Abstract:
An actuating device, specifically to actuate locking differentials on vehicles, having an actuating shaft, a drive unit to drive the actuating shaft, where the drive unit comprises an armature core non-rotatably mounted on the actuating shaft and a commutator non-rotatably mounted on the actuating shaft, having an electromagnetic brake unit to brake and/or to hold the actuating shaft, where the brake unit includes a brake hub flange non-rotatably mounted on the armature, and having a single- or multi-piece housing tightly enclosing the drive unit and the brake unit, where the free end of the actuating shaft extends from the housing.

Description:
The invention relates to an actuating device, particularly for actuating locking differentials on vehicles. 
   Actuating devices of this type find use particularly in a vehicle to assist the drive and brake systems. They normally comprise a drive unit to drive an actuating shaft and a braking unit to brake the actuating shaft. A locking differential can be engaged or disengaged by means of the actuating shaft. The drive unit assumes the actual shifting action. The brake unit keeps the actuating shaft in a predetermined position. 
   Severe demands are placed on actuating devices of this type. In particular, they must withstand operating temperatures up to 200° C. The actuating shaft can be subject to only relatively minor play in order to ensure functionally reliable actuation of the locking differential. In addition, the actuating shaft is supposed to be of simple construction and simple to install. The actuating shaft is also supposed to be of compact dimensions. 
   The object of the present invention is therefore to propose an actuating device which meets the stated requirements. 
   SUMMARY 
   To achieve this object, an actuating device is provided having an actuating shaft with a drive unit to drive the actuating shaft, where the drive unit has an armature core located non-rotationally on the actuating shaft and a commutator located non-rotationally on the actuating shaft, having an electromagnetic brake unit to slow and/or stop the actuating shaft, where the brake unit comprises a brake hub flange mounted non-rotationally on the armature shaft, and having a one-piece or multi-piece housing tightly enclosing the drive unit and the brake unit, where the open end of the actuating shaft extends out of the housing. 
   An actuating device of this type has the advantage that the drive unit and the brake unit lie spatially close to each other and are enclosed by a common, possibly multi-piece housing. The actuating device is consequently of very compact dimensions and is securely protected against environmental influences. 
   In a preferred aspect of the invention, the surface of the actuating shaft has splines running axially, which form a spline press fit with the inside of the brake hub flange. Joining by means of splines has the advantage that it creates a simple and positive connection in which the two parts of the joint do not have to be produced with too close and therefore expensive tolerances in diameter. In the spline press fit, the two parts of the joint are advantageously positively joined only in the area of the splines. As a result, the resulting insertion forces are considerably less in comparison to press fit joints made to close tolerances, acting over the entire circumference of the joined parts. In particular, thinner actuating shafts can be joined to the brake hub flange without the risk of undesirable distortion of the shaft. Even a minor distortion of the shaft results in tumbling and makes itself noticeable primarily as a distracting noise when the actuating device is operating. 
   When the shaft is joined to its mate, the splines advantageously embed themselves in the inside of the brake hub flange to form a positive and an interference fit. The inside of the brake hub flange does not need to satisfy any particular requirements for this to happen and otherwise needs no special machining. 
   It has proven to be advantageous if the height of the splines is in the range of about 0.02 mm. With splines of this type, an adequately good connection of the two parts of the joint is achieved with relatively low joining forces. 
   The brake hub flange is advantageously made of aluminum. By using such a soft material, the splines embed themselves advantageously into the aluminum, requiring relatively low insertion force. Since the shaft is of harder material than aluminum, no undesirable distortion of the shaft results when it is joined to the brake hub flange. 
   In a further, especially preferred aspect of the invention, each of the splines has a conical rise on at least one end. Providing a conical rise of this type has the advantage that when the two parts are joined, they are pre-centered because of the height of the splines, before maximum insertion force is brought to bear. The parts to be joined also cannot tilt, and the risk of scoring from any swarf pushed ahead of the parts being joined is avoided. 
   An advantageous aspect of the invention is created if the splines are located only in areas of the actuating shaft in which the brake hub flange is exposed to high radial forces. This has the advantage that the splines do not have to be formed over the entire length of the actuating shaft. Insertion forces are also reduced as a result. 
