Abstract:
A helical torsion valve spring assembly includes one or more helical torsion springs mounted within a frame and are held in a statically loaded state so that installation of a valve spring retainer can be easily performed. The entire helical torsion valve spring assembly is installed as a single part onto a cylinder head of an engine valvetrain. The helical torsion springs are mounted around a shaft to accurately locate the helical torsion springs so that the forces acting on the retainer and valve are precisely controlled. The assembly minimizes the size of the retainer, and applies only one bending mode to the helical torsion springs, which provides maximum utilization of the spring material and minimizes coil vibration. The assembly allows spring coils to be strategically packaged in the engine valvetrain to create space in critical areas.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to valve return spring arrangements for internal combustion piston engines, fluid pumps and similar machines. 
     The most commonly-used method for valve return springs in internal combustion piston engines today is the helical compression spring which is coupled to the valve at one end and is stationary at the other end, and is coaxial with the valve axis. 
     This method, while providing the basic function of springing the valve mechanism, is known to have undesirable characteristics that can compromise the valvetrain system function and ultimately the total engine function. One compromise that has been well-studied is the tendency for destructive coil surges that tends to increase as engine RPMs increase. The active coil of the helical-compression-type valve spring is often found to have too-low a natural frequency relative to the valve actuation frequency which is equal to the camshaft speed and is ½ of the engine operating speed for a 4-stroke engine. Coil surge is unwanted vibration of the active coil of a spring that causes cyclic increases and decreases in the forces that the spring is intended to produce and results in several problems: 1) higher fatigue stresses in the spring which requires the spring designer to adjust the nominal stresses downwards by using a heavier wire which tends to lower the coil frequency further and compounds the problem; 2) a coil surge away from the valve spring retainer during the valve lift event causes a lapse of force that may result in separation and violent re-engagement of the cam and follower that results in damage to the engine; 3) a coil surge away from the valve spring retainer at the end of a valve lift event causes a lapse in force that may result in valve bounce which can cause an undesirable exchange of air into or out of the cylinder that compromises engine performance; 4) a coil surge towards the valve spring retainer during the valve lift event may cause higher loading at the cam/follower interface and higher torsional loading for the camshaft timing drive system which exacerbates fatigue and wear of other engine components and necessitates the use of heavier more-expensive components. The problem of coil surge has been dealt with in several ways, including: 1) reducing the valve lift to reduce the spring force requirement which enables a higher frequency spring design, but may compromise engine performance; 2) using multiple concentric spring arrays to raise the coil frequency of the valve spring but increases the outside package diameter and requires use of a heavier valve spring retainer which increases the cost of the engine; 3) incorporating a spring damper to frictionally inhibit coil surge, or having concentric springs which interfere with each other to cause frictional damping—either of these may cause wear of the spring that may result in failure. 
     Another consideration for a valve spring may be the size and location of the spring package as it relates to other essential components in the engine cylinder head such as a spark plug, a direct-injection fuel injector or other features such as camshaft bearing structures and cylinder head bolt seats. The helical-compression-type valve spring, as it is applied almost universally, is concentric with the valve. Hence, the radial package around a valve axis in the upper part of a cylinder head is the outside radius of the valve spring which in some instances can lead to a compromise. In modern diesel engines, for example, it is often preferred to have the fuel injector in the center of a four-valve array with all four valves being parallel with the cylinder bore axis. However, for smaller cylinder bore diameters, due to the proximity of the helical-compression-type valve springs with the fuel injector, the four-valve array must be splayed outwards such that the valves are not parallel with the cylinder bore axis in order to obtain the necessary clearance between the fuel injector and the valve springs resulting in a compromised combustion chamber. 
     SUMMARY OF THE INVENTION 
     The helical torsion valve spring is another valve return spring arrangement that has been used in engines. As it has been typically applied, the axis of the spring coil is offset from the valve axis and lies on a plane that is perpendicular to the valve axis. The moving leg of one or more helical torsion springs contacts a retainer that is fastened to the valve and applies force to bias the valve to a closed position. The advantages of the helical torsion valve spring over the helical-compression-type valve spring are: 1) for a given set of parameters—valve-closed force, valve-open force, valve lift—there is a capability for higher spring coil natural frequency to reduce or eliminate the problem of coil surge; 2) reduced effective reciprocating mass at the valve; and 3) the ability to package spring coils in a chosen radial direction away from the valve axis thereby leaving more space in another radial direction to effectively make room for another component or design feature. 
     Regarding advantage (1), for having higher spring coil natural frequency—this is due to the helical torsion valve spring having a shorter and stiffer coil than can practically be done with a helical-compression-type valve spring. The moving leg of the helical torsion spring couples the spring coil to the valve spring retainer with a leverage effect such that the force at the coil is greater than the force at the valve, but the stroke is less. Hence, the helical torsion valve spring can have a shorter-stiffer coil than a comparable helical-compression-type valve spring which is direct-coupled to the valve necessitating a longer-stroking/lower-stiffness coil, by comparison. Holding the energy storage capacity constant, shorter-stiffer spring coils tend to have higher natural frequencies. This effect is dominant over the helical compression spring coil, which is primarily loaded in torsion, being approximately 20% more stress-efficient than a rectangular-wire helical torsion spring coil, which is primarily loaded in bending (“stress-efficiency” is the ratio of average stress to maximum stress in a loaded coil). In many cases studied for applications including diesel engines and high-speed gasoline engines, it has been found that the coil frequencies for helical torsion valve springs can be made high enough to practically eliminate the problem of coil surge in the running engine that is liable to occur using helical-compression-type valve springs. 
     A further benefit of the higher-coil-frequency tendency of helical torsion springs is the capability for lower spring rates such that, while maintaining a sufficient amount of force at the valve-closed position, the forces acting on the valve during the valve lift event can be reduced such that the overall valvetrain friction is reduced which allows the engine to operate with lower rates of fuel consumption. This capability applies mostly to turbocharged engines because the valve-closed force requirement is higher due to higher manifold pressures while the peak force requirement is lower because the maximum RPM is typically lower for turbocharged engines compared to naturally aspirated engines. Many turbo-diesel engines today operate with excessive amounts of spring force during a valve lift event due to helical-compression-type valve springs lacking a capability for lower spring rates. 
