Brake system for a vehicle axle

Abstract

The invention relates to a brake system (1) for a vehicle axle (2, 3), having at least the following components: - a wheel shaft (4), which can be connected to a vehicle wheel (5), and - a braking device (6) for a controllably variable deceleration of the wheel shaft (4). The brake system (1) is primarily characterized in that the braking device (6) is formed by a hydraulic displacement pump (7) together with a throttling device (8). By virtue of the proposed brake system, a motor vehicle can be decelerated to a standstill at any operating point with very low particulate emissions.

Description

[0001] Braking system for one vehicle axle

[0002] The invention relates to a braking system for a vehicle axle, a vehicle axle with such a braking system for a motor vehicle, and a motor vehicle with such a vehicle axle.

[0003] As a result of the desired decarbonization and reduction of particulate matter, there is a steady increase in hybrid and battery-electric vehicles, especially passenger cars and light commercial vehicles. To increase the range and efficiency of vehicles and simultaneously comply with the legally mandated reduction of particulate matter pollution in many countries (now or soon to be implemented), eddy current braking is frequently used. Through so-called recuperation, the deceleration energy is converted into usable electrical energy and stored in a vehicle battery. However, such recuperative braking is not feasible in every operating situation, for example, when the vehicle battery is already fully charged or when the battery temperature is in a critical range.Furthermore, deceleration to a standstill of the vehicle using regenerative braking is not possible. Therefore, an additional mechanical brake, such as a disc brake or drum brake, is necessary.

[0004] Based on this, the present invention aims to overcome, at least partially, the disadvantages known from the prior art. The features of the invention are defined in the independent claims, for which advantageous embodiments are shown in the dependent claims. The features of the claims can be combined in any technically meaningful way, whereby the explanations in the following description and features from the figures, which comprise supplementary embodiments of the invention, can also be used.

[0005] The invention relates to a braking system for a vehicle axle, comprising at least the following components: - a wheel shaft which can be connected to a vehicle wheel, and

[0006] - a braking device for controllably variable deceleration of the wheel shaft.

[0007] The braking system is characterized primarily by the fact that the braking device consists of a hydraulic displacement pump together with a throttling device.

[0008] Unless explicitly stated otherwise, ordinal numbers used in the preceding and following descriptions serve solely for unambiguous differentiation and do not indicate any order or ranking of the components referred to. An ordinal number greater than one does not necessarily imply the presence of another such component.

[0009] The braking system proposed here is designed for one vehicle axle. This braking system allows the vehicle axle, and therefore the entire motor vehicle, to be decelerated.

[0010] For example, the vehicle axle is designed as a trailing axle. A trailing axle has no drive motor of its own and is pulled along by the driven axle of the vehicle. Often, for space reasons, the trailing axle in two-axle battery-electric vehicles is the front axle. Frequently, (two-axle) battery-electric vehicles are equipped with two (driven) axles, each with at least one (separate) drive motor.

[0011] The braking system comprises at least one wheel axle, or in one embodiment, two wheel axles of a single vehicle axle. A wheel axle forms a torque-resistant connection between a vehicle wheel and the braking device, and, in the case of a driven vehicle axle, also between the wheel axle and a (for example, electric) drive motor. The vehicle wheel is configured (for example, conventionally) to transmit torque from at least one torque source to a surface, thus generating propulsion for the vehicle. In one embodiment, the wheel axle is a component of a (for example, otherwise conventional) vehicle axle and is connected to the vehicle wheel (preferably directly) in a torque-resistant manner and / or to the rotor shaft of an electric drive motor (preferably directly) in a torque-resistant manner.In another embodiment, the wheel shaft is an additional component which can be connected directly or indirectly to a vehicle wheel and / or an associated drive motor in a torque-resistant manner.

[0012] The braking system's braking mechanism is designed to decelerate the wheel axle, and thus a vehicle wheel or the respective vehicle axle, and therefore the entire vehicle. The braking mechanism is designed for controllable and variable deceleration of the wheel axle. The braking mechanism applies a braking force or torque purely hydraulically, which counteracts the vehicle's movement.

