TECHNICAL FIELD

The invention relates to a braking device and braking system for braking a vehicle. Further, the invention relates to a vehicle. Additionally, the invention relates to method for braking a vehicle. Further, the invention relates to a computer program, a computer readable medium, and a control unit.

The invention is applicable on vehicles. In particular, the invention is applicable on working machines within the fields of industrial construction machines or construction equipment. For example, a wheel loader or a paver is a working machine. Although the invention will be described with particular respect to a wheel loader, the invention is not restricted to this particular machine, but may also be used in other working machines such as articulated haulers, excavators and backhoe loaders or any other vehicle in general. It may be preferred that the vehicle is an electric vehicle, in particular an electric compact wheel loader or alike.

BACKGROUND

In connection with transportation of heavy loads at construction sites or the like, a working machine is often used. The working machines may be utilized for transportations in connection with road or tunnel building, sand pits, mines, forestry and similar environments. Thus, a working machine is frequently operated with large and heavy loads in rough terrain and on slippery ground where no regular roads are present. Thus, a reliable and user- friendly brake is required.

Today, most of the working machines, such as a compact wheel loader, are equipped with a service brake and a separate parking brake. Usually, the service brake is equipped with a dry disk brake that is actuated by pedal actuated brake piston. However, the durability of such kind of dry disk brake is relatively low. To increase the durability of the service brake, it is known to equip service brakes with a lamellar wet disk brake and a spring applied hydraulically released brakes.

From KR20200077015A a braking system is known that is capable of braking by using hydraulic pressure intelligently in an emergency using a service brake and a spring applied hydraulically released brakes as parking brake simultaneously depending on a detected time and pressure the pedal is pressed. Brake systems are also known from US 2020/0071910 A1 and JP H07 228242 A. US 2020/0071910 A1 relates to an adaptive park braking hydraulic circuit that may be in fluid communication with pressure sensors, a service brake assemblies and an adaptive park brake. JP H07 228242 A discloses an auxiliary brake device that provides an additional braking force for a hydraulic service brake according to a depression of the brake pedal detected by a brake actuation detector.

From EP 3 034 369 A1 a braking device is known.

The prior art has several disadvantages. There is a need for improvements in the field of braking vehicles, in particular in braking a mobile working machine, preferably in braking a compact wheel loader. In particular, lamellar wet disk brakes have the disadvantage that they require a large oil volume for actuating the brake in comparison to dry disk brakes. This makes the braking of a vehicle less user-friendly.

In order to assure proper braking of the vehicle and to meet the legal requirements one has to use a two-stroke piston for brake actuation if one uses a service brake comprising a lamellar wet disk brake. Such a two-stroke piston for brake actuation has several disadvantages. In particular, in comparison to dry disk brakes, the lamellar wet disk brake requires a high oil volume to be actuated. This need for high oil volumes of lamellar wet disk brakes is detrimental compared to dry disk brakes. Especially because the need for high oil volumes respectively high oil volume flows results in a high increase of brake pedal angle and pedal force.

SUMMARY

An object of the invention is to provide a braking device, braking system, a vehicle, a method, computer program, a computer readable medium, and a control unit to overcome the disadvantages of the prior art. In particular, an object of the invention is to provide a braking device, braking system, a vehicle, a method, computer program, a computer readable medium, and a control unit to improve the braking of vehicles. Preferably, an object of the invention is to provide a braking device, braking system, a vehicle, a method, computer program, a computer readable medium, and a control unit that enable braking a vehicle with a high durability of the braking device and at the same time allow user friendly braking of the vehicle, in particular in accordance to legal requirements. Most preferably, an object of the invention is to provide a braking device, braking system, a vehicle, a method, com- puter program, a computer readable medium, and a control unit that enable braking a vehicle with a high durability of the braking device and at the same time reduce the needed pedal angle to a minimum and enable the use of a minimum size of the second stroke of the two-stroke brake piston to reduce the needed brake pedal forces to a minimum.

According to one aspect of the invention, the object is achieved by a braking device for braking a vehicle according to claim 1 . In particular, the braking device is adapted for braking a mobile working machine, preferably for braking a compact wheel loader.

