US1982000A - Electrical speed governor - Google Patents

Description

Nov. 27, 1934 I R. G. GRIFFITH 0 ELECTRICAL SPEED GOVERNOR Filed July 22, 1952 INVENTOR RONALD G. GRIFFITH ATTORNEY Patented Nov. 27, 1934 UNITED STATES PATENT OFFICE signor to don, England Creed and Company,

Limited, Croy- Application July 22, 1932, Serial No. 624,060 In Great Britain June 16, 1932 Claims.

This invention relates to speed governors of the type in which a mass movable under the joint action of centrifugal force and a controlling force actuates a make-and-break contact mech- 5 anism for controlling speed varying means.

Electrical speed governors of this type are employed generally for controlling the speed of small electrcmotors for apparatus and light machinery which is required to be driven at a given speed within close limits of constancy. The make-and-break contact mechanism referred to above may, however, be employed in a variety of ways to maintain constant the speed of a rotatable member, by alternately shorting and inserting a resistance in the armature or field circuit of the driving motor for instance, or by controlling the circuit or circuits of brake or other speed varying means.

In some of these types of speed governor one of the contacts of the make-and-break contact mechanism is formed as a disc adapted to rotate with the governor or member the speed of which it is desired to govern and to make rubbing contact with a second contact which does not rotate, one or the other of the two contacts being movable relatively to the other to make and break contact therewith under the joint action of centrifugal force and a controlling force. In others a contact arm or member makes and breaks contact with a second contact as a simple pair of butt contacts, and it is to speed governors having this latter type of contact mechanism that the invention relates.

Many attempts have been made to produce a satisfactory governor of the type referred to. Considerable dlfliculty has been experienced in particular when the contacts are required to make and break rapidly a comparatively heavy current,'as it must be remembered that in these- 40 governors the action of the contacts is required to be very light, rapid and continuous. In such cases it has been found that despite careful preparation of the contacts by selection of suitable metals and preparation of the contact surfaces, after a comparatively short period of use, burning and irregular wear of the contact surfaces occur, a pit or crater being formed on one contact and a corresponding raised projection on the other. With the speed governors as previously constructed it would appear that the coacting contact faces can only make contact at one point. As the centrifugal force reduces the pressure on this point of the contact, heat is generated and welding takes place,'part of the contact being then transferred to the other concontact,

tact. This condition when started is of microscopic dimension but once started it continues to grow until a large crater is formed on one contact and a point on the other.

The object of the present invention is to reduce this form of contact trouble and it is claimed that the improvements which form the subject matter of the present invention have been proved by comparative trials to effect a considerable improvement in the results obtained.

According to the first and main feature of the invention, therefore, in a speed governor of the class referred to, the make-and-break butt contacts are adapted to effect relative movement between the contact surfaces under contact pressure. To this effect one or both of the contacts is arranged to be resiliently yielding under contact pressure and the simplest means of achieving this object is to form a contact on a face 76 near the end of a flat spring strip.

It should be noted that when one of the contacts is mounted on a resiliently yielding member such as a spring strip and is movable by the joint action of centrifugal force and a controlling force 80 into and out of contact with a relatively fixed it is necessary that the movable contact be actuated through the spring strip so as to obtain the relative movement on the contact surfaces under contact pressure. It is not suflicient for the contact itself, for instance, to be given suflicient mass to generate centrifugal force under rotation when mounted on the rotating governor, and the spring strip to supply the controlling force. In these circumstances no relative motion on the contact surfaces can take place under contact pressure.

Other features of the invention relate to the disposition of the contact surfaces firstly relative to the direction of movement of the movable member under the actuating forces so that the relative motion of the contact faces under contact pressure is increased, secondly relative to the direction of rotation when the contacts are mounted on the rotating member as it has been found by experiment that this is a great factor influencing the life of the contacts. Another feature relates to the provision of a plurality of governing contacts in a make-and-break contact mechanism.

In the accompanying drawing, Fig. 1 shows an example of contact mechanism of a governor according to the invention in which the switch mechanism is mounted directly on the rotating portion the speed of whichitis desired to govern.

Fig. 2 shows an improved form of the invention,-

' illustrating the invention have been omitted. The

slip rings and brushes or other means for connecting the contact mechanism on the rotatingportion in an external circuit, for instance, are

not shown. Moreover, although not further mentioned or described it will be appreciated that the two contacts of the make-and-break mechanism .are suitably mounted on the governor in a manner to be insulated from each other except when -in the closed condition.

Referring to Fig. 1 a shaft 1, the speed of which is to be regulated, carries a .disc member 2 on which is mounted a bracket 3 having an arm 4 pivotally connected at one end to bracket 3 by a flexible spring strip 5. Arm 4 constitutes a mass, the centre of which is movable during rotation of shaft 1 by centrifugal force in a substantially radial direction. Diametrically disposed across disc member 2 is a helical spring 6 connected at oneend to arm 4 near its centre of-mass and at the other end to the disc member 2 through the screw adjusting means 7, whereby the tension of spring 6 can be conveniently altered to regulate the governed speed. Helical spring 6 supplies the controlling force opposing the centrifugal force on the arm during rotation.

