PNEUMATIC BRAKE PEDAL MODULE

A pneumatic brake pedal module for a brake-by-wire brake system of a vehicle is disclosed. The brake pedal module includes a pivotably mounted brake pedal and a damping unit. The damping unit is mechanically coupled to the brake pedal to generate a resistance when the brake pedal is actuated. The damping unit comprises a housing and a piston, which is mounted movably in the housing and divides an internal space of the housing into a pressure chamber and a vacuum chamber. The pressure chamber and the vacuum chamber are connected to one another in terms of flow. The piston has on its running surface an encircling annular space in which a ring seal is accommodated in an axially movable manner. The ring seal is located at least in a flow path between the pressure chamber and the vacuum chamber and forms a restrictor in the at least one flow path, which restrictor frees different flow cross sections in the at least one flow path depending on the axial direction of movement, and damps the movement of the piston with differing degrees of strength depending on a direction of movement of the piston.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to German Patent Application No. 102021119439.3, filed Jul. 27, 2021, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The disclosure relates to a pneumatic brake pedal module for a “brake-by-wire” brake system of a vehicle.

BACKGROUND

In the case of “brake-by-wire” brake systems, a braking intention of a driver is detected electronically, and the brakes of the vehicle are actuated by one or more purely electric actuators. For this purpose, provision can be made for each of the brakes of the individual wheels to be assigned an electric-motor actuator, as known, for example, in the case of an “EMB” (electric-motor brake). However, provision can also be made for an electrohydraulic actuator to be activated centrally in order to actuate the brakes hydraulically in a conventional manner, as known, for example, in an “IBS” (integrated brake system). Furthermore, a “brake-by-wire” brake system can be embodied as a hybrid system in that the brakes of one vehicle axle, for example those of the front wheels, are assigned to an “IBS” and the brakes of another vehicle axle, for example those of the rear wheels, are each embodied as an “EMB”.

Since in “brake-by-wire” brake systems there is generally no mechanical connection between a brake pedal and the brakes, a reaction behaviour of the brake pedal is simulated, e.g. hydraulically or pneumatically. More precisely, a greater resistance acts with increasing travel when the brake pedal is actuated.

In order to impose a hysteresis on a movement of the brake pedal, there is usually a restrictor, which is connected to the brake pedal module by fluid lines and regulates a fluid pressure in a working space.

Although such systems give the driver a good simulation of a reaction behaviour of the brake pedal, they are complicated in terms of integration into a vehicle environment.

SUMMARY

What is needed is a brake pedal module which can be integrated particularly easily into a vehicle installation space and at the same time can simulate a reaction behaviour of the brake pedal in the best possible manner.

According to the disclosure, a pneumatic brake pedal module for a “brake-by-wire” brake system of a vehicle is provided. The brake pedal module has a pivotably mounted brake pedal and a damping unit, which is mechanically coupled to the brake pedal in order to generate a resistance when the brake pedal is actuated. The damping unit comprises a housing and a piston, which is mounted movably in the housing and divides an internal space of the housing into a pressure chamber and a vacuum chamber. The pressure chamber and the vacuum chamber are connected to one another in terms of flow and the piston has on its running surface an encircling annular space in which a ring seal is accommodated in an axially movable manner. The ring seal is located at least in a flow path between the pressure chamber and the vacuum chamber and forms a restrictor in the at least one flow path, which restrictor frees different flow cross sections in the at least one flow path depending on the axial direction of movement, and damps the movement of the piston with differing degrees of strength depending on a direction of movement of the piston.

According to the disclosure, the restrictor for adjusting damping is not arranged outside a housing of the damping unit but is integrated into the damping unit, into the piston. In this way, the brake pedal module, for example the damping unit, is particularly compact and can be positioned in a flexible manner in an installation space environment. Another advantage is that no fluid lines have to be connected to the damping unit, and this likewise contributes to the fact that the brake pedal module can be positioned in a particularly flexible manner.

The restrictor allows, a controlled fluid flow between the pressure chamber and the vacuum chamber. The larger the flow cross section freed by the restrictor, the less the damping, since a lower flow resistance prevails with increasing flow cross section. Consequently, the strength of damping can be adjusted by adjusting the flow cross section by the restrictor.

A further advantage of the brake pedal module according to the disclosure is that the strength of the damping is automatically adjusted to a suitable value depending on a direction of movement of the piston, the flow cross section changing when the direction of the piston changes. Thus, no control unit is necessary to regulate the flow cross section.

In particular, the flow cross section can assume two different values.

As a result, a hysteresis can automatically be imposed on the movement of the brake pedal.

