Power tool with hammer mechanism

Abstract

A power tool (1) with a hammer mechanism, comprising a housing, a hollow spindle (3) disposed within the housing, a hammering unit (2) including a piston (4) reciprocally mounted within the spindle, and a swash plate drive unit (5) for reciprocatingly driving the piston, the swash plate drive unit comprising swash plate fingers (10) engaging a rear end of the piston, the piston including a through opening (12) at its rear end substantially perpendicular to a longitudinal axis of the piston, the free ends (13) of the swash plate fingers being directly received within the through opening of the piston, at least a portion of an outer surface of the free ends of the fingers contacting at least a portion of an inner surface of the through opening during reciprocating motion of the piston. Such a direct connection between the swash plate fingers and the drive piston minimizes the number of parts and reduces the complexity and cost of the assembly.

Description

[Technical field]

[0001] The present invention relates to hand-held power tools, and more particularly to power tools having a hammer mechanism. [Background technology]

[0002] Hand-held power tools, particularly rotary hammers and chisel hammers, are already known that include a hammer mechanism and a swashplate drive unit with a swashplate body and a piston. In the hammer, the swashplate drive unit is generally used to convert a rotary drive from a motor into a reciprocating drive for the piston. In the known arrangement, the rotary drive from the motor is transmitted to an intermediate shaft mounted in the hammer housing substantially parallel to the axis of the spindle. A swashplate sleeve is rotatably mounted on the intermediate shaft. The swashplate sleeve is formed with a swashplate race that extends around the swashplate sleeve at an oblique angle to the axis of the intermediate shaft. A bearing is set to operate between this inner race and an outer race of a swashplate ring. Swashplate fingers extend outwardly from the swashplate ring to engage the rear ends of the pistons.

[0003] It is well known that the swashplate finger reciprocates the piston through a trunnion arrangement, which generally includes a pair of spaced arms extending rearwardly of the body of the piston, and a cross bolt. Each arm has a through hole through which the cross bolt is received. A central portion of the cross bolt, located between the two arms, has a through hole through which the end of the swashplate finger remote from the swashplate ring extends. Two washers, one on each side of the swashplate finger, are often combined with the cross bolt to form the connection between the swashplate finger and the piston. This arrangement is very difficult to assemble, since the cross bolt must be rotationally and axially positioned. Also, the driving piston, swashplate and washers must be in the correct position. The high number of parts results in high costs. The cross bolt is typically made from steel, which significantly increases the mass being accelerated, leading to higher vibration and increased wear.

[0004] Summary of the Invention SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide a power tool having a hammer mechanism which is easy to assemble and which experiences reduced wear and tear.

[0005] According to the present invention, there is provided a power tool with a hammer mechanism, comprising a housing, a hollow spindle disposed within the housing, a hammering unit including a piston reciprocally mounted within the spindle, and a swash plate drive unit for reciprocatingly driving the piston, the swash plate drive unit including swash plate fingers engaging a rear end of the piston, the piston including a through opening at its rear end substantially perpendicular to a longitudinal axis of the piston, the free ends of the swash plate fingers being directly received within the through opening of the piston, at least a portion of an outer surface of the free ends of the fingers contacting at least a portion of an inner surface of the through opening during reciprocating motion of the piston. Such a direct connection between the swash plate fingers and the drive piston minimizes the number of parts and reduces the complexity and cost of the assembly.

[0006] In one embodiment, the through openings define elongated slots having lengths oriented along the longitudinal axis of the piston, the lengths of the elongated slots decreasing from the top and bottom surfaces of the piston, respectively, to its central axis, such that the through openings on the pistons provide a matching counter shape by defining elongated slots having varying lengths along the longitudinal axis of the piston relative to the rocking motion of the swashplate fingers.

