US2847918A - Selective pressure control means for road rollers - Google Patents

Description

Aug. 19, 1958 J. F. HARRISON SELECTIVE PRESSURE CONTROL MEANS FOR ROAD ROLLERS Filed Dec. 18, 1952 4 Sheets-Sheet 1 INyENToR FIHQNI (Ju-M mi a@ I ATTORNEYS Aug. 19, 1958 J. F. HARRISON SELECTIVE PRESSURE CONTROL MEANS FOR ROAD ROLLERS 4 Sheets-Sheet 2 Filed Dec.

INVENTOR www Mam l ATTRNEYS Aug. 19,v 1958 l J. F. HARRISON 2,847,918

sELECTIvE PRESSURE CONTROL MEANS EOE ROAD RoLLERs Filed Deo). 18. 1952r 4 sheets-sheet :s

INVENTOR A. www BY Mig ATTORNEYS SRLECTIVE PRESSURE CONTROL MEANS FOR ROAD ROLLERS Aug.`19, 1958 J. F. HARRlspN 4 Sheets-Sheet 4 Filed Dec. 18|, 1952 du www BY a@ ATTORNEYS United States Patent O SELECTIVE PRESSURE CONTROL MEANS FOR ROAD ROLLERS John F. Harrison, Springfield, Ohio, assignor, by mesne assignments, to Koehring Company, Milwaukee, Wis., a corporation of Wisconsin Application December 18, 1952, Serial No. 326,735

4 Claims. (Cl. 941-50) cation Serial No. 290,183, filed May 27, 1952, tiled by Carl F. Greiner (now Patent 2,775,925, issued January 1, 1957), entitled Pressure Control Means for Road Rollers, which discloses means for controlling the pressure applied by the rolls of a three-axle road roller of the walking-beam type to the surface being rolled.

In present day road building practice, when compacting certain types of road building materials, care must be taken to see that the material is not overloaded on the rst pass of the roller. Hence, the pressure exerted on the material by the first roll of the road roller to pass thereover must not exceed the overload point for the material if best results are to be obtained. At the same time, it is desirable to approach the overload pressure as closely as possible without exceeding it, in order to compact the material to the maximum possible degree on the rst pass of the roller. The overload pressure of the various materials used in the building of roads, varies with the particular material being rolled and, hence, it is desirable to be able to vary the pressure applied'by the leading roll of the road roller'so as to cause it to apply a pressure which closely approaches but does not exceed this overload pressure for the material..

The conventional two-axle tandem road roller is not always able to meet the requirements imposed by the various types of road building materials since the load distribution on the rolls of this type of roller is fixed, usually in the ratio of 2: l, i. e., the pressure applied by the drive roll is twice the pressure applied by the guide roll. Also, when rolling materials which are not subject to overloading, such as soils, most ecient rolling can be accomplished by distributing the weight of the roller equally between the drive roll and the guide roll. It will therefore be seen'that it is desirable to be able to control the pressures applied by the several rolls of a road roller in various ways in order to best adapt the machine to the particular material being compacted, and to enable maximum densiiication of the material to be achieved by the fewest number of passes of the roller.

When the material described is operated on by a conventional 2axle tandem roller, a uniform high density is achieved, but humps caused by non-uniform thickness of the roadbed material and by unevenness of the base ment of material which is necessary to reduce the humps Y is diicult `to attain.

Any reduction of the humps is done by increasing the density of the semi-reduced humps, which results in uneven densities in the pavement.

It should be notedI at this point that there is a definite Patented Aug. 19, 1958 weight ratio between the weight (ground reaction) at the drive roll and the weight (ground reaction) at the guide roll, which ratio is preferred by highway authorities. Currently this ratio is approximately 2 to l, i. e., the reaction at the drive ro-ll representing two-thirds and the reaction at the guide roll representing one-third of the total weight of the machine.

The three-axle machine shown in Greiner Patent No. 2,015,891, dated October l, 1935, is customarily so built that, with all three rolls in contact with a plane surface, the roller approximates a two-axle tandem roller with an extra guide roll. That is, the ground reaction of each guide roll is one-half the ground reaction of the drive roll.

