Patent Publication Number: US-6910451-B2

Title: Valve timing control system and method of producing valve timing control system

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a valve timing control system for controlling open-close timing of an intake valve and an exhaust valve of an internal combustion engine, in accordance with engine operating condition. 
   Moreover, the present invention relates to a method of producing the above mentioned valve timing control system. 
   Japanese Patent Unexamined Publication No. H9(1997)-324611 discloses a valve timing control system for variably controlling open-close timing of an intake valve and an exhaust valve by rotatably operating an angle at which a timing sprocket (which rotates synchronously with a crank shaft of an engine) is mounted relative to a cam shaft (which has an external periphery formed with a drive cam). 
   The valve timing control system  14  (referred to as “VVT mechanism  14 ” in Abstract) according to Japanese Patent Unexamined Publication No. H9(1997)-324611 has the following constitution: A cam shaft  13  has an end portion which is integrally mounting a vane member  37  (referred to as “impeller  37 ” in Abstract). A tubular housing has an external periphery which is integrally formed with a timing sprocket  25  (referred to as “cam sprocket  25 ” in Abstract). A plurality of bulkhead portions  42  are disposed in the tubular housing. Vane member  37  has a vane portion  39  (referred to as “blade  39 ” in Abstract). Vane member  37  is housed in the tubular housing so that each of an advanced-angle oil pressure chamber  51  and a delayed-angle oil pressure chamber  52  is formed between vane portion  39  and one of two adjacent bulkhead portions  42 . In accordance with engine operating condition, oil pressure is preferably supplied to and drained from each of advanced-angle oil pressure chamber  51  and delayed-angle oil pressure chamber  52 . Thereby, when a high-pressure operating oil is supplied to one of advanced-angle oil pressure chamber  51  and delayed-angle oil pressure chamber  52 , the tubular housing and vane member  37  make relative rotation in one rotational direction. With this, timing sprocket  25  and cam shaft  13  vary in respect of rotational phase, to thereby vary open-close timing of an intake valve  19  and an exhaust valve  20 . 
   The valve timing control system according to Japanese Patent Unexamined Publication No. H9(1997)-324611 uses oil pressure to operate the vane member and the like which constitute a phase variation mechanism. Therefore, it is necessary to stringently control any leak of operating oil in the tubular housing in order to encourage operational response of the valve timing control system. Therefore, in order to prevent the operating oil from leaking, each component part should have high production accuracy-and-precision. However, since the tubular housing is comparatively large in dimension, the tubular housing is likely to deform during production and operation. 
   Sintering the tubular housing and the timing sprocket into an integrated part is under consideration recently. The tubular housing is likely to deform (into a shape of a barrel) due to temperature contraction and the like during sintering. Deformation of the tubular housing has to be prevented. Moreover, sintering the tubular housing and the timing sprocket has a difficulty in enhancing mold (compact) density higher than a predetermined level. This makes it impossible to enhance strength and mold accuracy-and-precision of a sprocket portion. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a valve timing control system causing less operating oil leak and enhancing operational response, by securely preventing deformation of a tubular housing during production and operation of the tubular housing. 
   It is another object of the present invention to provide a method of producing the valve timing control system having features in the former paragraph. 
   According to a first aspect of the present invention, there is provided a valve timing control system. The valve timing control system comprises: a tubular housing; a cam shaft having an external periphery formed with a drive cam for operating an engine valve; a phase variation mechanism disposed in the tubular housing, and varying a rotational phase of the sprocket portion relative to the cam shaft in accordance with oil pressure supplied to the phase variation mechanism; and an oil pressure control measures for controlling the oil pressure supplied to the phase variation mechanism. The tubular housing comprises: a housing body having a density, and a sprocket portion for receiving a drive force transmitted from a crank shaft of an engine by way of a chain. The sprocket portion is disposed integrally to the tubular housing, and has a density higher than the density of the housing body. The tubular housing is so mounted to the cam shaft as to make a rotation relative to the cam shaft when so required. The cam shaft receives the drive force transmitted from the sprocket portion, to thereby rotate as a follower. 
   According to a second aspect of the present invention, there is provided a method of producing a valve timing control system. The method comprises the following sequential operations of: sintering a housing body of a tubular housing, and a sprocket portion of the tubular housing, so as to form an integrated sintered body; and form-rolling the sprocket portion of the sintered body so that the sprocket portion is higher in density than the housing body of the sintered body. 
