US2178236A - Valve-control mechanism for steam engines - Google Patents

Description

Oct. 31, 1939. LINDARS I 2.178236 VALVE CONTROL MECHANISM FOR STEAM ENGINES Filed Oct. 27, 1936 2 Sheets-Sheet l INVENT?v A ham) EYS 0a. 31, 1939. H. LINDARS 2,178,236

VALVE CONTROL MECHANISM FOR STEAM ENGINES Filed Oct. 27, 1936 2 Sheets-Sheet 2 Patented Get. 31, 1939 VALVE-CUNTROL MEGHANISM FGR STEAM ENGINES Herman Lindars, London, England, assignor to firm So'ciete Dabeg, Paris, France DExploitation Des Procedes Application October 27, 1936, Serial No. 107,755 In Great Britain (lctober 29, 1935 6 Claims.

This invention relates to mechanism for the control of valves of steam engines of the type in which the valves are operated through oscillating members which are connected to the reversing gear of Walschaert or other form.

In the valve mechanisms of this type which have heretofore been proposed the oscillating member takes the form of a rocker arm which is connected by a connecting rod to the operating link of the reversing gear, and it is to be understood that when in the remainder of the specification the term rocker arm only is used, to save repetition, this word is to be regarded as including all appropriate forms of oscillating members.

In such valve mechanisms the diificulty arises that the angular movement which can be given to the rocker arm is relatively small. It is in many cases desirable to increase this angular movement of the rocker arm in order for example to increase the area and speed of valve openings, to avoid the necessity for fine valve adjustment and minimize the efiects of clearances.

If attempts were made to increase this angle by shortening the length of the rocker arm, then the angle between the rocker arm and the connecting rod would depart so far from the right angle that mechanical difiiculties would arise which would render the mechanism inefficient or impossible in practice.

In accordance with the present invention, I increase the angular movement of the rocker arm by the introduction, between it and the member connected to the reversing gear, of a multiplying mechanism so arranged that the diffi- .culty above referred to of the angular transmission of the forces is obviated.

In the preferred form ofthe invention, I use a linkage mechanism of the type known kinematically as a four bar chain, and I introduce into this mechanism a compensating linkage to ensure that the angular movement given to the driven member is at all parts of its range the same multiple of the angular movement given to the driving member.

Reference will now be made, by Way of ex: ample, to the accompanying drawings, wherein:

Fig. 1 represents in diagrammatic form a very simple link mechanism in accordance with the invention,

Fig. 2 represents in diagrammatic form the preferred link mechanism in accordance with the invention.

Fig. 3 illustrates one practical embodiment of the mechanism illustrated in Fig. 2,

Fig. 4 illustrates a slightly modified embodiment or the mechanism, and

Fig. 5 is a diagram illustrating one way in which my invention can be fitted into a Walschaert type valve gear organization.

Referring first to the diagram of Fig. 5, it will be seen that I have illustrated a Walschaert type valve gear mechanism having the usual main crank 33, eccentric crank 34, eccentric rod 135,

link 35, radius bar 37, combination lever 38, combination link 39, cross head arm it and connecting rod 22. The main crank 33, of course, is connected to the cross head ll by the main rod 42, and a piston rod 23 extends into the cylinder 45, where it is connected to the usual piston ii The steam passages ll? and are controlled by poppet valves,.the inlet valves #38 and it only being shown in the diagram, but it will be understood, of course, that similar valves may be employed for controlling the exhaust.

The valve stems 5b and ill project toward each other, being connected respectively to, suitable operating levers 52 and 53, which are pivoted at the points 5 5 and 55, and provided with suitable cam rollers 55 and 57.

A cam shaft 9 is located between the rollers, which shaft carries suitable actuating cams 58, the cam shaft 9 with its cams being arranged to oscillate under the influence of the rocker arm 8 in a manner which will be Well understood by those skilled in this art.

Various means for actuating the rocker arm 8 will now be described, attention being directed primarily to Figs. 1 to 4 inclusive.

In Fig. 1, the connecting rod 22 of a Walschaert or other valve gear is pivoted to a transmission lever 2i having a fixed pivot 33. The upper end 2 of this transmission lever has a slotted guide 3! in which slides a block 32 pivoted to the rocker arm 3 which turns on a pivot '9 the oscillation of which causes the valves to be operated.

In the proportions illustrated the rocker arm 8 moves through an angle which is twice that moved through by the transmission lever 2!.

Referring now to Fig. 2, a bifurcated transmission lever 25 having arms l and 2 is turned about its pivot 3 in response to movement applied at 20, by a link 22 which is the connecting rod to the Walschaert or other reversing motion.

A rocker arm 8 is mounted for angular move plication of the angular movement of the transmission lever about the pivot 3.