If, as the roller progresses, the end guide roll encounters a hump, the center guide roll is raised from the ground. The weight which was carried by the center roll is now shared by the end guide roll and the drive roll. The ground reaction of the end guide roll increases so that the hump receives a heavier than normal loading from Ithis roll. The ground reaction of the drive roll also increases so that the surface under this roll is subject to a heavier loading than any other part of the surface. This last condition is detrimental inasmuch as the surface under the drive roll is not abnormally above the desired plane surface.

As the roller progresses further, the center guide roll encounters the hump, raisingthe end guide roll from the ground. That portion of the weight which was normally `carried by the end guide roll now acts to increase the ground reaction under the center guide roll and to decrease the ground reaction under the drive roll. The ground roll reaction under the drive roll does not, however, decrease to the extent that there is an appreciable loss of traction. This condition is ideal in that only the hump is subject to an increased loading due to the so- -called transfer of weight. As the material in the hump is in a semi-fluid condition, the hump is easily reduced by this condition.

As the roller progresses still further, the drive roll operates on the hump, raising the center guide roll from the ground, and the weight which is normally carried by the center guide roll is now shared by the end guide roll and the drive roll. The ground reaction of the drive roll increases so that the hump receives a heavier loading under this roll. The ground reaction under the end guide roll also increases although this roll is not on the hump. This last condition', however, is stil-l not ideal.

U. S. Patent No. 2,132,059, issued October 4, 1938, to George E. Trembly for Road Rolling Machines, discloses a three-axle road roller in which it is possible to adjust the relative elevations of the axles so that the rolls of the machine may be made to follow any desired road contour, that is, either a flat surface, a concave surface, or a convex surface. lt is also possible, in the Trembly roller, to selectively elevate either the center roll or one of the end rolls off the ground to thereby cause dilferent pressures to be applied by the rolls to the surface being rolled. This expedient, however, enables but two optional pressure distributions on the rolls to be effected, neither of which may fully satisfy the requirements of the particular material being rolled.

In order to obviate this difliculty and provide for an unlimited number of pressure distributions on the rolls of a tandem roller having three or more axles, the application of Carl F. Greiner, Serial No. 290,183, filed vMay 27, 1952 (now Patent 2,775,925, issued January the initial pass of a roll can be made with the exact pressure required for best performance in the case of the particular material being rolled, instead of with a pressure which merely approximates the optimum pressure for that material. Also, in a roller constructed in the manner disclosed herein, the rolls of the machine will continuously follow the contour of the ground and will apply a constant, preselected pressure thereto regardless f any irregularities occurring in the ground.

With a roller constructed in accordance with said Greiner application Serial No. 290,183 (now Patent 2,775,925, issued January 1, 1957), it is possible to positively prevent an overload from being applied to the material being rolled. This may be accomplished by so selecting the pressure to be applied by the roll making the initial pass that it will be below the overload pressure for the material. Nor can the three-axle load transfer action of the road roller operate to cause the roll to apply a pressure greater than the overload pressure since the pressure control mechanism will permit the roll to yield before the overload pressure is reached, and thereby avoid application of an excessive pressure to the material being compacted.

Thus, the primary objects of the Greiner application Serial No. 290,183 (now Patent 2,775,925, issued January 1, 1957), are to provide a road roller having three or more rolls arranged in tandem, and to provide a pressure control device for enabling infinitely variable pressures to be applied by the rolls to the surface being rolled; also to provide a three-axle tandem road roller in which one of the guide rolls is mounted for vertical displacement relative to the frame.

The principal object of my present invention is to provide improved three-axle rollers, whether of pressure-controlled walking beam type, pressure-controlled sliding king pin type, or pressure-controlled tilting frame type, which have (a) the ability to operate as described in the above paragraphs; (b) the ability to operate with a continuous weight equalization between the two guide rolls with either or both guide rolls capable of vertical flotation; (c) the ability to operate with either guide roll raised clear of the ground, i. e., as a two-axle roller; (d) the ability to operate with both guide rolls floating and with the ground reaction pressure-controlled at any ratio between that ratio where the ground reaction ofthe end guide roll is zero, and the ratio where the ground lreaction of the center guide roll is Zero; and in addition (e) primarily the ability to so operate that, only that portion of the surface being rolled, which is above the desired smooth contour, whether it be a smooth flat plane or a smooth convex or concave surface, receives more than the normal pressure applied by the roller.

