LINEAR ACTUATOR, LENGTH ADJUSTMENT UNIT OF A SEAT AND MOTOR VEHICLE

Description

[0001] The present invention relates to a linear drive having the features of claim 1, a longitudinal adjustment unit for a seat having the features of claim 20 and a motor vehicle having the features of claim 21.

[0002] Linear drives are known in various designs from the prior art and are widely used as longitudinal adjustment units for adjusting the position of a seat in motor vehicles. Longitudinal adjustment units typically interact with a lower rail attached to a chassis and an upper rail arranged within this, wherein the upper rail is motor-driven and coupled to the seat by the longitudinal adjustment unit. In the prior art, the upper rail is typically adjusted by means of a spindle arranged within the upper rail and supported at its respective first and second ends. Such longitudinal adjustment units are known, for example, from DE 36 40 197 A1, DE 42 08 948 C2, DE 196 42 655 C2, DE 198 15 283 A1, DE 10 2004 013 009 A1 and DE 10 2006 052 936 A1.

[0003] From EP 0 612 935 A1 another linear drive is already known, wherein a motion conversion mechanism is used to move movable plates.

[0004] Due to the high demands placed on a linear actuator, which must not only perform a longitudinal adjustment function but also ensure accident safety, such linear actuators have different designs that require different manufacturing methods and processes. It has been shown that achieving backlash-free linear movement is very complex, and adapting the ultimate loads is a laborious process.

[0005] This is where the present invention comes in.

[0006] The invention is based on the object of proposing an improved linear drive that expediently eliminates the disadvantages known from the prior art. Furthermore, a linear drive with a particularly compact design is to be provided, which enables a virtually backlash-free linear movement with a simultaneously variable and adjustable breaking load. Furthermore, the linear drive according to the invention should be capable of achieving a high adjustment speed.

[0007] These objects are achieved by a linear drive having the features of claim 1, a longitudinal adjustment unit having the features of claim 20, and a motor vehicle having the features of claim 21. Further advantageous embodiments of the invention are specified in the subclaims.

[0008] The linear drive according to the invention with the features of patent claim 1 has a drive shaft that is arranged to rotate along a longitudinal axis. Furthermore, the linear drive has at least two drive teeth and at least one rack with a plurality of teeth, wherein the at least two drive teeth are capable of being moved transversely to the longitudinal axis and are drivingly coupled to the drive shaft in such a way that the at least two drive teeth can perform at least one cyclical lifting movement during one rotation of the drive shaft and can engage and disengage from the rack to generate propulsion along the longitudinal axis, or in other words, can engage and disengage from a tooth gap between two teeth of the rack.According to the invention, it is provided that the cyclic lifting movement of the at least two drive teeth takes place with a phase offset, wherein here and in the following, a phase offset is understood to mean an immersion and retraction of the at least two drive teeth into the rack at different angles of rotation of the drive shaft.

[0009] Furthermore, here and in the following, a cyclic stroke movement is understood to mean a movement sequence of the respective drive tooth in which the drive tooth enters the rack from a starting point once, completely emerges from the rack once, and returns to the starting point, and vice versa. The respective drive tooth can undergo one or more complete periods or cycles during one rotation of the drive shaft, whereby the number of periods or cycles always corresponds to a whole number.

[0010] When the respective drive tooth engages the rack, the teeth and the drive teeth come into operative contact, resulting in propulsion along the longitudinal axis. For this purpose, the respective drive tooth engages the rack or the space between two teeth, with the drive tooth and the rack tooth coming into operative contact at so-called friction surfaces, resulting in propulsion. This requires that at least the teeth and / or the drive teeth have friction surfaces shaped like a wedge surface.

[0011] According to an advantageous embodiment of the present invention, the at least two drive teeth are arranged at a first distance along the longitudinal axis, and the teeth of the rack are arranged at a second distance along the longitudinal axis, wherein the first distance is smaller than the second distance, or the second distance is smaller than the first distance. In other words, the first distances between the drive teeth and the second distances between the teeth of the at least one rack must be unequal.

