Electromechanical brake pressure generator for a vehicle hydraulic brake system and method of producing the same

Abstract

Title: Electromechanical brake pressure generator for a vehicle hydraulic brake system and method of producing the same Generator comprising a screw drive device (40) driving a piston / cylinder assembly (18) comprising a nut (72) driven by a motor (38), a spindle (84) with a thread (88) cooperating with the nut (72), a piston (92), a housing (64) surrounding the screw (84), the nut (72) and the piston (92). A rotational locking means (96, 100) of the spindle (84) comprises a torque support (96) produced on the piston (92) and penetrating into an axial recess (100) of the housing (64). Figure 3

Description

Title of the invention: Electromechanical brake pressure generator for a vehicle hydraulic brake system and method of producing the same Field of invention

[0001] The present invention relates to an electromechanical brake pressure generator for a vehicle hydraulic brake system and its method of production.

[0002] More specifically, the invention relates to an electromechanical brake pressure generator of a vehicle hydraulic brake system comprising a screw drive device for transforming the rotational movement on the drive side into a translational movement for actuating a piston / cylinder assembly actuated to generate the hydraulic brake pressure. The screw drive device comprises a nut driven in rotation by an electric motor, a spindle with a thread cooperating with the nut so that rotation of the nut axially moves the spindle, a hydraulic piston of the piston / cylinder assembly, a housing of the piston / cylinder assembly which at least partially surrounds the screw, the nut and the hydraulic piston, as well as a rotation locking means which locks the spindle during rotation of the nut.

[0003] The invention also relates to a method for producing such an electromechanical brake generator. State of the art

[0004] An electromechanical brake pressure generator comprises a screw transmission device for converting the rotational movement applied as input into a translational movement for generating the brake pressure.

[0005] Indeed, to brake the motor vehicle, the force exerted by the driver's foot is generally not sufficient, so vehicles are usually equipped with a brake force amplifier. Brake force amplifiers or brake boosters generally use the vacuum generated by the internal combustion engine. The pressure difference between the pressure in the engine and the ambient pressure is used to apply an amplified force in addition to the force exerted by the driver's foot, on the piston rod of the piston / cylinder assembly.

[0006] For future drive concepts for motor vehicles, other equipment is required to generate brake pressure because the vacuum is no longer available to operate a conventional vacuum brake booster. To overcome this, various electromechanical brake pressure generators have been developed.

[0007] In such systems, the actuating force of the piston / cylinder assembly is generated by an electric motor. Such electromechanical brake pressure generators can not only provide auxiliary or assisting force, but can also be used in electric brake systems as the sole means of providing the actuating force. For this reason, electromechanical brake pressure generators are particularly advantageous in the context of autonomous driving.

[0008] Document WO 2017 / 045804 A1 describes an electromechanical brake force amplifier shown in [Fig. 1]. Unlike this, the invention relates to an electromechanical brake pressure generator which can apply a brake force independently of the actuation of the brake pedal.

[0009] The known brake force amplifier 1 comprises a nut 2 and an electric motor (not shown) which rotates the nut 2 by means of a spur gear 3. The nut 2 is engaged with a screw (or spindle) 4 so that the rotation of the nut 2 produces a translational movement of the spindle 4 along its axis 5. So that the spindle 4 does not rotate during the rotation of the nut 2, the brake force amplifier 1 comprises a bearing device 6 secured to the spindle 4.

[0010] The bearing device 6 comprises a stirrup 6a whose edges come into two plain bearings 6b. The plain bearings 6b circulate on tie rod bodies 7 parallel to the axis 5 of the spindle. This bearing device 6 allows the spindle 4 to move in the axial direction while being blocked in rotation.

[0011] OBJECTIVE OF THE INVENTION

[0012] The aim of the present invention is to develop an electromechanical brake pressure generator comprising a screw drive device allowing more efficient rotational locking.

[0013] Description and advantages of the invention

[0014] To this end, the invention relates to an electromechanical brake pressure generator of the type defined above, characterized in that the screw drive device comprises a nut driven in rotation by an electric motor, a spindle with a thread cooperating with the nut so that the rotation of the nut axially moves the spindle, a hydraulic piston of the piston / cylinder assembly, a housing of the piston / cylinder assembly which at least partially surrounds the screw, the nut and the hydraulic piston, as well as a rotation locking means which locks the spindle in rotation during the rotation of the nut, this generator being characterized in that the rotation locking means comprises a torque support made on the hydraulic piston and penetrating into an axial recess of the housing, this recess providing a sliding surface for the torque support of the hydraulic piston.

