Technical field [001 ] The present invention relates to a tool for peening a surface of a bore according to the preamble of claim 1 .

[002] The present invention also relates to a method of peening a surface of a bore by subjecting the surface of the bore to a treatment of a tool according to the preamble of claim 10.

Background art

[003] A cylinder head of an internal combustion piston engine is operating in harsh circumstances which set high standards in strength to the material and structure of the cylinder head. [004] The fatigue strength of metallic materials is generally increased by a peening treatment. In addition, the peening repairs the material surface and prevents the crack initiation. Specifically, the material surface is smoothed microscopically so as to eliminate micro notches which may lead to cracks. Drilling edges or alike have a tendency to a crack initiation or cracks which need to be treated with peening.

[005] GB 1260355 A discloses a peening tool for a cylindrical bore comprising a cylindrical cage with radially moving peening members. The tool comprises an actuator that can give shot strikes or peens to the peening members so that the peening members move towards the bore surface. The actuator can rotate around the longitudinal central axis or move in the direction of the central axis of the cage.

[006] U.S. 3,934,443 A discloses a peening tool comprising a body having a plurality of ball peening members and openings. Inside the body is arranged rotatably an actuator comprising hammers to give shots to the peening mem- bers and then the peening members partially extend outside the body and be in contact with the surface to be peened.

[007] CN 102198631 A is related a yet another hammering tool that comprises an actuator that rotates inside a body. The actuator is formed so that it gives strike peens to the peening members while rotated around the central axis of the body.

[008] An object of the invention is to provide an on-site tool for peening a surface of a bore in which the performance is considerably improved compared to the prior art solutions.

Disclosure of the Invention

[009] Object of the invention is substantially met by a tool for peening a surface of a bore comprising a body having a space in a direction of a longitudinal central axis of the body, the body having at least one radially extending opening, at least one peening member, having an inner end and an outer end, arranged movably at least partially inside the opening, the peening member is arranged to extend outside the body through the opening, and an actuator arranged at least partially inside the space in the body and movably in the space. It is characteristic to the invention that the actuator is provided with at least one radial extension part, a surface of which is arranged to cause static thrust the peening member, and that the peening member and the opening are formed so that the peening member has an extreme radial position allowed by the forms of the opening and the peening member, and that the at least one radial extension part has its radial dimension selected so that it provides static thrust with the inner end of the peening member at least when the peening member is at its extreme position.

[0010] According to an embodiment of the invention the tool for peening a sur- face of a bore comprising an actuator arranged at least partially inside the space in the body and movably in the space, and the actuator is provided with at least one radial extension part, a surface of which is arranged to cause static thrust the peening member. The peening member and the opening are formed so that the peening member has an extreme radial position allowed by the forms of the opening and the peening member, and that the at least one radial extension part has its radial dimension selected so that it radially overlaps with the inner end of the peening member at least when the peening member is at its extreme position.

[001 1 ] By means of the tool for peening a surface of a bore according to the invention the performance is considerably improved. According to an embodiment, the tool can be advantageously used in a cylinder head for on-site peen- ing of an injector drilling bore and/or drillings for e.g. cooling fluid. On the contrary to the known peening tools and methods, instead of causing short impacts/impulses with the actuator to the peening member, the peening tool uses static force. The actuator statically presses the peening members when peening the surface. According to the invention the actuator does not need to pro- vide hitting movement to the peening members, but instead it slowly forces the peening members towards the surface. Advantageously, the peening procedure is better controlled and the peening surface would be smoother which owns extremely high fatigue strength. The depth of the area wherein the fatigue strength is increased can be controlled more accurately by using a static force with the peening members. In this context the wording "peening" according to the invention should be understood as "increasing fatigue strength". Thus, according to an embodiment of the invention, "a tool for peening" should be understood as "a tool for increasing fatigue strength". [0012] According to an embodiment of the invention, the body comprises at least two radially extending openings, at least two peening members, and having an inner end and an outer end, arranged movably at least partially inside the opening, the peening members are arranged to extend outside the body through the opening, and an actuator arranged at least partially inside the space in the body and movably in the space, and the actuator is provided with at least one radial extension part, a surface of which is arranged to cause static thrust the peening members. The peening member and the opening are formed so that the peening member has an extreme radial position allowed by the forms of the opening and the peening member, and that the at least one radial extension part has its radial dimension selected so that it radially presses statically the inner end of the peening member at least when the peening member is at its extreme position.

