Abstract:
A camshaft assembly includes a cam carrier and a camshaft that is rotatable relative to the cam carrier in a first configuration and fixed against rotation in a second configuration. The assembly further includes a cam target wheel that includes notches, a first and second half-wheel, and a groove. The assembly additionally includes a camshaft position sensor holder that includes a camshaft sensor bore that provides access to the groove. Also, the assembly includes a camshaft position sensor received in the camshaft sensor bore in the first configuration. Moreover, the assembly includes a locking mechanism received in the camshaft sensor bore in the second configuration. The locking mechanism includes an engagement member configured to selectively engage the groove for locking the camshaft into position relative to the cam carrier.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to GB Patent Application No. 1313584.3 filed Jul. 30, 2013, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The technical field relates to a cam carrier assembly for an internal combustion engine. 
     BACKGROUND 
     An internal combustion engine for a motor vehicle generally includes an engine block, which defines at least one cylinder accommodating a reciprocating piston, coupled to rotate a crankshaft. The cylinder is closed by a cylinder head that cooperates with the reciprocating piston to define a combustion chamber. A fuel and air mixture is cyclically disposed in the combustion chamber and ignited, thereby generating hot expanding exhaust gasses that cause the reciprocating movements of the piston. The fuel is injected into each cylinder by a respective fuel injector. The fuel is provided at high pressure to each fuel injector from a fuel rail in fluid communication with a high-pressure fuel pump that increases the pressure of the fuel received from a fuel source. 
     Each of the cylinders has at least two valves that selectively allow air into the combustion chamber from an intake port and alternately allow exhaust gases to exit through an exhaust port. Each of the valves of each cylinder is actuated by a respective cam rotating on camshafts in time with the crankshaft and being connected to the crankshaft by a series of pulleys and a belt or a chain. 
     Conventional internal combustion engines are also managed by an Electronic Control Unit (ECU) that may receive input signals representative of various physical parameters associated with the engine from various sensors and may execute suitable calculations to determine the relevant physical parameters of each fuel injection. 
     Among these sensors, a camshaft sensor is provided on one of the camshafts. The sensor is used in combination with a crankshaft sensor to monitor the opening and closing of the valves in relation with the position of the pistons and valves in the engine, especially but not exclusively in engines with variable valve timing. 
     The camshaft position sensor may be used in combination with a rotating cam target wheel provided with a series of notches on its circumference. The camshaft position sensor may detect a series of notches located on the cam target wheel as they pass in front of the sensor position during rotation of the camshaft. The camshaft sensor may be a Hall effect device or may be based on other detection principles such as an optical sensor or an inductive sensor. 
     In conventional internal combustion engines, the camshafts have to be installed in a cam carrier by inserting them through bearings provided in seats in the cam carrier while the cam target wheel is machined or already installed on one of the camshafts. In this case, the diameter of the target wheel of the camshaft is limited by the diameter of the bearings, because the camshaft must be moved through the bearings during assembly of the engine. However, a small target wheel diameter leads to a low or to a not optimal accuracy of the cam sensor output signal. 
     Furthermore, since the camshafts and the crankshaft must be synchronized together, during assembly of the engine, an intermediate locking phase of the camshafts is provided where the camshafts, once inserted into the cam carrier, must be temporarily locked into a fixed position to allow the synchronization with the crankshaft and the pistons of the engine. In order to perform this locking operation, current camshafts have a groove that is machined on their surface and cam carriers are provided with a lateral bore through which the camshaft is locked in place by a special tool that can be inserted into the bore in order to engage the groove. 
     SUMMARY 
     The present disclosure provides an improvement in the accuracy of the cam target wheel without the need of performing major design changes on the engine, which is a simple, rational and rather inexpensive solution. 
     An embodiment of the present disclosure provides a cam target wheel for a camshaft of an internal combustion engine. The cam target wheel includes a first and a second half-wheel, each being provided with connecting means for their reciprocal connection. An advantage of this embodiment is that it allows the use of a cam target wheel whose diameter is not limited by the diameter of the bearings of the cam carrier because the cam target wheel can be mounted on the camshaft after the camshaft has been inserted in the cam carrier. A larger diameter of the cam target wheel improves the accuracy of the cam sensor output signal. 
