Abstract:
A throttle valve for an internal combustion engine includes a cylindrical valve housing and a spherical segment valve disc mounted within the valve housing. The spherical segment valve disc seals with the valve housing without the need for abutting interference between the valve disc or throttle plate and the valve housing.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an air throttle valve for controlling the air flowing through an internal combustion engine, such as a spark ignited or compression ignition internal combustion engine. 
     Throttle valves have been used with internal combustion engines for well over a century. Most commonly used throttle valves include a round or oval plate, usually made of brass or aluminum. The throttle plate extends through a slotted, or slab cut, rotatable shaft which passes through the walls of an air passage. Typically, the air passage may be incorporated in a device such as a throttle body for use within a fuel injected engine; alternatively, the air passage may be incorporated into the housing of a mixing device such as a carburetor. Throttle devices with oval plates rely upon a nearly line-on-line contact between the majority of the throttle blade periphery and the throttle housing to achieve a near-zero or low airflow condition corresponding to engine idle operation. However, to avoid sticking of the throttle plate it is necessary to maintain a clearance between the throttle plate and the bore within which the plate is housed. Unfortunately, it is very difficult to achieve a precise low flow condition with conventional valve geometry, because air leakage through the clearance regions causes widely varying airflow. 
     A throttle valve assembly according to present invention solves problems inherent with known throttle valves by providing a throttle plate having a spherical section which rides directly upon the throttle bore, so as to provide superior sealing of the throttle plate in the bore. Because the spherical section throttle plate has only a single defining dimension, the orientation issues arising with other plate geometries are avoided. 
     SUMMARY OF THE INVENTION 
     A throttle valve for internal combustion engine includes a generally cylindrical valve housing having inside diameter and a throttle plate pivotally mounted within the valve housing. The throttle plate includes a valve disc having an outer rim shaped as a spherical segment, with the valve disc having an outside diameter proximate the inner diameter of the valve housing. Pivots extend through apertures formed in the valve housing and into contact with the valve disc. The present throttle valve further includes a sensor for determining the rotational position of the throttle plate and a motor assembly for positioning a throttle plate. In a preferred embodiment, the throttle plate and the generally cylindrical valve housing may be formed from the same type of powdered metal, such as powdered iron, or other types of powdered or other metals known to those skilled in the art and suggested by this disclosure. The valve disc and valve housing may advantageously be coated with a manganese phosphate finish which impedes corrosion while serving as a break-in coating of the parts. 
     In order to operate the present assembly efficiently, the motor assembly may include a motor connected with a double or triple reduction gear train. 
     According to another aspect of the present invention, valve disc used in the present throttle body includes a ring-shaped structure surrounding a thinner circular core. The ring-shaped structure has an outer diameter shaped as a spherical segment, which allows the present valve disc to rotate within the throttle valve body or housing without binding or sticking. 
     According to another aspect of the present invention, the valve body or housing may be formed as a two piece assembly by separating a preform along fracture path extending through pivot apertures formed in the preform. 
     According to another aspect of the present invention, the valve disc may have integral and unitary pivots or, alternatively, the valve disk may have trunnions for accepting pivots inserted inwardly through apertures formed in the valve housing. 
     It is an advantage of a system according to the present invention that airflow to an engine may be very precisely controlled, notwithstanding the presence of contamination of the throttle bore, or extreme thermal gradients. 
     It is a further advantage of a system according to the present invention that the present throttle system may be manufactured without a need for excessive hand fitting of throttle valve discs within throttle valve bores. 
     It is a further advantage of a system according to the present invention that the throttle body and throttle valve may be constructed of the same material, so as to avoid problems with uneven thermal growth of the components. 
     It is a further advantage of a system according to the present invention that the present throttle valve assembly is more compact than known throttle valves, and is therefore useful for technical applications including not only main air throttles, but also manifold control valves and other air-routing and controlling applications. For this reason, as used herein, the terms “throttle valve” and “throttle system” refer to all of the previously enumerated types of air valves. 
     It is a further advantage of a system according to the present invention that the present throttle valve assembly is more resistant to damage from thermal excursions, such as those experienced either during backfire events or with engines operated with high exhaust gas recirculation (EGR) rates. 
     Other advantages, as well as features and objects of the present invention, will become apparent to the reader of this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an assembled throttle valve according to the present invention. 
         FIG. 2  is an exploded perspective view of the throttle valve shown in  FIG. 1 . 
         FIG. 3  is an exploded view of a portion of a second type of throttle valve according to the present invention. 