[0013] It should be noted that controllable variable braking refers to the ability of the braking system to adapt the braking torque to a current driving condition, for example taking into account the load and / or the current surface of the vehicle, and integrated into a driving safety system, such as for lane keeping and / or against wheel lock-up to shorten the braking distance and maintain the steerability of the vehicle.

[0014] It is therefore proposed here that the hydraulic braking system be formed by a positive displacement pump, thus differing from a so-called retarder or intarder, as often used in trucks and heavy commercial vehicles, which employ a turbomachine (such as a torque converter in an automatic transmission). Such a turbomachine only operates above a certain minimum speed and is therefore unsuitable for decelerating a vehicle to a standstill.

[0015] A positive displacement pump is designed to pump a (brake) fluid, for example, hydraulic oil or (preferably also using) coolant. In one embodiment, the positive displacement pump is designed such that the fluid to be pumped is contained within it. The pumping resistance of the positive displacement pump is used to decelerate the wheel axle. The respective braking force can be controlled by means of a throttling device (for example, a fixed orifice and / or a variable throttle valve) via a (variable) throttle and / or (variable) pumping capacity.

[0016] Together with a throttling device, the positive displacement pump can decelerate the wheel axle. The throttling device regulates the flow rate and thus the resistance in the positive displacement pump, which is driven by the rotation of the vehicle wheel or, during its rotation, by the respective drive motor. Brake fluid flows from the wheel axle through the positive displacement pump via the torque-resistant connection between the brake system and the wheel axle (and, if applicable, a drive motor). The throttling device then allows for the adjustment of the flow rate of the positive displacement pump and thus the resistance in the wheel axle, thereby decelerating the vehicle wheel. The higher the resistance in the positive displacement pump, the greater the braking torque that opposes the applied torque of the vehicle wheel.It should also be noted that the drive motor and / or the displacement pump is connected to the wheel shaft via a transmission, but preferably the vehicle wheel and the displacement pump are directly connected to each other in a torque-resistant manner (i.e. without transmission, preferably with a backlash-free or low-backlash torque connection or by means of a one-piece wheel shaft).

[0017] In one embodiment, the throttling device is an integral part of the positive displacement pump. In another embodiment, the throttling device is a separate component located downstream in a hydraulic power line.

[0018] In one embodiment, the throttling device is designed as a throttle valve (for example, an electrically controlled one), allowing the flow rate and thus the resistance in the positive displacement pump to be adjusted. This enables the deceleration of the vehicle wheel to be controlled and variably implemented. The throttle valve thus allows for all states between an open throttle valve, which corresponds to the lowest possible flow resistance in the positive displacement pump for efficient propulsion of the vehicle, and a (nearly) closed throttle valve, which corresponds to maximum flow resistance against the pumping power of the positive displacement pump, resulting in a braking torque from the braking system sufficient to bring the vehicle to a standstill.For the lowest possible braking resistance (propulsion operation), a large flow cross-section is necessary; for a high braking resistance, a small flow cross-section is required.

[0019] Alternatively or additionally, the positive displacement pump can be decoupled from the rotation of the wheel shaft, for example by means of a coupling, so that the inertia of the positive displacement pump presents only minimal resistance. This is advantageous during constant driving, for example on a highway.

[0020] In an alternative embodiment, the delivery volume of the positive displacement pump, here implemented, for example, as a rotary vane pump or radial piston pump, is variable, preferably reducible to zero. This results in a delivery stroke of technically zero, leading to low resistance.

[0021] In a further advantageous embodiment of the braking system, it is proposed that the wheel shaft be part of a driven vehicle axle, preferably driven by an electric drive motor.

[0022] In most motor vehicles, such as passenger cars and light commercial vehicles, each axle comprises two wheels and thus two wheel axles. In one embodiment, a single drive motor is provided for both wheel axles of a (driven) vehicle axle, for example, a drive motor arranged parallel or coaxially between the two wheel axles of the respective vehicle axle. Alternatively or additionally, an electric drive motor is assigned to each wheel axle (independently), i.e., to each vehicle wheel. For example, these two drive motors are designed as so-called wheel hub motors.

[0023] In a preferred embodiment, the at least one drive motor is designed as an electric drive motor. In one embodiment, the coolant used to regulate the temperature of the at least one electric drive motor is used as brake fluid for the positive displacement pump of the brake system. Preferably, (at least a portion of) the waste heat is used to heat the vehicle battery, for example, to quickly bring it up to an optimal operating temperature (e.g., in winter).