The annular space and the ring seal are designed in such a way that, depending on the direction of movement, the ring seal rests selectively on one of two opposite axial boundary surfaces of the annular space and changes a flow cross section of the at least one flow path. Since the ring seal comes to rest against an axial boundary surface, the ring seal is positioned in a defined position in the annular space and changes the flow cross section depending on the direction of movement of the piston. In this way, the flow cross section likewise assumes a defined value, thereby also setting the strength of the damping to a defined value and consequently achieving a desired reaction behaviour of the brake pedal.

According to one exemplary arrangement, depending on which boundary surface it bears against, the ring seal seals a flow path from the annular space along the running surface past the piston either into the vacuum chamber or into the pressure chamber. In particular, the flow path does not have to be completely leaktight, but the flow has to be reduced as compared with a position on the other boundary surface. In other words, a fluid flow out of the annular space along the running surface of the piston in one direction of flow is blocked or reduced and released in an opposite direction of flow. This prevents a fluid flow along the running surface of the piston from adversely affecting damping.

Starting from the annular space, near the boundary surface which is closer to the pressure chamber, at least one first opening in the piston leads to the pressure chamber and, starting from the annular space, near the boundary surface which is further away from the pressure chamber, at least one second opening in the piston leads to the vacuum chamber. In particular, the ring seal is designed in such a way that, when the direction of the piston changes, the ring seal is moved automatically in the annular space to the at least one first opening or at least one second opening and changes an effective flow cross section of the openings. As a result, a volumetric flow can be regulated in a particularly simple manner and particularly efficient restriction can take place. Expensive restrictors can be dispensed with.

For example, the at least one first and/or at least one second opening is partially covered in the associated position of the ring seal. In this way, an effective flow cross section of the openings is changed in a particularly simple manner.

The position of the openings can be matched to the displaced positions of the ring seal in the annular space in such a way that, when the brake pedal is actuated, the ring seal reduces a flow path from the pressure chamber to the vacuum chamber and, upon return to the initial position, frees a flow path from the vacuum chamber to the pressure chamber, in particular to the maximum extent. This contributes to the strength of the damping being adjusted to a desired value depending on the direction of movement of the piston.

The at least one first opening has, in particular, a larger flow cross section than the at least one second opening.

Alternatively, the at least one first opening and the at least one second opening can have the same flow cross section, wherein the number of first openings is greater than the number of second openings.

This means that an overall flow cross section starting from the annular space into the vacuum chamber is smaller than an overall flow cross section starting from the annular space into the pressure chamber.

In this way, the advantage is achieved that fluid can flow only slowly out of the pressure chamber into the vacuum chamber via the at least one second opening when the brake pedal is actuated and a movement of the piston results therefrom, as a result of which strong damping is achieved when the brake pedal is actuated. When the brake pedal is released, fluid can flow more quickly out of the vacuum chamber into the pressure chamber via the at least one first opening, thereby achieving rapid resetting of the brake pedal.

The damping unit comprises a return spring, which is arranged in the pressure chamber. The return spring pushes the piston into an unactuated initial position. The piston is in the unactuated initial position when the brake pedal is not actuated. The return spring produces a resistance which contributes to producing the reaction behaviour of the brake pedal. However, the return spring serves primarily to move the brake pedal back into its unactuated position.

In one exemplary arrangement, the return spring is of progressive design. A spring of this kind has a non-linear characteristic curve. To be more precise, a progressive spring is relatively soft when subjected to little force and becomes harder when subjected to increasing load.

The damping unit is pneumatically self-contained. Specifically, the housing is pneumatically self-contained. A particular advantage here is that there are no fluid connections on the damping unit or no fluid lines need to be connected to the damping unit. Thus, the brake pedal module can be manufactured as a separate unit and positioned in an installation space environment independently of other components or fluid lines. Moreover, the damping unit can be particularly compact as a result.

The damping unit can be mechanically coupled to the brake pedal in such a way that the damping unit is subjected to tension or compression when the brake pedal is actuated. In this way, particularly flexible positioning of the damping unit relative to the brake pedal is possible.

The brake pedal module according to the disclosure is suitable for use in a “brake-by-wire” brake system, which is may be equipped with “EMB” brakes and/or is designed as an “IBS” system.

DETAILED DESCRIPTION

FIGS.1and2show a pneumatic brake pedal module10for a “brake-by-wire” brake system of a vehicle in a side view and a plan view.

In particular, the brake pedal module10may serve to electronically detect a braking intention of a driver.

The brake pedal module10comprises a pivotably mounted brake pedal12and a damping unit14, which is mechanically coupled to the brake pedal12.

The damping unit14is used to generate a resistance when the brake pedal12is actuated.

The brake pedal12is formed by a strut16.