     Regarding advantage (2), for having reduced effective mass at the valve—this is due to having the coil offset from the valve which reduces the moving velocity in the coil by a ratio that is approximately the coil radius divided by the distance from the coil axis to the valve axis—a ratio that is typically ⅓ to ½. The fraction of coil mass that is effective at the valve is this ratio squared and divided by three. The helical-compression-type valve spring that is direct-coupled to the valve, by comparison, has a ratio that is always one. Hence, the helical torsion spring is more than 75% lower effective mass at the valve for many cases studied. This advantage is bolstered by the ability to couple the moving spring leg to the valve spring retainer close to the valve stem enabling the retainer to be smaller and lighter than those typically used with helical-compression-type valve springs. Reducing the moving mass in a valvetrain system is known to provide capability for increasing the operating speed of the valvetrain system and/or increasing the area under the valve lift curve—both of these improvements may allow for improved engine performance. 
     Regarding advantage (3), the packaging advantage—the graphics contained in this application demonstrate that the helical torsion valve spring can be used to advantage to create increased space for critical systems in the engine by strategic placement of spring coils away from critical areas in a cylinder head. For example, in a modern diesel engine having four-valves-per-cylinder, a significant increase in package space for the D.I. fuel injector is achievable. 
     In summary, the helical torsion valve spring can reduce or practically eliminate coil surge and the problems associated with it while also reducing the reciprocating mass in the valve gear to provide an engine builder with the ability to improve engine function with regards to performance. There is also potential for improved packaging of critical components in the cylinder head such as a D.I. fuel injector. 
     The invention is directed to a helical torsion valve spring assembly having the following features: 1) provides all of the advantages of helical torsion valve springs for reducing coil surge and for reducing the effective reciprocating mass of the valve gear mechanism; 2) an engine builder can install the helical torsion valve spring assembly onto a cylinder head of an engine as a single unit, the same as one would install a helical-compression-type valve spring; 3) enables a safe, easy process for installation of a valve spring retainer using a single straight-line motion. This is achieved by having the moving leg(s) of the helical torsion spring(s) precisely held in a statically loaded state to allow a retainer to be placed directly around the valve stem and engage the torsion spring moving leg(s); 4) the helical torsion valve spring assembly is secured in the engine by the forces acting on the helical torsion springs and the reaction forces acting on the frame, without the need of any fasteners; 5) helical torsion springs are precisely mounted on a shaft; 6) the frame protects the outer surfaces of the spring coils which are the highest stressed surfaces of a helical torsion spring; and 7) provides capability for strategic packaging of spring coils to create space in critical areas of an engine. 
     A feature of the preferred embodiment is to have the helical torsion spring(s) mounted on a shaft or bushing to: a) accurately locate the spring to provide precise control the forces acting on the retainer and valve; b) to help minimize the size required for the valve spring retainer; c) to provide maximum utilization of the spring material by ensuring that a single mode of bending load is applied to the spring coil; and d) to help minimize vibration by limiting movement of the spring coil. 
     Another consideration for using a helical torsion spring for springing a valve is the method used to couple the torsion spring moving leg, which has rotary motion, with the engine valve which moves in a linear motion. A preferred embodiment of the invention is to use rectangular spring wire for the helical torsion spring which provides the highest stress-efficiency, and having a convex surface formed into the moving leg of the helical torsion spring. The convex surface contacts a flat surface of a valve spring retainer that is fastened to the valve, with the flat surface being perpendicular to the axis of the valve. The convex surface of the moving leg and the flat surface of the retainer remain in contact during the entire valve lift event such that there is always line contact at the interface to ensure that contact pressures are at acceptable levels. The normal force transmitted into the retainer biases the valve to the closed position, and frictionally-induced forces in the transverse direction can be absorbed by the valve stem/valve guide interface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While various embodiments of the invention are illustrated, the particular embodiments shown should not be construed to limit the claims. It is anticipated that various changes and modifications may be made without departing from the scope of this invention. 
         FIG. 1  is an exploded view of a helical torsion valve spring assembly having a single helical torsion spring for applying a biasing force to a single valve of an engine valvetrain according to an embodiment of the invention; 
         FIG. 2  is an isometric view of the assembly of  FIG. 1  and another helical torsion valve spring assembly that is the mirror-image of the assembly of  FIG. 1 ; 
         FIG. 3  is a top-hidden-line view of the assembly of  FIG. 1 ; 
         FIG. 4  is a front view of the assembly of  FIG. 1 ; 
         FIG. 5  is a side-hidden-line view of the assembly of  FIG. 1 ; 
         FIG. 6  is a rear view of the assembly of  FIG. 1 ; 
         FIG. 7  is an isometric view of a helical torsion valve spring assembly having two helical torsion springs with each spring intended for applying a biasing force to a single valve of an engine valvetrain according to an embodiment of the invention; 
         FIG. 8  is a top-hidden-line view of the assembly of  FIG. 7 ; 
         FIG. 9  is a side-hidden-line view of the assembly of  FIG. 7 ; 
         FIG. 10  is an end view of the assembly of  FIG. 7 ; 
         FIG. 11  is an exploded view of the assembly of  FIG. 7 ; 
         FIG. 12  is an isometric view of a helical torsion valve spring assembly having two pairs of helical torsion springs with each pair of springs intended for applying a biasing force to a single valve of an engine valvetrain according to an embodiment of the invention; 
