What is claimed is
1. A steerable vibrating roller, having a center line, particularly for rolling ground surfaces or the like, comprising a frame; at least a front and a rear ground-engaging roll having parallel axes and being rotatably attached to said frame; a spaced-apart pair of out-of-balance masses rotatably mounted on said frame; means to rotate said masses attached to said masses; and means to vary the phase relationship between said rotating masses located on said frame, said masses being so positioned on said frame that as the phase relationship between said masses changes, a resulting force is generated by said masses which acts to turn said frame about a vertical axis to thereby steer said roller.
2. A roller as defined in claim 1, wherein the plane of rotation of said out-of-balance masses is parallel to said axes of said rolls and said out-of-balance masses used for generating the steering forces are also used for producing the entire vibrating compacting forces for the roller.
3. A roller as defined in claim 2, wherein a front and a rear pair of out-of-balance masses are employed, one pair being adjacent to the front roll and the other pair adjacent to the rear roll, one mass of each pair being located on the left of the fore/aft center line of the roller and the other mass of said pair being on the right of said center line.
4. A roller as defined in claim 3, further comprising means for simultaneously advancing at the front, the mass on one side of the roller relative to the other mass of the front pair and retarding at the rear, the mass on the same side of the roller relative to the other mass of the rear pair, to give rise to oppositely directed displacement of said vibratory forces generated by said front and rear pairs which, together with the cyclicly varying pressures exerted by said front and rear rolls on the surfaces contacted thereby, generates an effective turning moment on said frame which acts about a point between the axes of said front and rear rolls.
5. A roller as defined in claim 4, further comprising a prime mover, a drive transmission connected to said prime mover and to one of each pair of said out-of-balance masses including shift means permitting a change in the phase relationship between said out-of-balance masses of each of said pairs to be obtained without stopping the rotation of said out-of-balance masses.
This invention relates to a vibratable roller of the kind comprising at least two ground-engaging rolls rotatably supported in a frame so that the axes of the rolls are parallel, the vibration of the roller being at least in part effected by a pair of masses rotating so that the centre mass of each mass follows a closed path during rotation, the phase relationship between the masses (hereinafter referred to as "out-of-balance masses") as they rotate being such that the combined effect of their rotation gives rise to resultant forces which periodically act on at least one roll to generate cyclical varying pressures on the surface or surfaces contacted by the roll or rolls. Throughout this specification such a roller will be referred to as a "vibratable roller of the kind specified."
Vibratable rollers of the kind specified have great utility since their compacting effect can be several times that of a roller of the same dead weight but which is not vibrating. The roller may be a tandem roller, (which may be "ride-on" or pedestrian operated) using two spaced-apart pairs of masses to give rise to pressure variations on the front roll which are 180° out of phase with the pressure variations generated by the rear roll. The planes of rotation of the out-of-balance masses may be normal to the axes of the rollers or parallel to the axes of the rollers. In a typical case the pressure variations associated with each roll occur many hundreds of times a minute. One vibratable roller of the kind specified is steered by a pedestrian operator commonly by providing the roller with a steering arm which is long enough to afford the operator sufficient purchase on the frame to haul the frame round when it is necessary to turn the roller. With all but the lightest rollers this arrangement places severe demands on the strength of the operator. Further, the considerable length of the steering arm makes it impossible to manoeuvre the roller in restricted spaces. There is a need therefore for an improved method of steering a vibratable roller of the kind specified.
According to the present invention a vibratable roller of the kind specified comprises a frame, two or more ground-engaging rolls rotatably attached to the frame, the axes of the rolls being parallel, a spaced-apart pair of out-of-balance masses rotatably mounted on the frame, means to rotate the out-of-balance masses and means to vary the phase relationship between the rotating out-of-balance masses, the positioning of the out-of-balance masses on the frame being such that as the phase relationship between them is changed the resultant vibratory force generated by the out-of-balance masses changes its direction and acts to turn the frame about a vertical axis.
