BRAKING SYSTEM FOR AN AT LEAST TWO-AXLE VEHICLE

A braking system for an at least two-axle vehicle. The braking system includes: a front axle unit including a first motorized brake pressure buildup device, a front-wheel wheel-brake cylinder mountable at a first front wheel, and a second front-wheel wheel-brake cylinder mountable at a second front wheel; and a rear axle unit hydraulically separate from the front axle unit, including a second motorized brake pressure buildup device, a first rear-wheel wheel-brake cylinder mountable at a first rear wheel, and a second rear-wheel wheel-brake cylinder mountable at a second rear wheel. The second motorized brake pressure buildup device is hydraulically connected via a first rear-axle hydraulic path at the first rear-wheel wheel-brake cylinder and via a second rear-axle hydraulic path at the second rear-wheel wheel-brake cylinder. A first separating valve is situated in the first rear-axle hydraulic path and/or a second separating valve is situated in the second rear-axle hydraulic path.

FIELD

The present invention relates to a braking system for an at least two-axle vehicle. The present invention also relates to a method for operating a braking system of an at least two-axle vehicle.

BACKGROUND INFORMATION

Braking systems for vehicles with at least two axles are described in the related art such as, for example, in German Patent Application No. DE 10 2016 208 529 A1, which include in each case four wheel brake cylinders, each wheel brake cylinder being hydraulically connected at a main brake cylinder of the respective braking system to a brake pedal situated upstream from the main brake cylinder.

SUMMARY

The present invention provides a brake cylinder for an at least two-axle vehicle and a method for operating a braking system of an at least two-axle vehicle.

The present invention provides braking systems for at least two-axel vehicles that have a comparatively compact design and are producible at relatively low manufacturing costs. As will become clear based on the following description, the conventional hydraulic lines between the at least two axles of the respective vehicle equipped with the braking system are omitted in a braking system according to the present invention. This produces a savings of a relatively large amount of installation space on the respective vehicle. This also facilitates a mounting of the braking system according to the present invention on the respective vehicle.

As also becomes clear based on the following description, it is possible in a braking system according to the present invention to fully automatically/fully autonomously set the respective brake pressure in its front-wheel wheel-brake cylinders and in its rear-wheel wheel-brake cylinders, i.e., without a driver braking force being provided by a driver. This may also be referred to as a fully automatic/fully autonomous pressure setting, which is possible for all wheel brake cylinders of the braking system according to the present invention.

In addition, according to an example embodiment of the present invention, at least the respective brake pressure in the rear-wheel wheel-brake cylinders of the braking system according to the present invention may be set individually. This may also be described as a wheel-specific fully automatic/fully autonomous pressure setting at least in the rear-wheel wheel-brake cylinders of the braking system according to the present invention. It is noted, however, that a switching of the valves of the braking system according to the present invention at least in the rear-wheel wheel-brake cylinders for the wheel-specific, fully automatic/fully autonomous pressure setting at least in the rear-wheel wheel-brake cylinders of the braking system according to the present invention is generally necessary only for a modulation such as, for example, an ESP control or ABS control. For this reason, valve switching noises occur relatively seldom during an operation of the braking system according to the present invention. Reference is therefore also made to a good noise vibration harshness (NVH) characteristic of the braking system according to the present invention.

In one advantageous specific embodiment of the braking system of the present invention, a rear-axle control device of the rear axle unit is designed and/or programmed, while taking into account at least one braking setpoint signal, which is output by at least one brake actuator sensor of the vehicle to the rear-axle control device by an automatic speed control system of the vehicle, by a front-axle control device of the front axle unit and/or by a further stabilizing device of the braking system, to activate the at least one second motorized brake pressure buildup device, the first separating valve and/or the second separating valve, so that at least temporarily, while at least the first separating valve is directed into its closed position, brake fluid is transferable via the second rear-axle hydraulic path into the second rear-wheel wheel-brake cylinder with the aid of an operation of the at least one second motorized brake pressure buildup device, and/or while at least the second separating valve is directed into its closed state, brake fluid is transferable via the first rear-axle hydraulic path into the first rear-wheel wheel-brake cylinder with the aid of the operation of the at least one second motorized brake pressure buildup device. A wheel-specific pressure setting is thus implementable in both rear-wheel wheel-brake cylinders of the specific embodiment of the braking described herein with the aid of the operation of the at least one second motorized brake pressure buildup device activated by the rear-axle control device. Alternatively, the rear axle unit may also be operated while the first separating valve and the second separating valve are open.

