Patent GB-722197-A (GB)
Title: Improvements in or relating to valve operating mechanism of internal combustion engines
IPC: F01L1/22
Filed: 1952-02-22
Abstract: 722,197. Valve gear. EATON MANUFACTURING CO. Feb. 22, 1952 [Feb. 24, 1951], No. 4713/52. Class 7 (6). A valve gear clearance adjusting device comprises screw and nut members 30, 34, Fig. 1, biased apart by a spring 36, a rotatable cam 12 having a lobe portion 64 and a base circle portion 60, which base circle portion has a projecting flange 62, Fig. 2, of narrower width than the lobe portion 64, and a freely reciprocable and rotatable tappet 14 reciprocable along an axis substantially at right angles to the axis of rotation of the cam 12 and having a part thereof engageable with either the screw 30 or nut 34, the flange 62 being engageable with the cam contacting surface 56 of the tappet at a radius to the axis of the tappet and the cam contacting surface being disposed or shaped so that a plane perpendicular to the axis of the tappet forms a slight angle with the cam contacting surface 56 at the point of contact with the flange 62, the said angle being equal to or greater than the maximum anticipated angular misalignment, due to manufacture, from true right angular relation between the axes of the tappet and cam. The inclined surface 56 of the tappet causes the tappet to rotate into a predetermined position in which it bears on the cam with line contact and avoids wear due to the aforesaid manufacturing misalignment. At the end of each valve opening period the torsion spring 36 moves the screw and nut members 30, 34, which form a push rod 16 having curved surfaces 40, 42, engaging frictionally in conical recesses 41, 46, in the tappet 14 and rocker 18 respectively, apart to take up any clearance in the valve mechanism. Alternatively, if expansion of the valve mechanism occurs, the valve 20 will not rest correctly when the tappet 14 is on the base circle portion 60 and due to the fact that the valve mechanism will remain under the load of the valve spring 22 the flange 62 causes rotation of the tappet 14 and hence screwing of the screw 30 into the nut 34 to shorten the push rod 16 until the valve seats correctly and the valve spring load is taken off the valve mechanism, when the rotation of the tappet by the flange 62 ceases. In a modification, Fig. 4, the nut member 72 engages the rocker arm through a one-way brake mechanism 78 comprising a pin 76 engaging frictionally in a socket 74 in the nut 72 and having a coil spring 90 wound round an extension 84 of the pin fitting inside a thimble 80 in the rocker. When the nut 72 and pin 76 tend to rotate clockwise due to rotation of the tappet and screw, the spring 90 expands to grip the thimble 80 and hold the nut against rotation, whereby the screw threads into the nut to shorten the push rod. The brakemechanism 78 however permits free anticlockwise rotation of the push rod to allow the tappet 14 to rotate to its correct bearing position on the lobe of the cam without causing alteration in the length of the push rod. In a further modification, Fig. 5, the screw and nut mechanism 102, 96, are situated inside the hollow tappet 92, the nut 96 having a flange 98 which bears with friction against a ledge 100 in the tappet and the screw 102 being rotatable with respect to the tappet by the torsion spring 106, a collar 104 serving to hold the screw in correct alignment. The screw 102 engages the end of the valve stem 128 through a collar 116 which bears with large friction on the end 114 of the screw, so that it will rotate therewith when necessary, and with small friction on the valve stem.