[0007] In an advantageous embodiment, said free end of the swash plate finger is formed as a cylindrical shape, and the minimum length of the elongated slot is equal to or greater than the diameter of the free end. Such a cylindrical swash plate finger is easy to manufacture and assemble, and the elongated slot, which is longer than the diameter of the finger, allows the swash plate finger to swing in the through opening and drive the piston back and forth.

[0008] In an advantageous embodiment, the through opening comprises a front contact surface at a front end of the elongated slot and a rear contact surface facing the rear end of the elongated slot, the front contact surface or the rear contact surface being at least partially in contact with the free end of the swash plate finger during reciprocating motion of the piston, so that the contact between the swash plate finger and the piston is a "surface contact", which results in reduced wear compared to a line contact.

[0009] In an advantageous embodiment, both the front and rear contact surfaces are formed as an arc shape in a vertical cross section along the longitudinal axis of the piston, the two ends of the arc shape being respectively at the top and bottom surfaces of the piston, and the apex of the arc being at the central axis. The arc shape of the inner surface of the through opening reduces the risk of the swash plate fingers sticking when the swash plate fingers are driven back and forth like a pendulum swing.

[0010] In an advantageous embodiment, the front contact surface includes a first inclined surface inclined from the top surface toward the central axis and a second inclined surface inclined from the bottom surface toward the central axis, and the rear contact surface includes a third inclined surface inclined from the top surface toward the central axis and a fourth inclined surface inclined from the bottom surface toward the central axis.

[0011] In an advantageous embodiment, the inclination angles of the first to fourth inclined surfaces are the same and are equal to half the pendulum angle of the swash plate finger. The inclined contact surfaces coincide with the free ends of the swash plate fingers during the finger's swing, so that the driving force applied to the pistons is more uniform and wear between the pistons and the fingers is reduced.

[0012] In an advantageous embodiment, the front and rear contact surfaces are characterized in that they have a semicircular shape along the length of the elongated slot to receive said cylindrical free ends of the swashplate fingers, the contact surfaces of the through openings providing a contour that matches the cylindrical swashplate fingers, thereby further reducing wear therebetween.

[0013] In another embodiment, the through opening defines an elliptical hole having a length oriented in the direction of a longitudinal axis of the piston, the length of the elliptical hole decreasing from both the top and bottom surfaces of the piston to a central axis.

[0014] In an advantageous embodiment, said free ends of the swash plate fingers are formed in an olive shape, the minimum length of the elliptical hole being equal to or greater than the maximum diameter of the olive shape of the swash plate fingers, whereby the matching contour elliptical shape of the swash plate fingers and the through openings provides an alternative direct connection between the swash plate fingers and the pistons, reducing wear and losses.

[0015] In an advantageous embodiment, the inner surface of the elliptical hole is formed as a curved surface corresponding to the olive shape of the finger, and during the reciprocating movement of the swash plate finger, the free end of the swash plate finger partially contacts the inner surface of the elliptical hole in a surface contact relationship, whereby the surface contact relationship increases the load-bearing capacity and the wear resistance.

[0016] In a further embodiment, a power tool with a hammering unit comprises a housing, a hollow spindle arranged in the housing, a hammering unit including a piston reciprocally mounted in the spindle, and a swash plate drive unit for reciprocatingly driving the piston, the swash plate drive unit comprising a rotatably driven swash plate sleeve, the swash plate ring being mounted on the swash plate sleeve via a bearing arranged at an oblique angle to the longitudinal axis of the sleeve, the swash plate fingers extending outside the swash plate ring for engaging the piston, the piston including at its rear end a through opening substantially perpendicular to the longitudinal axis of the piston, an additional part being added on the swash plate fingers to be received in the through opening of the piston, at least a part of the outer surface of the additional part contacting at least a part of the inner surface of the through opening. By adding an additional part to the free end of the swash plate fingers, the load to be driven can be significantly increased and the power tool can be used for high-load operations.

