Technical Field

The present invention relates to a rocker arm, and more specifically to a rocker arm for a type III valve train assembly for an internal combustion engine.

Background

Internal combustion engines comprise valve train assemblies. Valve train assemblies may comprise rocker arms for controlling opening and closing of valves the engine, i.e. intake or exhaust valves of a cylinder of an internal combustion engine. One type of valve train is a so-called type III valve train. A type III valvetrain comprises a single overhead cam (SOHC) arrangement. In a known type III valvetrain, a rocker arm is mounted on a rocker shaft, and a cam shaft comprises a cam arranged to engage with a first end of a rocker arm to cause the rocker arm to pivot about the rocker shaft, thereby to cause a second end of the rocker arm to push against a valve stem of a valve, thereby to cause a valve opening event.

It may be desirable to control or maintain a constant lash (i.e. clearance or total clearance between components of the valve train assembly) in type III valve train assemblies. A rocker arm with an adjustable system allows for adjustment of the lash, for example to absorb the stack up of dimensional tolerances in the valve train resulting from components thereof. However, such adjustment can lead to an increased engine assembly time. In addition, the adjustment system is susceptible to wear and may have to be re-adjusted during standard services.

It is an object of the present invention to mitigate at least some of the deficiencies of the prior art. Brief Description of the Drawings

Figure 1 illustrates schematically a side view of a portion of a valve train assembly according to an example.

Detailed Description

Referring to Figure 1, there is illustrated a valve train assembly 10 comprising a rocker arm 5 according to an example. The valve train assembly 10 is a type III valve train assembly, in a single overhead cam (SOHC) arrangement (the cam is not shown in Figure 1). The rocker arm may be referred to as a type III rocker arm. The valve train assembly 10 comprises a camshaft (not shown) comprising a cam (not shown), comprising a lift profile (not shown) and a base circle (not shown).

The rocker arm 5 comprises, at a first end 26 of the rocker arm 5, a roller follower 24 for following the cam (not shown) in use. The rocker arm 5 comprises a roller axle 28 on which the roller follower 24 is mounted, and about which the roller follower 24 is arranged to rotate in use. The axis of rotation of the roller follower 24 is the roller axis 6. The rocker arm 5 is itself mounted on a rocker shaft (not shown), and is arranged to pivot about the rocker shaft (not shown), about a rocker shaft axis 4. A second end (not shown) of the rocker arm 5, opposite to the first end 26 of the rocker arm 5, is for contacting a valve (not shown) (an exhaust or intake valve) of the overall internal combustion engine (not shown). The rocker arm 5 may comprise at the second end (not shown) for example a component for compression engine braking, and hence the rocker arm 5 may be, for example, configured for compression engine braking, or for example, part of a compression engine braking system, for example.

In general overview, when the roller follower 24 engages the lift profile (not shown) of the cam (not shown), the cam (not shown) causes the rocker arm 5 to pivot about the rocker shaft axis 4 (clockwise in the sense of Figure 1), which in turn may cause the second end (not shown) of the rocker arm 5 to push down on a valve stem (not shown) of a valve (not shown) of a cylinder (not shown) of the internal combustion engine (not shown) thereby for example to cause a valve opening event.

The rocker arm 5 comprises a biasing means 3 and a biasing means holder 7. In this example, the biasing means 3 is a bias spring 3, and the biasing means holder 7 will be referred to as a bias spring holder 3 accordingly.

The bias spring holder 7 is connected, at a first 7a end, to the roller axle 28 for sliding movement relative to the roller axle 28 over a fixed distance. Specifically, the bias spring holder defines at least one elongate slot 32 in which the roller axle 28 is slidably disposed. The slot 32 comprises closed ends 32a and 32b. The roller axle 28 may travel in the slot 32 between the closed ends 32a, 32b.

The bias spring holder 7 comprises at a second end 7b, opposite to the first end 7a, a holding portion 36 for supporting a first end 3 a of the bias spring 3. The second end 7b of the bias spring holder 7 is also arranged for contacting a reaction component 2 of the valve train assembly in use. The reaction component 2 may be, for example a bar 2 or the like and may be fixed relative to, for example fixed to, the engine cylinder head (not shown).

A second end (not visible) of the bias spring 3 is engaged with the roller axle 28. The bias spring 3 is arranged to bias the bias spring holder 7 away from the roller axle 28. The extent to which the bias spring holder 7 is biased away from the roller axis 28 is limited by the roller axle 28 engaging with the first closed end 32a of the slot 32 of the bias spring holder 7.

