DE19736734C2 - Linear actuator and preferred application - Google Patents

Description

The invention relates to a linear actuator for implementing a fast Drehbe movement with a low moment in a slow linear movement with high force.

Such actuators are in general mechanical engineering in a variety of ways leadership forms known, e.g. B. as a ball screw, roller screw or tarpaulin ten-roller screw drive.

Each of the known embodiments has its specific advantages or disadvantages, so that the selection to be made for the respective application is usually based on the most favorable compromise. Certain applications are known, in which with constructive solutions satisfying the known mechanisms cannot be achieved.

So is currently under the term "Brake by wire" taken from the English developed an electrical braking system for motor vehicles, which the previous Hy makes draulic superfluous. You should namely by electromotive drives to the Brake calipers to be replaced. A sensor measures how hard the driver depresses the brake pedal enters and reports its measurement result to the microprocessor of the system control, which the command from the driver's shoe sole to the motors on the brake calipers gives. All of this works faster and more precisely than in the hydraulic system. Here the electronic control can perform such functions as anti-lock braking system (ABS) or Anti-slip control (ASR) also take over and so the complex brake in the car simplify considerably.

An electrically operated brake system is known from PCT application WO 89/03490 knows, with an electric motor via a planetary gear with two ring gears and one integrated ball screw acts on a pressure plate, with a braking force on the Brake shoes of a floating caliper disc brake can be exercised. The proposed one Design requires a large number of individual parts with sometimes narrow tolerances or  high quality standards. This results in high manufacturing costs and high Ge important. The concept also requires the ball nut to be secured against Twist, e.g. B. by means of a pin or bolt displaceable in a groove.

With the published patent application DE 195 11 287 A1, different designs of a electric disc brake system proposed, the electric drive motor radially encompasses the reduction gear in order to save overall length. There at the proposed reduction or conversion gears consist of in Prin zip known roller screws z. B. with roller return or additional forehead Gear teeth of the planetary rollers. Ordinary roller screw drives, however no arbitrarily small reductions. Also, with very small spindles increases the basic load ratings very small, so that they for the proposed application not enough anymore. A single-stage roller screw drive would therefore be both stronger drive motor as well as a larger gearbox required ma chen. In the publication, integration is used to overcome this problem proposed an additional planetary stage. However, this is an increase in her costs and a reduction in overall efficiency. Is anyway the construction cost of the versions shown is quite high, here in particular the Costs for the roller screw drive with toothed planet rollers and for that Rolling bearings that absorb compressive forces are likely to have an impact. Even with the concept According to the cited document, an anti-rotation device is to act on the brake pad the gear element required, e.g. B. by means of in a bore of the brake pad engaging bolt.

Prototypes of such braking systems have unfortunately shown that the electric drive system in the form of a collective of drive motor and gearbox could not easily fulfill. Especially the one with the high part Reduction and the other part related to the working principle Efficiency of the transmission required high-performance electric motors in order to required pressure of the brake shoes with extremely short response times to the To reach brake discs. For the control of such powerful motors would be an open Armament of the current electrical system voltage from 12 to 60 volts inevitable, since the otherwise extremely high currents even with very large cable cross sections speaking electrical power losses in the electrical system. Furthermore large electric motors would also be heavier at the same time, which means that the unsprung Masses of the wheel would disadvantageously increase. It is also to be considered see that in the wheel house or in the area of the suspension only a little installation space Is available, so that bulky aggregates would not be accommodated anyway. In addition, such electrical braking systems are because of the still too high costs not competitive compared to previous hydraulic designs.

There was therefore, in particular for the above-mentioned application, the task of creating a linear actuator of high force in small strokes, which should be able to convert the electrical energy supplied into mechanical power with as little loss as possible. The task as a whole received its high level of difficulty due to the following requirement profile:

• - High efficiency
• - Smallest working strokes with very high power requirements
• - Sufficiently large working area to compensate for wear on the brake disc be and coverings
• - Small construction volume and low weight
• - Resistance to high temperatures and temperature changes
• - Resistance to pollution and moisture
• - absolute reliability
• - Vibration resistance
• - Ease of service in the event of poor service
• - low production costs

The above-described object is achieved according to the invention by a special roller drove solved, which due to its clever concept the above requirements is able to meet almost uncompromising requirements. The roller according to the invention drive is based on the idea of creating a translatory movement between two with their thread rolling bodies the relationship between the To make pitch circles unequal to the number of gears. The reduction of the rotation into a translational motion becomes infinite when the two named Ratios are the same. In this case the axial feed is zero. At very Small inequalities result in small feeds of high force. With the The invention is further proposed to direct the considerable axial forces from the roller drive to be transferred to the frame so that the other components are free from axial forces stay and mount the drive (e.g. in the form of an electric motor) stationary on the frame is cash.

