Abstract:
A clutch system according to an exemplary aspect of the present disclosure includes, among other things, a thrust bearing and a load sensor positioned relative to the thrust bearing and configured to measure a load exerted against the thrust bearing.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to a vehicle, and more particularly, but not exclusively, to a vehicle clutch system that includes a thrust bearing and a load cell configured to directly measure driveline engagement and disengagement loads exerted against the thrust bearing. 
       BACKGROUND 
       [0002]    Stop/start technology is known for selectively shutting down a vehicle engine during portions of a drive cycle to conserve fuel and reduce emissions. For example, a stop/start vehicle can turn its engine off while the vehicle is stopped rather than allow the engine to idle. The engine can subsequently be restarted when a driver depresses the accelerator pedal or when the vehicle is otherwise able to progress. 
         [0003]    For a variety of reasons, current restart strategies for stop/start vehicles have not resulted in extended stop/start operating ranges. The relatively harsh operating conditions of the clutch system that engages and disengages the engine from the transmission of the vehicle during the stop/start process have necessitated the use of relatively complex inferred or remote driveline detection techniques. However, in order to extend operating ranges of stop/start vehicles, a more direct manner of detecting driveline engagement/disengagement is desirable. 
       SUMMARY 
       [0004]    A clutch system according to an exemplary aspect of the present disclosure includes, among other things, a thrust bearing and a load sensor positioned relative to the thrust bearing and configured to measure a load exerted against the thrust bearing. 
         [0005]    In a further non-limiting embodiment of the foregoing clutch system, the load sensor is positioned against a rear face of the thrust bearing. 
         [0006]    In a further non-limiting embodiment of either of the foregoing clutch systems, the thrust bearing includes a front face that is rotatable and a rear face that is not rotatable. 
         [0007]    In a further non-limiting embodiment of any of the foregoing clutch systems, a concentric slave cylinder includes a housing and a guide that protrudes from the housing. 
         [0008]    In a further non-limiting embodiment of any of the foregoing clutch systems, the guide extends through a bore of each of the thrust bearing and the load sensor. 
         [0009]    In a further non-limiting embodiment of any of the foregoing clutch systems, a dust shield is positioned between the thrust bearing and a concentric slave cylinder. 
         [0010]    In a further non-limiting embodiment of any of the foregoing clutch systems, a piston is positioned between the thrust bearing and a concentric slave cylinder. 
         [0011]    In a further non-limiting embodiment of any of the foregoing clutch systems, a spring is received over a guide of a concentric slave cylinder. 
         [0012]    In a further non-limiting embodiment of any of the foregoing clutch systems, the load sensor is positioned between the thrust bearing and the spring. 
         [0013]    In a further non-limiting embodiment of any of the foregoing clutch systems, the load sensor is positioned between the spring and the concentric slave cylinder. 
         [0014]    In a further non-limiting embodiment of any of the foregoing clutch systems, wiring electrically connects the load sensor to a control unit of the clutch system. 
         [0015]    In a further non-limiting embodiment of any of the foregoing clutch systems, the load sensor is positioned remotely from a front face of the thrust bearing but is configured to measure the load applied directly at the front face. 
         [0016]    A vehicle according to another exemplary aspect of the present disclosure includes, among other things, an engine, a transmission operably connectable to the engine and a clutch system that selectively couples the transmission to the engine. The clutch system includes a concentric slave cylinder assembly that includes a load sensor configured to measure a load. 
         [0017]    In a further non-limiting embodiment of the foregoing vehicle, the load sensor is configured to measure a load exerted against a front face of a thrust bearing of the concentric slave cylinder assembly. 
         [0018]    In a further non-limiting embodiment of either of the foregoing vehicles, the concentric slave cylinder assembly includes a thrust bearing, a piston, a dust shield, a spring, and a concentric slave cylinder. 
         [0019]    In a further non-limiting embodiment of any of the foregoing vehicles, the load sensor is positioned between the thrust bearing and the spring. 
         [0020]    In a further non-limiting embodiment of any of the foregoing vehicles, the load sensor is positioned between the spring and the concentric slave cylinder. 
         [0021]    In a further non-limiting embodiment of any of the foregoing vehicles, the load sensor is positioned remotely from a front face of a thrust bearing of the concentric slave cylinder assembly. 
         [0022]    In a further non-limiting embodiment of any of the foregoing vehicles, the vehicle is a micro-hybrid vehicle that includes a stop/start system for selectively shutting down the engine during idling conditions. 
         [0023]    A method according to another exemplary aspect of the present disclosure includes, among other things, incorporating a load sensor into a clutch system of a vehicle and measuring a load exerted against a thrust bearing of the clutch system with the load sensor. 
         [0024]    The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
         [0025]    The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  schematically illustrates a powertrain of a vehicle. 
