Valve mechanism for an internal combustion engine

Abstract

A valve drive mechanism for actuating a valve of an internal combustion engine includes a camshaft that is rotated by a crankshaft of the internal combustion engine. The crankshaft has a cam with positive and negative acceleration portions. A swing member rocked on a support shaft by rotation of the cam. The swing member has a cam surface configured to drive the valve. The cam surface has a base circle portion, a lift portion, and a ramp portion extending between the base circle portion and the lift portion. The ramp portion is configured such that when the positive or negative acceleration portions of the cam actuate the swing member, a lift speed of the valve is substantially constant.

1 . A valve drive mechanism for actuating a valve of an internal combustion engine, the valve drive mechanism comprising; 
 a camshaft rotated by a crankshaft of the internal combustion engine and comprising a cam, the cam having positive and negative acceleration portions, and    a swing member that is configured to be rocked on a support shaft by rotation of the cam, the swing member having a cam surface configured to drive the valve; the cam surface having a base circle portion, a lift portion, and a ramp portion extending between the base circle portion and the lift portion;    wherein the ramp portion is configured such that when the positive or negative acceleration portions of the cam actuate the swing member a lift speed of the valve is substantially constant.    
   
   
       2 . The valve drive mechanism as in  claim 1 , wherein the valve is an intake valve.  
   
   
       3 . The valve drive mechanism as in  claim 1 , wherein the valve is an exhaust valve.  
   
   
       4 . The valve drive mechanism as in  claim 1 , further comprising means for varying the lift of the valve.  
   
   
       5 . A valve drive mechanism for actuating a valve of an internal combustion engine, the valve drive mechanism comprising; 
 a camshaft rotated by a crankshaft of the internal combustion engine and comprising a cam, the cam having positive and negative acceleration portions, and    a swing member that is reciprocally pivoted by rotation of the cam, the swing member comprising a cam surface having a base circle portion, a lift portion, and a ramp portion extending between the base circle portion and the lift portion, and    a variable drive mechanism configured to vary a lift amount of the valve;    wherein the ramp portion is configured such that when the positive or negative acceleration portions of the cam actuate the swing member a lift speed of the valve is substantially constant.    
   
   
       6 . The valve drive mechanism as in  claim 5 , wherein the ramp portion is configured to provide positive acceleration such that when the variable time mechanism is set in a minimum valve opening position a lift speed of the valve when the valve is being actuated by the ramp portion and the negative acceleration portion of the cam is substantially constant.  
   
   
       7 . The valve drive mechanism as in  claim 5 , wherein in a setting in which the ramp portion uses a positive acceleration section of the rotating cam under a state where the lift amount is variably controlled to be within a maximum range, the ramp portion is formed in a curved configuration so as to generate negative acceleration so that the lift speed of the valve in the portion corresponding to the ramp portion becomes substantially constant.  
   
   
       8 . The valve drive mechanism as in  claim 5 , wherein the valve is an intake valve.  
   
   
       9 . The valve drive mechanism as in  claim 5 , wherein the valve is an exhaust valve.  
   
   
       10 . The valve drive mechanism as in  claim 5 , wherein the variable valve mechanism comprises a roller arm that is positioned between the swing member and a rocker arm.  
   
   
       11 . The valve drive mechanism as in  claim 5 , wherein the variable valve mechanism comprises a roller arm that is positioned between the swing member and the cam.  
   
   
       12 . The valve drive mechanism as in  claim 5 , wherein a width of the base circle portion of the cam surface is smaller than a width of the lift portion of the cam surface.  
   
   
       13 . The valve drive mechanism as in  claim 12 , wherein the width of the base circle portion of the cam surface is at least 50% smaller than the width of the lift portion of the cam surface.  
   
   
       14 . A valve drive mechanism for actuating a valve of an internal combustion engine, the valve drive mechanism comprising 
 a cam rotated by a crankshaft of the internal combustion engine, the cam comprising positive or negative acceleration portions;    a swing member that is reciprocally moved by rotation of the cam, the swing member comprising cam surface for driving the valve; the cam surface comprising a base circle portion, a lift portion, and a ramp portion extending between the base circle portion and the lift portion; and    a variable drive mechanism configured to adjust a lift amount of the valve between a maximum valve opening setting and a minimum valve opening setting;    wherein the valve drive mechanism is configured such that when the positive or negative acceleration portions of the cam actuate the swing member, a lever ratio of the swing member or a rocker arm actuated by the swing member increases as the lift amount is adjusted into the minimum valve opening setting.    
   
   
       15 . The valve drive mechanism as in  claim 14 , wherein the cam comprises a base surface, and a nose surface projecting from the base surface, the nose surface of the cam being configured to provide for acceleration of the valve in all sections of the valve.  
   
   
       16 . The valve drive mechanism as in  claim 14 , wherein the valve drive mechanism includes a gap for absorbing errors or thermal expansion of respective portions of the valve drive mechanism system, the gap exists between components between the swing member and the valve.  
   
   
       17 . The valve drive mechanism as in  claim 16 , wherein a spring member brings the cam surface into constant contact another component of the valve drive mechanism.  
   
   
       18 . The valve drive mechanism as in  claim 14 , wherein the valve is an intake valve.  
   
   
       19 . The valve drive mechanism as in  claim 14 , wherein the valve is an exhaust valve.  
   
   
       20 . The valve drive mechanism as in  claim 20 , wherein a width of the base circle portion of the cam surface is smaller than a width of the lift portion of the cam surface.