The braking device comprises a hydraulically actuated service brake and a hydraulically actuated parking brake.

The hydraulically actuated service brake is configured for braking the vehicle. In particular, the hydraulically actuated service brake is configured for braking the vehicle if the parking brake fails. The service brake comprises a service brake cylinder and a disk pack unit. The service brake cylinder is configured to transfer a service braking force induced by a master brake cylinder, in particular a one-stroke brake piston and/or two-stroke brake piston, in operation to the disk pack unit while braking. For example, the master brake cylinder provides a braking force depending on a deflection of a braking pedal. The disk pack unit is configured for braking the vehicle depending on the braking force. Depending on the braking force induced, the one or more disks of the disk pack unit cause the braking of a vehicle. Usually, an increased number of disks or a larger diameter of the disks may increase the braking effect of the vehicle.

The disk pack unit may comprise one or more disks. The disk pack unit may be a dry disk brake or a wet disk brake. Preferably, the disk pack unit is a lamellar brake. In particular, the disk pack unit comprises a brake piston for braking. Usually, while braking, the brake piston the one or more disks of the disk pack unit are in mechanical contact with one another for braking the vehicle.

The hydraulically actuated parking brake is a spring applied hydraulic release brake that is configured for braking the vehicle depending on a parking brake force. The parking brake comprises a spring braking unit, a hydraulic park braking control unit, and a parking brake cylinder.

The brake device may comprise a brake device housing. Preferably, the service brake cylinder and the disk pack unit are arranged inside a housing. In particular, the brake device housing incorporates the service brake and the parking brake, most preferably in a fluid tight manner. It may be preferred that the brake device housing is a multi-piece housing. Preferably, the brake device housing could include a first housing unit and a second housing unit that are connected to each other in a fluid-tight manner. In particular, the first housing unit may incorporate the service brake and the second housing unit may incorporate the parking brake. It is to be understood that, preferably, the braking pack unit is provided in the housing, in particular in the first housing. Preferably, the disk pack unit comprises disks that are coupled to the housing, in particular to the first housing, in a torque-proof manner. Further, preferably, the disk pack unit comprises disks that are coupled to an axis in a torque-proof manner, wherein the axis may in turn be coupled to wheels of the vehicle in a torque-proof manner. It is to be understood that some or all disks of the disk pack unit are mounted axially displaceable. In particular, the disks that are coupled to the housing in a torque-proof manner may be mounted to the housing in an axially displaceable manner. Further, preferably, the disks that are coupled to the axis in a torque-proof manner may be mounted to the axis in an axially displaceable manner.

Preferably, the service brake and/or the parking brake are hydraulically coupled to a hydraulic source for actuating the service brake and/or the parking brake. In particular, the braking device comprises a first hydraulic source and a second hydraulic source that is different from the first hydraulic source. In particular, the first hydraulic source is for hydraulically actuating the service brake and the second hydraulic source is for hydraulically actuating the parking brake. Preferably, the brake device housing comprises a first and second hydraulic connection. In particular, the first housing unit comprises the first hydraulic connection and the second housing unit comprises the second hydraulic connection. The first hydraulic connection may be connected with a first hydraulic source and the second hydraulic connection may be connected with a second hydraulic source. It could be preferred that the first and second hydraulic source are the same hydraulic source. However, most preferably, the first and second hydraulic source are different hydraulic sources. The hydraulic connections are configured to be connected to the respective hydraulic source via hose, pipes or alike. Those hose, pipes or alike need to be configured to provide a pressurized hydraulic medium from the respective hydraulic source to the service brake and/or parking brake. The first and second hydraulic source are some kind of pump or alike. For example, the hydraulic source may be a two-stroke piston, a vibration pump, a rotatory pump or alike. In particular, it is preferred that the first hydraulic source is the maser brake cylinder. Further preferably, the second hydraulic source is a hydraulic accumulator, a hydraulic pump or alike. Preferably, the control valve is arranged between the second hydraulic source and the parking brake for controlling, i.e. actuating and/or releasing the parking brake. In particular, depending on the control valve the release force is controlled.