[0013] According to an embodiment of the invention, the actuator is arranged movably in the direction of the longitudinal central axis of the body, a surface of the radial extension of the actuator is arranged to cause static thrust to the peening member.

[0014] It is to be understood that while the static thrust is applied the actual movement of the actuator is small.

[0015] According to an embodiment of the invention, the actuator is arranged rotatably movable partially around the longitudinal central axis of the body and the at least one radial extension part surface is arranged to transform torsion applied to the actuator into static thrust to the peening members in radial direction.

[0016] According to an embodiment of the invention, the tool has an inactive state wherein the outer end of the peening member is located at a first distance from the longitudinal central axis of the body and an active state wherein the radial extension part of the actuator is in contact with the inner end of the peening member and outer end of the peening member is located at a second distance from the longitudinal central axis of the body, the second distance is greater than the first distance.

[0017] According to an embodiment of the invention, dimensions of the radial extension part surface are chosen so that movement of the actuator across the peening member in the space is prevented. [0018] According to an embodiment of the invention, a drive system is arranged to rotate the body.

[0019] According to an embodiment of the invention, a drive system is arranged to move the actuator in the space so as to affect the peening members.

[0020] Object of the invention is met also by a method of peening a surface of a bore by subjecting the surface of the bore to a treatment by means of a tool comprising a body having a space in a direction of a longitudinal central axis of the body, and an actuator arranged at least partially inside the space in the body and movably in the space, the tool comprising at least one peening member, the method comprising steps of arranging the body at least partially inside the bore such that the peening member may subject a treatment to the inner surface of the bore. It is characteristic to the method that the actuator subjects a static force to the peening member which is transformed into radially directed static force against the inner surface of the bore by the peening member. [0021 ] The static force is applied continuously during a predetermined period of time. The predetermined period of time is advantageously more than 0,5 seconds, and preferably more than 2 seconds.

[0022] According to an embodiment of the invention the static force is applied continuously during a predetermined period of time. The predetermined period of time is 10 - 30 seconds. This way each action of subjecting static thrust involves one or more continuous thrust treatment periods lasting 10 - 30 seconds. [0023] According to an embodiment of the invention, the method of peening a surface of a bore comprises steps of subjecting the surface of the bore to a treatment by means of the tool comprising the body having the space in the direction of the longitudinal central axis of the body, and the actuator arranged at least partially inside the space in the body and movably in the space, the tool comprising at least two peening members, the method comprising steps of arranging the body at least partially inside the bore such that the peening members may subject a treatment to the inner surface of the bore, and the actuator subjects a static force to the peening members which is transformed into radially directed static force against the inner surface of the bore by the peening members.

[0024] According to an embodiment of the invention, the actuator is moved inside the space so that at least one radial extension causes the peening members to extend partially outside from the body to treat the surface of the bore at least when the peening member is at its extreme position. [0025] According to an embodiment of the invention, the actuator moves in the direction of the longitudinal central axis of the body, and at least one radial extension part is causing a static thrust to the peening members. [0026] According to an embodiment of the invention, the torsion is applied to the actuator around the longitudinal central axis of the body and at least one radial extension part surface causes static thrust to the peening members in a radial direction. [0027] According to an embodiment of the invention, a drive system moves the actuator in the space so as to affect static force via the actuator to the peening members.

