Drive cap housing with improved noise attenuation

Abstract

The drive cap housing for a pile driver according to the invention is configured to be connected to a hammer device, which includes a striking head (20) configured to reciprocate in a striking direction. The drive cap housing comprises a drive cap (10) configured to receive the striking force of said striking head and to forward the striking force to a pile connected to the drive cap, a casing (30) enclosing said drive cap and extending in the striking direction of the striking head, into which casing said striking head is configured to enter when reciprocating in the striking direction and an attenuation assembly for attenuating vibrations propagating from the casing to the hammer device. Said attenuation assembly comprises at least two superimposed elastic damping layers (32a, 32b) separating the casing from the hammer device, when the drive cap housing is connected to the hammer device, which damping layers are made of a first material having a first modulus of elasticity.

Description

[0001] Drive cap housing with improved noise attenuation

[0002] Technical Field

[0003] The invention is related to a drive cap housing of a pile driver configured to be connected to a hammer device, which hammer device includes a striking head, a drive cap configured to receive the striking force of said striking head and to forward the striking force to a pile, a casing enclosing said drive cap and an attenuation assembly for attenuating vibrations propagating from the casing to the hammer device.

[0004] Background Art

[0005] When buildings and constructions are erected in areas, where the load bearing capacity of the soil is low, piling is often used to achieve sufficient bearing capacity for the foundations.

[0006] One factor limiting the application of piling is the fact that driving of piles by hammering into the soil causes relatively high noise, which can be found disturbing in the immediate surroundings, for example, in a residential neighborhood. In studies of noise caused by drive piling machines it has been disclosed, that the noise may rise above 100 dB in the vicinity of the pile driving machine during hammering of the pile into the soil.

[0007] A further factor to be considered in piling are empty strikes, or no-load strikes, when the hammer strikes but does not directly impact the pile. This may happen, if the pile penetrates to the ground more than a hard limit for movement of a drive cap positioned on a head of the pile. This can cause additional stress and wear to the shock absorption system, the hammer's attachments, or other structural parts of the machine, which absorb a striking force of the hammer instead of the pile. Such empty strokes can lead to premature wear and damage to the machine, which is why it is important to avoid them in pile driving operations.

[0008] Several attempts have been made to suppress the noise generated by the pile driving machine. Document WO2011 / 128490 A1 discloses a pile driving machine comprising a hammer device with a ram block and a drive cap housing enclosing a drive cap, which is configured to receive striking force from a reciprocation ram block and to forward the striking force to a pile connected to the drive cap. The machine comprises attenuation assembly between the hammer device and the housing and the housing has a sound suppressing layered structure for attenuating vibrations propagating from the housing. Although the pile driving machine disclosed WO2011 / 128490 A1 has managed to improve the noise suppression the of the machine, the generated noise level is still disturbing and may be even too high in some construction worksites.

[0009] An object of the invention is to provide pile driver, with which drawbacks relating to the prior art can be diminished.

[0010] The object of the invention is achieved with a pile driver, which is characterized in what is disclosed in the independent patent claims. Some preferred embodiments of the invention are disclosed in the dependent claims.

[0011] Summary of the invention

[0012] The drive cap housing for a pile driver according to the invention is configured to be connected to a hammer device, which hammer device includes a striking head configured to reciprocate in a striking direction. The drive cap housing comprises a drive cap configured to receive the striking force of said striking head and to forward the striking force to a pile connected to the drive cap, a casing enclosing said drive cap and extending in the striking direction of the striking head, into which casing said striking head is configured to enter when reciprocating in the striking direction and an attenuation assembly for attenuating vibrations propagating from the casing to the hammer device. Said attenuation assembly comprises at least two superimposed elastic damping layers separating the casing from the hammer device, when the drive cap housing is connected to the hammer device, which damping layers are made of a first material having a first modulus of elasticity.

[0013] In some embodiments of the drive cap housing according to the invention the attenuation assembly comprises one or more rigid bearing layers. Preferably, the one or more bearing layers are made of a second material having a second modulus of elasticity, which is significantly higher than the first modulus of elasticity.

[0014] In some embodiments of the drive cap housing according to the invention the one or more rigid bearing layers are alternated with the at least two superimposed elastic damping layers.

[0015] In some embodiments of the drive cap housing according to the invention at least one of said one or more rigid bearing layers of the attenuation assembly is a top layer towards the hammer device for serving as a shock absorber for hits from the striking head. In some embodiments of the drive cap housing according to the invention said attenuation assembly comprises a first opening through which the striking head is configured to enter to the casing, the first opening extending through each elastic damping layer and each bearing layer, the first opening having an edge surface configured to settle in contact with the side surface of the striking head, when the striking head is received inside the casing.

[0016] In some embodiments of the drive cap housing according to the invention the drive cap has an impact surface and the edge surface of the first opening is configured to steer the striking head towards said impact surface, when the striking head enters into the casing.

[0017] In some embodiments of the drive cap housing according to the invention at least one of the elastic damping layers comprises a rim portion, which is configured to be pressed against the side surface of the striking head, when the striking head is received inside the casing.

