US2202009A - Leveling device - Google Patents

Description

May 28,1940. s. L. G. KNox Er AL 2,202,009

LE'VELING DEVICE Filed May 21. 1938 4 Sheets-Sheet 1 'FE1 @L 7 C@ ATTORNEY.

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aegee-e PATENT LEVELING DEVICE Application May 21, 1938, Serial No. 209,226

13 Claims.

Our invention relates to new and useful improvements in leveling devices; and more particularly to leveling devices for such large power excavators as have four independent sets of caterpillar traction, each set supporting a corner of the main base of the excavator by means of a power-actuated jack.

Upon a vertical shaft through the center of the base `there is mounted a revolvable superstructure, which carries the excavating instrumentalities and the machinery which actuates them.

Such heavy machinery is impractical unless yprovided with automatic control of the leveling jacks, by means of 'a level-responsive controlling device. v

But leveling is not the only problem involved in the use of such large excavators. Owing t unevennesses of the ground over which they must travel, it has been found necessary to provide for automatically assuring a load-supporting contact of all four jacks with the ground at all times. This we. shall call equa1izing; although of course, strictly speaking, the pressure in the fouriacks is not equal.

Optional manual control for each jack sep-` arately may be added, if desired; such, for instance, as is shown and described in the copending Patent No. 2,128,273, Paul S. Stevens, August 30, 1938, for improvements in Leveling devices.

Accordingly it is the principal object of our invention to provide a system of four jacks, which shall be leveled automatically and be equalized automatically.

We have replaced the four pumps shown in the said Stevens application, by a single pump; thereby effecting a material simplification and economy. We effect a further economy over the said Stevens device, in that our pump acts only against a differential pressure, thus greatly economizing power.

We have provided a system which, though automatic, will not attempt to pump fluid either to,

We have also provided a system of interlocks which will effectually prevent either of the twomain functions of our device, viz., leveling and equalizing, from interfering with the action o'f the other.

A further object of our invention is to improve the details of each of these functions.

In addition to the objects stated above, we s have worked out a number of novel and useful details which will be readily evident as the description progresses.

Our invention consists in the novel parts, and in the combinations and arrangements thereof, l0 which are defined in the appended claims; and of which three embodiments are exemplifiedin the accompanying drawings, which are hereinafter particularly described and explained.

Throughout the description, the same refer- IB ence number is applied to the same member or to similar members.

Referring to the drawings, it will be seen that:

Figure 1 is a schematic diagram, showing jacks, pump and pump motor, solenoid valves, and 4pip- 20 ing connections, all of which are carried by the main base.

Figure 2`is an electric wiring diagram form of our complete invention.

Figures 3 and 4 are stability diagrams illusg5 trating certain limitations which we place on the length and location of the segments of the collector-ring of our equalizer."

Figure 5 shows the electric wiring for an alternative form of our invention.

Figure 6 shows the electric wiring for another alternative form of our invention.

Figure '7 shows the relation between our base, our turntable, our jacks, and our electrical contacts.

Referring now to Figure 1, we shall consider the lower right hand corner of` the sketch as corner I, the remaining corners being numbered counter-clockwise around the figure. For the proper understanding of the lvarious electrical A diagrams', Figures 2, 5 and 6, it is essential to remember that corner 3 is diagonally opposite to corner I, and that corner li is diagonally opposite to corner 2. These corners are correspondingly marked, in Figure 1, within the circles that diagrammatically represent the jacks. |The details of the jacks and the means for expanding and releasing them are not shown, as they form no part of our invention. The jacks and the means for expanding and releasing them might, for example, be such as areshown and described in the said Stevens patent.

