Brake booster for a vehicle

Abstract

A brake booster for a vehicle is provided, comprising: a pushrod piston actuated by a driver, which is slidably arranged in a booster body that is movable relative to the vehicle; an output element, which can be actuated by the pushrod piston with an input force and through which a piston of a master brake cylinder can be actuated with an actuating force; a force transmission unit, consisting of a first reaction unit with elastic properties and a second reaction unit adjacent to the first reaction unit, wherein the force transmission unit is slidably arranged at one end of the booster body relative to it;wherein the amplifier body has a radial recess in its interior, and the pushrod piston comprises a collar fixed thereon in the region of the recess, wherein a first spring element is clamped between the collar and an inner surface of the recess; wherein a stop element is fixed on the pushrod piston outside the amplifier body; wherein a second spring element is clamped between the stop element and a reference point device fixed relative to the vehicle; such that, when the pushrod piston is actuated, a dead travel between the stop element and the reference point device can be compensated by means of the second spring element.

Description

[0001] The present invention relates to a brake booster for a vehicle, in particular a brake booster with pedal travel reduction. State of the art

[0002] Document WO 2012 / 059259 A1 discloses a brake booster with an input element or push rod piston that can be actuated by a driver, an actuator for generating an assisting force, an output element that transmits a pressure force, which can be acted upon by the push rod piston and / or the actuator with an input force or the assisting force, and by which a further piston of a master brake cylinder can be acted upon with an actuating force, and a force transmission unit with elastic properties, which is arranged between the push rod piston and the actuator on the one hand and the output element on the other hand and transmits the input force and / or the assisting force to the output element and thus to the master brake cylinder.

[0003] In automotive braking systems, including a brake booster such as that described above, particular importance is generally attached to the design of a so-called dead travel, i.e. the distance traveled by the input element (or "brake pedal") actuated by the driver, i.e. the brake pedal travel subjectively perceived or "felt" by the driver, before an actual deceleration, i.e. a "braking", of the vehicle occurs.

[0004] The aim is to keep the dead distance relatively short in order to give the driver a "safe" feeling, i.e. that when the brake pedal is pressed a more or less immediate deceleration of the vehicle occurs, whereby the brake booster of the type described, i.e. electromechanically by means of an actuator, can have a supporting effect in order to achieve the deceleration of the vehicle as quickly as possible, particularly in dangerous situations where the vehicle ideally has to be brought to a standstill as quickly as possible (for example when a person appears immediately in the path of the vehicle), also with the aid of modern driver assistance systems that are familiar to the person skilled in the art.

[0005] In this respect, the disclosure of the teaching as described in the document WO 2012 / 059259 A1 is hereby incorporated by reference into the present application, since the subject matter of the present invention is based thereon.

[0006] Further prior art is disclosed in the following documents: [1] Dr.-Ing. B. Witte, Dr.-Ing. T. Barthenheier: “eBKV – the Electromechanical Brake Booster), VDI Reports No. 2000 / 2007” [2] DE 103 27 553 A1: “Electromechanical brake booster” [3] DE 10 2005 024 577 A1: ‘Device and method for electromechanical brake assistance’ [4] US 6,574,959 B2: “Electric brake booster with unrestricted manual push through” [5] DE 102 55 198 A1: ‘Electronically controlled braking system for motor vehicles’ Disclosure of the invention

[0007] The invention proposes, in a first aspect according to claim 1, a brake booster for a vehicle, comprising: a push rod piston which can be actuated by a driver and which is arranged displaceably in a booster body which is displaceable relative to the vehicle; an output element which can be acted upon by the push rod piston with an input force on the push rod piston and by which a piston of a master brake cylinder can be acted upon with an actuating force; a force transmission unit consisting of a first reaction unit with elastic properties and a second reaction unit adjacent to the first reaction unit, wherein the force transmission unit is arranged at one end of the booster body so as to be displaceable relative to the latter;wherein the booster body has a radial recess in its interior, and the push rod piston comprises a collar fixed thereon in the region of the recess, wherein a first spring element is clamped between the collar and an inner surface of the recess; wherein a stop element is fixed on the push rod piston outside the booster body; wherein a second spring element is clamped between the stop element and a reference point device fixed relative to the vehicle; so that upon actuation of the push rod piston, a dead travel between the stop element and the reference point device can be compensated by means of the second spring element.

[0008] Furthermore, the present brake booster is designed such that an air gap is smaller when the push rod piston is not actuated than is desired at the beginning of the braking process, whereby the desired air gap is only created when the push rod piston is actuated by a deliberately larger travel path of the push rod piston relative to the booster body, so that the travel path of a second piston is greater relative to the first push rod piston; the shorter necessary travel path of the first push rod piston thereby advantageously shortens the brake pedal travel.