The invention includes certain novel features of design, and combinations of parts, the essential elements' 1 of ,which are set forth in the appended claims; and a preferred form of embodiment will hereinafter be described with reference to the drawings which accompany and form a part of this specification.

In the drawings:

Fig. 1 is a side elevation of a three-axle tandem road roller of the walking beam type incorporating one embodiment of my invention.

' Fig. 2 is a top plan view of the steering end of the road roller shown in Fig. 1.

Fig. 3 is a side elevation showing the steering end of a modified form of a three-axle tandem road roller of the walking beam type embodying my invention.

Fig. 4 is an enlarged view showing the uid circuit foractuating the walking beam.

Fig. 5 is' an enlarged view of the main valve in the circuit shown in Fig. 4.

Fig. 6 is' an enlarged view of the hydraulically actuated selective means shown in Fig. 4.

Figs. 7 and 8 are views showing different positions of the 4-Way valve shown in Fig. 4.

As shown in Figs. l, 2 and 3, the road roller is of the three-axle walking beam type such as shown in my copending application Serial No. 169,749, filed June 22, 1950 (now Patent 2,755,713, issued .Tuly 24, 1956), and is also an improvement upon the application filed by Carl F. Greiner Serial No. 290,183, filed May 27, 1952 (now Patent 2,775,925, issued January l, 1957), the road roller shown in Figs. 1, 2 and 3 comprising parallel side members 1 suitably placed apart and forming the sides of the frame of the roller, said side frames carrying journals for axle 2 of the drive roll 3, said drive roll being driven by a motor 4 carried by the frame, the particular drive means, however, not being shown as same is well known, and the drive roller being adapted to be rotated in both directions.'

The opposite ends of the frames 1 are upwardly arched as at la and extend forwardly as at 1b, the portion 1b having an axial opening 1c extending rearwardly from its outer end adapted to accommodate walking beam 5, said walking beam 5 being journaled intermediate its ends on axle 6 whose ends are journaled in the outer ends of the portions 1b, as shown in Fig. 2, whereby walking beam S may pivot on a horizontal axis within opening 1c.

At the outer end of walking beam 5 is mounted a trunnion 7 for the king post 8 of a yoke 9 which carries and supports the end guide roll 10, while at the inner end of walking beam 5 is a trunnion 11 receiving the king post 12 of a yoke 13 which supports and carries the intermediate guide roll 14. Suitable means are provided'for simultaneously steering the yokes 9 and 13 of guide rolls 10 and 14, the same forming no part of my present invention. But, as shown, the means comprises an arm 15 on king post 8 and an arm 16 on king post 12, both arms extending in the same lateral direction and being connected by a link 17 so that the king posts will swing in unison.

A steering cylinder 18 is carried by the walking beam, the same carrying a piston 19, the rod 20 of which is connected to an extension 16a of the arm 16, whereby reciprocation of the piston 19 will cause the king posts 8 and 12 to swing in unison and in the same direction. Hydraulic means (not shown) is provided for actuating piston 19 in cylinder 18.

The inner end of Walking beam 5 has an ear 21 t0 which is pivotally connected piston rod 22 carrying a piston 23 housed in a cylinder 24 closed at both ends, said cylinder having pivots 24a which are journaled in brackets 25, Fig. 2, carried by the road roller frame, whereby as the walking beam 5 is raised or lowered the cylinder 24 may pivot in the brackets 25 to prevent binding. The opposite ends of the cylinder 24 are connected by pipe lines hereinafter described, whereby lluid under pressure can be introduced into either end of the cylinder 24 to cause the walking beam 5 to pivot. These pipe lines are connected in a uid circuit including a uid tank 26 (Figs. 1, 3 and 4) and a fluid pump 27 driven by a chain, belt, or the like 23 directly from the shaft of motor 4. The bottom of tank 26 is connected by a pipe line 29 to the' inlet of pump 27. The outlet of pump 27 is connected to a T-iitting or the like 30, Fig. 4, one branch of which leads to the inlet of a valve housed in casing 31., a prcssure gauge 32 being interposed between the T-itting 30 and the valve casing 31. The outlet of the valve casing is connected to a second T-iitting 33 or the like, one branch of which leads directly back to the tank 26. The other branch of T-tting 30 is connected by pipe 34 to one port of a 4way pilot valve 35, while the opposite port of valve 35 is connected by pipe 36 leading to the other branch of T-litting 33.

