Brake booster or braking force generator

Abstract

The invention relates to a brake booster or brake power unit (10) comprising an electric motor (14) and a gear unit (22, 46) which axially moves a brake piston (54) in order to apply braking pressure, wherein the gear unit (22, 46) has at least one leadscrew drive assembly (46) for converting a rotation into a translational motion. The gear unit (22, 46) comprises a worm gear set (22) having a worm (26) and a worm gear (30) interacting with the worm (26), wherein the worm gear (30) consists of a plastic material, and wherein at least the worm (26) or the worm gear (30) is at least semi-globoid.

Description

[0001] Description

[0002] Title:

[0003] brake booster or

[0004] The present invention relates to a brake booster or brake force generator comprising an electric motor and a gear unit that axially displaces a piston to apply braking pressure. The gear unit has at least one spindle drive arrangement for converting a rotational movement into a translational movement. The invention also relates to a motor vehicle having such a brake booster or brake force generator.

[0005] State of the art

[0006] In brake boosters and brake force generators, screw drives / spindle drives are used to convert a rotary motion into a translational motion. Ball screws and plastic threaded nuts are used for this purpose. The translational motion is coupled with a piston / plunger and a torque arm to generate hydraulic pressure. Several individual components with their different functions work together to achieve this function.

[0007] DE 102 03 069 A1 discloses a brake positioning device for a disc brake, in particular a disc brake of a rail vehicle. The disc brake consists of two symmetrically constructed disc-shaped brake pad holders arranged on both sides of a brake disc. Worm gears are attached to the brake pad holders. When braking is required, the worm gears move the pad holders, and thus the brake pads, toward the brake disc thanks to the multi-start thread. The worm gear consists of the driving worm and the driven worm wheel, whose axes normally intersect at an axial angle of 90°. Cylindrical worms and globoid worms are particularly suitable for this purpose.

[0008] The object underlying the invention is to provide a brake booster or brake force generator with which high braking forces can be applied, which is nevertheless more economical.

[0009] The object is achieved by a brake booster or brake force generator having the subject matter of patent claim 1. Preferred embodiments can be found in the dependent claims.

[0010] Disclosure of the invention

[0011] The invention provides a brake booster or brake force generator comprising an electric motor and a gear unit that axially displaces a piston to apply a braking pressure. The gear unit has at least one spindle drive arrangement for converting a rotational movement into a translational movement. The gear unit comprises a worm gear with a worm and a worm wheel cooperating with the worm. The worm wheel is made of a plastic material, and at least one of the worm and the worm wheel is at least semi-globoidal.

[0012] A brake booster is a device that amplifies the braking force applied via a brake pedal to brake a motor vehicle. A brake force generator, on the other hand, is a device that generates braking force based on the braking input at the brake pedal. A semi-globoidal design means that one edge of the worm wheel or worm follows the radius of the other. This means, for example, that one edge of the worm has the same radius as the worm wheel. Likewise, one edge of the worm wheel can have the radius of the worm. The contact area between the worm wheel and worm is thereby increased, so that the strength of the worm wheel can be reduced.

[0013] Accordingly, it is possible to construct the worm gear according to the invention from plastic material instead of metal. A plastic worm gear offers significant cost and functional advantages over a steel or metal worm gear. In particular, a plastic worm gear is significantly easier to manufacture using an injection molding process. In a worm gear, it is necessary for a worm gear to adhere to certain tolerances. This is made much easier by manufacturing using the injection molding process. This can reduce manufacturing costs. In addition, a plastic worm gear is significantly lighter than a metal worm gear, and the

[0014] The material costs of plastic are usually significantly lower than those of metal. This makes it possible to specify a brake booster or brake force generator that can apply high braking forces while remaining more economical.

[0015] In a preferred embodiment of the invention, at least the worm or worm wheel is of fully globoidal design. With a fully globoidal design, both edges of the worm or worm wheel are of globoidal design. This allows the contact area to be further increased and the surface load to be reduced. This makes it possible to use plastic materials, which are more cost-effective due to their lower strength. Accordingly, costs can be further reduced.

[0016] In a further preferred embodiment of the invention, the worm gear is designed as a double globoid. With a double globoid design, both the worm wheel and the worm are fully globoid. This also further reduces the contact area. Accordingly, more cost-effective plastic materials can be used, thus reducing manufacturing costs.

