Patent Publication Number: US-8967910-B2

Title: Eccentric weight shaft for vibratory compactor

Description:
TECHNICAL FIELD 
     The present disclosure relates to vibratory compactor machines, more particularly to an eccentric weight shaft for vibratory compactor. 
     BACKGROUND 
     Compactors are extensively used in the road construction industry for construction and repair of the road surfaces. There are a variety of compactors such as soil compactors, landfill compactors, vibratory compactors, tandem vibratory rollers, pneumatic rollers, etc. The present disclosure is directed to vibratory compactors. Vibratory compactors can be used to compact sand, gravel, or crushed aggregate for foundations, footings, or driveways; base preparation for concrete slabs, asphalt parking lots, etc. Vibratory compactors can also be used to compact the hot mix asphalt or the cold mix asphalt for a purpose of patching and repairing of roads, highways, sidewalks, parking lots, and the like. 
     A typical vibratory compactor includes at least one roller. The roller serves the purpose of compacting a surface. The roller is mounted on a main frame and is configured to compact the surface beneath the vibratory compactor. The roller includes a vibratory mechanism. The vibratory mechanism includes an eccentric shaft which is accelerated by a first motor, and imparts vibrations to the roller. A second motor is provided which rotates the roller, and hence the vibratory compactor moves forward/backward. Traditionally, the eccentric shaft has one or more weights press-mounted or welded on the eccentric shaft to achieve a desired eccentricity, thereby increasing manufacturing costs. The existing eccentric shaft is heavy in weight and more prone to bending failures. Also, the existing eccentric shaft has a high start-up torque. The high start-up torque may lead to high operating and wear and tear of the first motor. Hence, there is a need to reduce the weight, the manufacturing cost, and the bending failures. Also, there is a need to reduce the start-up torque. 
     SUMMARY OF THE DISCLOSURE 
     According to an embodiment of the present disclosure a vibratory compactor is provided. The vibratory compactor includes a roller configured to compact a surface. The roller is rotatably mounted on a main frame and may include a first vertical support and a second vertical support. The vibratory compactor may also include an eccentric shaft. The eccentric shaft is rotatably connected between the first vertical support and the second vertical support in the roller. In accordance with an embodiment of the present disclosure, the eccentric shaft includes a first end, a second end, a first eccentric weight, a second eccentric weight, and a center portion. The first eccentric weight is proximal to the first end and the second eccentric weight is proximal to the second end. The first eccentric weight is in a shape of a segment around the eccentric shaft subtending an arc of a predefined angle and the second eccentric weight is in the shape of the segment around the eccentric shaft subtending the arc of the predefined angle. The center portion may be disposed between the first eccentric weight and the second eccentric weight. The center portion may include at least one cavity on a surface of the center portion. The at least one cavity is elongated between the first eccentric weight and the second eccentric weight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a vibratory compactor in accordance with an embodiment of the present disclosure; 
         FIG. 2  is a sectional view of a roller of the vibratory compactor as illustrated in  FIG. 1  in accordance with an embodiment of the present disclosure; and 
         FIG. 3  is a perspective view of an eccentric shaft as shown in  FIG. 2  in accordance with an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a side view of a vibratory compactor  100  in accordance with an embodiment of the present disclosure. For example, the vibratory compactor  100  is an asphalt compactor. The vibratory compactor  100  includes at least one roller. For example, the vibratory compactor  100  includes a first roller  102 , and a second roller  104 . In an alternative embodiment of the present disclosure, the vibratory compactor  100  may include one roller with a vibratory mechanism. Further, in an exemplary embodiment of the present disclosure, the vibratory compactor includes a main frame  106 , an engine  108 , a first hydraulic pump  110 , a second hydraulic pump  112 , a first motor  114 , a second motor  116 , a first vibrating mechanism  118 , and a second vibrating mechanism  120 . The first roller  102  includes the first vibrating mechanism  118  and the second roller  104  includes the second vibrating mechanism  120 . The first roller  102  and the second roller  104  are rotatably mounted on the main frame  106 . 
     Further, the main frame  106  is configured to house the engine  108 . The engine  108  is operatively and conventionally connected to drive the first hydraulic pump  110  and the second hydraulic pump  112 . The first hydraulic pump  110  is operatively connected to the first motor  114  and the second hydraulic pump  112  is operatively connected to the second motor  116 . The first motor  114  is configured to accelerate the first vibrating mechanism  118  and the second vibrating mechanism  120 . The second motor  116  is configured to impart rotation to the first roller  102  and the second roller  104 . The rotation of the first roller  102  and the second roller  104  drives the vibratory compactor  100  in a desired direction to compact a surface  122  below the vibratory compactor  100 . The first roller  102  and the second roller  104  are structurally and functionally similar. Hence, the structural and operational description of the first roller  102  is equally applicable to the second roller  104 . 