[0017] An advantageous embodiment is characterized in that the through opening defines an elongated slot having a length oriented in the direction of the longitudinal axis of the piston, said elongated slot comprising a front contact surface at its front side and an opposing rear contact surface at its rear side, said contact surfaces being at least partially in contact with the outer surface of the additional part.

[0018] An advantageous embodiment is characterized in that the additional part is configured as a rectangular shape, the front contact surface and the rear contact surface being configured as a convex surface.

[0019] An advantageous embodiment is characterized in that the additional part is configured to be formed as an involute shape, with the front and rear contact surfaces being configured as substantially straight surfaces. The involute shape of the additional part on the finger is for creating a linear motion from a rotary motion, like a gear and a tooth rack. In the case of an involute tooth rack with a pressure angle of 0°, the geometry is a cylindrical hole, so the through hole is configured as a substantially straight line.

[0020] The present invention directly couples the swashplate fingers to the drive piston, thereby minimizing the number of parts and reducing the complexity and cost of the assembly. By judiciously selecting the geometry of the drive piston and swashplate fingers and choosing the appropriate material combination, wear and loss can be minimized. For very high loads and long life requirements, when a direct connection becomes overloaded, adding an additional part to the free end of the swashplate fingers increases the load-bearing capacity and wear resistance. [Brief description of the drawings]

[0021] Further features and advantages of the invention are explained in more detail below by way of example embodiments with reference to the drawings, in which: [Figure 1] 1 shows a partial schematic side view of a power tool with a hammering mechanism according to an embodiment of the present invention; [Diagram 2] 2 shows a partial schematic view of the connection between the swashplate fingers and the pistons according to the embodiment of FIG. 1. [Diagram 3]FIG. 3 shows a simplified partial schematic diagram of the connection between the swashplate fingers and the pistons according to the embodiment shown in FIGS. 1 and 2. [Figure 4] 13 shows a simplified partial schematic diagram of a swashplate finger and piston connection according to another embodiment of the present invention. [Diagram 5] 4 shows a simplified partial schematic diagram of a connection between the swashplate fingers and the pistons according to another embodiment of the present invention. [Figure 6] FIG. 2 shows a simplified partial schematic diagram of the connection of the swash plate fingers with additional parts and pistons. [Figure 7] 13 shows a simplified partial schematic diagram of the connection of the swashplate fingers with additional components and pistons according to yet another embodiment of the present invention.

[0022] In the drawings, like reference numbers are used to denote like parts throughout the various views. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Figure 1 shows a side view of a hand-held power tool 1 with a hammering unit 2 designed as a rotary hammer. The rotary hammer has a front part, shown in Figures 1 to 7, and a rear part incorporating a motor and a rear handle in a conventional manner. The rotary hammer comprises a housing (not shown), a hammering unit 2 comprising a hollow spindle 3 arranged in the housing, a hollow cylindrical piston 4 reciprocally mounted in the spindle 3, and a swash plate drive unit 5 for reciprocatingly driving the piston 4, the swash plate drive unit 5 comprising a rotatably driven swash plate sleeve 6, the swash plate ring 7 being mounted on the swash plate sleeve 6 via a bearing 9 arranged at an oblique angle to the longitudinal axis of the sleeve 6.

[0024] As best shown in Figures 1 and 2, the swash plate sleeve 6 is mounted on the intermediate shaft 8 and can rotate relative to the intermediate shaft. The swash plate sleeve 6 supports an inner race for a ball bearing 9 of the swash plate ring 7. The ball bearing 9 is mounted between the inner race and an outer race formed in the swash plate ring 7. The swash plate fingers 10 extend outwardly from the swash plate ring 7. Thus, when the swash plate sleeve 6 rotates, the free ends of the swash plate fingers 10, which are separated from the swash plate ring 7, are caused to reciprocate, thereby reciprocatingly driving the piston 4. During striking, the swash plate fingers 10 are driven to reciprocate back and forth by the swash plate drive unit 5, whereby the swash plate fingers 10 engage with the piston 4 to reciprocate the piston 4.