In Figures 2, 5 and 6, we have placed opposite certain of the instrumentalities the capital letters A, B, C, etc. Each of these letters refers col- 5E of one lectively to the four instrumentalities thatare to be found across the page, on a level with the particular letter. A11 of the four of any one such group are of the same kind, and serve a similar purpose. l Y

In Figure 2 are shown pump motor M, magnetic pump-starter Il, four similar collector-ring segments, of which one is numbered l2, and the collector shoe I3, the shoe being carried on shoesupporting means |4. The shoe-supporting means is shown as a circle for the reason that the shoe and its support, being the only elements shown in Figure 2 that are located on the revolvable superstructure, are therefore carried about with the superstructure as it revolves about its aXis, the axis being at the center of the circle |4. All the other elements shown in Figure 2, including the motor M, pump-starter collector ring segments I2 and all the wiring, being located on the base, therefore do not change their position with respect to the jacks 2, 3, 4, of Figure 1;

Turning to Figure 7, we see the jacks 2, 3 and 4, disposed between ground-engaging units I0| and base |02. Also the shoe I3, carried by shoe supporting means |4 on the superstructure |03; and the segments I2, carried by the base |02.

Although we have described element I3 as a shoe, carried about on shoe-supporting means I4 by the rotation of the upper frame, any equivalent, such, for instance, as a cam or other device operating a lever to make and break the electrical contacts, or even directly mechanically actuating the A valves, (later described), might be used.

With the exception of pump motor M, magnetic starter the four similar collector-ring segments of which one is numbered |2, collector shoe I3, shoe-supporting means I4, and solenoidactuated main switch I5, the diagram of Figure 2 naturally divides itself into four vertical bands, each associated with a corner of the machine. Calling the left-hand band, number and the successive bands numbers 2, 3, 4, each of these bands may be considered as referring directly to the similarly numbered corners of the machine. Therefore when We wish to specify any particular one of the instrumentalities shown in Figure 2, we shall designate it by the capital letter horizontally at the right, coupled with the number of the vertical band in which that instrumentality occurs. Thus, for example, the four mercury switches on the D horizontal line, proceeding from left to right, will be called, respectively, DI, D2, D3, D4; and similarly with the instrumentalities above these switches in the vertical bands.

The A elements are the four solenoids which i actuate the valves shown in Figure l as each lying in a direct line between two of the jacks; the AI valve lying between the jacks at corners andl 2; A2 in the line from corner 2 to corner 3, etc. Actuation of the solenoid opens the corresponding valve, allowing free flow between the two jacks.

The B elements are the actuating solenoids of the valves shown in detail in the center of Figure 1; the BI valve being the lowermost; those above it being B2, B3, B4 in the order named. The details of B3 and B4 are not shown,

as, for the discussion below, they may be supposed to have the same momentary conguration as valve B2.

'I'he C elements consist each of a magnetic relay, any one of which, when actuated, will l close two contacts of the corresponding relay, thereby actuating the corresponding B-valve solenoid, and at the .same time starting the pump-motor M, by means of magnetic starter The third contact will be 'discussed later.

The D elements are four mercury switches, arranged in pairs, the two elements of each pair being held in fixed relation to each other, though the pair may be tilted either way as a unit. It is to be noted that these switches are paired diagonally. Thus the pair of switches, D|D3 comprise a switch unit used to bring corners Aand 3 to the same level. The separate elements,

as DI and D3, of a switch unit, DI-D3, have sufficient opposite tilt, that, in the median position of the switch unit, i. e. when the base is level, neither element of the unit will pass electric current; but if the left hand end of D|-D3 be tilted down suiciently, connection will be made through D|; or if the right hand end oi D|-D3 be tilted down suiciently, current will pass through D3.

The switch unit D|-D3 might be merely rigidly set on the main base parallel to they diagonal between corners and 3; but in that case, because of the shortness of the individual elements, it would require a considerable difference of level to cause them to function at all. Therefore we make use of the device shown and described in Patent No. 2,101,837, to Luther E. Blanchett for improvements in Leveling devices, dated December 14, 1937, which patent is owned by our assignee. This device, by multiplying the difference of level of a much longer baseline, set parallel to the line between corners and 3, will tilt switch unit D|-D3 into operative position for a difference of level of only a few inches between corners I and 3.

The switch unit, D2-D4, is similarly arranged with respect to theI diagonal from corner 2 to corner 4.