Suitably the plane of rotation of the out-of-balance masses is parallel to the axes of the rolls and conveniently the out-of-balance masses used for generating the steering forces are also used for producing the entire vibrating compacting forces for the roller. It is not ruled out, however, that a proportion of the vibrating compacting forces could be derived from out-of-balance masses, whose mutual phase relationship is fixed, and which therefore, do not contribute to the steering forces described. These latter masses may also rotate in planes parallel to the axes of the rolls, or alternatively in planes normal to the axes of the rolls.
In this specification it is the phase relationships between two contra-rotating out-of-balance masses which together define a pair which is of concern. It should be noted that a reference to the masses of a pair being "in phase" means that the masses have the same angular speed, and relative to the centre of mass and the rotating axes of the masses, they are both to-dead-centre (TDC) at the same time. A reference to "advancing" the phase relationship of one specified mass of a pair relative to the other mass of the pair should be taken to mean moving said one mass of the pair in the direction of its rotation relative to the other mass of the pair away from the "in phase" condition so that said one mass of the pair has passed its TDC position before the other mass of the pair has reached its TDC position and "retarding" the phase relationship should be taken to mean moving one mass of the pair in the direction opposite to its direction of rotation relative to the other away from the "in phase" condition so that said one mass of the pair has not yet reached its TDC position when the other mass of the pair is passing its TDC position.
Conveniently two pairs of out-of-balance masses are employed one pair being adjacent to the front roll and the other pair adjacent to the rear roll. One mass of each pair is located on the left of the fore/aft centre line of the roller and the other mass of that pair is on the right of the centre line. Advancing the left hand mass of the front pair relative to the right hand mass of the front pair will give rise to a turning moment in one direction about the rear roll. Retarding the left hand mass of the front pair relative to the right hand mass of the front pair again produces a turning moment about the rear roll but this time the turning moment acts in the opposite direction. Turning moments about the front roll in one direction or the other can be produced by advancing or retarding the left hand mass of the rear pair relative to the right hand mass of that pair. Enhanced steering effects can be obtained by simultaneously advancing at the front, the mass on one side of the roller relative to the other mass of the front pair and retarding at the rear, the mass on the same side of the roller relative to the other mass of the rear pair, since this gives rise to oppositely directed displacements of the vibratory forces generated by the front and rear pairs which, together with the cyclicly varying pressures exerted by the front and rear rolls on the surfaces contracted thereby, gives rise to an effective turning moment on the frame which acts about a point between the axes of the front and rear rolls.
The pair of out-of-balance masses (or both pairs of out-of-balance masses) may be driven from the same prime mover, the drive transmission to one of the pair of out-of-balance masses (or one of each pair of out-of-balance masses) including shift means permitting a change in the phase relationship between the out-of-balance masses of the pair (or the out-of-balance masses of each pair) to be obtained without stopping the rotation of the out-of-balance masses.
Alternatively the out-of-balance masses may be connected to a prime mover via a drive shaft which permits angular displacement to occur between an out-of-balance mass and that part of the drive shaft connected to the prime mover. An arrangement for differentially braking the out-of-balance masses may be used to control the phase relationships and thus effect steering.
Embodiments of vibratable rollers in accordance with the invention will now be described, by way of example with reference to the accompanying drawings, in which:-
FIG. 1 is a schematic view of the roller,
FIG. 2 is an analysis of the instantaneous and resultant component forces generated at the front and rear ends of the roller of FIG. 1 during its operation,
FIGS. 3 to 8 are schematic illustrations of different forms of steering control which can be used in a roller in accordance with the invention, and
FIG. 9 is a schematic representation of a vibratable roller with a modified steering control.
Referring to FIG. 1, the tandem roller illustrated comprises a front roll 1, a rear roll 2 journalled in a frame (not shown) which includes a steering arm 3. The rolls are powered by a motor and transmission arrangement (not shown) so that the roller can be moved backwards and forwards under the control of an operator holding the steering arm 3.