At the free end of arm 4 is attached a spring strip 8 on the face of which is fixed a contact 9, a second contact 10 co-acting therewith being carried on a bracket 11 fixed to disc member 2. It will readily be understood that beyond a certain speed the centrifugal force of arm 4 exceeds the tension of spring 6 and the contacts 9 and 10 are opened. When the speed is reduced as a consequence of the opening of these contacts, spring 6 again draws the arm 4 radially towards -the axis of rotation, the faces of contacts 9 and 10 meet and further movement of arm 4 inwards causes spring strip 8' to yield resiliently and has the eflect of causing a slight relative sliding or rubbing motion between the contact surfaces. It is not presumed here to explain the precise effect which is brought about by this small relative motion as compared with that where no relative motion takes place. It may sufiice here to say that. the localized build up of one of the contacts previously referred to is greatly reduced and the contact surfaces gradually assume a matt appearance which does not interfere with the proper functioning of the contacts.

In Fig. 2 similar parts to thoseof Fig. 1 are employed and are correspondingly numbered, but

in this case the free end of arm 4 with spring strip 8 and contact 9 co-acting with the second contact 10 are arranged with the plane of the contact surfaces at an angle to the direction of motion of the movable contact as actuated by arm 4. Thiswill be seen to have the effect of increasviated and the life of the contacts is considerably increased. It will be noted that in this position the plane of the contact surface is substantially of the parts shown in Fig. 2, two separate advantages are, therefore, obtained as compared with that of Fig. 1.

In the arrangement shown in Fig. 3 the pivotally movable arm of the previous arrangements is replaced by a member 12, the mass of which is equally disposed on either side of a diametrical line on which the control spring 6 is situated. The member 12 is guided for radial movement along parallel lines by pins 13 and 14 sliding in brackets 15 and 16. On the two opposite extremities of member 14 are two resiliently yielding spring strips 17 and 18 respectively, each carrying contacts 19 and 20 co-acting with two corresponding contacts 21 and 22, fixed to brackets 23 and 24 on disc member 2 of the governor. This arrangement forms a balanced movement with double-break contact mechanism. Obviously both the contacts could be arranged at opposing angles corresponding to the angle of the arm in the arrangement of Fig. 2 to obtain the advantages described with reference thereto. With the arrangement of Fig. 3, however, aplurality of resiliently yielding contacts are provided which are in series in the governing circuit butif. desired a plurality of such contacts could be arranged in parallel in the circuit and adapted to be actuated together to make and break the circuit by the arrangements on the lines described.

Although the above description relates to contact mechanism mounted on the rotating member the speed of, which is to be governed it will be appreciated that if desired only the member which is actuated under the joint action of centrifugal force and a controlling force need be on the rotating portionwhilst the resiliently "motion between the contact surfaces in the manner substantially as previously described.

It will also be appreciated that although in the description above given the movable contact is arranged to furnish the yielding motion under contact pressure if desired, acontact, could be fixed to the movable member and the co-acting contact arranged on a spring. strip. Alternatively both contacts could be so arranged. The contact mechanism has moreover been shown in which the circuit is broken when the regulated speed is exceeded. With alternative speed varying means this could be reversed so that contact was made to complete the circuit when the speed was exceeded, by placing the a relatively fixed contact in a position radially outside the movable contact. A limiting stop in this case would be necessary to hold the movable member near its working position against the tension of the controlling spring when the governor was at rest.

Various other alternative arrangements within the scope of the invention as defined by the appended claims will suggest themselves to those skilled in the art.

What is claimed is:

1. In a speed governor, a rotatable member, a mass movable by centrifugal force, means supplying a controlling force for said mass, and resiliently yielding contact means actuated by the movements of said mass and having a contacting face disposed in a plane substantially tangential to the direction of rotation of said rotatable member.

2. In a speed governor, a rotatable member, an actuating mass movable thereon by centrifugal force, means supplying a controlling force for said mass, and a governing contact connected to said actuating mass through a yielding spring strip and having a contactface disposed in a plane substantially tangential to the direction of rotation of said rotatable member.

3. In a speed governor a rotatable member, a mass movable thereon by centrifugal force in a substantially radial direction, means supplying a. controlling force for said mass, and a governing contact disposed on one side of the centre of gravity of said mass with a contact face in a plane substantially tangential to the direction of rotation of said disc member and connected to said mass through a yielding spring strip.

4. In a speed governor, a rotatable disc member, an arm pivoted at one end thereon with its centre of mass movable in a substantially radial direction, a diametrically disposed helical controlling spring connected between said arm and said disc member, and a fiat contact spring fixed to the free end of said arm and disposed in a plane substantially tangential to the direction of rotation of said disc member and at an angle to the radial direction of motion of said arm.

5. In a speed governor, a rotatable member, a mass carried thereby and movable thereon by centrifugal force, means carried by said member and supplying a controlling force for said mass, and resiliently yielding butt contact means mounted on said member and actuated by the movement of said mass and disposed with the contact faces at an acute angle to the direction of the actuated movements.

. RONALD GEORGE GRIFFITH.

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