AN ECCENTRIC ELEMENT

Abstract: An eccentric element for generating oscillations in ground vibrators. The eccentric element comprises an eccentric mass (2) radially movable on a rotatable shaft (1), said mass being enabled to assume a position displaced in relation to the centreline (15) of the shaft when the shaft (1) is rotated, thus causing the amplitude of the generated oscillation to be changed. To enable control of the amplitude, the eccentric mass (2) is lockable by means of a displaceable locking piston (9) arranged in a recess (16) in the rotating shaft (1). The locking piston (9) can thus assume a position entirely thrustback into the recess (16), wherein the eccentric mass (2) is released, or a thrustout position in which the locking piston fixes the eccentric mass (2) in one of its end positions.

Description: An eccentric element The invention relates to an eccentric element for ground vibrators, said element including a radially movable eccentric mass arranged on a rotatable shaft, and which can be caused to assume a position displaced in relation to the centreline of the shaft as a result of the rotation of said shaft. It is often desirable to use the same ground vibrator, e.g. a vibrating roller, for compacting different types of paving material. However, since compacting of stone paving, for. example, will be more effective if compaction is performed with an applied oscillation of higher ampli¬ tude and lower frequency than for asphalt paving, ground vibrators intended for such a wide range of uses should be provided with the possibility of changing the ampli¬ tude and frequency of the oscillation. In such cases, the amplitude can be changed by providing radially displaceable eccentric masses on a rotating shaft. So that the amplitude will not be changed during starting and stopping, or forward and reverse traversing, the position of the eccentric mass should be independent of the frequency of the shaft as well as its direction of rotation, otherwise depressions can easily occur when rolling asphalt paving, for example. It is already known to dispose an eccentric mass displace- ably and lockably in a cylindrical chamber. The displace¬ ment is provided by a hydraulic liquid acting on the eccentric mass formed as a piston sealing tightly against the cylinder wall, the position of the mass in the cylinder being determined by the quantity of liquid pumped in. The position of the eccentric mass is thus independent of both frequency and direction of rotation. Ground vibrators with OMPI /,, IPO <. eccentric elements of the kind mentioned will be compli¬ cated and expensive, however, since a separate hydraulic system is required for operating the piston, furthermore the packings in the system are subjected to large stresse and therefore they often leak and give inexact positionin It is also known to arrange two radially displacable eccentric masses mutually lockable with the aid of a solenoid or locking pin. The eccentric masses are not commonly lockable however, but are kept in their rest pos tion by a spring means which is dimensioned such that the centrifugal force overbalances at a certain rotational speed, one or both eccentric masses thus assuming a dis¬ placed position. This eccentric apparatus will also be relatively complicated, and the electrical or mecanical locking device will be subjected to large stresses due to shaking or vibration. The present invention has the object of providing an eccentric element suitable for ground vibrators, and in¬ cluding a lockable eccentric mass, the displacement of which is independent of the direction of rotation and is not altered by alterations in speed of rotation, and whic is also not burdened by the disadvantages accompanying th known eccentric elements mentioned. The eccentric element in accordance with the invention includes an eccentric mass disposed radially movable on a rotatable shaft. Due to the rotation of the shaft, the mass can be caused to assume a position, displaced in relation to the centreline of the shaft. What is particu¬ larly characteristic for the invention is that the eccent ric mass is lockable in its end positions by the action o a displaceable locking piston arranged in a recess in the rotating shaft and which can be controlled to assume a position thrust completely into the recess, the eccentric mass thus being released, or a thrust-out position in OMP which the locking piston fixes the eccentric mass in one of its end positions. The invention is described in the following while referring to the appended drawings. Figure 1 is a longitudinal section through a rotating shaft provided with an. eccentric element in accordance with the invention, wherein the eccentric mass is arranged in a closed liquid-filled space and is locked in its inner position close to the centre¬ line of the shaft. Figure 2 illustrates the same eccentric element with the eccentric mass locked in its outer dis¬ placed position. Figures 3 and 4 illustrate another embodi¬ ment of the invention in corresponding positions, the eccentric mass being urged by a return spring. In the same way, Figures 5 and 6 illustrate a further embodiment. In this case the eccentric mass is arranged for displacement in a cylindrical through-hole. The same reference numbers have been used for designating corresponding parts in the different embodiments. The eccentric element according to Figures 1 and 2 is. thus disposed on a rotating shaft 1 and includes a