Abstract:
A transfer case for a four-wheel drive motor vehicle includes an electronic control unit (ECU) and a synchronizer which facilitates shift on the fly operations such as, for example, a shift from two wheel high to four wheel high. A temperature sensor disposed either in the transfer case or elsewhere in the motor vehicle provides a temperature signal to the ECU which is utilized to adjust the on time of the synchronizer to compensate for the viscosity of the lubricating fluid within the transfer case or other temperature related variables which affect the time required to synchronize the drive line components prior to engagement. Such temperature compensation also facilitates fault detection and system oversight since the ECU can accurately anticipate the variability of the operating parameters based upon temperature and determinate malfunctions when operation occurs outside such temperature based parameters.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to temperature sensing and compensating devices and, more particularly, to devices for sensing ambient or operating temperature of a motor vehicle transfer case or similar device and adjusting or compensating shifts or operating cycles in response to such sensed temperature. 
     In motor vehicle driveline components such as transmissions and transfer cases, operation over an extraordinarily wide range of both ambient and operating temperatures is acknowledged to occur. For example, starting and operation of vehicles at temperatures as low as −25° F. (−32° C.) and up to of 120° F. (49° C.) is a routine event of motor vehicle usage. Actual operating temperatures of components such as transmissions and transfer cases varies over an even wider temperature range inasmuch as such low temperatures will be achieved when the vehicle is started but operating temperatures will typically be 100° to 125° F. (55° to 70° C.) above ambient and thus such upper limits may well be 220 to 245° F. (104° to 118° C.) and higher. 
     Coupled with such known and acknowledged ambient and operating temperature ranges is the temperature related viscosity of virtually all lubricants. The resistance to motion of a lubricating fluid in a shift mechanism at −25° F. (−32° C.), for example, requires significantly greater effort and thus actuator power than at much higher temperatures. Even with a more powerful actuator, a mechanical system operating at such low temperatures will invariably require more time to achieve a given mechanical action relative to the time taken by the same device at an elevated, operating temperature. In order to ensure that a desired action such as a shift from high to low gear or a shift into or out of four wheel drive has safely occurred, the control device may have to assume a worst case scenario: cold weather and allow a completion time which is excessively long in all but the coldest conditions. Such an operating scheme artificially delays shift completion in, for example, warm weather and is undesirable. 
     The increasing sophistication of transmission and transfer case control systems, the increasing demands of engineering sophistication and consumer sensitivity to noise, vibration and harshness (NVH) has prompted continuing examination of transmission and transfer cases in order to constantly re-evaluate and improve both the mechanical and electronic components and their performance. The present invention is directed to such an improvement. 
     SUMMARY OF THE INVENTION 
     A transfer case for a four-wheel drive motor vehicle includes an electronic control unit (ECU) and a synchronizer which facilitates shift on the fly operations such as, for example, a shift from two wheel high to four wheel high. A temperature sensor disposed either in the transfer case or elsewhere in the motor vehicle provides a temperature signal to the ECU which is utilized to adjust the on time of the synchronizer to compensate for the viscosity of the lubricating fluid within the transfer case and other temperature related variables which affect the time required to synchronize the drive line components prior to engagement. Such temperature compensation also facilitates fault detection and system oversight since the ECU can accurately anticipate the variability of the operating parameters based upon temperature and determine malfunctions when operation occurs outside such temperature-adjusted parameters. 
     It is thus an object of the present invention to provide a motor vehicle transfer case having a temperature compensated controller for a shift synchronizer. 
     It is a further object of the present invention to provide a motor vehicle transfer case having a temperature compensated controller for a shift mechanism synchronizer. 
     It is a still further object of the present invention to provide a motor vehicle transfer case having a temperature compensated controller for a shift on the fly synchronizer. 
     It is a still further object of the present invention to provide a motor vehicle transfer case having an electronic control unit with a temperature input for adjusting the synchronization period of a synchronized clutch to facilitate on the fly shifts. 
     Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended drawings wherein like reference numbers refer to the same component, element or feature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic view of a motor vehicle having primary and secondary drivelines and a transfer case incorporating the present invention; 
     FIG. 2 is a side elevational view with portions broken away of a transfer case incorporating the present invention; 
     FIG. 3 is a flat pattern development of a portion of a ball ramp clutch operator assembly taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is a block diagram of the electronic control unit and components of a transfer case incorporating the present invention; 
     FIG. 5 is a side elevational view with portions broken away of a transfer case incorporating a first alternate embodiment of the present invention; and 
