US2488829A - Speed governor - Google Patents

Description

Patented Nov. 22, 1949 SPEED GOVERNOR Duncan Ramsay, Wahroonga, :New South Wales,

Au t alia assi o to M. Hobson Limited,

Lond nglo o c an o 'G otfir o Application September 12, 1947, Serial In Great Britain J l ly .28, L94

Section 1 Public Law 69,0, August 8,1948

Patent expires July 28,1963

f fl wle- '(Cl. 1,23,

This invention relates to engine installations comprising a hydraulic governor intended, ,at each speed selected by a control lever or the equivalent, to maintain the engine at the selected speed. The control-ling effect of the governor depends, of course, on the engine loading and the regulation of the governor, hereinafter expressed by th symbol?- s daemon the cha e o ee -Wi h en ine so that at low speeds the accuracy to which the governor will maintain the selected speed is low, and it is-impossible to expect the governor to give satisfactory control over a wide range of speeds. This disadvantage renders the centrifugal governor particularly unsuitable forpower boat installations, in which it is necessary to have a governor which will controldownto very low speeds. The present invention relates to hydraulic governors of the type comprising an engine-driven hydraulic pump, the discharge of which increases with speed, a variable-area orifice to which the whole of the discharge of the pump is supplied, a control lever or the equivalent for varying the selected speed .at which thegovernoris to control, displacement of said lever being arranged to vary the area of the orifice, a-device, responsive to the pressure difference across the orifice, and a servo.- motor controlled :by the pressure-responsive device and arranged to actuate a speed changing mechanism, in the event of change inthe area of the orifice or lof-the speed of the pump, so as to maintain a substantially constant pressure difference across the orifice. A hydraulic governor of this type, as later explained, has a regulation which is independent of engine speed.

' The invention provides, in or for an internal combustion engine, a hydraulic engine speed governor of the type specified, which employs fuel as the operating hydraulic fluid, the pump being constituted by the engine fuel pump and being 1'" arranged 5120 deliver fuel to the engine as well as to operate the se omoto The advantages of using fuel within the governor and se o are tha its i o y. nd her fore the vernor har ter t is s bstan a l independent, of changes in climatic conditions, and that n add iona e in d il ne d be 1 plied, .a a el um is sup ed in n l o i h be ropos d. in a es e ine o so: just the timing of the injection in accordance with vchan e i n in speed i 51 .1 o WW t obtain .qui ru ning b mea s o p ton at sponsive to the fuel pressure generated by an en gine driven gear pump. The whole of the dischar e of this pump was passed through a re.- strict/ed oriioe,,-wh; .oh c uld v o vari d in ar a by an adjustment screw, to an injection pump. The piston oper ted Qnmo bo :fQ oQnt Q1l X the injection im n thr u h the a enc 91- a servomotor deriving its motive fluid iron; the fuel pipe on the .exi t sid Of the res ni iod orific aforesaid. The apparatus incl d d a no ma y inop rative m mber fo va ing h d liv r o the injection pump T is was o era e by the servomotor in such a way as to i npose adefini-te maximum and minimum engine speed when, and only when, the movement of {the injection timing member in either direction reached a given limit.

This apparatus did not, like the governor acding to the i entio o rat to ma n a the engine running, within close limits, at any desired one of ,a series of selected speeds determined by the position ,of .acontrol lever or equivalent member for adjusting the area of the orifice, nor did it include a member responsive to the pressure difference across the orifice and arranged to adjust the speed changing mechanism in r ns o va ia i s in t e are o t e or fi e or in the engine speed, in such a way as to main tein sa d pr s d ff en s ta tia y 9 stant. 0n the contrary, the piston in the above mentioned P o osal was pons on o th pressure at the entry to theorifioe and was free to take up a considerable range of positions in response to variations in that pressure so that the device operated only to impose a maximum and a minimum permitted speed, while allowing of a relatively wide rangeof intervening speeds to which the injection timing is suitably correlated by the servomotor.

