Electric actuator and calliper brake comprising such actuator

An electric actuator (13) comprises a housing (7) which contains a screw mechanism (11) and an electric motor (5) which is driveably connected to the screw mechanism which provides a linear movement in response to a rotational movement of the electric motor (5), said screw mechanism (11) comprising a screw (12) and a nut (13) one of which is supported rotatably with respect to the housing (17) by means of an angular contact ball bearing (31), said angular contact ball bearing (31) comprising two pairs of contact points the working lines (40,41) of which intersect each other. One pair of contact points has a working line (41), the angle of which with respect to the axis (42) of the bearing (21) is smaller than the corresponding angle of the other working (40) line.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention is related to an electric actuator, comprising a screw
 mechanism and an electric motor which is driveably connected to the screw
 mechanism which provides a linear movement in response to a rotational
 movement of the electric motor, said screw mechanism comprising a screw
 and a nut one of which is supported rotatably with respect to the housing
 by means of an angular contact ball bearing, said angular contact ball
 bearing comprising two pairs of contact points the working lines of which
 intersect each other.
 2. Description of Related Art
 Such actuator is known from WO-A-9603301. The screw member thereof
 protrudes from a housing, in which housing said screw member is slidably
 guided by means of a pair of supports. In most applications, said known
 actuator behaves satisfactorily for providing a rectilinear movement.
 However, its proper behaviour can only be guaranteed in case said movement
 and also the loadings are strictly in line with the axis of the screw
 member. For applications in which the screw member is loaded transversely,
 and/or is displaced transversely due to external influences exerted by an
 external actuatable component, the actuator will be blocked and eventually
 destroyed.
 SUMMARY OF THE INVENTION
 The object of the invention is to provide an actuator of this kind which
 provides a better support of the nut, and thereby of the screw member, in
 relation to the transverse loadings and/or displacements. This object is
 achieved by one pair of contact points having a working line the contact
 angle of which with respect to the axis of the bearing is smaller than the
 corresponding contact angle of the other working line.
 In the actuator according to the invention, the nut is supported
 particularly well with respect to axial loadings in one direction, i.e. in
 the direction of forces which exert a load on the pair of contact points
 having a working line with a smaller contact angle with respect to the
 axis. In the other direction, a limited loading is also possible. The
 stability of the bearing with respect to bending moments is maintained to
 a large degree, and also with respect to combinations of such moments with
 respect to axial and radial loadings.
 The outer ring or the inner ring of the angular contact ball bearing is a
 split outer ring respectively a split inner ring comprising two axial
 halves, which are pressed against one another under axial forces for
 providing the desired bearing clearance (positive or negative).
 Furthermore, the axial ring halves may have facing radial abutment faces.
 The axial ring halves may be connected to each other, and may be preloaded
 in axial direction, by means of a clamping means.
 According to a first possibility, the nut is rotatably supported and
 driveably connected to the electric motor, and the screw mechanism may
 comprise a hollow screw having a central bore opening out at one end of
 the screw and accommodating an actuating member, which actuating member
 protrudes from the open end and is connected to the screw at a distance
 from said open end.
 The actuating member of the actuator according to this embodiment may be
 connected to an external component, which means that any transverse forces
 exerted on and/or displacements of such external component will have no
 direct influence on the screw member. Thus, said screw member will be
 exposed mainly to axial loadings, which safeguards its proper functioning.
 Preferably, the actuating member is accommodated with a radial play within
 the hollow screw. This radial play may be tuned with respect to the
 expected transverse displacements.
 The actuator can be connected to the hollow screw in several ways. For
 instance, the end of the actuator could be connected to the internal end
 wall of a bottom which closes the internal hollow space of the screw. In
 particular, the actuating member can be connected to the screw by means of
 a sleeve which fits between said member and screw, which sleeve is at a
 distance from the open end and which is shorter than said member and the
 bore.
 According to a second possibility, the screw may be rotatably supported and
 driveably connected to the electric motor, and the nut is connected to a
 brake pad support.
 In particular, the screw may be connected to a concentric mounting sleeve,
 which mounting sleeve at least partly surrounds the screw and which is
 connected to the inner ring of the angular contact ball bearing, the nut
 being accommodated at least partly between mounting sleeve and screw.
 The screw mechanism may comprise a roller spindle or a ball spindle. A
 particular favourable embodiment, which requires little space, is obtained
 in case the nut of the spindle forms an integral part of the inner bearing
 ring of an axial thrust bearing.
 The angular contact ball being may be either a single row four-point
 contact ball bearing, or a double row angular contact ball bearing.
 The actuator according to the invention can be applied in various fields.
