BRAKE SYSTEM

Description

[0001] The invention relates to a braking device of a mobile working machine with at least two brake circuits of a service brake, wherein one brake circuit comprises a directly actuated brake and the other brake circuit comprises an indirectly actuated external force brake, wherein the brake circuits are coupled via a common electronic control unit, wherein each brake circuit is operatively connected to a brake signal generator assigned to the respective brake circuit, which is configured to generate brake signals with which the respective brake circuit is controlled, and wherein each brake circuit has at least one brake pressure sensor and / or brake force sensor for measuring brake pressures or brake forces in the respective brake circuit, wherein the electronic control unit is operatively connected to the brake signal generators and the brake pressure sensors and / or brake force sensors and is configured toto evaluate the brake signals from the brake signal transmitters as well as the sensor data from the brake pressure sensors and / or brake force sensors and to control a variable brake force distribution between the brake circuits.

[0002] For the purposes of this invention, mobile work machines are understood to include industrial trucks, mobile agricultural and forestry equipment, and mobile construction machinery. Industrial trucks include, in particular, forklifts, tractors, and platform trucks. Such mobile work machines typically have a service brake and a parking brake.

[0003] Drum, disc, or multi-disc brakes are typically used as service brakes in mobile machinery. Two different braking concepts are employed: 1. Directly hydraulically or mechanically actuated brakes, which can consist of one or two brake circuits. Both variants can be equipped with a hydraulic, electric, or pneumatic brake booster. 2. Indirectly hydraulically or mechanically actuated brakes in the form of a power-assisted braking system that acts equally on all brake circuits. In power-assisted braking systems, the brake pedal actuation, hydraulically or mechanically, serves as a control variable in a valve to transmit the accumulator pressure of a hydraulic pressure accumulator proportionally to the wheel brake.

[0004] Direct-actuated systems are more commonly used in smaller vehicles, while indirect-actuated systems are used in larger vehicles. The decision is generally made based on pressure and volume requirements, taking into account the length of the brake system's lines.

[0005] Both systems have specific disadvantages: 1. Disadvantages of direct-acting brakes: The direct coupling creates a conflict between minimizing pedal force and minimizing pedal travel. This conflict can only be mitigated by a brake booster. Dual-circuit systems are difficult to design because they often involve different volumes and pressures in the respective brake circuits. Implementing brake assist systems (e.g., for emergency braking) in the hydraulic brake circuit is more challenging. In the event of a power supply failure in systems with brake boosters, significantly increased pedal forces (depending on the use and size of the energy storage devices) make braking difficult. 2. Disadvantages of indirect-acting brakes: If the power supply fails, the number of remaining braking maneuvers depends on the size and fill level of the energy storage device, such as a hydraulic pressure accumulator.Braking with an empty energy storage device, such as a hydraulic accumulator, is not possible. This is problematic during long ramp drives, towing operations, or when a parked vehicle rolls away. This results in a greater dependence on the functionality and modulation of the parking brake. With an empty energy storage device, such as a hydraulic accumulator, only the parking brake remains as a braking system. The vehicle cannot be driven until the energy storage device, such as a hydraulic accumulator, is charged. In a dual-circuit system, one energy storage device, such as a hydraulic accumulator, is required for each brake circuit. Achieving satisfactory sensitivity and modulation requires significant development effort.If the external power source (energy storage) fails in a single-circuit system, either braking is impossible (with positive actuation) or an uncontrollable full stop occurs (with negative actuation, for example, a hydraulically released spring-applied brake).

[0006] From EP 2 724 903 A2 a braking device for working machines and a method for actuating the braking device are known.

[0007] EP 3 034 369 A1 discloses a mobile working machine with a braking device.

[0008] A hydraulic vehicle braking system is known from US patent 2001 / 022254 A1.

[0009] EP 3 683 111 A1 discloses a braking device for a working machine.

[0010] In DE 10 2018 111 451 A1 a braking device of a mobile working machine is described in which the disadvantages described are to be reduced by combining two braking circuits, one of which is a directly actuated muscle-powered brake and the other of which is an indirectly actuated external power brake.

