EP1047874A1

EP1047874A1 - Electric motor with drive

Info

Publication number: EP1047874A1
Application number: EP99963199A
Authority: EP
Inventors: Martin-Peter Bolz; Ferdinand Grob; Stefan Tumback
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1998-11-14
Filing date: 1999-11-04
Publication date: 2000-11-02
Anticipated expiration: 2019-11-04
Also published as: JP4582607B2; US6409622B1; JP2002530570A; BR9906923A; WO2000029744A1; EP1047874B1

Abstract

The invention relates to an electric motor which can be switched such that it functions as both starter motor and generator of an internal combustion engine, notably of a motor vehicle. A two-step planetary gear system is provided for for coupling the motor to the shaft (4) of the internal combustion engine, a brake unit being assigned to each step for blocking a rotating movement of said step.

Description

ELECTRICAL MACHINE WITH GEARBOX

The present invention relates to an electrical machine which can be switched as a starter and generator for an internal combustion engine, in particular an internal combustion engine of a motor vehicle. Such machines have been developed because they enable the two functions of starting the internal combustion engine and generating electric current that are required for the on-board systems of a vehicle, such as ignition, lighting, etc., to be carried out in a single electric machine unite and thus save weight and costs.

In such electrical machines, however, the problem arises that different transmission ratios are required for the generator operation and for the starter operation of the electrical machine, so that a switchable transmission must be provided which provides these different translations depending on the function of the electrical machine currently required allowed to produce. A two-stage planetary gear is known from DE 36 04 395 AI. This document teaches the use of such a transmission in an automatic transmission of a motor vehicle for setting different transmission ratios which correspond to the different gears of a gear shift and act on the chassis of the motor vehicle. The power transmission takes place constantly in one direction, namely from the internal combustion engine to the chassis. The document does not provide information on the starter or alternator of the vehicle.

Another example of a two-stage planetary gear is known from DE 19 531 043 AI. The planetary gear dealt with in this document is provided in order to be driven by a motor, in particular a motor of an electrically operated tool such as a drilling machine, and to drive a tool with an adjustable translation. Only one of the two stages is assigned a locking device which can prevent any rotation of the ring gear of this stage.

Advantages of the invention The present invention, as defined in claim 1, creates an electrical machine for use as a starter or generator for an internal combustion engine, which can be switched over easily with gear ratios optimally adapted to the operation of the electrical machine as a starter or as a generator Funds allowed.

Desirable gear ratios are for

Example when using a claw pole machine

(Synchronous or asynchronous machine) as electrical

Machine a gear ratio range from 1.6 to 4 for generator operation or from 4 to 60 in starter operation. The spread, that is to say the ratio of the gear ratios to one another, should be at least 2.

The braking force can be exerted in a simple manner, in particular by engaging a braking device on a ring gear of the planetary gear. Brake devices in particular include shoe brakes, multi-disk brakes or friction band brakes.

In a first preferred embodiment of the electrical machine, the planetary gear comprises two fixedly connected to the internal combustion engine shaft. dene sun gears and two sets of each meshing with one of the sun gears and a ring gear planet gears, and the planet gears of both sets are rotatably mounted on a planet carrier, which in turn is fixedly connected to a starter or generator shaft to a rotational movement on the generator shaft or of the Transfer generator shaft to the planet carrier. In this construction, by braking one of the two ring gears, a rotational force can be transmitted between the sun gear of the braked stage of the two-stage transmission and the planet carrier, while the other stage rotates freely.

This construction enables a particularly compact structure in which the dimensions of the two ring gears are identical. This reduces the number of different components of the gearbox required and enables more efficient and cost-effective production.

According to a second preferred embodiment, the planetary gear comprises two sun gears, one of which is permanently connected to the internal combustion engine shaft or the starter or generator shaft, and two sets of planet gears meshing with one of the sun gears and one ring gear. The planetary wheels of the two sets connected in pairs on a common axis in a rotationally fixed manner. In a variant of this embodiment, the ring gear of a step can be omitted.

