Positive control (desmodromic) valve systems for internal combustion engines
Various types of valve systems are disclosed herein. In one embodiment, a positive control reciprocating sleeve valve system for use with an internal combustion engine includes opening and closing rockers controlled by corresponding opening and closing cam lobes. In one aspect of this embodiment, interference can be designed into the valve control system to provide additional “hold-closed” force to hold the valve against its seat during a portion of the engine cycle. In another aspect of this embodiment, positive control valve systems can include compliant components and systems, hydraulic systems, pneumatic systems, and/or mechanical spring systems to control valve lash, facilitate sealing, etc.
1. An internal combustion engine comprising:
a combustion chamber;
a reciprocating sleeve valve having a cylindrical bore and configured to cooperate with a valve seat to open and close a passage in fluid communication with the combustion chamber;
a camshaft operably coupled to the valve and configured to rotate about a central axis;
a cam lobe carried by the camshaft and having an exterior profile at least partially defined by a first surface portion and a second surface portion; and
a rocker arm operably disposed between the valve and the cam lobe,
wherein the first surface portion is spaced apart from the central axis by a first distance and the second surface portion is spaced apart from the central axis by a second distance, greater than the first distance, wherein the first surface portion positions the valve in contact with the valve seat and presses the valve against the valve seat with at most a first force, and
wherein the second surface portion presses the valve against the valve seat with a second force, greater than the first force, during rotation of the camshaft about the central axis.
2. The engine of claim 1 wherein the second surface portion defines a region of maximum lift of the cam lobe.
3. The engine of claim 1 wherein the first surface portion of the cam lobe defines a circular profile, and wherein the second surface portion of the cam lobe defines a raised profile adjacent to the circular profile.
4. The engine of claim 1 :
wherein the cam lobe is a valve closing cam lobe;
wherein the camshaft further carries a valve opening cam lobe; and
wherein the valve opening cam lobe has an exterior profile at least partially defined by a third surface portion that moves the valve away from the valve seat during rotation of the camshaft.
5. The engine of claim 1 , further comprising a piston configured to reciprocate in the cylindrical bore.
6. The engine of claim 1 , further comprising:
a piston configured to reciprocate in the bore between a bottom dead center (BDC) position and a top dead center (TDC) position, and wherein the second surface portion of the cam lobe presses the sleeve valve against the valve seat with the second force when the piston is proximate the TDC position.
7. The engine of claim 1 , further comprising:
a fulcrum to which the rocker arm is pivotally coupled; and
means for reciprocating the fulcrum in response to rotation of the camshaft.
8. The engine of claim 1 , further comprising:
a compliant support, wherein the rocker arm is pivotally coupled to the compliant support and depresses the compliant support in response to rotation of the camshaft.
9. The engine of claim 1 , further comprising:
a compliant support having a head portion, wherein the rocker arm is pivotally supported by the head portion of the compliant support and depresses the head portion in response to contact with the second surface portion during rotation of the camshaft.
10. The engine of claim 1 , further comprising:
a support member slidably disposed in a bore;
a biasing member operably disposed against the support member, wherein the rocker arm is pivotally coupled to the support member such that the rocker arm drives the support member into the bore and compresses the biasing member in response to contact with the second surface portion during rotation of the camshaft.
11. The engine of claim 1 , wherein the rocker arm is compliant and is configured to deflect in response to contact with the second surface portion during rotation of the camshaft.
12. The engine of claim 1 , wherein the rocker arm is compliant and deflects in response to contact with the second surface portion during rotation of the camshaft, and wherein the rocker arm exerts about 100 newtons of force against the valve per deflection of from about 0.01 mm to about 0.1 mm.
13. A method for operating an internal combustion engine having a reciprocating piston operably disposed in a cylindrical bore of a sleeve valve, wherein the bore of the sleeve valve at least partially defines a combustion chamber, the internal combustion engine further comprising a rocker pivotally disposed between the sleeve valve and a cam lobe, the method comprising:
moving the sleeve valve away from a valve seat to open a passage into the combustion chamber;
while the passage is open, moving the piston toward a bottom dead center (BDC) position in the bore to draw a combustible charge into the combustion chamber;
moving the sleeve valve toward the valve seat;
pressing the sleeve valve against the valve seat with a first force to close the passage into the combustion chamber, the pressing of the sleeve valve against the valve seat with the first force comprising deflecting the rocker a first amount;
while pressing the sleeve valve against the valve seat with the first force, moving the piston toward a top dead center (TDC) position in the bore to compress the combustible charge in the combustion chamber;
as the piston approaches the TDC position, pressing the sleeve valve against the valve seat with a second force, greater than the first force, the pressing of the sleeve valve against the valve seat with the second force comprising deflecting the rocker a second amount which is greater than the first amount; and
while pressing the sleeve valve against the valve seat with the second force, igniting the combustible charge to drive the piston toward the BDC position.
14. The method of claim 13 wherein moving the sleeve valve away from the valve seat includes driving the sleeve valve with a first cam lobe, and wherein moving the sleeve valve toward the valve seat includes driving the sleeve valve with a second cam lobe.
15. The method of claim 13 wherein the engine includes a cam lobe operably coupled to the sleeve valve, wherein pressing the sleeve valve against the valve seat with the first force includes driving the sleeve valve against the valve seat with a first surface portion of the cam lobe, and wherein pressing the sleeve valve against the valve seat with the second force includes driving the sleeve valve against the valve seat with a second surface portion of the cam lobe, the second surface portion having greater lift than the first surface portion.
16. The engine of claim 10 , further comprising a flange positioned between the biasing member and the support member, the biasing member applying a force against the flange which urges the flange against a part of a housing of the engine until the rocker arm applies a force against the support member that overcomes the force applied by the biasing member.