DE102024203870A1 - Piston/cylinder unit, in particular master brake cylinder for specifying a braking request in an electronically slip-controlled external power braking system of a motor vehicle. - Google Patents

Abstract

The invention relates to a piston/cylinder unit (10) with a hollow cylinder (12) and a piston (16) slidably mounted therein and actuated against the force of an elastic return element (20). The piston (16) defines a working chamber (18a) within the cylinder (12) which is filled with hydraulic fluid and whose chamber volume varies depending on the piston actuation. A hydraulic fluid passage (30) is formed on the piston (16) which connects the working chamber (18a) to a hydraulic fluid reservoir when the piston (16) assumes a starting position within the cylinder (12).
It is proposed that this pressure medium passage (30) be formed by means of at least one groove-shaped recess (30b) formed on an outer surface of the piston (16). This recess extends in the direction of a longitudinal axis L along a piston section at one end of the piston (16).
A piston (16) with such a pressure medium passage (30b) can be manufactured using forming techniques and is particularly cost-effective due to material savings and short machining times. Furthermore, forming techniques do not produce chips or burrs.

Description

State of the art

The invention relates to a piston/cylinder unit, in particular a master brake cylinder for specifying a braking request in an electronically slip-controlled external power braking system of a motor vehicle according to the features of the preamble of claim 1.

Master brake cylinders are used in conventional vehicle braking systems to generate brake pressure through muscle power by the driver, or in modern power-assisted braking systems in combination with a pedal position simulator to indicate a braking request by the driver. They consist of a piston/cylinder unit with at least one piston that can be actuated within a hollow cylinder against the force of an elastic return element and are therefore called mono-master brake cylinders. Tandem master brake cylinders with one piston/cylinder unit per brake circuit are also well-known.

Such piston/cylinder units are usually actuated by a pedal or a lever, which is coupled to the piston or to one of the pistons via a linkage.

The pistons of a piston/cylinder unit, together with the cylinder housing, define working chambers whose volume varies depending on the piston actuation. These working chambers are filled with a hydraulic fluid stored in an attached reservoir. Actuation of the piston/cylinder unit displaces the hydraulic fluid from the working chamber into a brake circuit or a pedal travel simulator. As soon as the piston, driven by an elastic return element, returns to its starting position after actuation, a hydraulic fluid connection is established between the reservoir and the working chamber, allowing for pressure equalization. If the working chamber pressure is low compared to atmospheric pressure, hydraulic fluid flows into the working chamber; conversely, if the working chamber pressure is high compared to atmospheric pressure, hydraulic fluid flows out of the working chamber into the hydraulic fluid reservoir. A vent in the hydraulic fluid reservoir typically maintains atmospheric pressure.

The aforementioned pressure medium connection between the working chamber and the pressure medium reservoir includes a pressure medium passage formed on the piston. In known piston/cylinder units, this passage consists of a plurality of radial bores arranged in at least one row along the circumference of a piston shaft, as described in the 1 and 2 shown in this document.

The working chamber of the piston/cylinder unit is sealed by at least one sealing ring located on the cylinder housing side in the area of the piston skirt. The radial bores are positioned along the longitudinal axis of the piston such that, in an actuated state of the piston, they are located beyond, i.e., in 1 to the left of this sealing ring, thus interrupting the connection between the working chamber and the pressure medium reservoir. However, when the piston returns to its original starting position after actuation, the radial bores are located on this side, i.e., as in the 1 To the right of the sealing ring, the connection between the working chamber and the pressure medium reservoir is open. The bores then establish a pressure medium connection between the outer circumference and the hollow interior of the piston, which is connected to the working chamber.

A disadvantage of radial bores along the circumference of a piston is that these radial bores must be machined in a separate, complex operation after the piston's outer contour has been manufactured. This can result in sharp-edged bore faces, burrs, or chips, which must be painstakingly removed in a subsequent operation. Otherwise, there is a risk of impaired function in components coupled to the piston/cylinder unit via pressure fluid lines, such as pressure-generating pumps, pressure-regulating valves, or sealing elements. Furthermore, machining a piston can damage the piston running surface or deform the piston contour, ultimately impairing piston movement in the cylinder and/or causing wear-inducing friction.