[0018] In some embodiments of the drive cap housing according to the invention the attenuation assembly further comprises one or more passages configured to support fluid flow from the casing to the hammer device and to attenuate propagation of sound waves from the casing to the hammer device through the one or more passages.

[0019] In some embodiments of the drive cap housing according to the invention the attenuation assembly further comprises groups of silencers arranged annularly to the first opening. Preferably the groups of silencers are arranged to positions that are outside of a projected landing area of the ram block on the attenuation assembly.

[0020] In some embodiments of the drive cap housing according to the invention said attenuation assembly comprises a first damping layer including said rim portion, and second bearing layer below the first damping layer, and the first opening of the second bearing layer has bevelled edge facing said rim portion.

[0021] In some embodiments of the drive cap housing according to the invention between each adjacent elastic damping layer and bearing layer there is a layer of adhesive material gluing said layers together.

[0022] In some embodiments of the drive cap housing according to the invention said elastic damping layers are made of rubber, neoprene or polyurethane. In some embodiments of the drive cap housing according to the invention said one or more bearing layers are made of metal, preferably steel.

[0023] In some embodiments of the drive cap housing according to the invention the attenuation assembly comprises two, three, four or five elastic damping layers and three, four, five or six bearing layers.

[0024] Some embodiments of the drive cap housing according to the invention have connecting means for connecting the drive cap housing to the hammer device.

[0025] In some embodiments of the drive cap housing according to the invention said connecting means comprise bolts and nuts and washers between the contact surfaces of the bolt or nut and the drive cap housing or the hammer device, which washers are made of elastic material, preferably polyurethane.

[0026] An advantage of the invention is, that it prevents airborne noise generated by the colliding striking head and drive cup from escaping from the casing through the first opening.

[0027] Further, the attenuation assembly centers the striking head in the middle of the first opening, which reduces the generation of structure-borne noise, when the striking head enters to the drive cap housing.

[0028] An advantage of an embodiment of the invention is, that it reduces the damages caused by the empty strokes.

[0029] Brief Description of the Drawings

[0030] In the following the invention will be described in detail, by way of examples, with reference to the accompanying drawings in which,

[0031] Fig. 1 a depicts an example of a drive cap housing according to the invention as a vertical cross section,

[0032] Fig. 1 b depicts an example of a vibration attenuation assembly for the drive cap housing depicted in fig. 1 a as a vertical cross section,

[0033] Fig. 1 c depicts the vibration attenuation assembly of fig. 1 b seen from above,

[0034] Fig. 1d depicts an example of a detail for a vibration attenuation assembly for the drive cap housing depicted in fig. 1 a as a vertical cross section, Fig. 1 e depicts an example of the vibration attenuation assembly of fig. 1 b with the detail of fig. 1d seen from above,

[0035] Fig. 1f depicts an example of a ram block of a hammer device,

[0036] Fig. 2a depicts a noise attenuation chamber detached from the drive cap housing as a vertical cross section,

[0037] Fig. 2b depicts a noise attenuation chamber of fig. 2a seem from above.

[0038] Detailed Description

[0039] In fig. 1 a an example of the drive cap housing according to the invention is depicted as a vertical cross section.

[0040] The drive cap housing is configured to be connected to a hammer device comprising a frame 16 and a ram block 18 inside the frame. To enable the connection the drive cap housing has connection means in form of bolts 22 and nuts 23 through which the housing can be attached to the flange 24 in the lower end of the frame. Between the contact surfaces of the bolt or nut and the drive cap housing and the hammer device there are washers 25 made of elastic material, preferably polyurethane. The purpose of the elastic wasters is to minimise the vibrations propagating from the casing to the hammer device via connection means. When the hammer device is in operation the hammer block is reciprocating up and down in a striking direction steered by guides (not shown) belonging to the frame. The reciprocating movement of the ram block is produced by means of gravity and by an actuator, which can be a double acting hydraulic cylinder, a pneumatic device, a combustion chamber or an electromechanical device. The hammer devices, for example, hydraulic hammers, pneumatic hammers, electric hammers and diesel hammers, are known as such with respect to their structure and working principle, so their structure and operation is not described in more in this context.

[0041] The drive cap housing comprises a drive cap 10 configured to receive the striking force generated by the reciprocating ram block and to forward, or transfer, the striking force to an object to be hammered, e.g. to a pile, whereby the object can be driven to the ground. The drive cap housing has a casing 30 enclosing the drive cap and extending in the striking direction of the ram block. The casing has a first end facing the hammer device and an opposing second end. In the first end of the casing there is a first opening 26, through which the striking head 20 of the ram block can enter into the casing for exerting the striking force to an impact surface 27, or a striking surface, or a top surface, of the drive cap 10 facing the striking head the drive cap 10. The impact surface may be provided by a first impact cushion 28 arranged on the side of the drive cap facing the striking head, i.e. on a top side of the drive cap, whereby the striking force may be communicated to the object to be hammered through the first impact cushion 28.

