US2081458A - Cam actuated poppet valve gear - Google Patents

Description

May 25, 1937. H. LENTZ CAM ACTUATED POPPET VALVE GEAR 2 Sheets-Sheet 1 Filed Sept. 17, 1935 In venfop:

?atented May 25, 1937 arem" or ies Application September 17, 1935, Serial No. 30,933

in Germany April 20, 1935 2 Claims.

In piston steam engines, especially locomotive steam engines, which operate with considerable difierences in speed with approximately the same throttle setting, the counterpressure increases at the high travelling speeds during the expulrapidly enough from the cylinder. the initial pressure of the compression lies highpressure lies higher than at lower speeds and even rises above the inflow pressure which is shown by a loop in the steam diagram. This means a loss of work and results in disagreeable J jolts in the engine.

To prevent the final compression pressure from rising above the inflow pressure. it has been proposed to vary the clearance for difierent speeds by providing spaces which can be added and shut 01?. This method is. however. inconvenient and makes the construction of the engine complicated.

A much simpler method exists. if a locomotive steam engine with poppet valve gear is employed, in which the valve spindles are actuated by cam discs through the intermediary of levers.

In this instance the timing of compression can be changed in simplest manner for high speed by making the rocking axles of thelntermediate levers for the exhaust valves adjustable indelO pendently of the main control in such a manner that with an increase of speed the compression occurs later and with a reduction of speed earlier so that with the same clearance the final compression pressure remains below the inflow pressure for all speeds. The adjusting of the intermediate levers which operate the valves may be eifected by hand.

Several embodiments of the invention are illustrated by way of example in the accompany- 0 ing drawings in which:

Fig. 1 shows in longitudinal section a total view of the gear on one end oi the cylinder.

Fig. 2 is a pressure diagram for a speed of 50 kilometers per hour with valve-lift curve for the 5 exhaust valve.

Fig. 3 is apressure diagram for a speed of 100 km. per hr. with the same throttle setting. 'In this diagram the course of the pressure during the return stroke of the piston with adjustment r of the exhaust valve to half travelling speed is shown in dot-dash lines.

Fig. 4 shows in elevation on a larger scale the adjusting arrangement for the intermediate lever employed in the arrangement shcwn in Winl.

In the form of construction of the valve gear illustrated in Fig. 1 an insert piece 3 is arranged in the middle of a bore in the cylinder block 2 parallel to the cylinder i, this insert piece having two axial bores 5 in which a steam feed conduit 4 terminates. Insert pieces 6 extend one from each side of the insert piece 3 and accommodate a valve cage 7 for the admission valve 8. The insert pieces 6 are secured in position by tubular exhaust boxes 9 mounted on the end faces of the m cylinder. A valve cage ii) for the exhaust valve H is accommodated in the exhaust boxes 9. the inner end of this cage engaging in the insert pieces 6 and bearing against the valve cage 7 of the admission valve 3. It is held by a hollow 15 cover l2 bolted on the exhaust box 9 and accommodating the driving elements for the admission valve l and exhaust valve id.

The admission and exhaust valves co-ordinate to each end of the cylinder form a gear aggregate which is actuated by a single driving memher. In the example illustrated the driving member consists of a cam fitted in the form of a 7 shoe We on a reversing shaft l3 of corresponding cross-sectional shape. This cam Isa oscillates about the axis of the reversing shaft l3 and acts on the admission valve 8 and exhaust valve Ii through the intermediary of levers l4 and i5 respectively. The rocking movement is imparted to the two reversing shafts is arranged one at each end of the cylinder by short levers arranged outside the hollow covers I? and connected to the reversing gear by a connecting rod IS.

The races of the cam l3a cooperate with the intermediate levers l5 and i5 after the manner of a rolling lever gear so that, owing to their great Width, they are subjected to only very little Wear and cause a smooth opening and closing of the valves because the rolling surface extends through the fulcrum. 40

The admission and exhaust valves 8 and H of an aggregate are closed by steam pressure which acts upon the ends of the spindle ll of the admission valve 8 as the inner end of this spindle extends into the bore The other end of the spindle Il extends into the cover l2. The spindle I 8 of the exhaust valve i9 is hollow and surrounds the spindle l! of the admission valve. The hollow spindle I 8 of the exhaust valve is slidable in a bore IS in the valve 5 cage 1 of the admission valve 8. This bore i9 communicates by a longitudinal bore and by transverse bores of the spindles ll of the admission valves 1 with the bores 5 which are under steam pressure, so that the steam pressure also 55 5 in the insert piece 3.