[0015] The invention also relates to a method for producing such an electromechanical brake pressure generator, characterized in that the method comprises the following: subsequent steps consisting of connecting the two parts constituting the housing by a material connection and producing recesses oriented in the axial direction and having sliding surfaces, the recesses and the sliding surfaces extending over the parts of the housing and forming, with the torque supports of the hydraulic piston, a means for locking the hydraulic piston and the spindle in rotation.

[0016] In other words, the subject of the invention is an electromechanical brake pressure generator for a hydraulic brake system of a vehicle. The electromechanical brake pressure generator comprises at least one screw drive device for transforming the rotational movement, on the drive side, into a translational movement to generate the brake pressure. The screw transmission device comprises for this purpose a screw nut driven in rotation by an electric motor, a spindle (or screw) cooperating with the thread of the nut so that the rotation of the axial nut moves the spindle, the hydraulic piston at least partially surrounding the spindle and the nut in the radial direction while being connected in rotation to the spindle, the rotation of the nut producing the axial displacement of the piston.

[0017] The screw transmission device is a simple screw or spindle drive in which the nut is in direct contact with the screw (or spindle), the drive may comprise a ball screw. The ball screw drive is a transmission with balls between the screw and the nut. The two parts each have a helical groove which forms by combination a common helical tube, filled with balls. The connection by the shape in the screw, transverse to the helical line is no longer made by the simple transmission between the nut and the body of the screw, but by means of the balls.

[0018] The screw transmission device further comprises a housing which at least partially surrounds the hydraulic piston and constitutes a hydraulic cylinder with an axially shaped recess in the hydraulic cylinder providing a rotational locking means for torque supports on the hydraulic piston; this rotational locking blocks the hydraulic piston and the spindle when the nut rotates. Preferably, the housing is composed of two parts connected by a material connection. The recess which passes through the housing parts constitutes a continuous and seamless (welded-free) axial sliding surface for the torque supports of the hydraulic piston.

[0019] According to the invention, the rotation is a movement around the axis of the spindle. The rotation of the driven nut produces the axial sliding of the spindle so that the rotational movement of the electric motor, i.e. the movement of the nut, is transformed into a translational movement of the spindle. The rotation is blocked by the torque supports which absorb the torque produced by the rotational movement.

[0020] The parts of the housing constitute elements produced independently of one another and connected by a material connection to form the housing. The parts of housing are preferably made of aluminum. The sliding surface is a surface that is particularly suitable for allowing the torque supports to slide. The sliding surfaces are continuous, i.e. they pass through both housing parts. In addition, the sliding surfaces are seamless, which means that the material bond does not create any disruptive transition of the sliding surface between the two housing parts. This reduces wear on the torque supports and increases the reliability of the electromechanical brake pressure generator.

[0021] According to the state of the art, to reduce wear at the disruptive junction, complementary rails are inserted while the sliding surfaces according to the invention are produced directly by the recess, which makes the installation of complementary rails unnecessary. This avoids an operation consisting of inserting sliding rails into the recess. Thus, the electromechanical brake pressure generator according to the invention is more efficient, simpler and more economical to manufacture.

[0022] According to a preferred development of the invention, the torque supports have a contact pad in the contact zone with the sliding surface and they are supported by these pads on the sliding surfaces, the contact pad being made of a material different from that of the hydraulic piston. A contact pad within the meaning of the invention is an element applied to the torque support and which comes into direct contact with the sliding surface. Preferably, the contact pad completely surrounds the torque support. The contact pad thus makes it possible to choose a material for the hydraulic piston which does not depend on sliding properties. The material of the contact pad is advantageously chosen to guarantee a good sliding combination between the material of the sliding surface and that of the contact pad.

[0023] According to a preferred development of the invention, the contact pad is made of plastic. The contact pad can be overmolded or glued to the torque support. Thus, this contact pad is produced simply and economically. In addition, the plastic material is a light and economical material. There is a very large choice of plastic materials having particular properties, thus making it possible to choose the most appropriate plastic material for the intended use.