         FIG. 13  is a top-hidden-line view of the assembly of  FIG. 12 ; 
         FIG. 14  is an end view of the assembly of  FIG. 12 ; 
         FIG. 15  is side-hidden-line view of the assembly of  FIG. 12 ; 
         FIG. 16  is a side view showing two helical torsion springs of the assembly of  FIG. 12  in four different states of loading: free state, statically loaded state, valve-closed state, valve-open state; 
         FIG. 17  is an exploded view of the assembly of  FIG. 12 ; 
         FIG. 18  is an isometric view of an engine valvetrain including six of the helical torsion valve spring assemblies of  FIG. 12 ; 
         FIG. 19  is a top view of the engine valvetrain of  FIG. 18 ; 
         FIG. 20  is an isometric cross-sectional view of the engine valvetrain taken along line  20 - 20  of  FIG. 19  with the camshafts and bearing caps removed for clarity; 
         FIG. 21  is an isometric sectional view of the engine valvetrain taken along line  21 - 21  of  FIG. 19 ; 
         FIG. 22  is an exploded view of  FIG. 21 ; 
         FIG. 23  is another isometric cross-sectional view of  FIG. 21 ; 
         FIG. 24  is a side cross-sectional view of  FIG. 23 ; 
         FIG. 25  is another side cross-sectional view of  FIG. 23  showing the exhaust cam lifting the exhaust valve; 
         FIG. 26  is another side cross-sectional view of  FIG. 23  showing the intake cam lifting the intake valve; 
         FIGS. 27 ( a - e ) are enlarged, partial isometric cross-sectional views of  FIG. 23  showing the sequence of steps for installing a valve spring retainer in accordance with a method of the invention; 
         FIG. 28  is an enlarged view of  FIG. 27( b ) ; 
         FIG. 29  is an enlarged, partial exploded side cross-sectional view of  FIG. 21  showing two of the helical torsion springs in a statically loaded state and a free state (in phantom); 
         FIG. 30  is an exploded view of a helical torsion valve spring assembly having a spring mounted on both ends of the frame with the pair of springs intended for applying a biasing force to a single valve; 
         FIG. 31  is an isometric view of the assembly of  FIG. 30 ; 
         FIG. 32  is a top-hidden-line view of the assembly of  FIG. 30 ; 
         FIG. 33  is an end view of the assembly of  FIG. 30 ; 
         FIG. 34  is a side-hidden-line view of the assembly of  FIG. 30 ; 
         FIG. 35  is an isometric view of an engine valvetrain for a pushrod-type valvetrain including eight helical torsion valve spring assemblies of  FIG. 30 ; 
         FIG. 36  is a top view of the engine valvetrain of  FIG. 35 ; 
         FIG. 37  is an enlarged cross-sectional view of the engine valvetrain taken along line  37 - 37  of  FIG. 36 ; 
         FIG. 38  is an exploded view of  FIG. 37 ; 
         FIG. 39  is an isometric cross-sectional view of the engine valvetrain taken along line  37 - 37  of  FIG. 36  and also includes lower valvetrain components to show both the exhaust and intake valves being closed; 
         FIG. 40  is a partial-side-hidden-line cross-sectional view of the engine valvetrain of  FIG. 39  showing the intake valve closed; 
         FIG. 41  is another isometric cross-sectional view of the engine valvetrain of  FIG. 39 , except showing the intake valve being open; and 
         FIG. 42  is a partial-side-hidden-line cross-sectional view of the engine valvetrain of  FIG. 41  showing the intake valve open. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIGS. 1 through 6 , a helical torsion valve spring assembly  100  having a helical torsion spring  12  which is intended for applying a biasing force to a valve is shown according to an embodiment of the invention. As shown in  FIG. 1 , the assembly  100  includes a frame  11 , which can be machined from rectangular tubing using conventional manufacturing processes. The frame  11  includes a pair of opposing side walls  22 ,  23 , each of which connects to a top wall  24  and a bottom wall  27 , and each of which has a hole  19 ,  18 . The holes  19 ,  18  interface with shaft  15  around which bushing  13  and spacer  14  are coaxially mounted, and with helical torsion spring  12  surrounding bushing  13 , all of which are captured inside the frame  11 . The shaft  15  can be secured by an interference fit with holes  19 ,  18 . The spacer  14  separates the helical torsion spring  12  and bushing  13  from side wall  22 . The helical torsion spring  12  has a coil  38 , a stationary leg  32 , which contacts the bottom wall  27  of the frame  11 , and a moving leg  34 , which contacts the top wall  24  of the frame  11 . One advantage of the invention is that the moving leg  34  contacts a spring contact surface  26  on the top wall  24  such that the helical torsion spring  12  is precisely held within the frame  11  in a statically loaded state to enhance the installation process of a valve spring retainer of an engine valvetrain. In the illustrated embodiment, spring contact surface  26  is in the form of a notch, and the like, that holds moving leg  34  of helical torsion spring  12  to provide a precise relationship of moving leg  34  and locating feature  21  to aid the installation of the assembly  100  into an engine valvetrain. The locating feature  21  interfaces with a conformal feature of a cylinder head. The seating surface  25  which is the underside of bottom wall  27  contacts a surface of a cylinder head during use, as described in more detail below. The moving leg  34  has a convex surface  36  that contacts a flat surface of a valve spring retainer to apply a biasing force to a valve during use, as described in more detail below. The frame  11  protects the coil  38 , which is highly-stressed during use. It can also be realized that the end of the frame  11  can be covered by an additional part to provide further protection for the coil  38 . 
       FIG. 2  shows a pair of helical torsion spring assemblies  100 ,  200 , which are mirror images of each other.  FIGS. 3-6  show four views of the helical torsion valve spring assembly  100 :  FIG. 3  is a top-hidden-line view,  FIG. 4  is a front view,  FIG. 5  is a side-hidden-line view, and  FIG. 6  is a rear view. It can be seen from  FIGS. 3-6  that the application of force to the convex surface  36  of the helical torsion spring  12  cannot cause the helical torsion valve spring assembly  100  to tip over. Furthermore, any undesirable sideways motion can be prevented by having locating feature  21  in the bottom wall  27  of the frame  11  disposed about a suitable feature of the cylinder head (not shown) having a complimentary shape. 