Between the pipe lines 34 and 36 is a lay-pass 37, Fig. 4, containing a relief valve 38. The third port of pilot valve 35 isyconnected, by pipe line 39 leading directly into the lower end of cylinder 24, while the diametrically opposite port is connected by pipe line 40 leading directly into the upper end of cylinder 24.

Between the pipe lines 39 and 40 adjacent to and substantially parallel with cylinder 24 is a by-pass 41 containing a valve 42 of the spring opening type adjacent cylinder 24, which valve in the position shown in Fig. 4 is in the open position, the same being shown in the closedposition in Fig. 6.

When the valve 42 is open, the pressures of the fluid at opposite ends of the cylinder 24 are equalized, the fluid owing through the by-.pass 41 freely from one end of the cylinder to the other, and when the valve 42 is closed, transfer of lluid from one end of the cylinder to the other is prevented.

In Fig. 4 the valve parts are shown in such position as to preventlluid under pressure from entering the pipe lines 39 or 40, the fluid pumped by pump 27 freely circulating from the pump through the pilot valve 35 to the tank 26 and back to the inlet of the pump.

Fig'. 'Sis a drawing of the pressure control valve 31, while Fig. 4 is a drawing of the hydraulic control system. Oil is supplied to inlet port 31a (Fig. 5) of control valve 31, by constant displacement pump 27, while the fluid from control valve 31 is discharged from port 31bat zero pressure, the same being returned to the uid tank 26.

Within valve 31 is a bore 31C in which is housed a piston 31a', the upper end of which piston 31d enters an annular guide 31e housed in an enlargement of bore 31C. Above the annular guide 31e is a bore 31)c connected by a duct 31g to a duct 31h disposed lbelow the bore 31e, the duct 31g communicating with outlet port 31b. The bore 31e communicates with outlet port 31b by a duct 311, the upper end of which forms a valve seat 31j for a valve 31k formed on the lower end of -piston 31d. Opposite inlet port 31a is a port 31l and above port 311 is a duct 31m communicating with the bore 31c below the annular washer 31e, and also communicating with the bore 311C, the duct 31m being normally closed by a valve 3111 disposed across bore 31f, said valve being normally depressed by a spring 31p, the upper end of which engages a screw 31q tapped into a bore therefor in the valve 31.

Contacting the'upper end of piston 31d is a spring 31r Whose upper end engages a screw 31s tapped into a suitable bore in the valve casing 31. The bores 31l and 31m are connected by a metering orifice 311 for the purpose hereinafter described.

As shown in Fig. 5, the two sides of piston 31d which are of equal area, are normally subject to system pressure on both sides, communicated through metering orifice 31r and chamber 31m. The piston 31d is, therefore, in hydraulic balance and held on its seat 31j by pressure of the light spring 31r. The system pressure also communicates through chamber 31m to the underside of pilot valve 3111, which is held on its seat by pressure-control spring 31p and adjusting screw 31g.

If the system pressure acting on pilot valve 3111 exceeds the pressure setting established by spring 31p and by adjusting screw 31g, the pilot valve 3111 is lifted from its seat and a ow of fluid occurs past pilot valve 3111, which oil returns to tank 26 through outlet port 3111. At the same time, ow of oil returns through the metering orifice 31r, inducing a pressure difference across the orifice, the pressure in duct 31m, however, tending to remain at the original or preselected system pressure level.

If the aforementioned system pressure at inlet 31a' resistance to flow from pressure port 31a to take return channel 31h will be compatible to the force of spring 31r plus that of spring 31p. Thus, such a valve provides a constant pressure at inlet port 31a for various rates of ow.

Referring to Fig. 4, oil is supplied from tank 26 through suction line 29 by constant-displacement pump 27. From pump 27 oil passes through T-fitting 30 to pressure-regulating valve 31 which controls the pressure in said line, as previously described. Oil which is by-passed by valve 31 returns to the oil tank 26 at zero pressure through T-litting 33.4 The pressure in T-tting 30 can'be selected by the operator by hand wheel 43 (Fig. 5), gauge 32 showing the pressure in said fitting 30.

