Patent Publication Number: US-11020830-B2

Title: System, method and tooling for flexible assembly of cylinder-head valve trains

Description:
This application is a division of U.S. application Ser. No. 14/190,320 filed Feb. 26, 2014, now U.S. Pat. No. 9,523,328 B2, the disclosure of which is hereby incorporated in its entirety by reference herein.  
     TECHNICAL FIELD 
     Various embodiments relate to systems, methods and tooling for flexible assembly of valve trains of cylinder-head assemblies. 
     BACKGROUND 
     A cylinder-head is mounted to an internal combustion engine block for enclosing one or more cylinders and providing at least a portion of the combustion chamber. Depending on the cylinder configuration of the engine, one, two or more cylinder-heads may be employed. The cylinder-head is sealed to the engine block and often provides porting for feeding fuel and air to the cylinder, while also exhausting the post-combustion exhaust. The porting is often regulated by a valve train, which is often assembled to the cylinder-head. Thus a cylinder-head in combination with a valve train is often referred to as a cylinder-head assembly. The operation of the valve train is driven by at least one camshaft. In overhead camshaft designs, the camshaft is supported for rotation in the cylinder-head assembly. 
     The valve train often includes poppet valves which are received for reciprocating translation in valve guides in the cylinder-head. During assembly, a valve stem is inserted into a combustion side of the cylinder-head. After installation, a valve plug is typically maintained in the installed position by a fixture or automation. The cylinder-head is typically flipped over, and valve springs, spring caps, and retainer keys are installed to the valve stem. The springs are compressed, permitting the spring cap and retainer keys to translate along the valve stem until the keys engage a notch on the valve stem. The compression is released so that the spring engages the spring cap thereby loading the valve plug into engagement with the cylinder-head. Installation of the valve train was previously performed manually. Subsequently, the installation was automated with the valves installed at a separated cell or station than the valves springs, springs caps and retainer keys. 
     SUMMARY 
     According to at least one embodiment, an assembly method is provided by orienting a cylinder-head at a first orientation. A first plurality of spring caps and a first plurality of retainer keys are installed into the cylinder-head in the first orientation by a first robot. A first plurality of valves is installed into the cylinder-head in the first orientation by a second robot, into engagement with the first plurality of retainer keys. 
     According to at least another embodiment, an end effector is provided with an adapter plate. At least one actuator is supported upon the adapter plate. At least one shaft extends from the actuator. A mating surface is provided on a distal end of the shaft to engage a spring cap. Porting is provided through the shaft to a central region of the mating surface to convey pressurized air upon a plurality of retainer keys within the spring cap. A plurality of gripper fingers extend from the distal end of the shaft to grip a valve spring while retaining a spring cap between the valve spring and the mating surface of the shaft. 
     According to at least another embodiment, an automation system is provided with an automation assembly to orient a cylinder-head for assembly at a first orientation. A first robot is provided with a first tooling assembly to install spring caps and retainer keys into the cylinder-head in the first orientation. A second robot is provided with a second tooling assembly to install valves into the cylinder-head in the first orientation. 
     According to at least another embodiment, an assembly method provides a kitted assembly of cylinder-head valvetrain components comprising a valve spring, a spring cap upon the valve spring and a plurality of retainer keys within a tapered aperture of the spring cap. An end effector is oriented over the kitted assembly so that a mating surface faces the spring cap. The end effector is translated towards the kitted assembly until the mating surface engages the spring cap such that a plurality of gripper fingers grip the valve spring. Pressurized air is conveyed through porting in the end effector to maintain an orientation of the retainer keys. 
