Electro-hydraulic braking system

Abstract

Title: Electro-hydraulic braking system Electro-hydraulic braking system (100) comprising: a master cylinder (1) of axis (XX) supplying pressurized hydraulic fluid to the wheel brakes (3), a brake pedal (6) via a control unit (2), connected by an interface (5) comprising a sensor, an electromechanical brake amplifier (4) with a pusher (41) movable about an axis (XA-XA) and whose front face (411) rests on the outside side (122) of the bottom (121) of the piston (12) forming a bearing surface (123). The piston (12) has a convex bearing surface (123), tangent at its point of intersection (123a) with the axis (XX) of the master cylinder (1) or of the piston (12) to the plane (P) perpendicular to the axis (XX), and the tappet (41) has a contact surface (411) with the bearing surface (123) of the piston (12) which is a flat surface, perpendicular to the axis (XX) of the tappet (4). Figure 2

Description

Title of the invention: Electro-hydraulic braking system. FIELD OF THE INVENTION

[0001] The invention relates to an electro-hydraulic vehicle braking system comprising: a master cylinder supplying pressurized hydraulic fluid to the wheel brakes via an electronic control unit; a brake pedal operated by the driver to request braking, connected via an interface including a sensor detecting the braking request to generate an electronic braking request signal; an electromechanical brake booster with a pushrod movable about an axis and whose front face rests against the outer side of the piston base, forming a bearing surface; the electromechanical brake booster receiving the braking request signal from the interface to generate a thrust transmitted by the pushrod to the master cylinder piston. PRIOR TECHNOLOGY

[0002] An electro-hydraulic vehicle braking system such as the one described above is already known. Generally, it is known to achieve the connection between the pushrod and the primary piston of the master cylinder by means of a bearing between a frustoconical shape, the apex of which terminates in a substantially spherical cavity in the face of the piston's bottom, and the spherical end of the pushrod. This corresponds to the contact of two spherical caps with similar but different radii of curvature, due to clearance.

[0003] In this connection, the contact, generally relatively localized between these two spherical surfaces, is not precisely defined and can be located in a wide area around the piston axis. This offset of the support point relative to the piston axis results in a tilting torque exerted on the piston, causing it to tilt and thus producing wear on the front and rear of the piston on either side of the piston crown.

[0004] PURPOSE OF THE INVENTION

[0005] The present invention aims to improve the guidance of the master cylinder piston by improving the piston / pushrod interface and reducing piston wear and leaks, particularly at the outlet of the brake fluid reservoir in the master cylinder.

[0006] DESCRIPTION AND ADVANTAGES OF THE INVENTION

[0007] To this end, the invention relates to a braking system of the type defined above, characterized in that the piston has a convex bearing surface, tangent at its point of intersection with the axis of the master cylinder, which is also that of the piston, to the plane perpendicular to the axis, and the pushrod has a contact surface with the bearing surface of the piston which is a surface at least locally flat, perpendicular to the axis of the pusher.

[0008] This braking system according to the invention has a fixed contact point between the pushrod and the piston, linked to the piston axis regardless of the pushrod's offset or inclination relative to the piston axis. This fixed contact point between the piston and the pushrod is maintained throughout the pushrod's stroke since it is linked to the piston axis. In other words, only the point of contact on the pushrod's front surface can vary. The stability of the contact with the piston and the thrust at this point, coaxial with the piston axis, do not generate any tilting torque on the piston, thus considerably improving the piston's guidance within its bore in the master cylinder and reducing wear, thereby improving the seal between the brake fluid reservoir and the master cylinder.

[0009] According to the invention, the contact between the at least locally flat surface of the pushrod and the spherical surface of the piston, which is linked to its axis, allows only axial loads to be transmitted, without transmitting radial loads responsible for wear of the master cylinder piston, to the contacts on the front side, which is the side exposed to the brake fluid, and on the rear side, i.e., the side facing the pushrod. Furthermore, unlike the distribution of forces in known braking systems, the stresses are shifted further rearward along the piston, which is very important from an operational standpoint.

