Abstract:
The present invention is directed to a self-bleed mechanism for a hydraulic system comprising a clutch pack hydraulically actuated by one or more fluid passageways; an elongated cylinder operably connected to the fluid passageways; a piston slidably disposed in the elongated cylinder where the piston controls actuation of the clutch pack by sliding in the elongated cylinder; and a valve connected to the elongated cylinder, wherein air inside of the elongated cylinder is vented through the valve. The valve is a check valve which vents to the general sump and includes a ball which rests in a tapered valve seat, and the ball is held in place with a spring. The piston has a nozzle on an end that unseats said check valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/613,981, filed Sep. 28, 2004. The disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to hydraulic systems that incorporate the use of an automatically operated bleed valve that purges air from the system during operation.  
       BACKGROUND OF THE INVENTION  
       [0003]     Hydraulic clutches are commonly used in automatic transmissions and transfer cases. These clutches can be actuated in a number of ways, one of which is through the use of an electric motor, along with a hydraulic fluid circuit.  
         [0004]     One problem that can occur when using a hydraulic circuit in any type of application is that air can get into the system and affect the hydraulic system performance. Occasionally, the system needs to “bleed off”, this is a process by which the air is purged from the system, so it can resume normal operation. Prior methods of allowing the system to bleed off include the use of a manually operated bleed valve. The manually operated bleed valve is part of a closed loop hydraulic system that can be used to purge air from the system prior to operation. The present invention is an automatically operated bleed valve that changes the system from a closed loop system to an open loop system.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention is directed to a self-bleed mechanism for a hydraulic system comprising a clutch pack hydraulically actuated by one or more fluid passageways. The hydraulic system also includes an elongated cylinder operably connected to the fluid passageways. A piston slidably disposed in the elongated cylinder controls actuation of the clutch pack. A valve is connected to the elongated cylinder allowing air inside the elongated cylinder to be vented through the valve.  
         [0006]     The bleed valve is a check valve which vents to the general sump and includes a ball which rests in a tapered valve seat, and the ball is held in place with a spring. The piston has a nozzle on an end that unseats the check valve. The valve is at a generally distal end of the cylinder opposite of the piston. The piston is mechanically actuated and is connected to a ball screw through the use of a ball nut so when the ball screw rotates, the nut and piston translate in the elongated cylinder. The ball screw includes a shaft upon which a gear is mounted; the gear is part of a gear train, which drives the ball screw.  
         [0007]     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  
       [0008]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0009]      FIG. 1  is a full sectional front view of an electrohydraulic clutch assembly according to the present invention.  
         [0010]      FIG. 2  is a full sectional side view of an electrohydraulic clutch assembly according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0012]     Referring now to  FIG. 1  the electrohydraulic clutch assembly  10  includes a preferably metal housing  12  having various bores, ports, slots, faces, passageways for receiving the various components thereof. A first end plate  14  is specially formed to receive various shafts, fits tightly on one end face of the housing  12  and is secured thereby a plurality of fasteners  18 . Disposed within a suitably sized region of the housing  12  is a bi-directional, fraction horsepower electric motor  20 . The electric motor  20  includes an output shaft  22  and includes a drive hub  26 . A driven pinion gear  28  which is freely rotatably disposed on the output shaft  22 , is driven by drive hub  26 .  
         [0013]     The pinion gear  28  is in constant mesh with a first spur gear  30 . The first spur gear  30  is supported upon a first shaft  32  and is coupled to or integrally formed with a smaller diameter second pinion gear  34  which is in constant mesh with a second spur gear  36 . The second spur gear  36  is likewise rotatably supported upon a second stub shaft  38 . The second spur gear  36  is coupled to or preferably integrally formed with a third pinion gear  40 . The third pinion gear  40  is in constant mesh with and drives a third spur gear  42 . The third spur gear  42  is coupled to or preferably integrally formed with fourth pinion gear  46 . The third spur gear  42  is supported by stub shaft  44 . The fourth pinion gear  46  is in constant mesh and drives fourth spur gear  48  which is secured to a drive shaft  50 .  