[0024] In an advantageous embodiment of the braking system, it is further proposed that a directly controllable throttling device with an input-side pressure spread of less than 10 bar to 400 bar, preferably 200 bar, particularly preferably up to 100 bar, is connected downstream for the controllable variable throttling of the displacement pump.

[0025] To represent all operating points of a vehicle with its braking system, a directly controllable throttling device is proposed here. This directly controllable throttling device includes at least one (preferably one per displacement pump) throttle valve, which can be controlled.

[0026] The throttling device for throttling the positive displacement pump is designed such that an inlet pressure differential of less than 10 bar up to 400 bar in one embodiment is achievable. In a preferred embodiment for a cost-effective implementation of the brake system (especially the positive displacement pump, the at least one throttle valve, and the lines), the maximum pressure is 200 bar, particularly preferably a maximum of 100 bar.

[0027] In a further advantageous embodiment of the brake system, it is proposed that the positive displacement pump has a controllably variable delivery stroke, preferably discretely variable in multiple stages. Here, a delivery stroke is understood to be the (delivery) volume of brake fluid delivered per pumping cycle (i.e., for a single piston, the complete displacement stroke, and for a single impeller, one full revolution). Because the delivery stroke is variable, a variable braking torque can be set in an embodiment with a constant orifice as a throttling device, since the flow resistance depends on the volume flow rate. For this purpose, it is advantageous if a zero stroke can be set, so that even a very small orifice (for standstill) does not cause an excessively high braking torque during propulsion.Preferably, an active, directly controllable throttling device, as described above, is provided. This device allows for the provision of the high flow resistance (small cross-section down to zero) necessary for standstill, while simultaneously providing a relatively large cross-section for a (preferably negligible) flow resistance, thus resulting in a low (preferably negligible) braking torque. By making the conveying stroke variable, the cross-sectional area required for a suitable throttling device can be significantly reduced, and the entire piping system can be made smaller and more cost-effective. For potentially necessary high pressures (see previous descriptions), a small piping cross-section is advantageous, both in terms of installation space and the cost of the braking system components.

[0028] A discretely multi-stage variable displacement pump, for example, has delivery sections that can be switched on and off via one or more valves, thus allowing the delivery stroke (i.e., the delivery volume) to be varied in stages. In an application, two states are predominant: firstly, braking, and secondly, low-resistance driving. In the first case, a large delivery stroke is advantageous, and in the second, a small delivery stroke. Adaptive control of the required braking torque is set, for example, by means of at least one throttle valve. It is not impossible to brake even with a small delivery stroke. Preferably, the small delivery stroke is a de facto zero stroke (i.e., a negligible delivery rate), or, alternatively, zero stroke altogether.For example, by adjusting the delivery stroke, the pressure range and / or the volumetric flow rate range (i.e., the operating window for the throttling device) is kept (at least nearly) constant regardless of the speed. Preferably, a discrete multi-stage variable displacement pump also includes at least one further state, namely a delivery stroke for a high speed range (or even other speed ranges) and a delivery stroke for a low speed range. This prevents excessive heating of the brake fluid at the throttling device due to an excessively high delivery rate.

[0029] In an advantageous embodiment of the braking system, it is further proposed that a fluidic pilot control circuit is provided for controlling the throttling device and / or the displacement pump for the controllable variable deceleration of the wheel shaft, wherein preferably the pilot control circuit can be supplied by means of an electric pump, and / or wherein preferably the pilot control circuit is operated with a supply pressure of up to 50 bar, preferably up to 10 bar, preferably at least 5 bar.

[0030] The pilot control circuit is implemented, for example, as a pneumatic or hydraulic control circuit. In many applications, a fluidic control circuit already exists in a motor vehicle for other purposes, which can be used for the braking system with minimal effort. Alternatively, electronic actuation of the throttling device and / or (the delivery stroke) of the positive displacement pump is provided.