[0042] For connecting to the object to be hammered or a part of the object to be hammered, e.g. a pile head, the drive cap has a sleeve14 protruding from a second surface of the drive cap. The second surface of the drive cap is located on an opposite side of the drive cap, or a bottom side of the drive cap, with respect to the first surface of the drive cap and facing the object to be hammered, whereby the striking force may be communicated by the drive cap to the object to be hammered via the second surface. A second impact cushion 29 may be arranged on the second surface of the drive cap facing the object to be hammered, whereby the striking force may be communicated to the object to be hammered through the second impact cushion 29 on the second surface of the drive cap. The sleeve is configured to border a connecting recess 12, where the object to be hammered or the part of the object to be hammered may enter. The free edge of the sleeve has a funnel-like enlargement 15 for easing the insertion of the object to be hammered or the part of the object to be hammered into the connection recess. It should be noted that the first impact cushion 28 facing the striking head and the second impact cushion 29 facing the object to be hammered are optional. For example, for driving concrete piles both of the impact cushions may be used. However, in some cases, e.g. for driving steel piles to the ground, the first impact cushion 28 on top of the drive cap may be omitted or the second impact cushion 29 below the drive cap may be omitted, or the first and second impact cushions 28, 29 both on top of the drive cap and below the drive cap may be omitted.

[0043] The casing has a first end facing the hammer device and an opposing second end. In the first end of the casing there is an attenuation assembly configured to attenuate vibrations propagating from the casing 30 to the hammer device. The attenuation assembly is positioned between the casing and the hammer device and comprises superimposed elastic damping layers 32 and rigid bearing layers 34 and a first opening 26 through which the reciprocating striking head 20 can enter into the casing and exit from the casing during reciprocating movement of the ram block. It should be noted that the number and thicknesses of the elastic damping layers 32 and the rigid bearing layers 34 of the attenuation assembly may be adapted according to need. The rigid bearing layers 34 are alternated with the elastic damping layers 32. In this way structural rigidity of the attenuation assembly may be supported by the rigid bearing layers as well as dampening of vibrations may be provided by the dampening layers between the rigid bearing layers. In an example, the attenuation assembly comprises three to eight layers. In an example thickness and number of layers of the attenuation assembly may be adapted for providing sufficient damping of vibrations propagating from the casing to the hammer device and to absorb striking force from empty strikes. An example thickness of damping layer is 30 mm. Total thickness of the attenuation assembly may be from 50 to 150 mm, for example 60 to 150 mm, for example 60 to 130 mm, for example 100-130 mm. The bearing layers may be thinner than the dampening layers, thus thickness of each bearing layer may be less than thickness of an adjacent dampening layers.

[0044] At least in some embodiments, at least one of said rigid bearing layers 34 is a top layer towards the hammer device for serving as a shock absorber for hits from the striking head 20. In this way layers of the attenuation assembly below the top layer may be protected against hits from the striking head, if the striking head would be misaligned with the opening 26. In an example, resilience of the top layer against deformation or being broken by hits of the striking head may be increased compared with other layers of the attenuation assembly. In this way the top layer may protect the attenuation assembly against empty strikes, where the striking force of the hammer is exerted to the attenuation assembly instead of the pile. In an example, the resilience of the top layer against deformation or being broken by hits of the striking head may be increased by increasing thickness of the top layer, e.g. compared with rigid bearing layers that are positioned at lower layers of the attenuation assembly, and by selecting material of the top layer based on hardness and impact strength of the material, e.g. steel.

[0045] In an example, the first layer of the attenuation assembly, i.e. the top layer, may be attached detachably to the other layers, whereby in case the first layer has been deformed or broken by hits of the striking head, the first layer may be replaced by a new rigid bearing layer 34 without replacing further layers of the attenuation assembly or the whole attenuation assembly.

[0046] The construction of the attenuation assembly is explained in more detailed manner in examples of fig 1 b and fig. 1d. Some of the advantages of the superimposed elastic damping layers described herein include that stress caused by the empty strikes to the pile driver, vibrations from the casing to the hammer device and travelling of sound waves outside of the casing may be reduced, and the striking head of the hammer device may be steered to an impact surface at the drive cap.

[0047] The casing 30 enclosing the drive cap 10 is configured to support the drive cap gliding inside the casing in the striking directing, when the striking head 20 reciprocates inside the casing and strikes to the drive cap 10. The wall of the casing has a layered structure comprising an outer jacket 40, an inner jacket 42 and a vibration suppression layer 44 between the outer jacket and the inner jacket. The outer jacket and the inner jacket are in contact to each other only through the vibration suppression layer. In this way the inner jacket may be moved with respect to the outer jacket.

[0048] The vibration suppression layer 44 attaches the inner jacket 42 to the outer jacket 40, whereby the inner jacket may be moved in a direction that is parallel with the striking direction. In this way, when during piling the striking head 20 moves in the striking direction, enters the drive cap housing and touches, or strikes, the inner jacket, the inner jacket may be moved, whereby vibrations to the casing may be reduced.

[0049] The thickness of the vibration suppression layer is 30-80 mm, preferably 40-70 mm, most preferably 50-60 mm and the hardness of the vibration suppression layer is 50 in Shore A scale. Preferably, the vibration suppression layer is made of polyurethane. The inner and outer jackets are cylindrical elements, which are made of metal, preferably steel.