According to an example embodiment of the present invention, the rear axle unit is preferably designed to be hydraulically separate from the front axle unit in such a way that the rear axle unit and the front axle unit are connected to one another at most via one signal line and/or bus line connected at the rear-axle control device and/or at the front-axle control device. Thus, the conventional hydraulic lines between a front axle and a rear axle of the vehicle equipped with the braking system described herein are omitted in the specific embodiment of the braking system described herein.

For example, the first front-axle hydraulic path and the second front-axle hydraulic path may extend through a shared front-axle brake circuit of the front axle unit and/or the first rear-axle hydraulic path and the second rear-axle hydraulic path may extend through a shared rear-axle brake circuit of the rear axle unit. Alternatively, however, the first front-axle hydraulic path may also extend through a first front-axle brake circuit of the front axle unit while the second front-axle hydraulic path extends through a second front-axle brake circuit of the front axle unit and/or the first rear-axle hydraulic path may extend through a first rear-axle brake circuit of the rear axle unit, while the second rear-axle hydraulic path extends through a second rear-axle brake circuit of the rear axle unit. Thus, a high degree of design freedom is possible in the design of the brake circuits of the braking system.

According to an example embodiment of the present invention, the front axle unit preferably also includes at least one first front-axle separating valve situated in the first front-axle hydraulic path and/or a second front-axle separating valve situated in the second front-axle hydraulic path. A wheel-specific pressure setting in this case is also possible in both front-axle wheel-brake cylinders.

As an advantageous refinement of the present invention, the front axle unit may also include a main brake cylinder, at which a brake actuator of the vehicle is connectable or is connected in such a way that at least one piston of the main brake cylinder delimiting at least one chamber of the main brake cylinder is adjustable with the aid of an actuation of the brake actuator by a driver of the vehicle, the at least one chamber of the main brake cylinder being hydraulically connected at the at least one first motorized brake pressure buildup device, at the first front-axle hydraulic path and/or at the second front-axle hydraulic path via at least one valveless or valve-equipped connecting line. Thus, with the aid of his/her driver braking force, the driver has the option of braking directly into the front-wheel wheel-brake cylinder in order in this way to also effectuate an (additional) brake pressure buildup in the front-wheel wheel-brake cylinder. The specific embodiment of the braking system described herein thus also includes a mechanical fall-back level.

According to an example embodiment of the present invention, the at least one first motorized brake pressure buildup device is preferably a plunger device and the at least one chamber of the main brake cylinder is hydraulically connected via the at least one connecting line at at least one plunger chamber of the plunger device, a respective opening of that least one connecting line at the at least one plunger chamber being designed in such a way that, if at least one adjustable plunger piston of the plunger device is present in its respective initial position, brake fluid is transferable out of the main brake cylinder through the at least one opening of the at least one connecting line into the plunger device, whereas, if the at least one adjustable plunger piston is moved out of its respective initial position, a brake fluid transfer out of the main brake cylinder through the at least one opening of the at least one connecting line into the plunger device is prevented with the aid of at least one sealing element attached at the at least one plunger piston and/or in the respective plunger chamber. Thus, during an operation of the plunger device, the main brake cylinder is automatically “decoupled” from the plunger device. Nevertheless, the specific embodiment of the braking system described herein is automatically transferred to its fall-back level in the case of a failure of the plunger device, in which the driver is able to brake into the front-wheel wheel-brake cylinder via the main brake cylinder and the plunger device with the aid of his/her driver braking force. A switching of a valve is therefore unnecessary for transferring the specific embodiment of the braking system described herein into the mechanical fall-back level.