According to a third preferred embodiment, the two-stage planetary gear comprises two sun gears, one of which is permanently connected to the internal combustion engine shaft or a starter or generator shaft, and two sets of planet gears meshing with one of the sun gears, the planet gears of the two sets in pairs comb together. Such a planetary gear requires only a ring gear.

In the second and third embodiment, the second brake device preferably does not engage a ring gear, but is designed to block the planetary movement of the planet gears, that is to say their rotation around the shafts.

For this purpose, the planet gears of both sets are preferably rotatably mounted on a common planet carrier, and the second braking device acts on this planet carrier.

In order to simplify the control of the planetary gear, a common actuating device is preferably Direction for actuating both braking devices is provided, which has at least one working position in which the first braking device is open and the second is closed, a working position in which the second braking device is open and the first is closed, and an idle position in which both are open. These positions can be set by a control element that can be moved with one degree of freedom. This degree of freedom is preferably a rotation, so that the actuating device can be actuated easily, for example with the aid of any conventional electric motor.

In order to ensure a smooth transition between the two transmission states of the transmission, each of which corresponds to a working position of the adjusting device, the adjusting device can preferably be moved from one working position to the other via the idle position.

It is also expedient that the actuating device can be moved beyond a working position into a braking position in which the braking device which is open in the working position is braked. "Braked" is understood to mean a state of the braking device in which the braking torque is different from zero, but is limited to such an extent that the transmission and the drive are overloaded. strand is excluded. The actuating device should only allow the complete closing of a braking device if the other braking device is not also closed at the same time.

In a first preferred embodiment of the adjusting device, in which the braking devices can be actuated by adjusting movements parallel to an axis of the transmission, the adjusting device comprises two ramps which can be rotated about this axis for converting a rotary movement into an adjusting movement of the braking devices. In order to couple the actuation of the braking devices, it is sufficient if the two ramps are connected in a rotationally fixed manner. Such an adjusting device is particularly suitable for use with multi-disc brakes as braking devices.

In a second embodiment of the actuating device, in which the braking devices can be actuated by an actuating movement perpendicular to an axis of the transmission, the actuating device has at least one cam disk and levers interacting with the cam disk for converting a rotation of the cam disk into an actuating movement of the braking devices. Of course, each lever and thus each braking device can also be assigned its own cam disk. These outcomes staltung is particularly suitable for use in conjunction with shoe brakes as braking devices.

Further features and advantages of the invention result from the following description of exemplary embodiments.

characters

Show it:

1, 2, 2a and 3 show schemes of configurations of planetary gears of the machine according to the invention,

Figure 4 shows a longitudinal section through a transmission according to the first embodiment; and

FIG. 5 shows a section along the line V-V in FIG. 4.

FIG. 6 shows an axial section through a transmission of the machine according to the invention with two multi-disc brakes and a common adjusting device for the two multi-disc brakes; FIG. 7 shows a perspective view of an adjusting ring of the adjusting device from FIG. 6, which has two ramps for adjusting a multi-disc brake in different operating positions;

FIG. 8 shows a graphical representation of the axial displacement of the multi-disc brakes as a function of the orientation of the adjusting ring;

FIGS. 9 and 10 each show views of an adjusting device for jointly setting two multi-disc brakes;

FIG. 11 shows a perspective view of a shoe brake;

Figure 12 is a schematic representation of the interaction of the shoe brake with a control element;

FIG. 13 shows a side view of a transmission which is equipped with two shoe brakes according to FIG. 11 and an adjusting device according to FIG. 12; and

FIG. 14 shows a schematic illustration of the arrangement of the machine according to the invention in the drive train of a motor vehicle. Description of the embodiments