     Referring now to  FIGS. 7 through 11 , a helical torsion valve spring assembly  300  having two helical torsion springs  320 ,  340  with each spring intended for applying a biasing force to a single valve of an engine valvetrain is shown according to another embodiment of the invention.  FIG. 11  shows details, including a frame  301 , which can be machined from rectangular tubing using conventional manufacturing processes. The frame  301  includes a side wall  308  which connects to top walls  309 ,  310  which each connect to a side wall  306 ,  307  each of which are opposite side wall  308 . A bottom wall  311  connects to side walls  306 ,  307 ,  308 . Spring contact surfaces  319 ,  314 , in the form of notches, and the like, are located on the top walls  309 ,  310 . Bottom wall  311  has a seating surface  312 , also shown in  FIG. 9 , on the underside and two locating features  316 ,  317  which are also shown in  FIG. 8 . 
     Opposing walls  308 - 306  have a pair of holes  304 - 305 , and opposing walls  308 - 307  have a pair of holes  302 - 303  with each pair of holes  304 - 305 ,  302 - 303  interfacing with a shaft  370 ,  371 . A helical torsion spring  320 ,  340  surrounding a bushing  360 ,  361  surrounds each shaft  370 ,  371 , all of which are captured inside the frame  301 . The shafts  370 ,  371  can be secured by an interference fit with the holes  304 - 305 ,  302 - 303 . 
     Each helical torsion spring  320 ,  340  has a coil  328 ,  348 , a stationary leg  322 ,  342  which contacts the bottom wall  311  of the frame  301 , and a moving leg  324 ,  344  which contacts a spring contact surface  319 ,  314  of the frame  301  such that the helical torsion springs  320 ,  340  are precisely held in the frame  301  in a statically loaded state to enhance the installation process of a valve spring retainer  516 ,  515  of an engine valvetrain  500 , as will be discussed in greater detail. A further benefit is to provide a precise relationship of the moving legs  324 ,  344  to locating features  316 ,  317  to aid the installation of the assembly  300  onto a cylinder head and valvetrain. The moving leg  324 ,  344  of each helical torsion spring  320 ,  340  has a convex surface  326 ,  346  that contacts a flat surface of a valve spring retainer during use, as will be described in more detail. The frame  301  protects the coils  328 ,  348 , which are highly-stressed during use. It can also be realized that each end of frame  301  can be covered by an additional part to provide further protection. 
     Referring now to  FIGS. 12 through 17 , a helical torsion valve spring assembly  400  including two pairs of helical torsion springs  440 - 441 ;  420 - 421 , each of which is intended for applying a biasing force to a valve of an engine valvetrain, is shown according to another embodiment of the invention.  FIG. 17  shows details, including the frame  401 , which can be machined from rectangular tubing using conventional manufacturing processes. The frame  401  includes a side wall  408  which connects to top walls  409 ,  410  each of which connects to a side wall  406 ,  407  which is opposite side wall  408 . A bottom wall  411  connects to side walls  406 ,  407 ,  408 . Spring contact surfaces  418 - 419 ,  414 - 415 , in the form of notches, and the like, are located on the top walls  409 ,  410 . Bottom wall  411  has a seating surface  412  on the underside, also shown in  FIG. 15 , and two locating features  416 ,  417  which are also shown in  FIG. 13 . 
     Opposing walls  408 - 406  have a pair of holes  404 - 405 , and opposing walls  408 - 407  have a pair of holes  402 - 403  with each pair of holes  404 - 405 ,  402 - 403  interfacing with a shaft  470 ,  471 . A pair of helical torsion springs  420 - 421 ,  440 - 441  surrounding a bushing  460 ,  461  surrounds each shaft  470 ,  471 , all of which are captured inside the frame  401 . The shafts  470 ,  471  can be secured by an interference fit with the holes  404 - 405 ,  402 - 403 . 
     Each helical torsion spring  420 ,  421 ,  440 ,  441  has a coil  428 ,  429 ,  448 ,  449 , a stationary leg  422 ,  423 ,  442 ,  443  which contacts bottom wall  411  of frame  401 , and a moving leg  424 ,  425 ,  444 ,  445 , which contacts a spring contact surface  418 ,  419 ,  414 ,  415  of the frame  401  such that the helical torsion springs  420 ,  421 ,  440 ,  441  are precisely held in frame  401  in a statically loaded state  482 ,  486  as shown in  FIG. 16  and described in detail below to enhance the installation process of a valve spring retainer  515 ,  516  of an engine valvetrain  500 , as described in  FIGS. 18-29 . A further benefit is to provide a precise relationship of the moving legs  424 ,  425 ,  444 ,  445  to locating features  416 ,  417  to aid the installation of the assembly  400  into an engine valvetrain  500  (referring to  FIGS. 18-21 ). The moving legs  424 ,  425 ,  444 ,  445  of each helical torsion spring  420 ,  421 ,  440 ,  441  have convex surfaces  426 ,  427 ,  446 ,  447  which contact a flat surface  536 ,  535  of a valve spring retainer  516 ,  515  during use, as described in more detail in  FIGS. 22-29  below. The frame  401  protects the coils  428 ,  429 ,  448 ,  449 , which are highly-stressed during use. It can also be realized that each end of frame  401  can be covered by an additional part to provide further protection. 
       FIG. 16  shows helical torsion springs  421 ,  441  in each of four states of loading. Listed in order of the magnitude of loading from zero to highest: a) a free state  481 ,  485 , which is a “zero-load” condition; b) a statically loaded state  482 ,  486  as the springs  421 ,  441  are held in place in the helical torsion valve spring assembly  400 ; c) a valve-closed state  483 ,  487 ; and d) a valve-open state  484 ,  488 . As used herein, a “statically loaded state” is defined as the state  482 ,  486  in which a moving leg  425 ,  445  of a helical torsion spring  421 ,  441  contacts the spring contact surface  419 ,  415  of the frame  401 . It will be appreciated that the “statically loaded state” as discussed for the helical torsion valve spring assembly  400  applies to all helical torsion valve spring assemblies discussed herein. It will also be appreciated that the statically loaded state  482 ,  486  as discussed for helical torsion springs  421 ,  441  applies to all helical torsion springs discussed herein. 