   The other objects and features of the present invention will become understood from the following description with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross section taken along lines I—I in  FIG. 2 , according to a preferred embodiment of the present invention; 
       FIG. 2  is a cross section taken along lines II—II in  FIG. 1 ; 
       FIG. 3  is a cross section taken along lines III—III in  FIG. 4 ; 
       FIG. 4  is a cross section taken along lines IV—IV in  FIG. 3 ; 
       FIG. 5  is a front view showing a method of producing a tubular housing, according to the preferred embodiment of the present invention; and 
       FIG. 6  is a cross section of a housing body  8 A of the tubular housing, in which FIG.  6 (A) shows the housing body  8 A deformed, and FIG.  6 (B) shows the housing body  8 A corrected (straightened). 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Hereinafter described is concerning constitution of valve timing control system, according to a preferred embodiment of the present invention. 
   As is seen in  FIG. 1 , there is provided a cam shaft  1  on an intake side of an engine. Cam shaft  1  is rotatably supported, by way of a bearing, to a cylinder head (not shown). Moreover, the cam shaft  1  has a backbone whose external periphery is provided with a drive cam (not shown) for opening and closing an intake valve (as an engine valve). A valve timing control system  2  under the present invention is disposed at a first end (left in  FIG. 1 ) of cam shaft  1 . 
   Valve timing control system  2  is constituted of a housing member  4 , cam shaft  1 , a vane member  5 , an oil pressure control measures  6 , and a lock gear  7 . Housing member  4  has an external periphery integrally formed with a timing sprocket  3  which is connected to a crank shaft (not shown) by way of a chain (not shown). e Housing member  4  is so mounted to the first end of cam shaft  1  as to rotate when so required. Vane member  5  is integrally mounted at the first end of cam shaft  1 , and is rotatably housed in housing member  4 . Oil pressure control measures  6  supplies and drains oil pressure for turning vane member  5  forward and backward relative to housing member  4  in accordance with engine operating condition. Lock gear  7  controls fluctuation of vane member  5 , which fluctuation is involved with rotational variable torque acting on cam shaft  1 . 
   Housing member  4  is constituted of a tubular housing  8 , a front cover  10 , and a rear cover  11 . Tubular housing  8  is integrally formed with timing sprocket  3  which is substantially in the center on an external peripheral surface of tubular housing  8  in an axial direction (horizontal in FIG.  1 ). Front cover  10  is shaped substantially into a circular plate, and is connected to a front end (left in  FIG. 1 ) of tubular housing  8  with a plurality of bolts  9 . Rear cover  11  is shaped substantially into a circular plate, and is connected to a rear end (right in  FIG. 1 ) of tubular housing  8  with the plurality of the bolts  9 . As is seen in  FIG. 2 , tubular housing  8  has an internal peripheral surface provided with four partition walls  12  which are disposed circumferentially at angular intervals of substantially 90 degrees. Each partition wall  12  has a cross section shaped substantially into a trapezium. 
   Vane member  5  is provided with a shell portion  13  and four vane portions  14 . Shell portion  13  is coupled with the first end of cam shaft  1 , and is shaped substantially into a cylinder. Shell portion  13  is disposed in a shaft center of housing member  4 . Four vane portions  14  project radially on an external peripheral surface of shell portion  13 . Each of four vane portions  14  is disposed between two adjacent partition walls  12  of tubular housing  8 . An advanced-angle oil pressure chamber  15  is defined between a first side surface of one of vane portions  14  and opposed partition wall  12 . A delayed-angle oil pressure chamber  16  is defined between a second side surface (opposite to the first side surface) of one of vane portions  14  and opposed partition wall  12 . 
   Moreover, vane portion  14  has a head end which is formed with a seal member  35 , as is seen in FIG.  2 . Seal member  35  has a seal portion  37  having a rigidity, and a spring  39  for biasing seal portion  37 . Seal portion  37  is made of synthetic resin material such as PTFE (polytetrafluoroethylene), PEEK (polyetheretherketone), PPS (polyphenylene sulfide) and the like. Otherwise, seal portion  37  is made of sintered metal. Spring  39  is shaped substantially into a plate, and biases seal portion  37  toward the internal peripheral surface of tubular housing  8 . 
   Moreover, seal portion  37  and spring  39  of seal member  35  are also disposed in an internal periphery of partition wall  12 , as is seen in FIG.  1  and FIG.  2 . 
   The paragraph [0019] and the paragraph [0020] are summarized as follows: In a condition that spring  39  (in vane portion  14  and in partition wall  12 ) is disposed in a recess formed in a longitudinal direction of seal portion  37 , seal member  35  is inserted into a groove which is formed at the head end of vane portion  14 , and the internal periphery of partition wall  12 . The above “longitudinal direction” is preferably exemplified in  FIG. 1  showing seal portion  37  and spring  39  in partition wall  12 . 