I does not extend into the gear cover i2,

mounted on an eccentric pin 22 acts on the inner end of the exhaust valve spindle l8 and closes the exhaust valve l i.

As the hollow spindle it of the exhaust valve it it is actuated by a hollow thrust rod 2b mounted on the hollow spindle it, the outer end of this rod coop crating with the intermediate lever 85.

The hub 23 of the intermediate lever it is arranged in the cover i2 and connected outside the cover with a lever 26 which can be adjusted between the two extreme positions a and b by meansof a rod system, not shown in the drawings, for example from the engine cab independently of the main valve gear of the engine. Thus, the eccentric and consequently the pivot axle of the intermediate lever is adjusted. The object of this adjustment is, to correspondingly adjust the timing of exhaust for different speeds. v

The operation of the adjusting device is hereinafter explained with reference to the diagrams shown in Figs. 2 and 3. i

Fig. 2 shows the pressure and volume diagram for a certain charge at a speed of 50 kilometres per hour. The lever 24 is then in the position a. In this position the intermediate lever opens the exhaust valve at A, whereas it closes it at C during the return stroke of the piston and thus deter-- mines the commencement of the compression oi the steam still present in the cylinder. The lift of the exhaust valve during the piston travel is indicated in dot-dash lines in the diagram.

If, for example with the same throttle setting and the same clearance the speed is doubled and the gear remains unchanged in the position a, the closing of the exhaust valvewould take place at i the point C at a higher pressure owing to thehigher losses from throttling occurring at the higher speed (see Figs. 2 and .3) The result would be a considerable increase of the compression beyond the admissionv pressure before the dead centre position, as shown by the dot-dash lines in Fig. 3. This would cause heavy shocks in the engine and loss of efliciency.

In order to avoid this, the lever 24 is oscillated into the position b and the pivot axle of the intermediate levor II is thus moved towards the lay shaft it. Thus, a negative overlapping is ad justed for the exhaust, so that the exhaust valve is lifted earlier and closed later than before the adjustment. closing of the valve results a greater deflection of the intermediate lever and consequently a greater valve-lift,as shown by the valve lift lines in Fig. 3. These two circumstances have the eflect that the counter pressure in the cylinder is kept lower for a longer time during the exhaust stroke and the From the earlier lifting and later ment lever to the engine cab.

- aosnssa throttling during the closing of the exhaust valve commences later. By the displacement a shitting of the timing of compression from C to C (Fig. 3) and consequently a less high final pressure is attained. s

The adjustment of the intermediate lever within its extreme positions may be effected according to the scale arranged in the cab and-gauged for the different speeds, so that the driver can at any time adjust the gear to the speed at which the engine is actually travelling. The compression work can also be reduced by this adjustment when starting up on a steep gradient in order to obtain as little counter pressure as possible and consequently a larger working surface in the pressure diagram.

The pins can be adjusted independently of the main gear from the cab by hand through the intermediary of suitable transmission elements for example by a rod 25' connected to the end of the adjusting lever 26 and extending to the engine cab.

By this arrangement the timing of compression can consequently be adjusted in dependency upon the speed, so that at all speeds the compression curve only ascends upto the pressure of the fed live steam, without changing the clearance by complicated addition of spac's.

v I claim:-

1. An arrangement for varying the compression in piston steam engines, especially locomotive steam engines with poppet valve gear, comprising in combination with the cylinder, an admission valve and an exhaust valve at each end of said cylinder, a hollow spindle connected, to said exehaust valve, a spindle connected to each of said admission valves and mounted in said hollow spindle, a cam chamber on said cy1inder,- said spindles projecting into said chamber, an oscillating cam in said chamber, two intermediate levers mounted in said chamber, one actuating said exhaust valve and the other actuating said admission valve, pivot axles one carrying each of said intermediate levers, the pivot axle carrying theintermediate lever of said admission valve being fixed, and means for adjusting the position of the pivot axle carrying the intermediate lever of said exhaust valve to close said exhaust valve later with approximately the same throttle setting but higher speeds.

2. An arrangement the exhaust valve is mounted on an oscillatable adjustment lever eccentrically to the pivot axle thereof and a rod system'leads from said adjustas specified in claim 1, in which the pivot axle for the intermediate lever ofv

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