Heavy-duty electric impact driver

Abstract

The present invention relates to a portable impact screwdriver comprising: an electric motor including: an internal stator, an external rotor movable in rotation about an axis X relative to said stator, means for guiding the rotation of said rotor relative to said stator; a motor housing housing said motor; a rebounding impact mechanism movable about an axis Y including an input connected to said rotor and an output connected to an output shaft of said screwdriver; an impact mechanism housing, linked to said motor housing, housing said impact mechanism.According to the invention, said impact mechanism housing includes a bearing for guiding rotation along said axis X of said rotor relative to said impact mechanism housing, said bearing being located between said impact mechanism and said rotor and ensuring by itself the guidance in rotation along said axis X of said rotor relative to said impact mechanism housing; said screwdriver including means for connecting said stator to said motor housing, the whole of said connecting means contributing only to ensuring: a stop in rotation along said axis X of said stator relative to said motor housing, or a stop in rotation and a stop in translation along said axis X of said stator relative to said motor housing.

Description

Title of the invention: Heavy-duty electric impact driver 1. Scope of the invention

[0001] The field of the invention is that of the design and manufacture of portable electric impact wrenches.

[0002] More particularly, the field of the invention is that of impact wrenches using an external rotor electric motor and in particular of impact wrenches capable of generating torques greater than 1000m. 2. Prior art

[0003] Portable electric impact screwdrivers are commonly used in various sectors to work towards carrying out screwing or unscrewing operations of assemblies.

[0004] This type of screwdriver generally comprises a motor rotationally linked to an impact mechanism. The impact mechanism includes an output shaft that can be rotationally linked to the screw to be tightened. The impact mechanism is driven in rotation by the motor and generates an impact on the output shaft with each revolution or half-revolution, which then drives the screw in rotation.

[0005] The screwing principle is therefore based on the conversion of the kinetic energy contained in the impact mechanism into clamping potential energy in the screw.

[0006] In the field of electric impact wrenches, two main families of impact mechanisms are known. These two families are described, for example, in patent document EP-B1-3 653 339. They are: - “spring loaded cam mechanism”, in English: impact mechanisms of this type have been designed to be able to be driven by an electric motor without the rotation of the latter being stopped during the impact of the impact mechanism; - Rebounding impact mechanisms: These impact mechanisms induce a sudden stop, or even a rebound, of the motor rotor upon impact. They are commonly used in pneumatic impact wrenches where rotor rebound is not a problem. However, integrating such an impact mechanism into an electric impact wrench requires controlling the electric motor's power supply using current regulation or electromagnetic torque regulation to prevent motor damage. Such control is the subject of the aforementioned patent and will not be described in further detail here.

[0007] Among these impact wrenches with a rebounding impact mechanism are, in particular: Maurer-type impact mechanisms: "Twin Hammer", "Twin lobe", "double dogs" in English; the "single dog" in English; the "rocking dog" in English; "Two jaws" in English; "pin clutch" in English.

[0008] The mechanism represented within the framework of the invention is a "two jaws" but any of the other mechanisms mentioned, and more generally any type of rebounding impact mechanism, could be considered.

[0009] These two families of impact mechanisms generate the impact in the same way: by striking a rotating mobile steel part (the hammer of the impact mechanism) on a surface belonging to the output shaft (the anvil).

[0010] There is another type of impact mechanism, called a hydraulic module, capable of converting the kinetic energy contained in the impact mechanism into a torque impulse transmitted to the screw to be tightened. In this case, following a free acceleration applied by the motor to the hydraulic module, oil contained in this module is forced to pass through a nozzle, causing a strong deceleration of the module and the motor rotor, this deceleration generating a torque impulse (impact) on the output shaft.

[0011] It is also known to implement pulse-driven electric impact wrenches. These wrenches do not include an impact mechanism. In this case, the functional clearances in the transmission between the motor rotor and the output shaft are used to generate impacts by supplying the motor with successive pulses of electrical current.

[0012] These mechanisms are well known in the prior art and will not be described in more detail here.

[0013] The torques generated by these tools range from a few tens of Nm for impulse wrenches to several thousand Nm for certain impact wrenches with an impact mechanism.