Owing to the capillary repulsion between glass and mercury, the mercury switches will not close the circuits of which they constitute parts until there is a difference of level of at least three or four inches between two corners. This is of advantage as it is not desirable that the mercury units be affected by ordinary vibrations. But the mercury connection having once been made, the cohesion of the mercury will maintain it until the difference of level is nearly zero.

'I'he single heavy line I6 represents the power line to the motor M. 'I'he control system is supplied with power through wires I'l and I8, respectively shown at top and bottom of the diagram. b

Pump motor M may be any type of prime mover capable of delivering power.

Pump P may be any type of unit capable of delivering hydraulic iiuid under pressure, when driven by a prime mover.

Solenoid valves AI, A2, A3, and A4 may be any standard hydraulic valves which, when open, will allow hydraulic iluid to pass through the valve in either direction, and will prevent iiuid valves, is provided with .two check valves, 2liv Each of these valves, which we shall call B- f check valves 2|, then whenever two or more `l3- valves are deenergized a free flow between the corresponding two or more jacks would be possible, even when all four A-valves, later to be described, are closed. These two possibilitiesare obviously undesirable, as rendering nugatory the controls established 'for the A-valve, which controls are primarily for the purpose of preventing instability.

Although the B-valves are shown in Figure 1 as being special double-acting valves, they might each be replaced by two valves, of which one would only allow pumping fluid into its corresponding jack, and the other would only allow pumping iluid out of its jack; Similarly each of the two check-valves could be built either integral with, or separate from, the valve or valves above-mentioned.

Main switch I5, when opened by the energizing of solenoid I9, will entirely cut out the auto-Y matic control of the leveling. Solenoid I9 is in parallel with some circuit that is energized in the machine for every varying unevenness of the ground over whichthe excavator is momentarily passing. When propelling ceases, switch I `closes automatically.

First suppose that, main switch I5 being closed, the pistons of all the jacks are in their mid/positions, and that the line from corner 2te corner 4 is level, while corner I is lower than its opposite corner 3. As a result, the left end of mercury switch unit DI-D3 will be tilted down, thereby allowing current to pass from switch I5 through wires 22 and 23, mercury switch DI, the solenoid of magnetic relay CI, Wire 24, to wire I1; thereby causing the iirst and second contacts of relay CI to close. After these contacts have closed, current will pass from wire 22, through wire 25, the left hand circuit of relay CI, and solenoid BI to wire II. It will also causecurrent to pass through the middley circuit of relay CI,

wirey 26, magnetic pump-starter II, to wire II.

The closing of the circuit through mercury switch DI has thus actuated CI, which in turn has caused pump motor M ,and pump P to opferring to the piping arrangement to these valves,

it will be seenfthat hydraulic iluid can readily pass from the discharge side of pump P through pipes 21 and 28 into valve BI, and discharge from valve BI by pipes 29 and 30 into the jack at corner i.

As the superstructure is a rigid, rectangular body, and may be considered as a plane, the sum of the heights of corners I and 3 above any given horizontal datum plane must always equal the sum of the heights of corners 2 and 4 above that plane; since each sum is twice the height of the center. Therefore, with one .exceptional case, to be noted later, the leveling device can raise low corner I only by pumping from the jack at corner 3. The pumping, Via pipes 3l, 32, valve B--3,

and pipes 33, 34 to the suction side of the pump,

and thence to jack I, as befredescrlbed, will continue until. corner l is level with corner 3.

