WO2000020730A1

WO2000020730A1 - Valve train assembly

Info

Publication number: WO2000020730A1
Application number: PCT/IB1999/001699
Authority: WO
Inventors: Majo Cecur
Original assignee: Eaton Automotive S.P.A.
Priority date: 1998-10-05
Filing date: 1999-10-05
Publication date: 2000-04-13
Also published as: JP4558938B2; BR9914635A; EP1119689B1; DE69914348T2; ITMI982136A1; DE69914348D1; ATE258271T1; EP1119689B2; JP2002526707A; EP1119689A1; IT1302601B1; DE69914348T3

Abstract

A valve train assembly for an internal combustion engine comprises a common carrier which supports the engine's rocker arms by means of individual fulcra each of which preferably forms a part of a hydraulic lash adjuster. Each rocker arm is constructed by deforming a metal sheet into a channel shape, the deformation also forming a part-spherical surface for mating with a surface of the fulcrum. The rocker arms can be snap-fitted on to the fulcra by means of an apertured, resilient sheet.

Description

VALVE TRAIN ASSEMBLY

The present invention relates to a valve train assembly for an internal

combustion engine, and to rocker arms for such an assembly. The invention

is particularly but not exclusively related to arrangements in which the

number of parts in the assembly is reduced, in which various parts can be pre-

assembled to facilitate engine assembly, and in which various parts are made

more simply.

Various aspects of the invention are intended to deal with a number of

separate problems in existing arrangements. For example, internal

combustion engines which have a plurality of valves for each cylinder tend to

use rocker arms which are mounted on a common pivot or axle and which

therefore need to have differing lengths in order to match the differing

positions of the valves. It is therefore necessary to manufacture two different

types of rocker arms.

It is also common, particularly for centre-pivoted rocker arms, to have

an hydraulic lash compensation device mounted at the valve end of the rocker

arm, the device therefore being continually reciprocated. This requires a

complex machined oil distribution path and makes it more difficult to feed oil

to the lash adjuster. Furthermore, the components of the rocker arm are heavy

and therefore strong valve return springs are required, and the rocker shaft has to be strong and therefore of large diameter, and heat-treated to harden the

surface in order to resist wear.

Various aspects of the present invention are set out in the

accompanying claims.

In a preferred embodiment, a valve train assembly for a internal

combustion engine comprises a valve train carrier having a plurality of

individual rocker arm fulcra, and a rocker arm attached to each fulcrum. The

carrier may also have one or more camshafts mounted thereto.

Such an arrangement can be provided as a pre-assembled unit for

fitting to a cylinder head having valves mounted therein, thus substantially

facilitating the assembly of an engine.

Each fulcrum may form part of a hydraulic lash adjuster. Accordingly,

since the lash adjusters would be fixedly mounted to the carrier, they are more

easily supplied with oil, so that a smaller oil pump producing relatively low

pressure can be used.

In a particularly advantageous arrangement, each rocker arm and its

associated fulcrum have co-operating part-spherical surfaces which permit not

only the pivoting motion required for operating the valves, but also a degree

of rotation about the length of the rocker arm, to provide a self-adjusting

function. Preferably, the rocker arm has a part-spherical recess into which a

part-spherical projection is located. (In practice the profile of the recess may

comprise several, e.g. three, spherical segments of slightly different diameter tangential to each other, sometimes referred to as a gothic socket.) The rocker

arm may be attached to the projection by means of a clip, possibly made of

spring steel, which is fitted over the head of the projection. As the rocker

arms do not need to be fitted to rocker axles, they may be made smaller and

lighter compared to existing aluminium or steel rockers. In a preferred

embodiment, the rockers are made of pressed sheet metal (with the final

thickness possibly increased or decreased by the pressing operation to provide

suitable weight/strength properties), and their lightness enables the use of

lighter valve springs resulting in lower energy consumption.

Because of the self-adjusting arrangement mentioned above, it is

possible to arrange for contact between a driving cam and the rocker arm to

extend laterally over a large distance, for example by having mounted on the

rocker a roller with a wide surface which is flat in a direction parallel to the

roller axis. This provides a greater area of contact than existing rockers which

rotate about an axle, and which need a roller having a convex surface to

ensure proper contact. As a result of the reduction in stress by increasing the

area of contact, the camshaft need not be so strong, and indeed it is possible to

use cast iron instead of more expensive steel.

