GB2082718A - Method of assembling a valve rain in an internal combustion engine - Google Patents

Abstract

A method of assembling a valve train in an internal combustion engine, which valve train comprises a camshaft (5), an hydraulic tappet (6), a valve rocker (1), a sliding contact element (9) fixed to one arm of the rocker (1) and effecting sliding contact between the hydraulic tappet (6) and the valve rocker (1). and a poppet valve (7) actuated by the other arm of the valve rocker, the method comprising the steps of (a) grading a supply of sliding contact elements (9) into a plurality of tolerance range groups corresponding to the amount by which the sliding contact elements would space the said one arm of the valve rocker from the hydraulic tappet, (b) assembling the camshaft (5), hydraulic tappet (6), valve rocker (1), and poppet valve (7) on the internal combustion engine, (c) measuring the gap (Y) between the said one arm and the hydraulic tappet which should be occupied by the sliding contact element, (d) selecting a sliding contact element (9) from the tolerance groups corresponding most closely to the measured gap, and (e) securing the selected sliding contact element (9) in the valve rocker (1) without disassembling the valve train. <IMAGE>

Description

SPECIFICATION Method of assembling a valve train in an internal combustion engine The invention relates to a method of assembling a valve train in an internal combustion engine.

A conventional internal combustion engine comprises for each cylinder valve, a valve train incorporating valve rockers supported on blocks disposed on stud boits and secured thereto by nuts. The rockers actuate suspended poppet valves and are thereby operated by an overhead camshaft via hydraulic tappets, an opening being provided in the arm of the valve rocker into which sliding contact elements are inserted against which the hydraulic tappet acts.

For such engines, the amount of free movement or play in the valve train increases as the engine warms up to its normal operating temperature.

This increase in play is taken up by the hydraulic tappets. However, since the hydraulic tappets themselves can accommodate only a limited change in play, the amount of play initially present in the valve train, which in turn depends upon the variations in size of the components within the manufacturing tolerances, must be reduced to within the limits which can be accommodated by the hydraulic tappet. This can be achieved by tightening the nut holding the block to the stud bolt whilst the hydraulic tappets are in contact with the base circle of the camshaft so that the block comes nearer to the cylinder head and is tensioned. However, this tightening process involves costly and time-consuming adjustment work.

According to the invention there is provided a method of assembling a valve train in an internal combustion engine, which valve train comprises a camshaft, an hydraulic tappet, a valve rocker, a sliding contact element fixed to one arm of the rocker and effecting sliding contact between the hydraulic tappet and the valve rocker, and a poppet valve actuated by the other arm of the valve rocker, the method comprising the steps of (a) grading a supply of sliding contact elements into a plurality of tolerance range groups corresponding to the amount by which the sliding contact elements would space the said one arm of the valve rocker from the hydraulic tappet, (b) assembling the camshaft, hydraulic tappet, valve rocker, and poppet valve on the internal combustion engine, (c) measuring the gap between the said one arm and the hydraulic tappet which should be occupied by the sliding contact element, (d) selecting a sliding contact element from the tolerance groups corresponding most closely to the measured gap, and (e) securing the selected sliding contact element in the valve rocker without disassembling the valve train.

The invention also includes a valve rocker for a valve train of an internal combustion engine having an opening towards the end of one arm for receiving a sliding contact element. the said opening comprising two parallel longitudinal edges, and two opposing lateral edges each of which is shaped to define an inwardly projecting arcuate lobe.

The invention also includes a sliding contact element for a valve train of an internal combustion engine comprising a head having a sliding contact surface and a rear face from which a shank of rectangular cross-section projects.

The measurement of the sliding contact elements during their manufacture and grading according to tolerance groups is a relatively simple process, and, when the components of the valve train are assembled, selection of a sliding contact element from the appropriate tolerance group can be effected simply and quickly.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the drawings, in which: Figure 1 is a vertical section through the valve train of an internal combustion engine which has been described in accordance with the method of the invention; Figure 2 is an enlarged section through a valve rocker incorporated in the valve train of Figure 1; Figure 3 is a view in the direction of arrow Ill in Figure 2; Figure 4 is a side view of a sliding contact element incorporated in the valve train of Figure 1; Figure 5 is a view in the direction of arrow V in Figure 4; and Figure 6 is a view in the direction of the arrow VI in Figure 4.

Referring to Figure 1, a valve train of an internal combustion engine comprises a metal valve rocker 1 supported on a block 2 which is braced by a nut 3 on a stud bolt 4 fixed in a cylinder head. One arm of the valve rocker 1 is actuated by an overhead camshaft 5 via an hydraulic tappet 6.