     According to another embodiment of the present disclosure, the half-wheels connecting means include bolts screwed into respective threaded holes of the half-wheels. An advantage of this embodiment is that it allows an easy assembly of the cam target wheel on the camshaft. 
     According to another embodiment of the present disclosure, the cam target wheel includes a groove in a circumferential portion thereof. An advantage of this embodiment is that it avoids performing an operation of machining of a groove in the camshaft. 
     According to another embodiment of the present disclosure, a cam carrier for housing a camshaft assembly is provided. The cam carrier includes a cam cover and a camshaft position sensor holder in the cam cover. The camshaft position sensor holder includes a bore suitable for housing a locking tool to engage the groove of the cam target wheel. An advantage of this embodiment is that it avoids to perform an operation of machining of a separate bore and thread in the cam carrier. 
     According to another embodiment of the present disclosure, the camshaft position sensor holder in the cam carrier is associated with a housing for a cam sensor bolt. The cam sensor bolt is suitable for locking into position the locking tool. An advantage of this embodiment is that the locking tool can be positioned using the already present structure of the camshaft position holder. Furthermore, only a simple tool is required to lock the camshaft, because the tool can be fixed with the cam sensor bolt. 
     Another embodiment of the present disclosure provides a method of mounting a camshaft assembly in a cam carrier of an internal combustion engine, the method including the steps of inserting a camshaft through bearings provided in seats of the cam carrier; mounting a first half-wheel of the cam target wheel on the camshaft; rotating the camshaft by 180° and mounting the second half-wheel of the cam target wheel on the camshaft; connecting together the first half-wheel and the second half-wheel. An advantage of this embodiment the camshaft assembly is mounted in a simple and straightforward manner while, at the same time, benefitting from a larger cam target wheel, therefore improving accuracy of the sensor. 
     Still another embodiment of the present disclosure provides temporarily locking the mounted camshaft into a fixed position by a locking tool inserted into the bore of the camshaft position sensor holder until a tip of the locking tool engages in the groove of the cam target wheel. An advantage of this embodiment is that it allows locking temporarily the camshaft assembly without the need of any machining in a lateral side of the cam cover. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements. 
         FIG. 1  shows an automotive system; 
         FIG. 2  is a cross-section of an internal combustion engine belonging to the automotive system of  FIG. 1 ; 
         FIGS. 3 and 4  represent a bottom and top portion of a cam carrier according to the prior art; 
         FIG. 5  represents a cam target wheel according to an embodiment of the present disclosure; 
         FIG. 6  represents a camshaft assembly including a camshaft equipped with a target wheel according to an embodiment of the present disclosure; 
         FIG. 7  represents a cam carrier according to an embodiment of the present disclosure; 
         FIG. 8  represents a camshaft equipped with a target wheel according to an embodiment of the present disclosure and a cam sensor; 
         FIG. 9  represents a cam carrier according to an embodiment of the present disclosure and a locking tool to lock the camshaft; 
         FIG. 10  represents a particular of a cam target wheel according to an embodiment of the present disclosure; and 
         FIG. 11  represents a camshaft equipped with a target wheel according to an embodiment of the present disclosure and engaged by a locking tool. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments will now be described with reference to the enclosed drawings without intent to limit application and uses. 
     Some embodiments may include an automotive system  100 , as shown in  FIGS. 1 and 2 , that includes an internal combustion engine (ICE)  110  having an engine block  120  defining at least one cylinder  125  having a piston  140  coupled to rotate a crankshaft  145 , the crankshaft  145  being housed in a crankcase  680 . A cylinder head  130  cooperates with the piston  140  to define a combustion chamber  150 . A fuel and air mixture (not shown) is disposed in the combustion chamber  150  and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston  140 . The fuel is provided by at least one fuel injector  160  and the air through at least one intake port  210 . The fuel is provided at high pressure to the fuel injector  160  from a fuel rail  170  in fluid communication with a high-pressure fuel pump  180  that increase the pressure of the fuel received from a fuel source  190 . Each of the cylinders  125  has at least two valves  215 , actuated by a camshafts  135 , 137  rotating in time with the crankshaft  145 . The valves  215  selectively allow air into the combustion chamber  150  from the port  210  and alternately allow exhaust gases to exit through a port  220 . Since the valves  215  control the flow of the air/fuel mixture intake and exhaust gases, they must be opened and closed at the appropriate time during the stroke of the piston  140 . For this reason, the camshafts  135 , 137  are connected to the crankshaft  145  either directly via a gear mechanism or indirectly via a belt or chain  157 . In some examples, a cam phaser  155  may selectively vary the timing between the camshafts  135 , 137  and the crankshaft  145 . A space in which the camshafts  135 , 137  are housed is defined as a camshaft ambient  570  ( FIG. 3 ). 
