SE2330243A1 - Power tool comprising a hydraulic pulse unit - Google Patents

Abstract

The present specification relates to a power tool comprising a motor, an output shaft (10), and a hydraulic pulse unit (20) including an inertia drive member (21) connected to the motor and rotatable about a rotation axis, an oil chamber (26) enclosed in the inertia drive member and impulse generating means arranged to transfer intermittently kinetic energy to an impulse receiving portion (11) of the output shaft received within the oil chamber, the power tool further comprising a front bearing (30) arranged on the output shaft to support the output shaft rotatably with respect to the housing. Wherein the output shaft and the front bearing form a front bearing shaft assembly (40) and wherein a rolling arrangement (50) is provided between the front bearing shaft assembly and the inertia drive member to provide a rolling contact there between.

Description

Technical field The present invention generally relates to power tools for tightening of threaded fasteners, more particularly to impulse type power tools having a hydraulic pulse unit.

Technical Background Electrical power tools for tightening are known to be used in various industries. For example, power wrenches ofthe impulse type comprising hydraulic pulse units are commonly used for continuous heavy production.

The hydraulic unit of such tools is filled with oil. ln such pulse tools, torque pulses may be delivered to the output shaft by means of a pulse generating mechanism dividing a fluid chamber into a low pressure side and a high pressure side, where fluid may flow between the sides during operation.

Such flows of fluid are however often associated with losses, and hence have a large effect on the efficiency of the pulse tool. ln order to alleviate some ofthe problems solutions have been proposed comprising various designs and combinations of fluid paths and/ or valves arranged to reduce losses related to these fluid flows. ln addition to losses associated with fluid flows in the tools, losses also occur due to friction between the various components between which relative movements occur.

Hence, there exists a need for improvement in the field of power tools comprising hydraulic pulse units.

Summary of the invention Accordingly, it would be desirable to provide a power tool where losses, for example due to friction, are lowered. ln particular, it would be desirable to provide an improved pulse tool in a compact and durable manner. To better address one or more of these concerns a power tool according to independent claim 1 is provided. Preferred embodiments are defined in the dependent claims.

According to a first aspect ofthe invention a power tool comprising a motor, an output shaft, and a hydraulic pulse unit including an inertia drive member connected to the motor and rotatable about a rotation axis, an oil chamber enclosed in the inertia drive member and impulse generating means arranged to transfer intermittently kinetic energy to an impulse receiving portion of the output shaft received within the oil chamber, the power tool further comprising a front bearing arranged on the output shaft to support the output shaft rotatably, wherein the output shaft and at least a portion of the front bearing form a front bearing shaft assembly and wherein a rolling arrangement is provided between the front bearing shaft assembly and the inertia drive member to provide a rolling contact there between.

According to the first aspect, the power tool (or impulse tool, pulse tool, power wrench or tightening tool, these terms are used interchangeably throughout the present specification) provides an inventive solution to the concerns described above by means of a design incorporating a rolling interface provided between the front bearing haft assembly and the inertia drive member.

More particularly, the design having a rolling arrangement provided between the front bearing assembly and the inertia drive member provides for a reduction of friction losses in the pulse unit during pulsing and hence the efficiency of the power tool is improved.

By provided, or arranged, between should be understood that the rolling arrangement, or interface, is arranged to mitigate friction between the front bearing shaft assembly and the inertia drive member. This could be achieved for example by arranging the rolling interface directly between the output shaft and the inertia drive member and/or between any component arranged to co-rotate with the output shaft and inertia drive member respectively during pulsing i.e. between parts between which relative rotation occurs as the pulse tool operates providing pulses. During run-down, i.e. the phase of the tightening where the fastener is seated and only a low torque is applied preceding the pulsing-phase where torque generated by the pulse generating unit is applied to the threaded fastener to actually tighten it (to target), the output shaft and inertia drive member co-rotate.

