Patent Abstract:
A vibratory mechanism having a first eccentric weight coaxially rotatable with a second eccentric weight and a clutch operatively connecting the first and second eccentric weights. The clutch allows for co-rotation of the first and second eccentric weights and the ability to index the first eccentric weight relative to second eccentric weight to vary the vibrational amplitude.

Full Description:
TECHNICAL FIELD  
         [0001]    This invention relates generally to a vibratory compactor machines and, more particularly, to an infinitely variable amplitude and frequency vibratory mechanism.  
         BACKGROUND  
         [0002]    Vibratory compactor machines are commonly employed for compacting freshly laid asphalt, soil, and other compactable materials. For example these compactor machines may include plate type compactors or rotating drum compactors with one or more drums. The drum type compactor functions to compact the material over which the machine is driven. In order to compact the material the drum assembly includes a vibratory mechanism including inner and outer eccentric weights arranged on a rotatable shaft within the interior cavity of the drum, for inducing vibrations on the drum.  
           [0003]    The amplitude and frequency of the vibratory forces determine the degree of compaction of the material, and the speed and efficiency of the compaction process. The amplitude of the vibration forces is changed by altering the position of a pair of weights with respect to each other. The frequency of the vibration forces is managed by controlling the speed of a drive motor in the compactor drum.  
           [0004]    The required amplitude of the vibration force may vary depending on the characteristics of the material being compacted. For instance, high amplitude works best on thick lifts or harsh mixes, while low amplitude works best on thin lifts and soft materials. Amplitude variation is important because different materials require different levels of compaction. Moreover, a single compacting process may require different amplitude levels because higher amplitude may be required at the beginning of the process, and the amplitude may be gradually lowered as the process is completed.  
           [0005]    Conventional vibratory compactor machines are problematic in that the amplitude and frequency of the vibration force can only be set to certain predetermined levels, or the mechanisms for adjusting the vibration amplitude are complex. One such vibratory mechanism is disclosed in U.S. Pat. No. 4,350,460 issued to Lynn A. Schmelzer et al. on Sep. 21, 1982 and assigned to the Hyster Company.  
           [0006]    The present invention is directed to overcome one or more of the problems as set forth above.  
         SUMMARY OF THE INVENTION  
         [0007]    In one aspect of the invention, a vibratory mechanism is provided that includes an inner eccentric weight rotatably supported within a housing. An outer eccentric weight is rotatably supported and positioned about the inner eccentric weight. A clutch operatively connects the inner and outer eccentric weights.  
           [0008]    According to another aspect of the invention, a method for controlling a vibration amplitude of a vibratory compactor includes abruptly changing a speed of one of an inner and outer eccentric weights to cause a clutch to slip, thereby causing inner and outer eccentric weights to move farther apart or closer together to change the vibration amplitude. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a side elevational view of a work machine embodying the present invention;  
         [0010]    [0010]FIG. 2 shows an axial cross section view taken along line  2 - 2  through a compacting drum of the work machine of FIG. 1 embodying the present invention;  
         [0011]    [0011]FIG. 3 is an enlarged sectional view of the vibrator pod shown in FIG. 2; and  
         [0012]    [0012]FIG. 4 is a system diagram. 
     
    
     DETAILED DESCRIPTION  
       [0013]    A work machine  10 , for increasing the density of a compactable material  12  or mat such as soil, gravel, or bituminous mixtures, an example of which is shown in FIG. 1. The work machine  10  is for example, a double drum vibratory compactor, having a first compacting drum  14  and a second compacting drum  16  rotatably mounted on a main frame  18 . The main frame  18  also supports an engine  20  that has a first and a second power source  22 , 24  conventionally connected thereto. Variable displacement fluid pumps or electrical generators can be used as interchangeable alternatives for the first and second power sources  22 , 24  without departing from the present invention.  
         [0014]    The first compacting drum  14  includes a first vibratory mechanism  26  that is operatively connected to a first motor  28 . The second compacting drum  16  includes a second vibratory mechanism  30  that is operatively connected to a second motor  32 . The first and second motors  28 , 32  are operatively connected, as by fluid conduits and control valves or electrical conductors and controls to the first power source  22 . It should be understood that the first and second compacting drums  14 , 16  could have more than one vibratory mechanism per drum.  
