Abstract:
An anti-lock braking and traction control system includes a sources of pressurized fluid, an actuator adapted to selectively supply the pressurized fluid to wheel brakes and a clutch. A controller communicates with the actuator to control the duration of magnitude of pressure supplied to the wheel brakes and the clutch.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to hydraulic systems for vehicles and, more particularly, to a combination braking and traction control system adapted for use in motor vehicle driveline applications.  
       BACKGROUND OF THE INVENTION  
       [0002]     In view of an increased demand for vehicles having anti-lock braking systems and traction control systems, many controls are currently being incorporated in vehicular driveline applications for transferring braking torque and/or drive torque to the wheels. A modern trend in vehicle design includes equipping a driveline with a transfer case having an electronically controlled transfer clutch. The transfer clutch is operable to automatically direct drive torque to the primary and/or secondary drivelines without any input or action on the part of the vehicle operator. The transfer clutch is typically actuated by a power-operated clutch actuator which responds to control signals sent from a traction control module. The control signals are typically based on current operating conditions of the vehicle (i.e., vehicle speed, interaxle speed difference, acceleration, steering angle, etc.) as detected by various sensors. For example, if traction is lost at the primary wheels, the transfer clutch can be engaged to establish an “on-demand” four-wheel drive mode. Thus, such “on-demand” transfer cases can utilize adaptive control schemes for automatically controlling torque distribution during all types of driving and road conditions.  
         [0003]     To assure vehicle stability is maintained during braking, many vehicles are also now equipped with an anti-lock braking system. The anti-lock braking system includes a hydraulic pressure source which supplies pressurized fluid to hydraulically-powered brake actuators for actuating the brakes located at each wheel end. The anti-lock braking system typically uses some or all of the sensor signals to control operation of the brake actuators. Specifically, a brake control mode receives sensor signals and functions to control coordinated actuation of the brakes. Typically, little to no interaction occurs between the control modules for the anti-lock braking system and the traction control system. However, some systems provide minimal communication to disable the traction control system so as to assure that the vehicle is not placed in a four-wheel drive mode when the anti-lock braking system is functioning.  
         [0004]     While the present anti-lock braking systems and traction control systems have operated sufficiently in the past, a need exists to reduce the complexity and cost of implementing such systems on a motor vehicle. For example, the size, weight and electrical power requirements of electrical motors needed to provide the described clutch engagement loads may make such systems cost prohibitive.  
       SUMMARY OF THE INVENTION  
       [0005]     Thus, it is an object of the present invention to provide a combination braking and traction control system having a source of pressurized fluid and an actuator adapted to selectively supply pressurized fluid to the vehicle wheel brakes and at least one transfer clutch. The transfer clutch is operable to selectively transfer drive torque from a first rotary member to a second rotary member. The anti-lock braking and traction control system also includes a controller in communication with the actuator to control the duration and magnitude of fluid pressure supplied to the wheel brakes and the transfer clutch.  
         [0006]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0008]      FIG. 1  is a schematic illustration of a vehicle equipped with a combination braking and traction control system of the present invention;  
         [0009]      FIG. 2  is a schematic illustration of a brake and AWD system of the present invention;  
         [0010]      FIG. 3  is a cross-sectional side view of an exemplary transfer case selectively operable by the braking and traction control system of the present invention; and  
         [0011]      FIG. 4  is a schematic illustration of a vehicle equipped with an alternate braking and traction control system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]     The present invention is directed to a combination braking and traction control system for adaptively controlling the brakes of the vehicle as well as a mechanism that modulates the torque transferred from a first rotary member to a second rotary member. The torque transfer mechanism finds particular application in power transmission devices for use in motor vehicle drivelines such as, for example, an on-demand clutch in a transfer case or in-line torque coupling, a biasing clutch associated with a differential assembly in a transfer case or a drive axle assembly, or as a shift clutch in a multi-speed automatic transmission. Thus, while the present invention is hereinafter described in association with particular arrangements for use in specific driveline applications, it will be understood that the arrangements shown and described are merely intended to illustrate embodiments of the present invention.  