The connection between the arms comprises a pair of links l2 and I3 and a compensating beam 5 l. One end of the link I2 is pivoted to the free end of the arm I of the transmission lever, whilst one end of the link 53 is pivoted to the free end of the arm 2 the other ends of the links are pivoted to the opposite ends of the cornpensating beam H, which is pivoted centrally at If! to the free end of the rocker arm 8.

In the proportions shown the arm 8 will be found to have twice the angular movement of the transmission lever 2! but the invention is not restricted to a mechanism giving this ratio of magnification. The ratio of multiplication may in some cases be less than unity so that the rocker arm turns through a smaller angle than the transmission lever.

Referring now to Fig. 3 the bifurcated transmission lever takes the form of a curved lever rigidly mounted on a spindle 3 and having arms I, 2; this spindle is adapted to receive angular motion from the reversing gear connecting rod of the engine, the valves of which are to be controlled.

An arm 8 is rigidly mounted on a rocker shaft 9 and is pivotally connected at H! to the centre of a compensating beam H, the opposite ends of which are connected by links l2 and [3 respectively to the free ends of the arms l and 2.

The provision of the compensating beam ll adapts the link mechanism faithfully to multiply angular motion imparted to the spindle 3 in transmitting it to the rocker shaft 9. The relative effective lengths of the various members of the mechanism illustrated are such that the angular motion of the shaft 9 is double that of the spindle 3.

In the modified form of mechanism shown in Fig. 4, the transmission lever carried by the spindle 3 is not bifurcated but comprises a single arm I4. In this case, the lever compensating beam I I is pivoted at one end to the rocker arm 8 and is connected by the two links Hi and It to the arm Hi. The links in this case are not of equal length, but the length of the one, I5, is double that of the other, 16.

The employment of a bifurcated arm is to be preferred since it enables a link (12 or l3) in tension to be effective in either direction of movement.

Cams may be carried by the rocker shaft 9 to act directly upon follower rollers carried by the ends of the stems of the valves, or to act upon the valve stems through the intervention of levers with or without follower rollers.

What I claim is:

l. Poppet valve operating mechanism for a steam engine having a variable cut-off valve gear of the reversing type which delivers a reciprocating motion to a valve connecting rod, comprising in combination an oscillating cam, a rocker arm for oscillating said cam, a transmission lever for transmitting the reciprocating movement of the valve connecting rod to the rocker arm, a compensating beam pivoted to the rocker arm, and a pair of links connecting the transmission lever to said compensating beam, said transmission lever being of greater length than the rocker arm and providing for transmission of multiplied angular oscillation to the rocker arm.

2. The mechanism of claim 1 wherein the transmission lever is bifurcated and one link is connected to one bifurcation and the other link to the remaining bifurcation.

3. Poppet valve operating mechanism for a steam engine having a variable cut-off valve gear of the reversing type which delivers a reciprocating motion to a valve connecting rod, comprising in combination with an oscillating valve actuating cam, an oscillating arm actuated by the valve connecting rod, an oscillating arm for actuating the cam, said arms being of different effective lengths, and mechanism interconnecting the oscillating arms and providing angular oscillation of the cam actuating arm different from the angular oscillation of the other arm but in direct proportion thereto.

4. Poppet valve operating mechanism for a steam engine having a variable cut-off valve gear of the reversing type which delivers a reciprocating motion to a valve connecting rod, comprising in combination with an oscillating valve actuating cam, an oscillating arm actuated by the valve connecting rod, an oscillating arm for actuating the cam of shorter effective length than the first arm, and mechanism interconnecting the oscillating arms and providing angular oscillation of the cam actuating arm which is multiplied as compared with the angular oscillation of the other arm in direct proportion thereto.

5. Poppet valve operating mechanism for a steam engine having a variable cut-off valve gear of the reversing type which delivers a reciprocating motion to a valve connecting rod, comprising in combination with an oscillating valve actuating cam, an oscillating arm actuated by the valve connecting rod, an oscillating arm for actuating the cam. of shorter effective length than the first arm, the axes of both arms being substantially parallel to each other, and mechanism interconnecting the oscillating arms and providing angular oscillation of the cam actuating arm which is multiplied as compared with the angular oscillation of the other arm in direct proportion thereto.

6. Poppet valve operating mechanism for a steam engine having a variable cut-off valve gear of the reversing type which delivers a reciprocating motion to a valve connecting rod, comprising in combination with an oscillating valve actuating cam, an oscillating arm actuated by the valve connecting rod, an oscillating arm for actuating the cam of shorter effective length than the first arm, the axes of oscillation of said two arms lying substantially in a common plane, and. mechanism inter-connecting the oscillating arms with freedom for relative movement of the free ends of the said arms in a direction generally paralleling said plane and providing angular oscillation of the cam actuating arm which is multiplied as compared with the angular oscillation of the other arm in direct proportion thereto.

HERMAN LINDARS.

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