     FIG. 6 is a graph presenting qualitative data regarding lubricant oil viscosity, temperature and synchronizer clutch operating time. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, a four-wheel motor vehicle drive train incorporating the present invention is diagrammatically illustrated and designated by the reference number  10 . The four-wheel vehicle drive train  10  includes a prime mover  12  such as an internal combustion or Diesel engine which is coupled to and directly drives a transmission  14 . The transmission  14  may either be an automatic or manual type. The output of the transmission  14  directly drives a transfer case assembly  16  which provides motive power to a primary or rear driveline assembly  20  comprising a primary or rear prop shaft  22 , a primary or rear differential  24 , a pair of live primary or rear axles  26  and a respective pair of primary or rear tire and wheel assemblies  28 . 
     The transfer case assembly  16  also selectively provides motive power to a secondary or front driveline assembly  30  comprising a secondary or front prop shaft  32 , a secondary or front differential assembly  34 , a pair of live secondary or front axles  36  and a respective pair of secondary or front tire and wheel assemblies  38 . The front tire and wheel assemblies  38  may be directly coupled to a respective one of the pair of front axles  36  or, if desired, a pair of manually or remotely activateable locking hubs  42  may be operably disposed between the pair of front axles  36  and a respective one of the tire and wheel assemblies  38  to selectively connect same. Finally, both the primary driveline  20  and the secondary driveline  30  may include suitable and appropriately disposed universal joints  44  which function in conventional fashion to allow static and dynamic offsets and misalignments between the various shafts and components. A control console or panel  46  which is preferably located within convenient reach of the vehicle operator includes a switch or a plurality of individual switches or push buttons  48  which facilitate selection of a particular operating mode of the transfer case assembly  16  as will be further described below. If desires two or more indicator lights  52  may be included in the control panel  46  to indicate, for example, four wheel drive modes such as four wheel, high and four wheel, low. 
     Referring now to FIGS. 2 and 3, the transfer case assembly  16  includes a multi-piece housing  60  having suitable flanges, openings, shoulders, bearing surfaces and blind apertures which receive, support and secure various elements and components of the transfer case assembly  16 . For example, an input shaft  62  which is supported in a suitable ball bearing assembly (not illustrated) includes a splined opening  64  which receives a complementarily splined output shaft (not illustrated) of the transmission  14 . The input shaft  62  drives a planetary gear speed reduction assembly  66 . By bypassing the planetary gear speed reduction assembly  66  a high gear, direct drive mode is provided to a primary output shaft  70 . By engaging the output of the planetary gear speed reduction assembly  66  a low gear, reduced speed output is provided to the primary output shaft  70 . A neutral or non-driving mode is also preferably available. Selection of such operating modes is typically made by the vehicle operator through use of the switches  48  of the control console  46  or similar means. 
     The planetary gear speed reduction assembly  66  includes a planet carrier  72  which receives a plurality of pinion gears (not illustrated) which are in constant mesh with a sun gear  74 , driven by and coupled to the input shaft  62 , and a ring gear  76 . A dog clutch  80  having suitable male or female axial splines is axially translatable from a leftmost position illustrated in FIG. 2 which directly couples the input shaft  62  to the primary output shaft  70 , thereby providing high gear or direct drive, through a center, neutral position to a low gear, reduced speed drive in which the dog clutch  80  engages the planet carrier  72  to provide a reduced speed output. A flange  82  or other suitable feature on the dog clutch  80  is engaged by a yoke  84  of a shift fork assembly  86 . 
     The transfer case assembly  16  also includes an electromagnetic clutch assembly  90  having an electromagnetic coil  92 , a ball ramp operator assembly  94  and a multiple disc, friction clutch pack assembly  96  which controllably provides drive torque from the primary output shaft  70  to a chain drive sprocket  98  coupled to the output of the friction disc pack assembly  96 . The electromagnetic clutch assembly  90  is preferably useful and used as both a synchronizer to bring the speed of the secondary driveline assembly  30  into synchronism with the primary driveline assembly  20  and as a torque transfer device to controllably transfer torque from the primary driveline assembly  20  to the secondary driveline assembly  30 . A chain  100  engages both the chain drive sprocket  98  and a driven chain sprocket  102  which in turn is coupled to and drives a secondary output shaft  104 . Further details of the electromagnetic clutch assembly  90  and the ball ramp operator assembly  94  are described in U.S Pat. Nos. 4,718,303 and 5,407,024 which are hereby incorporated by reference. 