At a first end18, the strut16has an actuating surface20, which can be actuated by a driver to signal a braking intention. In other words, a driver can exert a pressure on the actuating surface20with the foot to signal a braking intention.

The damping unit14is coupled to the strut16at an end section22opposite the first end.

Between the ends of the strut16, the brake pedal12is pivotably mounted on a mounting24fixed with respect to the vehicle.

In one exemplary arrangement, the pivotable mounting is implemented by a pivot joint26.

In the exemplary arrangement, the mounting24fixed with respect to the vehicle is a further strut, which can be screwed to a body part.

The strut16and the mounting24are plastic injection mouldings, for example.

The brake pedal module10furthermore comprises a sensor unit28for detecting a braking intention of a driver.

It can be seen fromFIG.1that the damping unit14is subjected to tension when the brake pedal12is actuated. This allows particularly flexible positioning of the damping unit14, thereby enabling the brake pedal module10to be integrated particularly well into an installation space environment.

For example, a distance of the damping unit14from the pivot joint26can be selected relatively freely.

Furthermore, in a further exemplary arrangement, the strut16, which is of relatively straight design in the exemplary arrangement shown, can be angled, in particular in the pivot joint26or between the pivot joint26and the damping unit14. As a result, the position of the damping unit14can also be selected in a flexible way in the longitudinal direction of the vehicle.

Compared with a damping unit which is subjected to compression, the damping unit14subjected to tension can thus be arranged in a particularly flexible manner in an installation space environment.

The damping unit14is explained in more detail with reference toFIGS.3and4, which each show a section through the damping unit14.

The damping unit14comprises a housing30, in which a piston32is accommodated and movably mounted.

A piston rod36extends from an end34of the piston32.

More precisely, the piston32has an annular surface38on the end34and a circular surface42on an opposite end40.

The annular surface38delimits a pressure chamber44in the housing30, which space is compressed by the movement of the piston32when the brake pedal12is actuated. Consequently, the piston rod36extends through the pressure chamber44.

The circular surface42delimits a vacuum chamber46in the housing30, the volume of which space is increased when the brake pedal12is actuated.

In the exemplary arrangement, the volume of the vacuum chamber46is initially zero since the circular surface42bears against a housing wall of the housing30.

Via the piston rod36, the piston32is coupled to the brake pedal12, an intermediate piece48being arranged between the piston rod36and the brake pedal12in the exemplary arrangement.

The connection between the piston rod36and the intermediate piece48and between the intermediate piece48and the brake pedal12is in each case implemented by a pin50,52.

The damping unit14further comprises a return spring54, which pushes the piston32into the unactuated initial position shown inFIG.3. In this state, the brake pedal12is not actuated by a user.

FIG.3also shows the structure of the sensor unit28.

In the exemplary arrangement, the sensor unit28comprises at least one Hall element56, which is arranged outside the housing30, and a magnet57, which is secured on the piston32.

In order to ensure that the sensor unit28functions reliably and a movement of the piston32is reliably detected, the piston32is mounted non-rotatably in the housing30.

The non-rotatable mounting of the piston32can be achieved by a non-circular cross section of the piston32and a correspondingly non-circular cross section of the housing30(seeFIG.2).

There is a flow connection between the pressure chamber44and the vacuum chamber46.

The flow connection is implemented by restrictor58, which is integrated into the piston32.

The restrictor58is designed in such a way that it restricts an air flow from the pressure chamber44into the vacuum chamber46when the brake pedal12is actuated more than an air flow from the vacuum chamber46into the pressure chamber44when the brake pedal12is reset.

The structure and mode of operation of the restrictor58is explained with reference toFIGS.5and6, which each show a detail view in the region of a running surface59of the piston32,FIG.5illustrating a state when the brake pedal12is actuated andFIG.6illustrating a state when the brake pedal12is being reset.

On its running surface59, the piston32has an encircling annular space60, which is formed, for example, by an encircling groove.

A ring seal62is accommodated in an axially movable manner in the annular space60.

The ring seal62is located in at least one flow path between the pressure chamber44and the vacuum chamber46and forms the restrictor58in the at least one flow path.

The annular space60is bounded by two opposite, axial boundary surfaces64,66.

Starting from the annular space60, near the boundary surface64which is closer to the pressure chamber44, a plurality of first openings68in the piston32leads to the pressure chamber44(see alsoFIG.3). For example, six first openings68are provided, which are distributed uniformly in the circumferential direction of the piston32.

Furthermore, starting from the annular space60, near the boundary surface66which is further away from the pressure chamber44, a plurality of second openings70in the piston32leads to the vacuum chamber46. For example, six second openings70are provided, which are distributed uniformly in the circumferential direction of the piston32.