During operation of the roller, the pressure which each roll exerts on the ground is made to vary by means of two pairs of out-of-balance masses 5a and 5b and 6a and 6b. The masses 5a and 6a are attached at opposite ends of a first drivable shaft 7a and the masses 5b and 6b are attached at opposite ends of two aligned half shafts 7b and 7b'. The shafts 7a, 7b and 7b' are driven by power means not shown, (normally the same means as is employed to drive the rolls 1 and 2), the rotation of the shafts being such that the masses move in the directions shown by the arrows A in FIG. 1. Since the masses 5a and 5b are rotating in opposite directions, and are "in phase" (as hereinbefore defined) they combine to generate a resultant vibrating force acting at the front of the roller which is directed vertically, the magnitude of the force varying periodically so that after being a maximum in the downward direction it becomes zero and then becomes a maximum in the upward direction. This means that the effective force exerted by the front roll 1 on the ground varies periodically (typically at a rate between 1,500 and 5,000 times a minute). The masses 6a and 6b are performing a similar operation at the other end of the frame, but are 180° out of phase with the masses 5a and 5b respectively so that when the pressure exerted on the ground by the front roll 1 is a maximum, the pressure exerted by the rear roll 2 is a minimum due to an upwardly direction force resulting from the masses 6a and 6b. These pressure variations greatly enhance the compacting abilities of the roller.
Pedestrian steering of a tandem roller, such as is shown in FIG. 1, is normally difficult but it has now been found that it can be greatly eased by the simple expedient of arranging for the phase relationship between the masses of the pair at one end of the roller to be advanced by a small amount and for the phase relationship between the masses of the pair at the other end of the roller to be retarded by a small amount. Thus, if for example, instead of the two front masses 5a and 5b being exactly in phase, 5b is retarded with respect to 5a by a small angle α and at the other end of the roller mass 6b is relative to mass 6a, advanced by the angle α, vibratory components at each end of the machine (shown by the arrows B) instead of both being directed in the vertical direction, are both turned through an angle α/2, one in a clockwise direction and the other in an anticlockwise direction (i.e., into the condition shown in dotted lines in FIG. 1.) The magnitude of the steering forces generated bears a relationship to the magnitude of the angle α. Typically values of α up to approximately 30° have been found to be adequate. The effect of this alteration in the direction of oscillation of the resultant forces introduces an effective turning moment on the frame of the roller which has the effect of causing it to "jig" round (to the right or left, depending on whether it is the front or rear pair of masses which experience a phase advance) roughly about the centre of mass of the roller. This tendency to turn means that steering is much easier and there is no longer any need for the operator to be physically strong or for the steering arm 3 to be very long.
Preferably one motor is used for all three shafts with means provided in the drive transmission to the shafts 7b and 7b' to enable the phase relationships between these shafts and the associated shaft 7a to be adjusted during rotation so that a range of phase relationships from -α through 0 to +α can be obtained.
A wide range of different mechanisms can be employed to vary the phase relationships between the two half shafts 7b and 7b' and the shaft 7a. Some possible arrangements (and it must be stressed these are representative of many other suitable arrangements) are shown in FIGS. 3 to 8.
FIG. 3 shows an arrangement for hydraulically adjusting the phase relationship between the shaft 7a and the two half shafts 7b and 7b'. A main drive belt 100 comes from the engine of the roller (not shown) to drive the shaft 7a and a toothed belt 101 transmits drive to a stub shaft 102 fast with a wide pinion 103. A narrower pinion 104, in mesh with the pinion 103, is fast on a spindle 105 whose outer ends are secured to cup members 106 and 107. The cup members are each received in a cylindrical recess 108 in a housing 109 supporting the integers 102 to 107. A sealing ring 110 forms an oil-tight seal with each cup member 106 and 107 and thus defines volumes 111 (only one of which is shown in FIG. 3), to which hydraulic fluid can be fed. It will be appreciated that the supply of fluid under pressure to one volume 111, while leaving the other open to exhaust, will move the pinion 104, spindle 105 and cup members 106 and 107 in the direction of one of the arrows E to increase the capacity of the pressurised volume 111.