Alternatively, according to an example embodiment of the present invention, at least one main brake cylinder decoupling valve may also be situated in the at least one connecting line. A transfer of the specific embodiment of the braking system described herein into its mechanical fall-back level is thus also possible by switching the at least one main brake cylinder decoupling valve.

The above=described advantages are also ensured when carrying out a corresponding method for operating a braking system of an at least two-axle vehicle. It is expressly noted that the method for operating a braking system of an at least two-axle vehicle may be refined in accordance with the specific embodiments of the braking system explained above.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG.1schematically shows a representation of a first specific embodiment of the braking system.

The braking system schematically represented inFIG.1is mountable/is mounted at an at least two-axle vehicle/motor vehicle, a suitability of the braking system not being limited to any specific vehicle type/motor vehicle type of the two-axle vehicle/motor vehicle.

The braking system includes a front axle unit10that includes at least one first motorized brake pressure buildup device12, a first front-wheel wheel-brake cylinder14amountable/mounted at a first front wheel of the vehicle and a second front-wheel wheel-brake cylinder14bmountable/mounted at a second front wheel of the vehicle. The at least one first motorized brake pressure buildup device12is hydraulically connected at first front-wheel wheel-brake cylinder14avia a first front-axle hydraulic path and at second front-wheel wheel-brake cylinder14bvia a second front-axle hydraulic path. Thus, in the braking system ofFIG.1, it is possible to fully automatically/fully autonomously set, i.e., without driver braking force being provided by a driver of the respective vehicle, a front wheel braking pressure in first front axle wheel-brake cylinder14aand the same front-wheel braking pressure in second front axle wheel-brake pressure14bwith the aid of the at least one first motorized brake pressure buildup device12. Merely by way of example, the first front-axle hydraulic path and the second front-axle hydraulic path in the specific embodiment ofFIG.1extend through a shared front-axle brake circuit16of front axle unit10. The design of the at least one first motorized brake pressure buildup device12visually depicted inFIG.1as at least one pump12is to be interpreted as merely exemplary. Instead of or in addition to the at least one pump12, it is also possible to use a plunger device that includes at least one adjustable plunger piston as the at least one first motorized brake pressure buildup device12at the front axle unit10.

The braking system also has a rear axle unit18designed to be hydraulically separate from front axle10. Rear axle18includes at least one second motorized brake pressure buildup device20, a first rear-wheel wheel-brake cylinder22amountable/mounted at a first rear wheel of the vehicle, and a second rear-wheel wheel-brake cylinder22bmountable/mounted at a second rear wheel of the vehicle. The at least one second motorized brake pressure buildup device20is hydraulically connected via a first rear-axle hydraulic path at first rear-wheel wheel-brake cylinder22aand via a second rear-axle hydraulic path at second rear-wheel wheel-brake cylinder22b. For example, the first rear-axle hydraulic path and the second rear-axle hydraulic path in this case extend through a shared rear-axle brake circuit24of rear axle unit18. In the example ofFIG.1, the at least one second motorized brake pressure buildup device20is a motorized plunger device20, whose single adjustable plunger piston is adjustable with the aid of an operation of its motor. It is noted, however, that the design of the at least one first motorized brake pressure buildup device20as plunger device20including only the one adjustable plunger piston graphically depicted inFIG.1is to be interpreted as only exemplary. A plunger device that includes multiple adjustable plunger pistons or (instead of or in addition to a plunger device) at least one pump may also be used as the at least one second motorized brake pressure buildup device20at rear axle unit18.

Rear axle unit18also includes a first separating valve26asituated in the first rear-axle hydraulic path and/or a second separating valve26bsituated in the second rear-axle hydraulic path. In the braking system ofFIG.1, therefore, a first rear-wheel braking pressure in first rear-wheel wheel-brake cylinder22aand a second rear-wheel brake pressure deviating from the first rear-wheel brake pressure in second rear-wheel wheel-brake cylinder22bmay be fully automatically/fully autonomously set with the aid of the at least one second motorized brake pressure buildup device20and with the aid of at least one of separating valves26aand26b. This may also be referred to as a wheel-specific fully automatic/fully autonomous pressure setting in the two rear-wheel wheel-brake cylinders22aand22bor as a wheel-specific fully automatic/fully autonomous brake pressure buildup in the two rear-wheel wheel-brake cylinders22aand22b.