[0025] According to one embodiment of the invention, the piston 4 has a hollow cylindrical shape with a central axis 11 that runs along the longitudinal axis to the center of the cylindrical piston. The rear end of the piston 4 is solid cylindrical and a through opening 12 is arranged at the rear end of the piston 4. The through opening 12 passes through the rear end of the piston substantially perpendicular to the longitudinal axis, so that the top of the through opening is on the upper surface 17 of the circumferential surface of the cylindrical piston 4 and the bottom of the through opening is on the bottom surface 18 (closer to the swash plate ring 7) of the circumferential surface of the cylindrical piston 4. Although the current design is vertical, it is known that slight angles of the through opening are also feasible.

[0026] The swash plate fingers 10 include free ends 13 that are inserted into the through openings 12. Without other parts such as a trunnion arrangement including cross bolts, the swash plate fingers 10 directly contact the sides of the holes, making the assembly process much easier and significantly reducing costs due to the reduced part count.

[0027] In an advantageous embodiment, the free ends 13 of the swash plate fingers 10 are formed as a cylindrical shape. As shown in Figures 1 to 3, the cross section of the free ends of the swash plate fingers 10 is circular. Alternatively, the free ends 13 of the swash plate fingers 10 can be formed as a tapered shape or any other suitable shape. In general, any shape that has a circular cross section is feasible.

[0028] Preferably, the through opening 12 defines an elongated slot 14 having a length oriented in the direction of the longitudinal axis of the piston. Furthermore, the length of the elongated slot 14 decreases from both the top and bottom surfaces 17 and 18 of the piston, respectively, to its central axis 11. The minimum length of the elongated slot is equal to or greater than the diameter of the free end. This allows the free ends 13 of the swashplate fingers 10 to swing within the elongated slot 14.

[0029] The through opening 12 has at its front side a front contact surface 15 and at its rear side an opposing rear contact surface 16. The front contact surface 15 and the rear contact surface 16 at least partially contact the free ends of the swashplate fingers.

[0030] As best shown in FIG. 3, the front contact surface 15 includes a first inclined surface 151 inclined from the top surface 17 toward the central axis and a second inclined surface 152 inclined from the bottom surface 18 toward the central axis, and the rear contact surface includes a third inclined surface 161 inclined from the top surface 17 toward the central axis and a fourth inclined surface 162 inclined from the bottom surface 18 toward the central axis. Preferably, the inclination angles from the first inclined surface to the fourth inclined surface are the same and are equal to half the pendulum angle of the swash plate finger 10. When the swash plate finger 10 is in its forward most position, the swash plate finger contacts the first inclined surface 151 and the fourth inclined surface 162 simultaneously. When the swash plate finger 10 is in its rearmost position, the swash plate finger contacts the second inclined surface 152 and the third inclined surface 161 simultaneously. This helps to reduce wear of the swash plate drive unit and improve working stability.

[0031] According to an advantageous embodiment, both the front contact surface 15 and the rear contact surface 16 are formed as semicircular shapes along the length of the elongated slot 14 to receive the cylindrical or conical shape of the free ends of the swashplate fingers. The contact surfaces 15 and 16 of the through openings provide a contour that matches the cylindrical swashplate fingers. Thus, the swashplate fingers 10 come into contact with the front contact surface 15 and / or the rear contact surface 16 over a large area, driving the pistons to reciprocate more smoothly and with less wear.

[0032] Alternatively, as shown in Fig. 4, the front contact surface 15 and the rear contact surface 16 are both formed as a circular arc shape in a vertical cross section along the longitudinal axis of the piston, with the two ends of the circular arc shape being at the top and bottom surfaces of the piston respectively, and the apex of the circular arc being at the central axis 11. This changes the contact principle from surface contact to line contact, thereby reducing the wear of the swash plate fingers.