     For the helical torsion valve spring assembly  400 , having the helical torsion spring pairs  420 - 421 ,  440 - 441  mounted on bushings  460 ,  461  provides precise location, and insures that there is only one mode of bending load applied to the coils  428 ,  429 ,  448 ,  449 . This is the most efficient use of the spring material and helps to achieve higher coil frequency, and causes rotary motion of the moving legs  424 ,  425 ,  444 ,  445  about the center of the bushing so that the movement of the convex surfaces  426 ,  427 ,  446 ,  447  is a controlled precision motion in relation to locating features  416 ,  417  and seating surface  412  of frame  401  so as to help minimize the size required for the valve spring retainer  515 ,  516 . It will be appreciated that this relationship as discussed for helical torsion valve spring assembly  400  applies to all helical torsion valve spring assemblies  100 ,  200 ,  300 ,  400 ,  700  described herein. It can also be realized that while frames  11 ,  301 ,  401  can be machined from rectangular tubing, a similar structure can be manufactured from stamped metal by using a design similar to frame  701  which is shown in  FIGS. 30-34 . One can also realize that while stationary legs  422 - 423 ,  442 - 443  of helical torsion springs  420 - 421 ,  440 - 441  are shown contacting bottom wall  411 , the same essential result can be achieved by having stationary legs  422 - 423 ,  442 - 443  contact a top wall  409 ,  410 . This principle applies to all helical torsion valve spring assemblies  100 ,  200 ,  300 ,  400 ,  700  discussed herein. 
     Referring now to  FIGS. 18 and 19 , an engine valvetrain  500  is shown according to an embodiment of the invention. In the illustrative embodiment, the engine valvetrain  500  is typical of a modern automotive diesel engine, except that in place of the conventional helical-compression-type valve springs, the engine valvetrain  500  incorporates a plurality of helical torsion valve spring assemblies  400 .  FIG. 20  is a cross-sectional view of a single-cylinder of the engine valvetrain  500  of  FIG. 19  and having the camshafts  550 ,  560  and bearing caps  536  removed to reveal the mounting hole  534  for a fuel injector not shown and two helical torsion valve spring assemblies  400 . However, it will be appreciated by one skilled in the art that the invention is not limited by the number of helical torsion valve spring assemblies  400  that are included in the engine valvetrain  500 , and the invention can be practiced with any desirable number of helical torsion valve spring assemblies  400 . 
       FIG. 21  is an isometric sectional view of the engine valvetrain taken along line  21 - 21  of  FIG. 19 . 
       FIGS. 20 and 21  reveal that the spring coils  428 ,  429 ,  448 ,  449  of the helical torsion valve spring assemblies  400  are packaged away from the fuel injector hole  534 . It can be appreciated by one skilled in the art that using helical-compression-type valve springs that are concentric to the valves  501 ,  502  and surround valve stem seals  512  shown in  FIGS. 21 and 22 , as they are typically utilized, would result in having less space for the fuel injector mounting hole  534  in the center of the cylinder. 
       FIG. 22  is an exploded view of the cross-sectional view of  FIG. 21  revealing a cylinder head  520 , an exhaust valve  501  and intake valve  502  each of which have a seat face  503 ,  504 , a stem  505 ,  506 , a keeper groove  509 ,  510  and an axis  507 ,  508  and are coaxially mounted in valve guides  523 ,  524  of the cylinder head  520 . A valve stem seal  512  is coaxially mounted on each valve guide  523 ,  524  and contacts a valve stem  505 ,  506 . A lash adjuster  511  is captured in each mounting hole  531 ,  532  of the cylinder head  520 , each having a spherical bearing surface  519  which interfaces with a spherical socket  542  of a roller finger follower  541 , which has a roller  543  and a valve tip pad  544  that contacts a valve  501 ,  502 . An exhaust camshaft  550  and an intake camshaft  560  each have cam lobes  551 ,  561  and base circles  552 ,  562  that interface with a roller  543  to transmit force through a roller finger follower  541  to control the motion of a corresponding valve  501 ,  502 . The seating surface  412  of the helical torsion valve spring assembly  400  seats on surface  530  of the cylinder head  520 , and the locating features  416 ,  417  interface with cylindrical features  525 ,  526  of the cylinder head  520  to achieve precise location and to prevent undesirable sideways motion of the helical torsion valve spring assembly  400 . A retainer  515 ,  516  is fastened to each valve  501 ,  502  in a conventional way having two keepers  513  contacting a retainer  515 ,  516  and a keeper groove  509 ,  510  of each valve  501 ,  502 . Force from each helical torsion spring pair  420 - 421 ,  440 - 441  biases a valve  502 ,  501  towards a closed position such that a seat face  504 ,  503  contacts a valve seat  528 ,  527  of the cylinder head  520 . 
     As shown in  FIGS. 18-26 , each retainer  516 ,  515  has a flat surface  536 ,  535  that contacts the convex surfaces  426 - 427 ,  446 - 447  of the moving legs  424 - 425 ,  444 - 445  of the helical torsion spring pairs  420 - 421 ,  440 - 441  to couple the reciprocating-rotary motion of the moving legs  424 ,  425 ,  444 ,  445  with the reciprocating-linear motion of the retainers  516 ,  515  in such a way that allows for acceptable contact pressures at the interface there between. 
       FIG. 23  is another isometric cross-sectional view similar to  FIG. 21 , and  FIGS. 24-26  are side views of  FIG. 21 . 
       FIG. 24  shows the base circles  562 ,  552  each contacting a roller  543  to cause the corresponding intake and exhaust valves  502 ,  501  to be in the closed position. The two visible helical torsion springs  421 ,  441  are in the valve-closed state  483 ,  487 . 
     In  FIG. 25 , the cam lobe  551  is now contacting a roller  543  to cause the exhaust valve  501  to be in the open position and the helical torsion spring  441  to be in the valve-open state  488 , while the base circle  562  is contacting a roller  543  to cause the intake valve  502  to be closed with the helical torsion spring  421  being in the valve-closed state  483 . 
     In  FIG. 26 , the cam lobe  561  is now contacting a roller  543  to cause the intake valve  502  to be in the open position and the helical torsion spring  421  to be in the valve-open state  484 , while the base circle  552  is contacting a roller  543  to cause the exhaust valve  501  to be closed and the helical torsion spring  441  to be in the valve-closed state  487 . 