   The grooves can extend advantageously continuously and/or with interruptions over the entire length of the actuating shaft. The inside of the commutator and/or of the armature core facing the actuating shaft, together with the brake hub flange, also forms a spline press fit. The advantages resulting in conjunction with the brake hub flange apply equally to the spline press fit of the actuating shaft with the commutator and/or with the armature core. 
   Under the invention the actuating shaft can also be ground in sections, with the grinding taking place advantageously before the splines are formed. This has the advantage that ground areas can be provided, particularly for installing bearing elements. When the actuating shaft is joined to the other part, the ground areas are not affected, since the diameter of the shaft in the area of the splines is greater than in the area of the ground parts. Consequently, the bearing elements can be joined to the ground sections of the actuating shaft after the actuating shaft is joined to the brake hub flange, the commutator and/or the armature core. In order to produce an extremely precise spline diameter, it can be arranged under the invention that the actuating shaft is ground completely before being joined to the other part, or the other parts, respectively. 
   In a further aspect of the invention, the brake unit can be slipped onto the actuating shaft axially over the free end of the actuating shaft for assembly of the brake unit. While it is being slipped over the shaft, the splines bite into the flange of the brake unit. Assembly in this manner has the advantage that it can be performed blind. 
   It is further conceivable that the inside of the brake hub flange has a section tapering conically toward the actuating shaft. A section such as this on the brake hub flange contributes to the self-centering action of the two parts of the joint. 
   In a particularly preferred aspect of the invention, four splines disposed at 90° to each other are located around the actuating shaft. In addition to the axial press fit, this provides an adequate safeguard against the two parts of the joint rotating with respect to each other. 
   In order to ensure that the actuating shaft is guided accurately, even during the braking process through the brake unit, a preferred aspect of the invention has the actuating shaft supported against the housing by at least one bearing element in the area of the brake unit. 
   Advantageously the bearing section on the shaft side of the bearing element is located directly on the actuating shaft. This has the advantage that the power flow is taken directly from the actuating shaft over the bearing element into the housing. 
   As an alternative it is conceivable that the bearing section on the shaft side is located on the brake hub flange. This has the advantage that the brake hub flange along with the bearing element can be pre-assembled and handled as an independent assembly. The brake hub flange along with the bearing element is then joined as one to the actuating shaft over the brake hub flange. 
   In an further aspect of the invention, the brake unit has a braking body secured against rotation against the housing and incorporating a brake winding and a brake rotor carrier with a brake rotor connected non-rotationally to the actuating shaft, where, when current is applied to the brake winding, the brake rotor is attracted to the brake body or repelled from the brake body. As a result, a brake unit is realized with a small number of components which meets the requirements for the actuating device. The brake rotor is preferably configured as a brake rotor ring, where in its assembled state, the actuating shaft passes through the central opening of the brake rotor ring. 
   Advantageously the brake body is configured as a magnetic brake body. This has the advantage that no additional permanent magnets need to be provided that achieve suitable braking action in conjunction with the brake winding. 
   In a particularly preferred aspect of the invention, the brake rotor can be moved axially with respect to the brake rotor carrier, where a spring element is positioned between the brake rotor and the brake rotor carrier which presses the brake rotor toward or away from the brake body. This has the advantage that the brake rotor, both with the brake unit activated and not activated, is in a specified position. This suppresses clattering noises when the actuating device is in operation. 
   The brake rotor carrier can be located directly or by means of a brake rotor hub on the actuating shaft. The brake rotor carrier or the brake rotor hub is configured as a separate component or in one piece with the brake hub flange. The single-piece configuration with the brake hub flange has the advantage that additional components are not necessary. Positional tolerances can be kept smaller as a result. 
   An additional aspect of the invention is characterized in that the brake body is attached on the brake hub flange, where a bearing, specifically a friction bearing, is located between the brake body and the brake hub flange. This has the advantage that the brake body with the brake hub flange can be configured as an independent component assembly which can be handled separately. 
   On the other hand, it is also conceivable under the invention that the brake body is attached on the housing side. In an aspect of the invention of this type in the assembled state, an air gap exists between the brake body and the brake hub flange or the actuating shaft. This has the advantage that a bearing element, specifically a friction bearing, does not have to be provided between the brake body and the brake hub flange or the actuating shaft. 