Oil is supplied to the 4-way pilot valve 35 through line 34, and oil is discharged at zero pressure' from pilot valve 35 through line 36 leading back to tank 26, when the parts of valve 35 are in the position shown in Fig. 4. Line 37 -contains relief valve 38 which protects the entire system from excessive pressure.

, Oil is supplied to opposite ends of cylinder 24 .by means of lines 39 and 40 which are interconnected by line 41 containing valve 42.

With the 4-way valve 35 set as shown in Fig. 4, oil supplied by pump 27 passes to tank 26 under zero pressure. If, at the same time, valve 42 is closed, oil cannot enter or leave either the top or Ibottom of cylinder 24, and piston 22-23 will be held rigidly in its position. If, on the other hand,V valve 42 is open, piston 23 can float from end to end in cylinder 24, forcing oil to flow back l and forth through line 41.

If 4way pilot valve 35 is rotated into the position shown in Fig. 7 while valve 42 is closed, the lower end of cylinder 24 is subject to 4the pressure as regulated by pressure-control valve 31, via lines 34 and 39; while the upper end of cylinder 24 is subject to zero pressure of tank 26 via lines 36 and 40. Piston 23 and rod 22 can oat up and down in cylinder 24 while always exerting a constant force in the upward direction. However, if the piston moves down, it will be noted that oil ows from the lower end of the cylinder via lines 39 and 34 through T-tting 30 to and through pressure regulating valve 31.

If 4-way pilot valve 35 is set in the position indicated in Fig.; 8 while valve 42 is closed, the same situation occurs as described in the previous paragraph except that the upper end of the cylinder 24 is subject to the regulated pressure and the lower end to zero pressure.

The above described construction is substantially the same as that disclosed in my copending applica-tion Serial No. 169,749, filed June 22, 1950, and the copending application of Carl F. Greiner Serial No. 290,183, filed May 27, 1952.

In accordance with my present invention in addition to the elements above described, I provide as shown in Figs. l and 2 a screw shaft 50 threaded in a nut 51 vertically mounted in the frames 1 1 of the road roller, said screw having a hand wheel 52 on its upper end, whereby when the hand wheel 52 is rotated the screw shaft 50 will be raised orlowcred with respect to the frames 1 1. The lower end of screw shaft 50 is adapted to engage an abutment pad 53 on the inner end of walking beam S when walking beam is rotated in an anti-clockwise direction.

By the above construction lthe walking beam 5 is adapted to rotate in a clockwise direction without interference lof the screw shaft 50 and pad 53, but rotation in a counter-clockwise direction is limited by the position at which the lower end of screw shaft 50 contacts abutment pad 53. By rotating hand wheel 52 the operator may adjust the position of the point of contact between screw shaft 50 and pad 53. Thus the limited position of walking beam 5 may be set to suit operation on a plane surface or operation on either convex or concave cylindrical surfaces. By manually setting the screw shaft 50 the amount of rise of the centerguide roll 14 may be so controlled that only that portion of the surface being rolled which is above the desired smooth contour, whether it be a smooth at plane or a smooth concave or convex surface, receives more than the normal pressure applied by the center roll 14.

In Figs. 3, 4 and 6 a modification of the above described trip is shown, the same being hydraulically operated. In this modification the piston 22 of cylinder 24 carries at its upper end an arm 60, and at its lower end an arm 61, which arms are disposed parallel and are connected at their outer ends by a vertically disposed bar 62 adjacent the valve 42, said arms carrying a series of indicia or gradations 63 as shown. The arms 60 and 61 are prevented from pivoting on pivot rod 22 by means of a rod 64 having its endssecured to the arms 60 and 61, said rod 64 slidably passing through bearings 65 and 66 extending from the ends of the cylinder 24. By the above construction as the piston 22 is raised or lowered the indicia bar 62 will be correspondingly raised and lowered adjacent the handle 42a of valve 4,2, as shown in Figs. 4 and 6.

Slidably mounted upon theindicia bar 62 is an adjustable bar 67 having lateral extensions 67a and 67b slidably receiving the bar 62, the main portion of the adjustable bar 67 being disposed parallel withv the bar 62 and in alignment with the handle 42a of valve 42. The extension 67a is provided with a threaded bore receiving the lower threaded end 68a of an adjusting screw 68 whose upper end is rotatably journaled in a bearing 69 mounted on the arm 60, the upper end of the adjusting screw 68 carrying a hand wheel 71) whereby when the shaft 68 is rotated by hand wheel 70 the adjustable bar 67 will be raised or lowered with respect to the gradations 63 of bar 62.