         [0013]     With particular reference to  FIG. 1  of the drawings, a drivetrain  10  for a four-wheel drive vehicle is shown. Drivetrain  10  includes a primary driveline  12 , a secondary driveline  14 , and a powertrain  16  for delivering rotary tractive power (i.e., drive torque) to the drivelines. In the particular arrangement shown, primary driveline  12  is the rear driveline while secondary driveline  14  is the front driveline. Powertrain  16  includes an engine  18 , a multi-speed transmission  20 , and a power transmission device, hereinafter referred to as transfer case  22 . Rear driveline  12  includes a pair of rear wheels  24  and  25  connected at opposite ends of a rear axle assembly  26  having a rear differential  28  coupled to one end of a rear prop shaft  30 , the opposite end of which is coupled to a rear output shaft  32  of transfer case  22 . Likewise, front driveline  14  includes a pair of front wheels  34  and  35  connected at opposite ends of a front axle assembly  36  having a front differential  38  coupled to one end of a front prop shaft  40 , the opposite end of which is coupled to a front output shaft  42  of transfer case  22 .  
         [0014]     With continued reference to the drawings, drivetrain  10  is shown to further include an electronically-controlled brake and all wheel drive (AWD) system  44  for providing anti-locking braking functions as well as traction control functions. In this regard, driveline  10  is equipped with a pair of front brakes  46  and  48  for decelerating front wheels  34  and  35  as well as a pair of rear brakes  50  and  52  for decelerating rear wheels  24  and  25 . Each brake includes a hydraulically-powered brake operator for applying the brakes. Additionally, brake and AWD system  44  includes one or more clutches that may be selectively actuated for transferring drive torque from engine  18  to one or more of the wheels. In one example, a transfer clutch  66  is positioned within transfer case  22  and may be selectively operated to transfer drive torque from rear output shaft  32  to front output shaft  42  for establishing part-time and on-demand four-wheel drive modes. Furthermore, front axle assembly  36  may be equipped with a front axle biasing clutch  68  for selectively varying the torque distribution delivered from front prop shaft  40  to front wheels  34  and  35 . Similarly, rear axle assembly  26  may include a rear axle biasing clutch  70  for selectively varying the torque distribution delivered from rear prop shaft  30  to rear wheels  24  and  25 . It should be appreciated that a vehicle may be equipped with one or more of these torque transfer clutches without departing from the scope of the present invention. Preferably, each of these torque transfer clutches includes at least one multi-plate friction clutch assembly and, as will be detailed, a hydraulically-powered actuator for controlling engagement of the friction clutch assemblies.  
         [0015]     Brake and AWD system  44  preferably includes a common brake/AWD system actuator assembly  54 . Pressurized hydraulic fluid is selectively supplied to each of the brake operators and/or the clutches by actuator assembly  54 . In operation, a hydraulic pump  56  is driven by a motor  58  to supply fluid to actuator assembly  54  and an accumulator  60 . Accumulator  60  stores pressurized fluid for use during peak demand situations. In addition vehicle sensors  62  detect certain dynamic and operational characteristics of the motor vehicle. Finally, a controller  64  controls the operation of components associated with actuator assembly  54  in response to signals provided by vehicle sensors  62 .  
         [0016]     With reference to  FIG. 2 , brake and AWD system actuator assembly  54  is shown to include a plurality of electro-hydraulic pressure modulators  72  that are each plumbed in fluid communication with pump  56  and accumulator  60 . Actuator assembly  54  also includes a plurality of pressure sensors  74 . Each pressure sensor  74  provides a signal to controller  64  that is indicative of the fluid pressure being supplied to the particular brake and/or clutch. Each brake and clutch may be individually controlled based on the current vehicle characteristics.  
         [0017]     In the example depicted in  FIG. 2 , a first fluid passageway  76 A interconnects the hydraulic brake operator  46 A associated with left front brake  46  to the high pressure fluid generated by pump  56 . A first pressure modulator  72 A is operable to controllably vary the fluid pressure supplied to brake operator  46 A for controlling engagement of left front brake  46 . Likewise, pressure sensor  74 A provides a signal to controller  64  that is indicative of the fluid pressure within passageway  76 A. Controller  64  is in communication with pressure modulator  78  and functions to controllably vary the fluid pressure within passageway  76 A. Preferably, first pressure modulator  72 A is an electro-hydraulic control valve capable of controlling the fluid pressure delivered to brake operator  46 A based on the value of an electric command signal generated by controller  64 .  