       FIGS. 27 ( a - e ) are partial isometric cross-sectional views of the upper section of  FIG. 21  showing the sequence of steps for installing a valve spring retainer  515  to couple the helical torsion valve spring assembly  400  to exhaust valve  501  in accordance with a method of the invention. In the illustrated method, the installation of a retainer  515  is described. The engine valvetrain  500  shown is partially completed with the intake and exhaust valves  501 ,  502 , valve stem seals  512  and helical torsion valve spring assembly  400  already in place, and having retainer  516  already installed onto intake valve  502 . It will be appreciated that installing a retainer  515  onto exhaust valve  501  is discussed herein, however the principles of the invention can also be applied to installing retainer  516  onto intake valve  502 . 
     First, a retainer  515  is positioned above exhaust valve  501  with the axis  507  of exhaust valve  501  being substantially aligned with a hole  517  of retainer  515 , as shown in  FIG. 27( a ) . 
     Next, as shown in  FIG. 27( b )  and  FIG. 28 , an enlarged version of  FIG. 27( b ) , the retainer  515  surrounds axis  507  and stem  505  of valve  501 , and flat surface  535  of retainer  515  contacts convex surfaces  446 ,  447  of moving legs  444 ,  445  of helical torsion springs  440 ,  441 . The moving legs  444 ,  445  each contact a spring contact surface  414 ,  415  of the frame  401 . One aspect of the invention is that the moving legs  444 ,  445  of the helical torsion spring assembly  400  are in the statically loaded state  486  while in contact with spring contact surfaces  414 ,  415  of the frame  401 . This enables the retainer  515  to be easily placed around axis  507  and stem  505  of exhaust valve  501  in a single straight-line motion to contact the convex surfaces  446 ,  447 , and without the need for the installer to engage the helical torsion springs  440 ,  441   
     Next, as shown in  FIG. 27( c ) , the installer applies force to push the retainer  515  down farther around the stem  505  of the exhaust valve  501 , thereby displacing moving legs  444 ,  445  out of contact with spring contact surfaces  414 ,  415  of the frame  401  and leaving keeper groove  509  exposed above the retainer  515 . Next, as shown in  FIG. 27( d ) , the two keepers  513  are installed in keeper groove  509  of valve  501  with retainer  515  held farther down the stem  505 .  FIG. 27( e )  shows both retainers  516 ,  515  installed with helical torsion springs  421 ,  441  being in the valve-closed state  483 ,  487  and the other helical torsion springs  420 ,  440  being in a likewise condition. All of the moving legs  424 - 425 ,  444 - 445  are out of contact with the frame  401  such that the force from each torsion spring pair  420 - 421 ,  440 - 441  is acting to bias valves  502 ,  501  into the closed position. This process for installing a retainer  515  onto a valve  501  applies to all of the helical torsion valve spring assemblies  100 ,  200 ,  300 ,  400 ,  700  discussed herein. 
     Hence, the helical torsion valve spring assembly  100 ,  200 ,  300 ,  400 ,  700  of the invention enables conventional processes for installing a helical torsion valve spring assembly  100 ,  200 ,  300 ,  400 ,  700  onto a cylinder head  520 ,  820  of an engine valvetrain  500 ,  800 , and for installing a retainer  515 ,  516 ,  815 ,  816  onto a valve  501 ,  502 ,  801 ,  802 . These processes are essentially the same as those for conventional helical-compression-type valve springs. Thus, the functional improvements associated with helical torsion valve springs  420 ,  421 ,  440 ,  441 ,  720 ,  740  can be realized with no undesirable aspects during the assembling or servicing of the engine valvetrain  500 ,  800 , and to avoid damage to an engine component, and also with regards to the safety of the engine builder. 
       FIG. 29  is an exploded-partial-side view of  FIG. 21  showing two helical torsion springs  421 ,  441  in a statically loaded state  482 ,  486  and a free state  481 ,  485  in phantom. This illustrates the advantages associated with having torsion springs  420 - 421 ,  440 - 441  held in a statically loaded state  482 ,  486  in the helical torsion valve spring assembly  400  of the invention in order to facilitate easy and safe installation of the retainers  515 ,  516 . One can realize that should an attempt be made to install helical torsion valve springs  420 - 421 ,  440 - 441  starting from the free state  481 ,  485  position it would require two coordinated motions—one for moving the spring legs  424 - 425 ,  444 - 445  in first a sideways and then a downwards direction, and second for pushing the retainer  515 ,  516  down around the valve stem  505 ,  506 . This process is more complicated and liable to result in damage to an engine component or possibly an accident of some kind—or could necessitate a larger, heavier retainer  515 ,  516 . It is an object of this invention to facilitate safe and easy installation of retainers  515 ,  516  to aid assembly of engines and servicing of engines. Furthermore, it can be realized that having the moving legs  424 - 425 ,  444 - 445  very close to the valve stems  505 ,  506  enables use of the smallest diameter for the retainer  515 ,  516 , which benefits the function of the valvetrain by minimizing the reciprocating mass. Also, having moving legs  424 - 425 ,  444 - 445  precisely held in spring contact surfaces  418 - 419 ,  414 - 415  can enhance the installation of valves  505 ,  506  into the cylinder head  520  after the helical torsion valve spring assembly  400  has been installed onto the cylinder head  520 . 
     Referring to  FIGS. 30 through 34 , a helical torsion valve spring assembly  700  contains two helical torsion springs  720 ,  740  which are intended for applying a biasing force to a single valve of an engine valvetrain, is shown according to another embodiment of the invention.  FIG. 30  is an exploded view that shows details including the frame  701 , which can be made from a single sheet metal stamping using conventional manufacturing processes. The frame  701  includes a pair of opposing side walls  706 ,  708 , which each have a top wall  709 ,  710  and each connect to a bottom wall  711 . The top walls  709 ,  710  are located in diagonally opposite corners of the frame  701  and each has a spring contact surface  713 ,  714 , in the form of a notch, and the like. Bottom wall  711  has opening  715 , locating feature  716  and a seating surface  712  on the underside. 