[0014] Finally, it is known in the state of the art of impact or impulse wrenches implementing external rotor motors.

[0015] External rotor motors have a bell-shaped rotor carrying permanent magnets and adapted to rotate around an internal stator. This type of motor is characterized by offering higher electromagnetic torque than an internal rotor electric motor of equivalent power and a lower speed.

[0016] Here we will review documents revealing impulse or impact wrenches using an external rotor motor.

[0017] Patent document EP-B1-2 726 251 describes an impulse screwdriver using a hydraulic module which is schematically represented in [Fig.1].

[0018] As shown, such a screwdriver includes a motor housing 10 housing the motor 11 equipped with a stator 19 and a rotor 16, and an impact mechanism housing 10' housing the impact mechanism in the form of a hydraulic module 12. The hydraulic module is capable of driving an output shaft 14 in rotation.

[0019] The engine housing 10 and the impact mechanism housing 10' are rigidly and coaxially joined to each other.

[0020] Similarly, the shaft 17 of the rotor 16 of the motor 11 and the hydraulic module 12 are linked in rotation by a rigid coaxial link 100.

[0021] The motor housing 10 includes a first bearing 15 and the impact mechanism housing 10' includes a second bearing 13 which enable the rotational guidance of the assembly formed by the hydraulic module 12 and the rotor 16 of the motor 11.

[0022] This first bearing 15 is located between the impact mechanism and the rotor.

[0023] Thus, according to this architecture: - the external rotor 16 of the motor 11 is mounted in cantilever in the motor housing 10. - the stator 19 is rigidly fixed in the motor housing 10 and coaxial with respect to the rotor 16.

[0024] The stator and rotor must be arranged in a perfectly coaxial manner. This requires that the functional surfaces supporting the stator be perfectly coaxial with the two bearings supported by the motor housing 10 and the impact mechanism housing 10' in the impact mechanism area.

[0025] This requires the implementation of a rigid and precise impact mechanism housing 10' and motor housing 10, which necessitates making them out of metal.

[0026] However, the use of a metal housing has drawbacks, namely that a machined metal housing is: - Dear ; - potentially heavy if this solution is transposed to a tool with a clamping capacity greater than 1000 Nm - potentially sensitive to shocks insofar as it can deform elastically or even plastically during a fall of the screwdriver which would impair the relative coaxiality of the rotor and the stator in a punctual or permanent way.

[0027] Patent documents EP-A1-1 930 124 and EP-B 1-3 653 339 describe another impact driver architecture schematically represented in [Fig.2].

[0028] As shown, such a screwdriver includes a motor housing 20 housing the motor 21 and an impact mechanism housing 20' housing the impact mechanism 22.

[0029] The engine housing 20 and the impact mechanism housing 20' are rigidly and coaxially joined to each other.

[0030] The external rotor 26 is guided in rotation relative to the stator 29 by means of the shaft 202 linked to the rotor and by means of rotational guidance means 201 in the form of bearings placed between the shaft 202 and the stator 29.

[0031] The motor housing 20 includes a first bearing 25 which supports the output shaft 27 of the rotor 26 in a hyperstatic manner.

[0032] The impact mechanism housing 20' includes a second bearing 23 to ensure the rotational guidance of the output shaft 24 of the impact mechanism 22.

[0033] The stator 29 is fixed inside the motor housing 20 in such a way that it is coaxial with the impact mechanism 22.

[0034] The shaft 27 of the rotor 26 is rotationally linked with the input 28 of the impact mechanism 22 by means of a short link 200 potentially slightly ballistic.

[0035] According to this architecture: - the impact mechanism 22 is guided in rotation by the first bearing 25 of the engine casing 20 and by the second bearing 23 of the impact mechanism casing 20'; - the rotational link 200 between the impact mechanism 22 and the rotor 26 is relatively short and not sufficient to ensure sufficient coaxiality between the impact mechanism 22 and the rotor 26. As a result, the rotor 26 is guided in rotation relative to the stator 29 by bearings 201 making the connection between the inside of the stator 29 and a shaft 202 linked to the rotor 26. - the stator 29 is rigidly fixed in the engine casing 20.