[0024] Preferably, the axial end on the outside of the housing has a matting so as to fix the bearing of the screw nut in the axial direction between a housing support and the matting. In mechanics, matting is a connection by force and shape between two parts. This connection is made by plastic forming. This forming of the edge area of ​​a part makes it possible to make a solid connection.

[0025] Such an edge zone is provided at the axial end of the housing. This edge zone of the housing has a material thickness allowing for peening. The peening axially locks the bearing pressed against the shoulder of the housing without requiring an additional part in the housing. The peening is carried out in a simple and economical manner. during manufacturing.

[0026] According to an advantageous development, the radially outer end of the recess has a rounded portion. The recess within the meaning of the invention is an area having no corner. This means that the area is produced at the radially outer end of the recess with a rounding. This rounding counteracts a wedging effect. In addition, such a recess with a rounding is produced more simply and more economically by milling.

[0027] The invention also relates to a method for producing such an electromechanical brake pressure generator as has already been developed. The method comprises the steps of producing a material connection between the two housing parts, developing a hydraulic cylinder extending over the housing parts and which receives a spindle or screw, a nut and a hydraulic piston; continuous recesses with sliding surfaces are produced in the region of the hydraulic cylinder with an axial orientation and the recesses and the sliding surfaces pass through the housing parts and thus constitute, together, torque supports for the hydraulic piston ensuring rotational locking of the hydraulic piston and the spindle. This method makes it possible to obtain the advantages already mentioned, of the electromechanical brake pressure generator.

[0028] Advantageously, the housing parts forming the housing are joined by friction welding, which creates a material bond. Friction welding generates the friction energy not by the relative movement of the two joining partners, but by means of a rotating, friction-resistant tool. The area between the two housing parts is heated by the rotating tool so that the two housing parts are joined by a material bond. This welding process requires neither additional material nor protective gas. In addition, this welding connection is carried out at a relatively low temperature, which reduces deformation of the housing parts.

[0029] According to another advantageous development, the axial end of the housing is caulked after the installation of a bearing receiving the screw nut so that the bearing is thus held in the axial direction. This caulking method is associated with the advantages already mentioned.

[0030] The invention also relates to a vehicle equipped with such an electromechanical brake pressure generator for a hydraulic brake system. This vehicle benefits from the advantages already mentioned of the electromechanical brake pressure generator. According to a preferred development, the vehicle is of automated or fully autonomous operation. Presentation of the drawings

[0031] The present invention will be described below in more detail using exemplary embodiments of an electromechanical brake pressure generator shown in the attached drawings in which:

[0032] [Fig-1] diagram of an electromechanical brake force amplifier according to the state of the technique,

[0033] [Fig.2] diagram of a vehicle hydraulic braking system with an electromechanical brake pressure generator,

[0034] [Fig.3] sectional view of an exemplary embodiment of a screw drive device according to the invention of the electromechanical brake pressure generator, and

[0035] [Fig.4] perspective view of an exemplary embodiment of the housing of the screw drive device of the electromechanical brake pressure generator.

[0036] Description of the embodiment of the invention

[0037] [Fig. 2] is a diagram of a vehicle hydraulic brake system 10 comprising an electromechanical brake pressure generator 14. The hydraulic brake system 10 comprises the electromechanical brake pressure generator 14. This brake pressure generator 14 comprises a piston / cylinder unit 18 supplied with brake fluid from a brake fluid reservoir 22.

[0038] The piston / cylinder unit 18 is controlled by the brake pedal 26 actuated by the driver and the resulting pedal travel is measured by a pedal travel sensor 30, the signal from which is transmitted to a control device 34.

[0039] Although [Fig. 2] shows the principle of a brake force amplifier, here the brake pedal travel is mainly measured using the pedal travel sensor 30. Braking pressure can also be generated without the brake pedal travel so that the vehicle can also be braked in autonomous mode.