For an overview, the arrangement of an electrical machine according to the invention in the drive train of a motor vehicle is first briefly illustrated using FIG. 14. This drive train comprises an internal combustion engine 30 which can be connected via a main clutch 31 to a manual transmission 32 which drives 37 wheels of the motor vehicle with various adjustable transmission ratios via an output shaft. An internal combustion engine machine shaft 4 passes through the manual transmission 32 and is connected to the transmission 33 of the electrical machine according to the invention. The gear 33 has two stages, each gear stage 34 _i , 34 _ii is a separate braking device 35 _i; 35 _1L assigned. With the aid of the braking devices, the transmission ratio between the shaft 4 and a shaft 6, which is connected to an electrical machine 36, can be set. One of the two transmission ratios of the transmission 33 is provided for the operation of the electrical machine 36 as a starter of the internal combustion engine 30 and the other for the operation as an alternator. Different configurations of gears 33 are now dealt with on the basis of FIGS. 1, 2, 2A and 3.

First, the highly schematic representation used here will be explained in general with reference to FIG. 1. Figures 1 to 3 show highly schematic axial sections through gears. Short horizontal lines 10 each represent the toothing of a gearwheel. Two such lines are connected by a vertical line 11, which symbolizes the disk of the gearwheel. An open circle 12 in the middle of line 11 indicates that the gear in question is freely rotatable about an axis, which is symbolized by a horizontal line running through circle 12. A closed round point 13 represents a fixed connection between the gear in question and its axis.

In the transmission shown in FIG. 1, the internal combustion engine is coupled via a shaft 4 to a planet carrier 5, which rotatably holds planet wheels 2 ₁ , 2 _{2 of} the two stages of the planetary gear. These planet gears each _mesh with a sun gear 1 or 1 _X1 and a ring gear 3 or 3 _xι . The sun gears are on one fixed to the (not shown) electrical machine shaft 6 mounted. In order to set a transmission ratio, a braking device (not shown in FIG. 1) engages on an outer surface 8 _i; B _i one of the ring gears 3 ^ 3 ^ and prevents this from rotating while the other ring gear is freely movable. In this way, a driving force is transmitted from the shaft 4 to the shaft 6 or in the opposite direction, depending on whether the electrical machine works as a starter or as a generator, through that of the two gear stages, the ring gear of which has just been braked. The planet and ring gears of the other stage run freely. The direction of movement of the free-running ring gear varies depending on the gear ratio set, but the path speed of the ring gear is in any case relatively low compared to that of a blocked ring gear in a single-stage planetary gear. Therefore, the mass moment of inertia of the two-stage planetary gearbox is surprisingly low despite the increased number of components compared to a single-stage gearbox, and enables fast and low-wear switching between different gear ratios.

FIG. 4 shows the structure of the two-stage planetary gear from FIG. 1 in one for illustration detailed axial section. The shaft 4 connected to the internal combustion engine carries a planet carrier 20 in the form of a plate-like flange, on the outer edge of which three pins 21 _x (see also FIG. 5) are let in at an angular distance of 120 °, which are the axes of rotation of the planet wheels 2 _{X of} the first gear stage define. The disks 22 _{^ of} the planet gears 2 have only a fraction of the axial dimension of the teeth and are also broken through in order to keep the moment of inertia of the wheels as low as possible. The ring gear 3 _X is screwed to a flange 23, which has a cylindrical projection 24 as an engagement surface for a braking device.

In each case diametrically opposite to a pin 21 _x , the planet carrier 20 has an arm 27 projecting over the axial width of the first geurium stage, at the end of which a further pin 21 _{1 is} anchored, each of which carries a planet gear 2 _{X1 of the} second gear stage. A flange 25 fixedly connected to the ring gear 3 _X1 forms a carrier for plates 26 of a plate brake.

FIG. 5 shows a simplified cross section along the line VV from FIG. 4. The gearwheels 1 _x , 2 _L , 3 _{X of} the first stage are shown in section, the sun gear 1 ,, is partially covered. By interim spaces that exist between the planet gears 2 _{^ of} the first stage, the arms 27 of the planet carrier 20, which hold the planet gears 2 _{1X of} the second stage. The dimensions of the ring gear 3 _xl of the second stage are identical to those of the ring gear 3 _{X of} the first. The suns are in Figure 5 with 1. and 1 ,. designated.