In the exemplary arrangement, the first openings68have, in total, a larger flow cross section than the second openings70in total. This can also be achieved if, when considered individually, the first openings68have a flow cross section which is smaller than or the same as that of the second openings70, but are present in a larger number.

The restrictor58frees different flow cross sections in the at least one flow path depending on the axial direction of movement, and damps the movement of the piston32with differing degrees of strength depending on a direction of movement of the piston32.

Specifically, depending on the direction of movement, the ring seal62rests selectively on one of the two opposite axial boundary surfaces64,66of the annular space60and thereby changes a flow cross section of the at least one flow path between the pressure chamber44and the vacuum chamber46.

In the event of a change in direction of the piston32, the ring seal62is automatically moved in the annular space60to the first openings68or the second openings70and changes an effective flow cross section of the openings68,70.

The position of the openings68,70is matched to the displaced positions of the ring seal62in the annular space60in such a way that, when the brake pedal12is actuated, the ring seal62reduces a flow path from the pressure chamber44to the vacuum chamber46and, upon return to the initial position, frees a flow path from the vacuum chamber46to the pressure chamber44, in particular to the maximum extent.

For this purpose, the first openings68and the second openings70are partially covered in the associated position of the ring seal62.

When the brake pedal12is actuated by a driver, the ring seal62comes to rest against boundary surface66, as illustrated inFIG.5. As a result, the ring seal62seals a flow path out of the annular space60along the running surface59of the piston32into the vacuum chamber46, with the result that in this state no or only a small amount of fluid can flow along the running surface59of the piston32into the vacuum chamber46.

This means that a fluid flow from the pressure chamber44into the vacuum chamber46must take place at least for the most part via the openings68,70.

In addition, the second openings70are partially covered by the ring seal62when the ring seal62is in the position illustrated inFIG.5.

The flow path of the fluid during actuation of the brake pedal12is illustrated by means of a dashed line inFIG.5.

When the brake pedal12is actuated, when the pressure chamber44is compressed and the vacuum chamber46is expanded, a vacuum is produced in the vacuum chamber46and an excess pressure is correspondingly produced in the pressure chamber44, with the result that fluid is sucked into the vacuum chamber46from the pressure chamber44.

However, since the fluid flow into the vacuum chamber46must take place via the relatively small second openings70, which are additionally covered by the ring seal62, a pressure equalization between the pressure chamber44and the vacuum chamber46takes place only relatively slowly when the piston32is actuated, with the result that there is strong damping of the piston movement.

When the brake pedal12is released, the piston32is moved back into its initial position by the return spring54.

In this case, the pressure chamber44is correspondingly expanded and the vacuum chamber46compressed, with the result that fluid which was sucked into the vacuum chamber46when the brake pedal12was actuated is forced out of the vacuum chamber46again and flows into the pressure chamber44.

As a result of the change in the direction of movement of the piston32, the ring seal62detaches from the boundary surface66remote from the pressure chamber44and comes to rest against the opposite boundary surface64, as illustrated inFIG.6.

In this state, the fluid flow along the running surface of the piston32is no longer sealed from the annular space60into the vacuum chamber46, but from the annular space60into the pressure chamber44.

Moreover, it is no longer the second openings70but the first openings68which are partially covered by the ring seal62.

In an alternative exemplary arrangement, the first openings68can be uncovered while the brake pedal12is being reset.

The fluid flow when the brake pedal12is released consequently runs from the vacuum chamber46, via the now uncovered second openings70, into the annular space60and, starting from the annular space60, once again through the first openings68into the pressure chamber44.

The flow path of the fluid when the brake pedal12is released is likewise illustrated by a dashed line inFIG.6.

Since the first openings68have a larger flow cross section than the second openings70and, in addition, are covered to a lesser extent by the ring seal62, the fluid flow from the vacuum chamber46into the pressure chamber44can take place more quickly when the brake pedal12is unactuated than when the brake pedal12is being actuated, as a result of which less pronounced damping of the piston movement and thus rapid resetting of the brake pedal12takes place.

As already mentioned above, the first openings68can also remain uncovered. This is achieved, for example, by extending the annular space60in the axial direction and locating the first openings68at a greater distance from boundary surface64than in the exemplary arrangement illustrated.

In the case of the brake pedal module10illustrated inFIGS.1to6, the damping unit14is subjected to tension.

However, it is also possible to arrange the damping unit14in such a way that the damping unit14is subjected to compression. A brake pedal module10of this type is illustrated schematically inFIG.7.

Nothing changes in the mode of operation of the restrictor58when the damping unit14is subjected to compression; only the arrangement of the pressure chamber44and the vacuum chamber46are interchanged.