[0012] The first distance and the second distance are each referenced to the geometric center of the respective drive tooth or rack tooth, respectively, and are measured parallel to the longitudinal axis. The different dimensioning of the first distance and the second distance ensures that during a cyclic movement of the at least two drive teeth with a phase offset, the respective drive teeth are positioned in different relative positions to the rack teeth.

[0013] It has also proven advantageous if the respective drive tooth and / or the tooth of the rack is or is formed rectangular, triangular, involute, or sinusoidal. A triangular or sinusoidal tooth shape is preferred. Furthermore, the teeth of the rack and / or the drive teeth are preferably arranged equidistantly parallel to the longitudinal axis. In the event that more than two drive teeth are provided, it is also preferred if these drive teeth are arranged parallel to the longitudinal axis in at least one row at an equidistant distance.

[0014] It has also proven advantageous if the respective drive tooth and / or the rack teeth are designed symmetrically. By designing the respective drive tooth and / or the rack tooth symmetrically, equal adjustment speeds can be achieved in both drive directions along the longitudinal axis, provided the drive shaft speed remains constant.

[0015] According to the invention, the respective drive tooth has a greater, equal to or lesser tooth length and / or a greater tooth height than the respective tooth of the rack. By increasing the tooth height and the tooth length of the rack teeth, the contact surface of the drive teeth on the tooth flanks or the friction surface on the tooth flanks is increased, whereby a more even power transmission between the rack and the drive teeth can be achieved. It is also possible for the tooth height and the tooth length of the drive teeth to be greater than the tooth height and the tooth length of the rack teeth, whereby a greater overlap can be generated, higher maximum loads can be achieved and the smooth running of the drive device can be improved.As a result, maximum loads and different running characteristics can be achieved by selecting the ratios between the drive teeth and the rack teeth. If the tooth length and height of the drive teeth are smaller than the tooth length and height of the rack teeth, more than one drive tooth can engage or disengage simultaneously in the space between two rack teeth.

[0016] Furthermore, it has proven advantageous if the at least two drive teeth and the teeth of the rack have a corresponding tooth shape. A corresponding tooth shape is understood to mean that the respective drive tooth, when fully inserted into the tooth space between two teeth of the rack, can bear flatly with its friction surface facing the teeth of the rack against at least one of the friction surfaces of the teeth of the rack. In particular, it has proven advantageous if both the respective drive tooth and the at least one tooth of the rack have the same tooth flank angle. In this context, it should be noted that the friction surface of the respective tooth flanks does not necessarily have to correspond to a plane, but can also be designed as a surface that is preferably curved outwards.

[0017] According to an advantageous embodiment of the linear drive according to the invention, it can be provided that the phase offset of the cyclic lifting movement of the at least two drive teeth with respect to one revolution φ of the drive shaft is at least 1 / 256φ, more preferably at least 1 / 128φ, 1 / 64φ, 1 / 32φ, 1 / 16φ or 1 / 8φ and preferably less than or equal to ½ φ. Preferably, the phase offset is less than 1 / 2 φ, in particular ⅓ φ or 1 / 4 φ. Preferably, the following applies to the phase offset: 360° / (number of drive teeth)<phase offset<360°-(360° / (number of drive teeth).

[0018] It may be advantageous if the mathematical inverse of the respective fraction (1 / n) of the phase shift specifies the minimum number k of drive teeth to be provided, namely k = (n / i)-1, where a number i is the number of cyclic stroke movements of a drive tooth during one revolution φ of the drive shaft. For example, at least two drive teeth are preferably provided if the phase shift between the drive teeth is 1 / 3 φ and the drive tooth performs a complete stroke movement per revolution.

[0019] Furthermore, it has proven advantageous if the drive shaft is designed as a crankshaft or camshaft and has at least one guide means that determines the cyclical stroke movement during the rotation of the drive shaft. Furthermore, it is preferred if at least two guide means are provided, which are arranged spaced apart from one another along the longitudinal axis, wherein each of the at least two guide means is assigned to at least one drive tooth.

[0020] According to a further advantageous embodiment of the present invention, the at least two guide means are arranged rotated at an angle about the longitudinal axis, wherein the angle specifies the phase offset between the cyclic lifting movements of the at least two drive teeth.