By appropriate positioning of the individual rocker arm fulcra, it is

possible to use rockers of equal length for all the valves. Accordingly, the

rockers can be substantially identical, thereby reducing manufacturing costs. .Arrangements embodying the invention will now be described by way

of example with reference to the accompanying drawings, in which:

Fig. 1 is a side view of a prior art rocker arm;

Fig. 2 is a side view, partly in section, of a rocker arm arrangement

according to the invention applied to a valve;

Fig. 3 is a side view of the rocker arm of Figure 2;

Fig. 4 is a plan view of the rocker arm shown in Fig. 3;

Fig. 5 is a section along the line V-V of Fig. 3;

Fig. 6 shows is a section along the line VI-VI in Fig. 3;

Fig. 7 is a section through a hydraulic tappet forming a fulcrum of the

rocker arm;

Fig. 8 is a transverse section showing a valve train carrier of the

present invention, for controlling two rows of valves with a single central

camshaft:

Fig. 9 is a plan view of the valve train carrier as shown in Fig. 7;

Fig. 10 is a side view showing another embodiment of a valve train

assembly in accordance with the invention; and

Fig. 11 is a perspective view, from below, of a valve train carrier of

the assembly of Fig. 10.

Fig. 1 shows a prior art rocker (B) made of pressed aluminium, and

comprising a lever of the first order mounted on a fixed axle (70), which also

carries other rockers arranged in a row. One end of the rocker (B) is in contact with a cam (C) by means of a roller (R'), while the other end has a

reciprocating and pivoting hydraulic lash adjuster, referred to also as a tappet

(80). The tappet has a spigot or projection (81) at the base acting on the head

of a valve (V). A double row of camshafts (A') acts on convex surfaces of

rollers (R').

Fig. 2 shows an example of a rocker arm arrangement according to the

present invention.

The rocker (B) of the present invention is again a lever of the first

order, i.e. it is a centre-pivoted rocker arm. However, the rocker (B) is

mounted on a tappet (4) placed between a first end of the rocker (B). which is

fitted with a roller (R) displaced and pushed against a cam (C) on the

camshaft, and a second end, which transmits the pressure to open the poppet

valve (V) against the resilient force of a spring (M).

The rocker (B) shown in Figs. 3 to 6 is made up of two lateral flanges

(12) and (12'), linked by an upper plate (13), with which it forms a U-shaped

section, and is formed by bending or stumping a sheet of steel.

In the process of pressing the rocker from sheet steel, a hemispherical

recess (14) is formed in the plate (13), suitable for mating with the

hemispherical head (41) of a spigot or projection (42) which is part of a lash

adjuster or tappet (4). The tappet (4) is fitted in its own fixed seat (45, Fig. 7)

formed by boring an aluminium cover (L) of the engine head. The cover (L)

constitutes a valve train carrier, and is discussed further below. Because of the co-operation of the part-spherical surfaces of the recess

(14) and the end (41) of the spigot (42) this spigot forms a fulcrum about

which the rocker arm (B) can reciprocate in order to operate the valve (V), and

around which the rocker arm may be laterally turned. It will be noted in

particular that the rocker arm can rotate about an axis X (Fig. 4) and about the

axis of the spigot (42). to provide a degree of self-adjustment for the purposes

set out below.

Rocker (B) comprises at one end a transverse opening (15) into which

a pivoting trunnion (16) is fitted, the trunnion (16) having opposing recesses

(17), one of which presses onto the head of the stem of the valve (V),

adjusting itself in accordance with the relative movement of the rocker arm

(B) of the valve shaft, which may vary depending on the type of engine.

At the other end is fitted roller (R) having needle bearings and located

on an axle (20) extending through openings (22) provided in flanges (12) and

(12').

Roller (R) is very simple, with a straight cylindrical outside surface

which closely fits the outside surface of cam (C) since as described above the

rocker, with its fulcrum on the hemispherical recess (14), automatically

compensates for any imperfection in transverse movement, thus making a

convex outside surface, as required in customary design, unnecessary.

In order to keep the trunnion (16) fixed in place at the first end of the

rocker, a resilient sheet (25) is used with flanges (26) folded back on themselves so that the lower section can be attached to the rocker flanges (see

Fig. 5). The resilient sheet has an inlet (27) at the top for the purpose of

lubricating the trunnion (16).