[0017] Preferably, the semi-globoidal configuration on the worm gear is arranged on a force introduction side. The force introduction side is the side on which the force is introduced. In the case of a worm gear, this is the side on which the electric motor is located. This arrangement of the globoidal configuration increases the contact area on the force introduction side, so that the surface loading is reduced precisely in this area where the greatest force acts.

[0018] In an advantageous refinement, the worm gear is made of a POM plastic material. The abbreviation POM stands for polyoxymethylene plastic. Such plastics are characterized by high strength, hardness, and rigidity. Furthermore, such plastics exhibit high abrasion resistance. These plastics are particularly advantageous because they exhibit particularly good tribological properties.

[0019] The worm gear advantageously has helical gearing. With helical gearing, the teeth do not run in the axial direction, but rather at an angle to the axial direction. A helical worm gear has the advantage that the worm gear is quieter and runs more smoothly. It also makes it possible to apply an axial force to the worm gear, thus reducing the axial force acting on a worm gear bearing during braking.

[0020] In a further advantageous embodiment, a tapered insertion bevel is formed on the tooth flanks of the at least semi-globoidal region of the worm wheel, beginning at one end of the head, through which a worm tooth of the worm can be inserted between the teeth of the worm wheel. The semi-globoidal region of the worm wheel is the region of the tooth that has a globoidal shape. Due to the globoidal shape, the diameter in this region is larger than in the remaining region of the tooth. The worm tooth therefore first comes into contact with the worm wheel in the semi-globoidal region.

[0021] This area features the lead-in chamfer. Starting at the tip of the tooth, the lead-in chamfer tapers. This lead-in chamfer ensures that there is no misalignment between the worm tooth and the worm wheel, even under high loads and deformations of the gear teeth. In the event of such a misalignment, the worm tooth would collide with the tip of the worm wheel teeth. This lead-in chamfer makes it possible to use cheaper, lower-strength plastics while preventing misalignment.

[0022] Such a lead-in chamfer also has the advantage of creating a narrowing gap, which allows for the development of a supporting lubricating film to separate the surface of the wheel tooth from the worm tooth. This can prevent wear in the load application area and increase efficiency, allowing the use of smaller drive motors. This would further reduce weight and manufacturing costs.

[0023] Additionally, a motor vehicle is provided which includes the brake booster or brake force generator according to the invention. Such a motor vehicle offers the aforementioned advantages.

[0024] Embodiments of the invention are illustrated in the drawing and explained in more detail in the following description. It shows:

[0025] Figure 1 partial sectional view of the brake booster or brake force generator according to an embodiment of the invention,

[0026] Figure 2a Top view of a worm gear of the brake booster or brake force generator according to a first embodiment of the invention,

[0027] Figure 2b shows a top view of a worm gear of the brake booster or brake force generator according to a second embodiment of the invention, Figure 3a shows a side view of a worm gear of the brake booster or brake force generator according to a third embodiment of the invention,

[0028] Figure 3b side view of a worm gear of the brake booster or brake force generator according to a fourth embodiment of the invention, and

[0029] Figure 4 View of a worm wheel according to a fifth embodiment of the invention.

[0030] Figure 1 shows a partial sectional view of the brake booster or brake force generator 10 according to an embodiment of the invention. The brake booster 10 comprises an electric motor 14, via which a shaft 18 is driven. Additionally, the brake booster 10 has a worm gear 22 formed from a worm 26 and a worm wheel 30 that mesh with each other. In the embodiment shown, the worm 26 is formed on the shaft 18 of the electric motor 14. The worm wheel 30 is rotatably mounted in a housing 38 of the brake booster 10 via a bearing 34.

[0031] In the illustrated embodiment, the worm gear 30 forms a spindle nut 42 of a spindle drive assembly 46. The spindle nut 42 engages with a spindle 50, so that with a rotation of the worm gear 30, the rotationally mounted spindle 50 can be moved translationally in order to axially displace a brake piston 54 arranged on the spindle 50.