[0050] The outer jacket 40 has a first flange 46 at the first end of the casing 30 for connecting the casing to the hammer device through the vibration attenuation assembly. The vibration suppression layer 44 extends and is supported to first flange. Between the first flange and the first end edge of the inner jacket there is a first annular gap 49 filled with vibration suppression material. The vibration suppression material is between the outer jacket and the inner jacket and attaches the inner jacket to the outer jacket. Correspondingly, at the second end of the casing the outer jacket has a second flange 48 for connecting a noise attenuation chamber 50 detachably to the casing with mechanical fixing means. The vibration suppression layer extends and is supported to the second flange and between the second flange and the second end edge of the inner jacket there is also a second annular gap 51 filled with the vibration suppression material. The inner jacket is thus “floating” on vibration suppression layer, i.e. there is no contact with the inner jacket and the outer jacket except through the vibration suppression layer. When the hammer device is in operation, the impact force generated by the striking head causes deformations to the drive cap in the direction perpendicular to the striking direction. Further, when the drive cap glides inside the inner jacket, the friction between the inner jacket and outer surface of the drive cap acts to the inner jacket in the striking direction. All these forces acting on the inner jacket create vibrations to the inner jacket. The “floating” connection between inner jacket and vibration suppression layer, an adequate thickness of the vibration suppression layer and the gaps 49 separating the inner jacket from the first and second flanges contribute to minimize the propagation on the vibrations from the inner jacket to the outer jacket thus reducing the noise level generated during piling.

[0051] The noise attenuation chamber 50 is detachably connected to the second end of the casing with screws. The noise attenuation chamber has outer wall 60, a fixing flange 53 in the first end of the outer wall for connecting to the second flange of the casing and a bottom plate 76 in the second end of the outer wall. The bottom plate is provided with a fitting opening 52, through which the end of the pile to be hammered is configured to enter into the drive cap housing. The fitting opening is furnished with a sealing structure for surrounding the pile entered into drive cap housing. The sealing structure comprises at least two superimposed flexible gasket sheets 54, each gasket sheet including a hole (fig. 2a) for the pile to go through. The edges of the gasket sheets are clamped between four corner plates 74 and the bottom plate 76 of the noise attenuation chamber. The construction of the sealing structure is explained in more detailed manner in figures 2a and 2b.

[0052] The inner surface of the outer wall 60 of the noise attenuation chamber 50 is covered with an insulation layer 62. The insulation layer is made of material, which can absorb sound waves, i.e. the insulation layer is arranged into the chamber for improving the sound attenuation properties of the noise attenuation chamber. Preferably, the insulation layer is made of polyurethane.

[0053] The connection recess 12 of the drive cap 10 extending into the attenuation chamber is bordered by a protruding sleeve 14, which is surrounded by a sound insulation shell 64 filled with sound insulation material, preferably polyurethane. The inner surface of the insulation layer and the outer surface of the sound insulation shell are cylindrical and the outer diameter of the sound insulation shell is dimensioned to allow the movement of the sound insulation shell inside the noise attenuation chamber with minimum clearance between the facing inner and outer surfaces. Minimum clearance guarantees, that a minimum amount of sound waves can escape from the casing 30 into the noise attenuation chamber 50 through said clearance. The sound insulation shell 64 comprises two guiding grooves 68 extending in the striking direction on the outer surface of the sound insulation shell 64 and the drive cap housing comprises two guiding projections 70 extending into said guiding grooves. The guiding grooves, each enclosing a tip of one guiding projection, are placed on the opposite sides of the periphery of the sound insulation shell. Correspondingly, the guiding projections are placed on the outer surface of the casing, which is provided with holes, through which the tip of the guiding projection can protrude and enter into the guiding groove. The guiding grooves and projections are configured to allow the movement of the drive cap 10 inside the drive cap housing in the striking direction, but to prevent the rotation of the drive cap 10 inside the drive cap housing about the imaginary center line CL of the drive cap housing. Thus, the connection recess 12 and the fitting opening stay in a same position in relation to the imaginary center line. The guiding groove is dimensioned to be long enough to ensure, that the movement range of the drive cap in the striking direction is not limited by the guiding groove. The protruding tips of the guiding projections act as brackets supporting the drive cap 10 when the drive cap is in the lowermost position inside the casing.

[0054] In fig. 1 b the vibration attenuation assembly shown in fig. 1 a is depicted as a vertical cross section and in fig. 1 c the same vibration attenuation assembly of fig. 1 b seen from above. Fig. 1d depicts an example of a detail for a vibration attenuation assembly for the drive cap housing depicted in fig. 1 a as a vertical cross section and fig. 1 e depicts an example of the vibration attenuation assembly of fig. 1 b with the detail of Fig. 1d seen from above. The purpose of the vibration attenuation assembly is to prevent airborne noise generated by the colliding striking head and drive cup from escaping from the casing through the first opening 26. Further, the attenuation assembly centers the striking head in the middle of the first opening, which reduces the generation of structure-borne noise when the striking head enters into the drive cap housing.