movable eccentric mass 2 in a cylinder part 3. The cylinder part is defined by the cylinder wall 4 as well as lower and upper defining surfaces 5 and 6, respectively. The eccentric mass is formed as a piston with a cross section corresponding to that of the cylinder. A groove 7 is made round the circumference of the piston and a through-hole 8 in its longitudinal direction. A recess 16 is made in the rotating shaft 1, for a locking piston 9, which is urged by a helical spring 10 to assume a position pro- jecting into the cylinder 3. The locking piston is formed with a central, projecting boss 11 adapted for maintaining the eccentric mass in its outwardly thrust position (Figure 2) . A hole 12 is made along the centre of the shaft 1 for supplying hydraulic liquid to the groove 7 and the cylinder " RE A IΓ rτ.T from a rotatable shaft coupling at the end of the shaft. A fixed eccentric weight 13 is further arranged on the shaft 1. The function of the eccentric element will now be describ In the position illustrated in Figure 1, the centre of gravity 14 of the eccentric mass 2 is situated at a small distance from the centreline 15 of the rotating shaft. When the shaft 1 rotates, an oscillating movement of larg amplitude occurs as a result of the eccentrically arrange mass 13. Centrifugal force acts on the eccentric mass 2 with a radial, outwardly directed force, but since the locking piston 9 engages in the groove 7, the eccentric mass 2 is retained in its inward position. If it is now desired to decrease the amplitude, the locking piston mus be withdrawn so that the eccentric mass 2 can be thrust out by the rotation towards the upper limiting surface 6 of the cylinder 3, the resultant eccentric moment of the fixed mass 13 and the movable eccentric mass 2 decreasing To achieve this, the pressure in the hydraulic liquid is increased via the communication 12 by a hydraylic pump. The liquid pressure will thrust back the locking piston 9 and the eccentric mass will be thrust out to its outward position according to Figure 2. The liquid pressure is subsequently decreased so that the piston 9 is urged against the eccentric mass 2 by the spring 10, the boss 11 thrusting in under the eccentric mass 2 and keeping it locked in its outer position. During movement of the eccentric mass, the hydraulic liquid flows through the hole 8, and movement of the eccentric mass can be dampene to a desirable degree by suitable adjustment of the size of the hole. The reverse setting from the position with low amplitude (Figure 2) to the position with high ampli¬ tude (Figure 1) takes place by stopping rotation, whereat the eccentric element assumes the position shown in Figures 1 and 2 with the larger fixed eccentric weight 13 situated bottommost. The hydraulic liquid pressure is thereafter increased so that the locking piston 9 is thrust into the recess 16, and the eccentric mass 2 falls down towards the lower defining surface 5 by gravity. The pressure is subsequently decreased and the locking piston 9 assumes the position where it is thrust into the groove 7. In the embodiment according to Figures 3 and 4, a spring 17 is arranged between the eccentric mass 2 and the lower defining surface 5 of the cylinder. The eccentric element in this embodiment gives the lesser amplitude when the eccentric mass 2 is situated near the centreline 15 (Figure 3) , whereas the higher amplitude is achieved when the eccentric mass has assumed its displaced position (4) . When the eccentric element is stationary, the eccen¬ tric mass 2 is urged towards the upper defining surface 6 of the cylinder by the action of the spring.17. The locking piston, which is operated in the same way as the previous embodiment, can thus engage in the groove 7. When the position with the higher amplitude is desired, the locking piston 9 is thrust back and the eccentric mass 2 is thrust out towards the lower defining surface 5, the spring 17 being compressed. When the eccentric mass has assumed its position (see Figure 4) , the locking piston can coact lockably with the eccentric mass by means of the boss 11. Setting in the opposite direction takes place by the rotation of the shaft 1 being caused to diminish such that the spring 17 can urge the eccentric mass 2 towards the upper defining surface 6 when the locking piston 9 is thrust back. In the embodiment according to Figures 5 and• 6, the eccentric mass 2 is movable in the cylinder 3, which is formed here as a cylindrical hole through the shaft 1 and the fixed eccentric mass 13. To limit the movement of the OMPI eccentric mass 2, it is formed with stops 18, 19, of which the one 19 has been given a greater mass, so that the centre of gravity 14 of the eccentric mass 2 can thus be given the desired position in relation to the centreline 15 of the rotating shaft 1. The locking pisto 9 is arranged in a recess in the shaft 1 and is kept in its thrust-back position in the recess by a spring 20. Hydraulic pressure can be supplied to the locking piston 9 via a hole 12 in the shaft.1, for moving it out to its locking position. In order to lock, the locking piston engages in one of t two grooves 21, 22 made on the eccentric mass 2. In the position according to Figure 5, the eccentric mass 2 is locked in its inwardly-thrust position with the centre o gravity 14 situated close to the central axis 15. An oscillation of high amplitude occurs in this position wh the shaft 1 is rotated, due to the effect of the fixed eccentric