         [0014]     The drive shaft  50  is preferably supported by a pair of antifriction bearings such as roller bearing assemblies  52 . The drive shaft  50  includes a ball screw  54 . Between the drive shaft  50  and the ball screw  54  are mounted a plurality of Belleville springs or washers  56  that function as a resilient stop. Disposed about the ball screw  54  is a ball nut  58 . The ball nut  58  includes a plurality of balls or roller bearings  60  which recirculate about the complementary configured grooves in the ball screw  54  and thus provide a low friction interconnection between the ball screw  54  and the nut  58 . As the shaft  50  bi-directionally rotates in response to bi-directional rotation of the output shaft  22  of the electric motor  20 , the ball nut  58  translates as well. The ball screw  54  and the ball nut  58  thus function as a rotary to linear motion transducer.  
         [0015]     The ball nut  58  is coupled to a master piston  62  which translates axially within an elongated cylinder  64  which also contains the ball screw  54 . The master piston  62  includes a pair of bi-directional seals  66  which are received within suitably configured circumferential grooves  68  near each end of the master piston  62 . Between the grooves  68  the cavity filled with fluid or oil. The master piston  62  is shown in  FIG. 1  in its retracted position. As the master piston  62  is extended by rotation of the ball screw  54 , it forces hydraulic fluid  81  and any air present in elongated cylinder  64  toward the top of elongated cylinder  64 . As the master piston  62  reaches the top of elongated cylinder  64 , a master cylinder piston nozzle  70  opens a check valve  72 , allowing any air trapped in elongated cylinder  64  to escape. The master cylinder piston nozzle  70  is a short projection located on the end of the master piston  62 . This configuration allows for electrohydraulic clutch assembly  10  to be self-bleeding. The elongated cylinder  64  is connected to the main oil flow passage  74 , which provides for communication and flow of the hydraulic fluid  81  to a pressure transducer  76  that controls the flow of hydraulic fluid  81  to the driven components of the electrohydraulic clutch assembly  10 .  
         [0016]     It is also possible to bleed air bubbles from the elongated cylinder  64  without having the piston nozzle  70  contact the ball  71 , but rather the check valve  72  will be actuated by the buildup of pressure below the seat  73 . One way of accomplishing this involves using a spring  75  that has a pre-determined spring rate. For example a spring  75  can be used that will allow the ball  71  to move away from the seat  73  when the pressure below the valve seat  73  reaches a level, without the piston nozzle  70  having to make contact with the ball  71 . Another way of arranging the check valve  72  so it can operate without direct contact by the piston nozzle  70  is to control the surface area of the valve seat  73 . The surface area of the valve seat  73  can be made smaller so that a smaller surface area of the ball  71  is exposed to the hydraulic pressure below the valve seat  73 . The surface area of the ball  71  being exposed though the valve seat  73  will control the amount of hydraulic pressure that will be needed to move the ball  71  away from the valve seat  73 .  
         [0017]     Turning now to  FIG. 2 , which is a sectional side view of the present invention shown in  FIG. 1 , the electrohydraulic clutch assembly  10  includes an input member or input shaft  77 , preferably including a set of external or male splines or gear teeth  78  and a smaller diameter threaded region  79 . The male or external splines or gear teeth  78  are engaged by complementarily configured female splines or gear teeth  80  formed on the interior of a cylindrical region  82  of the flange  84 . The flange  84  preferably includes a plurality of through apertures  86  which may receive threaded fasteners or other components (not illustrated) associated with a drive component to the electrohydraulic clutch assembly  10 . A retaining nut  88  as well as one or more flat washers  90  may be utilized to positively retain the flange  84  upon the input member or input shaft  77 . A roller bearing assembly  92  rotatably supports the input member or input shaft  77  within the housing  12  of the electrohydraulic clutch assembly  10 .  