     Referring now to FIGS. 2 and 4, the position of the dog clutch  80  and the shift fork assembly  86  is commanded by a shift control assembly  110 . The shift control assembly  110  is contained within an auxiliary housing  112 . The auxiliary housing  112  includes various openings and bearings which receive components of the shift control assembly  110  and protects such components as well. Secured within the auxiliary housing  112  is an electric drive motor  114  which drives an output shaft  116  through a speed reducing gear train  118 . Also contained within the auxiliary housing  112  is a printed circuit board  120  having various components of an electronic control unit (ECU)  122  including a microprocessor  124 . A multiple conductor electrical connector  126  is secured to the housing  112  and receives a multiple conductor electrical plug  128  which provides electrical power, signals from data sensors and commands from the switches or push buttons  48  to the electronic control unit  122  and specifically the microprocessor  124 . A temperature probe or sensor  130  which is mounted within a suitable threaded opening  132  in the transfer case housing  60  near the bottom of the transfer case assembly  16  in its installed position such that the temperature sensor  130  will be continuously submerged and in contact with lubricant  132  of the transfer case assembly  16 . The temperature sensor  130  is preferably a thermistor or similar device providing, for example, a variable resistance and, when excited, a varying voltage signal in response to varying temperature. An electrical cable  134  connects the temperature sensor  130  with the electrical plug  128  and thus provides a signal from the temperature sensor  130  to the electronic control unit  122  and the microprocessor  124  contained on the printed circuit board  120 . A cable  136  also connects the electromagnetic coil  132  with the electrical connector  128  and also with the printed circuit board  120  and the electronic control unit  122 . 
     The output shaft  116  of the shift control assembly  110  drives a single shift rail  140  which is received within suitable openings  142  in the transfer case housing assembly  60 . The shift rail  140  includes a pair of cam followers  144  which engage opposed parallel cams  146  on the ends of the shift fork body  150  which freely rotatably receives the shift rail  140 . As the shift rail  140  rotates, the cam followers  144  engage the cams  146  and, because the shift fork arm  84  is prevented from rotation, the shift fork assembly  86  translates bi-directionally to select the higher direct drive, neutral or lower reduced speed drive outputs of the planetary gear speed reduction assembly  66 . 
     Turning now to FIG. 4, the inputs and outputs of the electronic control unit  122  are illustrated. In accordance with conventional practice, power from the battery and ignition system  160  is provided through a voltage regulator  162  to the electronic control unit  122 . Information from various sensors such as the operating mode switches  48 , from a transmission or neutral switch  164 , a brake switch  166  and the temperature sensor  130  are provided to the electronic control unit  122 . The electronic control unit  122  and the microprocessor  124  provide signals to a motor drive device  168  such as a pulse width modulation (PWM) driver which drives the bi-directional electric drive motor  114  and receives signals from an output position sensor  172  which may be disposed on the printed circuit board  120  adjacent the output shaft  116 . Such a sensor  172  may be, for example, a multiple Hall effect sensor assembly such as disclosed in U.S. Pat. No. 5,867,092 which is hereby incorporated by reference. 
     The electronic control unit  122  drives the electromagnetic synchronization clutch  90  as well as the display or indicator lights  52  which may, if desired, be disposed on the control panel  46  or elsewhere in the dashboard of the motor vehicle. The axle disconnects  176  which perform a function similar to the remotely activatable locking hubs  42  may also be driven by the electronic control unit  122 . The electronic control unit  122  receives information from the UBP communication system  178  and also receives signals from a rear speed sensor  182  associated with the primary or rear driveline assembly  20  and particularly the primary or rear prop shaft  22 . 
     Referring now to FIG. 5, a first alternate embodiment of a transfer case with temperature compensation is illustrated and designated by the reference number  200 . Although designated as the first alternate embodiment transfer case assembly  200 , it should be understood from the outset that the first alternate embodiment  200  is of equal utility, applicability and function relative to the preferred embodiment transfer case assembly  16  and it should not be considered to be of lesser utility, applicability or function than the preferred embodiment transfer case assembly  16 . In this regard, many mechanical components of the two devices are the same. Accordingly, the following description will briefly note and explain those common components and provide full descriptions of those different or additional components. 
     The first alternate embodiment transfer case assembly  200  includes a multi-piece housing  60 ′, the input shaft  62  including the splined opening  64  and the planetary gear speed reduction assembly  66  driven by the input shaft  62 . By effectively bypassing the planetary gear speed reduction assembly  66 , a direct drive mode is provided to the primary output shaft  70 . By engaging the output of the planetary gear speed reduction assembly  66 , a low gear, reduced speed output is provided to the primary output shaft  70 . A neutral or non-driving mode is also preferably provided. Selection of such operating mode is typically made by the vehicle operator through use of the switches  48  on the control panel  46 . 
     The planetary gear speed reduction assembly  66  includes the planet carrier  72  which receives a plurality of pinion gears (not illustrated) which are in constant mesh with the sun gear  74 , driven by and coupled to the input shaft  62 , and the ring gear  76 . 
     The dog clutch  80  having suitable male or female axial splines is axially translatable from a left most position illustrated in FIG. 5 which directly couples the input shaft  62  to the primary output shaft  70 , providing, as noted above, high or direct drive, through a center, neutral position to a low gear, reduced speed drive, also as noted above, in which the dog clutch  80  engages the planet carrier  72 . The flange  82  or other suitable feature on the dog clutch  80  is engaged by the yoke  84  of the shift fork assembly  86 . The shift fork assembly  86  is freely, slidably received upon a fixed shift rail  202  seated within suitable blind bores  204  formed in the transfer case housing  60 ′. The shift fork assembly  86  also includes a radially oriented cam follower  206  which is received within a cam track  208  of a cam block  212  which is fixedly secured to a bi-directionally rotating shift control rod  214 . The cam track  208  may include regions of dwell to accommodate independent action between it and a commonly controlled clutch. 
