LINEAR UNIT

[0001] This application claims priority to German Patent Application Nos. 10 2009 029 075.3, filed Sep. 1, 2009; 10 2010 039 916.7, filed Aug. 30, 2010, and PCT/EP2010/062672, filed Aug. 31, 2010.

[0002] The invention relates to a linear unit for applying an axially acting force which may be implemented as part of a motor vehicle brake system. The linear unit is composed of a rotational/translational gear, which has a threaded spindle and a threaded nut, and of an electric motor with a rotor and with a stator which are arranged in a housing.

[0003] A linear unit of the above-referenced type is known from WO 89/03782 A1. In the previously known linear unit, the rotational/translational gear is formed by what is known as a ball screw, the threaded nut of which is connected directly to the rotor of the electric motor, while the threaded spindle transmits its translational movement by means of one end, designed as a push rod, to a master cylinder arrangement following the linear unit. Securing the threaded spindle against rotation, as is necessary for this purpose, is implemented in that the other end of the threaded spindle has a flattened form and is received by a correspondingly shaped perforation of the electric motor housing. The prior art unit is felt to have the disadvantages of a complicated set-up entailing high manufacturing costs and, in particular, the considerable axial overall length.

[0004] The object of the present invention, therefore, is to improve a linear unit of the abovementioned generic type to the effect that its set-up is simplified, while at the same time the packaging space required is reduced.

[0005] This object is achieved, according to the invention, by means of the features of the present invention.

[0007] As may be gathered from the drawing, the linear unit according to the invention is composed essentially of two premountable subassemblies, specifically of an electric motor 1 and of a further subassembly with a gear housing 22 which receives a rotational/translational gear 2 and also a force transmission member or piston 4. In the exemplary embodiment shown, the rotational/translational gear 2 is designed as a simple movement thread. To produce a functional unit, the subassemblies are plugged one into the other and are connected to one another by being fixed nonpositively by means of connection elements, not illustrated. In a further development, the actuator according to the invention is designed as a hydraulic actuator in that the force transmission member 4 is sealed off with respect to the gear housing 22 and functions as a piston rod. To build up a hydraulic pressure, the force transmission member 4 designed as a piston rod penetrates into a fluid-filled bore 32.

[0008] The electric motor 1 has an electric motor housing 10 in which are arranged a stator 11 and a rotor 12 which form the torque-generating parts of the electric motor 1. The rotor 12 is composed of a pot-shaped sleeve 13, on the surface of which permanent magnet segments 14 are arranged at regular angular intervals. To determine the angular position of the rotor 12 or sleeve 13 required for an in-phase application of current to the stator 11, a contactlessly operating position sensor 15 is provided, which, in the version illustrated, cooperates with a magnet 16 arranged in the rotor 12 or sleeve 13 and the signals of which are fed to an electronic control or regulation unit, not illustrated. Electrical contact elements 17 formed on the winding overhang and protected from damage, for example by means of a cover 23, serve for connecting the stator winding to a suitable electrical current source (not illustrated).

[0009] The abovementioned rotational/translational gear 2 serves for converting the rotational movement driven by the rotor 12 of the electric motor 1 into a translational movement of the force transmission member 4. For this purpose, the rotational/translational gear 2 has a gear housing 22, a threaded spindle 18 and a threaded nut 19 which is in engagement with the threaded spindle 18 and which is arranged nonrotatably in the force transmission member 4. In this case, the threaded nut 19 is in engagement with the force transmission member 4 by means of intermeshing crown (or “castle”) teeth 20 and 21 which is formed in each case on the threaded nut 19 and on the force transmission member 4, respectively. The constant engagement of the teeth 20 and 21 is ensured by a spring element which acts in the axial direction and which is supported axially on the piston 4 and is designed in the example shown as a cup spring assembly 34. Instead of the simple movement thread illustrated, which forms the rotational/translational gear 2, any other rotational/translational gear, such as, for example, a ball screw or a roller screw, may, of course, also be used.

[0010] As may be gathered from the drawing, furthermore, the sleeve 13 forming the rotor 12 surrounds radially a portion 25 of pot-shaped design of the gear housing 22. On the one hand, the housing 3 which may be part of a motor vehicle braking system master cylinder and, on the other hand, the housing 10 of the electric motor 1 are supported axially on a radial flange 33 of the gear housing 22. The portion 25 receives the rotational/translational gear 2 and the force transmission member or piston 4 and has two immovably arranged sealing elements 26 and 27 at its end facing the housing 3 and piston 4, the pot-shaped portion 25 forming a guide of the force transmission member or piston 4 in the radial direction. The force transmission member 4 has, at its end facing away from the master cylinder housing 3, a plurality of radial projections, one of which is illustrated and is given the reference symbol 28. The projections 28 form, together with longitudinal slots 29 made in the pot-shaped portion 25, a device for securing the piston 4 against rotation in the pot-shaped portion 25.

[0011] Finally, it is clear from the drawing that the threaded spindle 18 is supported on an axial bearing 30 arranged in the pot-shaped portion 25, while that end of the threaded spindle 18 which faces the housing 3 and piston 4 arrangement is guided in a radial bearing 31 provided in the pot-shaped portion 25 and is in torque-transmitting connection to the rotor 12 or sleeve 13.

[0012] The functioning of the linear unit constructed according to the invention, arises, in principle, from the disclosure content of the present application for the person skilled in the relevant technical art. When the arrangement shown is actuated or when current is applied to the electric motor 1, the pot-shaped rotor 12 or sleeve 13 is set in rotational movement which is transmitted to the threaded spindle 18. As a result of the rotational movement of the threaded spindle 18, a displacement movement of the threaded nut 19 to the right in the drawing takes place, during which the force transmission element or piston 4 is likewise displaced to the right, with the result that, in a pressure space 32 delimited by the piston 4 in the housing 3, a hydraulic pressure is built up which is transferred via a pressure connection to a hydraulic circuit, not shown, for example a hydraulic brake system of a motor vehicle.