GB2332710A - A desmodromic gas exchange valve actuation arrangement - Google Patents

Abstract

A gas exchange valve actuation device for an internal combustion engine comprises a valve and a camshaft; the camshaft having a vane member, for maintaining the valve in a closed position by engaging a first groove formed on the valve, and at least one pin for opening and closing the valve by engaging a second groove on the valve. The first and second groove may be formed on a tappet which is connected to the valve. The path of the second groove is not coincidental to the locus of the pin as it rotates forcing the valve to move and hence provide the valve lift. A tight seal of the valve is maintained in the closed position by a spring positioned on the inside of the vane member. This compensates for engine heat expansion. The tappet is formed in two parts and is held together by a bolt (figure 2). Lubrication may also be provided by oil passages in the camshaft (figure 5, 6).

Description

The Vane Camshaft (Dry & Wet Systems) The Dry System This invention relates to a reciprocating engine valve train.

Camshafts designs are an essential part of engine development in terms of volumetric efficiency and power output. The cam is used to operate the valves openings whether it be the inlet or exhaust.Valve trains usually have a high torque requirement from the crankshaft due to the spring stiffness of the valve spring.

According to the present invention a single camshaft is located above a conventional poppet valve.The tappet however comprises of split design, and runs along the vanes of the camshaft.No modification is done to cylinder head nor the manifolds.This design eliminates the use of valve springs,in doing so, the cam doesn't have to be built to withstand high torsional oscillation.

A specific embodiment of invention will now be described by way of example with reference to the accompanying drawing in which; Fig 1.A Shows the valve closure by the Camshaft vane 1.B Shows the valve transition period where the vane is leaving and the pin is activating.

1.C Shows the valve activation period by the pin.

Fig 2. Illustrates valve timing and components in greater detail.

Fig 3. Shows the tappet construction Fig 4. Shows the camshaft construction Fig 5. Illustrates the wet camshaft contruction Fig 6 Shows the oil circulation from camshaft main bearings Fig 7 Illustrates the oil lubrication around the tappet Fig 8 Illustrates the angles of high accelerations Fig 9 Shows the shape alteration of the of the pin to reduce the deformation the points of high accelerations.

Fig 10 Shows the tappet weight reduction.

Refering to the drawings, the valve system comprises conventional valves (I),the grooved tappets (2) are kept shut by the large vane (1.H) which runs in the hemispherical groove (2B) in fig.3 Inside this vane lies a spring designed to give a tight seal with approximately 120lbs/sq. in. As the cam rotates to relieve the large vane the pin (1.D) rotates in the second groove which has a smaller radius (1.F) to prevent the pin to run in the hemigroove.Once the pin is in the horizontal groove (2.A) the tappet is pushed down from a chord of (1.B) to the edge of the circle , this distance gives the valve lift (1.G).

The valve is held inside of the tappet by being placed in a cavity (2.D) fig 2 machined or casted to make the keeper groove fit.Once the two parts of the tappet are placed around the valve stem then the split-tappet is sandwiched together by bolt(3) on fig.3.In the closing vane groove there are two rolling pins(3.A) which keeps the sliding vane in a state of rolling friction with the underside of the tappet these are optional in case the contact friction are too high.

The Valve timing is achieved by finding the total valve opening angle then divide by two. ,this new angle (E) fig.2 is then placed before and after the pin.The angle (E) is placed in front of the pin so that the large vane clears the hemi-groove in time for valve actuation.As soon as the pin activates the valve it will do so for half the rotational speed of the crankshaft.The formula would be; Angle E = Total valve angle 2 Remember that angle E is added to both sides of the pin The Wet System With the wet system the main principle of pin activation and vane closure is still practiced but with oil film barrier between the contact surfaces , ie the vane and the tappet and the pin within its activation groove.

Refering to the drawings, the camshaft (5.A) provides oil from a centrally located oil passage to the oil injecting vane (5.B) via a screw (5.C).The oil travels through the centre of the screw and disperses oil outwards at its upper half (5.C) into the oil passages inside the vane (5.D) and finally to the vane orifices (5.E).

The Screw has two functions as being both a oil circulation unit and to hold the spring(5.F) in place.The spring provides the same function as the the one located in the Dry system in that it keeps valve closure when the valve has expanded due to combustion heat.

The circulation initially starts at the camshaft main oil bearing (6.A).which eventaully go to the vanes.

As shown in fig 7 the lubrication injection is continous,and gives boundary layer between the tappet and the vane (fig.7.1).The upper part of pin path in the tappet(fig7.2) is lubricated by the centre spray (7.A).This centre spray also lubricates the centre shaft as shown in fig 7.3 and 7.4.The side sprays(7.B) also have two functions in that they lubricates the bottom of the groove after pin has scraped the oil away,aswell as lead an oil path for the underside of the tappet during closure.

During engine operation the points of high stress are the points where the pin is located when the greatest acceleration occurs.According to the crank angle/valve lift graph(fig 8) this occurs from 1000 to 800.To reduce the stresses the pin is shaped to incorporate a large radius on the flank of the pin for the angles of high acceleration as shown in fig.9 This increased surface area at the stress point along with the addition of an oil film will allow this design to have a some reduction in its surface tension.

One the main causes of the high stresses is the additional weight imposed by the tappet.

The tappet as shown in fig 10 is shaped to fit completely inside the vane during closure, leaving only the valve holder section outside.The tappet is also made hollow to reduce inertia.Instead of employing a bolt to combine the two halves the two halves utilise a male and female interlocking stub and hole.These are interference fit.

Claims (6)

1. Claims 1) A camshaft design comprising of a closing vane and.two pins which is used to close and activate the valve respectively.
2. 2) A camshaft design as claimed in Claimed 1 has a tappet which runs along the profile of the cam without the aid of spring for closure.
3. 3) A camshaft design as claimed in Claims 1 and 2 uses the tappet to hold the valve through keeper groove located on the top of the valve.
4. 4) A camshaft design as claimed in Claim 3 allows the tappet to be a split design to give an easy construction of a valve train aswell as grip around the keeper groove of the valve.
5. 5) A camshaft design as claimed in Claim 4 has the tappet held together by a bolt placed through the tappet center or by intereference fit of a male and female tappet.
6. 6) A camshaft design as claimed in Claim 2 has a closing vane that utilizes an inside spring that keep the valve tightly sealed during engine heating.

   7)A camshaft design as claimed in claim 1 uses a lubrication system to give a oil boundary between the contact surfaces.