[0011] The brake circuits of such dual-circuit braking systems should ideally be designed and controlled separately. A fault in one of the two brake circuits should not cause the failure of both. However, both brake circuits of a dual-circuit braking system are usually controlled by a single signal source. The brake circuits are controlled either by pedal pressure or by the travel of a brake pedal.

[0012] Another problem with dual-circuit braking systems is that the vehicle's maximum braking deceleration must be appropriate for its weight. High braking forces result in a loss of traction in a light vehicle, and insufficient braking forces produce too little deceleration in a heavy vehicle.

[0013] In state-of-the-art dual-circuit braking systems, the individual brake circuits are fixed to the vehicle weight to prevent overbraking or insufficient braking performance. Subsequent adjustments for different vehicle weights and weight distributions are not possible.

[0014] The present invention is based on the objective of providing a braking device that has high reliability and allows adaptation to changing vehicle conditions without structural modifications.

[0015] This problem is solved according to the invention by the fact that the control device is designed to detect a failure of one of the brake signal generators by comparing the brake signals of the brake signal generators and the measured brake pressures and / or brake forces and to issue an error message.

[0016] The brake circuits are linked via a common electronic control unit. This electronic linkage allows for variable adjustment of the brake circuits and improved safety in the event of a fault in one of them.

[0017] According to the invention, each brake circuit is operatively connected to a brake signal generator assigned to that circuit. The brake signal generator is designed to generate brake signals that control the respective brake circuit. Furthermore, each brake circuit has at least one brake pressure sensor and / or brake force sensor for measuring brake pressures or braking forces within that circuit. The electronic control unit is operatively connected to the brake signal generators and the brake pressure and / or brake force sensors. The control unit is designed to evaluate the brake signals from the brake signal generators and the sensor data from the brake pressure and / or brake force sensors, and to control a variable brake force distribution between the brake circuits.

[0018] According to the invention, the control device is designed to detect a failure of one of the brake signal generators by comparing the brake signals of the brake signal generators and the measured brake pressures and / or brake forces and to issue an error message.

[0019] A preferred embodiment of the invention provides that the brake circuit with the indirectly actuated brake is designed as a hydraulic brake circuit with a hydraulic pressure accumulator as an external energy storage device, wherein the brake signal generator associated with this brake circuit comprises an operating lever or an operating pedal with lever-travel or pedal-travel-dependent brake signal generation, and wherein the control device is operatively connected to a controllable pressure reducing valve, in particular an electrically controlled pressure reducing valve, connected to the pressure accumulator, such that lever-travel or pedal-travel-dependent brake pressure control is enabled. The operating lever can, for example, have a manually operated lever mechanism, for instance in the form of a joystick, so that braking operations can be initiated by hand by the operator of the mobile work machine.A conventional brake pedal or accelerator pedal can be used as the control pedal, so that braking operations can be carried out with the foot, as is generally the case with vehicles.

[0020] The indirect brake can be actuated in two different ways: One variant is that the indirectly actuated power brake is designed as a positively actuated brake with a brake force-triggering actuation mechanism. In this case, actuating the operating lever or pedal, particularly a brake pedal, releases pressure in the power accumulator, depending on the lever or pedal travel, so that a brake pressure proportional to the lever or pedal travel is built up at the brake. In the case of a hydraulic brake circuit, the valve in the hydraulic circuit opens proportionally to the lever or pedal travel, so that the hydraulic fluid is released from the hydraulic pressure accumulator in a precisely metered manner and builds up brake pressure at the brake.

[0021] In another variant, the indirectly actuated power brake is designed as a negatively actuated brake with a release-force-triggering brake actuation. Examples of such power brakes are hydraulically released spring-applied brakes. In this case, the brake actuation is used solely to reduce the hydraulic release pressure in order to trigger the brake pressure that can be applied by a spring mechanism. In the case of a hydraulic brake circuit, the valve in the hydraulic circuit is opened when the operating lever or pedal, particularly the brake pedal, is actuated, depending on the lever or pedal travel, so that the hydraulic release pressure is reduced and the brake pressure generated by the spring mechanism is applied to the brake. This form of brake actuation is particularly suitable for emergency braking.