Two difierent forms of governor according to the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in -which Fig. 1 is a diagram showing a governor according to the invention suitable for installations in which fuel is to be fed to the carburetter at low pressures, and embodyin provision for preventing hunting of the throttle,

Fig. 2 is a diagram of an alternative form of governor according to the invention, suitable for installations in which the fuel is to be fed to the carburettor at a higher pressure, and in which hunting of the throttle is prevented in a different way, and

Fig. 3 shows graphically how hunting is avoided with the arrangements shown in Figs. 1 and 2.

Like reference characters indicate like parts throughout the figures.

Referring first of all to Fig. 1, fuel is fed by an engine-driven fuel pump In to an orifice ll controlled by a needle I2 linked to the control lever 3!. The whole of the pump discharge flows through the orifice, so that for a given area of the orifice, the pressure drop across it increases with speed. This pressure difference is applied across a diaphragm l3 loaded by a tension spring 14.

The diaphragm, as hereinafter explained, operates a servomotor, the servo piston l whereof is linked by a connection l5 to the throttle valve I30. The connection is arranged to increase the engine speed as the diaphragm rises and to decrease the engine speed as the diaphragm falls. Part of the fuel returns to the suction side of the pump through a relief valve l6, and the remainder fiows to the carburetor or the fuelmetering unit through a pressure regulating valve I8 and pipe 21. A safety valve 34 is provided so as to avoid damage to the pump should th area of the orifice be suddenly reduced when running at high speed.

The relationship between selected speed and needle movement depends on the profile of the needle itself, but if a plain tapered needle is used the change of speed with movement will be coarse at low speeds and fine at high speeds which is the characteristic required. If the pump discharge is proportional to speed, the selected speed will be proportional to jet area.

In order to study the behaviour of the governor, it is convenient in the first instance to assume that the rate of the spring I4 is very small compared with the movements of the diaphragm, i. e. to assume that the spring load remains constant over the range of diaphragm movements, and that the effort required to move the speedchanging mechanism is negligible.

In order to select a given engine speed, the variable area orifice II is adjusted to an opening A. The quantity of fiuid delivered by the pump per unit time is its, where S is the engine speed and k is some constant dependent on the pump characteristics. According to the natural laws of fluid flowing through an orifice, the pressure difference across the orifice is proportional to the square of the velocity through it, so that where K is a constant dependent on the characteristics of the pump and the orifice.

This pressure difference p exerts a force pD where D is the area of the diaphragm i3. If pD is less than load L on the diaphragm l3, the diaphragm will move in a direction to increase the engine speed and vice versa. As the engine speed increases, pD increases, and the process will continue till pD is equal to L and no further lecting a nominal speed S.

is increased, the diaphragm will move movement of the diaphragm will take place. When the state of equilibrium is attained,

where C is some constant.

It will thus be seen that the speed at which the engine will run is entirely dependent on the selected area of the orifice ll provided the load of the spring 14 remains constant.

In practice, however, the spring l4 must have a definite rate R, so that when the diaphragm I3 is in a position giving minimum power, the spring load will be greater than when it is in a position giving maximumfpower.

Suppose the diaphragm to be connected to the engine throttle, and suppose the load on the engine to be variable by .any external means. Let the control lever be placed in a position se- If the engine loading is very light, the engine will tend to overspeed and the diaphragm 13 will move to a position giving a very small throttle opening, and the spring load will be L. Now if the engine load to the wide open throttle position and the spring load will change to L-AL where AL is equal to 1R, 1 being the diaphragm movement and R the spring rate.

Let the change in speed be AS.

Then

an ALE Since L S-C'A D and C, A and D are maintained constant.

The percentage change in speed corresponding to any given change in engine loading is thus entirely dependent on changes in diaphragm loading which may be caused by either changes in spring loading or by changes in the effort required to move the throttle.

In practice it is desirable that the regulation of the governor should be as small as possible, and this is achieved by the provision of the servo mechanism which relieves the diaphragm of the duty of moving the speed-changing mechanism. The changes in diaphragm loading are then substantially independent of the effort required to move the speed-changing mechanism, and the movements of the diaphragm may be made as small as desired by suitable design of the servo mechanism, so that the effects of changes in spring load due to the rate of the spring can be made to conform with any desired accuracy of regulation.

From the above-stated mathematical expressions it will be observed that the selected speed is dependent solely on the area of the orifice under the pilots control if L and D are mainmained constant, and that the regulation is constant and independent of th selected speed.