[0031] In one embodiment, the throttling device, here implemented with at least one throttle valve, is controllable by means of the pilot circuit, whereby the flow cross-section of the at least one throttle valve of the throttling device can be adjusted by means of the pilot circuit. Due to the hydraulic adjustability of the at least one throttle valve, the resistance at the positive displacement pump can be adjusted, and thus the deceleration of the wheel shaft. The advantage of a fluidic pilot circuit is that a large stroke and / or a large force can be provided for positioning the at least one throttle valve.

[0032] In one embodiment, the positive displacement pump can be controlled via the pilot control circuit. For example, the delivery stroke of the positive displacement pump can be adjusted via the pilot control circuit, for instance in the case of a rotary vane pump or radial piston pump. Thus, the delivery stroke of the positive displacement pump, and therefore the braking performance of the braking system, can be adjusted.

[0033] In one embodiment, the required fluidic pressure for the pilot control circuit is provided by an existing (conventional) pneumatic or hydraulic system within the vehicle. For example, by an active suspension system and / or a cooling circuit, such as for a vehicle battery.

[0034] In a preferred embodiment, the pilot control circuit is hydraulically operated, and the required hydraulic pressure is provided by a separate electric pump. The electric pump is dimensioned according to the expected operating points of the vehicle and can be deployed with pinpoint accuracy. The electric pump generates the pressure required to control the throttling device and the positive displacement pump. Due to the electric design of the pump, its stroke and pressure can be controlled electronically in a cost-effective and stepless manner.

[0035] With a separate pump, the pilot pressure can be set independently of other vehicle components. With a shared pump, a required pilot pressure can be set, for example, via a switching valve, such as a slide valve. In one embodiment, the pressure in the pilot circuit is (almost) constant, and actuation (e.g., of the throttle device) is time-dependent and / or displacement-dependent, or alternatively or additionally controlled by measured values ​​from the positive displacement pump or the brake system line.

[0036] With a clever design of the actuators in the brake system's piping, the control forces are significantly lower than those required to decelerate the vehicle using the positive displacement pump. A fluidic control circuit with 50 bar [fifty bar] can be implemented cost-effectively. A control pressure below 5 bar [five bar] usually results in a considerable limitation of function or necessitates the use of more expensive (because more sensitive) components. A control pressure between 5 bar and 10 bar is therefore particularly cost-effective and, at the same time, comparatively simple in its technical handling (e.g., with regard to filling, maintenance, leak tightness, and robustness).

[0037] In an advantageous embodiment of the braking system, it is further proposed that a redundant braking unit is provided for decelerating the wheel shaft.

[0038] The displacement pump proposed here is capable of decelerating a motor vehicle to a standstill. In some applications, for example as a condition of approval or due to a legal requirement, a redundant braking system must be provided. To provide such redundancy for decelerating the wheel axle, for example in the event of a leak or other defect in the hydraulic braking system, a redundant brake unit is proposed here. The brake unit is of a conventional design, for example with a (preferably wet) disc brake and / or a (preferably dry) drum brake.

[0039] Using the hydraulic braking system proposed here, such a redundant braking unit can be smaller or designed for a lower maximum braking torque and / or less frequent use. This results in cost savings and, at the same time, low particulate matter emissions during a typical test cycle.

[0040] According to another aspect, a vehicle axle for a motor vehicle is proposed, having

[0041] - two wheel axles, one for each vehicle wheel; and

[0042] - at least one braking system according to an embodiment as described above for decelerating the wheel shafts.

[0043] It should be noted that in one embodiment, several brake systems or several displacement pumps and / or throttling devices are assigned to a vehicle axle or a vehicle wheel, whereby these can be coupled (preferably purely fluidically) for a respective speed range. For example, a brake system with low flow resistance or a small delivery stroke and / or a large flow cross-section is coupled by means of a switching valve for deceleration at high speed or low braking torque requirement, and for deceleration at low speed or high braking torque requirement, a brake system with high flow resistance or a large delivery stroke and / or a small flow cross-section is coupled. In one embodiment, more than two such brake systems are provided for different speed ranges and / or torque requirements.

[0044] In one embodiment, the vehicle axle is designed as a trailing axle. The trailing axle is not directly driven by a drive motor, but rather is independent of a drive motor and simply rolls along with the driven vehicle. The required torque for propelling the vehicle can be provided by a drive motor via a (preferably single) additional (driven) axle.