When the roller follower 24 is engaged with the base circle (not shown) of the cam (not shown), there is a bias spring lash or gap 1 between the reaction component 2 and the second end 7b of the bias spring holder 7. This is the situation illustrated in Figure 1. In other words, when the roller follower 24 is engaged with the base circle (not shown) of the cam (not shown), the bias spring holder 7 is preloaded against the roller axle 28 by the bias spring 3, and the first closed end 32a of the slot 32 of the bias spring holder 7 contacts the roller axis 28 to act as a hard stop, hence defining the maximum distance of the second end 7b of the bias spring holder 7 from the roller axle 28. This maximum distance sets the lash or gap 1 between the reaction component 2 and the second end 7b of the bias spring holder 7 when the roller follower 24 is engaged with the base circle (not shown) of the cam (not shown). The bias spring lash 1 between the reaction component 2 and the bias spring holder 7 may therefore be precisely defined thereby, and hence may not need adjustment, hence saving installation time and reducing costs.

When the lift profile (not shown) of the cam engages the roller follower 24, the bias spring holder 7 contacts the reaction component 2, and the bias spring holder 7 is thereby moved relative to the roller axle 28 to compress the bias spring 3, and as a result, the roller follower 24 is urged into contact with the cam (not shown). In other words, sliding movement of the bias spring holder 7 relative to the roller axle 28 when the bias spring holder 7 contacts the reaction component 2 when the lift profile (nots shown) of the cam (nots shown) engages the roller follower 24 causes the bias spring 3 to compress and thereby to urge the roller follower 24 into contact with the cam (not shown). More specifically, during the opening ramp of cam lift events (i.e. when the initial ramp of the lift profile of the cam (not shown) engages the roller follower 24, the rocker arm 5 rotates about the rocker shaft axis 4 (clockwise in the sense of Figure 1) and the bias spring holder 7 makes contact with the reaction component 2. As a result, the first closed end 32a of the slot 32 of the bias spring holder 7 bias spring holder loses contact with the roller axle 28 as the roller axle 28 moves up the slot 32 (for example up the slot 32 until the second closed end 32b), and the bias spring 23 is compressed between the roller axle 28 and the holding portion 36 or the bias spring holder 7. As a result, a load is asserted to the cam/roller interface (not shown) ensuring contact between the two. That is, the bias spring when compressed urges the rotation of the rocker arm 5 anticlockwise in the sense of Figure 1, against the cam, to urge the roller follower 24 into contact with the cam (nots shown)

The urging of the roller follower 24 into contact with the cam (not shown) during portions of the engine cycle when the lift profile (not shown) of the cam (not shown) is engaging the roller follower 24 may help ensure proper positioning of the rocker arm 2, and hence may help prevent or mitigate faults.

When the roller follower 24 again engages with the base circle of the cam, that is, when the roller follower 24 returns to the cam base circle (not shown) on the closing ramp of the lift profile (not shown), the bias spring 3 extends, the first closed end 32a of the slot 32 of the bias spring holder 7 bias spring holder 7 makes contact with the roller axle 28 again, and the bias spring lash 1 is again re-established. The bias spring holder 7 therefore may have only intermittent contact with the reaction component 2.

The bias spring holder 7 being anchored to the roller axle 28 allows that the maximum height of the bias spring holder relative to the roller follower 24, and to the base circle (not shown) of the cam (not shown), may be precise enough to remove any need for need for adjustment of the lash 1. The rocker arm 5 may therefore be installed into the cylinder head assembly (not shown) and on doing so may immediately have a bias spring lash 1 within a tolerable range, and hence may remove the need to adjust the bias spring holder 7 or rocker arm 22 to provide a bias spring lash 1 in a tolerable range, as with an existing system. The need for readjustment during engine service may also be eliminated. Assembly and service time may both therefore be reduced and hence cost may be reduced.

As described above, the type III valvetrain bias spring holder 7 has a fixed maximum length (i.e. a fixed maximum displacement relative to the roller axis 6 of the rocker arm 22). This may be as compared for example to adjustable systems that are adjustable to set the bias spring lash within a specified range. The adjustment is to absorb the stack up of dimensional tolerances that results from attachment of a bias spring holder to features unrelated to the rocker shaft axis. The adjustment can increase engine assembly time, and the adjustment system is susceptible to wear and may have to be re-adjusted during standard services. In examples of the present invention however, the bias spring holder 7 has a precise, fixed maximum length due to its direct relation to the roller axis 6 and so does not need adjustment during assembly, thus saving assembly time. The bias spring holder maintains a constant lash or gap 1 between the bias spring holder 7 and the neighbouring reaction component or components 2 in the cylinder head whilst on the cam base circle (nots shown), and the bias spring holder 7 makes contact with the reaction component 2 during cam lift (i.e. whilst on the lift profile of the cam, not shown), compressing the bias spring (3) and ensuring cam-to-roller contact.

All of the above examples are to be understood as illustrative examples only. It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the examples, or any combination of any other of the examples. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.