[0040] From the measured brake pedal travel, the control device 34 generates a control signal for the electric motor 38 of the brake pressure generator 14. The electric motor 38 connected to a transmission (not shown) of the brake pressure generator 14, amplifies the braking force provided by the brake pedal 26 in the case of a decoupled system, depending on the control signal. For this, depending on the actuation of the brake pedal 26, the electric motor 38 controls the screw transmission device 40 of the brake pressure generator 14 to transform the rotational movement of the electric motor 38 into a translational movement.

[0041] Actuation of the brake pedal 26 pressurizes the brake fluid of the piston / cylinder unit 18 with the aid of the brake pressure generator 14. This measured brake pressure is transmitted via a brake line 42 to the hydraulic brake unit 46. The hydraulic brake unit 46, which is shown here only in the form of a housing, applies a stability program, for example, electronic, ESP, through various valves and other components. The hydraulic brake unit 46 is additionally connected to at least one wheel brake system 50, which makes it possible to apply a braking force to the wheel brake system 50 through a corresponding circuit of valves.

[0042] [Fig. 3] is a sectional view of an exemplary embodiment of the screw transmission device 40 according to the invention of the electromechanical braking force generator 14. The screw transmission device 40 comprises a housing 64 formed of two halves 64a, 64b (see [Fig. 4]). The housing 64 made of metal constitutes a pot-shaped hydraulic cylinder 68.

[0043] The screw drive device 40 comprises a nut 72 mounted in the housing 64 by a bearing 76. An axial end of the nut 72 of this embodiment example carries a drive wheel 80 connected in rotation to the nut 72. This drive wheel 80 drives the nut 72 by the electric motor 38 not shown. The nut 72 thus rotates around its longitudinal axis.

[0044] The nut 72 surrounds a pin 84 engaged by a thread 88 with the nut 72. The pin 84 is rotationally fixed to the hydraulic piston 92 and the housing 64 forms a rotation locking means 96, 100 so that the rotation of the nut 72 allows the slide 84 and the hydraulic piston 92 to perform an axial movement. The hydraulic piston 92 thus performs a piston stroke.

[0045] The rotation locking means 96 of the hydraulic piston 92 of this embodiment is made using two torque supports 96 which are radially projecting and extend outwardly beyond the remainder of the hydraulic piston 92. The two torque supports 96 form an angle of 180° between them. The rotation locking means 100 of the housing 64 is made in two recesses 100, oriented axially and into which the torque supports 96 penetrate so that the hydraulic piston 92 and the spindle nut 72 are locked in rotation.

[0046] The recesses 100 form sliding surfaces 104 oriented in the axial direction and against which the torque supports 96 come. The recesses 100 have a radially outer end with a rounding 108. The rotation of the nut 72 causes the torque supports 96 to slide in the axial direction on the sliding surfaces 104 of the recesses 100. The torque supports 96 have a contact area with the sliding surface 104 of the contact pads 112 whose sliding characteristics are improved. In this exemplary embodiment, the contact pads 112 are made of plastic.

[0047] The bearing 76 by which the nut 72 is mounted in the housing 64 is located between a housing shoulder 116 and the axially outer end 120 of the housing 64 in the axial direction of the housing. This axial end 120, on the outer side, of the housing 64 has a caulking 124 for holding the bearing 76 in the axial direction between the housing shoulder 116 and the caulking 124. This caulking 124 is carried out after the bearing 76 has been put in place.

[0048] [Fig. 4] is a perspective view of an exemplary embodiment of the housing 64 of the screw transmission device 40 of the electromechanical brake pressure generator 14. To explain the characteristics, in this figure, the nut 72, the pin 84, the bearing 76 and the hydraulic piston 92 have been removed. This figure shows the matting 124 carried out after the installation of the bearing 76.

[0049] The figure shows the housing 64 composed of a first part 64a and a second part 64b. The second part 64b of the housing is connected to the first part 64a of the housing by a material connection, for example, by friction welding. After connecting the two parts 64a, 64b of the housing to each other, the hydraulic cylinder 68 and the recesses 100 with the sliding surfaces 104 are produced, for example, by milling. The material connection between the two housing parts 64a, 64b thus produces the continuous and seamless sliding surface 104. This avoids the need to install a rail so that it is sufficient to place the contact pads 112 on the torque supports 96.