Preferably, the brake device comprises a braking pedal. In particular, the braking pedal is connected with the first hydraulic source, preferably the master brake cylinder, in particular a one-stroke brake piston and/or two-stroke piston, for actuating the service brake cylinder. For example, the braking pedal is mechanically connected to the first hydraulic source, preferably the master brake cylinder, in particular the two-stroke piston. Most preferably, the braking pedal and the first hydraulic source, preferably the master brake cylinder, in particular the one-stroke brake piston and/or the two-stroke piston, are coupled for force transmission for braking the vehicle.

The spring braking unit is configured to generate a default parking brake force and to transfer the default parking brake force onto the parking brake cylinder. Preferably, the spring braking unit comprises or is a pressure or compression spring. Alternatively, the spring braking unit may also be or comprise a tension spring. The default parking brake force may depend on the stiffness and deflection of the spring unit.

The hydraulic park braking control unit is configured to generate a release force and to transfer the release force onto the parking brake cylinder in order to control the parking brake force. The parking brake cylinder is in mechanical contact with the disk pack unit. The parking brake cylinder is configured to transfer the parking braking force to the disk pack unit while braking depending on the control parking brake force and the default parking brake force. In particular, the parking brake cylinder and the disk pack unit are coupled for force transmission for braking the vehicle. Preferably, it is to be understood that merely the default parking brake force is transferred onto the parking brake cylinder if no hydraulic pressure is supplied to the parking brake. Thus, in this case, the parking brake supports the braking of the vehicle. If the parking brake is supplied with a hydraulic pressure, the release force generated acts in opposite direction of the default parking brake force. In this case, the braking of the vehicle is supported less by the parking brake. If the release force is equal to or exceeds the default parking brake force, the parking brake does not contribute to braking the vehicle at all. If the release force is smaller than the default parking brake force the parking brake contributes to braking the vehicle. In particular, the park braking cylinder is pressed against the disk pack unit, which leads to braking the vehicle. In particular, the parking brake cylinder is in mechanical contact with the disk pack unit if the release force hydraulically generated is smaller than the default parking brake force generated by the spring braking unit. Preferably, the parking brake cylinder is not in mechanical contact with the disk pack unit if the release force hydraulically generated is equal to or larger than the default parking brake force generated by the spring braking unit.

The hydraulic park braking control unit comprises a control valve that is hydraulically connected to the parking brake configured for controlling a hydraulic pressure inside of the parking brake depending on a braking signal for hydraulically actuating and/or releasing the parking brake. In particular, the control valve is configured to actuate the parking brake, in particular the spring applied hydraulic release brake, with a constant supply pressure. Depending on the control valve it is controlled to what degree the parking brake contributes to braking the vehicle as described above.

For example, a braking signal is a signal to brake the vehicle by means of the braking device. The braking signal may be a mechanical signal or an electric signal. For example, a braking signal may be generated by means of actuating a braking pedal. The braking pedal may be mechanically coupled to the parking brake in such a manner that, when actuating the braking pedal and, thus, generating a braking signal, the parking brake is actuated and/or release. In this case, the braking signal represents the degree of deflection of the braking pedal. For example, the braking signal may be defined as “zero” if the braking pedal is not actuated and, thus, not deflected and “one” if the braking pedal is fully actuated, i.e. fully deflected. Accordingly, if the braking pedal is fully deflected, the control valve is positioned in a pressure-release-position such that hydraulic pressure inside of the parking brake is minimized or equal to the atmospheric pressure in order to apply to default braking force provided by the spring braking unit onto the disk pack unit. In this position the hydraulic media is pushed outside of the parking brake by means of the spring braking unit. If, for example, the braking pedal is not deflected at all, the control valve is positioned in a pressure build-up-position such that hydraulic pressure inside of the parking brake is largerthan the default parking brake force induced by the spring braking unit.

By that the disk pack unit is already emptying the oil volume and slightly compressing the brake disc respectively the brake disks of the disk pack unit using the default parking brake force generated by the spring braking unit. Therefore, the service brake cylinder is not needed to provide the full oil volume and so a pedal actuation, for example an actuation angle, is greatly reduced. Since a one-stroke brake piston and/or a two-stroke piston is used the piston can directly shift over to the high force ratio and enable high brake forces at low brake pedal forces. In particular, since the invention reduces the oil volume needed for braking by using the spring applied hydraulically release brake, a one-stroke brake piston and/or a two-stroke piston of a smaller size may be used in comparison to regular braking devices.

