Valve system of V-type engine

Abstract

A valve system of a V-type engine in which a camshaft provided in each bank is formed with valve cams that open and close engine valves and a pump cam for driving a fuel pump, the phase of the pump cam relative to the valve cams is set such that the crank angle at which driving torque of the pump cam is maximized does not coincide with the crank angle at which driving torque of each of the valve cams is maximized.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and/or further objects, features and advantages of the invention will become more apparent from the following description of exemplary embodiments with reference to the accompanying drawings, in which like numerals are used to represent like elements and wherein:

FIG. 1 is a schematic view of a V-type engine in which a valve system according to a first embodiment of the invention is installed;

FIG. 2 is a schematic view showing a fuel supply system of the V-type engine of FIG. 1;

FIG. 3 is a view showing intake and exhaust camshafts of the valve system of FIG. 1;

FIG. 4A is an explanatory view showing the phase of a pump cam relative to a valve cam on the intake camshaft of the left bank in the first embodiment, and FIG. 4B is an explanatory view showing the phase of a pump cam relative to a valve cam on an intake camshaft of the right bank in the first embodiment;

FIG. 5A is a graph indicating torque fluctuations of the intake camshaft of the left bank, and FIG. 5B is a graph indicating torque fluctuations of the intake camshaft of the right bank;

FIG. 6 is a graph indicating changes in the maximum torque and the minimum torque with respect to the angle of advance;

FIG. 7A is an explanatory view showing the phase of the pump cam relative to the valve cam on an intake camshaft of the left bank in a second embodiment of the invention, and FIG. 7B is an explanatory view showing the phase of the pump cam relative to the valve cam on an intake camshaft of the right bank in the second embodiment;

FIG. 8A is a graph indicating torque fluctuations of the intake camshaft of the left bank, and FIG. 8B is a graph indicating torque fluctuations of the intake camshaft of the right bank; and

FIG. 9A is a graph indicating changes in the maximum torque and the minimum torque in the left bank with respect to the angle of advance, and FIG. 9B is a graph indicating changes in the maximum torque and the minimum torque in the right bank with respect to the angle of advance.

Claims

1. A valve system of a V-type engine comprising: a camshaft provided in each bank of the engine, formed with valve cams that open and close engine valves and a pump cam that drives a fuel pump, which feeds pressurized fuel to a fuel injection device, whereincrank-angle phase differences among cylinders in each bank of the V-type engine are set at unequal intervals; andthe pump cam has a plurality of cam noses, and the phase of the pump cam relative to the valve cams is determined such that a crank angle at which driving torque of the pump cam is maximized does not coincide with a crank angle at which driving torque of each of the valve cams is maximized.

2. The valve system as defined in claim 1, wherein: the V-type engine has four cylinders in each bank, and crank-angle phase differences between the cylinders of the engine are set at equal intervals of 90°CA, while crank-angle phase differences between the cylinders in each bank are set at unequal intervals including 90°CA and 270°CA;the pump cam of each bank has two cam noses that are formed in the same shape at equal intervals over the entire circumference of the pump cam, and the pump cams of the two banks are arranged to drive the corresponding fuel pump in phase with each other; andthe phase of the pump cam relative to the valve cams is determined in terms of the crank angle such that the phase in which a top of one of the cam noses of the pump cam acts on the fuel pump is advanced by an angle within a range of 120°CA to 180°CA from the phase in which a top of a cam nose of one of the valve cams for driving the corresponding engine valve of a specified cylinder of the engine acts on an actuator linked to the engine valve, the specified cylinder being located in the bank in which the pump cam is provided and providing a crank-angle phase difference of 270°CA with respect to the preceding cylinder in the same bank.

3. The valve system as defined in claim 1, wherein: the V-type engine has four cylinders in each bank, and crank-angle phase differences between the cylinders of the engine are set at equal intervals of 90°CA, while crank-angle phase differences between the cylinders in each bank are set at unequal intervals including 90°CA and 270°CA;the pump cam of each bank has two cam noses that are formed in the same shape at equal intervals over the entire circumference of the pump cam, and the pump cams of the two banks are arranged to drive the corresponding fuel pump in opposite phase to each other; andthe phase of the pump cam relative to the valve cams is determined in terms of the crank angle such that the phase in which a top of one of the cam noses of the pump cam acts on the fuel pump is advanced by an angle within a range of 240°CA to 300°CA from the phase in which a top of a cam nose of one of the valve cams for driving the corresponding engine valve of a specified cylinder of the engine acts on an actuator linked to the engine valve, the specified cylinder being located in the bank in which the pump cam is provided and providing a crank-angle phase difference of 270°CA with respect to the preceding cylinder in the same bank.

4. The valve system as defined in claim 1, wherein the fuel pump is disposed in each bank, and is driven by the camshaft of each bank.

5. The valve system as defined in claim 1, further comprising a variable valve timing mechanism that changes valve timing of the engine valves by changing the phase of the valve cams relative to a crankshaft of the V-type engine, wherein: the phase of the pump cam relative to the crankshaft is changed synchronously with a change in the phase of the valve cams relative to the crankshaft.