[0009] In a second aspect according to claim 10, the invention proposes a braking system for a vehicle, wherein the braking system comprises a brake booster according to one of claims 1 to 9. Advantages of the invention

[0010] The advantage of the proposed brake booster is that the driver's feeling for the brake pedal behavior is improved due to the pedal travel reduction.

[0011] Furthermore, due to the improved pedal feel, a larger adjustment range can be achieved due to the pedal travel shortening options.

[0012] In addition, if the brake booster fails, the necessary response force of the brake pedal from its zero position is only reduced by a small amount, so that - after overcoming the first few millimeters after the zero position - a relatively higher force must be applied, but the triggering of safety-relevant driver assistance functions is still guaranteed.

[0013] Preferably, when the push rod piston is actuated, the first spring element and the second spring element relax and the output element including the booster body are displaced relative to the vehicle by means of the force transmission unit exerting pressure on the piston of the master brake cylinder.

[0014] Advantageously, depending on the properties of the spring elements, a linear or non-linear force curve of the push rod piston upon actuation can be predefined, or any combination of both can be achieved. This is advantageous because the same brake booster can be used for different vehicle models, thus saving costs, and only the spring elements need to be selected depending on the desired brake response.

[0015] Furthermore, it is preferred that the second spring element be configured such that, upon actuation of the push rod piston, a resulting force component of the second spring element is zero before, during, or after a contact point between the push rod piston and the first reaction unit, which is elastic. This is advantageous because the braking behavior perceived or desired by the driver can be adjusted in a correspondingly simple manner, namely by selecting the second spring element.

[0016] Preferably, the first spring element and / or the second spring element are each designed as a spiral spring or as an elastic element with the properties corresponding to the respective spiral spring. Any type of spring-like element is conceivable, as long as they exhibit the required properties.

[0017] Advantageously, a damping element is arranged in the brake booster, which serves to compensate for undesirable interactions, such as undesirable vibrations, which result from the interaction of the spring elements during operation of the brake booster, between the spring elements when the push rod piston is actuated.

[0018] Furthermore, it is preferred that the first spring element and / or the second spring element are each formed by a combination of several spring elements, whereby certain force curve characteristics of the “braking feeling” perceived by the driver can be easily adjusted.

[0019] Furthermore, it is preferred that the second spring element be attached at one end to the reference point device or to the push rod piston or to a device firmly connected to the reference point device. This is advantageous because a defined desired behavior of the second spring element can be achieved.

[0020] Finally, it is also preferred that the fixed end of the second spring element is designed to be movable so that a desired preload can be adjusted as required.

[0021] Preferably, a third spring element is arranged between the fixed reference point and the stop element fixed to the push rod. This third spring element is supported on the one hand on the fixed reference point and on the other hand on the stop element. The third spring element is preloaded, i.e., compressed, when the push rod is not actuated, and is relaxed when actuated. Furthermore, it is preferred that the third spring element be attached either to the fixed reference point or to the stop element. This advantageously allows the driver to adjust the "behavior" of the stop (hard / soft) accordingly.

[0022] Advantageously, a rear end of the third spring element, which rests against the fixed reference point when not actuated, is designed to be movable, and / or a preload of the third spring element is adjustable by the fixed reference point. This also allows the driver to adjust the "behavior" of the stop (hard / soft) accordingly.

[0023] Furthermore, it is preferred that the first spring element and / or the second spring element and / or the third spring element are each designed as a coil spring or an elastic element with properties corresponding to the respective coil spring. This is advantageous because, on the one hand, relatively inexpensive spring elements can be selected, and, on the other hand, a spring element can consist of a combination of several spring elements in order to achieve a corresponding brake pedal force curve (linear / non-linear or a combination of both for different travel sections of the brake pedal force curve) based on the spring characteristics of the respective spring elements. Short description of the drawings

[0024] The invention is explained below using embodiments in conjunction with the figures, wherein: Fig. 1 shows a schematic representation of a basic embodiment of a brake booster; Fig. 2A shows a schematic representation of an embodiment of a brake booster with pedal travel reduction in an unactuated state; Fig. 2B is a schematic representation of the embodiment of Fig. 2A in an actuated state compared to the representation in Fig. 2A shows; Fig. 3 shows a schematic representation of another basic embodiment of the invention; Fig. 4A shows a schematic representation of another embodiment of the invention in an unactuated state; and Fig. 4B is a schematic representation of the further embodiment of Fig. 4A in an actuated state compared to the representation in Fig. 4A shows. Embodiments of the invention

[0025] Fig. 1 shows a schematic cross-sectional side view of a brake booster 10, with only essential components being shown for better understanding.