     Side walls  706 ,  708  contain two pairs of holes  705 - 704 ,  703 - 702  which each interface with a shaft  770 ,  771  that is surrounded by a bushing  760 ,  761 , and having a helical torsion spring  720 ,  740  surrounding each bushing  760 ,  761 , all of which are captured inside the frame  701 . The shafts  770 ,  771  can be secured by an interference fit with the holes  705 - 704 ,  703 - 702 . 
     Each helical torsion spring  720 ,  740  has a coil  728 ,  748 , a stationary leg  722 ,  742  which has a bottom surface  723 ,  743  which contacts a surface  773 ,  772  on the opposite shaft  771 ,  770 , as shown in  FIG. 34 . Each stationary leg  722 ,  742  is captured in between the end surface  763 ,  762  of a bushing  761 ,  760  and the inner surface  718 ,  717  of a side wall  708 ,  706 . Each helical torsion spring  720 , 740  also has a moving leg  724 ,  744  which contacts a spring contact surface  713 ,  714  of the frame  701  so that each helical torsion spring  720 ,  740  is precisely held in a statically loaded state to enhance the installation process of a valve spring retainer  815 ,  816  of an engine valvetrain  800 , as shown in  FIGS. 35-42 , in the same way as previously described for helical torsion valve spring assembly  400  in engine valvetrain  500 . The moving leg  724 ,  744  of each helical torsion spring  720 ,  740  has a convex surface  726 ,  746  which is intended to be the loaded interface as it is used in service. The helical torsion valve spring assembly  700  is shown in isometric view in  FIG. 31 , in a top-hidden-line view in  FIG. 32 , in end view in  FIG. 33 , and in side-hidden-line view in  FIG. 34 . 
     An axis  719  extends between side walls  706 ,  708  through opening  715 , as shown in  FIGS. 31-32  and  FIG. 34 , where it can be seen that the moving legs  724 ,  744  of the helical torsion springs  720 ,  740  are on opposite sides of axis  719 , and shafts  770 ,  771  are also on opposite sides of axis  719 . As used in service, axis  719  is intended to align with the axis  807 ,  808  of a valve  801 ,  802 , as described below. Frame  701  protects the spring coils  728 ,  748 , which are highly-stressed during use. It can also be realized that each end of frame  701  can be covered by an additional part to provide further protection. 
       FIGS. 35-38  show an engine valvetrain  800  with a plurality of helical torsion valve spring assemblies  700  according to an embodiment of the invention. Specifically,  FIG. 35  shows an engine valvetrain  800  that is typical for one bank of a V-8 engine having a pushrod-type valvetrain, except the engine valvetrain  800  contains eight helical torsion valve spring assemblies  700 .  FIG. 37  is an enlarged cross-sectional view of a single-cylinder group of the engine valvetrain  800  of  FIG. 36 . However, it will be appreciated by one skilled in the art that the invention is not limited by the number of helical torsion valve spring assemblies  700  that are included in the engine valvetrain  800 , and the invention can be practiced with any desirable number of helical torsion valve spring assemblies  700 . 
       FIG. 38  is an exploded view of  FIG. 37  showing one cylinder section of the engine valvetrain  800  revealing a cylinder head  820 , an exhaust valve  801  and intake valve  802  each of which has a seat face  803 ,  804 , a stem  805 ,  806 , a keeper groove  809 ,  810  and an axis  807 ,  808  with each valve  801 ,  802  coaxially mounted in valve guides  825 ,  824  of cylinder head  820 . A valve stem seal  812  is coaxially mounted on each valve guide  825 ,  824  and contacts a valve stem  805 ,  806 . The valve tip  811 ,  812  of each valve  801 ,  802  contacts a valve tip pad  844  of a rocker arm  842  that has a ball-socket  845  and that is rotatably coupled to a fulcrum  843  that is fixed to an extension  839  of cylinder head  820  such that reciprocating-rotary motion of a rocker arm  842  can cause opening and closing of an exhaust valve  801  or intake valve  802 . A pedestal  871 ,  872  has a bottom surface  873 ,  874  that seats against a flat surface  831 ,  832  of cylinder head  820 , and a round hole  877 ,  878  which interfaces with a cylindrical surface  833 ,  834  of cylinder head  820  to prevent sideways motion. A seating surface  712  of a frame  701  of a helical torsion valve spring assembly  700  seats against the top flat surface  875 ,  876  of a pedestal  871 ,  872 , and has a locating feature  716  interfacing with outside round surface  879 ,  880  of a pedestal  871 ,  872  to prevent sideways motion and to align a valve axis  807 ,  808  with axis  719 . A retainer  815 ,  816  is attached to each valve stem  805 ,  806  in the conventional way having a pair of keepers  813  engaging a keeper groove  809 ,  810  of each valve  801 ,  802 . The convex surfaces  726 ,  746  of both helical torsion springs  720 ,  740  of a helical torsion valve spring assembly  700  contact the bottom flat surface  835 ,  836  of a retainer  815 ,  816  to apply force to bias a valve  801 ,  802  towards the closed position such that a seat face  803 ,  804  contacts a valve seat  827 ,  828  of cylinder head  820 . The axis  807 ,  808  of each valve  801 ,  802  is essentially aligned with axis  719  of a helical torsion valve spring assembly  700  such that a pair of moving spring legs  724 ,  744  are on opposite sides of the stem  805 ,  806  of a valve  801 ,  802 , as shown in  FIG. 37 . 
     Convex surfaces  726 ,  746  of moving legs  724 ,  744  of helical torsion springs  720 ,  740  contact the flat surface  836 ,  835  of a retainer  816 ,  815  to couple the reciprocating-rotary motion of the moving legs  724 ,  744 , which angularly displace about the axis of a bushing  761 ,  760  during a valve lift event, with the reciprocating-linear motion of a retainer  815 ,  816 , which is coupled to a valve  801 ,  802 , in a way that allows for acceptable contact pressures at the contact interface. 