[0055] The attenuation assemblies shown in figs 1a, 1 b, 1 c, 1d and 1 e comprise superimposed elastic damping layers 32a, 32b and rigid bearing layers 34a, 34b, 34c, where a rigid bearing layer is at a top, i.e. a first layer of the pile of superimposed elastic damping layers 32a, 3b and rigid bearing layers 34a, 34b, 34c towards the hammer device. Below the top layer one or more elastic damping layers and rigid bearing layers are alternated thereby forming a layer structure, where each damping layer is between a rigid bearing layer. The attenuation assemblies shown in figs 1 a, 1 b, 1 c, 1d and 1 e comprise two superimposed elastic damping layers 32a, 32b and three rigid bearing layers 34a, 34b, 34c separating the casing 30 from the hammer device. The attenuation assembly comprises a first damping layer 32a including a rim portion 38, and second bearing layer 34b below the first damping layer 32a and the first opening 26 of the second bearing layer 34b has bevelled edge facing said rim portion 38. Referring to the example of the attenuation assembly in fig. 1 b a first bearing layer 34a is on top of the first damping layer 32a, thereby forming a top layer of the attenuation assembly towards the hammer device. A third bearing layer 34c is below the second damping layer 32b at a bottom of the attenuation assembly and a second bearing layer 34b, is between the first and second damping layers.

[0056] Referring to the example of the attenuation assembly in fig. 1d, the ordering of the damping and bearing layers is different from the ordering described with fig. 1 b. In fig. 1 d, a first bearing layer 34a forms top layer of the attenuation assembly towards the hammer device similar to the attenuation assembly described with fig. 1 b. However, in fig. 1d the first damping layer 32a is arranged on top of a second bearing layer 34b at a bottom of the attenuation assembly. Second damping layer 32b is arranged below the first bearing layer 34a. Third bearing layer 34c is between the first damping layer 32a and the second damping layer 32b.

[0057] The damping layers 32a, 32b are made of elastic first material having a low modulus of elasticity, such as rubber, neoprene or polyurethane, whereas the bearing layers are made of hard second material having a high modulus of elasticity, such as steel. Thus, the modulus of elasticity of the bearing layer 34a, 34b, 34c material is significantly higher that the modulus of elasticity of the damping layer material. In an example the damping layers of polyurethane may have shore value of 50-70 at A scale and the damping layers of rubber may have a shore value of 60-65 at A scale.

[0058] In an example in accordance with at least some embodiments, at least one of the damping layers 32a comprises a rim portion 38, which is configured to be pressed against the side surface 36 of the striking head 20, when the striking head 20 is received inside the casing 30. Diameter of the opening at the damping layer that comprises the rim portion is smaller than the diameter of the opening at other layers of the attenuation assembly. In this way the rim portion attenuates sound waves from the drive cap housing to the hammer device. In an example in accordance with at least some embodiments, the damping layer 32a comprising the rim portion 38 may be polyurethane. In this way attenuation of the sound waves may be supported.

[0059] In an example in accordance with at least some embodiments, damping layers 32b of the attenuation assembly that are without a rim portion are of rubber and the damping layer 32a comprising a rim portion 38 may be polyurethane. In this way the attenuation of sound waves may be performed by the polyurethane layer which has better performance for attenuation of sound waves than rubber.

[0060] In an example, the elastic damping layers and bearing layers may be attached together non-detachably to form a solid body of the attenuation assembly. In this way individual elastic damping layers or bearing layers cannot be detached from the attenuation assembly for service of the attenuation assembly without breaking the body or individual layers of the body. In an example, the non-detachable attachment may be achieved by attaching facing layers of the attenuation assembly together by a layer of adhesive material which glues the facing layers together. In another example, the non-detachable attachment may be achieved by mold casting elastic dampening layers to alternate with bearing layers. On the other hand, at least a part of the elastic damping layers and bearing layers may be attached together detachably, whereby one or more of the damping layers and bearing layers can be detached from the attenuation assembly for servicing the attenuation assembly without a risk breaking the at least part of the layers of the attenuation assembly. In an example, the elastic damping layers and bearing layers may be attached together detachably by screws that attach two or more of the damping layers and bearing layers together. Accordingly, each layer may be attached to at least one other layer by screws at attachment positions on the layer. Attachment positions at facing layers may be offset with respect to one another for distributing the attachment positions such that attachment positions are not aligned between the facing layers in the striking direction. It should be noted that instead of attaching individual layers by screws, also all the layers may be attached together by screws.

[0061] The attenuation assembly comprises a first opening 26 through which the striking head 20 can enter into the casing and exit from the casing during reciprocating movement of the ram block. The first opening extends through both elastic damping layers and through all three bearing layers. Thus, the first opening on the attenuation assembly has an edge surface, which is a composition of edge surfaces of the first openings of the superimposed damping and bearing layers. Preferably, the first opening is circular. The center of the first openings in the damping and bearing layers lies in a same imaginary center line CL. The first damping layer 32a comprises a rim portion 38, or a lip, extending around the periphery of the first opening 26. The diameter of the first opening of the first damping layer is slightly smaller than the diameters of the first openings of the second damping layer and the bearing layers of the attenuation assembly.

[0062] The rim portion 38 of the first opening of the first damping layer 32a is dimensioned to settle in contact with the side surface 36 of the striking head 20 (fig. 1 a, fig. 1 e), when the striking head is received inside the casing 30. The surface of the rim portion facing the striking head is partly bevelled to ease the striking head to pass through tightly fitted first opening. Thus, the rim portion of the first damping layer, which forms a part of the edge surface of the first opening, acts a guiding element centering the striking head into the first opening and steering the striking head towards the impact cushion 28, when the striking head enters into the casing. The first opening of the second bearing layer 34b directly below the first elastic damping layer 32a has bevelled edge facing said rim portion. The bevelled edge allows the rim portion to bend downward towards the drive cap 10, when the striking head protrudes through the rim portion.

