Abstract:
A starting device for a motor vehicle includes a pump connected to a prime mover and a turbine connected to a turbine shaft. The pump and turbine are hydrodynamically connected. A stator assembly is disposed between the pump and the turbine. The stator assembly houses a slidable throttle plate. In a first position, the throttle plate partially blocks a return fluid flow from the stator assembly, thereby effectively reducing the capacity of the starting device. In a second position, the throttle plate does not reduce the capacity of the starting device. The throttle plate position is a function of a balance of forces acting on the throttle plate by a biasing member and a flow of hydraulic fluid contacting the throttle plate.

Description:
CROSS-REFERENCE 
     This application claims the benefit of U.S. Provisional Application No. 61/434,589, filed Jan. 20, 2011. The entire contents of the above application are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a starting device for an automatic transmission and more particularly to a hydrodynamic starting device for a transmission having an integrated throttle plate. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     Hydrodynamic starting devices are often used in motor vehicles in order to improve the performance characteristics of the vehicle. One type of device includes the hydrodynamic launch or starting device. The hydrodynamic launch device is similar to a standard torque converter and generally includes three rotating elements: a pump, a turbine, and a stator. The pump is mechanically driven by a prime mover, such as an internal combustion engine or an electric motor. The turbine is mechanically coupled to a turbine shaft and is driven by fluid flow pumped by rotation of the pump. The stator is interposed between the pump and turbine and alters fluid flow returning from the turbine to the pump in order to multiply torque. In launch devices, the torque multiplication is only used at low gear speeds to improve the launch performance of the motor vehicle. Accordingly, the launch device is typically smaller than a standard torque converter. 
     While these launch devices are useful for their intended purpose, there is room in the art for a launch device that has efficient packaging, cost, and complexity while improving vehicle fuel efficiency by reducing the load on the engine while the motor vehicle is in idle. 
     SUMMARY 
     In one example of the principles of the present invention, a hydrodynamic launch or starting device for a motor vehicle is provided. The starting device is operable to reduce a load on driving prime mover by automatically reducing the capacity of the starting device during low speeds. The starting device includes a pump connected to the prime mover and a turbine connected to a turbine shaft. The pump and turbine are hydrodynamically connected. A stator assembly is disposed between the pump and the turbine. The stator assembly houses a slidable throttle plate. In a first position, the throttle plate partially blocks a return fluid flow from the stator assembly, thereby effectively reducing the capacity of the starting device. In a second position, the throttle plate does not reduce the capacity of the starting device. The throttle plate position is a function of a balance of forces acting on the throttle plate by a biasing member and a flow of hydraulic fluid contacting the throttle plate. 
     Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is cross-section view of a starting device in a powertrain of a motor vehicle in a first mode of operation; and 
         FIG. 2  is cross-section view of the starting device in a powertrain of a motor vehicle in a second mode of operation. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     With reference to  FIG. 1 , an exemplary powertrain for a motor vehicle is generally indicated by reference number  10 . The powertrain  10  includes an engine  12  interconnected to a transmission  14  through a starting device  16 . The engine  12  may be a conventional internal combustion engine or an electric engine, or any other type of prime mover, without departing from the scope of the present disclosure. The engine  12  supplies a driving torque to the transmission  14  through a flexplate  18  or other connecting device that is connected to front cover member  20  of the starting device  16 . 