If at the same time that I is lower than 3, corner 2 is lower than 4, the left end of the D2D4 switch unit will be tilted downward, and current will pass through the C2 solenoid; thereby ener- ,gizing the 'B-V2 solenoid which opens the corresponding B--Z valve to the pressure side of the pump. It is to be noted that leveling along one diagonal does not interfere with leveling on' the other, as, in this latter case, corner I must draw lfron corner 3 and corner 2 must draw from corner Y The one exception mentioned above is under the following circumstances: Suppose that all four feet of the excavator are not firmly bearing upon the ground. This might easily occur from any one of several causes, such as the crumbling away of the ground under that foot of the ex. cavator over which the machine is doing heavy digging. As before, let us suppose that corner I is low, while the 2-4 diagonal is level, and in addition, that the ground has fallen away under corner I or its opposite, corner 3. There will then be less pressure in both jacks I and 3, than there is in jacks 2 and .4, since the latter are now bearing the greater part of the weight. As the` lowness of corner I has set the pump working, and as the B-Valves are set to allow ilow from jacks 2, 3, and 4 to the suction side of the pump, iluid will first be drawn from those jacks in which there is the greater pressure, namely jacks 2 and 4, to fill jack I; until the pressure in jacks 2 and 4 becomes equal to that in jack 3. This will cause a suliicient lowering of the superstructure to take up the amount that the ground has fallen away The discussion above has, forsimplicity, been predicated upon the assumption that .corner I' was initially lower than corner 3, thus calling for the expansion of the jack at corner I and the contraction of the jack at corner 3. As the four vertical bands of Figure 2 plainly exhibit the symmetry of the circuits with respect to the four corners of the excavator, it is not considered necessary todiscuss the consequences of any other unlevel conditions.

Of course our device may occasionally be working upon a terrain where, having performed its greatest attempt towards leveling, the excavator still remains unlevel. This is not to be regarded as a defect of our invention, as obviouslyany leveling device, however eiiiciently devised, must of necessity have some limit` beyond which it cannot function further. y

Let us now consider thefequalizing device, socalled. It is a matter of common knowledge, derived from observation, that only rarely-and-accidentally will a rigid body, when resting on uneven ground, be supported at four points; and even when this occurs, quite rarely will each; of those points bear, a fair share of the load. Accordingly one of the objects'of our vir'vi'ventionis to provide means whereby, from time 'to; time, the load between two of the four corners 'is actually equalized. We thus temporarily convert our thereafter returning to a four point support, but with each of the four corners now bearing a substantial portion of the load; until a new departure from this desirable condition again calls this function of our invention into play. To this end we utilize the normal cyclic swinging of the upper works during digging and dumping, to make certain intermittent electric contacts, which will now be described.

Turning to the collector-ring assembly shown at the bottom of Figure 2, it will be seen that there are four equal segments of the collectorring, one of them being numbered I2. 'I'hese segments are securely mounted on the base, in such a way that collector shoe I3, which is mounted on the revolving upper works of the excavator, will successively contact these segments as the superstructure revolves. The optimum arrangement of shoe I3 is such that when, for example, the digging end of the excavator extends over that side of the base which lies between corners 2 and '3, the shoe will contact the segment I2 which controls the valve 35, Figure 1, by means of solenoid A4, which valve lies in the pipe connecting jacks I and 4. When this particular contact is made at a time when no leveling is taking place, current will pass from wire I8, through wire 36, then successively through the third contacts of relay CI, C2, C3, and C4, by wires 31,38 and 39, then by wire 40 to shoe I3, segment I2, wire 4I, A4, to supply wire I 'I. As all the A valves are normally closed, current passing through A4 solenoid will open valve 35. The transfer of hydraulic fluid from corner 4 to corner I', or vice versa, will cause the pressure to be equalized between these corners, thereby momentarily producing a three point support of the excavator by jack 2, jack 3, and the mid-point between jacks I and 4.

As the passage of current through shoe I3 in Figure 2 can occur only when the third contacts of all four of the C relays are closed, and as the tilting into action of any one of the D mercury switches is suilicient to open the third contact of the corresponding C relay, it is obvious that we have provided an interlock which will automatically and quite eiectually prevent om` device from attempting to equalize while leveling is going on.

Owing to the practical incompressibility of the fluid, the amount of fluid transferred in equalizing will be negligible, except in the case when the four corners are not all rmly resting on the ground. The preceding discussion has shown that the leveling feature of our invention can correct this condition, but only while the diagonal whose jacks have the lighter pressure is also sufliciently out of level to tilt the corresponding mercury switch into action. If the mercury switch is not sufiiciently tilted, the shoe in contacting a segment, will equalize between that pair of adjacent jacks that are furthest from the side over which the excavator is operating. If the equalizing disturbs the level of a diagonal, the mercury switch will immediately and automatically take charge of operations, to remedy this condition.

