GB2136048A - I.C. engine valve train - Google Patents

Abstract

An additional compression spring 12 acts on the lower end of the push rod 8 to bias the push rod against the tappet 9 and the tappet against the camshaft 11. Since this necessary force is produced locally at the bottom end of the push rod, the valve train components 3, 4, 5, 6 and 7 in the upper part of the arrangement can be made very much lighter, thus reducing stresses and inertia and allowing shorter valve opening times as well as an overall saving in weight. <IMAGE>

Description

SPECIFICATION A valve train arrangement in an internal combustion engine This invention relates to a valve train arrangement in an internal combustion engine which has rocker arms propelled by push-rods and/or tappets.

The cam shafts of such engines are heavily loaded, particularly when the engine is running at a low speed, and any steps which can be taken to reduce the cam shaft loading are advantageous.

According to the present invention, there is provided a valve train arrangement in an internal combustion engine which has valves and rocker arms for opening the valves, the rocker arms being propelled by a cam shaft through intermediate reciprocating members, the arrangement including first springs biasing the valves to a closed position and second springs biasing the reciprocating members towards the camshaft.

The invention therefore provides that the task of returning the valve train components to the "valve closed" position is split between two springs, rather than being done exclusively by a single spring surrounding the valve stem, as was previously the case. This splitting of the single conventional spring into two separate springs means that the contact forces and stresses between the various relatively moving surfaces are reduced, and as a result the overall inertia of the whole arrangement can be reduced with the resulting reduction in stress on the cam shaft.

The intermediate reciprocating members preferably include, for each valve, a push rod and a tappet. The second spring preferably acts between a fixed abutment on the engine and the lower end of the push rod.

The invention will now be further described, by way of example, with reference to the accompanying drawing, which is a section through part of an overhead valve internal combustion engine.

The drawing shows a cylinder head 1 and a cylinder block 2. A valve 3 is reciprocable in a bore in the cylinder head 1 and is controlled by the usual valve spring 4 held in place by valve spring retainer and collets 5. The valve is operated by a rocker arm 6 journaled on a shaft 7. A push rod 8 moves vertically against the opposite end of the rocker arm 6 so that raising of the push rod 8 rotates the rocker arm 6 and causes the valve 3 to be depressed to an open position.

The lower end of the push rod 8 acts against a tappet 9, and the tappet in turn is in contact with a cam surface 10 of camshaft 11. As the camshaft 11 rotates, the cam surface 10 causes the tappet 9 to move up and down resulting in up and down movement of the push rod 8, pivoting movement of the rocker arm 6 and opening and closing of the valve 3.

To ensure that the lower end of the push rod 8 is kept firmly in contact with the upper surface of the tappet 9, and the lower surface of the tappet 9 is kept firmly in contact with the cam surface 10, a compression spring 12 is provided around the lower end of the push rod 8. This spring bears against a flange 1 3 at the bottom of the push rod and against the lower edge of a sleeve 14 which is a push fit in a bore 1 5 in the cylinder block. The bush 14 is held firmly in place once the cylinder head 1 is secured down onto the top surface of the cylinder block. Any other suitable means of holding the spring in place could be used.

In the past, the force necessary to press the tappet against the cam surface 10 has arisen from the presence of the spring 4, and this force therefore had to be transmitted across the rocker arm 6 and its shaft 7 and down the push rod.

The arrangement described here, where the auxiliary compression spring 12 does the job of keeping the lower end of the push rod and the tappet in place, means that the necessary force no longer has to be transmitted through the rocker arm 6 and that consequently some components in the valve train can be reduced in size, thus reducing their weight and inertia, i.e. the valve spring 4, the valve spring retainer 5, the rocker arm assembly 6, the rocker shaft 7 and the tappet 9. The weight of the push rod itself may need to be increased as a result of the presence of the flange 13, and there is an additional component in the form of the compression spring 12. However the overall sum of the weights of the components in the arrangement described here can be below that of conventional components in an equivalent sized engine.There are also reduced contact forces and stresses not only between the tappet 9 and the cam surface 10, but between the other components also, and reduced buckling forces on the push rod 8 itself. As a result of the reduced inertia, shorter valve opening times are.possible.

The result of splitting the spring as described above is not, as may first be thought, simply a question of getting the same forces acting in different places. With this arrangement it is possible to actually reduce the contact force between the tappet 9 and the cam surface 10, because of the reduced inertia of the components throughout the system.

1. A valve train arrangement in an internal combustion engine which has valves and rocker arms for opening the valves, the rocker arms being propelled by a cam shaft through intermediate reciprocating members, the arrangement including first springs biasing the valves to a closed position and second springs biasing the reciprocating members towards the cam shaft.