In addition to maintaining the regulation constant for all selected speeds, the hydraulic governor has the further advantage over the conventional centrifugal governor that the needle valve can be accurately machined to give anydesired relationship between movement and area of th orifice, whereas dependence on the rate of .a spring to establish the relationship between control lever and engine speed involves the disadvantage that it is difficult to produce springs of a given rate with sufficient accuracy.

The pressure regulating valve I8 is coupled to the diaphragm I3 and the extent of opening of the valve I .8 is therefore governed by the position of the diaphragm. The servo piston I9 has its upper surface exposed to the pressure at the low pressure side of the diaphragm I3, which of course .is determined by the position of the regulating valve {8. The underside'of the piston I9 is exposed to the pressure at the outlet of the regulating valve 18 through a conduit 2|. The servo piston I9 takes up a position such that the pressure difference across :the regulating valve is balanced by the compression of a spring 22.

When the pressure difference across the diaphragm I3 is greater than that exerted b the tension of the spring I4 acting in the opposite direction, that is when the engine speed is greater than selected, the diaphragm I 3 moves to open the pressure regulating valve I8, so that the pressure drop across the valve I8 decreases. This allows the spring 22 to move the servo piston I9 in the direction to decrease the speed. The reverse process takes place when the engine speed is lower than that selected, so that eventually the diaphragm I3 positions the regulating valve I8 so that the servo piston is held in a position giving the desired engine speed.

It should be noted that the design of the pressure regulating valve I8, which slides to vary the effective area of overlapping slots 23, 24 in its movable outer member 25 and fixed inner member 26 respectively, is such that any changes in pressure difference across it cause no change in the effort required to hold it in any position. In this way the load on the diaphragm I 3 is governed only by the load applied to it by the spring I4.

As the rate of delivery from the pump and to the servomotor are roughly .proportional to the R. P. M. the maximum rate at which the throttle may open is small at low engine speeds but greater at higher speeds which is what is required.

The pressure of delivery of the fuel to the engine is governed by the relief valve I6 which allows excess fuel to return to the suction side of the pump I0, and the arrangement shown in Fig. 1 is suitable for use with carburetters which require only a very low fuel delivery pressure, e. g. of the order of 2 lbs/sq. in. the higher pressure at the inlet of the regulating valve I8 being used to operate the servo mechani m- The piston rod I5 of the servo piston? is connected toone arm of a bell crank 28 pivoted to an eccentric 29, the other arm of the bell cranl; being connected to the throttle Valve I 30 by a connection 30 and serving to open the throttle as the piston I9 falls and to close it as the ,piston rises.

The eccen tric 29 is rotatable by means of a control lever 3I, for the purpose of operating the needle I2 to vary the area of the orifice and hence the selected speed.

It will be appreciated that, instead of connecting the servomotor directl to the throttle valve, I may, in the case of an aircraft engine, connect it instead to the boost control.

I may, however, change the speed of the engine by varying its loading as distinct from varying the throttle position. Thus, in the case of an aircraft, I ma couple the servomotor .to the pitch changing mechanism of the airscrew, and 5 in vthe case of a power boat I may arrange for the servomotor to alter the pitch of the water screw.

The eccentric mechanism shown in Fig. 1 enables th r tt e to be iven a small manual movement from the control lever 31 to facilitate starting of the engine. The servo mechanism will then of course be inoperative, the servo piston I9 being held by the spring 22 at the upper end of its cylinder since there is no fluid 15 pressure available to move it I,

The fact that the servo mechanism is unable to close the throttle completely .does not prevent the governor from controlling the engine speed even at the lightest loading. This is because as the engine loading is decreased at constant engine speed, the throttle opening must be correspondingly decreased. When the engine loading attains its minimum possible value, the throttle will maintain its minimum possible opening for that particular engine speed, and this minimum opening will .ofcourse be greater the higher the selected speed. Even if the minimum load be zero, the minimum throttle opening will increase with the selected speed because of the internal friction .of the engine. The governor will therefore never be called upon to close the throttle beyond this minimum angle at each speed in order to maintain the'required speed.