It is thus seen that the task of bringing the excavator into level, with rm contact to the ground, will automatically devolve upon one or the other, or both, of the two main features of our invention.

It would be feasible, but not advisable, to have the shoe I3 differently oriented With respect to the digging end of the excavator, or even to have only one valve 35, with its solenoid A4, hitched up to all of the segments. But the system of four valves, and four segments, with the shoe oriented so as to connect the two jacks opposite from the momentary position of the digging end, provides far more stability during digging.

But regardless which of the above alternative arrangements be used, there are certain limitations on the length and location of the segments. The length and location of the segments must be limited in such a manner that no segment will cause any A-valve to be actuated when the center of gravity of the machine lies outside of the triangle whose vertices are the mid-point between .thel two jacks which the valve connects and the other two jacks; for otherwise the machine would tend to tip.

This tipping tendency could be offset by having the valve, even when fully open, be sufllciently constricted, as compared with the rate of pumping, so that the pump could maintain the device level in spite of the above mentioned position of the center of gravity; but this would introduce an undesirable intermittent action of the leveling pump. It is far better to limit the scope of the segments, as above suggested.

'- The proper limitation of the scope of the segments is illustrated by the two diagrams which constitute Figures 3 and 4. Figure 3 shows a square which represents the main base of the excavator, supported at its four corners by the four jacks, I, 2, 3 and 4. Let us now consider the limitations on a single collector ring segment, such, for instance, as segment I2, which actuates the valve which equalizes jacks I and 4, thereby causing the base to be momentarily supported by the mid-point between those two jacks, and by jacks 2 and 3. The triangle, shown in the ligure, joins those three points of support. 'Ihe center of gravity of the machine lies along the median line of the revolving works, and shifts back and forth along that lin. Normally it lies slightly to the rear of the center, on that line. But during digging and/or when the clipper is loaded, it shifts considerably forward of the center. We shall assume that the shoe is located on the rear of the median line. The larger of the two circles represents the sweep of the extreme rear position of the center of gravity in various orientations of the upper works with respect to the main base. The shaded part of that circle represents the danger space: i. e., if the center of gravity were to lie within the shaded part, when the machine is supported at the three points predicated, the machine would tend to tip as above described. Accordingly the valve now under discussion must not be opened when the center of gravity is in that danger space.

To insure against this, the valve under discussion should be prevented from opening except when the median line of the upper works lies4 between the two positions shown by the two intersecting dotted lines of Figure 3.

The inner circle represents the circle f the collector segments. If the shoe I3 be on the median line of the upper works, to the rear of the pintle center, then the heavy arc I2 represents the allowable limits of the segment which controls the valve which connects jacks I and 4.

Similar considerations determine the location and length of the three other segments, which respectively control the three other valves.

If, however, we content ourselves with only the one valve which connects jacks I and 4, it would be possible to control it by segmentIZ and only `8,909,009 lone additional segment instead ofthe other three shown inFigure 2. The limitations on this second segment will nowfbe discussed. Inasm'uch over theside between corners fl and 4. Turning to Figure 4, the'larger circle of'that ilgure represents'tlie sweep of the extreme forward position of the centerof gravity.v

Following the same reasoning employed in .establishing the limits on segment I2, we similarly establish the limits on auxiliary segment I'2a to control the same valve as I2. f

Instead of using one shoe and a pluralityl of segments, the same result would be accomplished by using one segment and a plurality of shoes.

It is to be understood'that no change whatever will be effected in any given design of our inven tion, by locating the shoe or shoes permanently at an angle to the median line of the 'upper works, provided that the angular location of all the collector ring segments be permanently changed tocorrespond.

The foregoing is a complete discussion of one embodiment of our invention; namely, that form .in which the occurrence of any leveling completely prohibits all equalizing. The major part of that discussion applies equally well to the alternative embodiments now to ybe discussed. It

will therefore be sufiicient to point out only those features in which the other embodiments differ from that shown in Figure 2, and to explain their action.