[0045] In an alternative embodiment, the vehicle axle is designed as a driven vehicle axle. A driven vehicle axle comprises at least one drive motor, preferably one electric drive motor per wheel axle. The electric drive motor is torque-fixed to the respective vehicle wheel, so that the torque of the drive motor can be transmitted to the vehicle wheel and propulsion can be generated.

[0046] To decelerate a vehicle axle, the axle comprises at least one braking system according to an embodiment as described above. With the braking system proposed here, deceleration of the vehicle axle at any operating point is possible with minimal particulate emissions, preferably allowing the axle to be decelerated to a standstill without the need for an additional braking unit. Furthermore, in an advantageous embodiment of the vehicle axle, it is proposed that at least one of the following components be provided individually for each wheel:

[0047] - a displacement pump for decelerating the relevant vehicle wheel;

[0048] - a throttling device for throttling an associated positive displacement pump; and

[0049] - an electric drive motor for powering the vehicle wheel in question.

[0050] With a wheel-specific arrangement of the displacement pump at each vehicle wheel, any known brake torque distribution (for example, for lane keeping) can be achieved solely by means of the displacement pump or the throttling device. In one embodiment, a displacement pump is provided for each vehicle wheel on a vehicle axle with two wheel shafts, but only a single (common) throttling device is provided, in which case the delivery stroke of the displacement pump is preferably variable.

[0051] In one embodiment, the vehicle axle includes a throttling device for each wheel. With a wheel-specific arrangement of the throttling device for each wheel, any known brake torque distribution (for example, for lane keeping) can be achieved solely by means of the throttling device or the displacement pump. In another embodiment, a throttling device is provided for each wheel on a vehicle axle with two wheel shafts, but only a single (common) displacement pump is provided, in which case the throttle cross-section is preferably variable.

[0052] Here, a wheel-specific electric drive motor is proposed to power the respective vehicle wheel of the vehicle axle, thus providing two electric drive motors on a single (driven) vehicle axle. Alternatively, a central (e.g., electric) drive motor for the entire vehicle axle, i.e., for example, two vehicle wheels, is provided. In one embodiment of a wheel-specific electric drive motor, the positive displacement pump is connected to the rotor shaft of the drive motor, for example, axially opposite (i.e., behind) the respective vehicle wheel. Alternatively, the positive displacement pump is arranged between the vehicle wheel and the electric drive motor.

[0053] In a further advantageous embodiment of the vehicle axle, it is proposed that the vehicle axle is driven and that at least one, preferably electric, drive motor is provided for driving the vehicle wheels.

[0054] It is proposed here that the vehicle axle includes a drive motor for each vehicle wheel to drive the vehicle wheel; preferably, the drive motor is designed as an electric drive motor. In one embodiment, the electric drive motor is arranged parallel to the axle or coaxially between the vehicle wheels.

[0055] In an alternative embodiment, an electric drive motor is arranged between the vehicle wheel and the positive displacement pump for each wheel axle. Preferably, the positive displacement pump is connected to the electric drive motor in a torque-fixed manner, so that the rotational speeds of the electric drive motor and the positive displacement pump are the same.

[0056] According to another aspect, a motor vehicle is proposed comprising a transport cell, at least one drive engine, at least one driven vehicle axle according to an embodiment as described above, and at least one vehicle wheel which can be driven by the drive engine via the driven vehicle axle to propel the motor vehicle.

[0057] The vehicle comprises a transport compartment in which, for example, goods and / or passengers can be transported safely. The vehicle is propelled by a (preferably electric) drive motor. The braking system proposed here allows the vehicle to decelerate at any operating point with minimal particulate emissions, preferably enabling deceleration to a standstill without the need for an additional braking unit.

[0058] The invention described above is explained in detail below against the relevant technical background with reference to the accompanying drawings, which show preferred embodiments. The invention is in no way limited by the purely schematic drawings, although it should be noted that the drawings are not dimensionally accurate and are not suitable for defining size relationships. It is illustrated in

[0059] Fig. 1: a driven vehicle axle with a braking system;

[0060] Fig. 2: a driven vehicle axle with a braking system in an alternative embodiment;

[0061] Fig. 3: a driven vehicle axle with a braking system in a further alternative embodiment;

[0062] Fig. 4: a driven vehicle axle with a braking system in a further alternative embodiment; and

[0063] Fig. 5: schematically shown in a top view of a motor vehicle with a braking system.