     Generally speaking, the transmission  14  receives driving torque from the starting device  16  and outputs the driving torque to a transmission output shaft (not shown). Disposed between the starting device  16  and the transmission output shaft is a gear and clutch arrangement or gearbox (not shown). The gearbox includes a plurality of gear sets, a plurality of clutches and/or brakes, and a plurality of shafts. The plurality of gear sets may include individual intermeshing gears, such as planetary gear sets, that are connected to or selectively connectable to the plurality of shafts through the selective actuation of the plurality of clutches/brakes. The plurality of shafts may include layshafts or countershafts, sleeve and center shafts, reverse or idle shafts, or combinations thereof. The clutches/brakes are selectively engageable to initiate at least one of a plurality of gear or speed ratios by selectively coupling individual gears within the plurality of gear sets to the plurality of shafts. It should be appreciated that the specific arrangement and number of the gear sets, clutches/brakes, and shafts within the transmission  14  may vary without departing from the scope of the present disclosure. In addition, it should be appreciated that the transmission  14  may be a front wheel drive transmission or a rear wheel drive transmission without departing from the scope of the present disclosure. The transmission output shaft (not shown) is preferably connected with a final drive unit (not shown) which may include, for example, propshafts, differential assemblies, and drive axles. 
     The starting device  16  is housed within a bell housing  22 . The bell housing  22  is generally cast aluminum and includes openings, counterbores, flanges, shoulders and other features which receive, locate and support the various components of the starting device  16 . The starting device  16  includes the front cover member  20  that is directly driven by the engine  12  via the flexplate connection  18  or other type of connection. The input  20  is located within the bell housing  22  and is connected to a pump  24  and a lock-up clutch  26 . The lock-up clutch  26  selectively mechanically connects the input  20  with a flywheel or isolator  28 . The flywheel  28  is interconnected (either indirectly, as shown, or directly) to a turbine shaft  30  which is connected with the transmission  14 . 
     The pump  24  is connected with a pump hub  32  that extends into the transmission  14 . The pump hub  32  may be connected with a positive displacement pump (not shown) for providing a source of pressurized hydraulic fluid flow. A plurality of impeller blades  33  are connected to and circumferentially spaced around an inside of the pump  24 . The pump  24  hydraulically drives a turbine  34  of the starting device  16 . A plurality of turbine blades  35  are connected to and circumferentially spaced around an inside of the turbine  34 . The impeller blades  33  and the turbine blades  35  have arcuate inner edges that form a split torus ring  36  which reduces fluid turbulence within the starting device  16 . The turbine  34  is mechanically connected to a turbine hub  37  which is in turn mechanically connected, for example by a splined connection  39 , to the turbine shaft  30 . 
     A stator assembly  40  is disposed within the bell housing  22  and located between the pump  24  and the turbine  34 . The stator assembly  40  includes a plurality of circumferentially spaced stator vanes  42  which are connected at their inner end to a stator hub  44 . The stator hub  44  has a camming surface mounted about a plurality of rollers  46  which act as a free wheel or one-way clutch to allow the stator vanes  42  to rotate in the same direction as the pump  24  and the turbine  34  during both hydrodynamic operation and lockup clutch operation. The rollers  46  are mounted on a race surface of a stationary stator reaction member  48 . It should be appreciated that other suitable types of one-way clutches may be used without departing from the scope of the present disclosure. The stator reaction member  48  is connected, such as by a spline connection  50 , to a stationary stator reaction shaft  52 . 
     Annular thrust bearings  54  are disposed between the stator reaction member  44  and the pump hub  32 , between the stator reaction member  44  and the turbine hub  37 , and between the pump hub  32  and the stator reaction shaft  52 . However, it should be appreciated that other bushings, retainer members and the like may be used and are illustrated in  FIG. 1  although not specifically described. 
