Work machine with redundant hydraulic braking system

Abstract

A working machine with a hydraulic system for controlling a service brake of the working machine, wherein the hydraulic system comprises two redundant hydraulic circuits (100a, 100b) that act on different brake actuators (106a, 106b), wherein the working machine has a primary control unit connected to a first power source and a secondary control unit connected to a second power source, wherein the primary control unit acts on a first of the hydraulic circuits (100a, 100b) and the secondary control unit acts on a second of the hydraulic circuits (100a, 100b), characterized in that the working machine is configured to transmit a received brake signal (51, 61) from the primary control unit to the secondary control unit in normal operation and, in emergency operation, to transmit a received brake signal (51, 61) to the secondary control unit, bypassing the primary control unit, which is configuredto implement this signal in the second hydraulic circuit.

Description

[0001] The invention relates to a working machine with a redundant and variably controllable hydraulic system for controlling a service brake.

[0002] Redundant hydraulic systems for controlling the service brakes of working machines are known in the prior art. For example, DE 103 25 875 A1 discloses a brake system with two hydraulic circuits, each with an associated brake actuator. Each hydraulic circuit comprises a brake valve and a mechanical-hydraulic pilot control.

[0003] Further brake systems are disclosed in DE 100 28 094 A1 and in DE 100 36 286 A1.

[0004] In the context of advancing vehicle automation for the implementation of remote control and autonomous driving concepts, extensions to existing redundant hydraulic systems for controlling service brakes are necessary. In particular, the redundancies must be fully maintained even when converting to electrical signals.

[0005] The object of the invention is to provide a redundant hydraulic system for controlling the service brakes of working machines, which allows the implementation of electrical braking commands and remains completely redundant.

[0006] Against this background, the invention relates to a working machine with a hydraulic system for controlling a service brake of the working machine, wherein the hydraulic system comprises two redundant hydraulic circuits that act on different brake actuators, wherein the working machine has a primary control unit connected to a first power source and a secondary control unit connected to a second power source, and wherein the primary control unit acts on a first of the hydraulic circuits and the secondary control unit acts on a second of the hydraulic circuits.

[0007] The two control units are autonomous due to the separate power supplies, and the service brake also functions in the event of failure or malfunction of the primary control unit or the first power source, since the second of the hydraulic circuits is controlled autonomously.

[0008] The primary control unit can be the central control unit of the machine. The secondary control unit can be a dependent emergency running unit with less functionality than the primary control unit. The two power sources can be different batteries.

[0009] In the case of a disc brake, the brake actuators can comprise a brake piston that acts on a brake disc, or in the case of a drum brake, a spreading wedge or brake cylinder that acts on a brake drum. The brake actuators can act on different axles of the machine, or alternatively, they can act on the same axle or even the same wheel.

[0010] The hydraulic circuits can still have separate hydraulic supplies, preferably separate hydraulic accumulator groups. In the case of supply by electrically driven pumps, the hydraulic pump of the first hydraulic circuit can be supplied by the first power source and the hydraulic pump of the second hydraulic circuit by the second power source.

[0011] In one conceivable embodiment, it can therefore be provided that the hydraulic pump of the first hydraulic circuit is connected to the first power source and the hydraulic pump of the second hydraulic circuit is connected to the second power source.

[0012] The redundancy therefore preferably extends not only to the signaling but also to the supply of the hydraulic circuits.

[0013] It may be provided that the primary control unit and the secondary control unit each have a receiver unit in order to receive a brake signal independently of each other. Preferably, the receiver units are configured for wireless reception of brake signals from a remote control or for wireless or wired reception of brake signals from a transmitter of an autonomous vehicle control system.

[0014] The two receiving units can be configured to receive different types of signals. For example, the receiving unit of the primary control unit can be configured to receive a digital signal, while the receiving unit of the secondary control unit can be configured to receive an analog signal. The braking signal can thus be transmitted redundantly to both the primary and secondary control units via two different channels.

[0015] In one embodiment, the primary and secondary control units are interconnected via signals. Preferably, the primary control unit is configured to forward a received brake signal to the secondary control unit, and the secondary control unit is configured to convert this signal in the second hydraulic circuit. The secondary control unit can be configured to treat any control signal received elsewhere as a secondary signal and only convert it if no brake signal is received from the primary control unit.