[0063] Position of the rim portion at the attenuation assembly may be adapted based on ordering of the elastic damping layers and rigid bearing layers of the attenuation assembly. The position of the rim portion affects a volume of fluid, e.g. air, entrapped within the drive cap housing, when the striking head is received through the first opening 26 inside the drive cap housing. During piling the volume of entrapped air should be managed for facilitating control piling e.g. stroke length, stroke frequency and temperature inside the drive cap housing. When the position of the rim portion is low, thus the rim portion is included to a dampening layer that is at a lowest position of the attenuation assembly in accordance with fig. 1 d, the volume of entrapped fluid is less than if the position of the rim portion is on a higher position at the attenuation assembly, for example at a highest position of the attenuation assembly in accordance with fig. 1 b.

[0064] In an example in accordance with at least some embodiments the attenuation assembly comprises one or more passages 39 configured to support fluid flow from the casing 30 to the hammer device and to attenuate propagation of sound waves from the casing 30 to the hammer device through the one or more passages 39. In this way propagation of sound waves from the drive cap housing to the hammer device may be attenuated while exhaust of the entrapped fluid may be provided. In an example, a silencer 35 may be installed to a passage for facilitating attenuation of the sound waves and letting the entrapped fluid out of the drive cap housing. The passage may be formed by adjacent dampening layers 32a, 32b and bearing layers 34a, 34b that have through-holes on top of each other. In an example at least one the dampening 32a, 32b layers and bearing layers 34a, 34b, 34c forming the passage may be configured to support the silencer within the passage. For example, a diameter of the hole through the bearing layer may be smaller than diameters of the other layers than for the passage, whereby silencer may be supported by edges of the hole of the bearing layer within the passage.

[0065] In an example shown in fig, 1e, in accordance with at least some embodiments, the attenuation assembly comprises groups of silencers 37 arranged annularly to the first opening 26. In this way the flow of fluid may be supported over the circumference of the first opening 26.

[0066] In an example, in accordance with at least some embodiments, the groups of silencers 37 are arranged to positions that are outside of a projected landing area of the ram block on the attenuation assembly. In this way the silencers may be provided at least two positions, for example three or four positions, whereby even distribution of the fluid flow may be supported while structural strength of the attenuation assembly is supported. In an example, the projected landing area of the ram block is an area on an upper surface of the attenuation assembly towards the hammer device. In case of an empty strike during piling, the striking head would be inside the opening 26, but the striking head would not hit the impact surface 27. In such case a body of the ram block above the striking head would strike the attenuation assembly. Since the silencers are outside of the projected landing area, the body of the ram block would not hit the attenuation assembly at the silencers. In an example, the projected landing area may be defined e.g. based on an envelope of the second end of the ram block 82. In an example, the area is on the surface of the attenuation assembly around the opening 26, where the striking head enters the drive cap housing. Therefore, a dimension of the projected landing area in a transverse direction with respect to the striking direction is larger than the diameter of the striking head or the diameter of the opening 26.

[0067] In an example the passage 39 may have a bottom opening that has a mouth 41 below the first damping layer 32a (fig. 1d). In this way the when the striking head has been received through the first opening 26 inside the drive cap and the striking head is in contact with the rim portion the entrapped fluid may flow out of the drive cap housing through the passage. In an example, the bearing layer 34b that is directly below the first elastic damping layer 32a may extend partially over the mouth 41 of the passage, whereby at least part of an edge of the mouth is supported by the bearing layer. The elastic damping layer may have a bevelled edge facing rim portion and the mouth of the passage, whereby fluid from the drive cap housing is guided by the bevelled edge into the mouth from a direction that is transverse with respect to the striking direction.

[0068] In an example the passage 39 may have a top opening that has a mouth 43 at the first bearing layer 34a towards the hammer device. In this way the entrapped fluid may flow out of the passage and enter the frame of the hammer device.

[0069] Fig. 1f depicts an example of a ram block of a hammer device. The ram block may be the ram block 18 in fig. 1 a. The ram block comprises a first end and a second that are separated in the striking direction 78 of the ram block. A striking head 20 is provided at a first end the ram block and at a second end the ram block is configured movable inside the hammer device. In an example, the second end may comprise connecting means 80 for connecting the ram block to an actuator for driving the ram block by the actuator in a reciprocating movement inside the frame 16. In an example, the second end may comprise guides 84 that extend in a longitudinal direction of the ram block for supporting movement of the ram block inside the frame in the striking direction 78. Examples of the connecting means comprises a loop. Examples of the actuators comprise hydraulic motors, pneumatic and electric motors that may be connected to exert a driving force to the ram block. In an example the second end of the ram block has a cross-section that substantially follows a rectangular envelope 82. The rectangular envelope may be defined by two sets of parallel sides 86 and corners that connect the sides. The guides may be arranged at the corners and they fall inside the defined rectangular envelope 81 . In an example, the first end of the ram block has a cross-section that substantially follows a circular envelope. The circular envelope may be defined by a circumference of the striking head. It should be noted that a diameter of the second end may be larger than the diameter of the striking head.