[0022] According to an advantageous embodiment of the invention, the brake circuit with the directly actuated brake is preferably designed as a hydraulic brake circuit with a hydraulic brake cylinder, wherein the brake signal generator associated with this brake circuit comprises an operating lever or an operating pedal with lever pressure or pedal pressure-dependent brake signal generation, and wherein the brake signal generator is directly in operative connection with the hydraulic brake cylinder, so that lever pressure or pedal pressure-dependent brake pressure control is enabled.

[0023] According to a further development of the invention, the brake circuit with the directly actuated brake is designed as an electric brake circuit with a generator, wherein the brake signal transmitter associated with this brake circuit comprises an operating lever or an operating pedal with lever-travel or pedal-travel-dependent brake signal generation, and wherein the brake signal transmitter is operatively connected to the generator, so that lever-travel or pedal-travel-dependent brake force control is enabled. The regenerative braking effect of an electric traction motor, for example in a battery-electric vehicle, can be used for the electric brake circuit.

[0024] The brake signal generator can advantageously include either a brake pedal or an accelerator pedal. When an accelerator pedal is used as the brake signal generator, the regenerative brake is advantageously fully activated when the accelerator pedal is not depressed. The position of the accelerator pedal can be detected via a pedal travel sensor.

[0025] In a particularly preferred embodiment of the invention, the mobile work machine has at least one electrically driven drive axle and at least one non-driven axle. The directly actuated brake is located on the drive axle, and the indirectly actuated power brake is located on the non-driven axle. Since the indirectly actuated power brake can generate higher braking pressures, it is advantageously used on the non-driven axle, where no further braking power is available. In contrast, the electrically driven axle can generate additional regenerative braking power through one or more electric drive motors. For example, an electric drive motor can convert the vehicle's kinetic energy into electrical energy during braking. In this process, the electric drive motor acts as a generator.Because of this additional braking power, the service brake on this electrically driven axle can be less powerful. Therefore, the directly actuated brake is sufficient here.

[0026] Preferably, the non-driven axle includes a steering axle. This prevents drive influences on the steering.

[0027] Advantageously, the drive axle is configured as the rear axle and the non-driven axle as the front axle of the mobile work machine. In this case, the directly actuated brake is located on the rear axle, while the indirectly actuated power brake, which can apply higher braking pressures, is located on the front axle. This is also advantageous because, generally speaking, the required braking forces are higher at the front axle than at the rear axle of a vehicle.

[0028] A further development of the invention provides that the brake circuit with the indirectly actuated external force brake includes at least one brake assist device. Brake assist devices can be integrated into such brake circuits in a particularly elegant manner.

[0029] Particularly when the indirectly actuated brake circuit is designed as a hydraulic brake circuit, the brake assist system can be integrated with relative ease. The brake assist system preferably comprises an electrically actuated valve that is connected to the hydraulic brake circuit. The electrically actuated valve is advantageously arranged between the hydraulic pressure accumulator and the brake, for example, a drum, disc, or multi-disc brake, in parallel with the pressure reducing valve controlled by the electronic control unit. In this way, the electrically actuated valve can initiate a braking process independently of the brake pedal actuation. The electrically actuated valve is operatively connected to a control unit of the brake assist system. The control unit can thus, for example, initiate emergency braking in detected hazardous situations.

[0030] The braking device according to the invention can be further supplemented by speed sensors, particularly in a front axle of the vehicle. If the wheels lock, the applied pressure can then be reduced again by appropriately controlling the electrically actuated pressure reducing valve on the indirectly actuated external power brake.

[0031] The invention is suitable for all types of mobile work machines, in particular for industrial trucks, mobile agricultural and forestry equipment, and mobile construction machinery. In a particularly preferred embodiment, the mobile work machine is designed as a tractor or platform vehicle.

[0032] The invention offers several advantages: It enables variable brake force distribution between the individual brake circuits of the dual-circuit braking system, thus allowing adaptation to different vehicle weights and weight distributions. Furthermore, it allows for the detection of a failure in either brake circuit if a fault occurs in one circuit. The presence of air in a brake line of the directly actuated brake circuit can also be ruled out by comparing the brake pedal travel with the pressure in the brake line. By controlling the brake circuits from different signal sources, such as the brake pedal travel and pressure, operational safety is significantly increased. The integration of driver assistance systems provides further safety benefits.For example, the brake pressure at the front axle can be built up more slowly than the brake pedal movement using the electrically controlled indirect brake circuit, thus preventing the vehicle from being overbraked. Furthermore, reducing the brake pressure at the front axle can simulate an anti-lock braking system.