[0036] The rigid connection between the stator 29 and the motor housing 20, associated with: - the rotational guidance of the rotor 26 relative to the stator 29, and with - the bearing 25 located between the rotor 26 and the motor housing 20,

[0037] leads to a hyperstatic assembly.

[0038] This necessary coaxiality between the motor and the impact mechanism, combined with the statically indeterminate mounting of the stator, requires, as in the previous example, that the motor housing and the impact mechanism housing be rigid and precise. Consequently, they are made of metal, with the disadvantages listed previously, namely that a machined metal housing is: - Dear ; - potentially heavy if this solution is transposed to a tool with a clamping capacity greater than 1000 Nm - potentially sensitive to shocks insofar as it can deform elastically or even plastically during a fall of the screwdriver which would impair the relative coaxiality of the rotor and the stator in a punctual or permanent way.

[0039] In summary, maintaining coaxiality between the motor and the impact mechanism, including during possible drops of the screwdriver, requires, according to prior art impact screwdriver architectures, the implementation of rigid and precise housings.

[0040] To be rigid and precise, the housings must be made of a metallic material, and the functional surfaces, which are used in particular for mounting the bearings, must be machined. This entails some disadvantages compared to housings made of plastic, namely: - a higher cost price; - a higher weight; - less impact resistance since, when the screwdriver is dropped, a metal casing can undergo permanent deformations that may affect the coaxiality between the motor and the impact mechanism.

[0041] The risk of deformation of the casing during a fall, and of disruption of the alignment between the motor and the impact mechanism, is all the greater the heavier the screwdriver.

[0042] Thus, for lightweight screwdrivers (for example, having a mass of around 2 kg), capable of carrying out screwing operations at low tightening torques (for example, on the order of a few hundred Nm), the risk of deformation of the housing and of disturbance of the coaxiality between the motor and the impact mechanism is significantly lower than for screwdrivers with a much higher tightening capacity (for example, on the order of 2000 Nm) and which consequently have a much larger mass (for example, on the order of 10 kg).

[0043] Indeed, since the kinetic energy acquired by a screwdriver during a fall is directly proportional to its mass, the kinetic energy to be dissipated during the impact of the screwdriver on the ground during a fall is therefore about five times greater for a screwdriver weighing 10 kg than for a screwdriver weighing 2 kg.

[0044] The risk of screwdrivers falling is common in heavy vehicle maintenance workshops where screwdrivers capable of delivering high tightening torques are mainly used.

[0045] According to the prior art screwdriver designs described above, the alignment bearings of the impact mechanism and the motor are distributed along the housing from the impact mechanism to the motor. These bearings are therefore far apart, which leads to an even greater risk of permanent deformation of the casing during a fall of the screwdriver and therefore a degradation of the coaxiality between the motor and the impact mechanism.

[0046] It could be considered to reduce this risk by reinforcing the metal housings of the screwdrivers. However, this would lead to a significant increase in the mass and cost of the screwdrivers.

[0047] One way to protect against this risk could therefore be to reinforce these housings, but this would induce a large increase in mass, which is not desirable.

[0048] Therefore, there is a need to improve portable electric impact screwdrivers. 3. Objectives of the invention

[0049] The invention aims in particular to provide an effective solution to at least some of these different problems.

[0050] In particular, according to at least one embodiment, an objective of the invention is to provide an electric impact wrench with a tightening capacity greater than 1000 Nm that is robust, particularly with regard to drops on the ground.

[0051] In particular, the invention aims, according to at least one embodiment, to provide such a screwdriver which does not induce degradation of the coaxiality between the motor and the striking mechanism during drops.

[0052] Another objective of the invention is, according to at least one embodiment, to provide such a screwdriver which is lightweight.

[0053] Another objective of the invention is, according to at least one embodiment, to provide such a screwdriver which is simple in design.

[0054] Another objective of the invention is, according to at least one embodiment, to provide such a screwdriver which is relatively cheap.

