Patent Publication Number: US-2012024244-A1

Title: Camshaft speed sensor target

Description:
TECHNICAL FIELD 
     The present disclosure is directed to a camshaft system for a combustion engine and, more particularly, to a camshaft system having a speed target. 
     BACKGROUND 
     A camshaft system of a combustion engine comprises a camshaft for driving valves of the cylinders. Commonly, the camshaft system also comprises a speed target radially extending from the camshaft and integrally formed therewith for enabling a cam rotation sensor to detect a rotation angle of the camshaft. 
     Machining the speed target into the camshaft is a relatively expensive process. Further, if an error occurs during the machining process, repairing is in practice not economically attractive. In addition, if the integrally formed speed target is damaged during operation of the combustion engine, restoring the camshaft system in the original state is rather expensive. The entire camshaft has to be repaired or replaced. 
     The European patent publication EP 1 471 213 discloses a ring-shaped flange having a speed target, the flange being manufactured separately from the camshaft. During assembly, the flange is attached to an axial end portion of the camshaft. Due to the modular approach, the manufacturing process might be cheaper. Further, in case of damage, the speed target flange can be replaced while maintaining the camshaft. 
     However, the number of locations on the camshaft that are suitable for assembling the separate speed target flange disclosed in EP &#39;213, is restricted due to the presence of lobes, also called cams, on axial positions of the camshaft. The lobes have an outer diameter that is larger than the outer diameter of the camshaft. Since the speed target has to be assembled on the camshaft, the inner diameter of the speed target is smaller than the outer diameter of the lobes. As a consequence, the speed target flange can not slide over the lobes. Therefore, the speed target flange of EP &#39;213 can not be placed between lobes without splitting the camshaft into multiple pieces. If the camshaft is of an integral, one-piece construction, this is impossible. As a result, the only practical axial position of the speed target flange is at an axial end portion of the camshaft. 
     The camshaft system of the present disclosure solves one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     One aspect of the present disclosure is directed to a method of constructing a speed target on a camshaft in a combustion engine. The method may include positioning a multiple number of ring segments around a portion of the camshaft, the multiple number of ring segments forming a closed ring having a variable outer magnetic surface for reading by a speed sensor. Further, the method may include securing the multiple number of ring elements in a radial direction and in a circumferential direction with respect to the camshaft. 
     Another aspect of the present disclosure is directed to a camshaft system for a combustion engine. The camshaft system may include a camshaft. Further, the camshaft may include a speed target including a multiple number of ring segments positioned around a portion of the camshaft, the multiple number of ring segments forming a closed ring having a variable outer magnetic surface for reading by a speed sensor, wherein the multiple number of ring segments are secured in a radial direction and in a circumferential direction with respect to the camshaft. 
     Yet another aspect of the present disclosure is directed to a speed target for assembling on a camshaft of a combustion engine. The speed target may include a multiple number of ring segments positioned around a portion of the camshaft, the multiple number of ring segments forming a closed ring having a variable outer magnetic surface for reading by a speed sensor, wherein the multiple number of ring segments are secured in a radial direction and in a circumferential direction with respect to the camshaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic partial perspective view of an exemplary disclosed combustion engine; 
         FIG. 2  is a schematic partial perspective view of an exemplary camshaft system; 
         FIG. 3  is a more detailed schematic partial perspective view of the camshaft system of  FIG. 2 ; 
         FIG. 4  is a schematic partial elevational cross sectional view of a further camshaft system; 
         FIG. 5  is a schematic partial elevational cross sectional view of yet a further exemplary camshaft system; 
         FIG. 6  is a schematic cross sectional view of another exemplary camshaft system; and 
         FIG. 7  is a flow chart illustrating an exemplary method of constructing a speed target on a camshaft in a combustion engine. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic partial perspective view of an exemplary disclosed combustion engine  2 . Combustion engines are typically used for driving vehicles, such as cars and construction machines. A combustion engine can embody any type of internal combustion engine, such as, for example, a gasoline or a gaseous fuel-powered engine. 