The front bearing shaft assembly may in some embodiments be described as including the components attached to the output shaft, and hence moving along with or co- rotating with the output shaft during pulsing. ln one embodiment, the front shaft bearing assembly is formed by the output shaft and a portion ofthe front bearing arranged on, and co-rotating with, the output shaft, for example an inner ring of the front bearing for the case where the front bearing is a ball bearing comprising an inner and an outer ring. ln some embodiments, the rolling arrangement is provided between a first assembly comprising the output shaft and the components co-rotating therewith during pulsing and on the other hand a second assembly comprising the inertia drive member and any components co-rotating with it during pulsing.

The pulse tool may further comprise a housing having a front end and a back end, and the output shaft may be arranged such that a front end of the shaft extends at the front end of the housing. The front bearing may be arranged to provide a rolling interface between the output shaft and the housing, i.e. to support the output shaft rotatably with respect to the housing. The front bearing may be arranged on the output shaft near or adjacent a front end ofthe housing and/or the output shaft.

The referenced power or pulse tool may be an electrically driven pulse tool or a pneumatically driven pulse tool for tightening of threaded fasteners. According to one embodiment, the power tool is a handheld electrically powered power tool. According to one embodiment, the power tool is a battery powered tool. As friction in the tool also causes heat generation, the invention may be particularly advantageous implemented in an electrically powered pulse tool where heat is a particular concern for the motor and possibly batteries.

According to one embodiment, the inertia drive member comprises a cylinder front piece and the rolling arrangement is arranged between at least a portion of the front bearing and the cylinder front piece. The rolling arrangement may for example be arranged directly between the front bearing and the cylinder front piece such that the front bearing bears against, i.e. engages, the rolling arrangement.

According to one embodiment, the rolling arrangement is arranged between, and possibly directly bears against, an inner ring ofthe front bearing and an outer surface of a front wall ofthe cylinder front piece. l.e., the inner ring ofthe front bearing which may be arranged on the output shaft, may in such an embodiment be in direct contact with, bear against and/or engage the rolling arrangement.

According to one embodiment, the rolling arrangement comprises a rolling element bearing. This rolling element bearing may for example as described above be arranged between the inner ring ofthe front bearing and the cylinder front piece. The rolling bearing may in some embodiments be an axial thrust bearing, i.e. a bearing design to withstand axial load as well.

According to one embodiment, the rolling element bearing is a needle bearing. According to another embodiment, the rolling element bearing may a cylindrical roller bearing. According to one embodiment, the rolling element bearing is a needle roller thrust bearing.

According to one embodiment, the inertia drive member further comprises a cylinder rear wall, wherein the rolling interface is arranged between the output shaft and the cylinder rear wall. The rolling arrangement may for example be arranged between the impulse receiving end of the output shaft, i.e. the end extending into the oil chamber which may also be defined as a rear end of the output shaft, and the wall.

According to one embodiment, the rolling arrangement comprises balls arranged in grooves.

According to one embodiment, the power tool further comprises a disc shaped separator element, wherein the grooves are provided in the disc shaped separator element. The disc shaped separator element may be arranged between the rear end ofthe output shaft and the cylinder rear wall and/or have a shape congruent to the rear wall. The separator element may further be arranged to co-rotate with the inertia drive member. ln other embodiments, the grooves may be provided in the rear wall. The balls may further be arranged to roll against a planar surface, to which the axis A-A is normal, provided on the output shaft.

According to one embodiment, the power tool further comprises a collar arranged on the output shaft, wherein the collar comprises a radially protruding shoulder against which the front bearing bears.

According to one embodiment, the front bearing is pre-loaded by an axially acting spring element. The spring element may for example be, or comprise, a wave spring or a disc spring. ln some embodiment, the power tool further comprises a rear bearing arranged so support the pulse unit with respect to the housing at a read end ofthe pulse unit. The rear bearing may be pre-loaded by an axially acting spring, possibly the same spring as the front bearing.