[0055] Another objective of the invention is, in at least one embodiment, to minimize the propagation of axial shocks to the motor, in other words, to isolate the motor from these axial shocks. Axial shocks are amplified by the impact mechanism parts moving axially with strong accelerations or decelerations. 4. Presentation of the invention

[0056] To this end, the invention proposes a portable impact screwdriver comprising: - an electric motor comprising: • an internal stator, • an external rotor that rotates about an X-axis relative to the stator, • means for guiding the rotation of said rotor relative to said stator; - an engine casing housing said engine; - a mobile, rotating, rebounding impact mechanism along a Y-axis comprising an input connected to said rotor and an output connected to an output shaft of said screwdriver; - an impact mechanism housing, linked to said engine housing, housing said impact mechanism.

[0057] According to the invention, said impact mechanism housing includes a bearing for guiding rotation along said axis X of said rotor relative to said impact mechanism housing, said bearing being located between said impact mechanism and said rotor and ensuring by itself the guidance in rotation along said axis X of said rotor relative to said impact mechanism housing;

[0058] said screwdriver comprising means for connecting said stator to said motor housing, the assembly of said connecting means contributing only to ensuring: - a stop in rotation along said X axis of said stator relative to said motor housing, or - a stop in rotation and a stop in translation along said X axis of said stator relative to said motor housing.

[0059] Thus, according to this aspect of the invention, the fact that the rotor is only guided in rotation relative to the housing of the impact mechanism by means of a bearing of the housing of the impact mechanism, and not by means of a bearing of the motor housing, makes it possible to make a motor housing out of plastic and thus: - to reduce costs, - to provide a lighter screwdriver, - to provide a more robust screwdriver insofar as the motor housing is less likely to deform plastically when the screwdriver is dropped, which leads to preserving the coaxiality between the rotor and the impact mechanism even in the event of a drop.

[0060] According to a preferred feature, said motor housing does not include: - a bearing for guiding the rotation of said rotor along said X-axis, - means of connecting the stator to the motor housing ensuring coaxiality between the X axis of the stator and the Y axis of the impact mechanism.

[0061] According to a preferred feature, said means of connecting said stator to said motor housing are suitable for allowing a radial displacement of said motor housing vis-à-vis said stator of an amplitude of up to 2 mm without said motor housing transmitting a radial force to said stator.

[0062] This prevents the motor housing from transmitting a radial force to the stator which could impair the coaxiality of X with respect to Y.

[0063] According to one possible feature, said means for connecting said stator to said engine housing comprise: - a lug with an orientation substantially perpendicular to the X-axis, said lug being linked to said stator or said engine casing, - a receptacle of complementary shape to said lug housing said lug, said receptacle being respectively linked to said engine casing or said stator,

[0064] said lug having for all of its surfaces a play vis-à-vis said receptacle, said play being at least 2 mm for the surfaces of said lug perpendicular to said orientation of said lug.

[0065] According to another possible feature, said means of connecting said stator to said motor housing comprise an Oldham joint connected on one side to said stator and on the other side to said motor housing coaxially to the X axis.

[0066] According to another possible feature, said means of connecting said stator to said motor housing comprise a bellows connected on one side to said stator and on the other side to said motor housing coaxially to the X axis.

[0067] According to another possible feature, said screwdriver is capable of delivering a screwing torque of at least 1,500 Nm

[0068] Thus, the invention provides an electric impact wrench with a tightening capacity greater than 1000 Nm which is robust, particularly with regard to drops on the ground.

[0069] According to one possible feature, said output shaft includes a screw socket drive square having a dimension on flat of at least ¾ inch.

[0070] According to one possible feature, said engine casing includes at least one gripping handle.

[0071] According to one possible feature, said engine housing is made of plastic material and said impact mechanism housing is made of metallic material.

[0072] The fact that only the housing of the impact mechanism is made of metal and that the motor housing is made of plastic reduces costs and provides an inexpensive screwdriver. 5. Description of the figures

[0073] Other features and advantages of the invention will become apparent from the following description of particular embodiments, given by way of simple illustrative and non-limiting example, and the accompanying drawings, among which:

[0074] [Fig-1] [Fig.1] illustrates a schematic view of a first architecture of impact screwdrivers according to the prior art;

[0075] [Fig.2] [Fig.2] illustrates a schematic view of a second architecture of impact screwdrivers according to the prior art;

[0076] [Fig.3] [Fig.3] illustrates a perspective view of an example of a screwdriver according to the invention;

[0077] [Fig.4] [Fig.4] illustrates a longitudinal cross-sectional view of the screwdriver in [Fig.2];

[0078] [Fig.5] [Fig.5] illustrates a detail of [Fig.4];

[0079] [Fig. 6] [Fig. 6] illustrates a cross-sectional view along the EE axis of the screwdriver [Fig.4];

[0080] [Fig.7] [Fig.7] illustrates a schematic view of the screwdriver shown in [Fig.4].