It is noted, however, that such a wheel-specific fully automatic/fully autonomous pressure setting in rear-wheel wheel-brake cylinders22aand22bis generally only necessary for a modulation such as, for example, for an ESP control or ABS control. During a “standard operation” of rear axle unit18, the same rear-wheel brake pressure is usually set in both rear-wheel wheel-brake cylinders22aand22b, so that no valve switching noises are able to occur. A driver of the vehicle is thus not irritated in such a situation by valve switching noises.

The hydraulically separate design of front axle unit10from rear axle unit18is understood to mean that no hydraulic line extends between front axle unit10and rear axle unit18. Since front axle unit10is designed to be hydraulically separate from rear axle unit18, the hydraulic lines traditionally required between the axles equipped with wheel brake cylinders14a,14b,22aand22bare omitted in the brake system ofFIG.1. The brake system thus has a very compact and space-saving design. A modular design of the brake system is, in particular, implementable at comparatively low manufacturing costs. Front axle unit10and rear axle unit18may also be mounted as two separate units at the two-axle vehicle equipped therewith. This also facilitates a mounting of the brake system described herein.

The at least one separating valve26aand26bmay optionally be a switch valve or a continuously controllable valve suitable for differential pressure setting. The at least one separating valve26aand26bis preferably a normally open valve.

Rear axle unit18preferably also includes a rear-axle control device28, which is designed and/or programmed to activate at least the at least one second motorized brake pressure buildup device20, first separating valve26aand/or second separating valve26bwith the aid of at least one control signal28swhile taking into account at least one brake setpoint signal30. Rear-axle control device28is preferably designed to operate rear axle unit18at least temporarily in a mode in which brake fluid is transferable/is transferred via the second rear-axle hydraulic path into second rear-wheel wheel-brake cylinder22bwith the aid of an operation of the at least one second motorized brake pressure buildup device20, while at least first separating valve26ais controlled in its closed state and, if present, second separating valve26bis controlled in an at least partially open state, so that an individual brake pressure increase takes place in second rear-wheel wheel-brake cylinder22b. Alternatively or in addition, rear axle unit18, with the aid of its rear-axle control device28, may also be at least temporarily operable in a mode in which brake fluid is transferable/is transferred via the first rear-axle hydraulic path into first rear-wheel wheel-brake cylinder22awith the aid of the operation of the at least one second motorized brake pressure buildup device20while at least second separating valve26bis controlled in its closed state and, if present, first separating valve26ais controlled in an at least partially open state, brake fluid is transferable/is transferred via the first rear-axle hydraulic path into first rear-wheel wheel-brake cylinder22awith the aid of the operation of the at least one second brake pressure buildup device20, which triggers an individual brake pressure increase in first rear-wheel wheel-brake cylinder22a.

The at least one brake setpoint signal30may be output, for example, to rear-axle control device28by a brake actuator sensor32of the vehicle, by an automatic speed control system of the vehicle (not delineated), by an (optional) front-axle control device34of front axle unit10and/or by a further stabilizing device of the braking system (not shown). The at least one brake actuator sensor32may, for example, be a rod path sensor and/or a differential path sensor. The automatic speed control system may, for example, be an automatic system for driverless driving of the vehicle, an adaptive cruise control and/or an emergency braking system. The further stabilizing device of the vehicle may be understood to mean, in particular, an ESP control unit or an ABS control unit. Rear-axle control device28may thus interact with a plurality of different electronic components for pressure setting in rear-wheel wheel-brake cylinders22aand22b. As an advantageous refinement, rear-axle control unit28may also be designed to receive and to evaluate sensor signals of a pre-pressure sensor of rear axle unit18(not shown), of at least one wheel pressure sensor of rear axle unit18(not delineated) and/or of at least one wheel rotation sensor of the rear wheels (not graphically depicted). As a further advantageous refinement, rear-axle control device28may also be designed to also activate at least one generator-driven motor of the vehicle used for recuperative braking of the vehicle which, however, is not delineated inFIG.1.