Advantages of the invention

In contrast, a piston/cylinder unit according to the features of claim 1 has the advantage that the pressure medium passage at the piston and thus the piston as a whole can be manufactured in a forming process, in particular in a cold-forging or deep-drawing process.

Consequently, the aforementioned machining of the piston to create the hydraulic passage is eliminated, as are the steps for removing chips or burrs. Forming the piston of the piston/cylinder unit saves material, time, and therefore costs.

According to the invention, the pressure medium passage on the piston comprises at least one groove-shaped recess formed on an outer surface of the piston, which extends in the direction of a longitudinal axis of the piston along a piston section at one of the ends of the piston.

Further advantages or advantageous developments of the invention will become apparent from the dependent claims or from the following description.

Furthermore, a circumferential collar projecting radially outwards can be produced with only a slight increase in effort using a forming technique for a piston. Such a collar can be used, for example, to create a mechanical stop against which the piston strikes a shoulder on the cylinder housing side when it has reached its starting position.

The collar can be closed along the circumference of the piston or alternatively consist of a plurality of collar segments, which are separated from each other by the recesses for forming the pressure medium passage on the piston.

A piston/cylinder unit designed according to the invention can be used to create a mono-master brake cylinder or a tandem master brake cylinder for a conventional muscle-powered or a modern power-assisted braking system of a motor vehicle. In the case of a tandem master brake cylinder, one or both pistons can be designed according to the invention.

For generating brake pressure, power-assisted braking systems have a hydraulic unit with a hydraulic block, on which, in addition to the master brake cylinder, a brake pressure generator, a motor for driving the brake pressure generator, valves for controlling and regulating the brake pressure supplied by the brake pressure generator, and optionally an electronic control unit for demand-based electrical control of the motor and the valves are arranged. In this case, the cylinder of a piston/cylinder unit according to the invention can be integrated into the hydraulic block.

drawing

• 1 zeigt eine aus dem Stand der Technik bekannte Kolben-/ZylinderEinheit im Längsschnitt;
• 2 zeigt den Kolben der Kolben-/Zylinder-Einheit nach 1 in räumlicher Ansicht;
• 3 zeigt eine erfindungsgemäße Kolben-/Zylinder-Einheit im Längsschnitt; 4 zeigt den Kolben der Kolben-/Zylinder-Einheit nach 2 in räumlicher Ansicht;
• 5 zeigt die Weiterbildung einer erfindungsgemäßen Kolben-/ZylinderEinheit im Längsschnitt und
• 6 zeigt den Kolben der Kolben-/Zylinder-Einheit nach 5 in räumlicher Darstellung.

Exemplary embodiments of the invention are shown in the drawing and are explained in detail in the following description. The drawing comprises a total of six figures, in which corresponding components are provided with uniform reference numerals.

• 1 shows a piston/cylinder unit known from the prior art in longitudinal section;
• 2 shows the piston of the piston/cylinder unit after 1 in spatial view;
• 3 shows a piston/cylinder unit according to the invention in longitudinal section; 4 shows the piston of the piston/cylinder unit after 2 in spatial view;
• 5 shows the further development of a piston/cylinder unit according to the invention in longitudinal section and
• 6 shows the piston of the piston/cylinder unit after 5 in spatial representation.

Description

The 1 Figure 1 shows a longitudinal section of a tandem master cylinder of an electronically controlled vehicle braking system. This tandem master cylinder comprises two piston/cylinder units arranged one after the other along a longitudinal axis L, of which only one piston/cylinder unit (10) is fully visible in the image. This unit includes a cylinder bore (12a) which is located on a hydraulic block (14) of a hydraulic power unit of this vehicle braking system. The cylinder (12) of the piston/cylinder unit is thus integrated into the hydraulic block (14).