[0028] The shape of the radial extension part of the actuator may be for exam- pie a wedge or alike. The actuator may comprise a separate extension part for each peening member or the extension part may be a continuous cone-like structure.

Brief Description of Drawings

[0029] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in which

Figure 1 illustrates a tool for peening a surface of a bore according to an em- bodiment of the invention,

Figure 2 illustrates the tool of figure 1 as a cross sectional view according to an embodiment of the invention,

Figure 3 a tool for peening a surface of a bore according to an embodiment of the invention,

Figure 4 illustrates the tool of figure 3 as a cross sectional view according to an embodiment of the invention,

Figure 5 illustrates a tool for peening a surface of a bore according to an embodiment of the invention,

Figure 6, illustrates a tool for peening a surface of a bore according to an em- bodiment of the invention, Figure 7 illustrates a cross sectional view of a tool for peening a surface of a bore according to an embodiment of the invention, and

Figure 8, illustrates a tool for peening a surface of a bore according to an embodiment of the invention.

Detailed Description of Drawings

[0030] Figure 1 depicts schematically a tool 10 for peening a surface of a bore 12. As an example, Fig. 1 illustrates the tool 10 for peening a cylinder head 30 that comprises an injector drilling bore 12 and drillings 32 for e.g. cooling fluid, later denoted also as cooling drillings in this context. The tool 10 for peening the inner surface of the bore 12 comprises a body 14 having a space 16 in a direction of a longitudinal central axis 18 of the body, the body 14 having at least two radially extending openings 20. The openings 20 are arranged preferably symmetrically in respect to the central axis 18. The tool 10 further comprises at least two peening members 22 arranged in connection with an opening 20 in the body 14. The number of peening members may vary according to the actual application. According to an embodiment of the invention the number of peening members is 4-6. The peening members are preferably equally distributed around central axis of the tool 10. In Fig. 1 it is illustrated that the peening members 22 are stroke peening balls. Obviously, any other shape for peening members than ball is conceivable. [0031 ] When the injector is taken out from the bore 12, or generally is not located in the bore, the tool 10 can be placed into the bore 12 of the cylinder head 30 without disassembling the cylinder head 30 from an engine. The body 14 is arranged at least partially inside the bore 12 to a desired position, at which the surface is to be treated by the peening members 20. Therefore, the tool 10 can be used to increase fatigue strength and to prevent crack initiation and growth easily on-site.

[0032] The peening members have an inner end 22.1 and an outer end 22.2 radially with respect to the longitudinal central axis 18. In other words, the sur- face of the outer end 22.2 is farther away from the longitudinal central axis 18 than the inner end 22.1 . Each or the peening members 22 is arranged movably at least partially inside the respective opening 20. In case the opening 20 has substantially cylindrical or cone-like shape having an inner end diameter and an outer end diameter and the peening members are or comprise balls, the outer end diameter of the opening is smaller than the diameter of the ball of the peening member 22. Respectively, the inner end diameter of the opening 20 is located nearer to the longitudinal central axis 18 than the outer end diameter of the opening. [0033] The tool 10 further comprises an actuator 24 arranged at least partially inside the space 16 in the body 14. The actuator 24 is arranged movably in the space 16. The actuator is mainly inside the body but part of the actuator extends out of the body in order to couple it with a drive system 26. The cross sectional shape of the space 16 in the body corresponds advantageously sub- stantially the cross sectional shape of the actuator.