       FIG. 2  is a sectional view  200  of the first roller  102  of the vibratory compactor as illustrated in  FIG. 1  in accordance with an embodiment of the present disclosure. The first roller  102  includes the first vibrating mechanism  118 . The first vibrating mechanism  118  includes an eccentric shaft  202 , a first vertical support  204 , and a second vertical support  206 . Further, the eccentric shaft  202  consists of a first end  208  and a second end  210 . The first end  208  and the second end  210  are pivoted and supported by the first vertical support  204  and the second vertical support  206 , respectively. Specifically, the first end  208  and the second end  210  are positioned within a first bearing  212  and a second bearing  214 , respectively. The first bearing  212  and the second bearing  214  are in turn housed inside a first bracket  216  and a second bracket  218 , respectively. The first bracket  216  and the second bracket  218  are attached and supported by the first vertical support  204  and the second vertical support  206 , respectively. Hence, the eccentric shaft  202  can be a shaft supported by the first vertical support  204  and the second vertical support  206 , at the first end  208  and the second end  210 , respectively. The first end  208  of the eccentric shaft  202  may be connected to a first coupling  220 . The first coupling  220  may be connected to the first motor  114 . Specifically, the first coupling  220  can transfer the rotational motion of the motor to the eccentric shaft  202 . Further, the second motor  116  is coupled with the first roller  102 , through a second coupling  222 . In other words, the first motor  116  is coupled to the first roller in manner so as to rotate the first roller  102 . It can be contemplated that a motor similar to the first motor  114  and the second motor  116  can be provided in the second roller  104 . 
     The eccentric shaft  202  further includes a first eccentric weight  226 , a second eccentric weight  228 , and a center portion  230 . The first eccentric weight  226  and the second eccentric weight  228  may be mounted on the eccentric shaft  202  at an equal distance from the center of the eccentric shaft  202 . In other words, the first eccentric weight  226  and the second eccentric weight  228  may be located proximal to the first end  208  and the second end  210 . Hence, the first eccentric weight  226  and the second eccentric weight  228  increase asymmetric mass of the shaft. Specifically, the eccentric weights  226  and  228  protrude out from the eccentric shaft  202  and thereby increase the asymmetric mass which is offset from the axis X-X of eccentric shaft  202 . Hence, the rotation of asymmetric offset mass results in net centrifugal force, when the eccentric shaft  202  is rotated. 
     In operation, the first hydraulic pump  110  supplies pressurized fluid to the first motor  114 . The first motor  114  is configured to rotate the eccentric shaft  202  through the coupling at the first end  208 . Subsequently, rotation of the eccentric shaft  202  is initiated as torque is applied at first end  208  by the motor  114 . As the eccentric shaft  202  is rotated a centrifugal force is generated. The centrifugal force is generated because of the first eccentric weight  226  and the second eccentric weight  228 . The first eccentric weight  226  and the second eccentric weight  228  increases asymmetric mass of the shaft, hence, a net centrifugal force is generated. At a certain rotational velocity, the eccentric shaft  202  attains an operating frequency and starts to vibrate due to net centrifugal force. Vibration of the eccentric shaft  202  induces a vibratory force on the first roller  102  through the first vertical support  204  and the second vertical support  206 . Hence, with the rotation of the eccentric shaft induces vibratory forces in the first roller  102 . Further, the vibration of the first roller  102  can be used to compact the surface  122  on which the vibratory compactor  100  is resting. In an embodiment a pair of rubber pads  224  may be provided to isolate the first vibrating mechanism  118  from the main frame  106 . 
     The second hydraulic pump  112  is configured to supply pressurized hydraulic fluid to the second motor  116 . The second motor  116  rotates the first roller  102 . It can be contemplated that a motor similar to the first motor  114  and the second motor  116  can be provided in the vibrating mechanism  120  of the second roller  104 . Subsequently, the rotation of the first roller  102  and the second roller  104  may propel the vibratory compactor  100  in a forward or backward direction, while compacting the surface  122 . 
