Patent GB-605949-A (GB)
Title: Improvements in or relating to the control of steam engines
IPC: B60K3/00
Filed: 1945-05-18
Abstract: 605,949. Fluid-pressure servomotor-control systems. STEVENS, A. H. (Stanley Steam Motors Corporation). May 18, 1945, No. 12592. [Class 135] A governing mechanism for a steam engine comprises a governing member to control the flow of steam from the throttle to the engine and so limit the maximum speed, means for producing a fluid-flow proportional to the engine speed, a pressure chamber having a movable wall connected to the governing member, and means for conducting at least a portion of the fluid from the flow-producing means to the chamber to produce a pressure therein tending to move the governing member to a speed-limiting position against the steam pressure, means being provided for varying the proportion of the fluid-flow supplied to the pressure chamber. The invention is specially applicable to a steam engine driving a bus or similar vehicle. As shown, an engine-driven oil pump 12, Fig. 1, supplies a governing device 10, a cut-off control device 11 and a byepass valve 13 through conduits 44, 76, 91 respectively, conduits 54, 78, 92 connecting these same devices respectively to a common return line 14. The conduits 44, 54 lead to opposite sides of a piston 34, Fig. 2, connected to a valve 32 controlling the connection between a conduit 16 connected to the boiler and a conduit 17 leading to the engine. The conduit 16 opens into a swirl chamber 24 containing a baffle 25 below which sediment settles. An aperture 27 connects the chamber 24 with a manually-operated throttle valve 22 and a passageway 30 connected to a relief valve. Pressure fluid can pass from a chamber 42 below the piston 34 through a calibrated orifice 49 to the space above the piston and thence through ports 51, 52 to the conduit 54. The piston 34 closes off a port 50 when it has risen a certain distance, but its lower edge re-opens the port 51 before its maximum travel is reached. The piston is guided by a sleeve 37 any leakage into which past the valve 32 is led away by a conduit 40 to a hot well 41. The control device 11, Fig. 3, comprises a plunger 57 connected to the operating arm 18 of a variable cut-off reversing valve gear and bearing a hollow head 61 with a piston flange 67 movable in a housing 55 against a spring 69 by pressure fluid admitted from the conduit 76 past a calibrated orifice 74 to a chamber 71. This movement is limited by a port 77 which opens to the return conduit 78 when the piston reaches a position corresponding to the short cut-off position of the valve gear. Pressure fluid may also be supplied to the space between the head 61 and a fixed piston 60 through a hollow post 59 and a conduit 65. This latter supply which is taken from the outlet of the valve 32 and passes by a pipe 83 through the hot well 41 is controlled by a rotary reversing valve 19, the handle 88 of which is connected to the usual reversing lever of the engine. Normally, the valve 19 connects the interior of the post 59 to exhaust through conduits 66, 86. However, when the lever 88 is moved counter-clockwise to the reversing position, the conduits 83 and 65 are connected and the fluid pressure moves the head 61 to the end of its travel beyond the port 77 whatever the pressure in the chamber 71. The valve 19 contains a check valve between the conduits 65 and 83 to prevent return flow from inside the post 59 when the valve gear is in the reversing position. The byepass valve 13 is normally open, but has a calibrated restricting orifice on its outlet side. Its operating arm 95 is connected to the means for declutching the engine so that when the engine is declutched the valve 13 is closed and all the fluid from the pump 12 flows to the devices 10 and 11. This results in the engine being throttled by the valve 32 and its cut-off shortened by the device 11 at relatively lower engine speeds which correspond to the idling condition. The restricted orifice in the valve 13 and the orifices 49 and 74 are chosen to allow operation of the devices 10, 11 at the desired speeds. The pressure builds up in the chamber 71 to move the gear to the short cut-off position only after the port 50 is closed and the speed at which this occurs increases with the load due to the increased steam pressure acting on the valve member 32 when the throttle 22 is wider open for greater loads. If an increase of load is encountered when the device 11 is in the short cut-off position, this may be sufficient to re-open the port 50 and so return the plunger 11 to the long cut-off position until the engine speed increases or the load is reduced. The port 51 re-opens at maximum speed.