It will be appreciated that, if there were unrestricted communication between the exit side of the orifice II and the undersurface of the diaphragm I3, the device shown in Fig. 1 would be liable to hunt in the following manner:

If the actual engine speed be momentarily slightly lower than the selected speed, the diaphragm I3 will respond, causing the regulating valve I8 to move quickly in a closing direction, so that the pump delivery pressure will rise quickly and so cause the throttle to open ,quicke ly. The increase in engine speed will lag :behind the increase in the throttle opening in terms of time due to engine inertia. The result is that when the engine eventually attains its selected speed and the throttle ceases to move, the throttle will be too far open and the engine speed will go on increasing so that the actual speed is above the selected speed. The diaphragm I3 will then respond to close the throttle, and the reverse procedure will take place so that there is a likelihood of a continuous oscillation being set up, known as throttle flutter or hunting. This effect is indicated by the line .ABCDE in Fig. 3.

Hunting is avoided, with the arrangement shown in Fig. 1, by causing the throttle to ap- 0 proach its final position very slowly, as indicated by the line AF in Fig. 3, so that the overopening effect is made sufficiently small to be negligible, for it will be appreciated that the slower the throttle moves, the smaller will be the time 65 lag between change in the throttle position and consequent change in engine speed.

This effect is obtained by placing a restriction 32 between the downstream side of the speed selecting orifice I I and the low pressure side of "the 10 diaphragm I3. Any movement of the throttle in an opening direction will then cause a pressure drop to occur across 32 so that the pressure difference acting across the diaphragm I3 will be greater than the pressure difference across the 75 orifice II. The resultis that the relay mechanism against the spring.v

will respond to arrest the throttle movement before the engine attains its selected speed, so that the rate of throttle movement becomes small as the engine speed approaches the desired speed.

Let s be the engine speed expressed as a percentage of the final and selected speed at any time t.

Let A be a parameter expressing the size of the restriction 32 relative to the bore and stroke of the servo piston.

It will be observed that the value of decreases as the engine speed attains its final value, and that the throttle attains its final position asymptotically.

In some installations it is essential that there should be absolutely no delay in closing the throttles should the engine overspeed: such a condition occurs when the engine is used to drive the propeller in a boat, for there are occasions when the screw comes out of the water and the engine speed increases almost instantaneously and would exceed a safe value if the throttles do not close equally rapidly.

It will be seen that the introduction of a nonreturn valve in the position shown at 33, Fig. 1, avoids any damping of the throttles in a closing direction and allows movement at the maximum possible rate. The tendency to hunting is in no way enhanced, as it is only essential to provide damping in one direction, for not more than one heat can occur under these conditions, i. e. on opening-up there will be no over-opening, but on closing down, the throttles may over-close, but the consequent movement in the opening direction will be damped.

In the arrangement illustrated in Fig. 1, the engine driven fuel pump I0 is required to deliver fuel at a pressure greater than that required by the carburetter, and the capacity of the pump must be such as will fulfil the demands of the engine.

In Fig. 2 is shown an arrangement in which the fuel pump is required to deliver fuel at the pressure required by the carburetter, but in a quantity greater than that demanded by the engine. In the case of Fig. 1, the excess pressure capacity of the pump is used to operate the throttle servo mechanism, while in the case of Fig. 2 the excess volume capacity of the pump is used to operate the servo mechanism. The arrangement of Fig. 2 is suitable for carburetters requiring a higher fuel delivery pressure, e. g. 30 lbs. sq./in., because, as will be seen, the actual fuel delivery pressure is used to operate the servo mechanism.

In Fig. 2, the speed responsive diaphragm I3 is associated with two relay valves controlling the flow of fluid to or from the servomotor in such a way that when the engine speed is lower than ther, but the engine speed 8. that selected, valve 35 will open, allowing fluid under pressure to flow, through conduit 31, to the servomotor and open the throttle against the return spring 22 until the speed has attained its selected value and the valve 35 is closed again by its spring 39.