 In particular however, said actuator is fit for a brake calliper,
 comprising a claw piece with two opposite brake pads and an electric
 actuator according to any of the preceding claims, said actuator
 comprising an electric motor and a screw mechanism which is driveably
 connected to the electric motor for providing a linear movement in
 response to a rotational movement of the electric motor, said screw
 mechanism comprising a screw and a nut which is supported rotatably with
 respect to the housing by means of full complement four-point contact ball
 bearing, said four-point contact ball bearing comprising two pairs of
 contact points the working lines of which intersect each other. Such brake
 calliper is also known from WO-A-9603301.
 In a brake calliper, the actuator is mainly loaded in one and the same
 direction, i.e. in the direction of pressing the brake pads onto the brake
 disc. According to the invention, advantageous use is made of the actuator
 described before, in that one pair contact points has a working line the
 angle of which with respect to the axis of the bearing is smaller than the
 corresponding angle of the other working line.
 In particular, the pair of contact points with a working line having an
 angle with respect to the axis of the bearing less than the corresponding
 angle of the other working line, is loaded by the brake force exerted on
 the brake pads.
 Preferably, the outer ring of the four-point contact ball bearing comprises
 two axial halves, which are pressed against one another under axial forces
 for providing the desired bearing clearance.
 The working line of the pair of contact points which is loaded by the brake
 force exerted on the brake pads, may have a contact angle with respect to
 the axis of the bearing less than 45.degree..
 In a preferred embodiment, the screw mechanism may comprise a hollow screw
 having a central bore opening out at one end of the screw and
 accommodating an actuating member, which actuating member protrudes from
 the open end and is connected to the screw within the bore at a distance
 from said open end, wherein the actuating member cooperates with one of
 the brake pads and the screw mechanism cooperates with the opposite brake
 pad.
 As is usual in disc brakes, the pads thereof have some transverse play
 within the claw piece, which play manifests itself as soon as said pads
 are pressed onto the rotating disc to be braked. The actuating member of
 the actuator according to this embodiment is perfectly fit for taking such
 play, thus preventing the screw mechanism from getting blocked.
 The stator of the electric motor may be connected to the claw piece, and
 the rotatable part of said motor may be connected to the screw mechanism.
 Furthermore, the electric motor can be accommodated on a support piece
 which is rotatably supported in the claw piece, and which is in
 cooperation with the nut of a roller spindle or a ball spindle.
 Preferably, the screw mechanism of the brake calliper is a roller spindle
 or a ball spindle; the nut of the spindle may form an integral part of the
 inner bearing ring of an axial thrust bearing.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 The brake calliper shown in FIG. 1 has a claw piece 1, which in the usual
 way comprises two brake pads 2, 3. Brake pad 2 is connected to flange 4 of
 the claw piece 1; by means of support 22, brake pad 3 is connected to an
 electric actuator, indicated in its entirety with 13.
 The electric actuator 13 comprises an electric motor 5, the stator 6 of
 which is connected to housing part 7 of the claw piece 1.
 The rotational part 8 of the electric motor 5 is connected to a shaft piece
 9, which by means of bearing 10 is rotatably supported in the housing
 portion 7 of claw piece 1.
 The actuator 13 furthermore comprises a screw mechanism, which comprises
 inter alia a hollow screw 12 and nut member of an inner ring 33. The inner
 ring 33 and the screw member 12 co-operate by means of rolls 14, and
 constitute a roller spindle, which is known per se.
 The rotational part 8 of the electric motor 5 is drivably connected to the
 nut member, such that upon rotation thereof the screw member 12 is
 displaced in axial direction via the rolls 14. In various embodiments, the
 rotation thereof is obtained by a hard turning operation.
 The hollow screw member 12, the hollow space of which is indicated by 15,
 contains an actuating member 16 which extends from the closed bottom end
 17 of the hollow screw member 12, and which protrudes from the open end
 thereof.
 The actuating member 16 is connected to the screw member 12 near the bottom
 end 17 thereof, by means of a clamping sleeve 18.
 At its protruding end, the actuating member 16 comprises an actuating head
 19, which rests against support 22 of brake pad 3. This actuating head 19
 is sealed with respect to the housing piece 7 of claw piece 1 by means of
 a bellows 20, which is known per se. As mentioned, between the brake pad 3
 and the actuating head 19, there is a support member 22, which by means of
 pin 21 is rotatably fixed with respect to said actuating head 19.
 As is usual, the brake pads 2, 3 have some play in a direction transverse
 with respect to the access of screw member 12. Thus, upon pressing the
 brake pads 2, 3 to a brake disc (not shown), said pads will exhibit some
 transverse movements with respect to the screw member 12. Due to the fact
 that the actuating member 16 is not rigidly connected to the screw member
 12, the latter one will not be exposed to said transverse movements or
 loadings. Instead, the actuating member 16 will flex somewhat within the
 hollow space 15 of hollow screw member 12, which flexing movement is
 possible due to the radial play which exists between the actuating member
 16 and the internal wall of the hollow space 15.
 According to the invention, a four-point contact ball bearing 31 has been
 applied. Said bearing may have a split inner ring or a split out ring.