[0064] Figure 1 shows a schematic view of a driven vehicle axle 2 with a braking system 1. The driven vehicle axle 2 comprises two wheel shafts 4, at each (outer) end of which a vehicle wheel 5 is fixedly mounted. In the embodiment shown here, each vehicle wheel 5 is driven by an electric drive motor 9. The braking system 1 comprises a positive displacement pump 7 arranged at (here optionally at the inner end) each wheel shaft 4, which is fixedly connected to both the electric drive motor 9 and the vehicle wheel 5, as well as a throttling device 8. In this embodiment, the positive displacement pump 7 is also driven by the electric drive motor 9 via the wheel shaft 4, which here is also the rotor shaft of the (electric) drive motor 9, so that during propulsion, a drag torque is applied by the drive motor 9 beyond the vehicle wheel 5.In one embodiment, recuperation is simultaneously performed to decelerate the vehicle wheel 5 (or the motor vehicle 13), so that the displacement pump 7 downstream here is optimally arranged to absorb excess torque or to boost the deceleration by means of recuperation.

[0065] The positive displacement pump 7 uses the wheel torque of the vehicle wheel 5 or the drive torque of the drive motor 9 to circulate brake fluid. To provide a braking torque, the positive displacement pump 7 is throttled by means of the throttling device 8, so that an (increased) pumping power must be supplied, from which a counter-torque (or a consumption torque) is delivered to the wheel shaft 4. The throttling device 8 is implemented here, for example, as a directly controllable throttle valve with an actuator 20 (here purely optionally electrical). The positive displacement pump 7 draws brake fluid from a reservoir 22 (shown here purely schematically) and delivers the brake fluid into an overflow 23, whereby the overflow 23 and the reservoir 22 are connected to each other (for example via a calming section and / or cooling section) so that the brake fluid is circulated.When the throttle valve of the throttling device 8 is fully open, the only back pressure (to a first approximation) is the line resistance (for example, according to the Reynolds number). This flow resistance is preferably as low as possible, i.e., a large hydraulic diameter is provided. If the (variable) flow cross-section of the throttle valve of the throttling device 8 is reduced, or even closed, an increasing (possibly insurmountable) back pressure is generated, thus decelerating the vehicle wheel 5 until it comes to a standstill. With a suitable design of the displacement pump 7 or a throttling device 8, the vehicle wheel 5 can even be locked, so that a motor vehicle 13 is sufficiently secured against rolling away solely with the hydraulic braking device 6 of the braking system 1 shown here.However, according to regulations in most countries, a redundant (e.g., positive-locking) parking lock must be provided, so that permanently locking the vehicle wheel 5 is not a necessary application for the braking system 1 described here. In an alternative embodiment, not shown here, only a single electric drive motor 9 is provided for the entire (driven) vehicle axle 2. This is connected to the braking system 1, or at least to a displacement pump 7, via a differential (not shown here) to transmit torque.

[0066] In both embodiments, the throttling device 8 (for example, by a control unit) adjusts the throttling of the displacement pumps 7 and thus the braking torque at the vehicle wheel 5 depending on the current deceleration request of the driver, a vehicle assistance system [FAS, or ADAS, English: Advanced Driver Assistance System] or a control unit for autonomous driving [ADS, English: Automated Driving System] or a current operating point.

[0067] It should be noted that the design of the brake systems 1 is identical for a trailing vehicle axle 3, except that there is no drive motor on this vehicle axle 3. It should also be noted that the drive motor 9 and / or the displacement pump 7 are connected to the wheel shaft 4 via a transmission, but preferably the vehicle wheel 5 and the displacement pump 7 are directly connected to each other in a torque-resistant manner (i.e., without a transmission, preferably with a backlash-free or low-backlash torque connection or by means of a one-piece wheel shaft 4). This also applies to the following embodiments.

[0068] Figure 2 shows an alternative embodiment of a driven vehicle axle 2 with a braking system 1. The embodiment shown here is largely identical to the embodiment in Figure 1, without exclusion of generality, and therefore reference is made to the description therein, with only the differences being discussed here.