   To realize non-rotation of the brake body against the housing, the brake body can be clinched against the housing in sections. It is further conceivable that the brake body has defined elevations, for example in the form of pins, that engage corresponding recesses, blind holes in the case of pins. 
   Advantageously the housing has a pot-shaped housing base and a housing cover with an opening for the actuating shaft. The drive unit can be located in the area of the housing base and the brake unit in the area of the housing cover. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     Additional advantageous aspects and details of the invention can be found in the description to follow, in which the invention is described in greater detail and explained on the basis of the aspects shown in the drawing. 
       FIG. 1  shows a longitudinal section through a first actuating device under the invention, 
       FIG. 2  shows a longitudinal section through a second actuating device under the invention, 
       FIG. 3  shows a longitudinal section through a third actuating device under the invention, 
       FIG. 4  shows a cross section through an actuating shaft of an actuating device under the invention; and 
       FIG. 5  a side view of an actuating shaft of an actuating device under the invention. 
   

   DETAILED DESCRIPTION 
   A first aspect of an actuating device  10  under the invention is shown in FIG.  1 . On the free end of an actuating shaft  12  the actuating device  10  has a pinion  14  through which a locking differential (not shown) of a vehicle can be actuated. The actuating device comprises a drive unit  16  and an electromagnetic brake unit  18 , where the drive unit  16  and the brake unit  18  are accommodated in a common housing  20 . The housing  20  comprises a pot-shaped housing base  22  which locates the drive unit  16 . Further the housing  20  comprises a housing cover  24  in which the brake unit  18  is accommodated. The housing cover  24  can be tightly bolted to the housing base  20  with fasteners  26 . 
   The drive unit  16  includes permanent magnets  28  on the housing side that interact with an armature core  30  located non-rotationally on the actuating shaft  12 . The drive unit  16  further includes a commutator  32  located non-rotationally on the actuating shaft  12 , with brushes  36  mounted in brush holders  34  acting against the outer surface of the commutator  32 . The brush holders  34  are attached on a brush rocker  40  positioned perpendicular to the longitudinal axis  38  of the actuating shaft  12 . Various additional electrical components, for example, interference suppression devices, are furnished on the brush rocker  40 . 
   The brake unit  18  comprises a brake hub flange  42  located on the actuating shaft  12  and prevented from rotating, and a brake body  46  which is prevented from rotating against the housing cover  24  and which includes a brake winding  44 . The brake unit  18  further includes a brake rotor  48 , configured as a brake rotor ring, which is prevented from rotating with respect to the actuating shaft  12  but which has limited axial movement. When current is applied to the brake winding  44 , the brake rotor  48  acts against the brake body  46 , which is likewise of annular shape. When current is applied to the brake winding  46 , the braking effect results, and the actuating shaft  12  is prevented from rotating against the housing  20 , or the housing cover  24 , through the brake hub flange  42 , the brake rotor  48  and the brake body  46 . To provide an arrangement whereby the brake body  46  does not rotate in the housing cover  24 , the brake body  46  is furnished with pins  50  running coaxially to the longitudinal axis  38 . The pins  50  protrude into correspondingly-shaped blind holes  52  in the housing cover  24 . To mount the brake body  46  securely inside the housing cover  24 , sections  54  are provided on the housing cover  24  which are staked into matching sections on the outer surface of the brake body  46 . 
   To ensure a specified position of the brake rotor  48  when the brake unit  18  is not actuated, a spring element  58  is furnished between the brake rotor  48  and a section of the brake rotor carrier  56  of the brake hub flange  42 , which presses the brake rotor  48  against the section of the brake rotor carrier  56 . 
   Two bearing elements  60  and  62  are provided to carry the actuating shaft  12 . 
   In the case of the actuating device  10  from  FIG. 1 , the shaft-side bearing section of the bearing element  60  is located on the brake hub flange  42 . This has the advantage that simple assembly of the actuating device  10  is possible, since the entire braking unit  18  with the bearing element  60  can be pressed, or inserted, into the housing cover  24 . The entire brake unit  18  with bearing element  62  can consequently be pre-assembled and handled separately as a cohesive assembly. An air gap  64  is provided between the interior outer surface of the brake body  46  and the side of the brake hub flange  42  facing this outer surface. As a result, bearing elements or bearing means between the brake body  46  and the brake hub flange  42  are not necessary. 