For a better understanding of the invention, the mode of operation will be explained in more detail using the exemplary embodiments shown in the three drawing figures. In Figs. 1 to 3 drawn representation is cut in a partially or aborted each presented an inventive ensemble, which is provided for integration in the disk brake system of a motor vehicle. Since the examples are essentially intended to clarify the functional principle, smaller details (e.g. circlips, additional seals, cable connections, plugs and the like) have been omitted for reasons of better clarity. For the same reasons, a slightly enlarged drawing scale was chosen.

The embodiment of the actuator shown in FIG. 1 has a housing 1 with a flange-like extension 2 for connection to the brake caliper of a disc brake. The inner area of the housing 1 is divided into two areas, of which the first, here on the left, houses the roller drive, while the second, here on the right, serves to accommodate an electric drive motor. Circumferential grooves are pierced in the housing 1 to create cooling fins 18 for better heat dissipation.

An axially movable piston 3 is accommodated on the left-hand side of the housing, the end face of which can act either directly or via a lateral force decoupling (e.g. roller) on the brake shoe lining carrier. In the example shown, the piston is arranged at a radial distance from the housing. Both parts are sealed against one another with a seal 19 in order to prevent the penetration of dirt and moisture. On the inside of the piston, a ring gear is formed with an internal thread 10, which in this case has three threads. In this ring gear, several (e.g. three) special planet rollers roll with their catchy thread, of which only the planet roller 8 is shown, so as not to block the view of the internal details of the roller drive. The planetary roller 8 is mounted in a cage 4 by means of a pin 9 . In this storage rolling elements, for. B. needle rollers, can be integrated. The cage merges to the right into a shaft 5 , the pin 6 of which is mounted in the housing 1 with a roller bearing 7 . The special planet rollers 8 supported in the cage 4 are subdivided in the axial direction, the left area being provided with the thread and the right area with circumferential ribs or grooves. These ribs or grooves rotating without a slope roll in a groove / rib profile 11 of the housing 1 . In the drawing, the side angles of the respective teeth of the thread or of the roller drive were set to approximately 45 ° for the example, a value which, for. B. is common with roller screws. For the general function of the unit according to the invention, however, the side angle is of subordinate importance. However, it seems to be advantageous to give the rolling flanks a spherical contour in order to realize approximately elliptical-like pressing surfaces of the rolling partners under load. The electromotive drive arranged in the right housing area of the exemplary embodiment is to be described below together for the three exemplary embodiments shown.

In the drawing figure 2 a modification of the embodiment shown in Fig. 1 is shown for example. In the housing 20 with flange 21 , a cylindrical fit 37 is incorporated, which forms the running surface for the piston 22 . As before, the piston is sealed against the housing with a seal 36 . External cooling fins 35 are also present in the area of the electric motor. The planetary rollers 25 are mounted in the cage 23 with bolts 26 . The cage goes to the right in a shaft stub 24 , which serves to couple the electric motor. The piston 22 is also a ring gear with a three-start internal thread 27 , while a groove / rib profile 28 is incorporated in the housing 20 . The right side on the planet roller len 25 lying groove / rib profile 28 rolls without play in that of the housing, so that a stable storage is created on all sides, which in principle makes an additional storage of the cage shaft 24 unnecessary.

Another modification of the previously described embodiments is shown in FIG. 3. Housing 38 with cooling fins 58 and flange 39 , piston 40 with seal 59 , fit 41 , planetary roller 44 with bolt 45 , three-start thread 46 and groove / rib profile 47 match the corresponding components in FIG. 1. However, the cage is not made in one piece here, but consists of cage disks ben 42 and 43 . In principle, these cage washers are still z. B. connectable by means of screwing or riveting, or can also be produced in one piece. However, sufficient space must remain in the center of the cage thus formed for a sun gear provided there. In the example shown, the sun gear is formed from a double-grooved gear 51 which corresponds to the groove / rib profile 47 of the planetary roller and which is part of a drive ring 48 . This merges into a shaft journal 49 , which in turn is mounted in the housing 38 by means of a roller bearing 50 .