   From shell portion  13  (of vane member  5 ) to cam shaft  1 , there are defined a first oil pressure passage  17  and a second oil pressure passage  19 . First oil pressure passage  17  supplies and drains operating oil to and from each advanced-angle oil pressure chamber  15 , while second oil pressure passage  19  supplies and drains operating oil to and from each delayed-angle oil pressure chamber  16 . A supply passage  20  is connected, by way of an electromagnetic switch valve  22  (for switching oil delivery passage), to first oil pressure passage  17 , while a drain passage  21  is connected, by way of the electromagnetic switch valve  22 , to second oil pressure passage  19 . Supply passage  20  has an oil pump  24  for force-feeding oil reserved in an oil pan  23 . Drain passage  21  has a first end communicating into oil pan  23 . A controller  25  controls electromagnetic switch valve  22 , and receives various input signals for indicating engine operating condition. 
   According to the preferred embodiment, oil pressure control measures  6  is constituted of controller  25 , electromagnetic switch valve  22 , oil pump  24 , oil pan  23 , and the like. A phase variation mechanism is constituted of vane member  5 , advanced-angle oil pressure chamber  15  (on the first side surface of each of vane portions  14 ), and delayed-angle oil pressure chamber  16  (on the second side surface of each of vane portions  14 ). 
   On the other hand, lock gear  7  mechanically locks a rotation of housing member  4  relative to vane member  5  when vane member  5  is so controlled as to rotate at delayed angle during engine start and the like. Lock gear  7  is constituted of a lock pin  26  and a spring member  27 . Moreover, lock gear  7  defines a lock hole  28 . Lock pin  26  is housed and supported in one of vane portions  14  of vane member  5  in such a manner as to axially move forward and backward. Spring member  27  biases lock pin  26  in a direction of projection (toward rear cover  11  in FIG.  1 ). Lock hole  28  is defined in a predetermined position on an internal surface of rear cover  11 . Lock pin  26  has a head end which engages with lock hole  28  when vane member  5  is in a position for making a maximum rotational displacement at delayed angle relative to housing member  4 . Moreover, lock hole  28  is formed with a bottom which communicates to advanced-angle oil pressure chamber  15 . When the head end of lock pin  26  engages with lock hole  28 , oil pressure in advanced-angle oil pressure chamber  15  acts on the head end of lock pin  26 . 
   Herein, the entire part of tubular housing  8  of housing member  4  is formed through sintering operation. Of the thus sintered tubular housing  8 , only timing sprocket  3  has a high mold (compact) density, namely, a partially high density. 
   Hereinafter described is concerning a method of producing tubular housing  8 , referring to  FIG. 3  to FIG.  5 . Timing sprocket  3  on tubular housing  8  is referred to as a sprocket portion  3 , and the other portion of tubular housing  8  is referred to as a housing body  8 A. 
   Firstly, metal powder is filled in a predetermined mold for forming, through sintering, an entire configuration including housing body  8 A and sprocket portion  3 . Thereby, a sintered body W is formed whose sprocket portion  3  has tooth face a little larger than its final shape (scale). 
   Then, sintered body W is subjected to recompression and the like. Then, sintered body W is mounted on a jig  30  for preventing deformation, as is seen in FIG.  3  and FIG.  4 . Then, sintered body W mounted on jig  30  is set on a form roller  31  for roll-forming sprocket portion  3  of sintered body W, as is seen in FIG.  5 . 
   As is seen in  FIG. 3 , jig  30  is constituted of a body block  30 A, and a pair of a first side block  30 B and a second side block  30 C. Body block  30 A is engaged inside housing body  8 A of sintered body W. First side block  30 B is disposed axially on a first side of body block  30 A, and second side block  30 C is disposed axially on a second side of body block  30 A, to thereby put therebetween housing body  8 A. By way of body block  30 A, first side block  30 B and second side block  30 C are so centered as to have respective axial centers coincide with each other. 
   Moreover, as is seen in  FIG. 4 , body block  30 A has an external configuration substantially along an inside configuration of housing body  8 A. When housing body  8 A is brought into engagement with body block  30 A, body block  30 A does not abut on the entire inside face of housing body  8 A. Body block  30 A abuts only on a thin wall portion  8 B which is susceptible (deformable) to an external force and is so shaped as to form a depression for receiving vane portion  14  of vane member  5 . Thereby, mold accuracy-and-precision is required only for the abutment of thin wall portion  8 B abutting on body block  30 A, thus achieving low production cost. 
   As is seen in  FIG. 5 , form roller  31  is provided with a drive die  32  and a follower die  33 , each of which is threaded with tooth face on an external periphery. Then, jig  30  mounting sintered body W is disposed between drive die  32  and follower die  33  for form rolling. More specifically, sprocket portion  3  of sintered body W which was originally set on jig  30  meshes with the tooth face of drive die  32 . Then, drive die  32  is rotated. Then, drive die  32  together with sintered body W is moved toward follower die  33 , so that sprocket portion  3  further meshes with the tooth face of follower die  33 . Above summarizes that drive die  32  and follower die  33  are pressed on sprocket portion  3  for continued rotation, to thereby form-roll sprocket portion  3 . 