The gear ratios of the gearbox are given by the formulas

when the ring gear 3 _X is braked to a standstill (n _3l = 0), and

with stationary ring gear 3 _X1 (n _3ll = 0), where U denotes the gear ratio and Z the number of teeth of a gear.

As can be seen from the following Table 1, with moderate number of teeth of not more than 75 for the ring gears, gear ratios U _X1 of approx.2.5 for the second stage and U _x of more than 5 for the first, and spreadings Φ = U ₁ / U ₁₁ from to reachable to 3 and more. Smaller ratios can also be achieved with this design, but large diameters of the ring gear and sun gear are required for this, which runs counter to the attempt to achieve a compact design. Table 1

Figure 2 shows the diagram of a second embodiment of a two-stage planetary gear for an electrical machine according to the invention. In this construction, the shafts 4 and 6 connected to the internal combustion engine and the electrical machine are each firmly connected to a sun gear l _x and l _lx . Planet gears 2 ₁ and 2 _{1X of} the two stages are firmly coupled to one another by a common axis 7. In this construction, basically three different transmission ratios can be set, two of them by locking a ring gear each and the third by locking the planetary movement, that is to say holding the axes 7 of the pairs of planet gears. The gear ratios are given by the formulas

,, 2 „( ^Z , +,„) _ _π z _h , {z _2l z _l + z _h z _2ll )

z z

(7, =, / ?, = 0

7 7

where the indication n _3ll = 0 or n _3l = 0 means that the ring gear 3 _X1 or 3., _ is locked and n _s = 0 means that the planetary movement is locked.

Exemplary results for gear ratios O _ll O ₂ , O _i and spreads Φ for the various combinations of tooth numbers Z of the individual gears are listed in Table 2 below.

Table 2

It can be seen that in each case the smallest transmission ratios U _{x are} achieved by holding the ring gear 3 _{1L of} the second stage, because at this stage the diameter of the planet gears 2_ is larger than that of the planet gears 2 _{1 of} the first stage. The greatest transmission ratio is achieved by holding the axles 7 in place. With this transmission, the ring gear of the first stage can therefore be dispensed with, unless this is necessary for the mechanical stability of the transmission.

To lock the movement of the axes 7 about the shafts 4 or 6, a braking device can be used which exerts a force in the axial direction on the ends of the axes 7, as indicated by the arrows 9 in FIG. 2, and so on the axes a planetary movement, but does not prevent the planet wheels from rotating about the axes.

A modification is shown in FIG. 2a. A planet carrier 20 'extends here between the two gear stages, and the axes 7 are held in bores of the planet carrier 20'. On a cylindrical outer surface 8, which the edge of the planet Carrier 20 'surrounds acts in the same way as on the ring gears of the embodiments described with reference to Figures 1, 4 and 5 or 2, a braking force F. With this construction, braking devices of the same type can be used to brake the movement of the axes 7 as well as the rotation of the ring gear 3 _X , which simplifies the construction.

3, the shaft 4 of the internal combustion engine is firmly connected to a large sun gear 1, which meshes with the planet gears 2 ₁ . These are rotatably mounted on a planet carrier 20 ″ and mesh with planet gears 2 _{X of} the second stage, which are mounted on the same carrier 20 ″. The latter are in engagement with a small sun gear l ₁ which is coupled via a shaft 6 to an electrical machine provided as a starter or generator of the motor vehicle. The gearbox has two gear ratios. In the first, the ring gear 3 _{XX of} the second stage is fixed, in the second it is the planet carrier 20 ″. No ring gear is required in the first stage, which has a clear advantage in terms of compactness and moment of inertia, since this ring gear, if it were present, would have to be significantly larger and heavier than that of the second stage. The planet carrier 20 ″ holds the planet gears 2 _{XX of} the second stage with the aid of arms which are partially cranked outside the sectional plane of the figure in the direction of the planetary movement, which is indicated in the figure by a broken line.

