Patent Publication Number: US-2003223817-A1

Title: Compaction roller

Description:
BACKGROUND OF THE INVENTION  
       [0001] The invention relates to a compaction roller as it is used for the compaction of materials in earthwork and road construction.  
       [0002] In earthworks or road construction, it is desirable to compact unbound and hydraulic-bound or bituminous-bound materials as rapidly as possible to the prescribed Proctor or Marshall density, but at the same time to prevent over-compaction and, in particular in the case of wearing courses, to minimize particle fragmentation of the mineral constituents.  
       [0003] In the case of bituminous road surfaces, smoothing of the surface during compaction should be avoided in order to ensure either good bonding between courses or, in the case of wearing courses, a high level of grip. The setting of optimum system parameters for short compaction times is an absolute necessity in the case of bituminous materials since cooling of the material causes the compactability to diminish and, in the most unfavorable case, the prescribed final density cannot be achieved. When compacting drain asphalt (open-pore asphalt), the pores in the region close to the surface must not be closed, so that the desired water drainage can be obtained and the effect known as “air-pumping” reduced when automobile tires roll in the contact zone between tire and roadway.  
       [0004] Where vibration amplitudes of the rolling body are excessively high or where vibration frequencies are close to the natural frequency of, for example, bridge structures or other structures, it is possible that these may become damaged, so that in these cases, especially where rollers with conventional eccentrically loaded rotating shafts are concerned, the vibration has to be switched off to avoid damage. The result of this then is that, in order to reach the prescribed final density, a greater number of static roller passes is required if the final density can be achieved at all by means of static rolling.  
       [0005] It is known that vibratory rollers for compacting unbound soils and hydraulic or bituminous courses can be equipped with an eccentrically loaded rotating shaft. In this case, at least one fixed unbalance is provided. It is additionally possible, as is usually the case, for an additional changeover weight to be provided in order to generate two different nominal amplitudes. However, there is no possibility of adjusting the amplitude between the two nominal amplitudes.  
       [0006] It is also known that asphalt compaction can be performed by means of what is known as oscillation using a rolling body without circular or directional vibrations, European Patent EP 0 053 598 B. However, compaction to depth does not take place, since here the material is compacted solely by a static linear load and alternating exposure to shear stress. The enforced slip between the rolling body and ground makes traction problems unavoidable. The oscillating moment is generated by two unbalanced shafts which are mounted parallel to the axis of rotation of the roller and of which their unbalances, offset by 180°, run synchronously in the same direction. In the case of bituminous materials, the oscillating effect can lead to undesirable ripples, to smoothing effects and to pore closure.  
       [0007] In compaction rollers, it is also known for the angle between an unbalance which can be rotated around the rolling body axis, and a fixed unbalance to be adjusted so that the resulting unbalance can be set in an infinitely variable manner.  
       [0008] German document DE 69425111 T2 discloses a compaction roller whose unbalance, which is arranged so as to be rotatable transversely with respect to the rolling body axis, can be adjusted in an infinitely variable manner via a hydraulic cylinder and a connecting rod. However, this is very expensive and complex.  
       [0009] In the compaction rollers which are described in German Patent Application DE 4 129 182 A1 and European Patent Application EP 0 954 187 A2, a directional vibrator comprises at least two exciter shafts which run in opposite directions and whose resulting force can be rotated without moment in an infinitely variable manner from a horizontal direction into a vertical direction. The nominal amplitude or unbalance is not changed in this system. It is also the case here, in particular where horizontal vibrations are concerned, that undesirable ripples, smoothing effects and pore closures can occur.  
       [0010] German Patent Application DE 100 31 617 A1 also discloses a vibration generator for a soil compaction machine in which an exciter shaft is provided with an unbalance, a cylinder arranged radially with respect to the exciter shaft and having a spring-loaded piston being used for the purpose of bringing about automatic adjustment of the unbalance by virtue of the centrifugal force changing through a change in the speed of rotation. Apart from the fact that the high degree of non-linearity of centrifugal forces having variable eccentricity and speed of rotation cannot completely compensate for the spring forces of metal or oil springs, it is also the case here that each frequency is assigned exactly one amplitude. In addition, from a standing start the unbalance shaft can only be accelerated with a high degree of unbalance.  
       SUMMARY OF THE INVENTION  
       [0011] It is an object of the invention to provide a compaction roller which permits optimum adaptation of the vibration to the particular road building materials or to the local circumstances, such as the presence of bridges and vibration-sensitive structures and installations.  