 This four-point contact ball bearing 31 comprises one series of rolling
 balls 32, the inner ring 33 which forms a unity with the nut member of
 screw mechanism, and an outer ring 34 comprising two outer ring halves 35,
 36. These outer ring halves 35, 36 together define a raceway 37, 38; the
 inner ring 33 defines a raceway 39.
 The raceways 37-39 are formed in such a way that four contact points are
 obtained, comprising two pairs which each define a working line 40, 41.
 According to the invention, the raceways 37-39 have been formed in such a
 way that the working lines 40-41 intersect the axis of the bearing 31
 under mutually different angles. Working line 40 intersects the axis 42
 under a greater angle than working line 41. Thus, four-point contact ball
 bearing 31 according to the invention is in particular fit for taking the
 axial loads exerted by the brake pads 2, 3 when these are pressed onto the
 brake disc (not shown). In various embodiments, the rotation of the
 bearing 31 is obtained by a hard turning operation.
 The particular orientation of the working lines 40, 41 is obtained by an
 oblique orientation of the raceways 37-39. This orientation results from
 the relatively large diameter of the inner surface or land 43 of outer
 bearing ring half 35, and the smaller inner diameter of the inner surface
 or land 44 of outer ring half 36.
 Also, the outer surface or land 45 of the inner ring 34 has a diameter
 which is larger than the outer surface or land 46 thereof.
 The four-point contact ball bearing 31 furthermore comprises a sensor 50,
 the parts of which are connected to outer ring halve 36 and to inner ring
 33. This sensor may serve basic functions such as giving information
 concerning wear compensation, maintenance indication, brake force feedback
 (ABS), traction control and for vehicle dynamic functions.
 The embodiment shown in FIG. 2 is to a large extent identical to the
 embodiment of FIG. 1. It has a similar brake calliper 1, brake pads 2, 3,
 support bearing configuration, flange 4, and an electric actuator 13.
 The electric actuator is connected to an electric motor 5, having a
 rotational part 8 and a stator 6 connected to housing part 7.
 The rotational part 8 is drivably connected to hollow support piece 51,
 which by means of needle bearing 52 and stub 53 is rotatably supported
 with respect to the housing 7. At its other end, the support piece 51 has
 a ring gear wheel 57 with outwardly extending teeth. Satellite gear wheels
 55 are accommodated on a flange of inner ring 58, and co-operate with a
 ring gear wheel 56, the outer surface of which is connected to the housing
 7. Furthermore, satellite gear wheel 55 co-operates with the ring gear
 wheel 57.
 The inner ring 58 of bearing 31 co-operates with screw member 59 through
 the rollers 60, which are contained in cage 61. Inner bearing ring 58,
 screw 59, roller 60 and cage 61 together form a screw spindle known per
 se, and will not be described in further detail.
 Inner ring 58 and outer ring half 36 furthermore carry rings which together
 form a sensor for measuring the amount of rotation of the inner ring 58.
 The embodiment of FIG. 3 is to a large extent identical to the embodiment
 of FIG. 1, however the screw mechanism now has a screw 62 which is
 rotatably supported and connected to the electric motor 5, whereas the nut
 63 is non-rotatably supported and connected to the brake support 64.
 The screw is connected to a concentric mounting sleeve 65, which surrounds
 the screw and is connected to the inner ring 33 of the four-point contact
 ball bearing 31. The nut 60 is accommodated between the mounting sleeve 65
 and the screw 62, and co-operates by means of rollers 60 with screw 62.
 Furthermore, the rotatable part 1 of the electric motor 5 co-operates with
 the mounting sleeve through the satellite gear wheel system comprises ring
 gear wheel 57. Said ring gear wheel engages satellite gear wheels 55
 connected to a flange of inner ring 58, which gear wheels 55 in turn
 engage ring gear 56 connected to the housing 7.
 Furthermore, by means of a self-centring spherical coupling 67, mounting
 sleeve 65 is connected to hand brake shaft 71.
 For purposes of sealing and damping, a sealing ring 66 is provided between
 mounting sleeve 65 and nut 60.
 Furthermore, the mounting sleeve 65 carries a damping ring 68 having
 external teeth 69, which is part of the satellite gear wheel system
 described before.
 The embodiment of FIG. 4 shows a part of the inner ring 72 of a four-point
 contact bearing, which inner ring forms a unity with support piece 73
 which is to be connected with a rotatable part 8 of the electric motor.
 The embodiment of FIG. 5 shows a four-point contact bearing comprising a
 unitary outer ring 75, and an inner ring 74 having two axial halves 76,
 77.
 Axial half 77 has internal screw thread 78, external teeth 79 which are
 part of the gear wheel system mentioned before, and a connecting groove 80
 for connecting a sealing bellows. By means of weld 81, ring halves 76, 77
 are mutually connected.