Inside the cylinder bore (12a), a (floating) piston (16) of the master brake cylinder is slidably mounted and defines a working chamber (18a) that is sealed off from the environment. The piston (16) is designed as a hollow piston and consists of a sleeve-shaped piston shaft (16a) and an inwardly recessed piston head (16b) at an end of the piston (16) facing away from the sealed end of the cylinder (12).

An elastic restoring element (20) in the form of a coil spring (20a) is housed in the working chamber (18a). This coil spring (20a) is supported at one end against an inner surface of the piston base (16b) that defines the working chamber (18a) and at the opposite end against the inner surface of the cylinder bore closure (12a), under axial preload. It thus exerts a restoring force on the piston (16) in the opposite direction of actuation. The coil spring (20a) is optionally equipped with a so-called spring retainer (22), which is located inside its coils and prevents complete relaxation of the coil spring (20a) or specifies a definable minimum axial preload.

This spring restraint (22) comprises a restraint sleeve (22a) and a restraint plunger (22b) slidably mounted therein. The restraint sleeve (22a) has a molded, radially outward projecting circumferential collar at its piston-side end, which lies between the associated end of the coil spring (20a) and the facing piston base (16b). With its opening formed at this end, the restraint sleeve (22a) is centered on a pin-shaped projection of the piston (16), which extends into its hollow interior.

The opposite end of the sleeve is shaped inwards to form a stop against which the tethering plunger (22b) rests with a thickened end. An opposing plunger end is received in a tethering plunger bearing (22c). This bearing is cap-shaped and sits with a rim between the closure of the cylinder bore and the end of the coil spring facing it. A raised central area of the tethering plunger bearing (22c) is matched to the inner diameter of the coil spring (20a) and ensures that the tethering plunger bearing (22c) is centered within the coil spring (20a).

The image section according to 1 Figure 1 shows an example of the so-called floating piston of a tandem master cylinder, which can be seen from a second coil spring (20b) that rests against the outer side of the piston crown (16b) with its associated second tappet bearing. The second coil spring (20b) is located in the second working chamber (18b) of this tandem master cylinder, which is bounded by a second piston (not shown), the so-called rod piston. The rod piston gets its name from its connection to an actuating element via a connecting rod, which, in the event of a braking request, can be actuated by the driver with a corresponding actuating stroke.

In the exemplary embodiment, the piston shown is actuated according to 1 This occurs indirectly via actuation of this rod piston and due to the resulting build-up of chamber pressure in the second working chamber (18b). In contrast, with a mono-master brake cylinder, the illustrated piston (16) would be directly coupled to the actuating rod.

Several grooves (24a-c) circumferentially surrounding the cylinder bore (12a) are cut into the wall of the bore of the cylinder (12). In the 1 In the leftmost and rightmost grooves (24a,c), a lip seal (26a,b) is arranged for sealing the working chamber (18a) against a piston (16) gap in the cylinder bore (12a). Between the two grooves (24a,c) for the lip seals (26a,b) is a third groove (24b) circumferentially around the piston (16), into which a pressure medium channel (28) enters from above and runs transversely to the cylinder bore (12a), and opens diagonally opposite it downwards. This pressure medium channel (28) supplies the working chamber (18a) of the master brake cylinder with pressure medium from a pressure medium reservoir (not shown), provided that the necessary pressure medium connection is open due to the current position of the piston (16) within the cylinder bore (12a).

For this purpose, a pressure medium passage (30) consisting of a plurality of radial bores (30a) is formed on the outer surface of the piston (16), which are arranged in a circumferential row along the piston circumference and connect the outside of the piston to the inside of the piston through the piston wall.

In the illustrated initial position of the piston, these radial bores (30a) are located between the leftmost groove (24a) and the central groove (24b), into which the pressure medium channel (28) to the pressure medium reservoir opens. Because the piston interior is connected to the working chamber (18a) of the master brake cylinder or the piston/cylinder unit (10), pressure equalization or pressure medium exchange takes place between the working chamber (18a) and the reservoir in the illustrated initial position of the piston (16), since the pressure medium passage (30) on the piston (16) is permeable.