[0026] The essential components are a push rod piston 30, which can be displaced in the longitudinal direction, ie in the drawing from left to right, by exerting a force 130 by a driver, ie by actuating a brake pedal (not shown here) coupled to the push rod piston 30. For this purpose, the push rod piston 30 can be guided in a booster body 20, as will be explained in more detail below.

[0027] The push rod piston 30 extends at a first end 50 into a through hole 40 of the booster body 20. The through hole 40 has a radial recess 60 within the booster body 20, the recess 60 extending along the through hole 40.

[0028] The amplifier body 20 or the through-bore 40 is closed at a second end 70 with at least one disc-shaped element 80. In the example shown, the disc-shaped element 80 comprises a first disc-shaped component 81, which is elastic, and a second disc-shaped component 82 adjacent thereto.

[0029] A collar 90 is fixed to the push rod piston 30 in the region of the recess 60, and a first spring element 110 is arranged between the collar 90 and an inner surface 100 in the recess 60, which spring element is supported on the one hand on the collar 90 and on the other hand on the inner surface 100.

[0030] The second disc-shaped component 82 is coupled to a further spring element 120, which is supported on the one hand on the disc-shaped element 82 and on the other hand on a piston (not shown here) of a master brake cylinder of a vehicle brake system.

[0031] An arrow 130 indicates a mechanical force F exerted on the push rod piston 30 - e.g. by the driver in while an arrow 140 indicates a force F resulting from the function of the brake booster out which ultimately represents the force applied to the piston of the brake cylinder (not shown here) for braking intervention.

[0032] The exact mode of operation of the brake booster 10 can be seen from the following figures and the associated description.

[0033] Fig. 2A shows the brake booster 10 from Fig. 1, where generally the same reference numerals refer to the same elements.

[0034] In Fig. 2A is in addition to the representation in Fig. 1 shows a reference point device 150, which is fixed to the vehicle body as a fixed reference point relative to the movable amplifier body 20. The type of attachment of the reference point device 150 to the vehicle body is unimportant for the invention, as is the precise design of the reference point device 150.

[0035] As in Fig. 2A, the push rod piston 30, with a stop element 160 fixed to it, rests firmly against a section 170 of the reference point device 150, wherein a second spring element 180 is arranged between the stop element 160 and one end 170 of the reference point device 150.

[0036] The brake booster 10 is located in Fig. 2A in an unactuated state, wherein the first spring element 110 and the second spring element 180 are each in a compressed state. That is, the forces F in and F out(130, 140) are each equal to zero. It should be noted at this point that the spring elements 110, 180 in Fig. 2A (as in the other figures) are shown as spiral springs, but spring elements of a different shape with corresponding spring characteristics are also conceivable.

[0037] Fig. 2B now shows the brake booster 10 in an actuated state, ie the forces F in and F out are greater than zero, which can be seen from the fact that the stop element 160 has moved away from the stop device 150 or the corresponding section 170 thereof by an amount x, namely to the right in the drawing. At the same time, a force generated by an electric motor M (see Fig. 3) applied force, by means of a pinion 21 arranged on the amplifier body 20, displaces the amplifier body 20 by an amount y to the "right". Thus, the motor M exerts a force F on the amplifier body 20 supporton the piston of the master brake cylinder (not shown here) for a braking operation, which is indicated by the F gegen The larger travel path of the push rod piston 30 relative to the booster body 20 relaxes the spring element 120, resulting in an unwanted, falling course of the counterforce against the piston (not shown here).

[0038] A sensor element 31 serves to measure the distance traveled by the push rod piston 30, wherein the information thereby provided can be provided, for example, to a driver assistance system and / or a control system of the engine M.

[0039] Fig. 4A and Fig. 4B correspond to the Fig. 2A and Fig. 2B situations (ie Fig. 4A: unactuated state of the brake booster 10, and Fig. 4B: activated state of the brake booster 10), but with the difference that in Fig. 4A and Fig. 4B instead of the reference point device section 170, the second spring element 180 is shown, which is arranged or braced in a supporting manner between the stop element 160 and section 170.