In the specific embodiment ofFIG.1, front axle unit10is designed to also include a first front-axle separating valve36asituated in the first front-axle hydraulic path and/or a second front-axle separating valve36bsituated in the second front-axle hydraulic path. A wheel-specific fully automatic/fully autonomous pressure setting is thus also possible in the two front-wheel wheel-brake cylinders14aand14b. The at least front-axle separating valve36aand36bmay optionally be a switch valve or a continuously controllable valve suitable for differential pressure setting. The at least one front-axle separating valve36aand36bis preferably a normally open valve. If front axle unit10is equipped with the at least one front-axle separating valve36aand36b, it preferably also includes front-axle control device34, with the aid of which at least the at least one first motorized brake pressure buildup device12, first front-axle separating valve36a, and/or second front-axle separating valve36bare activatable with the aid of at least one control signal34s.

Rear axle unit18and front axle unit10are connected to one another at most via at least one signal line and/or bus line38connected at rear-axle control device28and at front-axle control device34. The connection between rear axle unit18and front axle unit10implemented with the aid of signal line and/or bus line38is thus space-saving, yet still enables a good interaction between rear axle unit18and front axle10. The at least one signal line and/or bus line38may, for example, be a vehicle bus of the vehicle.

In addition, front axle unit10in the specific embodiment ofFIG.1advantageously also includes a main brake cylinder40, at which a brake actuator42of the vehicle is connectable or is connected in such a way that at least one piston delimiting an at least one chamber of main brake cylinder40is adjustable/is adjusted with the aid of an actuation of brake actuator42by a driver of the vehicle. It is expressly noted that in this case, rear axle unit18is not hydraulically connected at main brake cylinder40of front axle unit10.

Brake actuator42may, for example, be a brake pedal42. Moreover, the at least one chamber of main brake cylinder40is hydraulically connected via at last one connecting line44at the at least one first motorized brake pressure buildup device12, at the first front-axle hydraulic path, and/or at the second front-axle hydraulic path. Thus, at the braking system ofFIG.1, a mechanical fall-back level is formed, in which, in particular in the case of a failure of the at least one first motorized brake pressure buildup device12and/or the at least one second motorized pressure buildup device20, the driver is still able to effectuate a brake pressure buildup in front-wheel wheel-brake cylinders14aand14bwith the aid of his/her driver braking force applied to brake actuator42. Thus, even in the case of a failure of the vehicle electrical power system of his/her vehicle, the driver is still able to reliably bring the vehicle to a standstill with the aid of the brake pressure increase effectuated in front-wheel wheel-brake cylinders14aand14b.

The at least one connecting line44may optionally be a valveless or valve-equipped connecting line44. As an advantageous refinement, at least one main brake cylinder decoupling valve46may also be situated in the at least one connecting line44. Thus, by closing the at least main brake cylinder decoupling valve46, main brake cylinder40may be uncoupled from the at least one motorized brake pressure buildup device12during an operation of the at least one first motorized braking pressure buildup device12in such a way that the driver braking force applied to brake actuator42has no influence on the at least one front-wheel brake pressure present in front-wheel wheel-brake cylinders14aand14b. The at least one main brake cylinder decoupling valve46is preferably a normally open valve. Although not represented inFIG.1, a simulator may also be connected at main brake cylinder40, so that the driver actuating brake actuator42when the at least one main brake cylinder decoupling valve46is present in the closed state, has a standard brake actuation feel/pedal feel.