[0033] Further advantages and details of the invention are explained in more detail with reference to the exemplary embodiments shown in the schematic figures. These show Figure 1 shows a braking device according to the invention with a dual-circuit braking system with an indirectly actuated hydraulic power brake and a directly actuated hydraulic brake, and Figure 2 shows a braking device according to the invention with a dual-circuit braking system with an indirectly actuated hydraulic power brake and a directly actuated electric generator brake.

[0034] In both figures, the same features are labelled with the same reference numbers.

[0035] In the Figure 1 Figure 1 shows a braking device according to the invention with two brake circuits 15 and 16. The first brake circuit 15 has an indirectly actuated, electrically controlled, hydraulic power brake 20, while the second brake circuit 16 has a directly actuated brake 21 designed as a hydraulically actuated brake. The power brake 20 and the directly actuated brake 21 of the two brake circuits 15 and 16 are actuated by a common control pedal 28, designed as a brake pedal 9. A pedal position sensor 10 is integrated into the brake pedal 9 as a pedal-position-dependent brake signal transmitter 22 of brake circuit 15. Pressing the brake pedal 9 also generates pedal pressure in a pedal pressure line 23, which serves as a pedal-position-dependent brake signal transmitter 24 of brake circuit 16.

[0036] The key element here is the combination of the pedal pressure-dependent, directly actuated hydraulic brake circuit 16 with the pedal travel-dependent, electrically controlled, indirectly actuated hydraulic brake circuit 15.

[0037] The pedal-travel-dependent brake signal generator 22 of the brake circuit 15, designed as a pedal travel sensor 10, is connected to an electronic control unit 8 which controls an electrically controlled pressure reducing valve 5 of the brake circuit 5.

[0038] A pressure accumulator 4 serves as the energy source for pressure build-up in the electrically controlled brake circuit 15. The pressure accumulator 4 is supplied by a hydraulic pump 2, which draws hydraulic fluid from a reservoir 1. A check valve 3 prevents unwanted pressure release from the pressure accumulator 4.

[0039] The signal transmission from the pedal travel sensor 10 of the brake pedal 9 via the electronic control unit 8 to the electrically controlled pressure reducing valve 5 of the brake circuit 15 enables situation-dependent control of the brake pressure at a brake 6 of the brake circuit 15, for example a mechanical multi-disc brake or disc brake 6.

[0040] The second brake circuit 16 is supplied directly via a hydraulic brake cylinder 13, which is coupled to the brake pedal 9 by means of the pedal pressure line 23 and thus to the pedal pressure-dependent brake signal generator 24. The brake cylinder 13 then uses the pedal pressure of the brake pedal 9 to generate pressure at a brake 14 of the brake circuit 16 via a brake line 25, for example a mechanical multi-plate brake or disc brake 14.

[0041] The coupling of brake circuits 15 and 16 is effected via the electronic control unit 8, a brake pressure sensor 11 connected to the control unit 8, which detects the pressure of the second brake circuit 16, and the pedal travel sensor 10 of the first brake circuit 15 connected to the control unit 8 at the brake pedal 9. If brake pressure is detected at the brake pressure sensor 11 of brake circuit 16 without pedal travel at the brake pedal 9, then there is a defect in the pedal travel sensor 10 or in the brake pressure sensor 11.

[0042] To determine the pressure build-up within the first brake circuit 15, a brake pressure sensor 7 is also used here, which is connected to the control unit 8.

[0043] Depending on the vehicle weight, the pressure build-up in the first brake circuit 15 can be varied relative to the pressure build-up in the second brake circuit 16. The braking device according to the invention can therefore be used in vehicles of different weights without any structural or design modifications.

[0044] The Figure 2 Figure 1 shows a variant of a braking device according to the invention with the two braking circuits 15 and 16. Braking circuit 15 corresponds to the illustration of the Figure 1 The brake circuit 16 features, in the variant of the Figure 2 via a directly actuated electric generator brake 17, which is controlled by the control unit 8. By means of a generator M connected to a wheel shaft 26 of the vehicle, which also serves as the electric drive motor of the vehicle, the vehicle can be braked regeneratively.