Similarly, if the engine speed is higher than that selected, the diaphragm will open valve 36, allowing fluid to flow from the servomotor through conduits 31 and 38 to the low pressure side of the pump ID, the throttle being closed by the return spring 22 until the selected speed is attained and the valve 36 is closed by its spring 40. It will be observed that the valves 35, 36 are operated from the diaphragm I3, through the agency of a tappet 42 moving with lost motion between the valve stems. The restriction 32 controls the rate of throttle opening in the manner already described with reference to Fig. 1, to reduce the tendency to hunt.

As a second or additive means of preventing hunting, the valves 35 and 36 are provided with an overlap introduced by the lost motion between their stems and the tappet 42. This lost motion, when associated with a definite rate in the diaphragm-loading spring [4, causes the diaphragm load to change so that the speed at which valve 35 opens is greater than the speed at which valve 36 opens by an amount As. The amount As is then the overlap between the two valves.

Overlap prevents hunting in the following manner:

If the engine speed is momentarily lower than that selected, the valve 35 opens and the throttle begins to open. The consequent rise in engine speed lags behind the change in throttle position owing to the engine inertia. Thus, at the moment when the selected speed is attained, the throttle is over-opened; it will cease to open furwill increase slightly above the selected speed. Normally the valve 36 would now operate and the reverse procedure take place. Owing to the valve overlap, however, the valve 36 will not operate as long as the engine has not overspeeded by an amount greater than As, so that the engine will continue to run steadily at a speed slightly in excess of the selected speed.

If a small leak of fluid is allowed to take place across the servomotor, the throttle will slowly close while both valves 35 and 36 are closed, so that eventually the engine speed will fall again to the selected value when valve 35 will open sufliciently to hold the throttle in a constant position, the flow through the valve being the same as that leaking past the servo piston. It will be noticed that the valve 35 is shown slightly open in Fig. 2, and the leak across the servomotor takes place through a small orifice 43 in the servo piston IS.

The procedure is now as follows:

If the engine speed be momentarily below that selected, the valve 35 will react so that the speed rises to a value slightly higher than the selected speed s but less than s+As. Both valves 35 and 36 will then be closed, and the throttle will very slowly close till the selected speed is attained, when valve 35 will open sufficiently to prevent the throttle closing further. The fact that the leak past the servo piston is very small ensures that the throttle approaches its final :position very slowly, and hence the lag between change in throttle position and consequent change in engine speed becomes negligibl small, and hunting is prevented. The efiect is shown by the line AGH in Fig. 3.

Ini some installation 1 it is essential that there should be absolutely.nodelayin closing the throttlesrshould the. engine over-speed; such a condition occurs when the engine is used to drive the propeller in a boat, for 'thre are occasions when the, screw .comesout .of the water and the engine speed increases almost instantaneously and would exceed a safe value if the throttles do not close equally rapidly.

It will be seen that the free-flow of liquid from theyservp cylinder :permittedwhen valve 36 opens, awe s;, any damping of the throttles in aclosing direction and allows movement at the maximum possible rate. This will occur only after the engine has overspeeded by an amount As, and thus no rapid throttle movements will be caused by small amounts of overspeeding for a short time, which is a desirable feature to ensure stable operation so long as the amount or overspeeding is designed to be within the safe limits of the engme.

The leg of the relay system in terms of time is governed by the lost motion and the area of the diaphragm [3, that is the volume of liquid displaced by the diaphragm in moving through the lost motion range. The lag in terms of R. P. M. is governed by the rate of the spring M, the area of the diaphragm l3, and the loads required to operate valves 35 and 36, if any.

What I claim as my invention and desire to secure by Letters Patent is:

1. In an internal combustion engine, 1a. hydraulic governor comprising an engine-driven fuel pump for feeding fuel to the engine, means for changing the engine speed, a variable-area orifice, a conduit for supplying to said orifice the whole of the discharge f said pump, a valve for controlling the area of said orifice, a speed selecting member for varying the selected engine speed, a linkage between said speed selecting member and said valve for operating the valve to vary the area of the orifice when the speed selecting memher is moved to change the selected engine speed, a pressure sensitive device responsive to the fuel pressure difference across said orifice, a hydraulic servomotor controlled by the pressure sensitive device and actuated by fuel supplied by said fuel pump, and mechanism controlled by said servomotor for operating said speed changing means in response both to change in the area of said orifice and to change in the speed of said pump so as to maintain :a substantially constant fuel pressure difference across said orifice.