[0081] 6. Description of particular embodiments 6.1. Structure and operation

[0082] An example of a portable electric impact screwdriver according to the invention is described in relation to figures 3 to 7. Two crankcases

[0083] As shown, such a screwdriver includes a housing comprising: - a motor housing 30, and - an impact mechanism housing 31.

[0084] The motor housing 30 is made of plastic. It houses an electric motor 32.

[0085] This is an external rotor motor. In this embodiment, it is a permanent magnet synchronous motor.

[0086] Engine 32 comprises: - an internal 320 stator, and - an external rotor 321 that rotates about an X axis relative to the stator 320.

[0087] The rotor 321 is equipped with: - of a bell 3210, and - of a rotor shaft 3211.

[0088] The rotor shaft 3211 extends inside the stator 320.

[0089] The motor 32 can be supplied with electric current by wire or by battery(ies) carried by the screwdriver.

[0090] The impact mechanism housing 31 is made of metal and houses a rebounding type impact mechanism 33.

[0091] The rebounding impact mechanism 33 comprises: - an input 330 connected to the rotor shaft 3211, and - an output 331 connected to, or constituting the output shaft 34 of the screwdriver.

[0092] The moving part(s) of the rebounding impact mechanism move along a Y axis. This Y axis must be coaxial with the X axis for obvious operational reasons.

[0093] The output shaft 34 includes a square 341 for driving a screw socket. This square 341 has a flat dimension of at least ¾ inch.

[0094] The engine casing 30 can: - include a 300 gripping handle and possibly a fixing point (not shown) for an additional 300' handle; - house control means, an actuation trigger 302, a control for reversing the direction of rotation (not shown); - control means 303 of the screwdriver and the power supply of its motor.

[0095] The screwdriver may, for example, implement a design of the type described in patent document EP-B1-3 653 339. In this case: - a rigid and direct rotational link is made between the impact mechanism 33 and the rotor shaft 3211; - The impact mechanism 33 is of the rebounding type, in this case a "2 jaws" mechanism, known in the state of the art; other rebounding impact mechanisms can be considered such as a Maurer mechanism, a "pin clutch" mechanism... - a regulation of the motor 32 in electromagnetic torque (or current) by means of a vector control is implemented; - the electric motor 32 is a permanent magnet synchronous motor. Rotor-impact mechanism connection

[0096] A rear end 32111 of the rotor shaft 3211 is rotationally linked with the input 330 of the impact mechanism 33.

[0097] The link between the rotor shaft 3211 and the inlet 330 of the impact mechanism 33 is a short splined link, i.e. this link is capable of transmitting torque between the motor 32 and the impact mechanism 33 but cannot ensure a sufficient coaxial link of the rotor 321 vis-à-vis the impact mechanism 33.

[0098] Guiding the rotor relative to the impact mechanism housing

[0099] The impact mechanism housing 31 includes a first bearing 311 for guiding rotation along the X axis of the rotor 321 relative to the impact mechanism housing 31.

[0100] This first bearing 311 is located at the junction between the engine housing 30 and the impact mechanism housing 31.

[0101] In this embodiment, the first bearing 311 consists of a part 35 fixedly attached to the impact mechanism housing 31, between the motor housing 30 and the impact mechanism housing 31. This part 35 is made of metallic material.

[0102] The impact mechanism housing 31 is linked to the motor housing 30 in an area located around the first bearing 311. The part 35 is interposed in this area between the motor housing 30 and the impact mechanism housing 31.

[0103] Alternatively, part 35 could not be implemented and the first bearing 311 could be formed directly on the impact mechanism housing 31 rather than on this additional part 35 attached to the impact mechanism housing 31. This reduces the number of parts but leads to a more complex impact mechanism housing 31 and the insertion of the impact mechanism into the impact mechanism housing.