A second resilient sheet (30), with flanges (31) folded back on

themselves, is fitted over the hemispherical recess (14) to restrict relative

transverse movement of the spigot (42) of tappet (4). The sheet (30) may be

made of spring steel, and has an aperture which allows the rocker arm (B) to

be easily snap-fitted over the head (41) of the spigot (42) and thus attached to

the cover (L). The sheet (30) thus retains the rocker arm (B) on the cover (L)

without inhibiting any intended operational movement of the rocker arm.

In this embodiment, the projection or spigot (42) has a relatively

narrow neck leading to the enlarged, part-spherical head (41), so that the

aperture in the sheet (30), which has a diameter slightly larger than that of the

neck, can be used to hold the rocker arm in place. Preferably, as shown in

Fig. 4, the aperture is elongate, with its longitudinal axis extended

substantially parallel to the length of the rocker arm, so as to facilitate fitting

the rocker arm to the tappet (4), and to permit a degree of freedom of

movement in the longitudinal direction to ensure proper engagement with the

cam shaft and valve. However, alternative arrangements are possible. For

example, the rocker arm could be fastened to the head (41) by means of a rivet

or other member extending through the rocker arm into a recess at the end of

the head (41), possibly engaging therein by means of a screw thread or by a resilient enlarged portion which engages in an annular ridge within the recess.

In any event, it is desired that the means attaching the rocker arm to the

fulcrum be fairly loose, and arranged so as not to inhibit the intended

operational movement of the rocker arm.

Fig. 7 is a detailed view of the tappet (4), which keeps rocker (B)

pressed against one end of the valve head (V) by means of the pivoting

trunnion (16). and at the other end against the cam (C) by means of roller (R).

The spigot (42). carrying the hemispherical head (41) which forms the rocker

fulcrum, forms a plunger which is attached to a chamber (43) which slides in a

sleeve (44) inserted precisely into the seat (45) formed by boring in the cover

(L) of the engine block. Within the lower part of the chamber (43) is a high

pressure tappet chamber (47), whilst above is a plunger (48) which houses a

low-pressure oil reservoir (49). The oil is supplied through the inlet (50) and

channels (51 ) in the cover (L).

Inlets (46) and (46') are provided in the spigot (42) for the purpose of

lubricating the hemispherical end (41) which acts as the fulcrum.

By way of example, Figs. 8 and 9 show from the side and from above,

respectively, the arrangement of a valve control train using rockers (Bl), (B2),

... as described above, for operating valves VI, V2, ... in an internal

combustion engine with a single central camshaft (A).

Using such an arrangement facilitates the assembly of an engine. The

engine cylinder head has a lower head part (80) into which the valves (VI) and (V2) are installed. Their springs (M) are located in recesses (60) of the

lower head (80).

In a separate operation, the valve train carrier formed by the cover (L)

has fitted thereto the rocker arms (Bl) and (B2), together with any other

rocker arms required for the engine (see Fig. 9). This therefore forms a self-

supporting assembly which can be manufactured and sold separately from the

rest of the engine and provided in a pre-assembled state ready for fitting to the

engine. Thus, not only is the overall assembly facilitated by pre-assembling

the valve carrier, but the individual fitting of the rocker arms can be carried

out as a separate operation, so the final assembly of the engine is significantly

simpler.

If desired, a manufacturer can supply different versions of the valve

carrier, all for fitting to the same engine head, but made to different

specifications. For example, one version may have hydraulic lash adjusters

and rocker arms provided with rollers, and another, less-expensive one may

have mechanical lash adjusters and a fixed cam-engaging surface on the

rocker arms rather than rollers. This facilitates the production of different

types of engines, suited to the customer, while still enabling a simple

assembly procedure.

The location of the respective fulcra on the cover (L) can be selected

such that all the rocker arms may have the same length, and therefore can if

desired by constructed identically. Preferably, the camshaft is also fitted to the cover (L) during pre-

assembly.

Figs. 10 and 1 1. in which like reference signs represent like integers,

show an alternative embodiment of the invention, in which twin camshafts

(Al, A2) drive respective rows of rocker arms (B). The aluminium valve train

carrier (L) is best illustrated in Fig. 1 1 , which shows identical rocker arms (B)

mounted in two lines, the arms within each line being positioned in a

staggered arrangement so that they are suitably located for driving the inlet

and outlet exhaust valves. Although not shown in Fig. 1 1. the camshafts (Al,

A2) are also preferably mounted to the carrier (L) before the entire assembly

is fitted to the lower cylinder head of the engine.