[0010] In the braking system according to the invention, the pushrod transmits the axial force to the primary piston by means of contact between a flat surface and a spherical surface, such that even if the pushrod is radially misaligned with respect to the primary piston, its bearing surface remains perpendicular to the piston axis. Thus, the point of contact, always aligned with the axis of the primary piston, transmits the thrust in the direction of that axis. The primary piston is in contact with the bore by two distinct guide surfaces: one is the rear guide surface, i.e., on the pushrod side, and the other is the front guide surface, i.e., on the brake fluid side, on either side of the piston bottom.The forces applied to the piston attempt to tilt it, but the front guide is subjected to less stress than the rear guide, which is interesting because this rear guide surface is less critical since it is not located between the seals and cups of the master cylinder as is the case for the front guide surface.

[0011] According to an advantageous feature, the bearing surface is a surface machined in the outside side of the bottom of the piston, which limits the machining to the primary piston.

[0012] According to another feature, the convex bearing surface of the piston is a spherical bearing surface intersecting the axis of the piston at the point of support, which results in a large radius of curvature at the point of contact with the bearing surface of the pusher. The theoretically point contact is limited to a very small surface centered on the axis of the piston.

[0013] According to another feature, a plate is attached to the bottom of the piston and its outer surface forms the bearing surface whose bearing point is at the intersection of the surface with the axis of the piston.

[0014] According to another feature, the added plate is fixed in a cavity machined in the outer face of the piston, by crimping, gluing or welding.

[0015] This embodiment is particularly simple and efficient because the insert plate is machined separately and then assembled to the piston; this simplifies the manufacture of the piston by avoiding complicated machining.

[0016] In addition, this plate ensures a good distribution of the forces generated by the thrust exerted on a limited surface of the piston at the level of its axis.

[0017] According to another advantageous feature, the outer side of the piston is provided with a ball in the piston's axis, forming the bearing surface, the intersection of which with the axis constitutes the bearing point of the tappet. This embodiment has the advantage of simplicity, in particular, if the outer side of the piston has a cylindrical cavity machined in the piston's bottom along its axis, receiving the ball, which is then held in place, preferably by crimping. The ball is, for example, made of steel or stainless steel; the cost of machining the piston is low. The insert can be made of another material depending on the desired properties: a hard material to prevent deformation or marking of the piston; a less hard material for NVH (noise, vibration, roughness) properties.

[0018] Instead of a spherical surface with a large radius of curvature at the point of contact, the contact is made on a small sphere, i.e., the ball. The contact is then on a particularly small surface located precisely on the piston axis. The main advantages are retained: the point of contact is always on the piston axis regardless of the offset of the tappet axis, since the surface against which the contact is made is always a quasi-point surface synchronized with the piston axis. This solution has the advantage of reduced machining costs for the piston. The ball can be made of another material depending on the expected contact properties (a hard material to avoid piston marking deformations; a softer material for NVH properties). Brief description of the drawings

[0019] The present invention will be described in more detail below with reference to embodiments of a hydroelectric braking system shown in the accompanying drawings, in which:

[0020] [Fig-1] General diagram of an electromechanical braking system of the [Fig.1],

[0021] [Fig.1A] Simplified diagram of the electromechanical braking system of the [Fig.1],

[0022] [Fig.2] Cross-sectional view of the master cylinder and the pushrod positioned opposite the master cylinder piston,

[0023] [Fig.2A] Detailed view of [Fig.2] the brake booster assembled to the master cylinder,

[0024] [Fig.3] diagram analogous to that of [Fig.2] of an embodiment,

[0025] [Fig.4] diagram analogous to that of [Fig.2] of another embodiment,

[0026] [Fig.5] diagram similar to that of [Fig.2] of another embodiment.

