Valve timing adjusting apparatus

Abstract

A valve timing adjusting apparatus for an engine includes a casing, magnetorheological fluid, a control device, a brake rotor, a phase adjustment mechanism, and a sealing structure. The control device changes the degree of viscosity of magnetorheological fluid in the casing. The sealing structure seals a gap between the casing and the brake rotor. The sealing structure includes an annular permanent magnet and at least one annular magnetic flux guide. The at least one magnetic flux guide defines a guide gap between the at least one magnetic flux guide and the other one of the casing and the brake rotor. The direction of magnetic flux relative to an axial center of the brake rotor, which flux is generated by the control device is similar to a direction of magnetic flux relative to the axial center generated by the permanent magnet.

1 . A valve timing adjusting apparatus for an internal combustion engine having a camshaft and a crankshaft, the valve timing adjusting apparatus adjusting valve timing of a valve that is opened and closed by the camshaft through torque transmission from the crankshaft, the valve timing adjusting apparatus comprising:
 a casing that defines a fluid chamber therein;   magnetorheological fluid received in the fluid chamber, the magnetorheological fluid having a degree of viscosity changeable in accordance with magnetic flux that passes through the magnetorheological fluid;   control means for changing the degree of viscosity of the magnetorheological fluid by causing magnetic flux to pass through the magnetorheological fluid in the fluid chamber;   a brake rotor that extends through the casing from an interior to an exterior of the casing, the brake rotor being rotatably supported by the casing, the brake rotor contacting the magnetorheological fluid in the fluid chamber, the brake rotor generating brake torque in accordance with the degree of viscosity of the magnetorheological fluid;   a phase adjustment mechanism that is coupled with the brake rotor at the exterior of the casing, the phase adjustment mechanism adjusting a relative phase between the crankshaft and the camshaft in accordance with the brake torque generated by the brake rotor; and   a sealing structure that seals a gap between the casing and the brake rotor, wherein:   the sealing structure includes:
 an annular permanent magnet that is placed at the interior of the casing to extend in a rotational direction of the brake rotor, the permanent magnet generating magnetic flux, the permanent magnet being supported by one of the casing and the brake rotor; and 
 at least one annular magnetic flux guide that is placed at the interior of the casing to extend in the rotational direction, the at least one magnetic flux guide being supported by the one of the casing and the brake rotor, the at least one magnetic flux guide defining a guide gap, through which magnetic flux generated by the permanent magnet travels, between the at least one magnetic flux guide and the other one of the casing and the brake rotor; and 
   a direction of magnetic flux relative to an axial center of the brake rotor, which flux is generated by the control means, and which flux passes through the magnetorheological fluid, is similar to a direction of magnetic flux relative to the axial center generated by the permanent magnet.   
     
     
         2 . The valve timing adjusting apparatus according to  claim 1 , wherein:
 the at least one magnetic flux guide includes a plurality of magnetic flux guides that is arranged in a direction from the interior to the exterior of the casing.   
     
     
         3 . The valve timing adjusting apparatus according to  claim 2 , wherein:
 the guide gap is defined between (a) each of the plurality of magnetic flux guides and (b) a shaft portion of the brake rotor; and   the guide gap defined at each of the plurality of magnetic flux guides has a radial dimension that is increased and decreased in the direction from the interior to the exterior of the casing.   
     
     
         4 . The valve timing adjusting apparatus according to  claim 1 , wherein:
 the casing includes a bearing assembly that supports the brake rotor; and   the sealing structure is provided between the bearing assembly and the fluid chamber of the casing.   
     
     
         5 . The valve timing adjusting apparatus according to  claim 1 , wherein:
 the casing is fixed to the internal combustion engine;   the casing holds the at least one magnetic flux guide together with the permanent magnet; and   the guide gap is defined between each of the at least one magnetic flux guide and the brake rotor.   
     
     
         6 . The valve timing adjusting apparatus according to  claim 5 , further comprising:
 a leaked magnetic flux introducing part that is provided between (a) a route of magnetic flux, which is generated by the control means, and which passes through the magnetorheological fluid, and (b) a route of magnetic flux generated by the permanent magnet; and   the leaked magnetic flux introducing part is made of a magnetic material.   
     
     
         7 . The valve timing adjusting apparatus according to  claim 6 , wherein:
 the casing has a bottom wall part that defines the fluid chamber; and   the leaked magnetic flux introducing part projects from an inner surface of the bottom wall part toward the sealing structure.