     As illustrated, the combustion engine  2  may include a camshaft system for a combustion engine, the camshaft system having a first camshaft  4  and a second camshaft  6 . The second camshaft  6  may include, at a first end, a first valve characteristics changing device  8 . Further, the combustion engine  2  may include a chain/sprocket mechanism  10  and a crankshaft  12  that is interconnected to the first and the second camshaft  4 ,  6 , respectively, via the chain/sprocket mechanism  10  such that the camshaft rotation speed is half the crankshaft rotation speed. The crankshaft  12  may be connected, via connecting rods  14 , to a number of pistons  16 , one of them being shown in  FIG. 1 . The combustion engine  2  may further include two intake valves  18  and two exhaust valves  20  per piston  16 , driven by the second camshaft  6  and the first camshaft  4 , respectively. The engine  2  may further include a second valve characteristics changing device  22  and a third valve characteristics changing device  24  for changing a valve lift and opening angle of respective valves  18 ,  20 . 
     The camshaft system may further include, on the first camshaft  4  and on the second camshaft  6 , respectively, a speed target  26  for reading by a speed sensor so as to enable an angular position measurement of the first and second camshaft  4 ,  6 , respectively. The speed target  26  may be positioned at an end of the camshaft  4 ,  6  remote from the chain/sprocket mechanism  10 , thereby counteracting any damage to the speed target  26  caused either by handling abuse or auxiliary drive belt lash. The speed target  26  as shown in  FIG. 1  is described in more detail referring to  FIGS. 2-5 . 
       FIG. 2  is a schematic partial perspective view of an exemplary camshaft system. The camshaft system may include a camshaft  4  wherein a multiple number of ring segments  28 ,  30  may be positioned around a portion of the camshaft  4  thus forming a ring-shaped speed target  32  enclosing the camshaft  4 . The multiple number of ring segments may include two half-ring segments  28 ,  30 . The half-ring segments  28 ,  30  may have a variable outer magnetic surface  34  for reading by a speed sensor. As illustrated, the variable outer magnetic surface  34  may include protruding portions extending in a radial direction away from the camshaft. The variable outer magnetic surface  34  may be formed by a manufacturing operation such as forging or casting. Further, the two half-ring segments  28 ,  30  may be secured in a radial direction and a circumferential direction with respect to the camshaft  4 . 
     The two half-ring segments  28 ,  30  may be located in an axial position between radially extending portions of the camshaft, as an example between a first lobe  4 ′ and a second lobe  4 ″ on the camshaft  4 . The outer diameter of the lobes  4 ′,  4 ″ may be greater than the inner diameter of the closed ring that is formed by the two half-ring segments  28 ,  30 . 
       FIG. 3  is a more detailed schematic partial perspective view of the camshaft system as shown in  FIG. 2 . As illustrated, a portion  36  of the first half-ring segment  28  may overlap a portion  38  of the second half-ring segment  30 . In said portions  36 ,  38  the half-ring segment  28 ,  30  may include a pair of bores  40  that have been aligned. A pin  42  passes through said pair of bores  40  into a bore  44  that might be included on the camshaft  4 , so that the segments  28 ,  30  have been fixed on the camshaft  4 . At the diametrically opposite location of the camshaft the half-ring segments may be secured to the camshaft in a similar way. Since the pin may traverse through overlapping portions and each half-ring segment  28 ,  30  engages at the pin at two diametrically opposite locations, a single pin  42  may be used to secure the half-ring segments  28 ,  30 . The segments  28 ,  30  may be secured to the camshaft  4  by pinning through each other at overlapping portions. 
       FIG. 4  is a schematic partial elevational cross sectional view of a further exemplary camshaft system  2 . Here, the variable outer magnetic surface  34  may be formed using pressed steel components. However, the surface  34  can also be formed using another technique, e.g. by sintering, also known as metallurgy. In  FIG. 4 , a cross sectional view is shown at the location of the pin  42  passing through the pair of bores  40  in the half-ring segments  28 ,  30  into a bore on the camshaft  4 . As illustrated, the pin may be implemented as a rivet  42  for securing the half-ring segments  28 ,  30  to the camshaft  4 . As further illustrated, the bore  44  on the camshaft  4  may be implemented as a through hole extending from a first side of the camshaft  4  through a kernel  46  of the camshaft to a second side of the camshaft, opposite to the first side. As a result, a single bore  44  on the camshaft  4  can be used for securing the half-ring segments  28 ,  30  at opposite sides of the camshaft  4 . At a side opposite to the region wherein the half-ring segments  28 ,  30  overlap at portions  36 ,  38 , a similar securing construction may be applied. Also at the opposite side the half-ring segments  28 ,  30  overlap at further portions  48 ,  50 , respectively. Similarly, a second pin  56  may pass through a pair of mutually aligned bores  52  into the through bore  44  in the camshaft  4 . Hence, two separate pins  42 ,  56  may be used for securing the half-ring segments  28 ,  30 . It is noted that, as an alternative to the single through bore  44 , also two blind holes can be used for securing the half-ring segments  28 ,  30  at opposite sides of the camshaft  4 . Further, more than two holes can be applied, e.g. four holes for securing the half-ring segments at four holes to the camshaft. The application of multiple bores might help ensuring that the angular position of the target segments with respect to the camshaft is correct. As an example, by using two bores at asymmetric locations, it can be avoided that the segments are misaligned over an angle of e.g. 180° degrees. In general, multiple pin-hole connections may be applied for securing the half-ring segments  28 ,  30  in a circumferential, longitudinal and/or axial direction to the camshaft  4 . However, the half-ring segments  28 ,  30  can also be connected to the camshaft via a single pin-hole connection. In addition, also further fasteners may be applied, such as a screw connection, a bolt-nut connection or a glue connection. 