weight 13. If a setting to an oscillation with lower amplitude is desired, the exterior hydraulic pressure on the locking piston must be lowered so that the spring 20 can urge the locking piston back into its recess. The eccentric weight is then thrust by centrifug force to its displaceable position with the centre of gravity 14 situated at a greater distance from the centr axis 15 (Figure 6) . In this position the hydraulic press is once again increased on the locking piston 9, which i thrust into engagement with the groove 21. The reverse setting from high to low amplitude takes place by stoppi rotation and thrusting the locking piston back, the eccentric mass 22 falling into its inner position by the action of gravity. The invention is naturally not limited to the embodiment illustrated, and a plurality of variations are conceiv¬ able within the scope of the patent claims. It is thus f- OM also possible to control the locking piston in other ways than hydraulically, e.g. mechanically or electric¬ ally. It should be further emphasized that the cross- sectional surface of the cylinder does not need to be circular but can be of optional form, and that the form and operation of the locking piston in the embodiments according to Figures 1-4 can be as for the embodiment illustrated in Figures 5-6. OREXT OMPI

Claims: AMENDED CLAIMS (received by the International Bureau on 14 November 1980 (14.11.80)) mended) 1. An eccentric element intended for ground vibrators, said element including a radially movable eccentric mass (2) arranged on a rotatable shaft (1) , said mass being enable to assume an inward position and as a result of the rotation of the shaft an outward position in which the distance between the centre of gravity (14) of the eccentr mass and the centreline (15) of the rotating shaft is larg than in the inward position, c h a r a c t e r i z e d i that the eccentric mass (2) is lockable in both its inward 10 and outward position by the action of a displaceable locki piston (9) arranged in a recess (16) in the rotating shaft (1) , and which can be manoeuvered to assume a position entirely thrust back into the recess (16) wherein the eccentric mass (2) is released, or a thrust-out position 15 in which the locking piston (9) locks the eccentric mass. ( in its inward or outward position enabling the eccentric mass to be in its position independent of the speed of ro¬ tation of the shaft (1) . 2. An eccentric element as claimed in claim 1, 20 c h a r a c t e r i z e d i n that the eccentric mass (2) is movable in a cylinder (3) substantially at right angles to the rotatable shaft (1) , the recess .(16) for the locking piston (9) being made in the cylinder wall (4) (Amended) 3. An eccentric element as claimed in claim 1 or 2, 25 c h a r a c t e r i z e d i n that the eccentric mass (2) is formed with a groove (7) round its periphery, in which the locking piston (9) engages for locking the eccentric mass (2) in its inward position. 4. An eccentric element as claimed in any of the 30 preceding claims, c h a r a c t e r i z e d i n that the cylinder (3) and lower as well as upper defining surfaces (5) and (6) , respectively, form a closed, liquid-filled space and that the eccentric mass (2) is formed as a piston movable in said space. 5. An eccentric element as claimed in claim 4, c h a r a c t e r i z e d i n that the eccentric mass (2) is provided with a through-hole (8) in the direction of movement, liquid flowing through the hole (8) on movement of the eccentric mass (2) . (Amended) 6• An eccentric element as claimed in claim 4 or 5, 10 c h a r a c t e r i z e d b y a boss (11) formed on the locking piston (9) lockably coacting with one end surface of the eccentric mass (2) when the eccentric mass (2) is in its outward position, and that the liquid in the space can be put under pressure, the locking piston (9) then 15 being thrust back into the recess (16) for liberating the eccentric mass (2) . 'Amended) 7. An eccentric element as claimed in any of claims 4-6, c h a r a c t e r i z e d i n that a spring (17) is arranged in the liquid-filled space, said spring 20 urging the eccentric mass (2) in a direction towards the centreline. 8. An eccentric element as claimed in claim 1 or 2, c h a r a c t e r i z e d i n that the eccentric mass (2) is formed with two grooves (21, 22) round its 25 periphery, one for each respective locking position, the locking piston (9) engaging in either of these grooves (21, 22) when the eccentric mass (2) is locked, and that a spring means (20) is arranged to urge the locking piston (9) to assume the position thrust back into the cylinder 30 wall, and that an outside force must be applied to the locking piston (9) to cause it to assume the thrust-out locking position. _ STATEMENTUNDERARTICLE19 In the claims the following amendments have been made The positions of the eccentric mass are now called inward and outward and a definition is also made to declare what we mean by these positions. In claim 1 we have also made clear that the eccentric mass is lockable in both its inward and outward position enablinfa the eccentric mass to be in its position in¬ dependent of the speed of rotation of the shaft (1) . These amendments are for example supported in the basic documents on p 4, line 13 and line 22, p 6, lines 12-25 and p 2 lines 17-23.

Inventors: STURESSON R
Applicants: STURESSON R
Application year: 1980
Main classification: E02D3
IPC codes: B06B1, E01C19, E02D3