Valve train arrangement for multi-valve engine

A two-fingered cam follower adapted to operate two valves in unison has sliding faces which are arranged in parallel with the plane in which the cam follower swings being driven by a cam. The cam follower is pivotally mounted on a hydraulic lash adjuster which is in turn mounted on a cylinder head. The cylinder head is provided with a pair of guide arms which are arranged so as to interpose therebetween the cam follower. The guide arms have on the inboard sides thereof guiding faces respectively matched with the sliding faces of the cam follower in such a manner that a clearance is provided between the matched sliding and guiding faces. By setting the clearance in such a manner as to satisfy a certain relation, the sliding and guiding faces can be held out of contact with each other during normal operating condition of the engine.

BACKGROUND OF THE INVENTION 
1. Field of the invention 
The present invention relates in general to a multi-valve internal 
combustion engine having duplicated or tripricated inlet and/or exhaust 
valves per each cylinder and more particularly to a valve train 
arrangement used in such a multi-valve engine and having a cam follower 
adapted to operate two or three valves (inlet or exhaust) in unison. 
2. Description of the Prior Art 
In a known valve train arrangement for a multi-valve engine, a single cam 
follower is adapted to operate two valves in unison with a view to 
reducing the mass of the valve train movable parts thus enabling high RPM 
engine operation. The cam follower may be arranged so as to pivot upon a 
lash adjuster as disclosed in Japanese Provisional Patent Publication No. 
59-103907. 
In order that the two-fingered cam follower is correctly held in contact 
with the valve stems, it has been proposed to provide the cam follower 
with a guide means in the form of flanges as disclosed in co-pending U.S. 
patent application Ser. No. 900,844, filed Aug. 27, 1986 still pending. 
With this guide means, the cam follower however has a possibility of being 
displaced out of position relative to the valve stems when the engine is 
over-revved due to an errorneous work on the accelerator pedal or the 
like. This is because under such an engine over-revved condition the cam 
follower effects a so-called "jumping" or "bouncing action and moves apart 
from the valve stems by the amount exceeding the height of the flanges, 
resulting in that the cam follower is movable freely relative to the valve 
stems, i.e., movable upwardly and downwardly and tiltable laterally while 
pivoting upon the lash adjuster. When the cam follower is out of position, 
e.g., when the cam follower is put into a condition in which the guide 
means is clamped between the cam follower and the valve stems or the cam 
follower is disengaged from the valve stems, the valve train will be 
damaged and malfunction. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided a novel and 
improved valve train arrangement for a multi-valve internal combustion 
engine. The valve train arrangement comprises a pair of guide arms 
provided to a cylinder head in such a manner as to interpose therebetween 
a cam follower. The cam follower has on opposite sides thereof sliding 
faces. The guide arms have guiding faces respectively matched with the 
sliding faces in such a manner that a clearance (W) is provided between 
each of matched pairs of the guiding faces and the sliding faces. 
In one embodiment, the cam follower has two fingers provided with integral 
flanges which depend down on the inboard sides of valve stems. A clearance 
(C.sub.1) is provided between each of matched pairs of the flanges and the 
valve stems. The flanges each have a chamferred end of which guiding edge 
remotest from corresponding one of the fingers is arranged so that a 
clearance (C.sub.2) is provided between the guiding edge and corresponding 
one of the valve stems. The clearance (C.sub.1), (C.sub.2) and (W) are set 
so as to satify the relation C.sub.2 &gt;W&gt;C.sub.1. 
The above structure is quite effective for overcoming the above noted 
disadvantage inherent in the prior art device. 
It is accordingly an object of the present invention to provide a novel and 
improved valve train arrangement for a multi-valve internal combustion 
engine which is assuredly prevented from being damaged and malfunctioning 
even when the engine is over-revved. 
It is a further object of the present invention to provide a novel and 
improved valve train arrangement of the above described character which 
can assuredly prevent a cam follower from tilting or moving sideways 
relative to the valve stems even when the cam follower effects a so-called 
"jumping" or "bouncing" action and moves apart from the valve stems by the 
amount exceeding beyond the height of the flanges provided to the cam 
follower for location of same.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 to 5, a valve train arrangement of this invention is 
generally indicated by numeral 10 and shown as comprising a cylinder head 
12, a cam 14 rotatable with a cam shaft 16 which is in turn rotatably 
interlocked with the crankshaft of the engine, a Y-shaped or V-shaped cam 
follower 18, a hydraulic valve lifter or lash adjuster 20, and two inlet 
or exhaust valves 22 in the form of a poppet valve and having valve stems 
24. Indicated by numeral 26 is a valve spring retainer, and by 28 is a 
valve spring. 
The cam follower 18 is pivotally mounted at an end 18a on the lash adjuster 
20. The lash adjuster 20 is of the well known type and is provided with a 
spherically convexed or domed end 20a which is received in a corresponding 
spherically concave recess formed in the end 18a of the cam follower 18. 
The other end of the cam follower 18 is bifurcated to have two fingers 
18b, 18b which are brought into contact with the terminal ends of the 
valve stems 24, 24, respectively. 