In addition, at least one brake pressure buildup device decoupling valve48may also be used in front-axle brake circuit16in such a way that the at least one first motorized brake pressure buildup device12is decouplable/is decoupled from the at least one connecting line44during the mechanical fall-back mode by closing the at least one brake pressure buildup device decoupling valve48, and thus as a “volume sink,” does not adversely affect the brake pressure increase effectuated with the aid of the driver braking force in front-wheel wheel-brake cylinders14aand14b. For the at least one brake pressure buildup device decoupling valve48, a normally closed valve is preferred.

In the braking system ofFIG.1, the only chamber of main brake cylinder40is connected via only one connecting line44to a single main brake cylinder decoupling valve46at front-axle brake circuit16, an opening of the only connecting line44being located at front-axle brake circuit16between the at least one first motorized brake pressure buildup device12and a fork of front-axle brake circuit16. Since the braking system ofFIG.1has only a single brake pressure buildup device12, only a single brake pressure buildup device decoupling valve48is also inserted into front axle unit10. In this case, the opening of the only connecting line44is preferably located between the only brake pressure buildup device decoupling valve48and the fork of front-axle brake circuit16.

FIG.2schematically shows a representation of a second specific embodiment of the braking system.

In the braking system ofFIG.2, the at least one first motorized brake pressure buildup device12of front axle unit10is a first plunger device12including two plunger pistons that are adjustable with the aid of their motor. As a result, the first front-axle hydraulic path extends through a first front-axle brake circuit16aof front axle unit10connected at a first plunger chamber of first plunger device12, whereas the second front-axle hydraulic path extends through a second front-axle brake circuit16bof front axle unit10connected at a second plunger chamber of first plunger device12. Furthermore, main brake cylinder40connected at first plunger device12is a tandem main brake cylinder40, a first chamber of main brake cylinder40with the first plunger chamber of first plunger device12and a second chamber of main brake cylinder40with the second plunger chamber of first plunger device12being connected via one connecting line44each to one main brake cylinder decoupling valve46each.

Moreover, the at least one second motorized brake pressure buildup device20in the braking system ofFIG.2is designed as a second plunger device20including two adjustable plunger pistons. Accordingly, the first rear-axle hydraulic path extends through a first rear-axle brake circuit24aof rear axle unit18connected at a first plunger chamber of second plunger device whereas the second rear-axle hydraulic path extends through a second rear-axle brake circuit24bof rear axle unit18connected at a second plunger chamber of second plunger device20.

With regard to further features of the braking system ofFIG.2and their advantages, reference is made to the above-described specific embodiment ofFIG.1.

FIG.3schematically shows a partial representation of a third specific embodiment of the braking system.

Front axle unit10schematically shown inFIG.3differs from that represented inFIG.1in that the opening of connecting line44equipped with main brake cylinder decoupling valve46is located between first front-axle separating valve36aand first front-wheel wheel-brake cylinder14a. As an advantageous refinement, front axle unit10ofFIG.3therefore also includes a brake circuit connecting line50using a switchable valve52, the first opening of which is located between first front-axle separating valve36aand first front-wheel wheel-brake cylinder14a, and the second opening of which is located between second front-axle separating valve36band second front-wheel wheel-brake cylinder14b. In the case of the braking system ofFIG.3as well, the driver is still able to effectuate a brake pressure buildup in both front-wheel wheel-brake cylinders14aand14bin the mechanical fall-back level with the aid of his/her driver braking force applied to brake actuator42. Switchable valve52is preferably a normally open valve.

With regard to further features of the braking system ofFIG.3and their advantages, reference is made to the specific embodiment ofFIG.1. Rear axle unit18interacting with front axle unit10ofFIG.3may, in particular, be designed in accordance withFIG.1or2.

FIG.4schematically shows a partial representation of a fourth specific embodiment of the braking system.

In front axle unit10schematically represented inFIG.4(in contrast to the specific embodiment ofFIG.2), a first connecting line44connected at the first chamber of main brake cylinder40extends between first front-axle separating valve36aand first front-wheel wheel-brake cylinder14a, and a second connecting line44connected at the second chamber of main brake cylinder40extends between second front axle separating valve36band second front-wheel wheel-brake cylinder14b. The two connecting lines44are valveless.