As shown in Fig. 4 the handle 42a of valve 42 of spring opening type is positioned in open position, while in Fig. 6 the handle 42a is positioned in .closed position. By the above construction the adjustable bar 67 would normally have its lower end disposed below the handle 42a of the open valve 42, but when the piston rod 22 is raised as shown in Fig. 6, the upper end of the adjustable bar 67 will have moved upwardly with respect to the handle 42a of valve 42 suiciently to swing thev handle 42a into vertical position shown in Fig. 6, thereby closing the valve 42 according to the adjustment of the adjustable bar 67 elected by rotation of the handle wheell.

By the above construction the road roller may be set to roll a tangent plane, during which action the two guide rolls have equal ground reactions. The road roller when so adjusted is essentially a two-axle roller having an attached extra guide roll.

lf as the roller progresses the end guide roll 10 encounters a hump the two guide rolls with the parts set as indicated in Fig. 4 merely oat, the guide rolls 10 and 14 merely adjusting themselves to the ground contour and maintaining the same ground reactions. The road roller thus operates merely as a two-axle tandem roller with an extra guide roll.

As the roll progresses further, the center guide roll 14 encounters the hump, the two guide rolls 10 and 14 again merely oat adjusting themselves to the ground contour but with different ground reactions. The ground reactions are automatically changed so that the reaction` of the end guide roll approacheszero in value, while the reaction of the center guide roll is correspondingly in creased. At this time the ground reaction of the drive roll 3 is somewhat decreased but not to the extent that there is a loss of traction. The above rolling condition is ideal in that only the hump is subjected to an increase in loading, the exact ratio of ground reaction in the above condition being at some value which has been preselected by the operator. By manually setting the screw shaft 68 the amount of rise of the center guide roll 14 may be so controlled that only that portion of the surface being rolled which is above the desired smooth contour, whether it be a smooth flat plane or a smooth concave or convex surface, receives more than the normal pressure applied by the center roll 14.

As the roll progressesfurther, the center guide roll 14 passes off the hump and the guide rolls 10 and 14 are again disposed in a tangent plane and therefore the two guide roll reactions again become equal.

After further progress the drive roll 3 engages the hump, the two guide rolls 10 and 14 float, maintaining equal ground reactions and the roller thus operates in the same manner as when the end guide roll 10 is disposed on the hump.

When the roller moves in the opposite direction the above sequence of events occurs in reverse order. By a series of back and forth passes the machine reduces the working surface to a smooth at plane by heavily loading all surface projections while the material is in a plastic condition and capable of adjustment. By means of the cylinder 24 the operator may cause the above sequence of events to take place relative to a smooth concave or con vex surface of uniform curvature.

Summarizing, the arrangement of the mechanical or hydraulically actuated trips provides the following advantages:

(a) It achieves a uniform high density on the material on which it operates;

(b) It operates with the same weight distribution as that of a two-axle tandem roller;

(c) It reduces humps of material by operating on them with an above-normal loading while the material is in a semi-fluid or plastic state;

(d) It does not apply an excessive load to any part' of the surface which is not raised above the desired surface;

(e) The machine may be used to produce a smooth plane surface or a smooth concave or convex surface of constant curvature.

Fig. 4 shows the hydraulic control system of my novel machine, this system being similar to the walking beam three-axle roller shown in Harrison application Serial No. 169,749, led June 22, 1950 (now Patent 2,755,713', issued July 24, 1956), and in the Greiner application Serial` No. 290,183 tiled May 27, 1952 (now Patent 2,775,925, issued January 1, 1957), excepty for` a modi. cation of the hydraulic actuating cylinder. Spring-opening valve 42 is normally in the open position'as aforesaid. Thus no pressure difference can exist between the top and bottom sides of piston 23 in cylinder 24,' and therefore the piston 22 with attached piston 23 is free to oat up and down. Since piston 22 is attached to the. Walking beam 5 'as shown in Figs. l and 3, the piston rod will be moved upv and down as the walking beam 5 oscillates.

Attached to and moving with piston rod 22 in Figs. 3, 4 and 6 is the cam carrier bar 62. By manual adjustment of hand wheel 70 which rotates adjusting screw68, the position of `cam 67 along carrier bar 62 may be selected.

