TRANSMISSION SYSTEM UTILIZING CENTRIFUGAL CLUTCH BACKGROUND OF THE INVENTION RELATED APPLICATIONS [0001] This application is a continuation -in - part of provisional application 60/255358 filed December 13, 2000. [0002] This application is related to U.S. Serial No. 09/(00-rTRN-348) titled: CONTROL FOR TRANSMISSION SYSTEM UTILIZING CENTRIFUGAL CLUTCH and U.S. Serial No. 09/(00-rTRN-403) titled: CENTRIFUGAL CLUTCH, both assigned to EATON CORPORATION, assignee of this invention, and both filed the same day as this application. FIELD OF THE INVENTION [0003] The present invention relates to a centrifugal master clutch and a vehicular transmission system utilizing same. In particular, the present invention relates to an automated vehicular transmission system comprising an engine, a multiple ratio transmission, a centrifugally operated master friction clutch for drivingly coupling the engine to the transmission and a controller for controlling fueling of the engine during vehicle launch conditions, as a function of throttle position and other sensed system operating conditions such as at least one of engine speed, transmission input shaft speed, transmission output shaft speed, engine torque and engaged gear ratio. [0004] More particularly, a preferred embodiment of the present invention relates to a vehicular automated mechanical transmission system utilizing a centrifugal master friction clutch controlled solely by engine speed and a controller for controlling engine fueling during vehicle launch (i.e., start from stop) conditions on a closed loop basis to provide a target engine speed and/or engine torque. DESCRIPTION OF THE PRIOR ART [0005] Automated mechanical transmission systems not requiring the vehicle driver or operator to operate the vehicle master clutch (so called "two-pedal systems"), and clutch controls and actuators therefore, are known in the prior art as may be seen by reference to U.S. Patent No.'s: 4,081,065; 4,361,060; 4,936,428; 5,439,428; 5,634,867; 5,630,773; 5,960,916 and; 5,947,847, the disclosures of which are incorporated herein by reference. These systems are not totally satisfactory as separate clutch actuators, sensors and/or, electrical and/or fluid power (i.e., compressed and/or hydraulic) connections thereto are required which adds to the expense of providing, assembling and maintaining such systems. [0006] Centrifugally operated friction clutches are well known in the prior art and typically include a driving input member driven by a prime mover, usually an electric motor or internal combustion engine, and weights rotatable with the driving member which, upon rotation of the driving member, will move radially outwardly under the effect of centrifugal force to cause the driving input member to frictionally engage a driven output member. Examples of centrifugally operated clutches may be seen by reference to U.S. Patent No.'s: 3,580,372; 3,580,372; 3,696,901; 5,437,356; 3,810,533; 4,819,779; 5,441,137; 5,730,269; and; 4,610,343, the disclosures of which are incorporated herein by reference. [0007] Fully or partially automated mechanical transmission systems that, upon determining that a dynamic shift from a currently engaged ratio into neutral and then into a target ratio is desirable, will, while maintaining the vehicle master friction clutch engaged, initiate automatic fuel control to cause reduced torque across the jaw clutches to be disengaged, are known in the prior art as may be seen by reference to U.S. Patent No.'s: 4,850,236; 5,820,104; 5,582,558; 5,735,771; 5,775,639; 6,015,366; and 6,126,570, the disclosures of which are incorporated herein by reference. These systems include systems that attempt to fuel the engine to achieve a sustained zero driveline torque, and systems, which force torque reversals, see U.S. Patent No.: 4,850,236. These systems, upon sensing a neutral condition, will, while maintaining the master clutch engaged, cause the engine to rotate at a speed determined to cause synchronous conditions for engaging the target ratio. [0008] Vehicular driveline systems, especially for heavy-duty vehicles, utilizing centrifugal clutches have not been satisfactory as the engines were typically controlled by throttle device position, not on a closed loop basis based upon a target engine speed and/or engine torque, and thus did not provide acceptable control for smooth vehicle launch and low speed operation. Prior art vehicular driveline systems utilizing centrifugal master clutches were not provided with clutches having damage and/or overheating protection and/or were not configured to lock up and release at engine speeds selected to permit dynamic shifting with the master clutch engaged. SUMMARY OF INVENTION [0009] In accordance with the present invention, the drawbacks of the prior art are reduced or minimized by the