With regard to further features of the braking system ofFIG.4and their advantages, reference is made to the specific embodiments ofFIGS.1and2. Rear axle unit18interacting with front axle unit10ofFIG.4may, in particular, be designed in accordance withFIG.1or2.

FIG.5schematically shows a partial representation of a fifth specific embodiment of the braking system.

In the case of front axle unit10schematically represented inFIG.5, first connecting line44connected at the first chamber of main brake cylinder40extends, in contrast to the specific embodiment ofFIG.4, between the second plunger chamber of plunger device12and second front-axle separating valve36b, and second connecting line44connected at the second chamber of main brake cylinder40extends between the first plunger chamber of plunger device12and first front-axle separating valve36a.

With regard to further features of the braking system ofFIG.5and their advantages, reference is made to the specific embodiments ofFIGS.1,2, and4. Rear axle unit18interacting with front axle unit10ofFIG.5may, in particular, be designed in accordance withFIG.1or2.

FIG.6schematically shows a partial representation of a sixth specific embodiment of the braking system.

In the case of front axle unit10schematically represented inFIG.6, the at least one first motorized brake pressure buildup device12is a plunger device12. The at least one chamber of main brake cylinder40of front axle unit10is hydraulically connected at the at least one plunger chamber of plunger device12via the at least one connecting line44. A respective opening of the at least one connecting line44at the at least one plunger chamber is designed in such a way that, if at least one adjustable plunger piston of plunger device12is present in its respective initial position, brake fluid is transferable from main brake cylinder40into plunger device12through the at least one opening of the at least one connecting line44. However, if the at least one adjustable plunger piston is moved from its respective initial position, a brake fluid transfer from main brake cylinder40through the at least one opening of the at least one connection line44into plunger device12is prevented with the aid of at least one sealing element54a,54b, and54cattached at the at least one plunger piston and/or in the respective plunger chamber. The advantageously designed opening of the at least one connecting line44and the at least one sealing element54a,54b, and54cattached at the at least one plunger piston and/or in the respective plunger chamber thus ensure that main brake cylinder is “automatically” uncoupled from plunger device12during an operation of plunger device12of main brake cylinder40present in its functional state, and thus the driver braking force applied to brake actuator42has no influence on the at least one front-wheel brake pressure present in front-wheel wheel-brake cylinders14aand14b. In the case of a failure of plunger device12and/or the vehicle electrical power system of the vehicle, the at least one adjustable plunger piston is generally present in its respective initial position, as a result of which the braking system is “automatically” transferred into its mechanical fall-back level, in which the driver is still able to reliably effectuate with the aid of his/her driver braking force a brake pressure increase in front-wheel wheel-brake cylinders14aand14bsufficient enough to decelerate his/her vehicle. Equipping the braking system ofFIG.6with a main brake cylinder decoupling valve46is therefore unnecessary.

For example, the only chamber of main brake cylinder40in the brake system ofFIG.6is connected via only one valveless connecting line44to the only plunger chamber of plunger device12. The only plunger piston of plunger device12supports three sealing elements54a,54b, and54cattached thereto. A first sealing element54alocated closest to connecting line44when the plunger piston is present in its initial position is blocking for a pressure from the direction of the opening and permeable for a pressure from the (opposite) direction of the motor. A second sealing element54badjacent to first sealing element54ais permeable for a pressure from the direction of the opening and blocking for a pressure from the (opposite) direction of the motor. A third sealing element54clocated closest to the motor of plunger device12is also blocking for a pressure from the direction of the opening and permeable for a pressure from the (opposite) direction of the motor.

With regard to further features of the braking system ofFIG.6and their advantages, reference is made to the above-explained specific embodiments. Rear axle unit18interacting with front axle unit10ofFIG.6is designed, in particular, in accordance withFIG.1or2.

FIG.7schematically shows a partial representation of a seventh specific embodiment of the braking system.