     According to at least another embodiment, an assembly method provides an end effector for installing a valve spring, a spring cap upon the valve spring, and a plurality of retainer keys to a valve stem in a cylinder-head assembly. The end effector conveys pressurized air through porting toward the spring cap of the assembled valve stem, valve spring, spring cap and retainer keys. A pressure of the pressurized air is measure over time. The pressurized air measurements are compared to determine if the retainer keys are properly installed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of an assembly line according to an embodiment; 
         FIG. 2  is a perspective view of a flexible assembly cell of the assembly line of  FIG. 1  according to an embodiment, illustrated in a first assembly position; 
         FIG. 3  is another perspective view of the flexible assembly cell of  FIG. 2 , illustrated in another assembly position; 
         FIG. 4  is yet another perspective view of the flexible assembly cell of  FIG. 2 , illustrated in another assembly position; 
         FIG. 5  is a perspective view of an end effector for the flexible assembly cell of  FIG. 2 , according to an embodiment; 
         FIG. 6  is a partial section view of a gripper assembly of the end effector of  FIG. 5 , with a kitted valve spring, spring cap and retainer keys, illustrated in a first assembly position; 
         FIG. 7  is another partial section view of the gripper assembly and kit of  FIG. 6 , illustrated in a second assembly position; 
         FIG. 8  is a partial section view of the gripper assembly and kit of  FIG. 6  illustrated in a first assembly position during installation to a valve stem in a cylinder-head assembly; 
         FIG. 9  is another partial section view of the gripper assembly, kit and cylinder-head assembly of  FIG. 8 , illustrated in another assembly position; 
         FIG. 10  is another partial section view of the gripper assembly, kit and cylinder-head assembly of  FIG. 8 , illustrated in yet another second assembly position; 
         FIG. 11  is another partial section view of the gripper assembly, kit and cylinder-head assembly of  FIG. 8 , illustrated in another assembly position; 
         FIG. 12  is another partial section view of the gripper assembly, kit and cylinder-head assembly of  FIG. 8 , illustrated in yet another assembly position; 
         FIG. 13  is another partial section view of the gripper assembly, kit and cylinder-head assembly of  FIG. 8 , illustrated in a first test position; 
         FIG. 14  is another partial section view of the gripper assembly, kit and cylinder-head assembly of  FIG. 8 , illustrated in another test position; and 
         FIG. 15  is a graph of pressure over time for testing installation of the retainer keys. 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     With reference to  FIG. 1 , an assembly line  20  is illustrated according to an embodiment. The assembly line  20  is for assembly of cylinder-head assemblies. The assembly line  20  may be dedicated to assembly of a single cylinder-head assembly, or may be configured, to assemble various cylinder-head assembly configurations. The latter option permits reuse of equipment and plant floor space without incurring duplicate expenses. 
     The assembly line  20  includes a conveyor system  22  for transporting cylinder-head assemblies along the assembly line  20 . The cylinder-head assemblies may each be supported upon a pallet that is conveyed along the conveyor system  22 . The conveyor system  22  transports each cylinder-head assembly to multiple stations or work cells for various incremental assembly operations. The pallets may also provide kitted components for subsequent assembly, such as valve springs, spring caps and retainer keys. 
     The assembly line  20  includes an assembly cell  24  for installation of a valve train to the cylinder-head assemblies. The assembly cell  24  is automated and is surrounded by perimeter guarding  26  to provide a physical barrier between passersby and the automation equipment. The conveyor system  22  extends into and out of the guarding  26  to present the cylinder-head assemblies to the assembly cell  24 . The assembly cell  24  may also include additional secondary conveyor systems  28  for the introduction of additional assembly components, such as intake and exhaust valves into the assembly cell  24 . Alternatively, the secondary conveyor systems may also supply the kitted valve springs, spring caps and retainer keys. In another alternative, the valves may be provided on the pallets thereby omitting the secondary conveyor system  28 . The assembly line  20  may include a pair of redundant assembly cells  24  in order to duplicate a throughput of assembled cylinder-head assemblies, and to maintain production in case one of the cells  24  requires maintenance or repair. 
       FIGS. 2-4  illustrate one of the assembly cells  24  according to an embodiment. The cylinder-head assembly conveyor system  22  presents a pallet  30  with a cylinder-head  32  and kitted components into the assembly cell  24 . The assembly cell  24  includes three automation assemblies; and according to the depicted embodiment, the automation assemblies include a primary industrial robot  34 , a secondary industrial robot  36 , and an automated fixture  38 . The primary robot  34  transfers the pallet  30  and installs the kitted components. The secondary robot  36  installs the valves. The automated fixture  38  supports the cylinder-head  32  and presents the cylinder-head  32  at an orientation for the installations. Although two robots  34 ,  36  and one automated fixture  38  are illustrated and described, any combination of robots and fixtures is contemplated for providing the systems, methods and tooling. 