           [0027]      FIG. 2  illustrates portions of a clutch system of a vehicle. 
           [0028]      FIG. 3  illustrates a concentric slave cylinder assembly of a clutch system. 
           [0029]      FIG. 4  illustrates a front view of the concentric slave cylinder assembly of  FIG. 3 . 
           [0030]      FIG. 5  illustrates an exploded view of the concentric slave cylinder assembly of  FIG. 3 . 
           [0031]      FIG. 6  illustrates another concentric slave cylinder assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    This disclosure relates to a clutch system for a vehicle. The clutch system includes a thrust bearing, a concentric slave cylinder and a load cell positioned between the thrust bearing and the concentric slave cylinder. Incorporating the load cell into the clutch system enables a direct measurement of a load exerted against the thrust bearing during engagement and disengagement of a transmission input shaft relative to an engine flywheel. These and other features are discussed in greater detail herein. 
         [0033]      FIG. 1  schematically illustrates a powertrain  10  of a vehicle  12 . The vehicle  12  could be any type of vehicle. In one non-limiting embodiment, the vehicle  12  is a micro-hybrid vehicle that can employ stop/start technology. The vehicle  12  may be a rear wheel drive, front wheel drive, or all-wheel drive vehicle. 
         [0034]    The powertrain  10  may include an engine  14 , a clutch system  16  and a transmission  18 . The engine  14  may be selectively engaged and/or disengaged relative to the transmission  18  by the clutch system  16 . 
         [0035]    The engine  14  can be employed as an available drive source for the vehicle  12 . In one embodiment, the engine  14  is an internal combustion engine. Although not shown in this embodiment, the powertrain  10  could be equipped with additional propulsion devices, such as an electric machine (i.e. a motor, generator, or combined motor/generator), such as within hybrid vehicle embodiments. 
         [0036]    The transmission  18  may be a manual or an automatic transmission. The transmission  18  may include a gearbox having multiple gear sets (not shown) that are selectively operated using different gear ratios by selective engagement of friction elements such as clutches and brakes (not shown) to establish desired multiple discrete or step drive ratios. The friction elements are controllable through a shift schedule that connects and disconnects certain elements of the gear sets to control the ratio between a transmission input shaft  19  and a transmission output shaft  20  of the transmission  18 . 
         [0037]    The transmission  18  provides powertrain output torque to the transmission output shaft  20 . The transmission output shaft  20  may be connected to a differential  22 . The differential  22  drives a pair of wheels  24  via respective axles  26  that are connected to the differential  22  to propel the vehicle  12 . 
         [0038]    The powertrain  10  may additionally include an associated control unit  28 . While schematically illustrated as a single controller, the control unit  28  may be part of a larger control system and may be controlled by various other controllers throughout the vehicle  12 , such as a vehicle system controller (VSC) that includes a powertrain control unit, a transmission control unit, an engine control unit, etc. It should therefore be understood that the control unit  28  and one or more other controllers can collectively be referred to as a “control unit” that controls, such as through a plurality of interrelated algorithms, various actuators in response to signals from various sensors to control functions such as stopping/starting the engine  14 , selecting or scheduling shifts of the transmission  18 , actuating the clutch system  16 , etc. In one embodiment, the various controllers that make up the VSC may communicate with one another using a common bus protocol (e.g., CAN). In one embodiment, the control unit  28  is in electrical communication with each of the engine  14 , the clutch system  16  and the transmission  18  for controlling the powertrain  10 . 
         [0039]    In one exemplary stop/start sequence of the vehicle  12 , the engine  14  can be automatically shut down during times when the vehicle  12  is not moving and then automatically restarted as necessary when the vehicle  12  begins to move again or when it becomes necessary to operate accessories off of the engine  14 . In this regard, the vehicle  12  may include an automatic stop/start system that automatically shuts down and restarts the engine  14  to reduce the amount of time the engine spends idling, thereby reducing fuel consumption and emissions. Automatically shutting down the engine  14  can be advantageous for vehicles that spend significant amounts of time waiting at traffic lights or frequently operate in stop-and-go traffic. The vehicle  12  may enter an auto-stop mode (i.e., the engine  14  is auto-stopped) when certain vehicle propulsion conditions are met, such as when the driver has applied the brakes and the vehicle speed is below a predetermined speed threshold. Once the driver indicates a request for vehicle propulsion (e.g., by releasing the brake pedal), the control unit  28  may automatically command a restart of the engine  14 . 
         [0040]    In one embodiment, the engine  14  may be driveably connected to a crankshaft pulley that drives a belt integrated starter-generator (BISG)  29 . Although a belt-drive is disclosed, other types of drives could be used to provide a driving connection between the engine  14  and the BISG  29 . For example, a flexible chain drive or a geared drive could be used. The BISG  29  can be used to start the engine  14  during the stop/start sequence. 