Like the planet carrier 20 'from FIG. 2A, the planet carrier 20 ″ can be locked by a brake acting on a cylindrical outer surface 8.

The following table shows gear ratios ü ^ ü _{j of} the two gear ratios for different numbers of teeth Z of the different wheels.

Table 3

Here, too, gear ratios in the appropriate range and spreads of 2 or significantly higher with moderate number of teeth and consequently with an overall compact gear can be achieved.

FIG. 6 shows in axial section a gear 33 with two multi-disc brakes 35 _λ , 35 _{ι; L} and an actuating device for actuating the two multi-disc brakes together. The structure of the transmission corresponds to that of Figure 1 and will not be described again in detail. The disk brakes 35 ^ 35 ^ each comprise a disk set connected to a ring gear 3 ₁ , 3 _ll and a disk set connected to an axially displaceable carrier 40. The displaceable plate set is pressed by a spring (not shown) against an adjusting ring 41, which FIG. 7 shows in a perspective view. The adjusting ring 41 is axially clamped between the lamellae and a set of fixed rollers 42 by the force of the spring. As can be seen in FIG. 7, the adjusting ring 41 carries two ramps 43 extending in the circumferential direction, on the surface of which a roller 42 runs when the adjusting ring 41 is rotated about the shaft 4 or 6. Depending on the height of the ramps 43 at the points at which they are in contact with the rollers 42, the disk carriers 40 are axially displaced to different extents, that is to say the brake is applied to different extents.

The two adjusting rings 41 are connected via a bridge 44 to a telescopic mechanism in a rotationally fixed but axially displaceable manner. One of the adjusting rings 41 has on its outer periphery a ring gear which meshes with a pinion 45 which is driven by a motor 46 via a reduction gear 47. The ring gear extends over an angular segment, the size of which corresponds at least to the angle spanned by each ramp 43.

FIG. 9 shows a perspective view of the adjusting device from FIG. 6 and the geared motor arrangement 46, 47. The ring gear has the shape of a segment 48 fixedly mounted on an adjusting ring 41, from which the bridge 44 to the second adjusting ring 41 also extends. The bridge 44 consists of two interlocking, axially rail-guided elements.

The components 41 to 45 and 48 can be regarded as a single adjusting device which, by simply rotating the pinion 45, allows the braking devices 35 ^ 35 ^ to be brought into different positions in a coupled manner.

Which positions the brake devices each take together depends on the shape of the ramps 43.

FIG. 8 shows an example of a possible height profile of the ramps 43 of the two adjusting rings 41 from FIG. 6 along their circumference. The lower curve corresponds to the collar shown in FIG. 7. Corresponding positions of the adjusting ring 41 in FIGS. 7 and 8 are each identified by letters a to e. The circles on the curves in positions a to e each symbolize the roller 42 assigned to the ramp in different positions of its path. In a first position a, the ramp from FIG. 7 has a height h _a (see lower curve in FIG. 8) at which the assigned braking device brakes but does not block completely. In positions b and c and the area in between, the braking device is open. fen, between d and e the braking force increases until the brake is closed at d, between e and d the height of the ramp is constant. The course of the ramp assigned to the other braking device, which is shown in the upper curve in FIG. 8, is mirror-symmetrical to this. In position c both brake devices are thus open, the transmission 33 is in an idle state. By turning in the direction of position d, one braking device is gradually closed while the other remains open. This state is a working state of the transmission with one of the two possible gear ratios. The second transmission ratio is set by turning it in the opposite direction to position b. Rotations beyond the positions b, d also lead to states in which one braking device is closed and the other brakes the entire drive train of the vehicle with a limited braking force.

Figure 10 shows schematically a variant of an actuating device. Here, the adjusting rings 41 are both serrated on at least part of their outer circumference and mesh with pinions 45, which, mounted on a common shaft 49, are driven by the motor 46. The width of the pinion or the teeth of the adjusting wheels 42 is dimensioned such that the adjusting wheels are selectively move the ramps (not shown in this figure) with the braking devices axially, without coming out of engagement with the pinions 45.