However, if the piston (16) is actuated and, unlike the illustration, assumes an actuating position in which the radial bores (30a) are located to the left of the leftmost groove (24a), the middle groove (24b) is closed by the piston shaft (16a) and thus the pressure medium-conducting connection between the working chamber (18a) and the reservoir is interrupted.

The 2 shows the piston (16) of the piston/cylinder unit (10) after 1 For the sake of completeness, a spatial representation of the component is shown again. The radial bores (30a) arranged in a circumferential row along the piston circumference to form the aforementioned pressure medium passage (30) are easily recognizable. They are located near the open end of the hollow piston (16), i.e., in a section of the piston (16) facing the working chamber (18a).

The 3 Figure 1 shows a piston/cylinder unit (10) designed according to the invention in a longitudinal view. The latter differs from the prior art in the design of its piston (16), in particular in the design of the pressure medium passage (30), according to 1 . As can be seen particularly well from the 4 As can be seen, a piston (16) according to the invention does without radial bores.

According to the invention, the pressure medium passage (30) is provided by means of groove-shaped recesses (30b) or projections formed on the outer surface of the piston (16). These recesses (30b) extend in the direction of a longitudinal axis L of the piston (16) along a section of the piston where the piston (16) is open. By way of example, a plurality of similarly designed recesses (30b) are provided circumferentially at uniform angular intervals from one another. The extension length of these recesses (30b) in the direction of the longitudinal axis L of the piston (16) is dimensioned such that these recesses (30b) pass under the lip seal (26a) in the leftmost groove (24a) of the cylinder (12) and reach at least to the central groove (24b) which is in contact with the pressure medium channel (28) to the reservoir when the piston (16) assumes its initial position. The recesses (30b) have a first end open towards the working chamber (18a) and a second end closed, facing the central groove (24b). Preferably, the closed second end of the recess (30b) tapers continuously towards the outer surface of the piston (16).

With a suitable piston position within the cylinder bore (12a), a pressure medium passage (30) is created by the recesses (30b) between the working chamber (18a) of the piston/cylinder unit (10) and the pressure medium channel (28) to the reservoir, which now runs in the longitudinal direction L along the outer surface of the piston (16) and no longer radially through the outer surface into the interior of the hollow piston (16).

A particular advantage of this design of the pressure medium passage (30) is that it can be manufactured in a forming process just like the piston (16) itself, for example, in a cold forging process. A piston (16) with an integrally formed pressure medium passage (30) can thus be manufactured in fewer work steps than a piston with radial bores, preferably in just a single operation. Since no chips or burrs occur during a forming process, complex post-processing steps can, in principle, be omitted, and the piston (16) according to the invention is therefore easier and more cost-effective to manufacture.

An advantageous further development of the invention is shown by the following: 5 and 6 .

While the 1 and 3 Piston/cylinder units (10) in which the piston (16) is received floating in the cylinder bore (12a) and its initial position is thus determined by a prevailing equilibrium of the forces of the two coil springs (20a,b) acting on the piston (16) are disclosed by the 5 a piston/cylinder unit (10) in which a circumferential collar (32) is formed on the piston (16) with which this piston (16) rests against a cylinder-side stop shoulder (34).

This collar (32) is formed in one piece with the piston (16) and the pressure medium passage (30b) on the piston (16), is integrally formed on the piston shaft (16a) in the region of the open end, and projects radially outwards from its outer surface. Such a collar (32) can be produced in parallel with the manufacture of the piston (16) using a cold-forging process, i.e., by forming, and is therefore largely cost-neutral and, in particular, can be produced without an additional post-processing step.