     The primary robot  34  is provided with an end effector  40  that is illustrated in greater detail in  FIG. 5 . The end effector  40  includes an adapter plate  42  for mounting the end effector  40  to the primary robot  34  as an end of arm tooling. The end effector  40  includes a pallet gripper assembly  44  for gripping pallets  30 . Referring again to  FIG. 2 , the primary robot  34  grips the pallet  30  with the pallet gripper assembly  44 . Then the primary robot  34  lifts the pallet  30 , and places the pallet  30  on the automated fixture  38  as illustrated in  FIG. 3 . 
     The cylinder-head  32  is presented to the robots  34 ,  36  resting upon the engine side or combustion side of the cylinder-head  32 . Unlike the prior art, the cylinder-head  32  is not flipped in order to install the valves. The pallet  30  includes a clearance aperture  46  for access to valve guides from beneath the cylinder-head  32 . 
     The automated fixture  38  includes a support structure  48  such as an upright weldment for mounting to an underlying support surface. A rotary actuator  50 , such as a servo motor, is supported by the support structure. A table  52  is pivotally mounted to the support structure  48  and driven by the rotary actuator for various angular positions relative to the support structure  48 . The table  52  is a fixture for locating and supporting the pallet  30 . The table  52  also includes a clearance aperture  54  for access to valve guides from beneath the cylinder-head  32 . 
     After the pallet  30  and the cylinder-head  32  are placed upon the table  52 , the rotary actuator  50  rotates the table  52  so that an array of valve guides is oriented vertically, or in other words perpendicular to the floor. 
     Referring again to  FIG. 5 , the end effector  40  of the primary robot  34  includes an interchangeable adapter  56  mounted to the adapter plate  42 . The interchangeable adapter  56  permits the robot  34  to interchange tooling for various cylinder-head configurations, without requiring a manual tooling interchange. A tooling subassembly  58  is mounted to the interchangeable adapter  56  for installing valve springs, spring caps and retainer keys. The installation of these components is often referred to as key-up, and consequently, tooling for performing these operations is often referred to as key-up tooling. 
       FIGS. 4 and 5  illustrate various configurations of the key-up tooling subassembly  58 . The key-up tooling subassembly  58  has a frame  60  mounted to the interchangeable adapter  56 . A plurality of linear actuators  62  are mounted to the frame and spaced in a linear array, with the spacing aligned with a linear arrangement of valve spacing in the cylinder-head  32 . For the depicted embodiment, the linear actuators  62  may be pneumatic cylinders; however, any suitable linear actuator is contemplated. 
     Referring now to  FIGS. 5 and 6 , each linear actuator  62  drives a shaft  64 . In  FIG. 6 , the shaft  64  is illustrated approaching a kit  66  of valvetrain components. The linear actuators  62  are not pressurized at this time. The kit  66  includes a valve spring  68 , a spring cap  70 , and a pair of retainer keys  72 . The retainer keys  72  each include three beads  74  for engagement into corresponding grooves in the valve stems. Of course any retainer key configuration is contemplated. As discussed above, the kits  66  are provided on the pallets  30  for the depicted embodiment. 
     Each shaft  64  has a mating surface  76  provided on a distal end of the shaft  64  to engage the spring cap  70 . A pair of gripper fingers  78  is also mounted to the shaft  64 ; and the gripper fingers  78  are sized to grip the valve spring  68 . A spring loaded center pin  80  extends from the shaft  64  and through the mating surface  76  of the shaft  64 . The primary robot  34  orients the shaft  64  over and facing the kit  66 . The primary robot  34  translates the key-up tooling subassembly  58  towards the kit  66  such that the center pin  80  engages the retainer keys  72 . The center pin  80  maintains the retainer keys  72  in alignment during the installation process. 