[0027] DESCRIPTION OF EMBODIMENT METHODS OF THE INVENTION

[0028] According to [Fig. 1], the invention relates to a hydroelectric braking system 100 comprising a master cylinder 1 supplied from a brake fluid reservoir 7 and supplying pressurized compensating brake fluid to the wheel brake calipers 3 via an electronic control unit 2.

[0029] The system includes an electric brake pedal 6 actuated by the driver, which communicates the braking request to the pedal; this pedal 7 is connected to an interface 5 with a stroke sensor (not shown), generating a control signal SC representing the driver's braking request. This control signal SC is transmitted to an electromechanical brake amplifier 4 comprising a motor 42 actuating a pushrod 41 acting on the piston 12 of the master cylinder 1 to control braking by the master cylinder 1 through a mechanical transmission of the thrust F to the piston 12.

[0030] In general, the master cylinder 1 is a tandem master cylinder with a primary piston 12 and a secondary piston 12' (see [Fig.1A]), supplying two brake circuits Cl, C2 through the electronic control unit 2 which, for example, is a unit known by the designation ESP or ABS, to apply, in a programmed manner, the pressurized brake fluid to the wheel brakes 3 through the two circuits according to the braking program of the electronic control unit 2.

[0031] Fig. 1A is a simplified diagram of the braking installation 100 showing the tandem master cylinder 1 with its two pistons 12, 12' and the two circuits Cl, C2 which it supplies.

[0032] Figure 2 shows, in axial section, the portion of the master cylinder 1 with the primary piston 12 sliding along the axis XX of the master cylinder 1, which also receives the secondary piston. The seal between the piston 12 and the cylinder 1 is ensured by seals 111 and cups 112.

[0033] The piston 12 consists of a cylindrical skirt 120 barred by a bottom 121 separating the chamber 110 delimited by the primary piston 12 in the master cylinder 1 and the outside.

[0034] The outer side 122 of the bottom 121 forms a cavity bordered by the extension 12a of the piston 12, completing the cylindrical surface guiding the piston 12 in the master cylinder 1.

[0035] The outer side 122 forms a bearing surface 123 around its point of intersection 123a with the axis XX. The bearing surface 123 is convex and tangent at the point of intersection 123a to a plane P perpendicular to the axis X of the master cylinder 1 (or piston 12). The convex surface forming the bearing surface 123 thus has its apex along the longitudinal direction at its point of intersection 123a with the axis XX.

[0036] The brake booster 4 is a component assembled to the master cylinder 1 (and not a part thereof), therefore, the axis XA-XA of the pushrod 41 of the booster 4 may be offset relative to the axis XX while remaining parallel to it. This unavoidable offset A is shown in [Fig. 2].

[0037] The cylindrical pushrod 41 has a flat frontal surface 411, at least in the portion around the axis XA-XA, as will be seen later. This frontal surface 411 lies in the plane PA perpendicular to the axis XA-XA; it is also perpendicular to the axis XX due to the parallelism imposed by the assembly of the brake booster 4 with the master cylinder 1.

[0038] Thus, the contact of the pusher 42 against the outer side 122 of the piston 12 is always at point 123a regardless of the offset A between the axes XX and XA-XA so that the thrust F of the pusher 4 is always applied in the axis XX of the piston 12; the latter is thus subjected to a thrust strictly in the axis XX of the master cylinder 1 during the movement of the piston.

[0039] According to the geometric representation of [Fig.2], the contact between the front face 411 of the pusher 41 and the bearing surface 123 of the outer face 122 of the piston 12 will take place at the point 411a of intersection of the front face 411 and the axis XX of the master cylinder 1 (or of its piston 12) since the movement of the pusher 41 is a translation along its axis XA-XA, parallel, by hypothesis, to the axis XX.