Other variants concern the number of ramps on a collar, which can easily be greater than 2. It is also readily possible to arrange the ramps on the side of the adjusting rings facing the disk carrier and thus to allow the ramps to interact directly with the disk carriers instead of axially closing the entire adjusting ring 41 with the aid of the fixed rollers 42, as shown in FIG move.

A second embodiment of a braking device, in the form of a shoe brake, is shown in FIG. This shoe brake, designated by the reference numeral 50, comprises two arms 51 which can be pivoted about axes 52 which are stationary in relation to the gear 33 (not shown here). Each arm 51 carries a brake shoe 53. A tension spring 49 exerts a force on the arms 51 which acts to open the brake.

The arms 51 have at their ends opposite, tapering triangular lugs 54. An adjusting lever 55 is about a stationary axis 58 pivotable and carries on a first arm 57 a rider 59 with a recess in which the lugs 54 engage. The rider 59 can be moved in the direction of arrow A by a pivoting movement of the actuating lever 55 perpendicular to the axis of the transmission. The second arm 56 of the actuating lever 55 interacts, as shown in FIG. 12, with a cam disk 60 and thus determines the height of the rider 59 on the lugs 54. In order to make the profile of the cam disk more recognizable, it is about its center of rotation dash-dotted circle, the radius of which is equal to the maximum radius of the cam disk. The further the rider 59 in FIG. 11 is pressed down, the more the brake shoes 53 press against the (not shown) ring gear of the transmission arranged between them. The cam disk 60 can (like the adjusting ring of the previously described embodiments) assume positions which are denoted by letters a to e in FIG. 12 and correspond to the open, closed or braked states of the shoe brake 50 in the same way as the above-described states.

Figure 13 shows a side view of a transmission 33 with two shoe brakes 50 ^ 50 ^ with the structure described above, which are each assigned to the two stages 34 _i , 35 _{ii of} the transmission. Two cam disks are on a common shaft 49 connected to an actuator 46. The two cam disks are identically shaped, but arranged in mirror image to one another, so that in the position shown in FIG. 13 a second lever 56 is lowered, the associated shoe brake 50. thus open, and the other second lever arm 56 _lx raised, the shoe brake 50 _{1X is} closed accordingly.

In this embodiment, each control lever is assigned its own cam disk βü ^ öO ^. Alternatively, it would also be possible to have the two actuating levers engage on a common cam disk with an offset angle.

Claims

claims

1. Electrical machine, which is switchable as a starter and generator for an internal combustion engine, in particular a motor vehicle, characterized in that it comprises a two-stage planetary gear for coupling to a shaft (4) of the internal combustion engine, each stage having a braking device for holding on is assigned to a rotational movement of the stage.

2. Electrical machine according to one of the preceding claims, characterized in that at least a first of the braking devices on a ring gear (3 ^ 3 ^) acts.

3. Electrical machine according to claim 1 or 2, characterized in that the braking device is a shoe brake, a multi-disc brake or a friction band brake.

4. Electrical machine according to one of the preceding claims, characterized in that the two-stage planetary gear two with a star ter- or generator shaft (6) firmly connected sun gears (1 ₁ , 1 ₁₁ ) and two sets of each with one of the sun gears and a ring gear (3 ₁ , 3 ₁₁ ) meshing planet gears (2 ₁ , 2 ₁₁ ), the planet gears (2 ₁ , 2 ₁₁ ) of both sets are rotatably mounted on a planet carrier (20) which is firmly coupled to the internal combustion engine shaft (4).

5. Electrical machine according to claim 4, characterized in that the dimensions of the two hollow walls (3 ₁ , 3 ₁₁ ) are identical.

6. Electrical machine according to claim 4 or 5, characterized in that the translations of the two stages are between 2.4 and 7.5 and have a spread between 2 and 3.

7. Electrical machine according to claim 4, 5 or 6, characterized in that the speed of the internal combustion engine shaft (4) is substantially equal to the engine speed.