     The primary robot  34  further translates the key-up tooling subassembly  58  toward the kit  66  as illustrated in  FIG. 7 , thereby retracting the center pin  80  while maintaining the orientation of the retainer keys  72 . The gripper fingers  78  are formed from a spring alloy and are undersized relative to the valve springs  68 . As the gripper fingers  78  are pressed over the valve springs  68 , the gripper fingers  78  expand and are loaded about the valve springs  68 . The shaft  64  is translated until the mating surface  76  engages the spring cap  70  so that the gripper fingers  78  retain the valve spring  68 , spring cap  70  and retainer keys  72  therein. 
     As illustrated in  FIG. 7 , a seal  82  is provided at the distal end of the shaft  64  for providing a fluid tight seal at the mating surface  76  with the spring cap  70 . A spring loaded center bushing  84  is provided in the shaft  64  around the center pin  80 . Porting  86  is provided about the center bushing  84  to provide a fluid passageway from the shaft  64  to the spring cap  70 . According to one embodiment, the fluid passageway is pressurized to further maintain the retainer keys  72  in engagement with the spring cap  70  and the center pin  80  during travel of the end effector  40  and the kit  66 . Alternatively, a vacuum source may be applied to the passageway to urge the retainer keys  72  against the mating surface  76  about the center pin  80 . The actuators  62  may be stroked at an intermediate pressure, labeled as Pressure  1 , for retrieval of the kit  66 . 
     Referring again to  FIG. 4 , the primary robot  34  aligns the kits  66  with the valve guides in the cylinder head  32 . A reaction bar  88  is provided upon the frame  60  of the key-up tooling subassembly  58 . Likewise a stationary reaction beam  90  extends from the support structure  48  of the automated fixture  38 . The primary robot  34  raises the end effector  40  so that the reaction bar  88  engages the reaction beam  90 . Due to rotated position of the table  52 , and consequently the cylinder-head  32 , the valve guides are perpendicular to the reaction beam  90  to provide a reaction force while compressing the valve springs  68 . By distributing the reaction force to a static structure, the reaction forces are not distributed to the robot  34 . 
     Then, the linear actuators  62  are actuated by another intermediate pressure, labeled Pressure  2 , which is greater than Pressure  1 , thereby extending the shafts  64  as illustrated in  FIG. 8 . In this position, the spring cap  70  is pressed against the valve spring  68 , thereby compressing the valve spring  68  against a valve seal  92  disposed about a valve guide  94  in the cylinder-head  32 . Unlike the prior art, the valve stem is not yet present during this compression of the valve spring  68  thereby avoiding misalignment caused by engagement of the valve stem with the retainer keys  72 . 
     With reference again to  FIGS. 2-4 , the secondary robot  36  has an end effector  96  for retrieving valves  98  from dunnage  100  on the valvetrain component conveyor system  28 . The end effector  96  may apply vacuum cups  102  to combustion surfaces  104  of plugs  106  of the valves  98  for handling. In the first rotated position of the table  52 , the intake valve guides  94  are oriented generally vertical. Therefore, the secondary robot  36  selects intake valves  98  and inserts the intake valves  98  into the valve guides  94  through the clearance provided in the apertures  46 ,  54  in the pallet  30  and the table  52 . 
     Referring again to  FIG. 8 , the secondary robot  36  presses the valves  98  into the valve guides  94 . The translation may be provided by the secondary robot  36 , or by an actuator or an array of actuators on the secondary end effector  96 . As illustrated in  FIG. 9 , the secondary robot  36  continues to translate the valves  98  until a valve stem  108  extends past the valve seal  92  into engagement with the retainer keys  72 . Additionally, the actuators  62  are pressurized to Pressure  3 , which is greater than Pressure  2  so that the springs  68  are further compressed, and the actuators  62  reach a hard stop or a limit for full actuation. 
     Further advancement of the valve stem  108  presses retainer keys  72  through the pressurized air into engagement with the center bushing  84  in  FIG. 10 , while the valve stem  108  contacts and retracts the center pin  80  until the valve plug  106  is seated in the combustion surface of the cylinder-head  32 . The center pin  80  has a range of translation to accommodate for variations in tolerance in the length of the valve stems  108 . The actuators  62  are maintained at Pressure  3  during this step. 