According to one embodiment, the power tool is tranducerized tool, i.e. the tool comprises one or more sensors for retrieving data relating to the operation of the tool. According to one embodiment, the power tool comprises a torque transducer or sensor and/or a current sensor. According to one embodiment, the power tool further comprises an angular senor. The invention may be particularly advantageous when implemented in a tranducerized tool, since the friction which may affect the measurement is not only lowered, but also more even.

Further objectives of, features of and advantages of the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art realize that different features ofthe present invention can be combined to create embodiments other than those described in the following.

Brief description of the drawings The invention will be described in the following illustrative and non-limiting detailed description of exemplary embodiments, with reference to the appended drawing, on which Figure 1 is a perspective view of an exemplary pulse tool Figure 2 is a cross sectional view of a front end of an exemplary power tool according to one embodiment.

Figure 3 is a cross sectional view of a front end of an exemplary power tool according to one embodiment.

All figures are schematic, not necessarily to scale and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested.

Detailed description Figure 1 shows an exemplary pulse tool 1 according to one embodiment, in this case a battery powered hand held pistol type tool 1 comprising a housing 100 having a front end 100a and a back end 100b, in which a motor and a hydraulic pulse unit 20 is arranged, and further having a square ended output shaft 10 extending at the front end of the housing.

Fig. 2 shows the front end of an exemplary power tool 1 according to one embodiment and show an output shaft 10, and a pulse unit 20 including an inertia drive member 21.

The pulse unit, or impulse unit, 20 is adapted to be coupled to the motor and arranged to intermittently transfer torque pulses to the output shaft 10. The inertia drive member 21 includes a cylindrical front piece 25 and an end piece 24. The rear part 24, or end piece 24, is formed with a coupling portion 24a for connection to the motor. This inertia drive member 21 in turn comprises a hydraulic fluid chamber enclosed by the front- and end pieces, in this case an oil chamber, into which an impulse receiving portion 11 of the output shaft 10 extends. ln the illustrated embodiment, the impulse receiving portion 11 is formed in one piece with the output shaft 10 and extends into the fluid chamber via a central opening 27 in a front end wall 25a ofthe inertia drive member 21.

The impulse receiving output portion 11 is during use intermittently coupled to the drive member 21 via a hydraulic pressure pulse generating mechanism. ln order to achieve the pressure pulses, the output shaft 10 in this embodiment comprises a transverse cylinder bore in which movably guided pistons are arranged. The pistons are reciprocated in the cylinder bore by a cam comprising two cam lobes formed on the inner wall of the fluid chamber, acting on the pistons via rollers to drive hem inwardly thereby generating pressure peaks. The operation ofthe impulse mechanism per se is however known in the art and will not be described in any further detail, similar mechanisms has been previously described for example in US Patent 6,110,045 and US Patent 13,697,107.

The embodiment shown in fig. 2 further comprises a front bearing 30 arranged on the output shaft 10 to support the output shaft rotatably with respect to the housing 100. The front bearing 30 is arranged on the output shaft 10 adjacent the front end 100a of the housing and the front end wall 25a ofthe front piece 25 of the inertia drive member 21. An axially acting spring 32, in the illustrated embodiment a wave spring 32, preloads the front-bearing 30.

The front bearing 30, in the illustrated embodiment more particularly the inner ring 31 of the front bearing 30 which is rigidly attached to the shaft for example by means of a press fit or similar, together with the output shaft 10 form a front bearing shaft assembly 40. During pulsing, relative movement will occur between the rotating inertia drive member driven by the motor and the output shaft 10 (and hence the bearing inner ring 31 arranged thereon) which will engage the joint to be tightened. Further, the biasing force from the spring 32 acts to push the front bearing assembly including the output shaft against the front end wall 25a. ln order to reduce the resulting friction, a rolling arrangement 50 in the form of a needle roller thrust bearing 51, is therefore arranged between the inner ring 31 ofthe front bearing 30 and an outer surface of the end wall 25a to provide a rolling contact there between.