[0033] Figure 5 shows another embodiment of the invention. Different from the embodiment shown in figures 1 to 3, the through opening 10 is formed as an elliptical through hole with a length oriented in the direction of the longitudinal axis of the piston, the length of the elliptical hole decreasing from both the top and bottom faces of the piston to its central axis 11. In this case, the elongated slot 14 is elliptical rather than rectangular in shape at the top and bottom faces of the piston. On the other hand, the swash plate finger 10 is formed olive-shaped, the minimum length of the elliptical hole being equal to or greater than the maximum diameter of the olive shape of the swash plate finger. Thus, the front and rear contact surfaces have a counter shape that coincides with the swash plate finger.

[0034] Preferably, the inner surface of the elliptical hole is formed as a curved surface corresponding to the olive shape of the finger, and during reciprocation of the swashplate finger, the free end of the swashplate finger partially contacts the inner surface of the elliptical hole in a surface contacting relationship.

[0035] Figures 6 and 7 show another embodiment according to the invention, where in case of very high loads and high life requirements the direct connection between the swash plate fingers and the pistons becomes overloaded and the shape and geometry of the swash plate fingers and holes have to be modified to increase the load-bearing capacity. Compared to the power tool with hammering unit shown in Figures 1 to 4, the difference here is an additional part 20 added to the swash plate fingers 10, such that at least a part of the outer surface of the additional part 20 is in contact with at least a part of the inner surface of the through opening 12.

[0036] With reference to FIG. 6, here the add-on part 20 is formed with an involute shape, while the swash plate fingers are cylindrical pins inserted into the add-on part. Correspondingly, the through holes 12 are approximately straight. The add-on part 20 with an involute shape increases the load-bearing capacity. Essentially, the problem to be solved is to create a linear motion from a rotary motion, like a gear and a tooth rack. Therefore, any geometry that satisfies the basic laws of toothing can be used.

[0037] Now referring to Figure 7, in this further embodiment, the through opening 12 is similar to the through opening shown in the embodiment of Figures 1 and 2. However, the add-on part 20 added to the swash plate finger is rectangular in shape. Such a rectangular shaped add-on part is easy to assemble.

[0038] As materials, pressure-resistant materials such as steel are preferred, nevertheless, due to the low E-modulus of plastic materials, the contact surface can be increased (the parts flatten under pressure) and such materials can also be used.

[0039] While only selected embodiments have been chosen to illustrate the invention, it will be apparent to one skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Accordingly, the foregoing description of embodiments in accordance with the present invention is provided for illustrative purposes only and is not intended to limit the invention as defined by the appended claims and their equivalents.

Claims

1. 1. A power tool (1) with a hammer mechanism, comprising: a housing; a hollow spindle (3) disposed in the housing; a hammering unit (2) including a piston (4) reciprocally mounted within the hollow spindle (3); and a swash plate drive unit (5) for reciprocatingly driving the piston, wherein the swash plate drive unit (5) has a swash plate finger (10) engaging with the piston (4), the piston (4) including at its rear end a through opening (12) substantially perpendicular to a longitudinal axis of the piston (4), a free end (13) of the swash plate finger (10) being directly received in the through opening (12) of the piston (4), and at least a portion of an outer surface of the free end (13) of the swash plate finger (10) contacting at least a portion of an inner surface of the through opening (12).

2. 2. The power tool (1) of claim 1, wherein the through opening (12) defines an elongated slot (14) having a length oriented in the direction of the longitudinal axis of the piston (4), the length of the elongated slot (14) decreasing from the top and bottom faces (17) and (18), respectively, of the piston (4) to its central axis (11).

3. 3. The power tool (1) according to claim 2, wherein the free end (13) of the swash plate finger (10) is formed as a cylindrical shape and the minimum length of the elongated slot (14) is equal to or greater than the diameter of the free end (13).