[0021] According to a further advantageous embodiment of the present invention, the guide means have a contact surface, wherein the contact surface can have a flat, concave, convex, sinusoidal, or zigzag-shaped profile along the longitudinal axis. It is particularly preferred if the contact surface of the guide means provides a positive fit with the respective drive tooth or its corresponding contact surface, whereby axial forces can be transmitted from the respective drive tooth to the drive shaft.

[0022] The at least one guide means can comprise a camshaft pulley, wherein furthermore preferably the camshaft pulley is formed in cross-section as an eccentric, an ellipse, a polygon, a tetragon, a pentagon, a hexagon or a combination of these shapes. The camshaft pulley can therefore have one or more maxima of the radius over the circumference. An eccentric typically has a maximum, whereby the drive tooth operatively connected to the camshaft pulley performs a complete cyclic lifting movement during one rotation of the drive shaft. A number i of the maxima indicates, on the one hand, the number of complete cyclic lifting movements during the course of one rotation of the drive shaft, and, on the other hand, the number i can be used to determine the minimum number n of drive teeth to be provided.

[0023] Furthermore, it has proven advantageous if the respective drive tooth is pressed against the drive shaft by means of a spring and / or is drivingly coupled to the drive shaft by means of a connecting rod.

[0024] According to a further advantageous feature of the present invention, the respective drive tooth can be drivingly coupled to the drive shaft via a sliding contact or a single or multiple roller contact. It is also preferred if the respective drive tooth is coupled to the drive shaft by means of a single roller contact, a double roller contact, or a quadruple roller contact. The contact surface of the drive tooth or the contact surface of the drive shaft can roll on at least one contact roller of the respective roller contact, thereby reducing friction losses and wear on the respective contact surface.

[0025] According to a further embodiment of the present invention, the at least two drive teeth can be arranged in a row along an axis which runs parallel to the longitudinal axis.

[0026] In particular, it is preferred if at least two rows of propulsion teeth are arranged around the longitudinal axis, wherein at least one toothed rack can be assigned to the respective row, into which the respective propulsion teeth can engage and disengage to generate propulsion.

[0027] According to a further development of the present invention, the at least two racks can be arranged offset from one another. The offset describes a distance, measured in the direction of the longitudinal axis, between the tooth tips of the at least two racks. If the offset is zero, the at least two racks are arranged mirror-symmetrically or line-symmetrically to the longitudinal axis, whereas if the offset is greater than zero, the at least two racks are arranged asymmetrically with respect to the longitudinal axis. In a preferred embodiment, the offset can be half a distance, a quarter, or a third of the distance between two teeth of the respective rack, wherein the distance between two teeth of the at least two racks should preferably be selected to be the same.

[0028] According to a further advantageous embodiment of the present linear drive according to the invention, a carriage is provided in which the at least two drive teeth and the drive shaft are mounted. Preferably, the at least two drive teeth are held transversely to the longitudinal axis in the manner of a plain bearing, whereby the propulsion generated by the at least two drive teeth can be transmitted to the carriage. The carriage can be constructed in one or more parts and can have means by which it is held for linear movement relative to the at least one rack.

[0029] A further development of the linear actuator provides for a drive. The drive is preferably an electric motor that can drive the drive shaft.

[0030] Furthermore, it is advantageous if a gear is arranged between the drive and the drive shaft, wherein a planetary gear can be arranged particularly preferably between the drive and the drive shaft.

[0031] The drive and / or the gear unit can be arranged in the carriage according to one embodiment of the linear drive. The drive in the carriage can be supplied with power and / or control signals via a drag chain with appropriate electrical cables.

[0032] Furthermore, the present invention relates to a longitudinal adjustment unit with a linear drive according to the invention.

[0033] A further aspect of the present invention relates to a motor vehicle having at least one such linear drive according to the invention.