Fig. 3 shows the front end of an exemplary power tool 1 according to another embodiment. As for the embodiment described with reference to fig. 2, the power tool in fig. 3 comprises a pulse unit and a front bearing 30 arranged on the output shaft to support the output shaft rotatably with respect to the housing 100. A collar 80 comprises a protruding shoulder 81 arranged on the output shaft, such that the front bearing in this case bears against the shoulder 81. The front bearing 30, in the illustrated embodiment more particularly the inner ring 31 of the front bearing, together with the output shaft 10 form a front bearing shaft assembly 40.

As above, an axially acting spring 32 preloads the front-bearing 30. However, in this case, because ofthe collar 81, the front bearing shaft assembly 40 is not pushed against the front end wall 25a. lnstead, the biasing force from the spring 32 acts to push the front bearing assembly 40 including the output shaft 10 against the cylinder rear piece 24 of the inertia drive member 21. ln order to reduce friction, a rolling arrangement 50 is therefore arranged between the impulse receiving end 11 ofthe output shaft 10 and the cylinder rear piece 24 to provide a rolling contact there between. The rolling arrangement in this case comprises balls 52 arranged in grooves 53. More particularly, as the power tool in this embodiment comprises a disc shaped separator element 70 co- rotating with the inertia drive member 21, the grooves 53 are provided in this disc shaped element 70.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiment. The skilled person understands that many modifications, variations and alterations are conceivable within the scope as defined in the appended claims. Additionally, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, form a study of the drawings, the disclosure and the appended claims. ln the claims, the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the claims.

Claims (5)

Claims

1. Power tool comprising a motor, an output shaft (10), and a hydraulic pulse unit (20) including an inertia drive member (21) connected to the motor and rotatable about a rotation axis (A-A), an oil chamber enclosed in the inertia drive member and impulse generating means arranged to transfer intermittently kinetic energy to an impulse receiving portion (11) ofthe output shaft received within the oil chamber, said power tool further comprising: a front bearing (30) arranged on the output shaft to support the output shaft rotatably, wherein said output shaft and at least a portion of said front bearing form a front bearing shaft assembly (40), and wherein a rolling arrangement (50) is provided between said front bearing shaft assembly and said inertia drive member to provide a rolling contact there between.

2. Power tool according to claim 1, wherein the inertia drive member (20) comprises a cylinder front piece (2 5) and wherein the rolling arrangement is arranged between the front bearing and the cylinder front piece.

3. Power tool according to claim 2, wherein the rolling arrangement is arranged between an inner ring (31) of the front bearing and an outer surface (25a) ofa front wall of said cylinder front piece.

4. Power tool according to claim 2 or 3, wherein the rolling arrangement comprises a rolling element bearing (51).

5. Power tool according to claim 4, wherein said rolling element bearing is a needle bearing. Power tool according to claim 5, wherein said rolling element bearing is a needle roller thrust bearing (5 1). Power tool according to claim 1, wherein the inertia drive member further comprises a cylinder rear wall (24) and wherein the rolling interface is arranged between the output shaft and the cylinder rear wall. Power tool according to claim 7, wherein said rolling arrangement comprises balls (52) arranged in grooves (53). Power tool according to claim 8, further comprising a disc shaped separator element (70) co-rotating with the inertia drive member, wherein said grooves are provided in said disc shaped separator element. Power tool according to any one of claims 7-9, further comprising a collar (80) arranged on the output shaft, wherein said collar comprises a protruding shoulder (81) against which the front bearing bears. Power tool according to any one of the preceding claims, wherein said front bearing is pre-loaded by an axially acting spring element (32). Power tool according to any one of the preceding claims, wherein said power tool is a handheld electrically powered power tool. Power tool according to claim 12, wherein said power tool is a battery powered tool. Power tool according to any one of the preceding claims, further comprising an angular sensor.