[0034] The actuator 24 can be, for example, a rod or alike. In Fig. 1 , the actuator 24 is arranged movably in the space 16 in a direction of the longitudinal central axis 18 of the body 14. In other words, the actuator can be moved into a first direction A1 along the longitudinal central axis and a second direction A2 along the longitudinal central axis. The actuator 24 is provided with two radial extension parts 24.1 opposite to each other at its one end. The radial extension parts 24.1 are arranged to cause static radial thrust to the peening members 22 when the actuator is pulled in the second direction A2. The radial extension part has a gradually increasing radial distance from the centre line 18 so that the extension part transforms longitudinally directed static force, i.e. pulling force, of the actuator into radially directed static force of the peening member 22 against the surface to be treated. Using a static force in peening is advantageous when increasing the fatigue strength of intersection(s) of the bore and the drillings. In addition, more effective peening forces are generated compared to prior art solutions. The effect of the treatment may reach 2 - 20 mm depth from the surface into the bore material. The treating procedure is practised preferably a predetermined time of 0,5 seconds - 30 seconds. In other words each action of subjecting static thrust involves one or more treatment period lasting at least 0,5 seconds. Preferably the subjecting static thrust involves one or more treatment period lasting 10 - 30 seconds.

[0035] In other words, the radial extension part surfaces 24.1 can be moved in the direction of the longitudinal central axis 18 so that the radial extension part is in static thrust contact with the peening members 20 (cf. Fig. 3 and Fig. 4). As illustrated schematically, dimensions of the radial extension parts 24.1 are chosen so that movement of the actuator 24 across the peening member 22 in the space 16 is prevented. The actuator has a second part 24.2 which extends out from the body which is provided with means for coupling it with the drive system 26 to provide pulling force to the actuator. According to an embodiment of the invention the end of the second part 24.2 is provided with an outer thread 24.3. The drive system comprises a connector 26.1 arranged to connect with the thread 24.3 of the second part 24.2 of the actuator. The connector 26.1 is ar- ranged to transmit the static force from the drive system to the actuator.

[0036] The tool 10 may be arranged with the drive system 26 that controls the operation of the actuator 24. Drive system is arranged to at least operate the actuator 24. The drive system is arranged to move the actuator 24 in the space 16 and/or subject a static force to the actuator so as to affect the peening members 22. In an embodiment of Fig. 1 , the drive system 26 is also arranged to set the location of the actuator 24 in the direction of the longitudinal central axis 18 of the body 14 and apply static force to the actuator 24 and further via the radial extension to the peening members 22.

[0037] The drive system 26 may also be arranged to control the position of the body 14. The drive system can, for example, rotate the body 14 around the longitudinal central axis 18. This way the peening members may be rotationally positioned as desired.

[0038] Fig. 1 illustrates an inactive state wherein the outer end 22.2 of the peening member 22 is located at a first radial distance D1 from the longitudinal central axis 18 of the body 14. In an embodiment, the first distance D1 is the smallest possible distance between the outer end 22.2 of the peening member 22 and the longitudinal central axis 18. In Fig. 1 , the radial extension part 24.1 does not apply thrust to the peening member 22. [0039] Fig. 2 illustrates a cross-sectional view ll-ll of Fig. 1 . The tool 10 according to the embodiment of figure 1 comprises two peening members 22 arranged radially movably at least partially inside the opening 20 and the peening mem- bers are arranged to extend outside the body 14. Each of the peening members 22 has the inner end 22.1 and the outer end 22.2 as illustrated in Fig. 1 and Fig. 2. The peening members' 22 outer ends 22.1 are located at the first distance D1 from the longitudinal central axis 18. [0040] Similarly as Fig. 1 , Fig. 2 illustrates the inactive state. In this embodiment, the radial extension part 24.1 is not applying force to the inner end 22.1 of the peening members 22 but it can be in contact with the peening members 22 as illustrated. There is also shown the space 16 between the body 14 and the actuator 24. Thus the peening member 20 does not peen the surface of the bore 12 in this state.