       [0012] Thus, the invention concerns a compaction roller having at least one rolling body with a vibratory drive which comprises a drivable exciter shaft with an unbalance, said shaft being mounted axially with respect to the rolling body and in said body, the unbalance comprising an unbalance cylinder which is arranged centrally with respect to the axis of the rolling body, is held by the exciter shaft and has an unbalance piston which can be adjusted hydraulically radially with respect to the axis of the rolling body and to which hydraulic fluid can be supplied in a controlled manner from outside by means of an external adjusting device via a bore in the exciter shaft, with infinitely variable adaptation of the nominal amplitude to paving situations, the adjusting device having an actuating cylinder with an actuating piston and a chamber of the actuating cylinder communicating with the unbalance cylinder, wherein the chamber of the actuating cylinder in communication with the unbalance cylinder is connected via a controllable valve to a hydraulic oil source for the purpose of leakage oil replacement, which valve shuts in a central position of the unbalance piston, from which the nominal amplitude can be increased or reduced.  
       [0013] In this context, an actuating cylinder is provided whose chamber of the actuating cylinder in communication with the unbalance cylinder is connected via a controllable valve to a hydraulic source for the purpose of leakage oil replacement, which valve shuts in a central or intermediate position between the two end positions of the unbalance piston, from which the nominal amplitude can be increased or reduced.  
       [0014] This makes it possible to carry out leakage oil replacement and calibration, with the result that by so doing the compaction result is not impaired. Furthermore, it is possible in a structurally simple manner to adjust the nominal amplitude of the vibration of the rolling body. This further allows the vibration frequency and the traveling speed of the vibratory roller to be automatically adapted to the nominal amplitude, once again in order to obtain optimum compaction results. Thus, the compaction of great layer thicknesses, for example anti-frost layers, thin layer thicknesses, for example a surface layer for compact asphalt, and sensitive layers such as open-pore asphalt, can be ensured. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0015] The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawings in which:  
     [0016]FIG. 1 shows a schematic side view of a tandem compaction roller.  
     [0017]FIG. 2 shows a rolling body of the tandem compaction roller of FIG. 1, in section.  
     [0018]FIG. 3 shows a detail of FIG. 2.  
     [0019]FIGS. 4 a  and  4   b  show two embodiments of an adjusting device for adjusting the nominal amplitude of the tandem compaction roller of FIG. 1.  
     [0020]FIGS. 5 a  to  5   c  show three different operating settings for an embodiment of the tandem compaction roller of FIG. 1.  
     [0021]FIGS. 6 a  to  6   c  show three different operating settings for a further embodiment of the tandem compaction roller of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0022] The tandem compaction roller shown in FIG. 1 comprises a superstructure  1  with driver&#39;s cab, a rolling body  2  and  3  being mounted via steerable swivel couplings  4  at the front and rear underneath said superstructure. Situated between the two rolling bodies  2 ,  3  is an engine compartment  5  which houses a drive engine, usually a Diesel engine.  
     [0023] As shown in FIG. 2, the front and/or rear rolling body  2 ,  3  comprises two tire halves  6   a ,  6   b  arranged side by side in the axial direction and a respective radially extending tire endplate  7  with a central through-opening. A respective bearing flange  8  is fastened on the tire endplate  7 . The two tire halves  6   a ,  6   b  are connected to one another so as to be rotatable about the rolling body axis via the two bearing flanges  8  and a spacer tube  9 , by a bearing  10 , for instance a roller bearing, being arranged between a bearing flange  8  and the spacer tube  9 .  
     [0024] The swivel coupling  4  connected steerably to the superstructure  1  is connected elastically on both sides to a respective hollow hydraulic travel motor  12  via damping elements  11 , for example rubber-metal elements, and a flange plate  39 . On the output side the travel motors  12  are connected via a flange  13  to the adjacent bearing flange  8  and thus drive the respective tire halves  6   a ,  6   b.    
     [0025] Situated in the center of the rolling body is an exciter shaft  14  which is driven by a hydraulic vibration motor  15  and is mounted opposite the bearing flanges  8  via bearings. An unbalance cylinder  16  is mounted centrally in a bore in the exciter shaft  14 . For this purpose, the unbalance cylinder  16  has a corresponding collar and, on the opposite side, a threaded section for clamping by means of a clamping ring and a pair of nuts. The unbalance cylinder  16  accommodates an unbalance piston  17  such that it can be adjusted hydraulically radially with respect to the rolling body axis.  
     [0026] When changing the eccentricity by displacing the unbalance piston  17 , the unbalance in the exciter shaft  14 , which is sufficient to achieve the smallest nominal amplitude of the rolling body, can be added in an infinitely variable manner. The unbalance piston  17  may be filled with lead in order that where there is minimal construction space as large an adjustment range as possible for the nominal amplitude can be achieved.  
