US2965076A - Servomechanism - Google Patents

Description

Dec. 20, 1960 H. c, ZEISLOFT 2, 7

SERVOMECHANISM Filed Dec. 51, 1959 2 Sheets-Sheet 1 IN VEN TOR.

Dec. 20, 1960 H. c. ZIEISLOFT 2,965,076

- SERVOMECHANISM Filed Dec. 51. 1959 2 Sheets-Sheet 2 IN VEN T OR.

United States Patent SERVOMECHANISM Harry C. Zeisloft, Brookfield, Wis., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Dec. 31, 1959, Ser. No. 863,291

Claims. (Cl. 121-147) My invention relates to fluid-operated servomechanisms, and is particularly directed to new and improved means for controlling such mechanisms. The invention is particularly suited to mechanisms operated by air or other gases, but is also applicable to hydraulic servomotors.

There are many servomechanisms or power actuators which depend for control upon varying the pressure in a chamber or the relative pressures in two chambers. Some of these achieve this pressure variation by modulating an air jet. The jet may be allowed to flow freely from a nozzle to a port from which it is discharged to the mechanism to be actuated; or the flow may be partially or completely intercepted or diverted to reduce the pressure recovered in the discharge port.

My invention involves a mode of control for this purpose which, so far as I am aware, has not been known previously, and which has substantial advantages that will be apparent from the succeeding detailed description of preferred embodiments of the invention.

To summarize it, the control according to my invention embodies a continuously moving shutter-like mechanism which rapidly and intermittently obstructs the flow from the nozzle to the discharge port. The fraction of the period of rotation of the shutter during which the flow is obstructed may be varied by a suitable input control. The average pressure recovered in the discharge port is varied by varying the phasing of the shutter, or, in other words, varying the part of the period of rotation during which the shutter obstructs the flow.

The principal objects of the invention are to provide an improved servomechanism, and particularly a servomechanism which is highly responsive and accurate in its response.

The presently preferred embodiments of my invention are illustrated in the accompanying drawings, in which Figure l is a somewhat schematic sectional drawing of one form of the invention in which the shutter is controlled mechanically.

Figure 2 is a fragmentary sectional view of the same taken on the plane indicated by the line 2-2 in Figure 1.

Figure 3 is a partial schematic view of a second form of the invention embodying electrical mechanism for varying the shutter opening.

Referring first to Figure 1, there is illustrated an ap paratus in which a control device according to the invention actuates a relay or pilot valve which, in turn, controls the flow of actuating fluid to a power cylinder. The operating fluid will be referred to hereinafter as air in the interest of conciseness, although the invention is not limited to air as a motive fluid. The relay or pilot valve identified as ltl'comprises a housing 11 bored to provide a cylinder 12, one end of which is closed by a plug 13. A valve spool 14 freely reciprocable in the cylinder has relatively broad lands 17 at each end thereof and knife-edge leads 18 at the central portion of the valve spool. Air' under pressure is supplied from any suitable source through an inlet port 19 into a chamber 21, which connects with the cylinder 12 between the lands 18 in the neutral or centered position of the valve spool illustrated. The housing 11 also defines two passages 22 which communicate with the cylinder 12 between the lands 17 and 18 at each end of the spool. Suitable piping 23 or other means defining a conduit for the servo fluid connects the chambers 22 to the opposite ends of a 'power cylinder 25. Cylinder 25 houses a reciprocable piston 26 which supplies power to the device to be actuated through a piston rod 27. One end of the cylinder is closed by a removable head 29. The structure of the servomotor or power cylinder 25 and the piping to it are not described in detail, since they may be of any suitable structure and the details are immaterial to the invention. Air under pressure may be supplied to either end of cylinder 25 from port 19 through chamber 21 and a passage 22 upon displacement of valve spool 14 from 'a neutral position. Such displacement also uncovers one or the other of two vent ports 30* by which the air is discharged to atmosphere from the other end of the cylinder.

Movement of the spool 14 to control the servo cylinder 25 is efiected by a mechanism according to the invention which comprises a continuously rotating shutter 32 consisting of two sector disks 33 and 34 closely adjacent each other and rotating about a common axis. Disk 33 is integral with or fixed to a shaft 35, the lower end of which is supported in a bearing 37 in the housing 11. Disk 34 is integral with or fixed to a'hollow shaft 38 coaxial with shaft 35. Shaft 38 is supported in a suitable bushing in a casing 39 bolted to the upper surface of housing 11. Casing 39 and recesses in the upper surface of housing 11 define a chamber 41 within which the shutter 32 rotates. A converging nozzle '42 provided in the housing 11 discharged into the chamber 41. Nozzle 42 is supplied from the pressure fluid chamber 21, the fluid passing around the valve spool 14. A funnel-shaped or converging discharge port 43 in the casing 39 is coaxial with the nozzle 42. Discharge port 43 communicates through passages 45 and 46 in the casing 39 and housing 11 with a chamber 47 in one end of cylinder 12. It will be noted that the common axis of nozzles 42 and discharge port 43 lie within the radius of shutter 32. A passage '49 outside the periphery of the shutter connects the chamber 41 with a chamber 50 at the opposite end of cylinder 12 from chamber 47.