[0070] In fig. 2a the noise attenuation chamber 50 disclosed in fig. 1 is depicted as a vertical cross section and in fig. 2b the same the noise attenuation chamber is seen from above from the direction of the casing. In the figures the noise attenuation chamber is detached from the drive cap housing by unfastening the screws 72 connecting the second flange 48 of the casing 30 and the fixing flange 53 of the noise attenuation chamber. Removing the noise attenuation chamber can be reasonable for example in piling situations, where the end of the pile to be hammered is very close to the ground surface and the pile still needs to be hammered to achieve sufficient bearing capacity. When the noise attenuation chamber is removed, the drive cap housing can move closer to the ground surface, thus enabling few extra strikes to the pile end. Also, if the piling worksite is far away from the population center and noise generated during the piling work is not a problem, removing the attenuation chamber can be economically reasonable to minimize the wearing of the gasket sheets 54 of the sealing structure.

[0071] In the embodiment of the attenuation chamber shown in figs. 2a and 2b the sealing structure surrounding the fitting opening 52 comprises five superimposed flexible gasket sheets 54, each gasket sheet including a hole 56 for the pile to go through and slits 58 extending from the periphery of the hole 56 towards the edges of the fitting opening. The holes in the gasket sheets are smaller than the fitting opening, but thanks to the slits the holes can enlarge, when a pile end protrudes through the holes. Preferably, the holes in the gasket sheets are quadrangular or square, and the dimension of the holes match with the dimensions of the pile to be hammered at least when the holes are in enlarged size. The slits extending from the periphery of the hole are configured to provide sufficient enlargement capacity for the holes. Preferably, at least some of the slits extend substantially perpendicular from the periphery of the hole towards the periphery of the fitting opening.

[0072] The slits are arranged into the superimposed gasket sheets to minimize creation of open cracks extending through the sealing structure, through which cracks noise waves could propagate out of the attenuation chamber. Therefore, the sealing structure comprises at least a first gasket sheet 54a and an adjacent second gasket sheet 54b, wherein the slits 58 in the first and second gasket sheets 54a, 54b are not aligned. Preferably, the sealing structure comprises three, four or five gasket sheets and in each neighboring two gasket sheets the slits are not aligned. The slits are considered not to be aligned at least when the slits are not on top of each other. This can be achieved by an offset between slit positions at neighboring gasket sheets. On the upper surface of the pile of superimposed gasket sheets 54 there are four corner plates 74 made of steel, which cornet plates are attached to the bottom plate 76 with screws (not shown) extending through the gasket sheets. Thus, the edges of the gasket sheets are clamped between the corner plates and the bottom plate. Friction acting between the contact surfaces of the gasket sheets and the hammered piles causes wearing, why the gasket sheets must be replaced from time to time. Thanks to the detachable screw engagement of the sealing structure worn gasket sheets can be easily removed and replaced. In the embodiment of the attenuation chamber shown in figs. 2a and 2b the sealing structure surrounding the fitting opening 52 is a layered structure comprising five layers, wherein each layer includes only one gasket sheet 54. In some embodiments of the attenuation chamber at least one layer of the layered sealing structure com- prises a plurality gasket sheets 54, which gasket sheets are configured to create a hole 56 for the pile to go through and slits 58 extending from the periphery of the hole 56 towards the edges of the fitting opening 52, when the plurality of the gasket sheets of the layer are placed around the fitting opening. The number of the layers of the layered sealing structure may be 2, 3, 4, 5, 6, or more than 6 and the number of the gasket sheets in each layer may be 1 , 2, 3, 4, 5, or more than 5.

[0073] When the pile drive is in operation the end of the pile being hammered is inside the attenuation chamber and the striking force generated by the striking head is forwarded to the end of the pipe via the drive cap. Each impact force forwarded to the pile end generates airborne noise. The purpose of the sealing structure is to prevent the airborne noise escaping from the attenuation chamber 50 through the fitting opening 52.

[0074] Some preferred embodiments of the drive cap housing has been disclosed above. The invention is not limited to the solutions explained above, but the invention can be applied in different ways within the limits set by the patent claims.