Preferably, the hydraulically actuated service brake is part of a hydraulic service brake circuit and the parking brake is part of a hydraulic parking brake circuit that is hydraulically separate from the service brake circuit. In particular, in operation, the service brake cylinder is configured to transfer the service braking force to a disk pack unit while braking independent of the parking brake cylinder. This means that actuating the service brake cylinder by means of the master brake cylinder may lead to actuating the disc pack unit, i.e. bringing the discs of the disk pack unit in friction contact for braking regardless of whetherthe parking brake is actuated or not.

Due to safety reasons and legal requirements, it is to be understood that the service brake cylinder of the service brake is different from the parking brake cylinder of the parking brake. In particular, the service brake cylinder and the parking brake cylinder are two different components of the braking device.

In particular, the service brake and the parking brake may only be mechanically interconnected during a braking operation via the disk pack unit. Preferably, the disk pack unit is arranged between the service brake cylinder and the parking brake cylinder. Preferably, the service brake cylinder and the parking brake cylinder are arranged coaxially to each other.

In particular, the service brake cylinder comprises a service brake cylinder braking surface that comes into contact with the disk pack unit when the service brake is actuated and a service brake cylinder actuation surface that is in contact with the hydraulic media for braking the vehicle by means with the service brake. Preferably, the service brake cylinder braking surface is identical to the service brake cylinder actuation surface.

It is preferred that the service brake cylinder braking surface and the service brake cylinder actuation surface are arranged opposite to each other.

In particular, the service brake cylinder braking surface and/or the service brake cylinder actuation surface are annular shaped. Alternatively, it may be preferred that the service brake cylinder braking surface and/or the service brake cylinder actuation surface are kidney-shaped.

Preferably, the area of the area of the service brake cylinder braking surface is identical to the service brake cylinder actuation surface. It may be preferred that the area of the service brake cylinder braking surface is largerthan the area of the service brake cylinder actuation surface. Alternatively, it may be preferred that the area of the service brake cylinder braking surface is smaller than the area of the service brake cylinder actuation surface.

In particular, the parking brake cylinder comprises a parking brake cylinder braking surface that comes into contact with the disk pack unit when the parking brake is actuated for braking the vehicle and a parking brake cylinder actuation surface that comes into contact with the spring braking unit for providing a default braking force. Further, it is preferred that the parking brake cylinder comprises a parking brake cylinder opening surface that is in contact with hydraulic media for releasing the parking brake or minimizing the braking force provided by the parking brake.

It is preferred that the parking brake cylinder braking surface and the parking brake cylinder actuation surface are arranged opposite to each other. Further preferably, the parking brake cylinder opening surface is aligned opposite to the parking brake cylinder actuation surface and/or on the same side as the parking brake cylinder braking surface.

In particular, the parking brake cylinder braking surface and/or the parking brake cylinder actuation surface and/or the parking brake cylinder opening surface are annular shaped. Alternatively, it may be preferred that the parking brake cylinder braking surface and/or the parking brake cylinder actuation surface and/or the parking brake cylinder opening surface are kidney-shaped.

Preferably, the parking brake cylinder braking surface is identical to the parking brake cylinder actuation surface. Preferably, the area of the parking brake cylinder braking surface is identical to the parking brake cylinder actuation surface. It may be preferred that the area of the parking brake cylinder braking surface is larger than the area of the parking brake cylinder actuation surface. Alternatively, it may be preferred that the area of the parking brake cylinder braking surface is smaller than the area of the parking brake cylinder actuation surface. Further, it is preferred that the area of the parking brake cylinder braking surface is smaller than the parking brake cylinder opening surface. In particular, it may be preferred that the parking brake cylinder opening surface is smaller than the parking brake cylinder braking surface.

Since the service brake and the parking brake are used as a whole, the braking device is also compliant with legal requirements.