The basic functioning of the transmission system will be explained in more detail below. Rotates the cage 4 , 23 clockwise, the special planet rollers 8 , 25 are taken along and due to the friction circuit between their right-sided ribs / pairs of grooves and the corresponding inner profile 11 , 28 of the housing 1 , 20 with their own rolling circle on one the inner profile 11 , 28 unrolled with its own left rotation. The axial position of the planetary rollers remains unchanged. At the same time, the (single-start) thread of the planetary rollers lying on the left rolls frictionally on the internal thread 10 , 27 of the piston 3 , 22 . If the rolling circles of the two rolling groups involved are chosen to be the same size, there is no angular displacement between the housing 1 , 20 and the piston 3 , 22 . The piston will therefore not perform any rotational movement, even if a rotary stop, for. B. in the form of a groove guide or the like is missing. The function described is also achieved analogously if the special planetary rollers are driven directly, for. B. as shown in Fig. 3.

The gear ratio between the thread of the planet rollers 8 , 25 , 44 and the internal thread 10 , 27 , 46 of the piston must logically always be an integer and is approximately adapted to the diameter ratio, especially when very small resulting total pitches are required. Since the smallest number of gears for the single planetary roller is one, z. B. the number of gears for the internal thread 10 , 27 , 46 can be set to three if the pitch circle diameter of the planetary roller is un dangerous a third of the pitch circle diameter. This ratio was also chosen for the exemplary embodiments shown. In the cage z. B. easily install three or more planetary rollers. In principle, you will always try to accommodate the largest possible number of planetary rollers.

If the diameter ratio between the pitch circles of the threads of the tarpaulin rollers 8 , 25 , 44 and the internal thread 10 , 27 , 46 deviates from the integral gear ratio of the two rolling partners, an axial displacement of the piston results per revolution of the cage according to the following relationship:

Here are:
z = outward movement of the piston in mm per clockwise rotation of the drive
G _H = number of gears ring gear
G _P = number of gears planetary roller
D _H = pitch circle diameter ring gear
D _P = pitch circle diameter of planetary roller
s = slope jump (division) in mm

From the formula it is clear that z. B. at a gear ratio of 3 to 1 and a ratio of the pitch circle diameter of also 3 to 1 of the axial forward thrust of the piston becomes zero. If you put z. B. those taken from the drawing Pitch circle diameter of 45 mm for the ring gear and 14.25 mm for the planetary roller on, the result is a gear ratio of 3 to 1 and the gradient jump of 6 mm an axial feed of the piston of 0.3 mm per drive revolution hung. Since the sign is positive, in the case of a right-hand thread, the Axial movement outwards.

In principle, both right and right can be used for the roller drive according to the invention Left-hand thread can be used. There is also the option of the pitch circle diameter of the special planetary roller slightly in relation to the ring gear to be set larger or slightly smaller than the gear ratio. According to the formula given above, this results in a reversal the direction of rotation. However, each has a larger relative in a relative ratio Planetary roller increased security against slippage, because if the speci The planetary role of the pistons changes much faster with the gradient speed outside (e.g. against the brake pad) would have to be advanced.

In the three examples, an identical electric disc rotor motor is used to drive the roller drive. Its rotor consists of a disc-shaped magnet 12 , 29 , 52 with an axial multi-pole magnetization. It is fastened to the cage shaft by means of a carrier 13 , 30 , 53 made of non-magnetizable material. The corresponding stator is made up of two halves which oppose the side surfaces of the disk-shaped magnet via an air gap. The jeweili ge magnetic yoke 14/15, 31/32, 54/55 runs out into the stator teeth which correspond to those of the disk-shaped magnet in their number of poles. The magnetic excitation of the two stator halves z. Example by means of a two-phase driving is of annular coils 16/17, 33/34, 56 / adopted 57th

In general, the most varied of electric motors are for the rotary drive of the system ren usable, e.g. B. DC, AC, stepper motors or the like, and, under certain conditions, also rotary magnets with limited rotation kel. The actual braking force is z. B. via a regulation of the current, a Changing the frequency, or using a clock with variable pulse  / Pause time ratio adjustable. Closed control loops can also be used suitable transducers.