       FIG. 5  is a schematic partial elevational cross sectional view of yet a further exemplary camshaft system. Similar to the exemplary camshaft system shown in  FIGS. 2 and 3 , the variable outer magnetic surface  34  may be formed by a manufacturing operation such as a forging operation, or casting or sintering. As illustrated, the pin passing through the pair of bores  40  in the half-ring segments portions  36 ,  38  into the through bore  44  and through the pair of bores  52  in the half-ring segments portions  48 ,  50  at the opposite side of the camshaft  4 , may be implemented as a single roll pin or spring dowel, thereby simplifying an assemblage process of the camshaft system. 
       FIG. 6  is a schematic cross sectional view of another exemplary camshaft system. Here, two half-ring segments  28 ,  30  may have been arranged in a relative position around a portion of the kernel  46  of the camshaft  4 . A first end portion  58  of a first segment  28  may abut against a first end portion  60  of the second segment  30 . Similarly, a second end portion  62  may abut against a second end portion  64  of the second segment  30 , thereby forming a closed ring. Here, an individual half-ring segment may extend over merely 180°. In general, the sum of the angular extension of the individual ring segments amounts to 360°. The end portions  58 ,  60 ,  62 ,  64  of the first and second segment  28 ,  30  may be provided with bores  66 ,  68  that are pairs wise aligned at the corresponding end portions  58 ,  60 ,  62 ,  64  of said segments  28 ,  30 . In both pairs of bores  66 ,  68  a pin  70 ,  72  may be placed, thus interconnecting the corresponding end portions of the segments so as to secure the ring segments in a radial direction. The pin  70 ,  72  may be implemented as a screw. Further, an inner surface of at least one ring segment may correspond with a machined outer surface of the camshaft  4 . More specifically, an inner surface of at least one ring segment  28 ,  30  may include a flat portion  74 ,  76  corresponding with a flat machined outer surface portion of the camshaft  4 , thereby securing the ring segments in a circumferential direction. 
     It is noted that, in principle, various securing method of securing the multiple number of ring segments can be applied mainly independent on whether the segments overlap or not. As an example, a pinning connection through overlapping portions of the ring segments can be applied. Alternatively, the segments may be pinned separately to the camshaft. Further, adjacent portions can be interconnected without contacting the outer surface of the camshaft. It is further noted that the speed target might include more than two ring segments, e.g. three or more ring segments positioned around a portion of the camshaft. 
     INDUSTRIAL APPLICABILITY 
     Although illustrated and described above as being utilized in conjunction with an inline cylinder engine, the camshaft system may be applicable to any combustion engine, e.g. a V-type cylinder engine. Further, the camshaft system may comprise a single camshaft for driving both the intake valves and the exhaust valves. Further, the engine may have a single intake valve and a single exhaust valve per cylinder. 
     During operation of the combustion engine  2 , the camshaft rotation speed is half of the crankshaft rotation speed. Rotation and angular position information of the first and second camshaft  4 ,  6  may be monitored by a proximity sensor sensing the variable outer magnetic surface  34  of the ring-shaped speed target  32 . More specifically, the proximity sensor may be positioned to catch a magnetic pulse signal when a protruding portion of the variable outer magnetic surface  34  pass along the proximity sensor. By proper interpretation of caught magnetic pulse signals angular position information and/or rotational speed information of the camshaft may be deduced, e.g. for further processing and/or controlling of the engine such as controlling a fuel flow to a combustion chamber of a cylinder or when a fuel injector sequence should start. By implementing the variable outer magnetic surface  34  as a specific contour having protrusions with different height and/or width features, specific angular positions of the camshaft may be detected, such as a top dead center location of a cylinder. Similarly, it might be determined whether the camshaft runs in a forward or backward direction. Below, a method of constructing a speed target on a camshaft in a combustion engine will now be explained. 