         [0015]    In as much as, the first compacting drum  14  and the second compacting drum  16  are structurally and operatively similar. The description, construction and elements comprising the first compacting drum  14 , which will now be discussed in detail and as shown in FIG. 2, applies equally to the second compacting drum  16 . Rubber mounts  36  vibrationally isolate the compacting drum  14  from the main frame  18 . The first compacting drum  14  includes a propel motor  40  that is connected to the second power source  24 . For example, the propel motor  40  is connected to the main frame  18  and operatively connected to the first compacting drum  14  in a known manner. The second power source  24  supplies a pressurized operation fluid or electrical current, to propel motor  40  for propelling the work machine  10 .  
         [0016]    Referring now to FIG. 2, the vibratory mechanism  26  is contained within a housing  46  that is coaxially supported within the first compacting drum  26  in a known manner. The vibratory mechanism  26  includes a first/inner eccentric weight  50  and a second/outer eccentric weight  52 . An inner shaft  54  supports the inner eccentric weight and a pair of stub shafts  56  supports the outer eccentric weight  52 . Motor  28  is connected to a drive shaft  58  that is connected to one of the stub shafts  56  to supply rotational power to the vibratory mechanism  26  so as to impart a vibratory force on compacting drum  14 .  
         [0017]    The outer eccentric weight  52  is mechanically coupled to shaft  54  so that it is directly rotated by the vibrator propel motor  28 . The inner eccentric weight  50  is rotatably mounted concentrically with respect to the outer eccentric weight  52 , and is driven along with the outer eccentric weight  52 , via a torque limiting (slip) clutch  60  (see FIGS. 2 and 3) disposed between the inner shaft  54  and one of the stub shafts  56 . Clutch  60  may be internal to the vibratory mechanism  26 , as shown in FIG. 3 or external. The clutch  60  may be of a variety of types, such as but not limited to, a jaw type with spring tension, a ball ramp (such as shown in FIGS. 2 and 3), and a friction disk type. As shown in FIG. 3, the clutch  60  may be provided with a torque adjustment screw  62  and tension spring  64  for adjusting a clutch force.  
         [0018]    As shown in FIG. 3, the inner weight drive shaft  50  is supported by bushings  70  within the stub shafts  56 . In addition, the stub shafts  56  are supported by bearings  72  within the housing  46  of the vibratory mechanism  26 .  
         [0019]    Optionally, vibratory mechanism  26  may be modified to limit the rotation of the inner eccentric weight  50  within the outer eccentric weight  52  to 180 degrees with an internal stop mechanism, such as for example rubber covered stop pins  74  bolted through the stub shafts  56 . Inner eccentric weight  50  contacts the stop pins  74  at two different positions. This insures a positive location of the minimum amplitude (could be zero, e.g., when the weights are 180 degrees apart) and the maximum amplitude (e.g., when the weights are 0 degrees apart) settings. The stop pins  74  are useful to simplify the control of the vibratory mechanism  26 .  
         [0020]    Typically, as shown in FIG. 4, a controller  80  is positioned on the work machine  10 . Controller  80  receives input commands from an operator interface  120  and sends output commands to the first and second power sources  22 ,  24  for operating the vib motor  28  and propel motor  40  respectively. The operator interface  120  is defined as being any known device or combination of input devices such as touch screens, levers, rotary knobs, push buttons, joysticks and the like. The second power source  24  drives the propel motor  40 , and is also controlled by the operator interface  120  and/or by controller  80 .  
         [0021]    The controller  80  can monitor drum acceleration via one or more accelerometers  84  mounted on a frame  18  and vibrator speed via one or more speed sensors  86  on the drive shaft  56  and control the output from the power sources  22 , 24  per a preprogrammed decision algorithm (see FIG. 5, for example). The operator inputs commands from the operator interface  82  to the controller  80  when vibration is needed and the controller  80  would respond with the appropriate signal command to the power source  22 .  
         [0022]    Industrial Applicability  
         [0023]    During operation of the work machine  10 , an operator actuates the propel motor/motors  40  such that the drums  14 , 16  rotate around a central axis in the desired direction. Rotating the drums  14 , 16  in this manner causes the work machine  10  to move in forward or reverse over the material  12  to be compacted. In addition, the operator actuates the motor/motors  28 , 32 , which causes the drive shaft  58  (e.g., a cardan type flexible driveshaft shown in FIG. 2), along with the inner and outer eccentric weights  50 , 52 , to rotate.  