     [0027] The unbalance piston  17  is equipped with guide bands and a piston sealing ring. Deformations of the exciter shaft  14  (bending caused by centrifugal forces) are not transmitted to the unbalance cylinder  16 , as a result of sufficient play. The required amount of oil for displacing the unbalance piston  17  is made available through a bore  18  in the exciter shaft  14 . The oil pressure is transmitted to the head of the piston via a taper of the unbalance piston  17  and bores  19 .  
     [0028] Situated in one of the bearing flanges  8  is an oil inlet and outlet nipple  20  for the purpose of lubricating the space within the spacer tube  9 , and the adjacent bearings, etc.  
     [0029] As can be seen in FIG. 3, the pressurization of the unbalance piston  17  by means of an exactly metered amount of oil for displacing the unbalance piston  17  is performed via a rotary bushing  21  which, by virtue of rubber springs  22  and an additional vibrating mass  23 , is suspended with low vibration on one of the travel motors  12 . The vibrating mass  23  accommodates an adapter  24  which bears a piston  25  such that it can be displaced, the piston being connected via a tube  26  to a further piston  27  accommodated by the exciter shaft  14 . Radial and axial displacements between the rotary bushing  21  and the exciter shaft  14  as a result of thermal expansions are compensated for by seals  28  of the pistons  25 ,  27 . Pins  29  prevent rotational slip between the seals  28  and the exciter shaft  14  or the adapter  24  of the rotary bushing  21 .  
     [0030] According to the embodiment shown in FIG. 4 a , the required oil volume for changing the position of the unbalance piston  17  is metered by displacing an adjusting piston  34  of an actuating cylinder  40 . Here, the piston rod  30  of the adjusting piston  34  is connected to a trapezoidal or ball screw drive  31  whose spindle is not displaceable (self-locking) under the action of tensile or compressive stress. The screw drive  31  is driven by an electric or hydraulic motor  32 . An incremental travel measurement on the piston rod or, if appropriate, angular measurement on the screw drive  31  (preferably integrated therein and therefore not shown) is used to set the eccentricity of the unbalance piston  17  or the nominal amplitude. For the purpose of calibration and for leakage oil compensation, there is provided on the piston side an oil passage whose 2/2-way valve  33  can automatically be switched to the flow position as a function of the operating state.  
     [0031] According to the embodiment shown in FIG. 4 b , the required oil volume for changing the position of the unbalance piston  17  using the adjusting piston  34  and its piston rod  30  is modified on the piston rod side by a variable oil volume. To this end, electromagnets of a 3/3-way valve  35  are activated cyclically in such a way that the adjusting piston  34  can be displaced by very small distances. When the 3/3-way valve  35  is pressure-connected, the adjusting piston  34  moves in the piston side direction and when tank-connected, because of the centrifugal force of the unbalance piston  17 , in the piston rod side direction. The locking zero position of the 3/3-way valve  35  here replaces the self-locking action of the screw drive  31  of FIG. 4 a . The sole function of the adjusting piston  34  with piston rod  30  here is incremental travel measurement for the purpose of setting the eccentricity of the unbalance piston  17  or the nominal amplitude. The calibration and leakage oil compensation correspond to those of FIG. 4 a.    
     [0032]FIGS. 5 a  to  5   c  depict various positions of the unbalance piston  17  in combination with an adjusting device according to FIG. 4 a  (the same applies to the adjusting device of FIG. 4 b ). The unbalance piston  17  is in the position shown in FIG. 5 a  during the following four operating states:  
     [0033] 1. With the vibrating device at a standstill and the diesel engine running, the oil pressure at the unbalance piston  17  corresponds to the inlet pressure at the 2/2-way valve  33 , which is fundamentally connected to flow in this operating state. As a result, the leakage oil quantity is replaced and at the same time the unbalance piston  17  is forced in the direction of smallest eccentricity against the “minimum unbalance” stop (calibration).  
     [0034] 2. The vibratory drive should be accelerated as quickly as possible with the lowest mass moment of inertia until the minimum operating frequency has been reached. Consequently, resonance ranges are rapidly passed through with the smallest nominal amplitude so that adjoining assemblies such as rotary swivel couplings  4  or superstructure  1  and their connections are only slightly stressed. When the minimum operating frequency has been reached, the 2/2-way valve  33  blocks the oil flow. Leakage oil replacement and calibration are automatically ended at the same time.  