       FIG. 6  is a flow chart illustrating an exemplary method of constructing a speed target on a camshaft in a combustion engine. The method may include a step  100  of positioning a multiple number of ring segments  28 ,  30  around a portion of the camshaft  4 , the multiple number of ring segments forming a closed ring having a variable magnetic surface  34  for reading by a speed sensor. The method may further include a step  102  of securing the multiple number of ring segments in a radial direction and in a circumferential direction with respect to the camshaft. 
     The method may also include positioning the multiple number of ring segments at a specific axial position around the portion of the camshaft, between axially extending portions of the camshaft. Further, the method may include arranging at least two ring segments, e.g. two half-ring segments in a relative position around a portion of the camshaft wherein an end portion  36  of a first ring segment  28  overlaps an end portion  38  of a second ring segment  30 . 
     The method may further include a step  102  of placing at least one pin  42  through a pair of aligned bores  40  on the segments  28 ,  30  the pin also passing through the bores  28 ,  30  into a bore  44  on the camshaft. By passing through the bores of the segments  28 ,  30  as well as through the bore  44  on the camshaft, the single pin  42  retains both segments in place on the camshaft. The bores  40  on the segments  28 ,  30  may be aligned during placement of the pin  42  through the bores  40 . Alternatively, the bores  40  on the segments may be aligned prior to placing the pin  42  there through. The method may further include passing the pin through a through hole  44  of the camshaft and through a further pair of aligned bores on the segments  28 ,  30  opposite to the pair of aligned bores  40  on the segments  28 ,  30 , thereby realizing a single connection that secures the segments at two different, mutually opposite, locations to the camshaft. 
     The method may also include arranging at least two ring segments, e.g. two half-ring segments, in a relative position around a portion of the camshaft wherein an end portion  58  of a first ring segment  28  abuts against an end portion  60  of a second ring segment  30 . Then, the method may include placing at least one pin  70  through a pair of aligned bores  66  in the end portions  58 ,  60  of the first and second ring segment  28 ,  30 , wherein an inner surface  74  of at least one ring segment corresponds to a machined outer surfaced of the camshaft portion. 
     The method may further include applying a further connection of the segments  28 ,  30  to the camshaft, e.g. by realizing a further connection by inserting a further pin in a further pair of bores at another position on a segment. The pairs of bores can be located at different circumferential positions with respect to the camshaft. Further, the method may include positioning three or more ring segments around a portion of the camshaft, a portion of each segment overlapping another segment, and including placing pins through a pair of aligned bores of two segments, the pins also passing through said pair of aligned bores into a bore on the camshaft. 
     The method of constructing the speed target on the camshaft may be performed when the camshaft has already been assembled in the combustion engine or is positioned nearly in its final axial position in the combustion engine. If allowed by the outer diameter of the speed target, the method may also be applied when the camshaft itself is not yet assembled in the combustion engine. Further, the constructing method may advantageously be applied during maintenance or repairing activities, e.g. when the speed target has been damaged and replacement is desired. As such, the method may include removing a speed target from the camshaft prior to positioning the two half-ring segments around a portion of the camshaft. The removed speed target might be damaged. Further, the method can advantageously be applied when a speed target having another variable outer magnetic surface is desired, e.g. having another number of protrusions. Since the speed target may include two half-ring segments, replacement of the speed target may be a relatively easy operation as the half-ring segments may be removed and/or replaced one by one without de-assembling the camshaft itself. 
     Since the target is formed by a multiple number of ring segments, the target can be assembled and de-assembled at various axial locations on the camshaft, also between lobes of the camshaft, even if the outer diameter of the lobes is larger than the inner diameter of the target. This is due to the fact that the ring segments can be positioned on and removed from the camshaft following a mainly axial path. The ring segments are not required to shift over the lobes, thereby enabling a relatively easy repairing operation of the target without de-assembling the entire camshaft, while on the other hand providing a flexibility in specifying a target position at an axial position between lobes. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the method of constructing a speed target on a camshaft in a combustion engine of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the method of constructing a speed target on a camshaft in a combustion engine disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and their equivalents.