In Figure 5, the letters A, B, C, D, have exactly the same signiiicances as has been described above for Figure 2, and therefore the A and B elements arev as shown in Figure l. Also the reference numbers commonv to Figure` and Fig' ure 2 refer to exactly similar. elements, serving the same purpose as described in connection with Figui-e 2.

It will be noticed that the normally open first and second contacts of the C-relays of Figure are exactly similar to the first and second contacts of Figure 2; the first actuating the B solenoid to open the B-valve, and the second starting the pump. There are now, however, two normally closed contacts to each C relay, which so interlock the A-solenoids that no A-valve may be open, if a corner adjacent to it .is being pumped up.

Thus, suppose, as before, that corner I is low enough to cause current to flow through the DI mercury switch. This will actuate CI solenoid, closing contacts I and 2, and opening contacts 3 and 4. Motor M will then start the pump, and valve BI will be set as shown in Figure 1, thereby allowing fluid to pass from pump P, through pipes 21 and 28, valve BI, and pipes 29 and 3l), t'o the jack at corner I.

As contact 3 of CI relay will open, the AII solenoid is not actuated, and in consequence the pumped, solenoidA4 is not actuated, and valve 35 will not then be opened.

It is easy to see from Figure 5 that pumping at corner I will not-'prevent the passage of current through solenoid A2 or solenoid A3, when '5 l only corner I is being pumped. Therefore, while pumpingat corner I will prevent equalizing along either of the lines I-2 or I.-4, it may. still take place along either of the lines 2-3 or 3-4,

when the shoe .I3 contacts the appropriate segl0 ment.

As before, the symmetry of the wiring-.diagram renders it unnecessaryto discuss any other unlevel conditions.

The two embodiments of our invention discussed above contemplate cutting out undesired equalizing during leveling. As an alternative, it might be considered advisable to cut out leveling during equalizing. This is accomplished by the interlock shown in Figure 6.

In that figure, the A, B, C, and D elements are exactly similar to, and have the same functions as, the like-named elements of Figures 2 and 5; the E elements, taken collectively, constitute the interlock. s

It will be noted that equalizing is possible at any time that shoe I3 contacts any one ofthe four segments. Thus, for instance, in the configuration shown, current will pass from Wire I8, through wire 44, shoe I3, segment I2, wire 45, and A4 solenoid, to wire I1. The A4 solenoid will open valve 35, Figure 1, allowing equalizing between jacks I and 4.

But current will also take the parallel path from wire 45 through E4 solenoid and wire 46 to wire I1, thereby opening E4 relay. In order that any leveling may occur, current must ow fore. Therefore, if any equalizing is going on,

one or the other of the E relays will be open, and the circuit to theD switches will be broken.

In the foregoing, we have described a system of leveling in which the mercury switch opens the jack at any low corner to the pressure `side of the pump, leaving freely connected'to the suction side the jacks at all corners that are not lower than vtheir opposites. In other words, we have invented a device which may be said to pump up the low corner, drawing uid from whichever of the other corners will supply it. In the case we have called mixed leveling and equalizing, the pump will draw from more thanone corner.

Our invention will work equally well if we pump down thehigh corner, leaving freely connected to the pressure side of the pump all jacks that arel not higher than their opposites. The few changes in the system as described abovethat would be l necessary are quite obvious, but We may mention that the four individual mercury switches must each be given a tilt opposite to that shown, and the B-valves, when energized, must be open to the suction side of the pump, and only the deenergized valve or valves must be open to the pressure side. It may be mentioned that, in this case, mixed leveling and equalizing will occur only when the diagonal that is not being leveled is the one that is insecurely footed.

Although we have described our invention with respect to four independent supporting units, the

term fsupporting unit is to be understood asA also comprising one end of a ground-engaging device, which device supports the base through a jack at each end of such device. p

And although we have described our invention as used with hydraulic jacks, it is obvious that it can be equally well applied to a system using any variety of power-actuated means for raising and lowering the corners.