   In the section from  FIG. 1 , two grooves, or splines,  66  and  68  are furnished on the actuating shaft  12  along one line. Spline  66  is in the area of the brake hub flange, and spline  68  is in the area of the drive unit  16 . 
   As can be seen from the cross-section from  FIG. 4 , the actuating shaft  12  has a total of four splines  66  and four splines  68  each. The splines  66 ,  68  are offset to each other at an angle of 90°. The splines as such have a notch angle in each case of 90°. The height h of the splines is in the region of about 2/100 mm. The actuating shaft  12  has no splines in the area of the bearing elements  60  and  62 . These areas can be ground to achieve a high degree of accuracy. The splines  66 ,  68  can be created in the actuating shaft following the grinding procedure. 
   As can be seen from  FIG. 5 , the splines  66 ,  68  have conical sections  70  at their respective ends which extend over length  1  in an axial direction. 
   To assemble the actuating shaft  12  to the brake hub flange  42 , the end of the actuating shaft having the pinion  14  is inserted into the central opening of the brake hub flange  42  without the pinion. The inside of the brake hub flange  42  has a conical section  72  tapering toward the actuating shaft  12 . Because of the conical sections  70  and the conical section  72 , the result is a self-centering action when the brake hub flange  42  is joined to the actuating shaft  12 . When they are joined, the peaks of the spline  66 ,  68  embed themselves into the inside of the brake hub flange  42 , which is preferably made of aluminum. The result is a spline press fit between the brake hub flange  42  and the actuating shaft  12 , which can be achieved with relatively low insertion force. 
   In the assembled state, the grooves  68  interact with the armature core  30  and with the commutator  32 , as shown in FIG.  1 . Because of the conical sections  70  of the grooves  68 , there is a self-centering action here as well when they are joined. Since the positive interference fit between the actuating shaft  12  and the commutator  32  or the armature core  30  advantageously takes place only at the peaks of the splines  68 , the insertion force can be kept relatively low. The ground section of the actuating shaft  12 , which interacts with the bearing element  62  in its installed position, is not damaged when the actuating shaft  12  is joined to the commutator  32  and the armature core  30 . 
   A second actuating device  80  under the invention is shown in  FIG. 2 , and in  FIG. 3  a third actuating device  90  under the invention. The components corresponding to the actuating device  10  are given the same reference numbers in the actuating devices  80  and  90 . 
   One way in which actuating device  80  differs from actuating device  10  is that the brake unit-side bearing element  82  has a bearing section located directly on the actuating shaft  12 . Further, the brake body  46  is not located on the housing cover side, but is located by means of a friction bearing  84  on the brake hub flange  42 . To ensure that the brake body  46  cannot rotate, a lug  86  is provided, which engages teeth located the housing cover side, as shown in FIG.  2 . 
   The aspect from  FIG. 2  has the advantage that the air gap to be provided between the brake body  46  and the brake rotor  48  can be set in the assembly containing the brake body  46  and the brake rotor  48 . 
   A further difference between the actuating device  10  from FIG.  1  and the actuating device  80  from  FIG. 2  is that, in the case of actuating device  80 , there are not two splines  66  and  68  positioned along one line. Instead, splines  88  are provided which extend over the drive unit  16  and the brake unit  18 . The shape of the splines  88  is as shown in  FIGS. 4 and 5 . They are simpler to manufacture because no breaks in the grooves  88  are planned. 
   In the case of the actuating device  90  from  FIG. 3 , the bearing element  82  is located lying directly against the actuating shaft  12 , as is the case with the actuating device  80  from FIG.  2 . Actuating device  90  differs from actuating device  80  in that the brake rotor carrier  56  is formed separately from the brake hub flange  42  as an independent component. The brake rotor carrier  56  is positioned on the actuating shaft  12  by means of a brake rotor hub  57 . In this embodiment, the air gap between the brake rotor  48  and the brake body  46  can still be advantageously set during assembly of the brake hub flange  42 , or of the section of the brake rotor carrier  56 . 
   All the features shown in the description, the claims to follow and the drawing can be fundamental to the invention both individually and in any combination.