     Rotation of the shift control rod  214  and thus the axial position of the shift fork assembly  86  and the dog clutch  80  is controlled by the shift control assembly  110 . The shift control assembly  110 , as illustrated in FIG. 2, includes the auxiliary housing  112 , the electric drive motor  114 , the output shaft  116  and the speed reducing gear train  118 . The printed circuit board  120  preferably includes a temperature sensing, variable resistance thermistor  220  which, when excited by a reference voltage, provides a variable electrical signal to the electronic control unit  122 . The multiple conductor electrical connector  126  receives a multiple conductor electrical plug  128  which connects the electronic control unit  122  to the various components illustrated in FIG.  4 . 
     Turning again to FIG. 5, the first alternate embodiment temperature compensated transfer case assembly  200  also includes a synchronizer or synchronizing clutch assembly  230 . The synchronizer  230  includes a synchronizer collar  232  which is coupled for rotation with a drive sleeve or quill  234  by an assembly of interengaging splines  236 . The synchronizer collar  232  receives a plurality of pairs of frusto-conical synchronizer segments  238  which are retained on the synchronizer drive collar  232  by at least one circumferential spring  240 . The pairs of synchronizer clutch segments  238  engage opposite faces of an oblique clutch plate  242  having lugs received within a synchronizer hub  244 . The synchronizer hub  244  is coupled for rotation with the primary output shaft  70  by an assembly of interengaging splines  246 . 
     The synchronizer collar  232  includes external splines or gear teeth  248  about its periphery and the synchronizer hub  244  likewise includes external splines or gear teeth  252  about its periphery equal in size and number to the gear teeth  248  on the synchronizer collar  232 . A clutch collar  254  having internal splines or gear teeth  256  is slidably and continuously engaged with gear teeth  248  on the synchronizer collar  232  and engageable with the gear teeth  252  on the synchronizer hub  244  to positively engage and directly drive the synchronizer clutch collar  232  from the primary output shaft  70  through the synchronizer hub  244 . The quill or sleeve  234  is coupled through an interengaging spline set to the chain drive sprocket  98 . A flange  258  on the clutch collar  254  is engaged by a second shift fork assembly  260  which is slidably received upon the cylindrical shift rail  202 . A cam follower  262  extends radially from the second shift fork assembly  260  and is received within a cam track  264  in a second cam block  266  secured to the shift control rod  214 . The cam track  264  may also include regions of dwell to accommodate independent operation of the dog clutch  80 . When the shift control rod  214  and the second shift fork assembly  260  translates the clutch collar  254  to the right as viewed in FIG. 5, it engages outer portions of the synchronizer segments  238  and compresses them against the oblique clutch plate  242 , commencing synchronization. 
     In operation, the temperature compensated synchronizers for the transfer case assemblies  16  and  200  provide an appropriate operating time of the synchronizing clutch  90  or  230  relating to the sensed temperature before full engagement thereof or activation of the automatic locking hubs  42  or the axle disconnects  176  in the preferred embodiment transfer case assembly  16  or the locking hubs  42  or axle disconnects  176  and the clutch collar  254  in the first alternate embodiment transfer case assembly  200 . 
     FIG. 6 illustrates qualitatively the relationship between lubricant viscosity, temperature and synchronizer operation time. If certain assumptions regarding the viscosity of a lubricant  132  utilized within the transfer case assembly  16  or  200  are made, a relatively straight line relationship may be utilized if two temperature end points and synchronizing times are determined. Alternatively, multiple temperature points may be determined to more closely fit the time to actual viscosity and operation conditions. Such high and low temperature end points or multiple temperature points and their corresponding operating times to synchronization are preferably determined experimentally, that is, by subjecting a specific vehicle and transfer case assembly  16  or  200  to exposure in a cold room at various temperatures to determine the actual time synchronization occurs at various depressed and, preferably, elevated temperatures. The synchronization times as well as an acceptable tolerance or window may be stored in memory in the electronic control unit  122  in a mathematical equation (relationship) between time and temperature or in a lookup table. 
     Alternatively, and in order to simplify the system and computations by the electronic control unit, the temperature/time relationship can be blocked into ranges wherein temperatures within a certain range provide a specific clutch synchronization time and temperatures in another range provide another, distinct time. This can be achieved by utilizing the signal from the temperature sensor  130  or thermistor  220  to drive two comparators set to switch states at appropriate temperatures and an appropriate logic and timer circuit. The following Table I presents such range related data. The time values presented are for purposes of illustration only. While only three distinct times are presented, it will be appreciated that additional comparators may be utilized to provide four, six or eight distinct states and operating times, if desired. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 Temperature 
                 Temperature 
                   