         FIG. 4  is an end elevation of a throttle plate according to one aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in  FIGS. 1 and 2 , valve assembly  10  has valve housing  14 , with inside diameter  18 . Bearing races  42  ( FIG. 2 ) provide housings for a plurality of bearing balls  46  which allow stub shafts  50  to pivot with respect to valve housing  14 . Throttle position sensor  24  and housing  82 , which mounts throttle positioning motor  78 , are located on opposite sides of valve housing  14 . As shown in  FIG. 3 , each stub shaft  50  accommodates additional hardware. In one case, rotor  32 , including brushes  33  of throttle position sensor  24 , is locked to one of stub shafts  50 . On the opposite side of valve assembly  10 , stub shaft  50  is locked to gear  78 , which is mounted within housing  82  and ultimately driven by motor  78 . 
     Valve assembly  10  is useful for employment with a drive-by-wire system in which the control of an engine throttle is achieved solely by means of electronics, as opposed to a more conventional mechanical cable assembly. Because valve housing  14  is generally cylindrical, the housing may be mounted conveniently in an air induction system or, even in an air inlet manifold, without the need for additional threaded fasteners. 
       FIGS. 1 and 2  also show throttle plate, or valve disc,  22 , which has an outer rim illustrated as a ring-shaped structure,  26 , which surrounds circular core  30 . This construction is shown more particularly in section in  FIG. 4 . Rim  26  is shaped as a spherical segment having an outside diameter which is slightly less than the inside diameter  18  of valve housing  14 . Because outer rim  26  of throttle plate  22  is shaped as a spherical segment, throttle plate  22  is resistant to becoming corked or stuck in the closed position within valve housing  14 , as sometimes occurs with known throttle plates. 
     Throttle plate  22  has two trunnions,  34 , formed integrally with ring-shaped structure  26  and circular core  30 . As shown in  FIG. 4 , each of trunnions  34  has a female spline,  38 , formed therein, which matches and is engaged by splines  52  formed at the inboard end of each of stub shafts  50 . Acting together, female spline  38 , and male spline  52  assure that throttle plate  22  is not free to rotate except as driven by motor  78  and gear train  66 . Each of trunnions  34  has an outer surface,  39 , which contacts the inner diameter  18  of housing  14 . Because surfaces  39  are spherical segments having the same radius of curvature as the outermost surface of ring-shaped structure  26 , surfaces  39  may ride freely upon inner diameter  18 , while at the same time providing optimal airflow control, particularly at the idle airflow position. Throttle plate  22  has three locating depressions  36  formed therein. Depressions  36  provide a convenient structure for mounting throttle plate  22  in a machine tool during manufacturing of the throttle plate. 
     Throttle disc  22  and valve housing  14  may advantageously be coated with a manganese phosphate finish which impedes corrosion, while serving as a break-in coating for these parts. The manganese phosphate coating also serves as an abradable seal between disc  22  and inner diameter  18  of housing  14 . 
       FIG. 3  illustrates a second embodiment of a throttle valve assembly according to present invention in which throttle plate  22  has integral stub shafts  56 , which are cast in place with the balance of throttle plate  22 . In order to permit mounting of throttle plate  22  within housing  82  upon pivot apertures  86 , housing  82  is formed as a two-piece assembly manufactured by separating a preform along fracture paths extending within shoulders  90  and through pivot apertures  86  Housing  82  is assembled by means of retainers  57  and snap rings  58 , which fit about shoulders  90 . Bearings  48  are provided to allow pivoting action of throttle plate  22  within housing  82 . Torsion spring  88  urges throttle plate  22  to its idle airflow position. Either one or two such torsion springs would be employed with the embodiment of  FIGS. 1 and 2 . 
     Notwithstanding that ball bearings  46  and  48  are shown with the various embodiments of the present invention, other types of antifriction bearings, or even plain bearing elements, could be used to practice present invention. 
     The inventors of the present throttle valve determined that the valve may be advantageously constructed from powdered metal such as ferrous or non-ferrous metals, or alternatively, other metallic or non-metallic composites or die or pressure-cast metals known to those skilled in the art and suggested by this disclosure. One advantageous combination is powdered iron, used for both throttle plate  22  as well as for housings  14  and  82 . Forming throttle plate  22  and housings  14  and  82  from the same material will avoid problems due to differential thermal expansion, while allowing the spherical outer surface of throttle plate  22  to be finished by grinding to a very fine surface detail, including the outboard-most surfaces,  39 , of trunnions  34 . In this manner, the outer portions of trunnions  34  will remain in contact with valve housing  14  when valve disk  22  is rotated by the throttle operator, in this case motor  78  and gear train  66 . 
     Although the present invention has been described in connection with particular embodiments thereof, it is to be understood that various modifications, alterations, and adaptations may be made by those skilled in the art without departing from the spirit and scope of the invention set forth in the following claims.