The structure of shutter 32 will be more clearly apparent from Figure 2. Each sector disk 33 and 34 comprises a central disk 51 and two sector-shaped lobes 53 extending outwardly therefrom. The lobes 53 are preferably about 78 degrees in arcuate extent. As shown in the drawings, the lobes on the two disks are partially overlapped so that the shutter 32 obstructs flow from the nozzle to the port 43 through approximately degrees in each degrees of rotation. Thus, the two sets of lobes obstruct the flow during approximately of a cycle of rotation of the shutter. A greater period of obstruction can be had by increasing the phase difference of the disks 33 and 34; or, by decreasing the phase difference, the relative period of obstruction may be decreased to a minimum of approximately 43% of the total period of revolution.

At some phase angle between the two disks, the relative obstruction to flow from nozzle 42 through discharge port 43 as compared to that from nozzle 43 through outlet 49 will be such that the average pressures in the chambers 47 and 50 will be equal. Decreasing the phase angle of the disks from this point will increase pressure in chamber 47 and decrease pressure in chamber 50. Increasing the phase angle from this pointwill reduce the pressure in chamber 47 and increase it in chamber 50. It will be understood that during that part ofthe cycle in which the flow is unobstructed between the nozzle and discharge port 43, the pressure in chamber 47 is higher than that in chamber 50 because of the pressure recovery resulting from the direct flow from nozzle 42 into port 43 and because of the aspirating action of the flow which reduces the pressure in chambers 41 and 50. Because of the rapid or intermittent fluctuations of pressure as the shutter rotates, valve spool 14 has a slight tendency to oscillate or jitter, which greatly reduces static friction and hysteresis of the valve 14.

Proceeding now to the mechanism illustrated in Figure l for driving the shutter and varying the phase angle of the dis-ks, this mechanism is mounted in a case 54 which comprises a lower part 55 bolted to the upper surface of housing 39 and an upper part 56 bolted to the lower part 55. The case 54 houses driving mechanism for the shafts 35 and 38 which is powered by a small motor 57 mounted on a bracket 58 extending from the part 56. Motor 57 may conveniently be an electric or air-driven motor.

The shaft of motor 57 is pinned to the hub 61 of a driving pinion 62. This hub is internally splined to receive the splined upper end 63 of shaft 35, which is thus driven directly by motor 57. Pinion 62 drives a pinion 65 integral with a shaft journalled in a fixed point in the part 56. Pinion 65, in turn, meshes with an internally toothed ring gear 66, the hub of which is rotatable on shaft 35. Ring gear 66 has a second set of internal teeth which mesh with a planet pinion 67 rotatably mounted on a spider 69 journalled in the lower case part 55 so as to be rotatable about the axis of shafts 35 and 38. The upper end of the outer shaft 38 is journalled in the spider 69 and mounts a pinion 70 which meshes with pinion 67. An arm 71 integral with the spider 69 extends through a slot in case 54. The outer end of arm 71 may have a hole 73 by which it may be connected to any suitable linkage or other device which provides the input to the servomechamsm.

Pinions 62 and 70 are of the same diameter and number of teeth, and likewise pinions 65 and 67. Therefore, for anygiven fixed position of spider 69, the shafts 35 and 38 are driven at the same speed by motor 57. Movement of arm 71, through the planetary action between gear 66 and pinions 67 and 70, adds or subtracts to the movement of disk 34 by the motor and thereby changes the phase angle between the disks. Therefore, if arm 71 is moved in either direction from the position at which the pressures on valve spool 30 are balanced, the pressures in chamber 47 and 50 will be unbalanced to move the valve spool in one direction or the other, depending upon the direction of movement of the input 71.

It will be noted that the disposition of the vent ports 30 is such that they act to prevent excessive displacement of valve spool 14, since such excessive movement vents the chamber 47 or 50 which has the higher pressure and is tending to cause the valve overtravel.

Figure 3 is a fragmentary view illustrating another type of mechanism for operating the shutter 32. The structure of the servomechanism, except as illustrated in Figure 3, may be the same as that already described in connection with Figures 1 and 2. The shafts 35 and 38' correspond respectively to shafts 35 and 38 of Figure 1. In the mechanism of Figure 3 each shaft is driven by a synchronous electric motor, and the phase relation of the shutter disks is varied by varying the relative Phase of the operating currents of the motors. As illustrated, shaft 35' is connected through bevel gears 75 and shaft 77 to a two-phase motor 78. Shaft 38' is connected through bevel gears 79 to the shaft 81 of a two-phase motor 82. The two motors are energized from a mum mon two-phase A.C. supply 83. Motor 82 is directly connected to the three wires 85, 86 and 87 of the two phase supply. Motor 78 is energized through leads 89, and 91 by a phase shifting transformer 93 energized from the leads 85, 8'6 and :87. The relative phase of the current supplied to the two motors may be varied by the control handle 94 of the phase shifter.