As the center guide roll 14 rises on a hump, piston rod 22 with its attached parts will move upwardly and: cam 67 will strike and turn the valve handle 42a, thereby closing valve 42, and therefore la pressure difference between the opposite sides of piston 23 can now exist as determined by the setting of regulating valve 31v andas determined by the position of four-way pilot valve 35..

The position of cam 67 on carrier bar 62 as indicated;

by indicia 63, and as set at the discretion of the operator by vmeans of hand wheel 70, determines the point at which valve 42 will be closed, which in turn determines the character of the rolling operation to produce a plane surface, or a concave or convex curved surface. Obviously valve 42 may be opened and closed manually so 9 that the machine may operate as a pressure controlled three-axle roller.

My invention is not limited to use on the walking beam type of roller, since it may readily be adapted to rollers of the sliding king pin and tilting frame types of three-axle rollers. My invention, moreover, is not limited to the exact forms shown since the operation of valve 4Z may be accomplished by means of a limit-switch arrangement, or by other means. From the foregoing it is apparent that a roller equipped and constructed as above described may operate in the same manner as a conventional three-axle tandem roller or a pressure-controlled three-axle tandem roller. Moreover, my invention is not limited to a three-axle roller since it may apply equally well to multiple axle machines having more than three axles, the same having means whereby only that portion of the surface being rolled which is above the desired smooth contour, whether it be a smooth at plane or a smooth concave or convex surface, receives more than the normal pressure applied by the center guide roll 14.

I claim:

l. A self-propelled road roller comprising a frame, a drive roll and a plurality of guide rolls arranged in tandem on said frame; means for supporting at least one of said guide rolls for vertical displacement relative to the other rolls; fluid pressure means connected between said frame and said supporting means for applying a downward pressure on said one guide roll in opposition to the reaction vforce exerted thereon by the source being rolled; means for adjusting said pressure applying means to control the downward pressure exerted thereby on said one guide roll whereby the proportion of the total Weight of the roller carried by said one guide roll may be selected as desired and maintained constant during rolling operations; and means for positively limiting the upward movement of the said -one guide roll; said fluid pressure means including a fluid cylinder on the frame; a piston in said cylinder; a piston rod connecting said piston and the one said guide roll support; a uid circuit for supplying fluid under pressure to either end of said cylinder; a by-pass connecting both ends of said cylinder; a normally open valve in said by-pass having a handle; a bar carried by said piston rod; an adjustable member slida- 10 bly mounted on said bar and adapted when raised to engage the handle and lclose said valve; and manually operable means on the bar for adjusting said member thereon.

2. A self-propelled roller comprising a frame; a drive roll mounted on one end of said frame; a beam mounted on the other end of said frame to rock about a horizontal axis; a pair of guide rolls in tandem relation mounted in said beam to swivel about vertical axes located fore and aft of the horizontal axis about which said beam rocks; fluid pressure means for applying a constant torque to one end of said beam, means for adjusting the torque exerted by said pressure means to any desired value whereby the proportion of the total weight of the roller carried by each of said guide rolls may be selected as desired and maintained constant during rolling operations; and means for selectively and positively limiting the upward movement of the rear end of beam when the middle roller encounters a raised portion in the roadway.

3. In -a self-propelled road roller as set forth in claim 2, said limiting means comprising a manually operated screw shaft vertically disposed in the frame adjacent one end of the beam; and an abutment pad carried by the beam adapted to be engaged by the lower end of the screw shaft when the beam is rocked in one direction.

4. In a self-propelled road roller as set forth in claim 2, said uid pressure means including a Huid cylinder; a piston in said cylinder; a piston rod connecting said piston and one end of said beam; a uid circuit for supplying fluid under pressure to either end of said cylinder; a bypass connecting both ends of said cylinder; a normally open valve in said by-pass having a handle; a bar carried by said piston rod; an adjustable member slidably mounted on said bar and adapted when raised to engage the 11andle and close said valve; and manually `operable means on the bar for adjusting said member thereon.

References Cited in the le of this patent UNTTED STATES PATENTS 2,089,591 Aitken Aug. 10, 1937 2,127,485 Owens Aug. 16, 1938 2,132,059 Trembly Oct. 4, 1938

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