2. A valve train arrangement as claimed in Claim 1, wherein the reciprocating members are, for each valve, a push rod and a tappet.

3. A valve train arrangement as claimed in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A valve train arrangement in an internal combustion engine This invention relates to a valve train arrangement in an internal combustion engine which has rocker arms propelled by push-rods and/or tappets. The cam shafts of such engines are heavily loaded, particularly when the engine is running at a low speed, and any steps which can be taken to reduce the cam shaft loading are advantageous. According to the present invention, there is provided a valve train arrangement in an internal combustion engine which has valves and rocker arms for opening the valves, the rocker arms being propelled by a cam shaft through intermediate reciprocating members, the arrangement including first springs biasing the valves to a closed position and second springs biasing the reciprocating members towards the camshaft. The invention therefore provides that the task of returning the valve train components to the "valve closed" position is split between two springs, rather than being done exclusively by a single spring surrounding the valve stem, as was previously the case. This splitting of the single conventional spring into two separate springs means that the contact forces and stresses between the various relatively moving surfaces are reduced, and as a result the overall inertia of the whole arrangement can be reduced with the resulting reduction in stress on the cam shaft. The intermediate reciprocating members preferably include, for each valve, a push rod and a tappet. The second spring preferably acts between a fixed abutment on the engine and the lower end of the push rod. The invention will now be further described, by way of example, with reference to the accompanying drawing, which is a section through part of an overhead valve internal combustion engine. The drawing shows a cylinder head 1 and a cylinder block 2. A valve 3 is reciprocable in a bore in the cylinder head 1 and is controlled by the usual valve spring 4 held in place by valve spring retainer and collets 5. The valve is operated by a rocker arm 6 journaled on a shaft 7. A push rod 8 moves vertically against the opposite end of the rocker arm 6 so that raising of the push rod 8 rotates the rocker arm 6 and causes the valve 3 to be depressed to an open position. The lower end of the push rod 8 acts against a tappet 9, and the tappet in turn is in contact with a cam surface 10 of camshaft 11. As the camshaft 11 rotates, the cam surface 10 causes the tappet 9 to move up and down resulting in up and down movement of the push rod 8, pivoting movement of the rocker arm 6 and opening and closing of the valve 3. To ensure that the lower end of the push rod 8 is kept firmly in contact with the upper surface of the tappet 9, and the lower surface of the tappet 9 is kept firmly in contact with the cam surface 10, a compression spring 12 is provided around the lower end of the push rod 8. This spring bears against a flange 1 3 at the bottom of the push rod and against the lower edge of a sleeve 14 which is a push fit in a bore 1 5 in the cylinder block. The bush 14 is held firmly in place once the cylinder head 1 is secured down onto the top surface of the cylinder block. Any other suitable means of holding the spring in place could be used. In the past, the force necessary to press the tappet against the cam surface 10 has arisen from the presence of the spring 4, and this force therefore had to be transmitted across the rocker arm 6 and its shaft 7 and down the push rod. The arrangement described here, where the auxiliary compression spring 12 does the job of keeping the lower end of the push rod and the tappet in place, means that the necessary force no longer has to be transmitted through the rocker arm 6 and that consequently some components in the valve train can be reduced in size, thus reducing their weight and inertia, i.e. the valve spring 4, the valve spring retainer 5, the rocker arm assembly 6, the rocker shaft 7 and the tappet 9. The weight of the push rod itself may need to be increased as a result of the presence of the flange 13, and there is an additional component in the form of the compression spring 12. However the overall sum of the weights of the components in the arrangement described here can be below that of conventional components in an equivalent sized engine.There are also reduced contact forces and stresses not only between the tappet 9 and the cam surface 10, but between the other components also, and reduced buckling forces on the push rod 8 itself. As a result of the reduced inertia, shorter valve opening times are.possible. The result of splitting the spring as described above is not, as may first be thought, simply a question of getting the same forces acting in different places. With this arrangement it is possible to actually reduce the contact force between the tappet 9 and the cam surface 10, because of the reduced inertia of the components throughout the system. CLAIMS

1. A valve train arrangement in an internal combustion engine which has valves and rocker arms for opening the valves, the rocker arms being propelled by a cam shaft through intermediate reciprocating members, the arrangement including first springs biasing the valves to a closed position and second springs biasing the reciprocating members towards the cam shaft.

2. A valve train arrangement as claimed in Claim 1, wherein the reciprocating members are, for each valve, a push rod and a tappet.

3. A valve train arrangement as claimed in Claim 1 or Claim 2 wherein the second spring acts between a fixed point on the engine itself and a flange at the lower end of the push rod.

4. A valve train arrangement substantially as herein described with reference to the accompanying drawing.