As will be apparent, the form of the device shown in Figure 3 could be energized directly by the phase shift between two circuits which individually respond to two quantities which are to be brought into some desired relation by the operation of the servomotor. For example, the servomotor could respond to the relative phase angles of two generators to control the supply of operating fluid to the prime mover of one of the generators for synchronizing purposes, in which case the motors 78 and 82 could be connected to the two generators and the phase shifter would not be required.

For the reasons outlined in the preceding paragraph, and also because of its mechanical simplicity, the device of Figure 3 has some advantages. However, in other installations, the mechanical phase shifting device of Figure 1 may be advantageous. One advantage of the servomotor of Figure l is that the motor 57 may be of any type. It may be an electric motor of any type or, if desired, it could be a small fluid motor supplied from the same source that supplies motive fluid to the inlet port 19.

In general, it is apparent that many varieties of structure may be adopted to utilize the principle of intermittent obstruction of one of the ports leading to the device to be controlled, exemplified by the shutter mechanism illustrated in Figures 1 and 2. It will also be apparent that for some installations, where a high degree of force is not required from the output device, a member corresponding to the valve spool 14 may be the output member of the servomotor rather than a relay member which in turn controls a power cylinder such as 25. It is not essential for the shutter shafts such as 35 and 38 to be coaxial or even parallel. It is only necessary that the sector disks be disposed so as to overlap between nozzle 42 and collector port 43.

The detailed description of preferred embodiments of the invention for the purpose of explaining the principles thereof is not to be considered as limiting the invention, since many modifications within the scope of the invention may be made by the exercise of skill in the art.

I claim:

1. A fluid-operated servomechanism comprising, in combination, means defining a chamber, a nozzle discharging into the chamber, means defining a pressure fluid inlet to the nozzle, means defining a discharge port from the chamber coaxial with the nozzle, means defining an outlet from the. chamber remote from the nozzle, a displaceable member connected to the discharge port and the outlet port so as to be biased in opposite directions by the pressures of fluid communicated to the member through the said ports, and means for inversely modulating the said pressures comprising a continuously rotating variable shutter disposed between the nozzle and the discharge port so as to intermittently pass and obstruct flow from the nozzle to the discharge port, and means for varying the configuration of the shutter so as to vary inversely the relative duration of passage and obstruction of the said flow to the discharge port.

2. A fluid-operated servomechanism comprising, in combination, means defining a chamber, a nozzle discharging into the chamber, means defining a pressure fluid inlet to the nozzle, means defining a discharge port from the chamber coaxial with the nozzle, means defining an outlet from the chamber remote from the nozzle, a displaceable member connected to the discharge port and the outlet port so as to be biased in opposite directions by the pressures of fluid communicated to the member through the said ports, and means for inversely modulating the said pressures comprising two continuously rotating sector disks disposed between the nozzle and the discharge port so as to intermittently pass and obstruct flow from the nozzle to the discharge port, and means for varying the relative phase angle of the disks so as to vary inversely the relative duration of passage and obstruction of the said flow to the discharge port.

3. A servomechanism as recited in claim 2 including a motor driving coupled to both sector disks and phase shifting mechanism connecting the motor to one of the sector disks.

4. A servomechanism as recited in claim 2 including two motors, one motor being drivingly coupled to each sector disk, and means for varying the phase relation of the motors.

5. A fluid-operated servomechanism comprising, in combination, means defining a chamber, a nozzle discharging into the chamber, means defining a pressure fluid inlet to the nozzle, means defining a discharge port from the chamber coaxial with the nozzle, means defining an outlet from the chamber remote from the nozzle, a displaceable member connected to the discharge port and the outlet port so as to be biased in opposite directions by the pressures of fluid communicated to the memaseaoao her through the said ports, and means for inversely modulating the said pressures comprising a continuously rotating variable shutter disposed between the nozzle and the discharge port, so as to intermittently pass and obstruct flow from the nozzle to the discharge port, means for varying the configuration of the shutter so as to vary inversely the relative duration of passage and obstruction of the said flow to the discharge port, and means responsive to a predetermined displacement of the displaceable member for venting the pressure applied to the said member tending to displace the said member.

References Cited in the file of this patent UNITED STATES PATENTS 1,590,558 Stenhouse June 29, 1926 1,777,758 Mathieson Oct. 7, 1930 1,988,749 Reswick Jan. 22, 1935 2,079,041 Ryan et a1. May 4, 1937 2,198,543 Lauterbach Apr. 23, 1940 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent Nb, 2,965 O76 v December 20 1960 Harry Cc Zeisloft It is hereby certifiedthat error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5 line 4, for "driving" read drivingly =0 Signed and sealed this27th'day of June 19610 (SEAL) I I Attest: v

ERNEST W. SWIDER I DAVID L. LADD Atte ting Officer I Commissioner of Patents

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