According to a preferred embodiment the control valve is a proportional valve and/or a 3/2 directional valve and/or a spring reset valve. Such a valve allows safe operation of the brake device and is easy to operate. Further, such a device may be easily signal coupled to existing devices and an existing control unit of the vehicle.

Based upon a further preferred embodiment, the braking device comprises a sensor unit that is adapted for detecting the braking signal for braking the vehicle.

Yet in another preferred embodiment, the sensor unit comprises an angle sensor that is configured for detecting an angle of a braking pedal, and/or a position sensor that is configured for detecting a position of the braking pedal and/or a position of the service brake cylinder, and/or a hydraulic pressure sensor that is configured for detecting a hydraulic pressure inside of the parking brake. In particular, by using the angle sensor that is configured for detecting an angle of a braking pedal, the spring applied hydraulic release brake can be applied proportionally to the service brake actuation.

According to a further preferred embodiment, the control valve controls the hydraulic flow into the parking brake for releasing the parking brake and/or out of the parking brake for braking the parking brake depending on the braking signal detected by the sensor unit.

Further, according to a preferred embodiment, the parking brake is configured to being actuated depending on an opening pressure, and/or the service brake is configured to being actuated depending on an actuation pressure. Preferably, the opening pressure is the pressure for releasing the parking brake. In particular, the opening pressure is to defined depending on the area of the parking brake cylinder release surface. In particular, the opening pressure is to be selected in such a manner that the release force resulting depending on the opening pressure and the area of the parking brake cylinder release surface is larger than the default parking brake force. The actuation pressure is the pressure for actuating the service brake, i.e. for pressing the service brake cylinder, in particular the service brake cylinder braking surface against the disk pack unit for braking. According to yet another preferred embodiment, the service brake comprises a hydraulic service braking control unit that is configured to generate the service braking force and to transfer the service braking force to the service brake cylinder, wherein preferably, the hydraulic service braking control unit comprises a master brake cylinder that is hydraulically connected to the service brake cylinder for generating the service braking force and/or a brake pedal that is connected to the master brake cylinder. Preferably, the hydraulic service braking control unit comprises the first hydraulic source. In particular, the first hydraulic source is the master brake cylinder.

According to a further aspect of the invention, the object is achieved by a braking system for braking a vehicle according to claim 8. In particular, the braking system is adapted for braking a mobile working machine, preferably for braking a compact wheel loader.

The braking system comprises a braking device as described above. Further, the braking system comprises a hydraulic pump for providing a hydraulic medium inside of the parking brake, and/or a hydraulic accumulator for providing a hydraulic medium inside of the parking brake, and/or a check valve, preferably arranged between the hydraulic pump and the control valve, in particular arranged between the pump and the hydraulic accumulator.

Preferably, the braking device, in particular the parking brake, and/or the hydraulic pump and/or the hydraulic accumulator and/or the check valve and/or the control valve are in fluid communication. Preferably, the control valve is arranged between the parking brake and the hydraulic pump. Further preferably, the check valve is arranged between the control valve and the hydraulic pump. In particular, the hydraulic accumulator is arranged between the control valve and the hydraulic pump, more preferably between the control valve and the check valve.

As to the advantages, preferred embodiments and details of the braking system, reference is made to the corresponding aspect and embodiments of the brake device described herein above as well as of the further aspects and their embodiments described herein below.

According to a further aspect of the invention, the object is achieved by a vehicle according to claim 9. In particular, the vehicle is a mobile working machine, preferably a compact wheel loader. The vehicle comprises a braking device and/or a braking system as described above. As to the advantages, preferred embodiments and details of the vehicle, reference is made to the corresponding aspect and embodiments of the brake device and/or braking system described herein above as well as of the further aspects and their embodiments described herein below.

According to a further aspect of the invention, the object is achieved by a method according to claim 10 for braking a vehicle as described above. In particular, the method is adapted for a mobile working machine, preferably for a compact wheel loader.

The vehicle comprises a braking device and/or a braking system as described above.