The cam follower 18 is adapted to engage on the first side, i.e., on the 
lower side thereof with the lash adjuster 20 and the valves 22, 22 and on 
the second side opposite to the first side, i.e., on the upper side and at 
a location intermediate between the above described opposite ends with the 
cam 14 so that as the cam shaft 16 rotates the cam follower 18 swings 
about the lash adjuster 20 toward and away from the valves 22, 22 thus 
driving the same to reciprocate correspondingly. 
The cam follower 18 has on the sides opposing in the direction crossing at 
right angles the direction in which the first and second sides are 
opposed, i.e., on the horizontally opposed left-hand and right-hand sides 
thereof smoothly finished, planar sliding faces 30, 30 which are arranged 
in parallel with the plane "P" of swinging of the cam follower 18, i.e., 
the plane "P" in which the cam follower 18 swings being driven by the cam 
14. 
The cylinder head 12 has a pair of integral guide arms 32, 32 which are 
arranged so as to interpose therebetween the cam follower 18. More 
specifically, the guide arms 32, 32 has on the inboard sides thereof 
guiding faces 34, 34, respectively. The guiding faces 34, 34 are arranged 
so as to be respectively matched with the sliding faces 30, 30 of the cam 
follower 18 in such a manner that a clearance "W" is provided between the 
matched guiding and sliding faces 30, 34. 
The fingers 18b, 18b of the cam follower 18 are respectively provided with 
integral flanges 36, 36 which depend down on the inboard sides of the 
valve stems 24, 24. The flanges 36, 36 limit lateral movement of the cam 
follower 18 relative to the valve stems 24, 24 so that the cam follower 18 
is held in place relative to the valve stems 24, 24. 
A clearance "C.sub.1 " is provided between the flange 36 and the valve stem 
24. The flange 36 has a chamferred end of which guiding edge remotest from 
the finger 18b is arranged so that a clearance "C.sub.2 " is provided 
between the guiding edge of the flange 36 and the valve stem 24 matched 
therewith. The clearances "C.sub.1 " and "C.sub.2 " are set in respect to 
the clearance "W" in such a way as to satisfy the relation C.sub.2 
&gt;W&gt;C.sub.1. 
By designing the valve train in such a way as to satisfy the above 
relation, the matched sliding and guiding faces 30, 34 can be held out of 
contact under normal operating condition of the engine, i.e., when the 
engine is operated at a speed lower than a predetermined maximum RPM, thus 
preventing the matched sliding and guiding faces 30, 34, from producing 
noise and friction. 
The guiding faces 34, 34 of the guide arms, 32, 32 are adapted to lap over 
the sliding faces 30, 30 of the cam follower 18 by the length "H" when 
viewed in the elevational view of FIG. 2 and when the cam follower 18 is 
held in contact with the base circle portion of the cam 14. The length "H" 
is set in view of the extent of swinging of the cam follower 18. 
In operation, rotation of the cam shaft 16 causes the cam follower 18 to 
swing about the lash adjuster 20 being driven by the cam 14. During normal 
operation of the engine, the cam follower 18 swings in the plane "P" while 
transmitting through the fingers 18b, 18b the motion of the cam 14 to the 
terminal ends of the valve stems 24, 24. In this instance, due to the 
provision of the clearance "W", the sliding faces 30, 30 of the cam 
follower 18 are held out of contact with the guiding faces 34, 34 of the 
guide arms 32, 32, thus preventing production of noise and friction. 
During abnormal operating condition of the engine, i.e., when the engine is 
over-revved due to a certain errorneous work on the accelerator pedal or 
the like, the valves 22, 22 may effect a so-called "jumping" or "bouncing" 
action to allow the fingers 18b, 18b to move away from the terminal ends 
of the valve stems 24, 24 by the amount exceeding the height of the 
flanges 36, 36. In this instance, the sliding faces 30, 30 of the cam 
follower 18 come in contact with the guiding faces 34, 34 of the guide 
arms 32, 32 so that movement of the cam follower 18 is guided by the guide 
arms 32, 32, thus preventing the cam follower 18 from being displaced out 
of position relative to the cam 14 and the valves 22, 22, e.g., preventing 
the flanges 36, 36 from being clamped between the fingers 18b, 18b of the 
cam follower 18 and the terminal ends of the valve stems 24, 24. The valve 
train arrangement of this invention is therefore assuredly prevented from 
being damaged and malfunctioning even when the engine is over-revved. 
When RPM of the engine lowers below a predetermined maximum value, the 
valve train returns to its normal operating condition and enables the cam 
follower 18 to accurately transmit the motion of the cam 14 to the valves 
22, 22. 
The cam follower 18 has, as shown in FIG. 4, a channel-shaped sectional 
portion to which the sliding portions 30, 30 are provided. This is 
advantageous from the point of view of light weight and simple structure. 
The cam follower 18 can be produced by forging or the like without 
increasing the weight as compared with the comparable prior art cam 
follower. 
Referring to FIG. 6, this embodiment differs from the previous embodiment 
in that the cam follower 18' is provided with a roller 38 at a portion for 
contact with the cam 14. By the provision of the roller 38, the friction 
between the cam 14 and the cam follower 18' can be reduced considerably, 
thus improving the fuel consumption and the output of the engine. 
While the guide arms has been described and shown as being integral with 
the cylinder head so as to be made of an aluminium alloy and produced by 
casting at the time of casting of the cylinder head, they are not limited 
to be so. For example, the guide arms can be independent parts which are 
bolted or otherwise secured to the cylinder head.