[0040] It should be emphasized that, according to the diagram in [Fig.2], the axis XA-XA of the pusher 41 is in the plane of [Fig.1], which is always achieved since the axes XX and XA-XA are parallel although the orientation of the axis XA-XA and the offset A are unpredictable, resulting from the inevitable imprecision at this scale, of the assembly between the amplifier 4 and the master cylinder 1. But, by hypothesis, this offset being small, the point of contact 41la of the front face 411 of the pusher 41 with the outer side 122 will always be at the intersection 41la of the axis XX and the front face 411 because this flat face is in the plane PA perpendicular to the axis XA-XA and therefore also to the axis XX.

[0041] The contact point 41la of the front face 411, against the support point 123a, will, due to the offset A and the pivoting of the axis XA-XA by the assembly of the brake amplifier 4 relative to the master cylinder 1, be within a geometric disk of the front face 411 around its axis XA-XA. This disk has a small radius compared to the diameter of the pushrod 41 and must be a flat surface perpendicular to the axis XA-XA. For the piston 12, the contact point 41la, imposed by the support point 123a on the axis XX, allows the thrust F of the pushrod 41 to be transmitted to the piston 12, always oriented exactly on the axis XX of the piston 12.

[0042] Although the notions of point support and point contact are theoretical and the contact between the surface of the pusher 4 and the surface of the piston 12 is made on a very limited surface corresponding to the crushing of the surfaces in contact, this quasi-point surface is practically controlled to the axis XX of the piston 12 so that the thrust F is transmitted along the axis XX of the master cylinder 1.

[0043] The convex part on the outer side 122 is set back from the plane P and extends along a sufficient radius from point 123a, so as not to have a point of contact with the pushrod for all possible offsets of the axis XA-XA with respect to the axis XX within the limits of the precision of the assembly of the brake booster 4 against the master cylinder 1.

[0044] Fig. 2A shows the assembly of the brake booster 4 and the master cylinder 1 with the front face 411 of the pusher 41 coming into contact with the support point 123a of the piston 12 highlighting the contact of this point 41a in the extension of the axis XX of the primary piston 12 and not in the extension of the axis XA-XA.

[0045] According to [Fig. 3], the convex outer surface 122, with respect to plane P, machined in the outer side 122 of the bottom of the primary piston 12, is a spherical bearing surface 124 whose apex, i.e., the point closest to plane P, is on the axis XX and constitutes the bearing point 124a. Since this spherical bearing surface 124 is tangent to plane P, the center of curvature of the surface is on the axis XX.

[0046] The spherical domed shape of the surface is easy to machine to have sufficient clearance set back from the contact plane preventing the front surface of the pusher, which may only be flat on a limited part around its axis XA-XA, from coming into contact with the piston at a point of contact of a surface with a large radius of curvature.

[0047] According to another embodiment, ([Fig.4]) the bearing surface is on a plate 130 itself fixed to the outside side 122 of the bottom 121 of the primary piston 12; the face of the plate 130 is the bearing surface 131 of convex shape, for example, spherical, tangent at its point of intersection 131a with the axis XX to the plane P perpendicular to the axis XX.

[0048] The convex shape, in particular spherical, of the bearing surface of the plate allows good contact with the flat surface of the pusher avoiding local deformation of this flat surface to allow good transverse sliding of the face of the pusher relative to its support point on the axis XX, avoiding the induction of transverse force components which could be generated by the hooking of the surface of the pusher in the direction perpendicular to the axis XX.

[0049] The piston 12 is, for example, made of aluminum with, in particular, an anonization coating.

[0050] The combination of the plate 130 with the piston 12 simplifies the machining of the piston and allows the use, for the plate 130, of a different material than that of the piston 12, for example: aluminium, steel, stainless steel to adapt this combination to particular characteristics, avoid deformation of the piston 12 and improve the stability of the contact of the tappet and the NVH (noise, vibration, roughness) performance.

[0051] According to another embodiment ([Fig.5]) a ball 140 is set in a housing 126 in the outer side 122 in the axis XX of the piston 12. This allows precise positioning of the ball 140 so that the apex 141a of the spherical bearing surface 141 formed by the ball is perfectly in the axis XX and also simplifies the making of the bearing surface of the piston.