         [0041]    Of course, this view is highly schematic. It should be appreciated that the powertrain  10  of the vehicle  12  could employ various additional components within the scope of this disclosure. Additionally, although illustrated and described in the context of the vehicle  12 , which may be a micro-hybrid vehicle, it is understood that embodiments of this disclosure could be implemented on other types of vehicles having different powertrain topologies, including full hybrid electric vehicles or even basic/entry level systems with a traditional starter motor and engine flywheel ring gear. 
         [0042]      FIG. 2  illustrates a clutch system  16  that may be employed by the powertrain  10  of  FIG. 1 , or any other powertrain. The clutch system  16  is disposed between an engine  14  and a transmission casing  32  of a transmission  18 . The clutch system  16  selectively couples the transmission  18  to the engine  14 . More particularly, the clutch system  16  driveably couples the transmission input shaft  19  to a flywheel  44  of the engine  14 . 
         [0043]    In one embodiment, the clutch system  16  includes a concentric slave cylinder (CSC) assembly  30 , a pressure plate  36  and a friction plate  38 . The clutch system  16 , including the CSC assembly  30 , the pressure plate  36  and the friction plate  38 , is housed within a bell housing  40 . The bell housing  40  is disposed between a rear portion of the engine  14  and a forward portion of the transmission casing  32 . 
         [0044]    The transmission input shaft  19  of the transmission  18  extends into the bell housing  40  through a wall  41  of the transmission casing  32  and is concentrically surrounded by the CSC assembly  30 . The transmission input shaft  19  may further extend through a thrust bearing  42  of the CSC assembly  30 , and then through the friction plate  38 , to selectively engage the flywheel  44  of the engine  14 . The friction plate  38  is supported on the transmission input shaft  19  by a splined interface  45 . The flywheel  44  may also be housed within the bell housing  40 . 
         [0045]    The CSC assembly  30  may be connected to a clutch pedal  46  located in a passenger compartment of a vehicle. Although not shown, a master cylinder may be connected between the CSC assembly  30  and the clutch pedal  46 . 
         [0046]    In operation, upon the application of pressure on the clutch pedal  46 , hydraulic fluid pressure forces linear movement of the CSC assembly  30  (in the direction of arrow X in  FIG. 2 ) such that the thrust bearing  42  contacts the pressure plate  36 . As the CSC assembly  30  linearly travels, the thrust bearing  42  presses against fingers  48  to relieve the outer circumferential pressure applied against the friction plate  38  and therefore reduce the clamping pressure between the friction plate  38  and the flywheel  44 . Once this clamping pressure has been relieved, the drive (or torque) from the engine  14  will be disengaged from the transmission input shaft  19  due to the decoupling of the friction plate  38  from the flywheel  44  and the pressure plate  36 . 
         [0047]    Conversely, as the clutch pedal  46  is released, the thrust bearing  42  of the CSC assembly  30  is biased in a direction opposite to the direction X to relieve the pressure being applied at the thrust bearing  42 . The pressure applied against the thrust bearing  42  becomes less than the pressure on the pressure plate  36 , thereby returning the fingers  48  of the pressure plate  36  to increase the clamping pressure applied to the friction plate  38  between the friction plate  38  and the flywheel  44 . The transmission input shaft  19  drive or torque may then be engaged at the splined interface  45 . 
         [0048]      FIG. 2  represents but one non-limiting example of the clutch system  16 . The clutch system  16  could alternatively be operated hydraulically with a cantilevered arm and a slave cylinder, via a semi-hydraulic or full cable system, or any other configuration. 
         [0049]      FIGS. 3 ,  4  and  5  illustrate an exemplary CSC assembly  30  that may be incorporated into the clutch system  16  of  FIG. 2 .  FIG. 3  shows a side view,  FIG. 4  a front view, and  FIG. 5  an exploded view of the CSC assembly  30 . 
         [0050]    The exemplary CSC assembly  30  includes a thrust bearing  42 , a piston  50 , a dust shield  52 , a spring  54  and a concentric slave cylinder (CSC)  56 . The CSC  56  includes a housing  58  and a guide  60  that protrudes from the housing  58 . The housing  58  may include one or more openings  62  (see  FIG. 4 ) for mounting the CSC assembly  30 . For example, the openings  62  may accommodate fasteners for securing the CSC assembly  30  to a transmission casing. There are three openings  62  shown in  FIG. 4  but there could be less or more. Other methods may alternatively be used to secure the CSC assembly  30  to a transmission casing. A bore  64  extends through housing  58  and the guide  60  for accommodating a transmission input shaft (not shown in  FIGS. 3 ,  4  and  5 ). 
         [0051]    The guide  60  of the CSC  56  may be received through each of the spring  54 , the dust shield  52 , the piston  50  and the thrust bearing  42 . In other words, each of the spring  54 , the dust shield  52 , the piston  50  and the thrust bearing  42  include a bore (i.e., the components are hollow) in order to accommodate the guide  60  in a concentric relationship. In one embodiment, the CSC assembly  30  is disposed about an axis A. 