     The air may be distributed to the air intake port(s)  210  through an intake manifold  200 . An air intake duct  205  may provide air from the ambient environment to the intake manifold  200 . In other embodiments, a throttle body  330  may be provided to regulate the flow of air into the manifold  200 . In still other embodiments, a forced air system such as a turbocharger  230  having a compressor  240  rotationally coupled to a turbine  250  may be provided. Rotation of the compressor  240  increases the pressure and temperature of the air in the duct  205  and manifold  200 . An intercooler  260  disposed in the duct  205  may reduce the temperature of the air. The turbine  250  rotates by receiving exhaust gases from an exhaust manifold  225  that directs exhaust gases from the exhaust ports  220  and through a series of vanes prior to expansion through the turbine  250 . The exhaust gases exit the turbine  250  and are directed into an exhaust system  270 . This example shows a variable geometry turbine (VGT) with a VGT actuator  290  arranged to move the vanes to alter the flow of the exhaust gases through the turbine  250 . In other embodiments, the turbocharger  230  may be fixed geometry and/or include a waste gate. 
     The exhaust system  270  may include an exhaust pipe  275  having one or more exhaust after treatment devices  280 . The after treatment devices  280  may be any device configured to change the composition of the exhaust gases. Some examples of after treatment devices  280  include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NO x  traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. Other embodiments may include an exhaust gas recirculation (EGR) system  300  coupled between the exhaust manifold  225  and the intake manifold  200 . The EGR system  300  may include an EGR cooler  310  to reduce the temperature of the exhaust gases in the EGR system  300 . An EGR valve  320  regulates a flow of exhaust gases in the EGR system  300 . 
     The automotive system  100  may further include an electronic control unit (ECU)  450  in communication with one or more sensors and/or devices associated with the ICE  110 . The ECU  450  may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE  110 . The sensors include, but are not limited to, a mass airflow and temperature sensor  340 , a manifold pressure and temperature sensor  350 , a combustion pressure sensor  360 , coolant and oil temperature and level sensors  380 , a fuel rail pressure sensor  400 , a cam position sensor  410 , a crank position sensor  420 , exhaust pressure and temperature sensors  430 , an EGR temperature sensor  440 , and an accelerator pedal position sensor  445 . Furthermore, the ECU  450  may generate output signals to various control devices that are arranged to control the operation of the ICE  110 , including, but not limited to, the fuel injectors  160 , the throttle body  330 , the EGR Valve  320 , the VGT actuator  290 , and the cam phaser  155 . Note, dashed lines are used to indicate communication between the ECU  450  and the various sensors and devices, but some are omitted for clarity. 
     More specifically,  FIG. 3  shows a schematic illustration of a cam carrier according to the prior art, globally indicated with the reference number  500 . The cam carrier  500  includes a bottom portion  505  cooperating with a cam cover  525  ( FIG. 4 ) to define a camshaft ambient  570  in which camshafts  135 , 137  are housed. The bottom portion  505  has seats  507  for the camshafts  135 , 137 . The seats  507  include bearings  510  into which the camshafts  135 , 137  are mounted by inserting them according to the direction of the arrow F of  FIG. 3 . 
     A camshaft position sensor  410  is located in a camshaft position sensor holder  415  having a camshaft sensor bore  647  for holding the sensor  410  and a housing  417  for a cam sensor bolt  645 , the function of which will be explained in the following description. The camshaft position sensor holder  415  is located in the top of the cam cover  525  of the cam carrier  500 . The cam cover  525  covers the bottom portion  505  of the cam carrier  500 . 
     A camshaft locking bore  530  is provided in a lateral portion of the cam cover  525  of the prior art ( FIG. 4 ) through which the camshaft  135  is temporarily locked in place by means of a special tool (not represented for simplicity) that can be inserted into the locking bore  530  in order to engage with a groove on the camshaft  135  to allow the synchronization with the crankshaft  145  and the pistons  140  of the engine  110 . 
