The potentiometer  348  is mounted on the actuator housing  246  and measures the position of the clutch linkage. A linear potentiometer  348  as used in accordance with the present invention is available from Maurey Instrument Corp., Chicago, Ill. 60629. The linear potentiometer  348  measures the travel of the actuator and gives closed loop control. The potentiometer  348  is mounted on the actuator and measures the position of the clutch linkage. Since the potentiometer drive pawl  350  is connected downstream of the wear compensator  230 , the wear of the clutch  260  can be measured. This will allow the control computer to adjust for changing modes as the clutch  260  wears and will also allow for the computer to determine when the clutch  260  is worn out. 
     The ball screw assembly  214  has an overrunning feature at each end of its stroke. The overrunning feature allows the ball screw assembly  214  to be operated to drive the ball screw nut  226  to the end of its stroke in order to zero-in the potentiometer travel. The motor is run against its stop for a short duration to ensure that the wear adjustment is complete and then the potentiometer reading is taken. This is used for the starting point for the release travel. The ball screw assembly having an overrunning feature is available from Motion Systems Corporation, Eaton Town, N.J. 07724. With conventional bail screw assemblies which do not have the overrunning feature, the ability to drive the ball screw nut  226  to the end of the shaft  224  is limited due to the fact that if the ball screw nut  226  is driven too tightly against the end, a lock-up may occur. Therefore, with the overrunning feature, any lock-up associated with a standard ball screw assembly can be avoided, and a zeroing-in of the potentiometer travel can be properly achieved. 
     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, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.