[0104] In this embodiment, the first bearing 311 houses two ball bearings 3111 with angular or non-angular contact. Alternatively, these could be two tapered roller bearings, a double-row ball bearing, or possibly one or more plain bearings...

[0105] The two bearings 3111 guide rotation relative to the impact mechanism housing 31 respectively: - the rotor shaft 3211, and - bell 3210.

[0106] The combination of the two bearings 3111 is sufficient to ensure the rotational guidance of the rotor comprising a shaft 3211, a bell 3210 and a shaft 3211.

[0107] The motor housing 30 does not include a bearing, and more generally no means, for guiding the rotation of the rotor 321 along the X axis, the first bearing alone ensuring the rotational guidance along the X axis of the rotor relative to the impact mechanism housing and more generally to the housing.

[0108] Guiding the output shaft relative to the impact mechanism housing

[0109] The impact mechanism housing 31 includes a second guide bearing 312 in rotation, along the X axis, of the output shaft 34 relative to the impact mechanism housing 31.

[0110] The second bearing 312 in this embodiment houses a bushing 3121. It could alternatively be a bearing with ball or roller bearing(s).

[0111] Guiding the impact mechanism relative to the impact mechanism housing

[0112] The impact mechanism 33 is thus guided in rotation along the X axis by means of: - of the second bearing 312 supporting the output shaft 34, and - of the rotational link between the rotor shaft 3211 and the input 330 of the impact mechanism 33 which ensures concentricity between the inlet 330 of the impact mechanism 33 and the rotor shaft 3211, therefore the effect of a bearing.

[0113] The rotational link between the rotor and the impact mechanism, even if it does not ensure coaxiality, ensures concentricity of the input of the impact mechanism 300 and the end of the rotor shaft. Thus, it acts as a simple bearing, which associated at the second output shaft guide bearing, ensures rotational guidance of the impact mechanism. Rotor guidance relative to the stator

[0114] The screwdriver includes means for guiding the rotation 36 of the rotor 321 relative to the stator 320. These guiding means allow, among other things, the necessary coaxiality between the rotor 321 and the stator 320 to be ensured, guaranteeing compliance with the regularity of the air gap.

[0115] These guiding means 36 comprise at least two third bearings 360, 361: - one of these third bearings 360 is disposed at an anterior end 32112 of the rotor shaft 3211 located opposite the posterior end 32111 of the rotor shaft 3211 guided in rotation relative to the impact mechanism housing 31 via the first bearing 311, - the other of these third bearings 361 is disposed between the anterior end 32112 and the posterior end 32111 of the rotor shaft 3211.

[0116] The bearings 360, 361 comprise bores formed inside the stator 320.

[0117] In this embodiment, the third bearing 360 houses a ball bearing 3600 or roller bearing, and the third bearing 361 houses two ball or roller bearings 3610. The number and type of bearings housed in these bearings 360 and 361 could, however, be different. They could also be plain bearings.

[0118] These guiding means 36 ensure the coaxiality of the impact mechanism 33 with the stator 320, and the robustness of the impact mechanism housing 31 preserves this coaxiality in case of shocks caused during drops of the screwdriver.

[0119] To meet the objective of avoiding a degradation of the coaxiality between the impact mechanism 33 and the motor 32 following a fall, it was chosen to join the surfaces allowing the alignment of the impact mechanism 33 and the motor 32, i.e. the surfaces of the first bearing 311 and the second bearing 312, on the impact mechanism housing 31 which is a compact and robust part.

[0120] Indeed, the impact mechanism housing 31 is by its nature designed: - compact because its size is defined by that of the impact mechanism 33 itself, which is compact, and - robust on the one hand because it has to withstand many shocks due to its exposure at the front of the screwdriver, and on the other hand because of its role in containing the impact mechanism 33 in case of malfunction of the latter. Stator rotation stopped

[0121] The impact wrench includes means for stopping rotation along the X axis of the stator 320 relative to the motor housing 30.

[0122] Their function is to achieve a rotational stop of the stator 320 relative to the motor housing 30, without exerting additional stress on the stator 320. It is therefore necessary that the motor housing be able to deform without exerting radial stress on the stator.