Each cup member 106, 107 is connected to the adjacent half shafts 7b, 7b' by means of pegs 112 engaging in helical grooves 113 formed in the inner ends of the half shafts. This arrangement ensures that axial movement of the spindle 105 in either direction will have the effect of advancing one mass 5b (or 6b) relative to its associated mass 5a (or 6a) and retarding the other mass 6b (or 5b) relative to mass 6a (or 5a), the phase displacements occurring as the pegs 112 move along the helical grooves 113 on each half shaft.
Any movement of the spindle 105 in the directions of the arrows E is resisted by coil springs 114 (only one of which is shown) located one in each cup member 106 and 107.
Referring to the arrangement of FIG. 4, the drive to the half shafts 7b and 7b' is provided via left- and right-hand helical gears 8b and 8b' which are in mesh with comparably sensed helical gears 10 and 11, respectively, on a sub-shaft 12 which gears are movable in the directions of the arrows C. The sub-shaft 12 is driven in exact synchronism with the shaft 7a and in a central position of mesh between the gears 8b, 10 and 8b', 11, respectively, the two half-shafts 7b and 7b' are also exactly in phase with the shaft 7a. However, moving the gears 10 and 11 in the axial direction of the shaft 12 away from these central positions, has the effect of advancing one half-shaft relative to the shaft 7a and retarding the other half-shaft relative to the shaft 7a to generate the aforedescribed steering forces. Moving the gears 10 and 11 to the other sides of the central positions will generate steering forces in the other direction. Thus with an arrangement as shown in FIG. 4, the roller steering control will be any convenient mechanism which can move the gears 10 and 11 in the axial direction of the sub-shaft 12 on either side of their central positions of mesh with the gears 8b, 8b'.
In the arrangement shown in FIG. 5, the two half-shafts 7b and 7b' are driven via a toothed belt 13 acting on a central drive drum 14. Each half-shaft also has a drive drum (15 and 15' in the drawing) and these are each individually linked to the central drum 14 via a series of linkages 17 and 18 (only one of each of which is shown in the drawing). Each drum 15 and 15' can be moved axially along the end of the appropriate half-shaft but is keyed to that half shaft and is thus non-rotatable relative thereto (e.g., the end of the half-shafts are splined and the drums 15 and 15' are keyed to the splines). For one given position of the central drum 14 relative to the two outer drums 15 and 15', the half shafts 7b and 7b' are in phase with the shaft 7a but if the drums 15 and 15' are both moved to the left (as illustrated in FIG. 5) relative to the central drum 14, one half-shaft is advanced in phase relative to the shaft 7a, and the other half-shaft is retarded relative to the shaft 7a, the reverse situation occurring when both the drums 15 and 15' are moved to the right relative to the central drum 14.
Thus the steering control, in the case of the arrangement of FIG. 5 becomes some device capable of moving the drums 15 and 15' to the left or to the right relative to the central drum 14. It will be appreciated that a modified arrangement could be provided by mounting the central drum 14 for movement in its axial direction in the space between the two outer drums 15 and 15'.
A further arrangement is shown in FIG. 6 which employs, for each half shaft 7b, 7b' an endless chain drive 16 passing round a sprocket 22 on the shaft 7a and a sprocket 23 on the respective shaft 7b, or 7b'. Each chain 16 is longer than is necessary for providing a direct drive between the shafts (note that the chain must be crossed to provide the desired contra-rotation between the shaft 7a and either shaft 7b or 7b'), the excess chain being formed into two bights 19 and 20 by means of a sprocket-ended control arm 21. Each control arm 21 can be moved in the directions of the arrows D to increase the size of one bight at the cost of the other and thus either advance or retard the phase relationship between the respective shaft 7b or 7b', and the shaft 7a. In order to get oppositely directed steering forces at each roller, the arms 21 of the two chain drives may be interconnected whereby when the half-shaft 7b is advanced in phase with respect to the shaft 7a, the half-shaft 7b' is retarded in phase with respect thereto, and vice versa.
The arrangement shown in FIGS. 7 and 8 employs a bevel differential unit having bevel planets 50 and 51 each rotatably mounted within a planet carrier 52. The carrier 52 can rotate about the common axes of the half shafts 7b and 7b', and may, for example, be driven by a chain sprocket or toothed belt pulley (not shown)) in contra-rotation to the shaft 7a (also not shown).
