GB722568A - Valve gear for two-stroke uniflow scavenging engines to facilitate braking - Google Patents

Abstract

722,568. Starting turning gear ; valves. SUDWERKE MOTOREN UND KRAFTWAGENFABRIKEN GES. Sept. 26, 1952 [Sept. 27, 1951 ; July 23, 1952 ; Aug. 4, 1952], No. 24177/52. Classes 7 (5) and 7 (6). In a two-stroke uniflow scavenged engine adapted also to function as a compressor and thus act as a vehicle brake, there is provided a rotating shaft, such as a camshaft 8, Fig. 2, for actuating the exhaust valves 6, Fig. 1, the shaft being angularly adjustable relative to the crank shaft during engine operation to effect displacement of the commencement of opening of the exhaust valves from a normal position about 90 degrees before T.D.C. appropriate for engine operation, to a position which coincides approximately with T.D.C. to effect braking. The piston-controlled inlet ports 5, Fig. 1, admit scavenging air from a blower 4 into the cylinder 3 whilst the exhaust valve 6 is actuated from a cam 7 on the camshaft 8. An extension 9, Fig. 2, of the camshaft 8 is provided with a slidable but non-rotatable sleeve 10 having a multi-start quick-pitch thread 12 engaging a correspondingly threaded part in a toothed wheel 13 which is driven from the crankshaft by a gear 15. Braking. As illustrated the parts are in position for normal engine operation but to effect braking the sleeve 10 is moved rightwardly by a lever 18 so giving the camshaft an angular movement in the direction of engine rotation and concomitantly the fuel is cut off. The pitch of the thread 12 is such that the rotating wheel 13 tends to push the sleeve 10 to the left. The valve 6 may be replaced by a rotary valve, and a release valve may be positioned in the blower pressure line whilst the camshaft may be angularly moved by hydraulic or pneumatic means, not shown. The braking effect may be varied, depending upon the angular movement of the cam shaft, the greatest effect being obtained when the displacement between the opening of the inlet and the closing of the exhaust valve is a maximum which is achieved by either reducing the period that the valves are open, for example, by shortening the exhaust cams and/or moving the inlet ports to B.D.C. or by turning the camshaft 8 still further and arranging a throttle in the path of the outflowing air which is automatically cut out when normal engine operation is resumed. Facilitating starting and barring. By turning the camshaft so that the exhaust valves close before the inlet ports whilst preventing the braking action from taking place, the compression in the cylinder is increased and starting facilitated. If the camshaft is turned in either direction with the fuel cut off until the closure of the exhaust valves occurs at such a position that the total work done per cycle is a minimum, then the engine may be readily turned over for assembly or repair purposes. Reversing. After changing the auxiliaries for a reverse direction of engine rotation it is then only necessary to turn the camshaft in the reverse direction until the exhaust valve timing has been adjusted for reverse engine operation ; the cams are formed symmetrically about a centre line. A connection may be provided between the camshaft adjustment means and a device for reversing the starter and a device for changing over the fuel pump drive and any other auxiliary drives.