[0041 ] Fig. 3 illustrates schematically the tool 10 for peening the surface of the bore 12 where the location of the actuator 24 differs from the location shown in Fig. 1 . Namely, in Fig. 2, the actuator has moved in the second direction A2 along the longitudinal central axis 18 such that the radial extension part 24.1 partly overlaps with the inner end 22.1 of the peening member 22i .e. the radial extension part 24.1 is arranged to press statically the inner end 22.1 of the peening member 22. Thus the peening members 22 partially extend from the openings 20 outside the body 14 against the inner surface of the bore 12. The drive system 26 is arranged to move the location of the actuator 24 and static force is acting on the peening members 22. By means of the above construction is possible to effectively provide static press against the peening member and t inner surface of the bore 12. [0042] Particularly the actuator 24 controlled by the drive system 26 is pulled so that the radial extension part surface 24.1 partially overlaps in the longitudinal direction with the inner end 22.1 of the peening member 22. The dimensions of the radial extension part 24.1 and the peening member 22 are chosen so that the radial extension part surface 24.1 cannot move across the peening member 20 in the space 16 i.e. its movement across the peening member is prevented. Thus, the static force is acting on the peening members 22. It should be noted that during the peening, the radial extension part surface 24.1 of the actuator 24 does not impact / hit intermittently the peening members 22. Instead, the radial extension part surface 24.1 of the actuator 24 is arranged to be in static contact with the peening balls 22 so as to provide uniform force distri- bution to peening members 22 in practical circumstances. In other words, oscillation of the actuator 24 or reciprocating motion of the actuator 24 is not required during peening.

[0043] Fig. 3, illustrates an active state wherein the radial extension part sur- face 24.1 of the actuator 24 is in contact with the inner end 22.1 of the peening member 22 and outer end 22.2 of the peening member 22 is located at a second distance D2 from the longitudinal central axis 18 of the body 14, the second distance D2 is greater than the first distance D1 . Thus the force in the direction of the longitudinal central axis 18 is transferred into a radial force because the radial extension part surface causes static thrust to the peening members 22 and the peening members 22 are moved to the radial direction and extending outside the body 14. The active state illustrated in Fig. 3 refers to a case wherein the peening member 22 is at its position pressed against the surface of the bore 12. The drive system 26 can alter the rotational position the body 16 around the longitudinal central axis 18 so as to treat the inner surface of the bore 12 at each rotational location and increase the fatigue strength of the surface of the bore 12. Specifically, the tool 10 can also increase the fatigue strength of the intersection of the bore 12 and the cooling drillings 32. Therefore, the size and/or form of the peening members 22, specifically the outer end thereof, and the openings 20 can be designed depending on the purpose whether to increase the fatigue strength of the bore 12 or particularly to increase the fatigue strength of the intersection of the bore 12 and the cooling drillings 32. [0044] Fig. 4 illustrates a cross section the tool according to an embodiment of the invention. The tool 10 according to the embodiment of figure 4 comprises six peening members 22 equally spaced and arranged radially movably at least partially inside the opening 20. The peening members are arranged to extend outside the body 14. [0045] Fig. 5 illustrates the tool 10 for peening an inner surface of a bore 12 according to an embodiment of the invention. The bore 12 shown in Fig. 5 is located in an element 31 which can be, for example, a cylinder head of an internal combustion engine. The tool 10 comprises the actuator 24 that comprises three radial extension parts 24.1 ', 24.1 " and 24.1 "' arranged one after the other in the direction of the longitudinal axis 18. The actuator 24 further comprises substantially tapered parts 24.2" and 24.2"' between the radial extension parts 24.1 " and 24.1 "'. Fig. 5 illustrates an inactive state wherein the tapered part 24.2", 24.2"' of the actuator 24 is located at the same longitudinal position with respect to the longitudinal central axis 18 as the peening members 22.