In contrast to the specific embodiment ofFIG.6, “only” first sealing element54alocated in its initial position closest to the opening of connecting line44, which is blocking for a pressure from the direction of the opening and permeable for a pressure from the (opposite) direction of the motor, and third sealing element54clocated closest to the motor of plunger device12, which is also blocking for a pressure from the direction of the opening and permeable for a pressure from the (opposite) direction of the motor, are attached at the plunger piston in the braking system ofFIG.7. As a result, a main brake cylinder decoupling valve46is also situated in connecting line44.

With regard to further features of the braking system ofFIG.7and its advantages, reference is made to the above-explained specific embodiments. Rear axle unit18interacting with front axle unit10ofFIG.7may, in particular, be designed according toFIG.1or2.

FIG.8schematically shows a partial representation of an eighth specific embodiment of the braking system.

In front axle unit10reproduced inFIG.8as well, the first chamber of main brake cylinder40is connected to the first plunger chamber via a first connecting line44and the second chamber of main brake cylinder40is connected to the second plunger chamber via a second connecting line44, the opening of each connecting line44at the plunger chamber assigned to them being designed in accordance withFIG.6. Each of the two plunger pistons also supports sealing elements54a,54b, and54calready described above.

With regard to further features of the braking system ofFIG.8and their advantages, reference is made to the above-explained specific embodiments. Rear axle unit18interacting with front axle unit10ofFIG.8may, in particular, be designed according toFIG.1or2.

All of the braking systems described above require no new technology for their manufacture. Instead, it is possible to resort to already existing components/parts when manufacturing the braking systems described above.

FIG.9shows a flowchart for explaining one specific embodiment of the method for operating a braking system of an at least two-axle vehicle.

The method described below is implementable with any braking system that includes a front axle unit including at least one first motorized brake pressure buildup device, which is hydraulically connected via a first front-axle hydraulic path at a first front-wheel wheel-brake cylinder of a first front wheel of the vehicle and via a second front-axle hydraulic path at a second front-wheel wheel-brake cylinder of a second front wheel of the vehicle, and a rear axle unit designed to be hydraulically separate from the front axle unit, including at least one second motorized brake pressure buildup device, which is hydraulically connected via a first rear-axle hydraulic path at a first rear-wheel wheel-brake cylinder of a first rear wheel of the vehicle and via a second rear-axle hydraulic path at a second rear-wheel wheel-brake cylinder of a second rear wheel of the vehicle. A feasibility is limited neither to a particular type of braking system nor to a specific vehicle type/motor vehicle type of the vehicle/motor vehicle equipped with the braking system.

As at least one of method steps S1and S2, the at least one second motorized brake pressure buildup device, a first separating valve situated in the first rear-axle hydraulic path, and/or a second separating valve situated in the second rear-axle hydraulic path are activated taking at least one brake setpoint signal into account. The at least one brake setpoint signal is output by at least one brake activation element sensor of the vehicle, at least one automatic speed control system of the vehicle, at least one front-axle control device of the front axle unit and/or at least one further stabilizing device of the braking system. As a method step S1, the at least one second motorized brake pressure buildup device, the first separating valve and/or the second separating valve are activated in such a way that at least temporarily, while at least the first separating valve is directed into and/or held in its closed position, brake fluid is transferable via the second rear-axle hydraulic path into the second rear-wheel wheel-brake cylinder with the aid of an operation of the at least one second motorized brake pressure buildup device. Alternatively or in addition, as method step S2, the at least one second motorized brake pressure buildup device, the first separating valve and/or the second separating valve are activated in such a way that, at least temporarily, while the at least second separating valve is directed into and/or held in its closed state, brake fluid is transferred via the first rear-axle hydraulic path into the first rear-wheel wheel-brake cylinder with the of the operation of the at least one second motorized brake pressure buildup device. An implementation of the method described herein yields the advantages already enumerated above. Optionally, it is possible in a non-delineated method step to actuate the at least one second motorized braking pressure buildup device when the first separating valve is open and when the second separating valve is open.

All of the front axle units and rear axle units described above may be used to carry out the method described herein. A feasibility of the method is, however, not limited to the use of these front axle units and rear axle units.