[0034] An embodiment of the present invention and further developments of the present invention are described in detail below with reference to the accompanying drawings. They show: Figure 1 is a perspective view of a linear drive according to the invention, comprising a carriage arranged in a rack housing with at least two drive teeth, which are drivingly coupled to a drive shaft and, during one rotation of the drive shaft, engage in a cyclical stroke movement to generate a drive in at least one rack of the rack housing, Figure 2 is a plan view of the linear drive according to the invention according to Figure 1 , Figure 3 a plan view according to Figure 1 , where the components in the carriage are visible, Figure 4 a perspective and detailed representation of the carriage according to Figure 3 , Figure 5 a detailed view of the components of the carriage in perspective according to Figure 4, Figure 6 a simplified representation of the drive shaft of the drive tooth and a rack, Figure 7 a simplified representation of the drive shaft of the drive tooth and a rack according to Figure 6, wherein on diametrical sides of the drive shaft a row with a drive tooth and a rack is arranged, Figure 8 a simplified representation of the drive shaft of the drive tooth and a rack according to the Figures 6 or 7, wherein four drive teeth are arranged circumferentially symmetrically in one plane around the drive shaft, Figure 9 shows an enlarged perspective view of the drive shaft, wherein it can be seen that the drive shaft is designed as a camshaft along a longitudinal axis and has a plurality of camshaft disks, by which the cyclical lifting movement of the drive teeth is predetermined during one revolution of the drive shaft, Figure 10a-e shows a schematic representation of the cross section of the camshaft disks, Figure 11a-b shows schematic representations of contact rollers, by which the cyclical lifting movement of the drive teeth is predetermined during one revolution of the drive shaft, Figure 12a-e shows schematic representations of different designs of contact surfaces of the guide means, Figure 13a-b shows schematic representations of different designs of the teeth of the rack,Figure 14a-c schematic representations of different size ratios of the rack teeth and the feed teeth, and Figure 15a-b schematic representations of different arrangements of the racks.

[0035] In the following, identical or functionally equivalent components are identified by the same reference symbols. For the sake of clarity, not all identical or functionally equivalent parts are provided with a reference number in the individual figures.

[0036] Figure 1 shows a linear drive 1 according to the invention comprising a rack housing 35 and a carriage 40, which is movably mounted along a longitudinal axis X between two racks 30. The linear drive 1 can be used in a (not shown) longitudinal adjustment unit 2 for adjusting a (not shown) seat in a (not shown) motor vehicle 3.

[0037] The rack housing 35 can be cuboid-shaped, as in the illustrated embodiment, and at least partially enclose a space 38. On each of the two diametrical sides facing the space 38, one of the racks 30 is arranged, each formed from a plurality of teeth 31, which are preferably arranged equidistantly along the longitudinal axis X. A corresponding inter-tooth space 32 is formed between each two teeth 31.

[0038] The rack housing 35 can be designed such that it forms a stop in the longitudinal axis X in a first end region and in a second end region, by which the maximum travel path of the carriage 40 within the space 38 is predetermined.

[0039] In the illustrated embodiment, the teeth 31 of the two racks 30 are identical, but the teeth 31 of the racks 30 can have different tooth shapes as well as different distances A2.

[0040] The respective distance A2 is determined as in Figure 2 is shown, measured in each case relative to the geometric center of the respective tooth 31. In the case of symmetrical teeth 31, a tooth tip is typically formed in the geometric center, from which two symmetrical tooth flanks extend as friction surfaces 36. In the illustrated embodiment, the two flanks enclose an angle of approximately 135°, wherein the flanks preferably enclose an angle of less than or equal to 180° and greater than 30°.

[0041] The carriage 40 can, as in Figure 4shown, have a two-part housing consisting of a first housing part 43 and a second housing part 44. The housing has a first end region 41 and a second end region 42, which can cooperate with the rack housing 35 as an end stop.

[0042] Figure 3 shows that in the housing of the carriage 40, a drive shaft 10 is arranged coaxially to the longitudinal axis X, which is rotatably mounted in the longitudinal axis X by means of bearings 48. The drive shaft 10 can be coupled to a drive 50 by means of a gear 55, whereby the drive shaft 10 can be set into a rotary movement about the longitudinal axis X by the drive 50.

[0043] The drive 50 can preferably be an electric drive and furthermore preferably be coupled to the drive shaft 10 via the gear 55, which is designed as a planetary gear. The gear 55 can increase or decrease the speed of the drive 50 to a speed of the drive shaft.

