Variable valve train of internal combustion engine
View Patent ↗This variable valve train has a camshaft, a rocker shaft, and a rocker arm mechanism for transmitting a motion of a cam formed on the camshaft to a valve. The rocker arm mechanism includes a first arm which drives the valve, a second arm, a third arm, and a variable mechanism which rocks the rocker shaft. The first arm is rockably supported on the rocker shaft. The second arm is driven by the cam and rocks around a universal joint as a pivot on the side of the rocker shaft. The third arm is displaced to drive the first arm as the second arm rocks.
1. A variable valve train an internal combustion engine, comprising:
a camshaft provided for rotation in the internal combustion engine;
a rocker shaft provided in the internal combustion engine; and
a rocker arm mechanism which is driven by a cam formed on the camshaft and opens and closes an intake or exhaust valve, wherein the rocker arm mechanism comprises:
a first arm rockably supported on the rocker shaft and configured to drive the intake or exhaust valve;
a second arm which is driven by the cam and rocks around a pivot on the side of the rocker shaft;
a third arm which is rockably provided on a support shaft located near the rocker shaft and is configured to be displaced to drive the first arm as the second arm rocks; and
a variable mechanism which displaces the pivot for the second arm on the side of the rocker shaft,
wherein the third arm has a transmission surface portion which is displaced as the second arm rocks and touches the first arm to drive the first arm, and the transmission surface portion is provided with a conversion portion at which the distance from the center of the support shaft to the transmission surface portion changes so that the rocking amount of the second arm is converted to drive the first arm.
2. A variable valve train according to claim 1 , wherein the variable mechanism displaces the pivot by rotating the rocker shaft, and moves a portion of the second arm in contact with the cam in the circumferential direction of a base circle of the cam, thereby changing the rotational phase of the second arm with respect to the cam.
3. A variable valve train according to claim 2 , wherein the transmission surface portion has a nonconversion portion at which the distance from the center of the support shaft to the transmission surface portion makes no substantial change in the direction of rotation of the third arm, and the nonconvertible portion cancels a rocking amount of the second arm substantially equivalent to a given angle from the start of rocking motion with the rotational phase of the second arm with respect to the cam advanced for the given angle by the variable mechanism.
4. A variable valve train an internal combustion engine, comprising:
a camshaft provided for rotation in the internal combustion engine;
a rocker shaft provided in the internal combustion engine; and
a rocker arm mechanism which is driven by a cam formed on the camshaft and opens and closes an intake or exhaust valve, wherein the rocker arm mechanism comprises:
a first arm rockably supported on the rocker shaft and configured to drive the intake or exhaust valve;
a second arm which is driven by the cam and rocks around a pivot on the side of the rocker shaft;
a third arm which is rockably provided on a support shaft located near the rocker shaft and is configured to be displaced to drive the first arm as the second arm rocks;
a variable mechanism which displaces the pivot for the second arm on the side of the rocker shaft; and
a spring provided on the third arm,
wherein the second arm has a proximal end portion thereof rotatably supported by a connecting member provided on the side of the rocker shaft, and an abutting portion provided at a part of the second arm and an operating portion provided on the other side of the second arm abutting against the cam and the third arm, respectively, and
wherein the spring urges the third arm to displace the second arm in a direction such that the abutting portion of the second arm abuts against the cam.
5. A variable valve train according to claim 4 , wherein the first arm has bifurcated shaft fitting portions, through which the rocker shaft passes, that bifurcate from an end portion on the side of the valve, and a part of the second arm is situated between the bifurcated shaft fitting portions.
6. A variable valve train according to claim 4 , wherein the portion near to the proximal end portion of the second arm bifurcates from the portion near to the operating portion, and a part of the first arm is situated between two branches of the bifurcated proximal end portion.
7. A variable valve train according to claim 4 , wherein the first arm has a power transmission portion which abuts against the third arm and is offset in the axial direction of the rocker shaft with respect to a region for driving the valve.