[0040] The difference to the Fig. 2A and Fig. 2B is that the spring force of the second spring element 180 is different from the embodiment shown in Fig. 4A and Fig. 4B, counteracts the reduction in the spring force of the spring element 120 and thus prevents an undesirable drop in the counterforce against the push rod piston 30. By appropriately selecting the spring properties of the second spring element 180, the force curve perceived by the driver can be adjusted accordingly.

[0041] Fig. 4A and Fig. 4B correspond to the Fig. 2A and Fig. 2B situations (ie Fig. 4A: unactuated state of the brake booster 10, and Fig. 4B: activated state of the brake booster 10), but with the difference that in Fig. 4A and Fig. 4B, in addition to the second spring element 180, a fixed stop in the form of a projection 190 protruding from the section 170 is shown.

[0042] This projection 190 can, for example, be a fixable threaded bolt, so that there is a further adjustment possibility of the stop, which can be adjusted according to the needs of the driver, or can be used to set a definitive end position of the push rod piston 30 in the unactuated state.

[0043] The second spring element 180 in Fig. 2A to 4B may be attached at one end either to the stop element 160 or to the section 170, as already mentioned above.

[0044] For the sake of completeness, it should be mentioned that due to the elasticity of the so-called “Reaction Disc”, a projection of 200 (see Fig. 2B and Fig. 4B) against which the push rod piston 30 strikes or contacts in the actuated state in order to thus apply the applied force F in 130 to be transferred (F out 140). The second spring element 180 and / or the first spring element 110 can be selected such that the force component supporting the driver becomes zero below, at, or above the so-called jump-in point (i.e., the time of contact between the reaction disc and the push rod piston 30).

[0045] Please note that the dimensions shown are not necessarily to scale.

Claims

[1] Brake booster (10) for a vehicle, comprising: a push rod piston (30) which can be actuated by a driver and which is displaceably arranged in a booster body (20) which can be displaced relative to the vehicle; an output element which can be acted upon by the push rod piston (30) with an input force (130) on the push rod piston (30) and by which a piston of a master brake cylinder can be acted upon with an actuating force (140); a force transmission unit (80) consisting of a first reaction unit (81) with elastic properties and a second reaction unit (82) adjacent to the first reaction unit (81), wherein the force transmission unit (80) is arranged at one end (70) of the amplifier body (20) so as to be displaceable relative thereto; wherein the booster body (20) has a radial recess (60) in its interior, and the push rod piston (30) comprises a collar (90) fixed thereon in the region of the recess (60), wherein a first spring element (110) is clamped between the collar (90) and an inner surface (100) of the recess (60); wherein a stop element (160) is fixed on the push rod piston (30) outside the booster body (20); wherein a second spring element (180) is clamped between the stop element (160) and a reference point device (150) fixed relative to the vehicle; so that upon actuation of the push rod piston (30), a dead travel between the stop element (160) and the reference point device (150) can be compensated by means of the second spring element (180). [2] Brake booster (10) according to claim 1, wherein upon actuation of the push rod piston (30), the first spring element (110) and the second spring element (180) relax and the output element together with the booster body (20) is displaced relative to the vehicle by means of the force transmission unit (80) exerting pressure on the piston of the master brake cylinder. [3] Brake booster (10) according to claim 1 or 2, wherein, depending on the properties of the spring elements (110, 180), a linear or non-linear force curve of the push rod piston (30) can be predeterminably set upon actuation, or any combination of both. [4] Brake booster (10) according to one of the preceding claims, wherein the second spring element (180) can be designed such that upon actuation of the push rod piston (30), a force component of the second spring element (180) which is established before, during or after a contact time between the push rod piston (30) and the first reaction unit (81), which is elastic, is zero. [5] Brake booster (10) according to one of the preceding claims, wherein the first spring element (110) and / or the second spring element (180) are each designed as a spiral spring or as an elastic element with the properties corresponding to the respective spiral spring. [6] Brake booster (10) according to one of the preceding claims, wherein a damping element (200) is arranged in the brake booster (10), which serves to compensate for undesirable interactions between the spring elements (110, 180) upon actuation of the push rod piston (30). [7] Brake booster (10) according to one of the preceding claims, wherein the first spring element (110) and / or the second spring element (180) are each formed by a combination of several spring elements. [8] Brake booster (10) according to one of the preceding claims, wherein the second spring element (180) is attached at one end to the reference point device (150) or to the push rod piston (30) or to a device (190) fixedly connected to the reference point device (150). [9] Brake booster (10) according to claim 8, wherein the fixed end of the second spring element (180) is designed to be movable so that a desired preload can be set. [10] A braking system for a vehicle, the braking system comprising a brake booster (10) according to any one of claims 1 to 9.

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