[0052] NOMENCLATURE OF MAIN ELEMENTS

[0053] 100 Electro-hydraulic braking system

[0054] 1 Tandem master cylinder

[0055] 11 Cylinder

[0056] 110 Room

[0057] 111 Joints

[0058] 112 Cups

[0059] 12 Piston / primary piston

[0060] 12' Secondary Piston

[0061] 120 Cylindrical sleeve

[0062] 121 Background

[0063] 122 Outer side of the bottom

[0064] 123 Piston bearing surface

[0065] 123a Support point

[0066] 124 Spherical surface

[0067] 124a Support point

[0068] 126 Ball housing

[0069] 130 Report plate

[0070] 131 Support bracket

[0071] 131a Support bracket

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] 140 Ball bearing 141 Support bracket 141a Support bracket 2 Electronic control unit 3 Wheel brakes 4 Electromechanical brake amplifier 41 Amplifier pushrod 411 Pushrod front face 411a Contact point 42 Motor 5 Interface 6 Brake pedal 7 Hydraulic fluid reservoir XX Piston axis 12 XA-XA Amplifier pushrod axis 4 P Plane perpendicular to axis XX PA Plane containing the bearing surface 421 of the push button 42 F Push button push button

Claims

Demands

1. An electro-hydraulic vehicle braking system (100) comprising: a master cylinder (1) with axis (XX) supplying pressurized hydraulic fluid to the wheel brakes (3) via an electronic control unit (2) (ESP, ABS), a brake pedal (6) actuated by the driver to request braking, connected by an interface (5) comprising a sensor detecting the braking request to generate an electronic braking request signal (Sc), an electromechanical brake booster (4) with a pusher (41) movable about an axis (XA-XA) and whose front face (411) bears against the outer side (122) of the bottom (121) of the piston (12) forming a bearing surface (123), the electromechanical brake booster (4) receiving the braking request signal (Sc) from the interface (5) to generate a thrust (F) transmitted by the pusher (11) to the piston (12) of the master cylinder (1),braking system characterized in that - the piston (12) has a convex bearing surface (123), tangent at its point of intersection (123a) with the axis (XX) of the master cylinder (1) or of the piston (12) to the plane (P) perpendicular to the axis (XX) and, - the pushrod (41) has a contact surface (411) with the bearing surface (123) of the piston (12) which is a flat surface, perpendicular to the axis (XX) of the pushrod (4).

2. Braking system according to claim 1, characterized in that the bearing surface (123) is a surface machined in the outside side (122) of the bottom (121) of the piston (12).

3. Braking system according to claims 1 and 2, characterized in that the convex bearing surface of the piston (12) is a spherical bearing surface (124) intersecting the axis (XX) of the piston at the bearing point (124a).

4. Braking system according to claim 1, characterized in that it comprises a plate (130) attached to the bottom (121) of the piston (12) whose outer surface forms the bearing surface (131), and the bearing point (131a) is at the intersection of the surface (131) with the axis (XX) of the piston (12).

5. Braking system according to claim 4, characterized in that the pad (130) is fixed to the base (121) by: - ​​crimping, welding and bonding in a cavity machined in the face (121).

6. Braking system according to claim 4, characterized in that the piston (130) is made of aluminium or anodized aluminium.

7. Braking system according to claim 1, characterized in that the outer side (122) of the piston (12) is provided with a ball (140) in the axis (XX) of the piston (12) forming the bearing surface (141) whose intersection with the axis (XX) forms the bearing point (131a).

8. Braking system according to claim 7, characterized in that the outer side (122) of the piston (12) has a cylindrical cavity (126) machined in the bottom (121) in the axis of the piston (XX) and receiving the ball (140).

9. Braking system according to claim 7, characterized in that the ball (140) is made of steel or stainless steel.

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