         [0018]     Similarly, a second fluid passageway  76 B interconnects brake operator  48 A associated with right front brake  48  to the high fluid pressure generated by pump  56 . A second electro-hydraulic pressure modulator  72 B provides metered pressurized fluid to hydraulic brake operator  46 B for controlling engagement of right front brake  48 . A pressure sensor  74 B outputs a signal indicative of the fluid pressure within passageway  78  to controller  64 . With continued reference to  FIG. 2 , a third passageway  76 C and a fourth passageway  76 D provide fluid communication between pump  56  and respective left and right rear brake operators  46 C and  46 D. Third and fourth electro-hydraulic pressure modulators  72 C and  72 D are provided to control the fluid pressure supplied to brake operators  46 C and  46 D, respectively. As seen, pressure sensors  74 C and  74 D are provided downstream of pressure modulators  72 C and  72 D to provide pressure signals to controller  64 . Finally, fifth passageway  76 E, sixth passageway  76 F and seventh passageway  76 G provide fluid communication between pump  56  and corresponding ones of clutch operators  66 A,  68 A and  70 A associated with transfer clutch  66  and axle biasing clutches  68  and  70 , respectively. Corresponding electro-hydraulic pressure modulators  72 E,  72 F ad  72 G and pressure sensors  74 E,  74 F and  74 G are provided in these passageways. Variable control of the hydraulic pressure supplied to each of the clutch operators function to control variable or “adaptive” engagement of each clutch.  
         [0019]     The brake/AWD system depicted in  FIG. 2  provides the greatest amount of vehicle control because each brake or clutch is equipped with a pressure modulator and sensor. One skilled in the art will appreciate that a simplified system having a reduced number of pressure modulators and sensors is also contemplated as being within the scope of the present invention. Specifically, left front brake  46  and right front brake  48  may be controlled with a single pressure modulator and pressure sensor.  
         [0020]      FIG. 3  depicts an exemplary transfer case  22  equipped with transfer clutch  66 . Transfer case  22  is shown to include a multi-piece housing  85  from which rear output shaft  32  is rotatably supported. Rear output shaft  32  includes an internally-splined first end segment  86  adapted for connection to the output shaft of transmission  20  and a second end segment  87  to which a yoke  88  is secured for connection to rear prop shaft  30 . Front output shaft  42  is likewise rotatably supported in housing  85  and includes an integral yoke segment  89  adapted for connection to front prop shaft  40 .  
         [0021]     Transfer clutch  66  is operably arranged to transfer rotary power (i.e., drive torque) from rear output shaft  32  to front output shaft  42  through a transfer assembly  90 . Transfer assembly  90  includes a first gear  92 , a second gear  94 , and a third gear  96  that is in meshed engagement with first gear  92  and second gear  94 . First gear  92  is shown to be rotatably supported on rear output shaft  32  via a bearing assembly  98  and likewise be rotatably supported from housing  85  via a pair of laterally spaced bearing assemblies  100 . Second gear  94  is coupled via a spline connection  102  to front output shaft  42  and is rotatably supported from housing  85  by a pair of laterally spaced bearing assemblies  104 . Finally, third gear  96  is rotatably supported by bearing assemblies  106  on a stub shaft  108  that is non-rotatably secured to housing  85 . It is contemplated that geared transfer assembly  90  could be replaced with a well-known chain and sprocket type transfer system if desired.  
         [0022]     Transfer clutch  66  includes a multi-plate friction clutch assembly  110  and clutch operator  66 A, hereinafter referred to as clutch actuator assembly  112 . Clutch assembly  110  is shown to include a clutch drum  114  fixed via a spline connection  116  to a tubular segment  118  of first gear  92 , a clutch hub  120  fixed via a spline connection  122  to rear output shaft  32 , and a multi-plate clutch pack  124  operably disposed between drum  114  and hub  120 . Clutch pack  124  includes a set of outer clutch plates that are splined for rotation with and axial movement on an outer cylindrical rim segment  126  of drum  114 . Clutch pack  124  also includes a set of inner clutch plates that are splined for rotation with and axial movement on clutch hub  120 . Clutch assembly  110  further includes an apply plate  128  splined for rotation with rim segment  126  of drum  114 , and a pressure plate  132  splined to a fixed support  134 . A thrust bearing  135  is provided between apply plate  128  and pressure plate  132  to accommodate relative rotation therebetween during concurrent axial movement. Clutch actuator assembly  112  includes a piston  136  positioned within a pressure chamber  138  formed in support  134 . A passageway  140  extends through support  134  and housing  85  to allow pressurized fluid supplied from pressure modulator  72 E to enter chamber  138  and act on piston  136 . Apply plate  128  is arranged to exert a compressive clutch engagement force on clutch pack  124  in response to translational movement of pressure plate  132  and piston  136 .  