Having now described and illustrated several forms of our invention, we wish it to be understood that we do not intend our claim of invention to be limited to the specic forms or arrangements of parts hereinbefore described, nor to any speciiic feature or combination of features claimed in any claim or claims.

We claim:

1. VIn combination: a base; a plurality of ground-engaging units; a plurality of uid pressure jacks, one connected to and supported by each ground-engaging unit, and connected to and supporting the base; a single pump to actuate these jacks; valves to expand and release the Jacks selectively; electric controls for these valves; two'level-responsive switch devices, each responsive to the departure from level of one of a pair of normally horizontal lines in the base, which lines are at substantially right angles to each other; means whereby said controls automatically effect leveling of the base; and means whereby said controls automatically eiect equalizing of the pressure on the supporting units.

2. In combination: a base; a plurality of ground-engaging units; a plurality of jacks, one connected to and supported by each groundengaging unit, and connected to and supporting the base; means to expand each jack; means to release each jack, so as to permit it to contract; electric controls for the expanding and releasing of the jacks; two level-responsive switch devices, each responsive to the departure from level of one of a pair of normally horizontal lines in the base, which lines are at substantially right angles to each other; means whereby said controls automatically effect leveling of the base; and means, whereby said controls automatically effect equalizing of the pressure on the supporting units.

3. In combination: a base; a plurality of ground-engaging units; a plurality of jacks, one connected to and supported by each groundengaging unit, and connected to and supporting the base; means to expand each jack; `means to release each jack, so as to permit it to contract; electric controls for the expanding and releasing oi the jacks; two level-responsive switch devices, each responsive to the departure from level of one of a pair of normally horizontal lines in the base, which lines are at substantially right angles to each other; means whereby said controls automatically effect leveling of the base; means whereby said controls automatically effect equalizing of the pressure on the supporting units; and means to prevent, during leveling, any equalizing between a certain one of the two jacks which are effecting leveling and either of the jacks adjacent to such certain jack.

4. In combination: a base; a plurality of ground-engaging units; a plurality of jacks, one connected to and supported by each groundengaging unit, and connected to and supporting the base; means to expand each jack; means to release each jack, so as to permit it to contract; electric controls for the expanding and releasing of the jacks; two level-responsive switch devices, each responsive to the departure from level of one of a pair of normally horizontal lines in the base, which lines are at substantially right angles to each other; means whereby said controls automatically effect leveling of the base; and means tol prevent the simultaneous expanding and to preventA the simultaneous releasing of any pair of diagonally opposite jacks.v

5. In combination: a base; a plurality of ground-engaging units, a plurality of jacks, one

connected to and supportedl by each ground-engaging unit, and connected to and supporting the base; means to expand eachjack; means to release each jack, so as to permit it to contract; electric controls for the expanding and releasing of the jacks; two level-responsive switch devices, each responsive to the departure from level of one of a pair of normally horizontal lines in the base, which lines are at substantially right angles to each other; means whereby said controls automatically effect leveling of the base; means whereby said controls automatically eiect equalizing of the pressure on the supporting units; a revolving turntable on the base; and means, actuable by the position of the turntable, whereby the equalizing control is rendered effective only in certain predetermined positions of the turntable.

6. In combination: a base; a plurality of ground-engaging units; a plurality of jacks, one connected to and supported by each ground-engaging unit, and connected to and supporting the base; means to expandeach jack; means to release each jack, so as to permit it to contract; electricxcontrols for the expanding and releasing of the jacks; two level-responsive switch devices, each responsive to the departure from level of one of a pair of normally horizontal lines in .the base, which lines are at substantially right angles to each other; means whereby said controls automatically effect leveling of the base; means whereby said controls automatically effect equalizing of the pressure on the supporting units; a revolving turntable on the base; and means, actuable by the position of the turntable,

whereby the equalizing control is rendered effective, as between any two adjacent jacks, only in certain predetermined positions of the turntable.