[0050] NOMENCLATURE OF MAIN ELEMENTS

[0051] 10 Hydraulic brake system

[0052] 14 Brake pressure generator

[0053] 18 Piston / cylinder assembly

[0054] 22 Brake fluid reservoir

[0055] 26 Brake pedal

[0056] 30 Pedal travel sensor

[0057] 34 Control device

[0058] 38 Electric motor

[0059] 40 Screw transmission device

[0060] 42 Brake line

[0061] 46 Hydraulic brake circuit

[0062] 50 Wheel brake device

[0063] 64 Housing

[0064] 64a,64b Housing parts

[0065] 72 Nut

[0066] 76 Landing

[0067] 80 Drive pinion

[0068] 84 Screws

[0069] 92 Hydraulic piston

[0070] 96 Rotation locking means / torque support

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077] 100 Means for locking the housing against rotation 104 Sliding surface 108 Rounded end 112 Contact pad 116 Shoulder of the housing 120 End on the outer side of the housing 124 Caulking

Claims

Claims

1. Electromechanical brake pressure generator (14) for a hydraulic brake system (10) of a vehicle having a screw drive device (40) for converting a rotational movement on the drive side into a translational movement and having a piston / cylinder assembly (18) actuated by the screw drive device (40) for generating the hydraulic brake pressure, the screw drive device (40) comprising: - a nut (72) driven in rotation by an electric motor (38), - a spindle (84) whose thread (88) cooperates with the nut (72) so that rotation of the nut (72) axially moves the spindle (84), - a hydraulic piston (92) of the piston / cylinder assembly (18), - a housing (64) of the piston / cylinder assembly (18) which at least partially surrounds the screw (84), the nut (72) and the hydraulic piston (92), - a means of rotation lock (96, 100) locking the spindle (84) in rotation during rotation of the nut (72),generator characterized in that the rotation locking means (96, 100) comprises: - two torque supports (96) made on the hydraulic piston (92), projecting radially and extending externally beyond the remainder of the hydraulic piston (92 and forming an angle of 180° between them, - two recesses (100) in the housing (64 forming continuous sliding surfaces (104), * the rotation locking support (96) penetrating the respective axial recess (100), forming the sliding surface (104) of the locking support (96).,

2. Electromechanical brake pressure generator (14) according to claim 1, characterized in that the housing (64) comprises two housing parts (64a, 64b) connected to each other by a material connection, the recesses (100) occupying the housing parts (64a, 64b) and the sliding surface (104) being continuous and seamless in the axial direction.

3. Electromechanical brake pressure generator (14) according to claim 1 or claim 2, characterized in that the torque supports (96) comprise a contact pad (112) in the contact zone with the sliding surface (104), the torque supports (96) coming into contact by the pad against the sliding surface (104), the contact pad (112) being made of a material different from that of the hydraulic piston (92).

4. Electromechanical brake pressure generator (14) according to claim 3, characterized in that the contact pad (112) is made of a plastic material.

5. Electromechanical brake pressure generator (14) according to one of the preceding claims, characterized in that the outer axial end (120) of the housing (64) has a matting (124) for locking in the axial direction, the bearing (76) of the spindle nut (72) between the matting (124) and the housing shoulder (116).

6. Electromechanical brake pressure generator (14) according to one of the preceding claims, characterized in that the radially outer end of the recess (100) comprises a rounding (108).

7. Method for producing an electromechanical brake pressure generator (14) according to one of claims 1 to 6, wherein the method comprises the following steps: connecting the two housing parts (64a, 64b) constituting the housing (64) by a material connection, and producing recesses (100) oriented in the axial direction and having sliding surfaces (104), the recesses (100) and the sliding surfaces (104) being produced on the housing parts (64a, 64b) and forming, together with the torque supports (96) of the hydraulic piston (92), the rotational locking means (96, 100) of the hydraulic piston (92) and the spindle (84).

8. Method according to claim 7, characterized in that the housing parts (64a, 64b) constituting the housing (64) are connected to each other by a material connection made by friction welding.

9. Method according to claim 7 or claim 8, characterized in that after placing a bearing (76) receiving the spindle nut (84), mat the axially outer end (120) of the housing (64) to hold the bearing (76) in the axial direction.

10. Vehicle comprising an electromechanical brake pressure generator (14) for its hydraulic brake system (10) according to one of claims 1 to 6.

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