As the 6 Furthermore, as shown, the collar (32) can consist of a plurality of segmentally circumferential collar segments (32a) which are formed successively in the circumferential direction on the piston shaft (16a). Between each pair of collar segments (32a) there is at least one of the recesses (30b) of the pressure medium passage (30) on the piston circumference. This recess (30b) extends along the longitudinal axis L in both directions beyond the cross-sections of the adjacent collar segments (32a) and runs transversely to these collar segments (32a).

Apart from that, the 5 a sealing cover (36) with which the working chamber (18a) in the cylinder bore (12a) is sealed from the environment. This sealing cover (36) is cup-shaped and is inserted from the outside into a corresponding cover receptacle at the opening of the cylinder bore (12a).

On the outer contour of the closure cover (36) and on the inner contour of the cover receptacle, circumferential sealing surfaces are formed, tapering conically inwards in the same direction. These surfaces abut each other to seal the working chamber (18a) to the outside. For example, a retaining ring (38) centered on the closure cover (36) is provided, through which the closure cover (36) is subjected to an axial force in the direction of the longitudinal axis L. The retaining ring (38) is pressed into the cover receptacle, riveted to the cover receptacle, or screwed into the cover receptacle. Alternatively A retaining ring could be dispensed with by attaching the closure cover (36) directly to the cylinder (12), for example by means of direct riveting or a welded connection. Of course, modifications or additions to the described embodiments beyond these explanations are conceivable, which are covered by the scope of protection specified by the following claims.

In this context, it should be mentioned that a piston according to the invention, after its forming process, e.g. in a cold forming process, can of course be machined to create recesses for components, e.g. for transmitting or detecting an actuation path of the piston.

Claims (9)

Piston/cylinder unit (10), in particular master brake cylinder for specifying a braking request in an electronically slip-controlled external power braking system of a motor vehicle, with a hollow cylinder (12); a piston (16) slidably mounted in the cylinder (12) and actuated against the force of an elastic return element (20) and a working chamber (18a) bounded by the piston (16) and filled with pressure medium, wherein a pressure medium passage (30) is formed on the piston (16) through which the working chamber (18a) is contacted with a pressure medium connection (28) to a pressure medium reservoir when the piston (16) assumes a starting position in the cylinder (12), characterized in that the pressure medium passage (30) comprises at least one groove-shaped recess (30b) formed on a cylindrical surface of the piston (16), which extends in the direction of a longitudinal axis L of the piston (16) along a piston section at one of the ends of the piston (16). Piston/cylinder unit according to Claim 1 , characterized in that the recess (30b) has an end open towards the working chamber (18a). Piston/cylinder unit according to Claim 1 or 2 , characterized in that the piston (16) is designed as a hollow piston with an open first end and with a second end closed by a piston base (16b) and that the elastic restoring element (20) is supported on an inner side of the piston base (16b) which limits the working chamber (18a). Piston/cylinder unit according to Claim 3 , characterized in that the pressure medium passage (30b) is formed on the piston section where the open end of the piston (16) is located. Piston/cylinder unit according to one of the Claims 1 until 4 , characterized in that a collar (32) is formed on the piston section in which the pressure medium passage (30b) is formed, projecting radially outwards and extending along the circumference of the piston (16). Piston/cylinder unit according to one of the Claim 5 , characterized in that the collar (32) is divided into collar segments (32a), wherein a recess (30b) of the pressure medium passage (30) is formed between two collar segments (32a) and the recess (30b) runs transversely to the collar segments (32a). Piston/cylinder unit according to Claim 5 or 6 , characterized in that the piston (16) with the pressure medium passage (30b) and the collar (32) or the collar segments (32a) is manufactured as one piece in a forming process, in particular in a cold forming process. Piston/cylinder unit according to Claim 7 , characterized in that the piston (16) is machined to create recesses for components, in particular for transmitting or detecting an actuation path. Piston/cylinder unit according to one of the Claims 1 until 8 , characterized in that the cylinder (12) is integrated into a hydraulic block (14) of a hydraulic unit of a vehicle brake system for an electronically slip-dependent control of the brake pressure.