[0044] The drive shaft 10 has a plurality of guide means 12 arranged spaced apart between the two bearings 48. The guide means 12 are each arranged in a plane orthogonal to the longitudinal axis X and can have an eccentric, eccentric, elliptical, or polygonal configuration—as will be described in more detail below. The drive shaft 10 forms a type of camshaft, and the guide means 12 are formed by camshaft pulleys 13.

[0045] The guide means 12 are, as in particular the Figures 6 and 9can be seen, are arranged along the longitudinal axis X rotated at an angle α to one another, wherein in the present exemplary embodiment the guide means 12 designed as an ellipse and the camshaft disks 13 are arranged rotated about the longitudinal axis X by an angle α = 22.5°.

[0046] Further with regard to Figure 3 It can be seen that a plurality of guide recesses 45 are arranged in the housing, which are arranged transversely to the longitudinal axis X in the center and on diametrical sides to the guide means 12 or the camshaft discs 13.

[0047] A drive tooth 20 is inserted into the respective guide recess 45, which is movable in the guide recess 45 and, as indicated by the double arrow, can perform a lifting movement 21 which runs radially or secantial to the longitudinal axis X.

[0048] Two rows, each with seven drive teeth 20, are arranged symmetrically to the longitudinal axis X around the drive shaft 10. The rows are aligned parallel to the longitudinal axis X. The guide recess 45 forms a bearing for the respective drive tooth 20, whereby the drive tooth 20 is mounted for smooth movement transversely to the longitudinal axis X and can slide in and out of one of the tooth spaces 32 of the rack 30 through the guide recess 45.

[0049] In the unloaded state, the respective drive tooth 20 can be guided along the longitudinal axis X over a tooth tip of a tooth 31 of the rack.

[0050] The respective drive tooth 20 can preferably be adapted to the shape of the teeth 31 of the rack 30, whereby the tooth flanks of the drive tooth 20, when the drive tooth 20 is fully immersed in the inter-tooth space 32, lie flat against the flanks of the teeth 31. The width of the respective drive tooth 20 can correspond to the distance A2 between two teeth 31. However, it is essential that a distance A1 between two drive teeth 20 is greater or smaller than the distance A2 between two teeth 31. Thus, A2 < A1 or preferably A1 > A2. In other words, A1 ≠ A2 must be.

[0051] The respective drive tooth 20 further comprises a tooth base 22 with a contact surface 24. The tooth base 22 can have a constant cross-section and corresponding surfaces on which it can slide linearly guided along the guide recess 45 with minimal friction during the cyclic lifting movement.

[0052] The drive shaft 10 and the drive teeth 20 are coupled to one another in such a way that the respective drive tooth 20 performs at least one cyclical stroke movement 21 during one revolution φ of the drive shaft 10. The cyclical stroke movement 21 can be described, for example, as a complete period of a sine curve, wherein the respective drive tooth 20, within one cyclical stroke movement 21, plunges once into the rack 30 or a tooth gap 32, completely emerges once, and returns to the starting position. However, within the meaning of this invention, it is also possible for the respective drive tooth 20 to perform several cyclical stroke movements 21 during one revolution φ, as will be explained below.

[0053] Due to the guide means 12 rotated at an angle α around the longitudinal axis X, the cyclic lifting movement 21 of the respective drive teeth 20 occurs in a phase-shifted manner, whereby the drive teeth 20 engage and disengage from the respective rack 30 at different angles of rotation of the drive shaft 10. In other words, the drive teeth 20 engage in a tooth gap 32 at different times at a constant speed of the drive shaft 10.

[0054] The guide means 12 have a contact surface 14, which forms the outer side facing the drive tooth 20. The contact surface 14 and the contact surface 24 of the respective drive tooth 20 slide against each other, whereby the contact surface 14 applies a radially or secantally acting force to the respective drive tooth 20, by which the drive tooth 20 is pushed through the guide recess 45 in the direction of the rack 30.