Various modifications of the system are still available with the invention posed. It is proposed to use a rotary magnet as a rotary drive and this with a freewheel (e.g. a wrap spring or sprag freewheel) to couple the roller drive. The angle of rotation of the rotary magnet is then for the actual Chen brake stroke responsible during the to compensate for wear on the brake pads and brake discs automatically compensate the required stroke via the freewheel is sizable.

As a further modification, the drive motor shaft is offered with a equip straight or helical gear in the form of a sun gear, and to have this mesh with an additional toothing of the planetary rollers. This Gearing is either axially shifted on the planet rollers, or in the Roller heads of the planetary rollers can be inserted. So formed as a quasi-planetary gear Gear stage not only brings about an additional reduction, but also reduces it the moment of inertia of the overall system. This allows the response speed of the brake system can be increased. The one with the toothing of the Special meshing planetary teeth of the sun gear is shown here struck design simultaneously to the angular harmonization of the special len planetary roles. Without the quasi-planetary stage, one turns angular equilibrium position of the special planet rollers automatically.

The design according to the above proposal can be expanded to a full planetary stage if a toothed ring gear is added to the housing 1 , 20 , 38 . The toothed sun gear of the drive then meshes with the teeth of the planets, while they mesh with the toothed ring gear.

In order to ensure the frictional engagement of the system, which is essential for the function further proposed to radially adjust at least one of the special planet rollers make or in the role area by inserting z. B. a disc spring and a ring preload axially on the non-force-transmitting side.

The sun gear may further in accordance with the embodiment of FIGS. 3 and (z. B. hollow cylinder) be designed as glat ter cylinder and run len to the tooth tips of the Planetenrol, which are then preferably flattened. Such a hollow cylinder is then z. B. can be pretensioned by being slotted helically over the corresponding length with a large pitch. If the cylinder length should extend into the thread area of the planetary rollers, it is advisable to perform the helical slot of the hollow cylinder in opposite phase to the direction of the planetary roller thread and with a different pitch, so that a possible locking effect when rolling over is excluded.

The linear actuator according to the invention can also be used in an extremely simple embodiment, for. B.  realized for manual adjustment on a machine or a machine element if the motor drive side is replaced by a simple handwheel. It are then very sensitive or higher force adjustments with ease speed achievable.

Overall, the invention provides a linear actuator which usable for a whole range of applications and in a wide variety of designs gene can be produced. In particular, it seems the requirements as part of an elek trisch operated brake system of a motor vehicle in an optimal way to meet can. Because of the pure rolling friction, it is extremely effective degree, consists of a relatively small number of components, and is therefore in a very to realize compact size. It can come at a fairly low cost be put. Among other things, this opens the way to the advantages of the electrical or electronic technology in the motor vehicle also for the area of the brake system to make it usable.

Claims (20)