7. In combination: a base; a plurality of ground-engaging units; a plurality of jacks, one connected to and supported by each groundengaging unit, and connected to and supporting the base; means to expand each jack; means to release each jack, so as to permit it to contract; electric controls for the expanding and releasing of the jacks; two level-responsive switch devices, each responsive to the departure from level of one of a pair of normally horizontal lines in the base, which lines are at substantially right angles to each other; means whereby said controls automatically eiect leveling of the base; means whereby said controls automatically effect equalizing of the pressure on the supporting units; a revolving turntable on the base; and means, actuable by the position of the turntable, whereby the equalizing control is rendered effective, as between any two adjacent' jacks, only in certain predetermined positions of the turntable, said last named means consisting of electric segments carried by one of the base and turntable, and cooperating contact-shoes carried by the other.

8. In combination: a base; aplurality of ground-engaging units; a plurality of jacks, one connected to and supported by each groundengaging unit, and connected to and supporting release each jack, so as' to permit it to contract;

electric controls for the expanding and releasing of the jacks; two level-responsive switch devices, each responsive to the departure from level of one of a pair of normally horizontal lines in the base, which lines are at substantially right angles to each other; means whereby said controls automatically effect leveling of the base; means whereby said controls automatically effeet equalizlng of the pressure on the supporting units; and electric interlocks to prevent leveling and equalizing from taking place simultaneously.

9. In combination: a base; a plurality of ground-engaging units; a plurality of jacks, one connected to and supported by each ground, engaging unit, and connected to and supporting the base; means to expand each jack; means to release each jack, so as to permit it to contract; electric controls for the expanding and releasing ofthe jacks; two level-responsive switch devices, each responsive to the departure from level of one of a pair of riormally horizontal lines in the base, which lines are at substantially right angles to each other; means whereby said controls automatically effect leveling of the base; means whereby said controls automatically effect equalizing of the pressure on the supporting units; and electric interlocks to prevent leveling from taking place during equalzing.

10. In combination: a base; a plurality of ground-engaging units; a plurality of jacks, one connected to and supported by each groundengaging unit, and connected to and supporting the base; means to expand each jack; means to release each jack, so as to permit it to contract; electric controls for the expanding and releasing of the jacks; two! level-responsive switch devices, each responsive to the departure from level of one of a pair of normally horizontal lines in the base, which lines are at substantially right angles to each other; means whereby said controls automatically effect leveling of the base; means whereby said controls automatically effect equalizing of the pressure on the supporting units; and electric interlocks to prevent equalizing from taking place during leveling 11. In combination: a base; a plurality of ground-engaging units; a plurality of fluid-pressure jacks, one connected to andvsupported by each ground-engaging unit, and connected to and supporting the base; a single pump to actuate these Jacks; valves to expand or release the jacks selectively; electric controls for these valves; two level-responsive switch devices, each responsive to` the departure from level of one of a pair of normally horizontal diagonal lines in the base, which lines are at substantially right angles to each other; and means whereby said controls automatically e'ect mixed leveling and equalizing of the base, by transferring iiuid between one jack, to be leveled, and the otherthree jacks.

dered eiectlve; as between any two adjacent jacks. only in certain predetermined positions of the turntable, said last named means consisting of electric segments carried by one of the base and turntable, and cooperating contact-shoes 'carried by the other.

13. In combination: a base; a plurality of ground-engaging units; a plurality of fluid pressure jacks, one connected to and supported by each ground-engaging unit, and connected to and supporting the base; means to expand each jack; means to release each jack, so as to permit it to contract; electric controls for the expanding and releasing of the jacks; two level-responsive switch devices, each responsive to the departure from level of one of a pair of normally horizontal lines in the base, which lines are at substantially right angles to each other; means whereby said controls automatically effect leveling of the base; means, including valves to connect adjacent jacks, whereby said controls automatically effect equalizing of the pressure on the supporting units; and means to render inoperative, during leveling, and equalizing val'ves adjacent to a certain one of the two jacks which are eiecting leveling.

SAMUEL L. G. KNOX. :FRANCIS o. BLACKWELL, Jn.

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