                   
                 Time 
               
               
                 ° F. 
                 ° C. 
                 Comparator 1 
                 Comparator 2 
                 (e.g.) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 −68° 
                 to 32° 
                 −50° 
                 to 0° 
                 0 
                 0 
                 8 
               
               
                 32° 
                 to 105° 
                 0° 
                 to 40° 
                 0 
                 1 
                 4 
               
               
                 105° 
                 to 300° 
                 40° 
                 to 150° 
                 1 
                 1 
                 2 
               
               
                   
               
             
          
         
       
     
     It should be appreciated that the specific combinations of components described with regard to the preferred embodiment transfer case assembly  16  and first alternate embodiment transfer case assembly  200  are not to be construed as limiting but rather as illustrative and exemplary combinations of components. Hence, it should be well understood that, for example, the temperature sensor  130  illustrated in the preferred embodiment may certainly be utilized with the first alternate embodiment transfer case assembly  200  and that, for example, the single shift rail  140  of the preferred embodiment transfer case assembly  16  may also be utilized with the two shift fork assemblies  86  and  260  of the first alternate embodiment transfer case assembly  200 . Furthermore, the thermistor  220  of the first alternate embodiment transfer case assembly  200  may be disposed in other locations of the vehicle and, for example, may be utilized generally as an ambient temperature sensor for other features in the vehicle with such information also being supplied to the electronic control unit  122 . 
     The foregoing disclosure is the best mode devised by the inventor for practicing this invention. It is apparent, however, that apparatus incorporating modifications and variations will be obvious to one skilled in the art of temperature sensing and compensating. Inasmuch as the foregoing disclosure is intended to enable one skilled in the pertinent art to practice the instant invention, it should not be construed to be limited thereby but should be construed to include such aforementioned obvious variations and be limited only by the spirit and scope of the following claims.