The other arm of the valve rocker 1 actuates a poppet valve 7. An opening 8 is provided in the end of the arm of the valve rocker 1 interacting with the hydraulic rod 6 and a sliding contact element 9 is mounted in the opening 8. The form of the opening 8 and the sliding contact element 9 are illustrated in greater detail in Figures 2-6.

The element 9 reduces the initial free movement in the valve train sufficiently to ensure that the amount of movement which can be accommodated by the hydraulic tappet 6 is sufficient to compensate for changes in the free movement resulting from increases in the temperature of the engine, and is not used up in accommodating the amount of free movement initially present in the view train as a result of variations of the sizes of the components of the valve train within manufacturing tolerances. The opening 8 in the valve rocker 1 must therefore accurately position the sliding contact element 9 relative to the rocker 1.The opening 8 in the valve rocker 1 is suitably made by stamping and, in order to ensure that the formation of the aperture does not introduce uncertainty into the positioning of the element 9, the aperture is shaped so that its longitudinal edges 10 correspond to the maximum width of the slider 9 and have outwardly turned stamping radii, whilst the narrower edges of the aperture are provided with inwardly projecting arcuate lobes 11 which engage the sides of the slider 9.

The sliding contact element 9 shown in Figures 4-6 has a head 12 with a sliding surface 13 and a rectangular shank 14 which extends from a flat contact surface 1 5. After manufacture of the elements 9, the dimension X between the sliding surface 13 and the contact surface 1 5 is determined by measurement and the elements 9 are graded according to a plurality, e.g. four, tolerance groups.

In the assembly of the internal combustion engine the components of the valve train shown in Figure 1, i.e. the camshaft, tappet, rocker and poppet valve are assembled, but without the element 9 and then the dimension marked Y in Figure 1, i.e. the gap between the surfaces on the arm of the valve rocker 1 and on the hydraulic rod 6 which abut the contact surfaces 13 and 1 5 of the element 9 is determined by measurement. By disengaging the valve spring from the valve member 7 and swinging up the arm of the valve rocker a slider selected from a tolerance group corresponding to the measured gap can be inserted. The valve rocker 1 can be brought back into engagement with the valve member 7 and the hydraulic tappet, and the valve spring re-engaged with the valve member 7. In this way a reliable reduction in the initial valve clearance can be carried out during mass production assembly at low cost.

Claims (7)

1. A method of assembling a valve train in an internal combustion engine, which valve train comprises a camshaft, an hydraulic tappet, a valve rocker, a sliding contact element fixed to one arm of the rocker and effecting sliding contact between the hydraulic tappet and the valve rocker, and a poppet valve actuated by the other arm of the valve rocker, the method comprising the steps of (a) grading a supply of sliding contact elements into a plurality of tolerance range groups corresponding to the amount by which the sliding contact elements would space the said one arm of the valve rocker from the hydraulic tappet.

(b) assembling the camshaft, hydraulic tappet, valve rocker, and poppet valve on the internal combustion engine, (c) measuring the gap between the said one arm and the hydraulic tappet which should be occupied by the sliding contact element, (d) selecting a sliding contact element from the tolerance groups corresponding most closely to the measured gap, and (e) securing the selected sliding contact element in the valve rocker without disassembling the valve train.

2. A method according to Claim 1 wherein the poppet valve comprises a valve member and spring biasing the valve member into engagement with the said other arm of the valve rocker, and the selected sliding contact element is secured in the valve rocker by disengaging the spring from the valve member, rocking the said one arm of the valve rocker away from the hydraulic tappet, securing the sliding contact element in the said one arm, and re-engaging the spring with the other arm of the valve rocker.

3. A method according to Claim 1 or Claim 2 wherein the valve rocker has an opening in the said one arm which provides two parallel longitudinal edges and inwardly projecting lobes on its lateral edges.

4. A method according to any one of Claims 1 to 3 wherein the sliding contact elements comprise a head having a sliding contact surface and a shank of rectangular cross-section projecting from the near face of the head, the rear face forming a contact surface which in use engages with the valve rocker arm.

5. A method of assembling a valve train substantially as hereinbefore described with reference to the drawings.

6. A valve rocker for a valve train of an internal combustion engine having an opening towards the end of one arm for receiving a sliding contact element, the said opening comprising two parallel longitudinal edges, and two opposing lateral edges each of which is shaped to define an inwardly projecting arcuate lobe.

7. A sliding contact element for a valve train of an internal combustion engine comprising a head having a sliding contact surface and a rear face from which a shank of rectangular cross-section projects.