         [0023]     Apply plate  128  is axially moveable relative to clutch pack  124  between a first or “released” position and a second or “locked” position. With apply plate  128  in its released position, a minimum clutch engagement force is exerted on clutch pack  124  such that virtually no drive torque is transferred from rear output shaft  32  through clutch assembly  110  and transfer assembly  90  to front output shaft  42  so as to establish the two-wheel drive mode. In contrast, location of apply plate  128  in its locked position causes a maximum clutch engagement force to be applied to clutch pack  124  such that front output shaft  42  is, in effect, coupled for common rotation with rear output shaft  32  so as to establish the part-time four-wheel drive mode. Therefore, accurate control of the position of apply plate  128  between its released and locked positions permits adaptive regulation of the amount of drive torque transferred from rear output shaft  32  to front output shaft  42 , thereby establishing the on-demand four-wheel drive mode.  
         [0024]      FIG. 1  illustrates vehicle sensors  62  grouped together in a block format. However, it is contemplated that the sensors required for controlling the combination brake and traction control system includes individual wheel speed sensors  62 A through  62 D, engine speed sensor  62 E and transmission gear sensor  62 F. Obviously, such sensors are used in virtually all conventional vehicles such that the present invention can be easily incorporated into vehicles utilizing an ABS arrangement.  
         [0025]      FIG. 4  depicts an alternate embodiment brake and AWD system  200 . System  200  is substantially similar to system  44  except that system  200  includes a brake system actuator  202  that is plumbed to a brake supply circuit  204  and an AWD actuator  206  that is plumbed to a separate AWD supply circuit  208 . Due to the substantial similarity between brake and AWD system  44  and system  200 , common elements will retain their previously introduced reference numerals.  
         [0026]     One skilled in the art will appreciate that brake system actuator  202  and AWD actuator  206  are both controlled by controller  64 . Preferably, controller  64  is the main vehicle controller. However, controller  64  may be separate from and in addition to a main vehicle controller.  
         [0027]     Brake supply circuit  204  includes a motor  210  drive a pump  212 . The output from pump  212  supplies an accumulator  214  and brake system actuator  202 . Accumulator  214  functions to provide pressurized fluid to brake system actuator  202  if pump  212  is unable to provide the requested demand. Brake system actuator  202  is substantially similar to the brake and AWD actuator previously described. As such, brake system actuator  202  selectively supplies pressurized fluid to each of the hydraulically-powered brake operators to control engagement of the wheel brakes based on signals provided by controller  64 .  
         [0028]     AWD supply circuit  208  includes a motor  216  driving a pump  218 . The output from pump  218  supplies an accumulator  220  as well as AWD actuator  206 . AWD actuator  206  selectively provides pressurized fluid to transfer clutch  66 , front axle clutch  68  and/or rear axle clutch  70 . As previously mentioned, the number and location of clutches implemented within the vehicle at  FIG. 4  is merely exemplary and that virtually any number of clutches may be selectively controlled by AWD actuator  206 .  
         [0029]     Based on the description of brake and AWD system  200  previously provided, one skilled in the art will appreciate that brake system actuator  202  and AWD actuator  206  may be controlled to operate simultaneously, alternately or entirely independently from one another. Separate supply circuits  204  and  208  provide further support for independent control of brake system actuator  202  and AWD actuator  206 . However, a single supply circuit may be used to provide fluid to both brake system actuator  202  and AWD actuator  206  without departing from the scope of the present invention. Depending on the volume requirements of brake system actuator and AWD actuator  206 , it may be more efficient to construct a single slightly larger supply circuit than two individual smaller supply circuits.  
         [0030]     Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations may be made therein without department from the spirit and scope of the invention as defined in the following claims.