[0055] The operation of the linear drive 1 is based on the fact that the respective drive tooth 20 comes into frictional contact with a flank of one of the teeth 31 of the rack 30 when it engages a tooth gap 32 of the rack 30. When the respective drive tooth 20 engages, a first flank or one of the friction surfaces 26 comes into contact with the flank or friction surface 36 of one of the teeth 31. Due to their wedge-shaped design, the two friction surfaces 26, 36 generate a propulsion directed along the longitudinal axis X, by which the carriage 40 is displaced in the space along the longitudinal axis X. As soon as one of the drive teeth 20 is fully engaged in the rack 30, another drive tooth 20 follows with a phase shift, which is arranged offset from the center of another tooth gap 32. The further drive tooth 20 engages another tooth gap 32, generating a propulsion.Meanwhile, the first drive tooth 20, which is completely immersed in the interdental space 32, emerges from the interdental space 32 either spring-loaded or through the contacting friction surfaces 26, 36. Additional drive teeth 20 can follow offset or simultaneously, thereby generating further propulsion.

[0056] In the present embodiment according to the Figures 1-5the guide means 12 are elliptical in design, whereby the respective drive tooth 20 undergoes two complete cycles or periods with one revolution φ. Accordingly, the respective drive tooth 20 engages and exits the rack 30 twice with one revolution φ of the drive shaft 10. Due to the angular offset of 22.5° between two guide means 12 spaced apart along the longitudinal axis X, the phase offset Δφ relative to one revolution φ of the longitudinal axis X is 1 / 32φ. In other words, the drive shaft 10 must be rotated by 11.25° so that after the engagement of a first drive tooth 20, a second drive tooth 20 engages into a further tooth space 32.

[0057] The linear drive 1 has at least two drive teeth 20, which, as shown in Figure 6 shown, may be arranged in a single row parallel to the longitudinal axis X.

[0058] As already mentioned in connection with the Figures 1-5However, as explained above, the driving teeth 20 can be arranged in two spaced rows according to Figure 7 be arranged, with a rack 30 being assigned to the respective row of drive teeth 20. The two rows can be arranged arbitrarily around the longitudinal axis X, but a circumferentially symmetrical arrangement is preferred.

[0059] Figure 8 a further development of the linear drive 1 can be seen, wherein four drive teeth 20 are arranged orthogonally or transversely to the longitudinal axis X in a plane, each of which can engage and disengage from a rack 30.

[0060] The Figures 10a-10e show different cross sections of the guide means 12, wherein the guide means 12 have in common that the course of the radius measured to the longitudinal axis X over the circumference has at least one local minimum and one local maximum. The elliptical cross section according to Figure 10ahas two maxima and two minima, whereby the drive teeth in operative contact with the guide means 12 designed in this way perform two cyclic lifting movements 21 during one revolution φ of the drive shaft 10, during which the eccentric cross section according to Figure 10b only leads to a cyclic stroke movement 21 during one revolution φ of the drive shaft 10. The polygon cross sections according to the Figures 10c-10e have several corners, whereby the number of corners determines the number of cyclic stroke movements 21 during one revolution of the drive shaft 10.

[0061] As an alternative to a camshaft with camshaft pulleys 13, the drive shaft 10 can have roller contacts 15, which are formed by contact rollers 16 arranged radially to the longitudinal axis X. The respective contact roller 16 forms the contact surface 14, which, however, in contrast to the cam pulleys, rolls on the contact surface 24 of the respective drive tooth 20. The roller contacts 15 can be designed as a double roller contact 15 according to Figure 11a , or as a multiple roller contact 15, for example as a quadruple roller contact 15 according to Figure 11b be designed, whereby the number of contact rollers 16 can be chosen as desired.

[0062] The Figures 12a-e show different designs of the contact surfaces 14 of the guide means 12, wherein the contact surfaces are arranged according to the Figures 12b-ecan have a concave, a convex, a zigzag or a sinusoidal configuration, whereby a partial positive connection can be achieved between the respective drive tooth 20 and the guide means 12, by means of which an axial force in the longitudinal axis X can be transmitted from the drive tooth 20 to the drive shaft 10.

[0063] Also, both the teeth 31 of the rack 30 and the drive teeth 20 (not shown) can have different tooth geometries. Examples are shown in the Figures 13a the teeth 31 sinusoidal and in Figure 13b zigzag-shaped with two flanks symmetrical about a symmetry line S. Also, either the teeth 31 or the drive teeth 20 can be rectangular, wherein at least the teeth 31 of the rack 30 or the drive teeth 20 have a friction surface 26, 36 for generating propulsion, which friction surface is wedge-shaped for generating propulsion.