8. Electrical machine according to claim 2 and one of claims 4 to 7, characterized in that the second braking device acts on the other ring gear.

9. Electrical machine according to one of claims 1 to 3, characterized in that the two-stage planetary gear two sun gears (l _x , l _xx ), one of which is permanently connected to the engine shaft (4) or a starter or generator shaft (6) is, and comprises two sets of planet gears (2 _X , 2 _1X ), each meshing with the sun gears and at least one ring gear (3 _X , 3 _XX ), the planet gears (2 _X , 2 _XX ) of the two sets in pairs on one common axis (7) are rotatably connected.

10. Electrical machine according to one of claims 1 to 3, characterized in that the two-stage planetary gear two internal gears (l _x , l _xx ), one of which is connected to the internal combustion engine shaft (4) or a starter or generator shaft (6) and comprises two sets of planet wheels (2 _X , 2 _XX ) each meshing with one of the sun wheels (l _x , l _xx ), the planet wheels of the two sets meshing in pairs.

11. Electrical machine according to claim 9 or 10, characterized in that the second braking device is able to block the rotation of the planet gears (2 _X , 2 _XX ) around the shafts (4,6).

12. Electrical machine according to one of claims 9 to 11, characterized in that the Planeuenrä- (2 _X , 2 _XX ) of the two sets are rotatably mounted on a common planet carrier (20 ', 20'').

13. Electrical machine according to claim 12, characterized in that the second braking device on the planet carrier (20 ', 20' ') engages.

14. Electrical machine according to one of claims 1 to 13, characterized in that the braking devices (35 _x , 35 _xx ; 50 _x , 50 _xx ) by a common actuating device (41, 42, 43, 44, 45, 48; 49, 60 _x , 60 _X1 , 56 _x , 56 _xx ) can be actuated, the at least one working position (b) in which the first braking device is open and the second is closed, a working position (d) in which the second braking device is open and the first is closed, and an idle position (c), in which both are open, can assume and can be adjusted into the positions by a control element (45, -49) that can be moved with one degree of freedom.

15. Electrical machine according to claim 14, characterized in that the adjusting device can be moved from one working position (b, d) to the other via the idle position (c).

16. Electrical machine according to claim 14 or 15, characterized in that the adjusting device is movable over a working position (b, d) into a braking position (a, e), in which the braking device open in the working position (b, d) is braked is.

17. Electrical machine according to claim 14, 15 or 16, characterized in that the actuating device permits the closing of a braking device (35 _x ; 35 _xx ; 50 _x ; 50 _xx ) only if the other braking device is not closed at the same time.

18. Electrical machine according to one of claims 14 to 17, characterized in that the braking devices (35 _x , 35 _xx ) can be actuated by adjusting movements parallel to an axis (4, 6) of the transmission, and in that the adjusting device (41, .. ., 45, 48) has two ramps (43) rotatable about the axis for converting a rotary movement into an actuating movement of the two braking devices (35 _x , 35 _xx ).

19. Electrical machine according to claim 18, characterized in that the ramps (43) of the two braking directions (35 _x ; 35 _xx ) are rotatably connected.

20. Electrical machine according to claim 18 or 19, characterized in that the braking devices (35 _x , 35 _xx ) along the axis (4,6) are each arranged between the planetary gear (33) and the associated ramp (43).

21. Electrical machine according to one of claims 18 to 20, characterized in that the braking devices (35 _x , 35 _xx ) are multi- _{disc brakes} .

22. Electrical machine according to one of claims 14 to 17, characterized in that the braking devices (50 _x , 50 _xx ) can be actuated by an adjusting movement (A) perpendicular to an axis of the transmission, and in that the adjusting device (49, 60 _x , 60 _xx , 55, 59) has at least one cam disk (60) and lever (55) interacting with the cam disk (60) for converting a rotation of the cam disk (60) into an actuating movement of the braking devices (50, 50 _l ).

23. Electrical machine according to claim 22, characterized in that the braking devices (50 _x ; 50 _xx ) are shoe brakes.