[0075] Reference Signs: 43 mouth at top opening

[0076] 44 vibration suppression layer

[0077] 10 drive cap 46 first flange

[0078] 12 connection recess 48 second flange

[0079] 14 sleeve 49 first annular gap

[0080] 15 enlargement 50 noise attenuation chamber

[0081] 16 frame 51 second annular gap

[0082] 18 ram block 52 fitting opening

[0083] 20 striking head 53 fixing flange

[0084] 22 bolt 54 gasket sheet

[0085] 23 nut 54a first gasket sheet

[0086] 24 flange 54b second gasket sheet

[0087] 25 washer 56 hole

[0088] 26 first opening 58 slit

[0089] 27 impact surface 60 outer wall

[0090] 28 first impact cushion 62 insulation layer

[0091] 29 second impact cushion 64 sound insulation shell

[0092] 30 casing 68 guiding groove

[0093] 32a first damping layer 70 guiding projection

[0094] 32b second damping layer 72 screw

[0095] 34 bearing layer 74 corner plate

[0096] 34a first bearing layer 76 bottom plate

[0097] 34b second bearing layer 78 striking direction

[0098] 34c third bearing layer 80 connecting means

[0099] 35 silencer 81 envelope of the first end of the

[0100] 36 side surface ram block

[0101] 37 silencer group 82 envelope of the second end of

[0102] 38 rim portion the ram block

[0103] 39 passage 84 guide

[0104] 40 outer jacket 86 side

[0105] 41 mouth at bottom opening CL center line

[0106] 42 inner jacket

Claims

Claims1 . A drive cap housing for a pile driver, which drive cap housing is configured to be connected to a hammer device, which hammer device includes a striking head (20) configured to reciprocate in a striking direction, comprising- a drive cap (10) configured to receive the striking force of said striking head (20) and to forward the striking force to a pile connected to the drive cap (10),- a casing (30) enclosing said drive cap (10) and extending in the striking direction of the striking head (20), into which casing (30) said striking head (20) is configured to enter when reciprocating in the striking direction and- an attenuation assembly for attenuating vibrations propagating from the casing (30) to the hammer device, characterised in that said attenuation assembly comprises at least two superimposed elastic damping layers (32a, 32b) separating the casing (30) from the hammer device, when the drive cap housing is connected to the hammer device, which damping layers (32) are made of a first material having a first modulus of elasticity.

2. A drive cap housing according to claim 1 , characterized in that the attenuation assembly further comprises one or more rigid bearing layers (34a, 34b, 34c).

3. A drive cap housing according to claim 2, characterized in that the one or more bearing layers (34a, 34b, 34c) are made of a second material having a second modulus of elasticity, which is significantly higher than the first modulus of elasticity.

4. A drive cap housing according to claim 2 or 3, characterized in that the one or more rigid bearing layers (34a, 34b, 34c) are alternated with the at least two superimposed elastic damping layers (32a, 32b).

5. A drive cap housing according to claim 2 to 4, characterized in that at least one of said one or more rigid bearing layers (34a, 34b, 34c) of the attenuation assembly is a top layer towards the hammer device for serving as a shock absorber for hits from the striking head (20).

6. A drive cap housing according to any of the claims 1 to 5, characterized in that said attenuation assembly further comprises a first opening (26) through which the striking head is configured to enter to the casing (30), the first opening (26) extending through each elastic damping (32) layer and each bearing layer (34), thefirst opening (26) having an edge surface configured to settle in contact with the side surface (36) of the striking head (20) , when the striking head (20) is received inside the casing (30).

7. A drive cap housing according to claim 6, characterized in that, the drive cap has an impact surface (27) and the edge surface of the first opening (26) is configured to steer the striking head (20) towards said impact surface (27), when the striking head (20) enters into the casing (30).

8. A drive cap housing according to any of the claims 1 to 7, characterized in that at least one of the elastic damping layers (32a, 32b) comprises a rim portion (38), which is configured to be pressed against the side surface (36) of the striking head (20), when the striking head (20) is received inside the casing (30).

9. A drive cap housing according to any of the claims 1 to 8, characterized in that the attenuation assembly further comprises one or more passages (39) configured to support fluid flow from the casing (30) to the hammer device and to attenuate propagation of sound waves from the casing (30) to the hammer device through the one or more passages (39).

10. A drive cap housing according to any of the claims 1 to 9, characterized in that the attenuation assembly further comprises groups of silencers (37) arranged annularly to the first opening (26).

11. A drive cap housing according to claim 10, characterized in that the groups of silencers (37) are arranged to positions that are outside of a projected landing area of the ram block on the attenuation assembly.

12. A drive cap housing according to any of claims 6 to 11 , characterized in that said attenuation assembly comprises a first damping layer (32a) including said rim portion (38), and second bearing layer (34b) below the first damping layer (32a), and the first opening (26) of the second bearing layer (34b) has bevelled edge facing said rim portion (38).

13. A drive cap housing according to any of the claims 2 to 12, characterized in that between each adjacent elastic damping layer (32a, 32b) and bearing layer (34a, 34b, 34c) there is a layer of adhesive material gluing said layers together.

14. A drive cap housing according to any of the claims 2 to 13 characterized in that said elastic damping layers (32a, 32b) are made of rubber, neoprene or polyurethane.

15. A drive cap housing according to any of the claims 2 to 14 characterized in that said one or more bearing layers (34a, 34b, 34c) are made of metal, preferably steel.

16. A drive cap housing according to any of the claims 2 to 15, characterized in that the attenuation assembly comprises two, three, four or five elastic damping layers (32a, 32b) and three, four, five or six bearing layers (34a, 34b, 34c).

17. A drive cap housing according to any of the claims 1 to 16 characterized in that it has connecting means for connecting the drive cap housing to the hammer device.

18. A drive cap housing according to the claim 17, characterized in that said connecting means comprise bolts (22) and nuts (23) and washers (25) between the contact surfaces of the bolt (22) or nut (23) and the drive cap housing or the hammer device, which washers (25) are made of elastic material, preferably polyurethane.

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