     In  FIG. 11 , the linear actuators  62  of the key-up tooling subassembly  58  are retracted by reducing the pressure to Pressure  4 , which is less than Pressure  3 . Each valve spring  68  expands during the retraction, thereby pressing the corresponding spring cap  70  toward the retainer keys  72 . The pressurized air is maintained upon the retainer keys  72  to urge the retainer keys  72  into cooperation with the valve stem  108 . Otherwise misalignment may be caused, such as by oil upon the retainer keys  72  adhering the retainer keys  72  to the center bushing  84 , center pin  80  or the seal  82 . During the retraction, beads  74  upon the retainer keys  72  align with grooves  110  in the valve stems  108 . 
     In  FIG. 12 , the linear actuators  62  continue to retract by reducing the cylinder pressure to Pressure  5 , which is less than Pressure  4 . As the valve spring  68  presses the spring cap  70  into the retainer keys  72 , a tapered aperture  112  in the spring cap  70  causes the retainer keys  72  to converge into locked engagement with the beads  74  in the grooves  110  on the valve stem  108 . In the locked arrangement, the valve spring  68  is still partially compressed thereby maintaining the locked engagement and completing the assembly of the valvetrain. 
     Unlike the prior art, the cylinder-head  32  is maintained in one position during assembly of the valvetrain, thereby avoiding additional manufacturing equipment, manufacturing steps, and plant floor space. The secondary robot  36  maintains the valves  98  in the installed position during assembly of the spring caps  70  and retainer keys  72 , thereby avoiding any additional hardware or automation to maintain the seated position of the valves  98 . The compactness of the key-up tooling subassembly  58  permits installation of the kits  66  without removing camshaft caps from the cylinder-head  32 , which further simplifies manufacturing equipment, manufacturing steps, and plant floor space. 
     Cylinder-head assemblies are often inspected by automation to determine if the valvetrain is properly assembled. Such inspection is often performed by additional equipment, which may even add an additional cell to the assembly line. In contrast, the key-up tooling subassembly  58  is configured to perform the inspection from a position approximate to the completion of assembly of the valvetrain to minimize additional cycle time. In  FIG. 13 , the key-up tooling subassembly  58  is translated towards the cylinder-head  32  until the center pin  80  contacts the valve stem  108 . In  FIG. 14 , the key-up tooling subassembly  58  is further translated until the seal  82  engages the spring cap  70 . The pressurized air is maintained and measured during these steps. 
       FIG. 15  illustrates a graph with time on the abscissa and pressure on the ordinate. Range  1  illustrates a back pressure of the tooling, which may be a positive pressure or a negative pressure for vacuum systems as known in the art. Range  2  is measured as the pressure is enabled. Range  3  is measured during the inspection. If the retainer keys  72  are properly installed, the pressure of the air increases over time. If one or both retainer keys  72  are not installed, the pressure does not increase over time. Therefore, a failure can be detected immediately after installation before full retraction of the key-up tooling subassembly  58 . The inspection value at Range  3  is compared to the Range  2  to determine proper installation of the retainer keys  72 . Back pressure of tooling and its associated plumbing may vary over time. Therefore, the difference between Range  3  and Range  2  is utilized to determine whether there is a proper installation. Likewise, the difference between Range  2  and Range  1  is utilized to determine if there is an improper installation. Utilization of the difference in ranges compensates for variations in back pressure. 
     Cylinder-heads, such as the cylinder-head  32  depicted herein, include intake and exhaust valvetrains. After installation of one valve train, such as the intake valvetrain assembly process described above, the automated fixture  38  pivots the table  52  to a second orientation whereby the exhaust valve guides are oriented vertically, which is perpendicular to the reaction beam  90 . Then the assembly steps for the intake valvetrain are repeated for the exhaust valvetrain by utilizing exhaust valves  114 . 
     For V-configured engines with left and right cylinder-heads, the assembly cell  24  is flexible for assembling the valvetrain components for both cylinder-heads. The assembly cell  24  can assemble various configurations of cylinder-heads by interchanging the tooling that is specific to a particular configuration. 
     While various embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.