         [0052]    The spring  54  is positioned between the thrust bearing  42  and the CSC  56 . In one embodiment, the spring  54  is received over the guide  60  of the CSC  56 . The spring  54  exerts a biasing force against the thrust bearing  42 . In one embodiment, the spring  50  is a preloaded coil spring that is biased in a direction toward the CSC  56 . However, other biasing members are also contemplated as within the scope of this disclosure. 
         [0053]    The dust shield  52  may be positioned between the thrust bearing  42  and the spring  54 . The dust shield  52  may partially cover portions of the piston  50  (see, e.g.,  FIG. 3 ). The dust shield  52  is configured to block the ingress of dust or other debris into the thrust bearing  42  and other components of the CSC assembly  30 . 
         [0054]    The piston  50  is adjacent to the thrust bearing  42 . The piston  50  may move to axially displace the thrust bearing  42  in response to hydraulic pressure that is applied to the CSC  56 . 
         [0055]    In one embodiment, the thrust bearing  42  includes a front face  66  and an opposing rear face  68 . The front face  66  is rotatable, whereas the rear face  68  does not rotate. However, the rear face  68  can linearly travel in response to the application of hydraulic pressure applied to the CSC assembly  30 . 
         [0056]    The CSC assembly  30  may additionally include a load sensor  70  (see  FIG. 5 ). The load sensor  70  could be positioned anywhere within the CSC assembly  30 . In one embodiment, the load sensor  70  is positioned between the thrust bearing  42  and the CSC  56 . In another embodiment, the load sensor  70  is positioned against the rear face  68  of the thrust bearing  42  (see  FIG. 5 ). In yet another embodiment, the load sensor  70  is sandwiched between the housing  58  of the CSC  56  and the spring  54  (see  FIG. 6 ). The load sensor  70  could be positioned on either side of the spring  54  and can be disposed in either a wet or a dry environment. 
         [0057]    The load sensor  70  could include any type of sensor. In one non-limiting embodiment, the load sensor  70  is a load cell that includes one or more strain gauges and is positioned on the rear face  68  of the thrust bearing  42 . The load sensor  70  could also include a multi-cell arrangement. The load sensor  70  may convert a force into an electrical signal, as discussed in additional detail below. 
         [0058]    In one embodiment, the load sensor  70  is configured to directly measure a load applied against the front face  66  of the thrust bearing  42  during engagement/disengagement of a vehicle driveline (i.e., engagement of a transmission relative to an engine). The “load” refers to a force exerted on the thrust bearing  42  during actuation of the CSC assembly  30 . The load sensor  70  enables a point of source measurement of driveline engagement/disengagement. The rear face  68  of the thrust bearing  42  will experience the same load as the front face  66  because the load applied against the front face  66  is transferred to the rear face  68  through ball bearings of the thrust bearing  42 . Therefore, the load sensor  70  can directly measure loads at the front face  66  even though it is remote from and not in direct contact with the front face  66 . 
         [0059]    The load sensor  70  may also include a bore  72  (see  FIGS. 5 and 6 ). In other words, the load sensor  70  is hollow. The bore  72  can accommodate the guide  60  of the CSC  56  to facilitate insertion of a transmission input shaft. Once assembled, the dust shield  52  may at least partially circumscribe the load sensor  70  to protect it from the relatively harsh operating environment of the clutch system (see, e.g.,  FIG. 3 ). 
         [0060]    The load sensor  70  may be connected to a control unit (see control unit  28  of  FIG. 1 , for example) via wiring  74 . The wiring  74  transfers load information detected by the load sensor  70 , in the form of electrical signals, to a control unit for further processing. 
         [0061]    The load information sensed by the load sensor  70  may be representative of an actual, real time driveline status of a vehicle (i.e., a preload, biting point, full load, etc.). Directly measuring these loads can improve performance of vehicles equipped with stop/start systems. For example, incorporating the load sensor  70  into the driveline for directly measuring loads at the thrust bearing  42  enables the stop/start operating range to be extended, thereby providing reductions in CO 2  and other emissions. The load information can also be used to observe clutch system wear such that applied tolerance or hysteresis factors can be eliminated to further improve the clutch system, may aid in identification of internal failures within the clutch set, or for other error detection. The control unit  28  can log an error fault code and/or illuminate a dashboard service warning light in response to identifying any such errors. 
         [0062]    Although the different non-limiting embodiments are illustrated as having specific components or steps, the embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. 
         [0063]    It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should be understood that although a particular component arrangement is disclosed and illustrated in these exemplary embodiments, other arrangements could also benefit from the teachings of this disclosure. 
         [0064]    The foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.