[0064] As soon as a drive tooth 20 enters a tooth space 32, a positive connection is achieved between the rack 30 and the carriage 40, whereby the carriage 50 is fixed approximately free of play in the longitudinal axis X. The drive teeth 20 therefore wedge the carriage 50 in the longitudinal axis X and the drive teeth 20 engaging with the rack 30 determine the breaking load, which can be arbitrarily designed both by the number of drive teeth 20 in a row and by the number of rows.

[0065] Figures 14a to 14cshow different size ratios of the drive teeth 20 and the teeth 31 of the rack 30. The respective drive tooth 20 has a tooth length L1, a tooth height H1, and a tooth flank angle γ1. Likewise, the teeth 31 of the rack 30 have a tooth length L2, a tooth height H2, and a tooth flank angle γ2. Typically, the tooth flank angles γ1 and γ2 can be selected to be equal so that surface contact can be formed between the tooth flanks of the drive teeth 20 and the rack 30. However, it should be noted that at least one of the tooth flanks can also have a curved shape.

[0066] Figure 14a shows schematically exemplary size relationships between the drive tooth 20 and the teeth 31 of the rack 30 according to the Figures 1-3. It can be seen that the distance A1 between the drive teeth 20 is greater than the distance A2 between the teeth 31 of the rack 30 and that the tooth heights H1, H2 and the tooth lengths L1, L2 are approximately the same.

[0067] An enlargement of the teeth 31 of the rack 30 in relation to the drive teeth 20 is Figure 14b , wherein it is also evident from this figure that several drive teeth 20 can penetrate into a tooth gap 32 between two teeth 31. By enlarging the teeth 31 of the rack 30, the contact surface of the drive teeth 20 on the tooth flanks 36 of the teeth 31 is increased, whereby a more even power transmission can take place.

[0068] A higher contact ratio between the drive teeth 20 and the tooth flanks 36 of the teeth 31 of the rack 30 can be achieved by increasing the tooth length L1 or by increasing the tooth height H1, whereby the following applies: A1 > A2, L1 > L2, and H1 > H2. A higher contact ratio between the drive teeth 20 and the tooth flanks 36 allows a higher maximum load to be achieved and the smooth running of the drive device 1 to be increased.

[0069] Figure 15a is an arrangement of the rack 30 on two opposite sides of the longitudinal axis X according to the Figures 1-3 , where it is evident that the teeth 31 and the interdental spaces 32 are arranged symmetrically (mirrored on the longitudinal axis X). However, according to a further development, which is described in Figure 15 bAs shown, the rack 30 can be arranged asymmetrically displaced with an offset ΔA, wherein in the illustrated embodiment the offset ΔA is half a distance A2. List of reference symbols

[0070] 1Drive device 2Longitudinal adjustment unit 3Motor vehicle 10Drive shaft 12Guide means 13Camshaft pulley 14Contact surface 15Roller contact 16Contact roller 19Coupling 20Drive tooth 21Stroke movement 22Tooth root 24Contact surface 26Friction surface 30Rack 31Tooth 32Tooth gap 35Rack housing 36Friction surface 38Space 40Slide 41First end area 42Second end area 43Housing part 44Housing part 45Guide recess for 20 48Bearing 50Drive 55Gearbox A1Distance between two drive teeth 20 A2Distance between two teeth 31 ΔAVisplacement H1Height of 21 H2Height of 31 L1Length of 21 L2Length of 31 SSymmetry line XLongitudinal axis αAngle of 13 γ1Tooth flank angle of 21 γ2Tooth flank angle of 31 φRevolution ΔφPhase offset

Claims

1. Linear drive (1), comprising - a drive shaft (10) which is arranged along a longitudinal axis (X), - at least two propulsion teeth (20), and - at least one rack (30) having a plurality of teeth (31), - wherein the propulsion teeth (20) are liftable transversely to the longitudinal axis (X) and are drivingly coupled to the drive shaft (10) in such a way that the at least two propulsion teeth (20) perform at least one cyclical lifting movement (21) in the course of a rotation (φ) of the drive shaft (10) and dip into and out of the at least one rack (30) for generating a propulsion, and - wherein the cyclical lifting movement (21) of the at least two propulsion teeth (20) occurs with a phase offset (Δφ), characterised in that the the propulsion is created in the longitudinal axis (X), and wherein the respective propulsion tooth (20) has a greater tooth length (L1) and a greater tooth height (H1) than the tooth (31) of the rack (30), or wherein the respective propulsion tooth (20) has the same or a smaller tooth length (L1) compared with the tooth (31) of the rack (30).