         [0018]     The electrohydraulic clutch assembly  10  also includes a multiple plate friction clutch pack assembly  94 . Driving the friction clutch pack assembly  94  are a plurality of male or external splines or teeth  96  disposed on the input member or input shaft  77  which engage complementarily configured female splines  98  on the first plurality of smaller diameter friction clutch plates or discs  100 . The first plurality of friction clutch plates or discs  100  are interleaved with a second plurality of larger diameter friction clutch plates or discs  102 . The friction clutch plate or discs  100  and  102  include suitable clutch paper or friction material in accordance with conventional practice. Each of the second plurality of larger inner diameter friction clutch plates or discs  102  includes male or external splines  104  which engage and drive complementarily configured female splines  106  formed on the interior of a cylindrical portion  108  of a clutch housing  110 . The clutch housing  110  is rotationally isolated from and stabilized within a portion of the input member or input shaft  77  by a thrust bearing assembly  112 . A thrust bearing assembly  122  is also disposed between the input member or input shaft  77  and the clutch housing  110 .  
         [0019]     An output member or output shaft  83  preferably includes internal or female splines or gear teeth  114  which are complementary to and engage suitably configured male splines or gear teeth (not illustrated) disposed within the rear differential assembly (not illustrated) which receive torque from the electrohydraulic clutch assembly  10 .  
         [0020]     The main oil flow passage  74  illustrated in  FIG. 1  communicates with second oil flow passage  128  shown in  FIG. 2 , which feeds the hydraulic fluid  81  into cylinder  116  which receives an annular slave piston  118 . The annular slave piston  118  engages a thrust bearing  120  which permits relative rotation between the annular slave piston  118  and thrust bearing plate  134 . The thrust bearing plate  134  has an apply area  124 , which transfers axial motion and force from the annular slave piston  118  to the friction clutch pack assembly  94 . The apply thrust bearing plate  134  includes female or internal splines  126  which are complementary to and engage the male splines  96  on the input member or input shaft  77 . Thus, the thrust bearing plate  134  rotates with the input member or input shaft  77 .  
         [0021]     The operation of the electrohydraulic clutch assembly  10  will now be described with reference to all the drawing figures. A signal is provided to the electric motor  20  commanding it to rotate in one of two directions to increase or decrease the pressure of the hydraulic fluid  81  in main oil flow passage  74 , and second oil flow passage  128 , and thus the torque transferred through the friction clutch pack assembly  94 . If the command is to increase torque, the electric motor  20  rotates in a direction to advance the ball nut  58  and advance the master piston  62  within the elongated cylinder  64 . As the master piston  62  translates, hydraulic fluid  81  is transferred, pressure increases and the annular slave piston  118  translates, compressing the friction clutch pack assembly  94 . A command for the electric motor  20  to reduce torque transferred through the friction clutch pack assembly  94  results in the opposite action. In this regard, it should also be noted that the pressure transducer  76  provides information regarding the current, actual pressure of the hydraulic fluid  81  which corresponds to a level of torque throughput.  
         [0022]     The present invention provides an automatic bleed feature that allows air bubbles built up in the hydraulic fluid  81  located in the elongated cylinder  64  to automatically bleed off through the check valve  72 . As the master piston  62  moves toward the check valve  72  air bubbles will migrate toward the check valve  72 . The check valve  72  has a ball  71  positioned in a valve seat  73 . The valve seat  73  is tapered so when the ball  71  is pressed into the valve seat  73 , the ball  71  is directed to a specific position allowing it to become unseated by the master cylinder piston nozzle  70 . The ball  71  is held in place at the valve seat  73  by a compression spring  75 . When air bubbles build up next to the ball  71  the air will bleed past the ball  71  and valve seat  73 . As the master piston  62  moves closer to the check valve  72  the master cylinder piston nozzle  70  will pass through an orifice in the valve seat  73  and make contact with the ball  71 . As the master piston  62  continues to move toward the check valve  72  the master cylinder piston nozzle  70  will push against the ball  71  in the check valve  72  and compress the spring  75  to cause the check valve  72  to move to a fully open position thus allowing any air bubbles to be freely bled from the electrohydraulic clutch assembly  10 .  
         [0023]     The design of the housing  12  as well as the arrangement of components provides a passive oiling or lubrication system to the various components within the electrohydraulic clutch assembly  10 . Thus, not only is the need for specific lubricating means such as a pump avoided, but the assembly exhibits improved durability and service life.  
         [0024]     The description of the invention is merely exemplary in nature and, thus, 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.