[0069] The braking system 1 comprises, in addition to the hydraulic braking device 6, a dry (preferably purely redundant) braking unit 12. The dry braking unit 12 is, for example, conventionally designed (as schematically indicated) as a disc or drum brake. With the hydraulic braking device 6 proposed here, such a redundant braking unit 12 can be smaller or designed for a lower maximum braking torque and / or for less frequent use (with a potentially lower maximum heat capacity). This results in cost savings and, at the same time, low particulate matter emissions in a given test cycle.

[0070] Figure 3 shows a driven vehicle axle 2 with a braking system 1 in a further alternative embodiment. The embodiment shown here is, without exclusion of generality, largely identical to the embodiment shown in Figure 1, and therefore reference is made to the description therein, with only the differences being discussed here.

[0071] In the embodiment shown here, the throttling device 8 is controllable by means of a hydraulic pilot circuit 10. The throttle valves of the hydraulic brake device 6 are each controllable by means of a pilot valve 15. The throttle valves of the throttling devices 8 are thus controllable by means of a hydraulic actuator 21, which in turn is controlled by a hydraulic pilot circuit 10. The hydraulic diameter in the hydraulic brake device 6 is required to throttle the positive displacement pump 7 and thus to adjust the flow cross-section of the throttle valves. With a hydraulic actuator 21, greater forces and / or larger strokes can be achieved than with an electric actuator 20, or these can be achieved (at least in the area of ​​the throttling device 8) in a smaller installation space.

[0072] In this embodiment, the pump 11 of the pilot circuit 10 is driven by a pump drive 18 (e.g., electric). It should be noted that the pilot overflows 24 are connected to the pilot reservoir 25 (e.g., via a calming section and / or cooling section). The pilot circuit 10 includes pilot valves 15, which here (purely optionally) have electric actuators 20. These pilot valves 15 control the hydraulic diameter of the respective throttling device 8. Furthermore, a pressure relief valve 19 is shown, by means of which a pressure in the pilot circuit 10 can be controlled, or further components of a more complex pilot circuit 10 (not shown here) can be controlled and / or compensated, for example, to ensure a constant system pressure.

[0073] Figure 4 shows a driven vehicle axle 2 with a braking system 1 in a further alternative embodiment. The embodiment shown here is largely identical to the embodiment shown in Figure 3, without exclusion of generality; therefore, reference is made to the description therein, and only the differences are discussed here. It should be noted that in one embodiment, the throttling device 8 of the hydraulic braking system 6, in the form of an adjustable throttle valve, can be omitted. In another embodiment, the throttling devices 8 of the hydraulic braking system 6 shown are controllable by an electric actuator 20 (as shown in Figures 1 and 2).

[0074] The pilot control circuit 10 comprises, in addition to the hydraulically adjustable pilot valves 15 for the throttle valves of the throttling device 8 of the hydraulic brake device 6, a stroke control valve 16 for the respective positive displacement pump 7. A control piston 17 of the positive displacement pump 7 can be adjusted by means of the stroke control valve 16, so that the delivery stroke of the positive displacement pump 7 can be adjusted by means of the control piston 17. Due to the adjustability of the delivery stroke, the flow cross-section of the throttling device 8 can be reduced or can also be represented by means of a rigid orifice. In a preferred embodiment, the delivery stroke can be reduced to zero, so that a drag torque during driving is negligible or no greater than the friction torque in a conventional dry brake unit 12.

[0075] In addition to setting a delivery stroke for deceleration or low-resistance propulsion operation, a delivery stroke is preferably also adaptable to the current rotational speed of the wheel shaft 4, for example to a small delivery stroke (down to zero) at a high rotational speed (without braking requirement) and a large delivery stroke at a low rotational speed (for example, when parking the vehicle 13). For example, by adjusting the delivery stroke, the pressure range and / or the volume flow range (i.e., the operating window for the throttling device 8) is kept (at least almost) constant regardless of the rotational speed.