     The stator hub  44  includes an annular groove  60  located radially inwardly of the stator blades  42 . The groove  60  extends axially into the stator hub  44 . A throttle plate  62  is slidably disposed within the annular groove  60 . The throttle plate  62  includes a first radial portion  62 A, an axial portion  62 B connected to the first radial portion  62 A, a second radial portion  62 C connected to the axial portion  62 B, and a flange portion  62 D connected to the second vertical portion  62 C. The portions  62 A and  62 B are disposed within the annular groove  60 . The flange portion  62 D is at a non-right angle with respect to the portion  62 C and the flange portion  62 D extends out away from the stator hub  44  towards the pump  24  and is axially located between the pump  24  and the stator blades  42 . The throttle plate  62  is moveable between at least two positions, shown in  FIGS. 1 and 2 , as will be described in greater detail below. A return spring or other biasing member  64  is located within the groove  60  between a retainer ring  66  and the throttle plate  62 . The return spring  64  biases the throttle plate  62  to a first position, shown in  FIG. 1 . For example, a first end of the return spring  64  contacts the retainer ring  66  and a second end of the return spring  64  contacts the first portion  62 A and exerts an axial force on the throttle plate  62  in a direction towards the turbine  34 . It should be appreciated that other types of biasing members may be employed. In the first position, the first and second vertical portions  62 A and  62 C abut the stator hub  44 . In the example provided, the stator blades  42  have an angled edge (i.e. a corner cut)  68  that is substantially parallel with the flange portion  62 D of the throttle plate  62 , thereby allowing the throttle plate  62  to fully abut the stator hub  44  when in the first position without contacting the stator blades  42 . In a second position, shown in  FIG. 2 , the throttle plate  64  is urged against the force of the return spring  64  and slides or translates axially towards the pump  24 . In the second position the second vertical portion  62 C may abut the inner surface of the pump  24  and the flange portion  62 D is disposed substantially parallel to the inner surface of the pump  24 . 
     The operation of the starting device  16  will now be described. Rotation of the flexplate  18  by the engine  12  causes the front cover member  20  to rotate. Since the front cover member  20  is connected to the pump  24 , the pump  24  also rotates. The fluid within the starting device  16  is set into motion by the rotation of the pump  24  and impeller blades  33  and kept filled by the fluid pressure from a pump (not shown) driven by the pump hub  32 . The impeller blades  33  carry the hydraulic fluid and as the hydraulic fluid is spun around by the impeller blades  33 , the hydraulic fluid is thrown outward by centrifugal force and into the turbine blades  35  at an angle. The hydraulic fluid strikes the turbine blades  35 , thus imparting torque, or turning effort to the turbine  34  and causing the turbine  34  to rotate. Since the turbine  34  is connected to the turbine hub  54  which is, in turn, connected to the turbine shaft  30 , the turbine shaft  30  rotates with the turbine  34 . The hydrodynamic coupling between the pump  24  and the turbine  34  may be bypassed by engaging or applying the lock-up clutch  26  such that the cover member  20  is directly connected to the turbine hub  44  through the flywheel  28 , thereby rotating the turbine shaft  30 . 
     When the engine  12  is operating at low speeds such as during an idle condition, the force of the rotating hydraulic fluid on the flange portion  62 D of the throttle plate  62  returning from the turbine  34  and the stator assembly  40  is insufficient to overcome the force exerted on the throttle plate  62  by the return spring  64 . Accordingly, at engine idle speeds, the throttle plate  64  is in the first position, thereby partially blocking the flow of hydraulic fluid from the stator assembly  40 . This in turn effectively reduces the capacity of the starting device  16  and therefore the load on the engine  12 . This can result in a fuel efficiency gain of approximately 0.05 to 0.07 miles per gallon with a 2.5 Nm load reduction based on 800 rpm engine idle speed. 
     At higher engine speeds, such as during motor vehicle launch, the force on the flange portion  62 D of the throttle plate  62  returning from the rotating hydraulic fluid returning from the turbine  34  and the stator assembly  40  is sufficient to overcome the force exerted on the throttle plate  62  by the return spring  64 . Accordingly, at higher engine speeds, the throttle plate  64  moved to the second position. Since the flange portion  62 D has an angle or contour similar to that of the pump  24 , the throttle plate  62  does not block the flow of hydraulic fluid from the stator assembly  40 . Therefore, the capacity of the starting device  16  is not reduced during higher engine speeds  12 . During coasting at higher engine speeds, the lock-up clutch  26  is applied to bypass the pump  24  and turbine  34  to avoid the throttle plate  62  from moving to the first position. Finally, the throttle plate  62  can be used with negative retention stator blade tuning to maximize the idle loss reduction. 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.