Variable valve timing apparatus

Abstract

A phase adjusting mechanism is engaged with a brake shaft, and adjusts a rotation phase between a crankshaft and a camshaft according to a braking torque acting on a rotor. The rotation phase is adjusted in a predetermined direction when the braking torque is increased. A torque input mechanism inputs a return torque into the phase adjusting mechanism to return the rotation phase in an opposite direction opposite from the predetermined direction. The torque input mechanism increases the return torque corresponding to the rotation phase as an environmental temperature of the variable valve timing apparatus is lowered.

1 . A variable valve timing apparatus that controls valve timing of a valve which is opened and closed by a camshaft driven by torque transmission from a crankshaft in an internal combustion engine, the apparatus comprising:
 a case defining a fluid chamber inside;   magnetic viscosity fluid kept in the fluid chamber, the magnetic viscosity fluid having a viscosity variable in accordance with magnetic flux passing through;   a control device which carries out variable control of the viscosity of the magnetic viscosity fluid by varying the magnetic flux;   a rotor having a brake shaft penetrating the case to come into contact with the magnetic viscosity fluid so that the rotor receives a braking torque according to the viscosity of the magnetic viscosity fluid;   a phase adjusting mechanism engaged with the brake shaft at an outside of the case, the phase adjusting mechanism adjusting a rotation phase between the crankshaft and the camshaft according to the braking torque acting on the rotor, the rotation phase being adjusted in a predetermined direction when the braking torque is increased; and   a torque input mechanism inputting a return torque into the phase adjusting mechanism to return the rotation phase in an opposite direction opposite from the predetermined direction, wherein the torque input mechanism increases the return torque corresponding to the rotation phase as an environmental temperature of the variable valve timing apparatus is lowered.   
     
     
         2 . The variable valve timing apparatus according to  claim 1 , wherein
 the torque input mechanism has
 an elastic member connected to the phase adjusting mechanism in a state where the elastic member has an elastic deformation, the elastic member inputting the return torque corresponding to the rotation phase using a recovering force of the elastic member from the elastic deformation, and 
 a deformation increasing portion connected to the elastic member, the deformation increasing portion increasing the return torque by increasing an amount of the elastic deformation of the elastic member as the environmental temperature of the variable valve timing apparatus is lowered. 
   
     
     
         3 . The variable valve timing apparatus according to  claim 2 , wherein
 the deformation increasing portion has
 a contraction part that is contacted as the environmental temperature of the variable valve timing apparatus is lowered, 
 a contraction casing defining an accommodation chamber that accommodates the contraction part, and 
 a displacement part penetrating the contraction casing, the displacement part increasing the amount of the elastic deformation of the elastic member at outside of the contraction casing by being displaced by the contraction of the contraction part in the accommodation chamber. 
   
     
     
         4 . The variable valve timing apparatus according to  claim 3 , wherein
 the deformation increasing portion further has a biasing part that biases the displacement part toward the contraction part, inside of the contraction casing.