[0045] The generator M receives the brake signal from the pedal travel sensor 10 on the brake pedal 9.

[0046] Another possibility is to evaluate a control pedal 29 of the vehicle, configured as an accelerator pedal 19, as a brake signal transmitter 27 of the brake circuit 16. When the accelerator pedal 19 is not depressed, the generator brake 17 is fully activated. The position of the accelerator pedal 19 is detected by a pedal travel sensor 18, which is connected to the control unit 8.

Claims

1. Braking device for a mobile working machine having at least two brake circuits (15, 16) of a service brake, wherein one brake circuit (16) comprises a directly actuated brake (21) and the other brake circuit (15) comprises an indirectly actuated power-assisted brake (20), wherein the brake circuits (15, 16) are coupled via a common electronic control device (8), wherein each brake circuit (15, 16) is operatively connected to a brake signal transmitter (22, 24) assigned to the respective brake circuit (15, 16), which brake signal transmitter is configured to generate brake signals with which the respective brake circuit (15, 16) is controlled, and each brake circuit (15, 16) possesses at least one brake pressure sensor (7, 11) and / or brake force sensor for measuring brake pressures or brake forces in the respective brake circuit (15, 16), wherein the electronic control device (8) is operatively connected to the brake signal transmitters (22, 24) as well as to the brake pressure sensors (7, 11) and / or brake force sensors and is configured to evaluate the brake signals of the brake signal transmitters (22, 24) as well as the sensor data of the brake pressure sensors (7, 11) and / or brake force sensors and to control a variable brake force distribution between the brake circuits (15, 16), characterized in that the control device (8) is configured to detect failure of one of the brake signal transmitters (22, 24) by comparing the brake signals of the brake signal transmitters (22, 24) with the measured brake pressures and / or brake forces and to output an error message.

2. Braking device according to Claim 1, characterized in that the brake circuit (15) having the indirectly actuated power-assisted brake (20) is configured as a hydraulic brake circuit (15) having a hydraulic pressure accumulator (4) as a power-assisted accumulator, wherein the brake signal transmitter (22) assigned to this brake circuit (15) comprises an operating lever or an operating pedal (28) with lever-travel- or pedal-travel-dependent brake signal generation, and wherein the control device (8) is operatively connected to a controllable pressure reducing valve (5), in particular an electrically controlled pressure reducing valve (5), connected to the pressure accumulator (4), in such a way that lever-travel- or pedal-travel-dependent brake pressure control is made possible.

3. Braking device according to either one of Claims 1 and 2, characterized in that the brake circuit (16) having the directly actuated brake (21) is configured as a hydraulic brake circuit (16) having a hydraulic brake cylinder (13), wherein the brake signal transmitter (24) assigned to this brake circuit (16) comprises an operating lever or an operating pedal (28, 29) with lever-pressure- or pedal-pressure-dependent brake signal generation, and wherein the brake signal transmitter (24) is directly operatively connected to the hydraulic brake cylinder (13) such that lever-pressure- or pedal-pressure-dependent brake pressure control is made possible.

4. Braking device according to one of Claims 1 to 3, characterized in that the brake circuit (16) having the directly actuated brake (21) is configured as an electrical brake circuit (16) having a generator (M), wherein the brake signal transmitter (22, 27) assigned to this brake circuit (16) comprises an operating lever or an operating pedal (28, 29) with lever-travel- or pedal-travel-dependent brake signal generation, and wherein the brake signal transmitter (22, 27) is operatively connected to the generator (M) such that lever-travel- or pedal-travel-dependent brake force control is made possible.

5. Braking device according to one of Claims 1 to 4, characterized in that the brake signal transmitter (22, 24, 27) comprises a brake pedal (9) or accelerator pedal (19).

6. Braking device according to one of Claims 1 to 5, characterized in that the brake circuit (15) having the indirectly actuated power-assisted brake (20) has at least one brake assistance device.

7. Braking device according to Claim 6, characterized in that, in the case where the brake circuit (15) is configured as a hydraulic brake circuit (15), the brake assistance device comprises an electrically actuated valve in the hydraulic brake circuit (15).

8. Mobile working machine having a braking device according to one of Claims 1 to 7, characterized in that the mobile working machine is configured as a tractor or platform vehicle.