[0076] Figure 5 schematically shows a top view of a motor vehicle 13 with a braking system 1. The motor vehicle 13 comprises a passenger compartment 14 for transporting persons and / or payload. In this embodiment, the motor vehicle 13 optionally includes two electric drive motors 9 for propelling the motor vehicle 13, each assigned to one of the driven vehicle axles 2. Here, the front vehicle axle 2 is directly and rigidly connected to an electric drive motor 9. The electric drive motor 9 is arranged coaxially with the vehicle axle 2. The rear electric drive motor 9 is connected to the rear vehicle axle 2 via a transmission 26 to transmit torque.

[0077] For example, the front vehicle axle is a trailed vehicle axle 3 with two brake systems 1 (as shown here), but without the drive motor 9 shown. Alternatively, for example, the rear vehicle axle is a trailed vehicle axle (different from as shown here) without the drive motor 9 shown.

[0078] In one embodiment, one of the two (driven) vehicle axles 2 shown is a trailed vehicle axle 3, i.e. without a drive motor 9, but preferably with a brake system 1 (as proposed herein) for this vehicle axle 3 or (as shown here and above) with such a brake system 1 for each of the vehicle wheels 5 of the (driven or trailed) vehicle axle 2,3.

[0079] With the braking system proposed here, a motor vehicle can be decelerated to a standstill at any operating point with minimal particulate emissions. (List of reference symbols)

[0080] Braking system, driven vehicle axle, trailed vehicle axle, wheel shaft

[0081] Vehicle wheel hydraulic brake system displacement pump

[0082] Throttle device, electric drive motor, pilot control circuit

[0083] Pump dry brake unit motor vehicle transport cell

[0084] Pilot valve, stroke control valve, actuating piston

[0085] Pump drive, relief valve, electric actuator, hydraulic actuator, reservoir overflow

[0086] Input overflow, input reservoir, gearbox

Claims

Patent claims 1. Braking system (1) for a vehicle axle (2,3), comprising at least the following components: - a wheel axle (4) which can be connected to a vehicle wheel (5), and - a braking device (6) for controllably variable deceleration of the wheel shaft (4), characterized in that the braking device (6) is formed by a hydraulic displacement pump (7) together with a throttling device (8).

2. Braking system (1) according to claim 1, wherein the wheel shaft (4) is part of a driven vehicle axle (2), preferably driven by an electric drive motor (9).

3. Braking system (1) according to claim 1 or claim 2, wherein a directly controllable throttling device (8) with an input-side pressure spread of less than 10 bar to 400 bar, preferably 200 bar, particularly preferably up to 100 bar is connected downstream for controllably variable throttling of the displacement pump (7).

4. Braking system (1 ) according to one of the preceding claims, wherein the displacement pump (7) has a controllably variable delivery stroke, preferably discretely multi-stage variable.

5. Braking system (1) according to claim 3 or claim 4, wherein a fluidic pilot control circuit (10) is provided for controlling the throttling device (8) and / or the displacement pump (7) for the controllable variable deceleration of the wheel shaft (4), wherein preferably the pilot control circuit (10) can be supplied by means of an electric pump (11), and / or wherein preferably the pilot control circuit (10) is operated with a supply pressure of up to 50 bar, preferably up to 10 bar, preferably at least 5 bar.

6. Braking system (1) according to one of the preceding claims, wherein a redundant braking unit (12) is further provided for decelerating the wheel shaft (4).

7. Vehicle axle (2,3) for a motor vehicle (13), comprising - two wheel axles (4) for each vehicle wheel (5); and - at least one braking system (1 ) according to one of the preceding claims for decelerating the wheel shafts (4).

8. Vehicle axle (2,3) according to claim 7, wherein at least one of the following components is provided wheel-specifically: - a displacement pump (7) for decelerating the relevant vehicle wheel (5); - a throttling device (8) for throttling an associated positive displacement pump (7); and - an electric drive motor (9) for driving the vehicle wheel (5) in question.

9. Vehicle axle (2) according to claim 7 or claim 8, wherein the vehicle axle (2) is driven and at least one, preferably electric, drive motor (9) is provided for driving the vehicle wheels (5).

10. Motor vehicle (13) comprising a transport cell (14), at least one drive motor (9), at least one driven vehicle axle (2) according to claim 9 and at least one vehicle wheel (5) which can be driven by means of the drive motor (9) via the driven vehicle axle (2) to propel the motor vehicle (13).

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