provision of a centrifugal master friction clutch, and a vehicular automated transmission system utilizing same, which utilizes closed loop control to provide acceptable performance for heavy duty vehicle launch operations and low speed operation and is configured to allow dynamic shifting with the master clutch engaged. Preferably, the closed loop control will provide protection from damage and/or overheating. [0010] The above is accomplished by providing a centrifugal clutch structure which will initially lockup at an engine speed below the speed at which upshifts are required and will not release from a lockup condition at engine speeds above (i) the highest speeds at which down shifts are required and (ii) the lowest allowable expected engine speed after completion of an upshift and by controlling fueling of the engine during launch to cause engine speed and/or engine torque to equal or not exceed a target value determined as a function of sensed input signal values indicative of two or more of throttle device position, engine speed, engine torque, transmission input shaft speed, transmission output shaft speed, transmission engaged ratio and clutch slip. [0011] The centrifugal master clutch requires no external clutch actuator or sensor, and no connections to mechanical linkages, electrical power and/or fluid power. [0012] Accordingly, it is an object of the present invention to provide a new and improved centrifugally operated vehicular master friction clutch and automated mechanical transmission system utilizing same. [0013] This and other objects and advantages of the present invention will become apparent from a reading of the following description of the preferred embodiment taken in connection with the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0014] Fig. 1 is a schematic illustration of a vehicular drivetrain using the centrifugal clutch and engine fuel control of the present invention. [0015] Fig. 2 is a schematic illustration, in graphical format, of the clamp force characteristics of the centrifugal clutch of the present invention at various engine speeds. [0016] Fig. 3 is a schematic illustration, in graphical format, of target engine speeds for various throttle positions at vehicle launch for the system of the present invention. [0017] Fig. 4 is a partial top view, in section, of the cover and centrifugal mechanism of the clutch of the present invention. [0018] Fig. 5 is a partial sectional view of the roller, ramp, and clamp force limiting spring mechanism utilized with the centrifugal mechanism of Fig. 4. [0019] Fig 6A and 6B are partial sectional views illustrating the position of the flyweights in the fully radially inward clutch disengaged position and the fully radially outward clutch fully engaged position, respectively. [0020] Fig. 7 is a schematic partial sectional view of the present invention. [0021] Fig. 8A and 8B are schematic illustrations, in flowchart format, of the launch logic of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT [0022] An at least partially automated vehicular drivetrain system 10 using the centrifugally operated friction master clutch and control of the present invention is schematically illustrated in Fig. 1. System 10 may be fully automated, as seen by way of example in U.S. Patent No.: 4,361,060, partially automated, as seen by way of example in U.S. Patent No's: 4,648,290 and 5,409,432, or manual with controller assist, as seen by way of example in U.S. Patent No's: 4,850,236; 5,582,558; 5,735,771; and 6,015,366. [0023] In system 10, a change-gear transmission 12 comprising a main transmission section 14 connected in series with a splitter-type auxiliary transmission section 16 is drivingly connected to an internal combustion engine 18, such as a well- known gasoline or diesel engine, by the centrifugal master friction clutch 20 of the present invention. Transmissions 12, by way of example, may be of the type well known in the prior art and are sold by the assignee of this application, EATON CORPORATION, under the trademarks "Super-10" and "Lightning", and may be seen in greater detail by reference to U.S. Pat. No's: 4,754,665; 6,015,366; 5,370,013; 5,974,906; and 5,974,354, the disclosures of which are incorporated herein by reference. [0024] Engine 18 includes a crankshaft 22, which is attached to a driving member 60 of centrifugal master clutch 20, which frictionally engages with, and disengages from, a driven member 62, which is attached to the input shaft 28 of the transmission. A transmission output shaft 30 extends from the auxiliary transmission section 16 for driving connection to the vehicular drive wheels, as through a drive axle 31 or transfer case. [0025] The terms "engaged" and "disengaged" as used in connection with a master friction clutch refer to the capacity, or lack of