The method comprises the step of determining the braking signal detected by a sensor unit, wherein preferably, the braking signal is an angle of a braking pedal and/or a position of the braking pedal and/or a position of the service brake cylinder and/or the master brake cylinder, and/or the hydraulic pressure inside of a parking brake; and the step of controlling the hydraulic pressure inside of the parking brake and/or the service brake depending on the determined braking signal for hydraulically actuating and/or releasing the parking brake in order to brake the vehicle.

As to the advantages, preferred embodiments and details of the method, reference is made to the corresponding aspect and embodiments described herein above as well as of the further aspects and their embodiments described herein below.

According to a preferred embodiment of the method the parking brake is actuated depending on, in particular proportionally to, the determined braking signal, in a regular operation of the parking brake. Proportionally to the brake signal input provided by the sensor unit to the spring applied hydraulic release brake is actuated by the hydraulic park braking control unit to conduct the service brake request of the driver. The hydraulic service braking control unit has only minor impact to the brake characteristic. In particular, the parking brake is in regular operation if the parking brake is not in a failure operation. Preferably, the parking brake is in regular operation, if the vehicle and/or the parking brake itself are not malfunctioning due to a defect or a damage of the parking brake and/or vehicle. In particular, the parking brake is in failure operation, if the vehicle and/or the parking brake itself are malfunctioning due to a defect or a damage of the parking brake and/or vehicle.

Additionally or alternatively, the service brake is actuated depending on the determined braking signal in a failure operation of the parking brake. In case of a failure of the hydraulic park braking control unit brake actuating the spring applied hydraulic release brake, the hydraulic service braking control unit conducts the service brake request of the driver. In this case, the hydraulic service braking control unit has fully impact to the brake characteristic.

According to a further preferred embodiment, the parking brake is released if the control parking brake force resulting from the hydraulic pressure inside of the parking brake is larger than the default parking brake force induced by the spring brake unit. Additionally or alternatively, the parking brake is hydraulically actuated if the control parking brake force resulting from the hydraulic pressure inside of the parking brake is smaller than the default parking brake force induced by the spring brake unit.

According to a further aspect of the invention, the object is achieved by a computer program according to claim 13. The computer program comprises program code means for performing the steps described above when said program is run on a computer.

As to the advantages, preferred embodiments and details of the computer program, reference is made to the corresponding aspect and embodiments described herein above as well as of the further aspects and their embodiments described herein below.

According to a further aspect of the invention, the object is achieved by a computer readable medium according to claim 14. The computer readable medium is carrying a computer program comprising program code means for performing the steps described above when said program product is run on a computer.

As to the advantages, preferred embodiments and details of the computer readable medium, reference is made to the corresponding aspect and embodiments described herein above as well as of the further aspect and their embodiments described herein below.

According to a further aspect of the invention, the object is achieved by a control unit according to claim 15. The control unit is configured for controlling a braking device described above and/or for controlling a braking system described above, wherein the control unit is configured to perform the steps described above.

As to the advantages, preferred embodiments and details of the control unit, reference is made to the corresponding aspect and embodiments described herein above. Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

In the drawings:

Fig. 1 is a schematic view of a vehicle in a preferred embodiment;

Fig. 2 is a schematic view of a braking system in a preferred embodiment;

Fig. 3 is a schematic view of a braking system in a preferred embodiment based upon the braking device shown in Fig. 2; and

Fig. 4 is a schematic block diagram of the method in a preferred embodiment.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Figure 1 is a schematic view of a vehicle 3 in a preferred embodiment having a braking system 2 in a preferred embodiment. The braking system 2 comprises a braking device 1 .

Figure 2 is a schematic view of a braking device 1 in a preferred embodiment. The braking device 1 is adapted for braking compact wheel loader or a vehicle 3 alike.

The braking device comprises a hydraulically actuated service brake 10. The service brake 10 is configured for braking the compact wheel loader s. For this purpose, the service brake 10 comprises a service brake cylinder 11 and a disk pack unit 12. The service brake cylinder 1 1 is configured to transfer a service braking force to the disk pack unit 12 while braking the compact wheel loader 3. The disk pack unit 12 is configured for braking the compact wheel loader s depending on the braking force.