4. 4. The power tool (1) according to claim 3, wherein the through opening (12) has a front contact surface (15) at a front end of the elongated slot (14) and a rear contact surface (16) facing a rear end of the elongated slot (14), the front contact surface (15) or the rear contact surface (16) at least partially contacting the free end (13) of the swash plate finger (10) during reciprocating motion of the piston (4).

5. 5. The power tool (1) according to claim 4, wherein the front contact surface (15) and the rear contact surface (16) are both formed as an arc shape in a vertical cross section along the longitudinal axis of the piston (4), the two ends of the arc shape being respectively on the top surface (17) and the bottom surface (18) of the piston (4), and the apex of the arc being on the central axis (11) of the piston (4).

6. 5. The power tool (1) according to claim 4, wherein the front contact surface (15) includes a first inclined surface (151) inclined from the top surface (17) toward the central axis (11) of the piston (4) and a second inclined surface (152) inclined from the bottom surface (18) toward the central axis (11) of the piston (4), and the rear contact surface (16) includes a third inclined surface (161) inclined from the top surface (17) toward the central axis (11) of the piston (4) and a fourth inclined surface (162) inclined from the bottom surface (18) toward the central axis (11) of the piston (4).

7. 7. The power tool (1) according to claim 6, wherein the inclination angles of the first inclined surface to the fourth inclined surface (151, 152, 161, 162) are the same and are equal to half the pendulum angle of the swash plate finger (10).

8. 8. The power tool (1) according to claim 7, wherein the front contact surface (15) and the rear contact surface (16) have a semicircular shape along the length of the elongated slot (14) for receiving the free end (13) of the swash plate finger (10).

9. 3. The power tool (1) according to claim 2, wherein the through opening (12) defines an elliptical hole having a length oriented in the direction of the longitudinal axis of the piston (4), the length of the elliptical hole decreasing from each of the top and bottom faces (17) and (18) of the piston to a central axis (11) of the piston (4).

10. 10. The power tool (1) according to claim 9, wherein the free ends (13) of the swash plate fingers (10) are formed in an olive shape, and the minimum length of the elliptical hole is equal to or greater than the maximum diameter of the olive shape of the swash plate fingers (10).

11. 10. The power tool (1) according to claim 9, wherein the inner surface of the elliptical hole is formed as a curved surface corresponding to the olive shape of the swash plate finger (10), and during the reciprocating motion of the piston (4), a free end (13) of the swash plate finger (10) partially contacts the inner surface of the elliptical hole in a surface contact relationship.

12. 1. A power tool (1) with a hammer mechanism, comprising: a housing; a hollow spindle (3) disposed in the housing; a hammering unit (2) including a piston (4) reciprocally mounted in the hollow spindle (3); and a swash plate drive unit (5) for reciprocatingly driving the piston (4), wherein the swash plate drive unit (5) has a swash plate finger (10) engaging with the piston (4), the piston (4) including a through opening (12) at its rear end, the through opening being substantially perpendicular to a longitudinal axis of the piston (4), and an additional part (20) received in the through opening (12) of the piston (4) is added on the swash plate finger (10), and at least a portion of an outer surface of the additional part (20) contacts at least a portion of an inner surface of the through opening (12).

13. 13. The power tool (1) according to claim 12, wherein the through opening (12) defines an elongated slot (14) having a length oriented in the direction of the longitudinal axis of the piston (4), the through opening (12) comprising a front contact surface (15) in front of the elongated slot (14) and an opposing rear contact surface (16) in the rear of the elongated slot (14), the front contact surface (15) or the rear contact surface (16) being at least partially in contact with an outer surface of the additional part (20) during reciprocating movement of the piston.

14. 14. The power tool (1) according to claim 13, wherein the additional part (20) is configured to be formed as a rectangular shape, and the front contact surface (15) and the rear contact surface (16) are configured to form a convex surface.

15. 14. The power tool (1) according to claim 13, wherein the additional part (20) is configured to be formed as an involute shape and both the front contact surface (15) and the rear contact surface (16) are configured to be formed as substantially straight surfaces.

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