2. In an internal combustion engine, a hydraulic governor comprising an engine-driven fuel pump for feeding fuel to the engine, means for changing the engine speed, a variable-area orifice, a conduit for supplyin to said orifice the whole of the discharge of said pump, a valve for controlling the area of said orifice, a pressure regulating valve for controlling the fiow of fuel from said orifice to the engine, a speed selecting member for varying the selected engine speed, a linkage between said speed selecting member and said valve for operating the valve to vary :the area of the orifice when the speed selecting member is moved to change the selected engine speed, a pressure sensitive device responsive to the fuel pressure difference across said orifice, a connetion between said pressure senitive device and said regulating valve for opening said regulating valve when the fuel. pressure difference across said orifice increases and for closing said regulating valve when the fuel pressure difierence across said orifice decreases, a hydraulic servomotor ill comprising a servo piston movable in a cylinder and. a exposed to the; fuel "pressure difference across-said regulating valve, and a spring for balancing said servo piston against said fuel :pressure. difference, and. mechanism. controlled by saidservo-piston foruoperating said speed changing means,.in response. both-to change in the area 'OfL'S'aIid-OI'ifiCB and to changev in the speed of said pump so asto maintain a substantially constant fuel pressure difference across said orifice.

3. ;In.,an internal, combustion engine, a hy-- draulic; governor, as claimed in claim pl, wherein the speed changing means is constituted by an engine throttle, and comprising a linkage connecting said servo motor to said engine throttle for controlling the engine speed tomaintain a substantially constant fuel pressure difference across said orifice, said linkage being operable by said speed selecting member to enable manual opening of said throttle by said speed selecting member when starting the engine.

4. In an internal combustion engine, a hydraulic governor as claimed in claim 1, wherein the low pressure side of said pressure sensitive device communicates with the low pressure side of said orifice by a restricted connection only, said restricted connection serving to retard movement of a servo piston in said servomotor in the direction to increase the engine speed.

5. In an internal combustion engine, a hydraulic governor as claimed in claim 1, wherein the low pressure side of said pressure sensitive device communicates with the low pressure side of said orifice by a restricted connection only, said restricted connection serving to retard movement of a servo piston in said servomotor in the direction to increase the engine speed, and comprising a normally closed non-return valve associated with said servomotor, said non-return valve permitting rapid movement of said servo piston in the direction to decrease the engine speed.

6. In an internal combustion engine, a hydraulic governor as claimed in claim 1, wherein said servomotor comprises a servo cylinder, a servo piston movable in said servo cylinder and connected to said mechanism for operating the speed changing means, a conduit for supplying fuel under pressure to one end of said servo cylinder, an exhaust conduit communicating with the other end of said servo cylinder, and a spring for balancing said servo piston against the fuel pressure acting thereon, and comprising a pair of relay valves, each having a stem, for respectively connecting the high pressure end of said servo cylinder to pressure and exhaust, said relay valves being normally closed, and a tappet operable by said pressure sensitive device and moving with clearance between the stems of said relay valves, said tappet serving to open the pressure relay valve when the engine speed falls below the selected value and to open the exhaust relay valve when the engine speed rises above the selected value. v

7. In an internal combustion engine, a hydraulic governor as claimed in claim 1, wherein said servomotor comprises a servo cylinder, a servo piston movable in said servo cylinder and connected to said mechanism for operating the speed changing means, a conduit for supplying fuel under pressure to one end of said servo cylinder, an exhaust conduit communicating with the other end of said servo cylinder, means providing for a small leak of fluid across said servo piston,

11 and a spring for balancing said servo piston against the fuel pressure acting thereon, and comprising a pair of relay valves, each having a. stem, for respectively connecting the high pressure end of said servo cylinder to pressure and exhaust, said pressure relay valve being normally slightly open and said exhaust relay valve being normally closed, and a tappet operable by said pressure sensitive device and moving with clearance between the stems of said relay valves, said tappet serving to open the pressure relay valve when the engine speed falls below the selected value and to open the exhaust relay valve and allow the 10 Number The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 2,177,120 Schaeren Oct. 24, 1939 2,407,115 Udale Sept. 3, 1946

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