The carriers (L) of either embodiment may have channels for

distributing oil to the valve trains; indeed, all the required oil channels may be

located in the carrier.

Claims

CLAIMS:

1. A valve train assembly for an internal combustion engine, the

assembly comprising a valve train carrier having a plurality of individual

rocker arm fulcra and a rocker arm attachable to each fulcrum.

2. An assembly as claimed in claim 1. wherein each fulcrum

forms part of a lash adjuster.

3. An assembly as claimed in claim 2, wherein each lash adjuster

is an hydraulic lash adjuster.

4. An assembly as claimed in any preceding claim, wherein each

rocker arm constitutes a lever of the first order.

5. An assembly as claimed in any preceding claim, wherein each

rocker arm has a part-spherical surface for mating with a corresponding

surface of the fulcrum to which it is attached.

6. An assembly as claimed in any preceding claim, wherein each

rocker arm has been formed by deformation of a sheet.

7. An assembly as claimed in any one claims 1 to 4. wherein each

rocker arm has been formed by deformation of a sheet, said deformation also

forming a part-spherical surface for mating with a corresponding surface of

the fulcrum to which the rocker arm is attached.

8. An assembly as claimed in any preceding claim, wherein the

rocker arms are all of substantially the same length.

9. An assembly as claimed in claim 8, wherein the rocker arms

are substantially identical.

10. An assembly as claimed in any preceding claim, wherein each

rocker arm is provided with a resilient apertured member for fitting over the

associated fulcrum in order to attach the rocker arm to the fulcrum.

11. An assembly as claimed in any preceding claim, the assembly

also having mounted thereto at least one camshaft.

12. An assembly as claimed in any preceding claim, the carrier

having formed therein channels for conveying oil to the fulcra.

13. An assembly as claimed in any preceding claim, wherein each

rocker arm carries a roller for engagement with a cam of a camshaft, and

wherein each roller has a substantially flat cylindrical outer surface.

14. An assembly as claimed in any preceding claim, the carrier

supporting rocker arms for inlet and exhaust valves for a plurality of

cylinders.

15. An internal combustion engine having a valve train assembly

as claimed in any preceding claim, the engine comprising a plurality of

cylinders each having inlet and exhaust valves, said carrier supporting rocker

arms for said inlet and exhaust valves.

16. A method of assembling an internal combustion engine, the

method comprising:

(a) providing a valve train carrier having a plurality of individual

rocker arm fulcra;

(b) attaching a rocker arm to each fulcrum; and

(c) mounting the carrier with the attached rocker arms on a

cylinder head such that each rocker arm is brought into

functional relationship with a respective engine valve.

17. A method as claimed in claim 16. the method including the

step of mounting at least one camshaft to the carrier before mounting the

carrier on the cylinder head.

18. A method as claimed in claim 16 or claim 17. wherein each

rocker arm is mounted to a respective fulcrum by means of an apertured sheet

which is snapped-fitted over the fulcrum.

19. A rocker arm for an internal combustion engine, the rocker arm

having a part-spherical surface for mating with a corresponding surface of a

fulcrum which is arranged to permit reciprocation of the rocker arm in order

to operate a valve, the rocker arm further comprising means for attaching the

arm to the fulcrum.

20. A rocker arm as claimed in claim 19, wherein the rocker arm is

channel-shaped in section and has been formed by deformation of a sheet.

21. A rocker arm as claimed in claim 20, wherein the part-

spherical surface of the rocker arm has been formed by deformation of said

sheet.

22. A rocker arm as claimed in any one of claims 19 to 21. wherein

the attaching means comprises a resilient, apertured member for fitting over

the fulcrum.

23. A rocker arm as claimed in any one of claims 19 to 22, the

rocker arm having a roller for engagement with a cam of a camshaft, the roller

having a substantially flat cylindrical surface.

24. A valve train assembly for an internal combustion engine, the

assembly comprising a plurality of rocker arms each arranged for pivoting

about a respective fulcrum, the rocker arms being of substantially equal

length.

25. An assembly as claimed in claim 24, including a common

carrier supporting the rocker arms by means of said fulcra.

26. An assembly as claimed in claim 24 or claim 25, wherein each

fulcrum forms part of a lash adjuster.