capacity, respectively, of the clutch to transfer a significant amount of torque. Mere random contact of the friction surfaces, in the absence of at least a minimal clamping force, is not considered engagement. [0026] As may be seen from Fig. 1, centrifugal clutch 20 requires no external clutch actuator and is operated as function of the rotational speed (ES) of the engine. Centrifugal clutch 20 also requires no connections to operating linkages, command signal inputs, power electronics and/or compressed air and/or hydraulic conduits. The most economical application of the present invention is with a dry clutch, however, the present invention is also applicable to wet clutch technology. [0027] Transmission system 10 further includes rotational speed sensors 32 for sensing engine rotational speed (ES), 34 for sensing input shaft rotational speed (IS), and 36 for sensing output shaft rotational speed (OS), and providing signals indicative thereof. A sensor 37 provides a signal THL indicative of throttle pedal position or of torque demand. The signal is usually a percentage (0% to 100%) of fuel throttle position. Engine 18 may be electronically controlled, including an electronic controller 38 communicating over an electronic data link (DL) operating under an industry standard protocol such as SAE J-1922, SAE J-1939, ISO 11898 or the like. [0028] An X-Y shift actuator, which by way of example may be of the types illustrated in U.S. Pat. No's: 5,481,170; 5,281,902; 4,899,609; and 4,821,590, may be provided for automated or shift-by-wire shifting of the transmission main section and/or auxiliary section. Alternately, a manually operated shift lever 42 having a shift knob 44 thereon may be provided. Shift knob 44 may be of the type described in aforementioned U.S. Pat. No: 5,957,001. As is well known, shift lever 42 is manually manipulated in a known shift pattern for selective engagement and disengagement of various shift ratios. Shift knob 44 may include an intent to shift switch 44A by which the vehicle operator will request automatic engine fueling control to relieve torque lock and allow a shift to transmission neutral. A shift selector 46 allows the vehicle driver to select a mode of operation and provides a signal GRT indicative thereof. [0029] System 10 includes a control unit 50, preferably a microprocessor-based control unit of the type illustrated in U.S. Pat. No's: 4,595,986; 4,361,065; and 5,335,566, the disclosures of which are incorporated herein by reference, for receiving input signals 54 and processing same according to predetermined logic rules to issue command output signals 56 to system actuators, such as engine controller 38, shift actuator 40, and the like. [0030] As is known, to disengage a jaw clutch in a vehicular mechanical transmission, especially in a heavy-duty vehicle, it is necessary to relieve torque lock at the engaged jaw clutch. If opening the master friction clutch 20 is not desirable, torque lock can be relieved by fueling the engine to cause assumed zero driveline torque and/or by forcing torque reversals, which will positively cause crossings of zero driveline torque. [0031] Fully or partially automated mechanical transmission systems that, upon determining that a shift from a currently engaged ratio into neutral and then into a target ratio is desirable, will, while maintaining the vehicle master friction clutch engaged, initiate automatic fuel control to cause reduced torque across the jaw clutches to be disengaged, are also known in the prior art as may be seen by reference to above- mentioned U.S. Patent No.'s: 4,850,236; 5,582,558; 5,735,771; 5,775,639; 6,015,366; and 6,126,570. Shifting with the master clutch remaining engaged is preferred in many situations, as such shifts tend to be of a higher shift quality and/or cause less wear on the driveline. These systems include systems that attempt to fuel the engine to achieve and maintain a zero driveline torque, see U.S. Patent No.: 4,593,580, the disclosure of which is incorporated herein by reference, and systems that fuel the engine to force one or more torque reversals, see U.S. Patent No.: 4,850,236. Upon sensing a transmission neutral condition, the clutch is maintained engaged and the engine speed commanded to a substantially synchronous speed for engaging a target gear ratio (ES=OSxGRT). [0032] Control of engine torque to achieve a desired output or flywheel torque is known as and may be seen by reference U.S. Pat No. 5,620,392, the disclosure of which is incorporated herein by reference. Engine torque as used herein refers to a value indicative of an engine torque, usually gross engine torque, from which an output or flywheel torque may be calculated or estimated. The relationship of gross engine torque to flywheel torque is discussed in U.S. Pat. No's: 5,509,867 and 