         [0024]    The position of the inner and outer eccentric weights  50 , 52 , with respect to each other, determines the amplitude of the vibrations in the drum member. For example, if the inner and outer eccentric weights  50 , 52  are positioned 180° from each other, their weights counteract and zero amplitude (or a minimum amplitude) is obtained. If the inner and outer eccentric weights  50 , 52  are positioned 0° from each other, their weights combine and maximum amplitude is obtained. The inner and outer eccentric weights  50 , 52  can be positioned in an infinite number of positions, so that infinite vibration amplitude levels can be obtained.  
         [0025]    During operation the vibratory mechanism  26  functions as follows:  
         [0026]    When the work machine  10  is started the vibratory mechanism  26  is at rest with the inner and outer eccentric weights  50 , 52  at 180 degrees out of phase, so that the net amplitude is minimal or at zero. The operator signals for vibration from the operator interface  82 . The controller  80  then increases the output from the power source  22 , increasing the power supplied to the motor  28  at a relatively slow rate of speed. (2-8 seconds) In turn, the motor  28  accelerates the inner and outer eccentric weights  50 , 52  up to speed slowly enough that the slip clutch  60  does not activate (and therefore the amplitude does not change). At 90-100% of desired speed (or at some speed faster than frame resonance), the power source  22  suddenly surges to full output for a short period of time (20 milliseconds to 0.5 seconds estimated), which causes the clutch  60  to slip and increase the amplitude as the inner and outer eccentric weights  50 , 52  are moved out of 180 degree opposition. (Note: power source  22  output may be larger than what is required to drive the motor  28  at maximum frequency so that the amplitude adjustment can occur at a predetermined speed.)  
         [0027]    The controller  80  monitors the response in the vibration of the drum  14  and may also determine the response of the material  12  being compacted via accelerometers  84  mounted on the drum  14  and frame  18 . Conventional controllers  80  and other hardware (such as made by Geodynamik, for example) could be used for this application, which is in effect a compaction indicator combined with a compactor control system.  
         [0028]    If the vibration sensed is not adequate for compaction, the amplitude is changed until the desired amplitude is reached. This is sensed by identifying the point (amplitude) at which de-coupling of the drum  14  from the surface of the material  12  being compacted occurs, and then backing off slightly.  
         [0029]    The entire system can be monitored via the accelerometers  84  and/or the speed sensors  86 . Normally, the accelerometers  84  could be used to determine the vibrator speed, but at low/no amplitude the speed sensors  86  may be needed.  
         [0030]    Additionally, the computer controller  80  can monitor ground speed and based on input parameters, limit or control ground speed by controlling operation of power source  24  which drives the drive motor  40 . This would be useful to control impact spacing for producing pavements with superior ride characteristics or to manage the compaction process to optimize the productivity of the machine.  
         [0031]    When the vibratory mechanism  26  is stopped suddenly, the slip clutch  60  operates and allows the inner and outer weights  50 , 52  to rotate relative to each other to be 180 degrees out of phase and at zero amplitude. Stop pins  74  could be provided to limit the rotation of the inner and outer weights  50 , 52  to 180 degrees total rotation in either direction. This concept would also work with weight shafts that had continuous rotation capability, using a slightly more complex control theory.  
         [0032]    The entire concept can also work if the orientation of the weights is reversed. That is, the vibrator decreases amplitude with sudden increases in speed and increases amplitude with sudden decreases in speed. From one perspective, this might work better as the vibrator could be suddenly turned on and it would go to zero or very low amplitude and high RPM. As the RPM was suddenly dropped, amplitude would increase and a new lower speed would be set at the same time. However, normally compaction could be expected to start at low RPM and high amplitude and increase RPM and decrease amplitude as the soil or asphalt mat was being compacted and got stiffer.  
         [0033]    Shown and described are several embodiments of the invention, though it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. Therefore it is intended that the appended claims cover all such changes and modifications as fall within the true spirit and scope of the invention.

Technology Classification (CPC): 1