   Sintered body W through the form rolling by means of form roller  31  has sprocket portion  3  with a high entire mold (compact) density since the tooth face of sprocket portion  3  is pressed. On the other hand, side portion and the like of sprocket portion  3  free from abutting on the tooth face of each of drive die  32  and follower die  33  has a little excess thickness. Therefore, after form-rolling sintered body W, such excess thickness should be removed. 
   Thereafter, sintered body W is subjected to heat treatment and the like as the final process. 
   Described hereinafter is concerning operation of valve timing control system  2 . 
   Operating electromagnetic switch valve  22  supplies high-pressure operating oil to delayed-angle oil pressure chamber  16 . With this, vane member  5  makes a rotational displacement to a most delayed angle relative to housing member  4 . Then, lock pin  26  engages with lock hole  28  of housing member  4 , to thereby mechanically lock vane member  5  to housing member  4 . With this, a rotational drive force inputted from a crank shaft (not shown) to sprocket portion  3  of housing member  4  is transmitted, by way of housing member  4  and vane member  5  (which are mechanically coupled at the most delayed angle), to cam shaft  1 , to thereby open and close the intake valve at a delayed-angle timing by way of the drive cam (not shown). 
   Under the above condition, operating electromagnetic switch valve  22  communicates advanced-angle oil pressure chamber  15  to supply passage  20 , and communicates delayed-angle oil pressure chamber  16  to drain passage  21 . Then, high-pressure operating oil introduced into advanced-angle oil pressure chamber  15  acts on the head end of lock pin  26  by way of lock hole  28 , to thereby allow the operating oil to press lock pin  26  backward. With the thus backward lock pin  26 , lock pin  26  disengages from lock hole  28 , to thereby rotationally displace vane member  5  to a most advanced angle relative to housing member  4 . Thereby, the intake valve is opened and closed at an advanced-angle timing. 
   In valve timing control system  2 , tubular housing  8  is entirely sintered. Sprocket portion  3  (of tubular housing  8 ) to which drive force is inputted by way of the chain (not shown), however, has a partially high mold (compact) density. Therefore, valve timing control system  2  has mechanical strength and production accuracy-and-precision good enough to obtain durability during operation. 
   Though housing body  8 A of tubular housing  8  does not have high mold (compact) density, housing body  8 A is unlikely to deform for the following feature of sprocket portion  3 : Sprocket portion  3  surrounding housing body  8 A substantially in the axial center of housing body  8 A has a high mold (compact) density for enhanced strength. 
   Moreover, in valve timing control system  2  according to the preferred embodiment, in order to make sprocket portion  3  of tubular housing  8  high in mold (compact) density, sprocket portion  3  is form-rolled. Thereby, housing body  8 A is unlikely to deform not only after production, but also during sintering operation. 
   More specifically, forming tubular housing  8  through sintering is likely to cause a deformation to housing body  8 A, namely, a deformation shaped substantially into a barrel, as is seen in FIG.  6 (A). However, form-rolling sprocket portion  3  after sintering causes a heavy load. By way of sprocket portion  3 , the thus caused load is applied substantially to the axial center of housing body  8 A. During this period, a bulge substantially in the axial center of housing body  8 A is automatically corrected (straightened), as is seen in FIG.  6 (B). 
   Especially in the preferred embodiment, jig  30  on the internal peripheral surface of housing body  8 A acts for securely preventing housing body  8 A from causing a great deformation during the form rolling. 
   Therefore, in valve timing control system  2  in the preferred embodiment, the internal peripheral surface of tubular housing  8  closely abutting on vane member  5  is free from deformation. With this, vane member  5  and tubular housing  8  has a high sealing capability, to thereby encourage response to input. 
   In the preferred embodiment described above, the phase variation mechanism is constituted of vane member  5 , advanced-angle oil pressure chamber  15  (on the first side surface of each of vane portions  14  of vane member  5 ), and delayed-angle oil pressure chamber  16  (on the second side surface of each of vane portions  14  of vane member  5 ). The present invention is, however, not limited to this. 
   The entire contents of U.S. Pat. No. 5,592,909 is herein incorporated by reference, disclosing the phase variation mechanism constituted of gear mechanism and the like which can be rotatably operated with oil pressure. 
   Moreover for example, the spring  39  can be a coil spring, instead of being shaped substantially into a plate, and the spring  39  can be made of rubber and the like instead of PTFE (polytetrafluoroethylene), PEEK (polyetheretherketone), PPS (polyphenylene sulfide) and the like. 
   Further modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. 
   The entire contents of basic Japanese Patent Application No. P2000-258494 (filed Aug. 29, 2000) of which priority is claimed is incorporated herein by reference. 
   The scope of the present invention is defined with reference to the following claims.