Furthermore, the braking device comprises a hydraulically actuated parking brake 20. The parking brake 20 is a spring applied hydraulic release brake. The spring applied hydraulic release brake is configured for braking the compact wheel loader 3 depending on a parking brake force. For this purpose, the parking brake 20 comprises a spring braking unit 21 , a hydraulic park braking control unit 23, and a parking brake cylinder 22.

The spring braking unit 21 is configured to generate a default parking brake force and to transferthe default parking brake force onto a parking brake cylinder 22. The hydraulic park braking control unit 23 is configured to generate a release force and to transferthe release force onto the parking brake cylinder 22 in order to control the parking brake force. Finally, the parking brake cylinder 22 is in mechanical contact with the disk pack unit 12. Thereby, the parking brake cylinder 22 is configured to transfer the parking braking force to the disk pack unit 12 while braking depending on the control parking brake force and the default parking brake force.

The hydraulic park braking control unit 23 comprises a control valve 24. The control valve 24 is hydraulically connected to the parking brake 20 and configured for controlling a hydraulic pressure inside of the parking brake 20. The hydraulic pressure inside of the parking brake 20 is controlled depending on a braking signal for hydraulically actuating and/or releasing the parking brake 20.

Figure 3 is a schematic view of a braking system 2 in a preferred embodiment based upon the braking device 1 as elaborated above with respect to Figure 2.

In this preferred embodiment, the control valve 24 is a proportional 3/2 directional valve with a spring reset. The control valve 24 controls the hydraulic flow into the parking brake 20 for releasing the parking brake 20 and out of the parking brake 20 for braking the parking brake 20 depending on the braking signal detected by a sensor unit 30. The sensor unit 30 is adapted for detecting the braking signal for braking the compact wheel loader 3. Hereto, the sensor unit 30 may comprise different kind of sensors that are adapted to detect a respective braking signal. For example, the sensor unit may comprise an angle sensor, a position sensor, and/or a hydraulic pressure sensor. In this preferred embodiment, the sensor unit 30 comprises an angle sensorthat is configured for detecting an angle of a braking pedal 3a.

For controlling the braking of the compact wheel loader, the service brake 10 comprises a hydraulic service braking control unit 40 that is configured to generate the service braking force and to transfer the service braking force to the service brake cylinder 11 . In this preferred embodiment, the hydraulic service braking control unit 40 comprises a master brake cylinder 41 that is hydraulically connected to the service brake cylinder 1 1 for generating the service braking force. It is to be understood that the parking brake 20 is actuated depending on an opening pressure and the service brake 10 is actuated depending on an actuation pressure.

Figure 4 is a schematic block diagram of the method 1000 in a preferred embodiment. The method comprises the step of determining 1010 the braking signal detected by a sensor unit 30. In this preferred embodiment, the braking signal is an angle of the braking pedal 3a. However, it is to be understood that the braking signal could also be a signal of a position of the braking pedal 3a and/or a position of the service brake cylinder 11 , and/or the hydraulic pressure inside of a parking brake 20.

Further, the method comprises the step of controlling 1020 the hydraulic pressure inside of the parking brake 20 and the service brake 10 depending on the determined braking signal for hydraulically actuating and releasing the parking brake 20 in order to brake the compact wheel loader s. In this preferred embodiment, in a regular operation of the parking brake 20, the parking brake 20 is actuated depending on and proportionally to the determined braking signal. Further, in a failure operation of the parking brake 20, the service brake 10 is actuated depending on the determined braking signal.

According to this preferred embodiment, the parking brake 20 is released if the control parking brake force resulting from the hydraulic pressure inside of the parking brake 20 is larger than the default parking brake force induced by the spring brake unit. In turn, the parking brake 20 is hydraulically actuated if the control parking brake force resulting from the hydraulic pressure inside of the parking brake 20 is smaller than the default parking brake force induced by the spring brake unit.

Reference signs

1 braking device

2 braking system

3 vehicle 3a braking pedal

10 service brake

11 service brake cylinder

12 disk pack unit

20 parking brake 21 spring braking unit

22 parking brake cylinder

23 hydraulic park braking control unit

24 control valve

30 sensor unit 40 hydraulic service braking control unit

41 master brake cylinder

50 hydraulic pump

60 hydraulic accumulator

70 check valve