To advance the shaft 7b relative to the carrier 52 (and at the same time to retard the shaft 7b' relative to the carrier) the shaft 7b would be retarded by the application of a braking force. Conversely, to advance the shaft 7b' relative to the carrier 52 and to retard the shaft 7b relative to the carrier 52 the shaft 7b' is retarded in any suitable way.
In order to prevent the shafts 7b and 7b' continuing to turn at different speeds after the desired phase separation has been achieved, some means is necessary to limit the degree of phase separation occasioned by a braking action on one or other of the half shafts. This means can take many different forms (for example, by limiting the extent to which the planets 50 and 51 can turn about their rotating axes) but in the embodiment shown in FIGS. 7 and 8 (FIG. 8 being a section on the line VIII--VIII of FIG. 7) a peg 53 on one sun gear 54 is located in an arcuate groove 55 in the other sun gear 56. To steer a roller with an arrangement as shown in FIGS. 7 and 8, one or other of the shafts 7b or 7b' would be braked depending on the direction of steer, some spring means (not shown) acting to restore the peg 53 to the centre of the groove 55 at the termination of each steering operation.
If desired, the control of the mechanism for altering the phase relationships between the masses can be brought out to a control lever 4 movably mounted on the end of the arm 3 as an extension thereof, deflection of the lever 4 to the right or left of its centre position operating a hydraulic valve to adjust the phase-shifting mechanism to turn the roller to the right or left, respectively.
The arrangement shown in FIG. 9 comprises brake drums 30, 31 associated with the out-of-balance weights 5a and 5b and brake drums 32, 33 associated with the weights 6a and 6b. The weights 5a and 6a are at opposite ends of a torsionally flexible drive shaft 7a and the weights 5b and 6b are at opposite ends of a similar shaft 7b. The two shafts are driven in opposite directions from points roughly centrally located between the weights at the ends thereof by a suitable prime mover (shown schematically at 34).
A steering arm 35 is mounted on the frame of the roller to turn about an axis 36, the arm supporting four brake pads 37 each adapted to act on a different one of the drums 30 to 33. The median position of the arm 35 is shown by the chain line 38 and when in its median position, no brake pad is contacting a brake drum and there is no steering effect in evidence.
When the arm 35 is pulled from its median position as shown in the drawing, by a force applied to a handle 4, drums 32 and 31 are braked but not drums 30 and 33. The braking effect generates a torsional strain in the ends of the shafts 7a and 7b adjacent to the weights 6a and 5b, causing a retarding of the phase of these out-of-balance weights relative to the other weights 6b and 5a, respectively, of the appropriate pair. Thus a turning moment (in the direction in which the arm 35 has been deflected) is generated.
Moving the arm 35 to the other side of the median position represented by the line 38 will brake the weights 6b and 5b and generate torsional strain in the opposite ends of the shafts 7a and 7b to turn the roller in the opposite direction, since it is now the weights 6b and 5a of the respective pairs of weights which are retarded in phase relative to the other weights of the pairs.
Limit stops 40 can be provided on the frame of the roller against which the arm 35 can bear if an excessive force is applied to the handle 4 in one turning direction or the other.
Although it is preferred that the oscillations induced by the front pair of out-of-balance masses 5a and 5b be 180° out of phase with the oscillation induced by the rear pair of out-of-balance masses (i.e., mass 5a is at TDC when mass 6a is at BDC) it is not essential that this 180° difference exists.
A preferred design of road roller weighing one long ton has four out-of-balance masses each weighing 14 lbs and rotating at a speed of 2,800 RPM. The eccentricity of each mass is 0.75 inch giving an instantaneous maximum downward force of about 2,350 lbs wt. at each mass. With the four masses (two at the front and two at the rear) this means the roller alternately (at a frequency of 47 c.p.s.) exerts total forces of 4,700 lbs wt. at the front and rear rolls.
The steering system described is suitable for rollers with a deadweight between 1/2 and 21/2 long tons and although it has particular utility in the case of steering pedestrian-controlled tandem rollers but it is not excluded that it also be used for ride-on rollers.