       FIG. 5  illustrates a cam target wheel  630 , according to an embodiment of the present disclosure.  FIG. 6  illustrates a camshaft assembly  700  including a camshaft  135  equipped with the cam target wheel  630  of  FIG. 5 . The cam target wheel  630  includes two half-wheels  610 , 620  that may be connected by means of bolts  580  screwed into respective threaded holes  583  to form the cam target wheel  630 . The threaded holes  583  may be machined in the half wheels  610 , 620  and have a depth that allows the bolts  580  to be hidden from the camshaft position sensor  410  in order not to interfere with its operation. Other threaded or non-threaded connecting means known in the art may be used without departing from the various embodiments of the present disclosure. 
     The cam target wheel  630  is provided with a series of notches  585  on its circumference, suitable to be sensed by a camshaft position sensor  410 . 
     According to an embodiment of the present disclosure ( FIG. 10 ) a groove  660  is provided in the cam target wheel  630 . The groove  660  is provided in a circumferential portion  665  of the cam target wheel that is free of notches  585 . 
       FIG. 7  represents a cam cover  625  of a cam carrier  600  according to an embodiment of the present disclosure. The cam cover  625  has a camshaft position sensor holder  415 . 
       FIG. 8  represents a camshaft  135  equipped with a cam target wheel  620  according to an embodiment of the present disclosure and connected to a camshaft position sensor  540 . 
     The camshaft position sensor  540  has a connection element  545  and a hole  547  in the connection element  545 . The camshaft position sensor  540  is suitable to be inserted into the camshaft position sensor holder  415  and blocked into position by inserting the cam sensor bolt  645  into the hole  547  of the connection element  545  and then into the housing  417  for the cam sensor bolt  645 . The camshaft position sensor  540  may detect the notches  585  located on the cam target wheel  630  as they pass in front of the sensor position during rotation of the camshaft  135  in order to determine the position of the cams. 
       FIG. 9  represents a cam cover  625  for a cam carrier  600  according to an embodiment of the present disclosure. The cam cover  625  is provided with a locking tool  650  to lock the camshaft  135 . The locking tool  650  can be inserted into the camshaft sensor bore  647  of the camshaft sensor holder  415 . 
       FIG. 10  represents a particular of a cam target wheel  630  according to an embodiment of the present disclosure in which groove  660  is provided. The groove  660  is provided in a circumferential portion  665  of the cam target wheel that is free of notches  585 . 
       FIG. 11  represents a camshaft equipped with a target wheel according to an embodiment of the present disclosure and engaged by the locking tool  650 . The locking tool  650  being equipped with a tip  655  that engages in the groove  660  of the cam target wheel  630 . The locking tool  650  is also provided with a connection element  670  having a hole  675  for the cam sensor bolt  645 . 
     When the engine  110  is assembled, the camshafts  135  are inserted through the bearings  510 . The first half-wheel  610  of the cam target wheel  630  is then inserted on the camshaft  135 . The camshaft  135  is then rotated by 180° and the second half-wheel  620  of the cam target wheel  630  is mounted over the first half-wheel  610  and connected thereto by bolts  580 . This mounting procedure allows for the use of a cam target wheel  630  having a larger diameter, not limited by the bearings  510  diameter, in order to improve the accuracy of the cam sensor output signal 
     Since camshaft  135  has to be synchronized with the crankshaft  145 , an intermediate locking phase of the camshafts is provided where the camshafts, once inserted into the cam carrier  600 , must be temporarily locked into a fixed position to allow the synchronization with the crankshaft  145  and the pistons  140  of the engine  110 . This operation may be executed by using the locking tool  650  which is inserted into the camshaft sensor bore  647  until the tip  655  of the locking tool  650  engages in the groove  660  of the cam target wheel  630  in order to lock the camshaft  135  into position. The locking tool  650  can be fixed into position by means of with the cam sensor bolt  645  without any additional fixing means ( FIG. 9 ) in a similar fashion as the fixing in place of the camshaft position sensor  410 . Once the intermediate locking phase is done, the locking tool  650  can be removed and the cam sensor  540  can be mounted in its place. 
     While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.