1. Device for converting a rotational movement into a translational movement, be standing from a roller drive with at least one planetary roller rotating in a ring gear with thread, characterized in that this planetary roller ( 8 , 25 , 44 ) has an external thread and at least in a first section in a second section has at least one pitch-free circumferential contact surface, or a groove / rib profiling with at least one groove or rib, wherein during the rotation of this planetary roller its external thread on the internal thread ( 10 , 27 , 46 ) of this first ring gear and At the same time, their circumferential contact surface without pitch or their groove / rib profile rolls on at least one circumferential contact surface without pitch or a groove / rib profile ( 11 , 28 , 47 ) of a second ring gear, the ratio between the pitch circle diameter of the external thread of the planetary roller and the pitch circle diameter of the internal thread the ring gear is not equal to the gear ratio between the external thread of the planetary roller and the internal thread of the ring gear and this results in an axial relative movement between the planetary roller and the ring gear with an internal thread in the rolling operation. 2. Device according to claim 1, characterized in that the respective between the planetary roller and the ring gear with internal thread or the ring gear with circumferential contact surface or groove / rib profiling formed rolling circles have the same diameter, so that when rotating the planetary roller between  no angular displacement occurs between the two ring gears. 3. Device for converting a rotational movement into a translational movement, be standing from a roller drive with at least one running around a threaded spindle Planetary role, characterized in that this planetary role at least in one he Most section an external thread and in a second section at least one steep continuous circumferential contact surface or a groove / rib profile with at least has a groove or rib, wherein during the rotation of this planetary roller you External thread on the external thread of the spindle and at the same time its pitch circumferential contact surface or their groove / rib profiling on the without gradient rolling the running contact surface or the groove / rib profiling of an axle journal, the ratio between the pitch circle diameter of the external thread of the Pla netenrolle and the pitch circle diameter of the external thread of the spindle un equal to the gear ratio between the external thread of the planetary roller and the The external thread of the spindle is an axially relative one movement between the planetary roller and the threaded spindle results. 4. The device according to claim 3, characterized in that the respective between the planetary roller and the threaded spindle or the journal with no pitch running contact surface or grooved / ribbed rolling circles formed the same Chen diameter, so that when the planetary roller rotates between the profit despindel and the journal there is no angular displacement. 5. The device is / are according to any of the preceding claims, characterized in that the planetary rollers rotatably supported in a cage (4, 23, 42/43) axially parallel thereto. 6. The device according to claim 5, characterized in that the rotative driving in rotation with said cage (4, 23, 42/43) is connected. 7. The device according to claim 5, characterized in that the planetary rollers is / are additionally provided with a spur gear toothing and via a with the rotary Drive connected sun gear with corresponding toothing will be driven. 8. The device according to claim 5, characterized in that the planetary rollers are / are rotated via their groove / rib profiling by means of a sun gear ( 51 ) with a corresponding groove / rib profiling. 9. The device according to claim 5, characterized in that the planetary rollers over its outer diameter (e.g. over flattened rib tips) by means of an im Principle of cylindrical sun gear is / are driven in rotation, this Sun gear either as a solid cylinder, as a hollow cylinder or as a hollow cylinder with z. B. in opposite phase to the thread pitch of the planetary rollers like slitting is executed.   10. The device according to claim 5, characterized in that the planetary rollers with a spur gear toothing to harmonize their rotary position is / are provided, which in an additional ring gear teeth of the ring gear with the Groove / rib profiling engages, the respectively between the two teeth gene or between the rolling circles formed between the two groove / rib profiles have the same diameter. 11. The device according to claim 5, characterized in that the planetary rollers is additionally provided with a spur gear toothing, which is in an additional Ring gear toothing of the ring gear engages with the groove / rib profiling, wherein each between the two teeth or between the two grooves / rip Rollprofile formed pitch circles have the same diameter, and the Planetary rollers via a sun gear connected to the rotary drive is driven with corresponding toothing. 12. The device according to one or more of the preceding claims, characterized in that the ring gear is fixedly connected to the housing ( 1 , 20 , 38 ) of the device with a circumferential contact surface or groove / rib profiling ( 11 , 28 , 47 ). 13. The device according to one or more of the preceding claims, characterized in that the ring gear provided with internal thread ( 10 , 27 , 46 ) is part of an axially movable piston ( 3 , 22 , 40 ). 14. The device according to one or more of the preceding claims, characterized characterized in that the only planet role, or at least one of several pla netenollen is radially adjustable to achieve freedom from play, or by means of a appropriate contact pressure to ensure frictional engagement with the respective rolling partner. 15. The device according to one or more of the preceding claims, characterized characterized in that the only planet role, or at least one of several pla netenollen using tools such. B. from ring and disc spring, preferably on the Working stroke with compressive forces not used, in the axial direction against the circumferential ramp surface is preloaded. 16. The device according to one or more of the preceding claims, characterized characterized in that in the power transmission path between the drive and the rest Roller drive is a freewheel (e.g. wrap spring or sprag freewheel) is switched. 17. The device according to one or more of the preceding claims, characterized characterized in that the drive consists of a handwheel. 18. The device according to one or more of the preceding claims, characterized characterized in that the drive is driven by an electric motor (e.g. asynchronous, DC, reluctance, step, disc rotor motor).   19. The apparatus according to claim 16, characterized in that the drive means a rotary magnet is formed. 20. Use of the device according to one or more of the preceding An say as part of a braking system in a vehicle (e.g. motor vehicle), ei rail vehicle or airplane.