       FIGS. 39 and 41  are additional views of the engine valvetrain  800 , and also include the lower valvetrain components including a camshaft  901 , which has exhaust and intake cam lobes  913 ,  914 , each associated with a base circle  911 ,  912 , and having lifters  931 ,  932  which intermittently contact either a base circle  911 ,  912  or a cam lobe  913 ,  914 . Pushrods  941 ,  942  each engage a lifter  931 ,  932  in a conventional way and at the other end engage a ball socket  845  of a rocker arm  842  such that rotary motion of the camshaft  901  causes the valves  801 ,  802  to be intermittently lifted. 
     In  FIG. 39 , each lifter  931 ,  932  contacts a base circle  911 ,  912 , hence both exhaust and intake valves  801 ,  802  are closed such that seat faces  803 ,  804  each contact a valve seat  827 ,  828 . 
     In  FIG. 41 , lifter  932  is now contacting cam lobe  914  causing intake valve  802  to be open such that seat face  804  is no longer contacting valve seat  828 . 
       FIGS. 40 and 42  are partial-side-hidden-line views showing only certain components from  FIGS. 39 and 41 , respectively: the intake valve  802 , valve guide  824 , pedestal  872 , valve stem seal  512 , helical torsion valve spring assembly  700 , retainer  816  and keepers  813 . 
     In  FIG. 40 , which is a partial view of  FIG. 39 , the intake valve  802  is closed, and the moving legs  724 ,  744  of the helical torsion valve spring assembly  700  are contacting the flat surface  836  of the retainer  816 . 
     In  FIG. 42 , which is a partial view of  FIG. 41 , the intake valve  802  is now open, and the moving legs  724 ,  744  of the helical torsion valve spring assembly  700  are contacting the flat surface  836  of the retainer  816  and can be seen having been displaced in response to the intake valve  802  being lifted. 
     A further advantage of this configuration can be realized if the helical torsion springs  720 ,  740  are identical and are mounted around shafts  770 ,  771  which are parallel and equidistant from axis  719 , and having moving legs  724 ,  744  equidistant from axis  719 . Using this arrangement, zero side-loading on the valve stem during the valve lift event will result because the frictionally-induced forces in the transverse direction are equal and opposite to cancel each other out. Furthermore, forces that are applied normal to the flat surface  835 ,  836  of a retainer  815 ,  816 , at any time during the valve lift event, are at two points which are equidistant from, and on opposite sides of, a valve axis  807 ,  808  such that the net loading on a retainer  815 ,  816  is precisely centered on the valve axis  807 ,  808 . Hence, a biasing force to a valve  801 ,  802  can be applied while incurring zero side loading to a valve  801 ,  802  to help minimize wear at the interface of a stem  805 ,  806  and valve guide  825 ,  824  and to reduce friction. Conversely, a helical-compression-type valve spring that is mounted coaxially with a valve  801 ,  802 , due to having its active coil terminating at a point offset from the valve axis  807 ,  808 , incurs offset force application into a retainer  815 ,  816  that results in loading at the stem  805 ,  806  and guide  824 ,  825  interface. 
     The arrangement shown in  FIGS. 35-38  shows each helical torsion valve spring assembly  700  mounted on a pedestal  871 ,  872 , which enables one helical torsion valve spring assembly  700  design to be applied to exhaust and intake valves  801 ,  802  having different valve lift or spring force requirements by adopting different sizes of pedestals  871 ,  872 . Likewise, this arrangement allows the same helical torsion valve spring assembly  700  to be applied to different engines, as well. However, it can be appreciated by one skilled in the art that a bottom extension can be added to the frame  701  such that the seating surface  712  is offset from the bottom wall  711  to eliminate the need for the pedestal. This principle also applies to all of the helical torsion valve spring assemblies  100 ,  200 ,  300 ,  400 ,  700  discussed herein. It can also be realized that while the frame  801  is stamped-metal type of construction, a similar structure can be manufactured by machining a section of rectangular tubing similar to frames  301 ,  401  which were previously described. 
     It should be noted that the helical torsion valve spring assembly  700  as shown in engine valvetrain  800  is not constrained from rotating about axis  719 . However, the frictional hold torque between the seating surface  712  of the frame  701  and the top surface  875 ,  876  of the pedestal  871 ,  872  can be expected to exceed the torque generated by the two springs  720 ,  740  during a valve lift event because the contact radius of the pedestal  871 ,  872  is larger than the retainer  815 ,  816 . Hence, the frame  701  can remain stationary during operation. This same principle applies to helical torsion valve spring assemblies  100  and  200 . It can also be realized that anti-rotation features can be implemented to prevent undesired rotation. 
     One can realize that bushing  760 ,  761 , and other bushings previously described, can be eliminated by increasing the outside diameter of shafts  770 ,  772  such that they provide a mounting surface for helical torsion springs  720 ,  740 . One can also realize that while stationary legs  422 - 423 ,  442 - 443  of helical torsion springs  420 - 421 ,  440 - 441  are shown contacting bottom wall  411  of frame  401 , the same essential result can be achieved by having a stationary leg  422 - 423 ,  442 - 443  contacting a top wall  409 ,  410  or any other feature of the assembly  400  that grounds a stationary leg  422 - 423 ,  442 - 443  to the frame  401  either directly or indirectly. One can also realize that while frame  401  has top walls  409 ,  410  with spring contact surfaces  418 ,  419 ,  414 ,  415  for mounting the moving leg  424 ,  425 ,  444 ,  445  of a helical torsion spring  420 ,  421 ,  440 ,  441 , it is possible replace a top wall with an additional part attached to the frame to provide the same feature. One can also realize that while seating surface  412  for contacting a cylinder head  520  is part of the bottom wall  411  of frame  401 , it is possible to eliminate the bottom wall  411  and have the edge of a side wall  406 ,  407 ,  408  form a seating surface  412  to achieve the same result. Furthermore, while the engine valvetrain  500  described herein has a single seating surface  412  of the bottom wall  411  of a frame  401  contacting a single surface  530  of the cylinder head  520 , it can be realized that a plurality of contact interfaces between a frame  401  and a cylinder head  520  can be used to achieve the same result. These principles apply for all helical torsion valve spring assemblies  100 ,  200 ,  300 ,  400 ,  700  discussed herein. 
     While the invention has been specifically described in connection with various embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.