5,490,063, the disclosures of which are incorporated herein by reference. [0033] One or more engine torque's or torque limit values may be commanded on, or read from, an industry standard data link, DL, such as an SAE J-1922, SAE J- 1939 or ISO11898 compliant datalink. [0034] By way of example, datalinks complying to the SAE J1939 or similar protocol, allow the system controller 50 to issue commands over the datalink for the engine to be fueled in one of several modes, such as (i) in accordance with the operator's setting of the throttle, (ii) to achieve a commanded or target engine speed (ES=EST), (iii) to achieve a commanded or target engine torque (ET=ETT) and (iv) to maintain engine speed and engine torque below limits (ESESMin) , said clutch has a driving member (60) rotatable with said engine output member and a driven member (62) rotatable with "said input shaft, said clutch having a degree of engagement dependent upon the rotational speed of said driving member, said clutch being disengaged at engine idle speed, said clutch becoming incipiently engaged at an incipient engagement engine speed (ESIE) greater than said engine idle speed (ESIE>ESIDLE), said clutch achieving a maximum engagement (74/76) at least a lockup engine speed (ESLOckup), said lockup engine speed greater than said incipient engagement engine speed (ESLOCKUP>ESiE), said clutch remaining at said maximum engagement at a disengagement engine speed (ESdiSENGACE) less than said lockup engine speed and less than said minimum expected engine speed (ESMIM) expected after an upshift (ESLOCKUP>ESdiSENGACE ) and ESMIM>ESdiSENGACE). 2.The transmission system as claimed in claim 1, wherein said system controller issues commands for transmission down shifts at an engine speed no less than a minimum downshift value (ESDEMIM), said lockup engine speed greater than said minimum downshift value (ESMDI»>ESDEMIM) . 3.A vehicular automated transmission system comprising an electronically controlled internal combustion engine having an engine output member, an engine controller having at least one mode of operation for controlling engine fueling to control at least one of engine speed and engine torque, a multiple speed mechanical change gear transmission having an input shaft, a master friction clutch for drivingly connecting said engine output member to said input shaft, a manually operated throttle for manually requesting a degree of engine fueling, a system controller for receiving input signals having two or more of signals indicative of (i) engine speed, (ii) throttle position, (iii)engaged transmission ratio, (iv) input shaft speed, (v) vehicle speed and (vi) engine torque, and processing said signals according to logic rules to issue command output signals to system actuators including at least said engine controller, said system characterized by : said master friction clutch being a centrifugally operated clutch; said system controller having at least one mode of operation wherein command signals are issued to said engine controller to control engine speed as a function of sensed engine speed; and said system controller issuing command signals to a shift actuator to cause shifting of said transmission, said controller causing upshifts only if an estimated engine speed at completion of an upshift into a target ratio (ES=OS*GRf) exceeds a minimum reference value (ES>ESmiN) , said clutch has a driving member rotatable with said engine output member and a driven member rotatable with said input shaft, said clutch having a degree of engagement dependent upon the rotational speed of said driving member, said clutch being disengaged at engine idle speed, said clutch becoming incipiently engaged at an incipient engagement engine speed (ESIE) greater than said engine idle speed (ESIE>ESIDLE), said clutch achieving a maximum engagement (74/76) at least a lockup engine speed (ESLOCRUP) , said lockup engine speed greater than said incipient engagement angina speed (ESLOCRUP>ESIE), said clutch ramaining at said maximum angagamant at a disangagamant angina spaad (ESDISENGAGE) less than said lockup angina spaad and less than said minimum expected engine speed (ESMIN)expected after an upshift (ESlockup>ESDISENGAGE and ESMIN>ESDISENGAGE). 4.The transmission system as claimad in claim 3, wherein said system controller issues commands for transmission downshifts at an engine speed no less than a minimum downshift value (ESDEMIN), said lockup engine speed greater than said minimum downshift value (ESmIN>ESDEMIN) . A vehicular transmission system (10) including a centrifugally operated master friction clutch (20) for drivingly coupling an engine (18) to an input shaft (28) of a mechanical transmission (12). Closed loop engine speed (ES) control is utilized to control engagement of the clutch during vehicle launch conditions.