[0123] For this purpose, the motor housing 30 includes a rotational stop element 304, along the X axis, of the stator 320 relative to the motor housing 30. This stop element 304 includes a receptacle 3201 provided in the motor housing 30.

[0124] This receptacle 3201 is suitable for housing a stop lug 3200 of complementary shape provided on the stator 320. For this purpose, the stator 320 includes a stop lug 3200 with an orientation substantially perpendicular to the X axis. This lug forms a projection in a plane orthogonal to the X axis.

[0125] As illustrated in [Fig.7], alternatively, the receptacle 3201 could be formed on the stator 320 and the stop lug 3200 could be formed on the motor housing 30.

[0126] These rotation stop means (304, 3200) must resist the electromagnetic torque of the motor 32 which is on the order of a few Nm, i.e. a tangential force at the level of the lug on the order of a few tens of N.

[0127] During the assembly of the screwdriver, and in particular when closing the motor housing 30, the locking lug 3200 is fitted into the corresponding receptacle 3201. Thus, the stator 320, which is located along the X-axis in the rotor 321, cannot rotate relative to the motor housing 30 along the X-axis.

[0128] Therefore, when the stator 320 is powered following the actuation of the screwdriver control means by the user, the stator 320 can exert a driving torque on the rotor 321 and thus rotate the impact mechanism 33 to achieve tightening or loosening.

[0129] The lug has clearance on all its surfaces with respect to the receptacle. In particular, clearance exists between all the external surfaces of the stop lug 3200 and the internal surfaces of the receptacle 3201.

[0130] In particular, a radial clearance J along an axis orthogonal to the X-axis, i.e., for the surfaces of the lug perpendicular to the orientation of the lug, is provided between the retaining lug 3200 of the stator 320 and the receptacle 3201 of the motor housing 30 in which it is housed. This radial clearance allows for radial deformation, i.e., orthogonal to the X-axis, of the motor housing 30 relative to the stator 320.

[0131] This radial clearance is preferably at least equal to 2 mm.

[0132] This radial play is determined in such a way that in the event of a fall, if the point of contact of the screwdriver on the ground is exerted on the motor housing 30 and its wall happens to move radially with respect to the X axis, then the stop lug 3200 moves in the corresponding receptacle 3201 before returning to their original position when the stresses exerted on the motor housing 30 disappear and the motor housing 30 has consequently recovered its original shape.

[0133] During such a displacement of the wall of the motor housing 30, no radial force is therefore transferred to the stator 320 because: - the end of the stop lug 3200 cannot, due to radial play, touch the bottom of the receptacle 3201 in which it is located; - The cross-section of the retaining lug 3200 is slightly smaller than that of the receptacle 3201, so there is no friction between the two.

[0134] The precision required for manufacturing the receptacle 3201 is moderate, so this motor housing 30 can be made of impact-resistant plastic. This embodiment thus contributes to the lightness of the screwdriver and its moderate cost. This embodiment also allows the complex shapes of the handle and control means to be integrated into this motor housing.

[0135] The stop stinger here constitutes a reaction tic.

[0136] The rotational stop described above could be achieved, alternatively to the implementation of the stop lug and the receptacle, by: - an Oldham joint coaxial to the stator and providing rotational support along the X-axis between the stator and the engine casing, or - a bellows seal linked on one side to the stator and on the other side to the motor casing coaxially to the X axis. Stator translation stop

[0137] In one variant, the motor housing 30 further includes at least one translational stop element 37 along the X axis of the stator 320 relative to the motor housing 30.

[0138] The means for stopping the translation of the stator 320 along the X axis can be integrated into the means for stopping the rotation (3200, 304) of the stator 320 without harming the objectives of the invention.

[0139] In this case, for example, the stop lug 3200 can bear against a surface of the receptacle 3201 orthogonal to the axis X and thus forming a stop in translation along this axis X.

[0140] However, these means of stopping in translation 37 can just as easily be in the links between stator 320 and rotor 321, then between rotor 321 and the first bearing(s) 311 by means of conventional elastic rings. Screwdriver output torque

[0141] A screwdriver according to the invention is preferably capable of delivering a screwing torque of at least 1,500 Nm. More precisely, it is preferably capable of generating a tightening torque of between 1,500 and 3,000 Nm for a mass of the order of 10 to 15 kg.