[0046] The actuator 24 arranged movable in the direction of the longitudinal central axis 18. The peening member 22 can extend outside the body 14 at least when one of the radial extension part surfaces 24.1 ', 24.1 " and 24.1 "' is in trust contact with the inner end 22.1 of the peening member 22. This can be done by pulling or pushing the actuator 24 controlled by the drive system 26 so that the radial extension part surface 24.1 ', 24.1 " and 24.1 "' radially overlaps with i.e. statically presses the inner end 22.1 of the peening member 22. The dimensions of the radial extension part surfaces 24.1 ', 24.1 " and 24.1 "', and the peening member 22 are chosen so that the radial extension part surface 24.1 ', 24.1 " and 24.1 "' cannot move across the peening member 20 in the space 16. Thus, the static force may be arranged to act on the peening members 22 when the radial extension part surface 24.1 ', 24.1 ", 24.1 "' partially radially overlaps with i.e. statically presses the inner end 22.1 .

[0047] Fig. 6 illustrates schematically the tool 10 for peening the surface of the bore 12 according to an embodiment of the invention. The actuator 24 comprises the radial extension part surface 24.1 . The actuator 24 is arranged to move in a direction of the longitudinal central axis 18 of the body 14. In this embodi- ment the peening member 22 comprises several parts. Here the peening member 22 is formed of three peening balls. The outer end 22.2 of the peening member 22 is located farther away from the longitudinal central axis 18 of the body 14 than the inner end 22.1 . The extension part 24.1 is in thrust contact with the inner end 22.1 of the peening member 22. In this embodiment, in the inactive state and in the active state the radial extension part surface is in con- tact with the inner end 22.1 of the peening member 22. When the actuator 24 is pulled by using the drive system 26, the static force moves the peening members 22 to partially extend from the openings 20. In Fig. 6, the tool 10 is in the inactive state and the peening members 22 are located at the first distance D1 from the longitudinal central axis 18. The opening 20 where the parts of the peening members 22 are located is formed such that its inner end is opening axially into the space 16 and its outer end is opening radially through the body 14. The opening 20 is acting as a guide for the peening members i.e. balls via which the longitudinal pulling force is transformed into radial thrust.

[0048] Even if not shown, instead of peening balls the peening member may also be a swivel structure one end of which arranged in thrust contact with the actuator and another end of which is arranged to extend substantially radially out of the body 14.

[0049] Fig. 7 illustrates cross sectional view of a tool 100 for peening the surface of the bore according to a further embodiment of the invention. The tool 100 comprises a body 140, peening members 220, each of the peening members 220 has an inner end 220.1 and an outer end 220.2. The tool 100 further comprises an actuator 240 arranged at least partially inside a space 160 in the body 140 and rotatable in the space 160 around the central axis 180 thereof. The actuator comprises a radial extension part 240.1 . The actuator 240 is rotatable in a first rotational direction R1 and in a second rotational direction R2. However, the actuator 240 cannot rotate 360 ° around the longitudinal axis 180 of the body 140 because also in this embodiment the at least one radial extension part 240.1 has its radial dimension selected so that it radially overlaps with i.e. presses statically the inner end 220.1 of the peening member 220 at least when the peening member 220 is at its extreme position. Movement of the actuator 240 across the peening member 220 in the space 160 is prevented. In other words, the peening members 220 stop the actuator 240 so as to preventing the actuator 220 to rotate over the peening members 220. Thus also in this embodiment of the invention, the peening members 220 are under a static force by the radial extension part 240.1 of the actuator 240. [0050] Figure 8 shows an embodiment of the invention which is otherwise similar to that shown in figure 1 but where the tool for peening a surface of a bore comprising a body 14 having one radially extending opening 20, one peening member 22, having an inner end 22.1 and an outer end 22.2, arranged movably at least partially inside the opening 20, the peening member 22 is arranged to extend outside the body 14 through the opening 20, and an actuator 24 arranged at least partially inside the space 16 in the body and movably in the space 16, and the actuator 24 is provided with at least one radial extension part 24.1 , a surface of which is arranged to cause thrust the peening member 22. Even if this embodiment is not as efficient as the one shown in figure 1 , mainly due to having only one peening member, it still applies the same operational principle.

[0051 ] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in con- nection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.