[0032] Figure 2a shows a plan view of the worm gear 22 of the brake booster 10 according to a first exemplary embodiment of the invention. In this exemplary embodiment, the worm 26 is semi-globoidal. The worm 26 is therefore not completely cylindrical, but has a globoidal curvature 58 towards one edge. The curvature 58 has approximately the radius of the worm wheel 30. In the exemplary embodiment shown here, the worm 26 is globoidal on a force introduction side. The force introduction side corresponds to the side on which the electric motor 14 is arranged. Through such a design, the contact area between the worm 26 and the worm wheel 30 is increased, so that the surface pressure is reduced and durability is improved.

[0033] Figure 2b shows a plan view of the worm gear 22 of the brake booster 10 according to a second exemplary embodiment of the invention. This exemplary embodiment differs from the example in Figure 2a in that the worm 26 has a globoidal curvature 58 on both sides. The worm 26 is accordingly fully globoidal. This allows the contact area between the worm 26 and the worm wheel 30 to be increased again, thus reducing the surface pressure.

[0034] Figure 3a shows a side view of a worm gear 22 of the brake booster 10 according to a third exemplary embodiment of the invention. In this exemplary embodiment, the worm gear 30 has helical teeth. The worm gear 30 additionally has a globoidal curvature 58 on one edge. The worm gear 30 is thus semi-globoidal. The radius of this curvature corresponds to a radius of the worm 26.

[0035] Figure 3b shows a side view of a worm gear 22 of the brake booster 10 according to a fourth embodiment of the invention. In this embodiment, a globoidal curvature 58 is formed on both edges of the worm gear 30, so that the worm gear 30 is fully globoidal.

[0036] Although in the figures, for the sake of clarity, only either the worm 26 or the worm wheel 30 is of globoidal design, the worm 26 and the worm wheel 30 can also be of globoidal design in different variations. Thus, it is possible for both the worm wheel 30 and the worm 26 to be of fully globoidal design. Such a design is a double globoidal worm gear 22. Figure 4 shows a view of a worm wheel 30 according to a fifth exemplary embodiment of the invention. This shows a partial perspective view of a worm wheel 30 and a schematic side view. The worm wheel 30 shown is of semi-globoidal design. On tooth flanks 62 of the worm wheel 30 of the globoidal area 66, a

[0037] An insertion bevel 70 is formed. The insertion bevel 70 begins at a head side 72 of teeth 74 of the worm gear 30 and tapers. Due to the insertion bevel 70 on the globoid-shaped area 66, the worm 26 is inserted early between the teeth 74 of the worm gear 30, thus preventing a worm tooth 78 from striking the teeth 74 of the worm gear 30, especially under high loads, and thus causing a misalignment.

[0038] The insertion bevel 70 additionally forms a narrowing gap, which enables the build-up of a supporting lubricating film, so that wear is reduced and efficiency is increased.

Claims

Claims 1 . Brake booster or brake force generator (10) comprising an electric motor (14) and a gear unit (22, 46) which axially displaces a brake piston (54) to apply a braking pressure, wherein the gear unit (22, 46) has at least one spindle drive arrangement (46) for converting a rotary movement into a translatory movement, characterized in that the gear unit (22, 46) comprises a worm gear (22) with a worm (26) and a worm wheel (30) interacting with the worm (26), wherein the worm wheel (30) is made of a plastic material, and wherein at least the worm (26) or the worm wheel (30) is at least semi-globoidal.

2. Brake booster or brake force generator (10) according to claim 1, characterized in that at least the worm (26) or the worm wheel (30) is fully globoidal 3. Brake booster or brake force generator (10) according to claim 1, characterized in that the worm gear (22) is double-globoidal 4. Brake booster or brake force generator (10) according to claim 1 or 2, characterized in that the semi-globoidal formation on the worm (26) is arranged on a force introduction side 5. Brake booster or brake force generator (10) according to one of the preceding claims, characterized in that the worm wheel (30) is made of a POM plastic material 6. Brake booster or brake force generator (10) according to one of the preceding claims, characterized in that the worm gear (30) has helical gearing.

7. Brake booster or brake force generator (10) according to one of the preceding claims, characterized in that a tapered insertion bevel (70) is formed on tooth flanks (62) of the at least semi-globoidal region of the worm gear (30), starting from a head side (72), via which a worm tooth (78) can be inserted between teeth (74) of the worm gear (30).

8. Motor vehicle comprising a brake booster or brake force generator (10) according to one of the preceding claims.

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