[0142] However, it can also be implemented for lower output torques, although higher capacity screwdrivers are more subject to the risk of falling. 6.2. Advantages

[0143] In summary, integrating the motor 32 into an impact wrench according to the invention leads to the following: - The axial positioning of the motor 32, including the stator 320, is achieved by surfaces supported by the housing of the impact mechanism 31, with the following advantages: - good robustness and precise axial positioning of the motor relative to the impact mechanism 33, i.e. coaxiality, due to the robustness of the impact mechanism housing 31, and - a moderate machining cost for these surfaces, - The rotation of the stator 320 is stopped by a point support type connection between the stator 320 and the inside of the motor housing 30, with the following advantages: - the possibility of manufacturing the engine casing 30 using plastic injection molding, an inexpensive process that allows for the integration of complex shapes such as the handle or control mechanisms, - good shock resistance limiting the risk of introducing permanent deformations in the engine casing 30 and stresses likely to degrade the coaxiality of the engine 32 with respect to the impact mechanism 33.

[0144] The invention thus enables: - to achieve good coaxiality between the motor and the impact mechanism, and - to maintain this coaxiality when the screwdriver is subjected to shocks during drops, - while providing a compact, lightweight and inexpensive screwdriver.

Claims

Demands

1. A portable impact screwdriver comprising: - an electric motor comprising: • an internal stator, • an external rotor movable in rotation about an X axis relative to said stator, • means for guiding the rotation of said rotor relative to said stator; - a motor housing enclosing said motor; - a rebounding impact mechanism movable in rotation about a Y axis comprising an input connected to said rotor and an output connected to an output shaft of said screwdriver; - an impact mechanism housing, connected to said motor housing, enclosing said impact mechanism;characterized in that said impact mechanism housing comprises a bearing for guiding rotation along said X axis of said rotor relative to said impact mechanism housing, said bearing being located between said impact mechanism and said rotor and ensuring by itself the guidance in rotation along said X axis of said rotor relative to said impact mechanism housing; said screwdriver comprising means for connecting said stator to said motor housing, the whole of said connecting means contributing only to ensuring: - a stop in rotation along said X axis of said stator relative to said motor housing, or - a stop in rotation and a stop in translation along said X axis of said stator relative to said motor housing.

2. Screwdriver according to claim 1 in which said motor housing does not include: - bearing for guiding the rotation of said rotor along said x-axis, - means for connecting the stator to the motor housing ensuring coaxiality between the X-axis of the stator and the Y-axis of the impact mechanism.

3. Screwdriver according to claim 1 or 2 wherein said means of connecting said stator to said motor housing are capable of permitting a radial displacement of said motor housing vis-à-vis said stator of an amplitude of up to 2 mm without said motor housing transmitting a radial force to said stator.

4. Screwdriver according to any one of claims 1 to 3 in which said means for connecting said stator to said motor housing comprise: - a lug with orientation substantially perpendicular to the X axis, said lug being connected to said stator or to said motor housing, - a receptacle of complementary shape to said lug housing said lug, said receptacle being connected respectively to said motor housing or to said stator, said lug having for all of its surfaces a clearance with respect to said receptacle, said clearance being at least 2 mm for the surfaces of said lug perpendicular to said orientation of said lug.

5. Screwdriver according to any one of claims 1 to 3 in which said means for connecting said stator to said motor housing comprise an Oldham joint connected on one side to said stator and on the other side to said motor housing coaxially to the X axis.

6. Screwdriver according to any one of claims 1 to 3 in which said means for connecting said stator to said motor housing comprise a bellows connected on one side to said stator and on the other side to said motor housing coaxially to the X axis.

7. Screwdriver according to any one of claims 1 to 6, wherein said screwdriver is capable of delivering a screwing torque of at least 1,500 Nm

8. Screwdriver according to any one of claims 1 to 7 wherein said output shaft comprises a screwdriver socket drive square having a dimension on flat of at least ¾ inch.

9. Screwdriver according to any one of claims 1 to 8 wherein said motor housing comprises at least one gripping handle.

10. Screwdriver according to any one of claims 1 to 9 wherein said motor housing is made of plastic material and said impact mechanism housing is made of metallic material.

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