     [0035] 3. The smallest nominal amplitude is set at the maximum vibrator frequency. The 2/2-way valve  33  is opened, with the result that leakage oil is replaced and calibration takes place.  
     [0036] 4. When the vibratory drive is switched off, the unbalance piston  17  automatically moves in the direction of smallest nominal amplitude in order to brake the vibratory drive with a small mass moment of inertia. As soon as the position of the adjusting piston  34  corresponds to that of FIG. 5 a , the inlet pressure at the 2/2-way valve  33  is connected to flow. From this point in time, leakage oil can be replaced and the system calibrated.  
     [0037] The unbalance piston  17  is in the position shown in FIG. 5 b  only with the nominal amplitude set manually or automatically to maximum and with minimum operating frequency. The 2/2-way valve  33  is here connected to flow and the oil pressure corresponds to the inlet pressure of the directional valve. In this operating state, leakage oil can be replaced and the system calibrated. As soon as the adjusting piston  34  has reached the position of FIG. 5 b , the 2/2-way valve  33  is immediately automatically closed. The nominal amplitude from this operating state can subsequently be reduced in an infinitely variable manner. The operating frequency is subject to follow-up control in the direction of smaller nominal amplitude, for example by means of characteristic map control, to avoid exceeding the permissible centrifugal force of the unbalance piston  17 .  
     [0038] When the unbalance piston  17  is in the position shown in FIG. 5 c , the 2/2-way valve  33  is closed and leakage oil replacement and calibration are not possible. The nominal amplitude can be increased or reduced in an infinitely variable manner from this operating state. The operating frequency is subjected to follow-up control in the direction of smaller nominal amplitude, as is the position of the unbalance piston  17  in the direction of larger nominal amplitude.  
     [0039] When the vibratory drive is switched off, the unbalance piston  17  is displaced from the positions shown in FIGS. 5 b  and  5   c  immediately in the direction of smallest nominal amplitude, independently of the decreasing operating frequency.  
     [0040] To achieve optimum soil or asphalt compaction, the vibration frequency is matched to the nominal amplitude, as described above. It is possible at the same time to automatically set the optimum rolling speed as a function of the vibration frequency and for this to be displayed to the roller driver. The position of the unbalance piston  17  can either be adjusted manually or automatically controlled as a function of the density (stiffness) of the ground. In tandem vibratory rollers, it is possible for either only the front or only the rear or for both rolling bodies  2 ,  3  to be fitted with an unbalance which can be adjusted in the manner described above.  
     [0041] In the embodiment shown in FIGS. 6 a  to  6   c , a directional valve  35  is provided instead of the hydraulic motor  32  of FIGS. 5 a  to  5   c , this valve being connected to the chamber of the actuating cylinder  34  on the piston rod side while the directional valve  33 , in this case a three-way valve, is again connected to the chamber of the actuating cylinder  40  upstream of the adjusting piston  34 .  
     [0042] In the embodiment shown in FIG. 6 a , where the vibration is switched off after the adjusting piston  34  is completely retracted, the unbalance cylinder  16  is filled up with oil from the hydraulic source via a pump  37 . For this purpose, at the same time as the vibration is switched off, the directional valve  33  is connected as shown in FIG. 6 a . A pressure-limiting valve  36  is connected to the line from the pump  37  to the directional valve  33 . If said valve  36  responds, this means that the unbalance cylinder  16  is completely filled with oil.  
     [0043] On reaching the state when the unbalance cylinder  16  is completely filled with oil, FIG. 6 b , the directional valve  33  is switched over so that oil can flow back to the hydraulic source from the actuating cylinder  40 , specifically from the chamber upstream of the adjusting piston  34 , via a pressure-limiting valve  38 , whereas the previously closed directional valve  35  is opened so that hydraulic oil can adjust the adjusting piston  34 . Consequently, the quantity of oil in the adjusting cylinder  40  is returned completely to the hydraulic source, as a result of which the system is calibrated at the same time.  
     [0044] If this state is reached, the directional valves  33 ,  35  are closed and the vibration can be switched on, FIG. 6 c . If then a certain frequency, for example 28 Hz, is reached, the amplitude is adjusted from the position of smallest amplitude shown in FIG. 6 c  by corresponding opening of the directional valve  35 .  
     [0045] In this embodiment, apart from leakage oil replacement and calibration, there also simultaneously takes place an additional exchange of at least a large proportion of the total amount of hydraulic oil in the system comprising the cylinders  16  and  40  on each occasion that vibration compaction is stopped or interrupted. This is advantageous as regards ageing of the hydraulic oil and cooling thereof.  
     [0046] While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.