2. Linear drive (1) according to claim 1, characterised in that the at least two propulsion teeth (20) are arranged at a first spacing (A1) in the longitudinal axis (X), and that the teeth (31) are arranged at a second spacing (A2) along the longitudinal axis (X), wherein the following applies: A 1 < A 2 oder A 1 > A 2 .

3. Linear drive (1) according to either claim 1 or claim 2, characterised in that the respective propulsion tooth (20) and / or the tooth (31) of the rack (30) is or are configured to be rectangular, wedge-shaped, involute-shaped, or sinusoidal.

4. Linear drive (1) according to any of the preceding claims, characterised in that the respective propulsion tooth (20) and / or the tooth (31) is or are configured symmetrically.

5. Linear drive (1) according to any of the preceding claims, characterised in that the respective propulsion tooth (20) and the respective tooth (31) have the same tooth flank angle (α1, α2).

6. Linear drive (1) according to any of the preceding claims, characterised in that the at least two propulsion teeth (20) and the teeth (31) have a corresponding geometry.

7. Linear drive (1) according to any of the preceding claims, characterised in that for the phase offset (Δφ) of the cyclical lifting movement (21) of the at least two propulsion teeth (20) with respect to a rotation (φ) of the drive shaft (10), the following applies: 1 / 256 φ ≤ Δφ ≤ ½ φ.

8. Linear drive (1) according to any of the preceding claims, characterised in that the drive shaft (10) is configured as a crankshaft or camshaft and comprises at least one guide means (12) which specifies the cyclical lifting movement (21) during the rotation (φ) of the drive shaft (10).

9. Linear drive (1) according to claim 8, characterised in that the at least one guide means (12) has a contact surface (14), and that the contact surface has a flat, concave, convex or sinusoidal course in the longitudinal axis.

10. Linear drive (1) according to either claim 8 or claim 9, characterised in that the at least one guide means (12) comprises a camshaft (13) which is configured as an eccentric, ellipse, polygon, tetragon, pentagon or hexagon in cross-section.

11. Linear drive (1) according to any of the preceding claims, characterised in that the respective propulsion tooth (20) is pressed in a sprung manner against the drive shaft (10) and / or is drivingly coupled to the drive shaft (10) by means of a connection rod.

12. Linear drive (1) according to any of the preceding claims, characterised in that the respective propulsion tooth (20) is drivingly coupled to the drive shaft (10) via a sliding contact or a simple or multiple roller contact (15).

13. Linear drive (1) according to any of the preceding claims, characterised in that the at least two propulsion teeth (20) are arranged in a row along an axis in parallel with the longitudinal axis (X).

14. Linear drive (1) according to claim 13, characterised in that at least two rows of propulsion teeth and at least two racks (30) are arranged around the longitudinal axis (X).

15. Linear drive (1) according to either claim 13 or claim 14, characterised in that the at least two rows and the at least two racks are arranged in a peripherally symmetrical manner around the longitudinal axis (X).

16. Linear drive (1) according to any of claims 13 to 15, characterised in that the at least two racks (20) are arranged so as to be shifted relative to one another by an offset (ΔA).

17. Linear drive (1) according to any of the preceding claims, characterised in that a slide (40) is provided, and in that the drive shaft (10) and the at least two propulsion teeth are held mounted in the slide.

18. Linear drive according to any of the preceding claims, characterised in that a drive (50) is provided, wherein the drive (50) drives the drive shaft (10).

19. Linear drive (1) according to claim 18, characterised in that a transmission (55), in particular a planetary transmission, is arranged between the drive (50) and the drive shaft (10).

20. Longitudinal adjustment unit (2) comprising a linear drive (1) according to any of the preceding claims.

21. Motor vehicle (3) comprising a linear drive (1) according to any of claims 1 to 19.