       FIG. 3  is a perspective view of the eccentric shaft  202 . The eccentric shaft  202  is shown to include the first end  208 , the second end  210 , the first eccentric weight  226 , the second eccentric weight  228 , and the center portion  230 . Each of the first eccentric weight  226  and the second eccentric weight  228  are in shape of a segment of the eccentric shaft  202  subtending an arc of a predefined angle. The first eccentric weight  226  is disposed proximally to the first end  208 . The second eccentric weight  228  is disposed proximally to the second end  210 . In other words, the first eccentric weight  226  and the second eccentric weight  228  are positioned offset from the center of the eccentric shaft  202  and proximal to the first end  208  and the second end  210 , respectively. The first eccentric weight  226  and the second eccentric weight  228  are positioned in a manner to asymmetrically increase the weight of the eccentric shaft  202  at the first end  208  and the second end  210 . The first eccentric weight  226  and the second eccentric weight  228  are in a shape of a segment around the eccentric shaft  202  and subtending an arc of a predefined angle. Specifically, the first eccentric weight  226  and the second eccentric weight  228  are in form of thick discs mounted at the first end  208  and the second end  210 . The thick discs subtend an arc of a predefined angle. Hence, the first eccentric weight  226  and the second eccentric weight  228  are in form of thick discs running around the shaft  202 . In an embodiment, the thick discs may not form a complete circle around the shaft  202  but subtend an arc of the predefined angle around the eccentric shaft  202 . The angle may be selected based on the size of the machine and type of compactor. The part of the eccentric shaft  202  between the first eccentric weight  226  and the second eccentric weight  228  can be referred to as the center portion  230 . The center portion  230  may include a first cavity  232  on surface of the center portion  230 . In an alternate embodiment a second cavity can be provided on surface of the center portion  230 . Each of the first cavity  232  and the second cavity is casted along a length of the center portion  230 . In an embodiment, the second cavity is casted diametrically opposite to the first cavity  232 . In an embodiment of the present disclosure, each of the first cavity  232  and the second cavity may be longitudinally elongated and disposed along the length of the center portion  230 , between the first eccentric weight  226  and the second eccentric weight  228 . Each of the first cavity  232  and the second cavity may have a longitudinal section and with uniform width and uniform depth throughout the longitudinal section. In other words, the eccentric shaft  202  can be a shaft having two longitudinally elongated cavities opposite to each other and located at a center portion  230  and between the first eccentric weight  226  and the second eccentric weight  228 . 
     The proposed eccentric shaft  202  may be light in weight and may require lesser start-up torque and the moment of inertia. In an exemplary embodiment of the present disclosure, the eccentric shaft  202  may be manufactured by casting the center portion  230  as an I-beam section, as shown in  FIG. 3 . In another embodiment, the center portion  230  can be machined. In one exemplary embodiment, the disclosed eccentric shaft  202  weighs between 15 kg and 20 kg, and may have moment of inertia in the range of 0.02836 kgm2. The start-up torque required to initiate the rotation of the eccentric shaft  202  to a rotational frequency of about 65 Hz over a 4 second start-up time period is about 2.89 Nm. 
     Industrial Applicability 
     The vibratory compactor  100  operates to compact the surface  122 . The operator may actuate the vibration to the first roller  102  by using a user interface. As the operator actuates the vibration command on the user interface, a controller sends command signals to the first hydraulic pump  110 . The first hydraulic pump  110  supplies pressurized hydraulic fluid to the first motor  114 . The first motor  114  is actuated to accelerate the eccentric shaft  202 . In other words, the eccentric shaft  202  is rotated. The eccentric shaft  202  accelerates to reach an operating frequency, for example, 65 Hz. As the eccentric shaft  202  reaches the operating frequency, the eccentric shaft  202  starts vibrating due to the first eccentric weight  226  and the second eccentric weight  228 . The vibrations of the eccentric shaft  202  are induced in the first vibrating mechanism  118 . The vibrations are imparted to the first roller  102  through the first vertical support  204  and the second vertical support  206  of the first vibrating mechanism  118 . The vibrations in the first roller  102  compacts the surface  122  below the vibratory compactor  100 . 
     Further, the operator actuates the second hydraulic pump  112 . The second hydraulic pump  112  supplies pressurized hydraulic fluid to the second motor  116 . The second motor  116  is actuated to rotate the first roller  102  and the second roller  104  in the desired direction. A rotation of the first roller  102  and the second roller  104  moves the vibratory compactor  100  in a reverse direction or a forward direction over the surface  122  to be compacted. Hence, the vibratory compactor  100  moves over the surface  122  while the first roller  102  is vibrating. Such vibration causes compacting action of the vibratory compactor  100 . In one embodiment, the second roller  104  can also include a similar vibrating mechanism and the operator may choose to actuate the vibrating mechanism of the second roller  104 . 
     In an exemplary embodiment of the present disclosure, the vibrations may be produced at the operating frequency of 65 Hz. While the eccentric shaft  202  is accelerating to reach the operating frequency of 65 Hz, the start-up time taken to attain the operating frequency of 65 Hz is about 4 seconds. The eccentric shaft  202  has a lesser moment of inertia, for example, 0.02836 kgm2. As a result of reduced moment of inertia of the eccentric shaft  202 , the start-up torque is substantially lesser. A lesser start-up torque in the proposed eccentric shaft  202  implies a lesser torque is required to initiate rotation of the eccentric shaft  202 . The lesser start-up torque of the eccentric shaft  202  decreases the operating costs and wear and tear of the first motor  114  and the first hydraulic pump  110  of the vibratory compactor  100 . Also, the proposed design for the eccentric shaft  202  has a reduced weight as compared to the weight of the existing eccentric shaft. 
     It should be understood that the above description is intended for illustrative purposes only and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure, and the appended claim.