[0016] In one embodiment, the machine or its braking system can be operated in normal mode, in which no fault is present, and in emergency mode, in which a fault is present. According to the invention, the machine is configured to transmit a received brake signal from the primary control unit to the secondary control unit in normal mode, and in emergency mode, a received brake signal is transmitted to the secondary control unit, bypassing the primary control unit. The secondary control unit is configured to convert this signal in the second hydraulic circuit.

[0017] Preferably, each of the two hydraulic circuits has an electrically controlled section with a working line, on which an electrically actuated release valve and an electrically actuated control valve are arranged in series. The release valve and the control valve of the first hydraulic circuit are signal-connected to the primary control unit. The release valve and the control valve of the second hydraulic circuit are signal-connected to the secondary control unit.

[0018] The release valves are preferably normally closed directional control valves which, in the open position, establish a hydraulic connection between the respective control valve and a pressure source, preferably hydraulic supply units, preferably separate hydraulic accumulator groups or hydraulic pumps. In the closed position, the connection between the pressure source and the control valve is interrupted. Instead, a return flow connection from the control valve to a manifold is preferably opened.

[0019] The valves are preferably energized and open.

[0020] The control valves are preferably electrically adjustable pressure reducing valves, which are preferably normally closed (de-energized) and whose pressure limit decreases with increasing current. In the at least partially open switching position, provided the release valve is also open, the pressure source and the brake actuator are hydraulically connected to generate a braking effect. In the closed switching position, this connection is interrupted. Preferably, a return flow connection to a manifold is opened instead.

[0021] In one embodiment of the invention, the two hydraulic circuits each have a mechanically controlled section with a working line, to which a brake valve is arranged, actuated mechanically and / or mechanically-hydraulically by means of a preferably common brake pedal. The brake valves are preferably pressure-reducing valves in which the output pressure increases with the current applied or, in the case of the pedal, with the actuation angle / force.

[0022] It is conceivable that these valves are closed in the brake pedal's initial position and that their pressure limit decreases with increasing pressure on the brake pedal or its angle, or that their initial pressure increases with increasing actuation angle / force. In the closed switching position, a return flow connection to a collector is preferably opened.

[0023] The working lines of the electrically controlled and mechanically controlled sections of the two hydraulic circuits can each combine at a changeover valve, which passes the pressure of the higher-pressured working line to the brake actuator.

[0024] In another embodiment of the invention, a brake pedal with sensors for detecting the pedal position is arranged in the machine, the sensors being signal-connected to the primary and secondary control units. In this embodiment, a mechanically controlled section as described above is preferably omitted in both hydraulic circuits. The signal connection can be wired. The sensors preferably comprise electrical sensors for detecting a linear or angular position of the brake pedal. In this way, a mechanical brake actuation can be completely eliminated, and the brake commands from either a transmitter, optionally a remote control, or a brake pedal can be implemented purely electronically.

[0025] The sensors can be implemented redundantly, with a first sensor for detecting the pedal position being connected to the primary control unit and a second sensor for detecting the pedal position being connected to the secondary control unit. The processing of the sensor signals at the control units preferably occurs analogously to the processing of brake signals received at the respective receivers of the control units.

[0026] The first sensor can be connected to the first power source and the second sensor to the second power source. This ensures the complete autonomy of the redundant systems.

[0027] In one embodiment, branch lines extend from the final sections of the working lines of the two hydraulic circuits, where the pressure acting on the brake actuator is present. These branch lines converge at a further changeover valve, which directs the higher pressure to a hydraulic switch of a brake light and / or to a pressure sensor. The pressure sensor can be connected to the primary control unit of the wheel loader. The primary control unit can be configured to perform a functional check of the enabling and regulating valves using the pressure sensor signal, for example, when the wheel loader is started up.

[0028] In a preferred embodiment, the machine according to the invention can be a wheel loader.

[0029] Further details and advantages of the invention will become apparent from the exemplary embodiment discussed below with reference to the figures. The figures show: Fig. 1: a simplified circuit diagram of a hydraulic braking system of a wheel loader according to the invention in one embodiment; and Fig. 2: a more simplified circuit diagram of the in Fig. 1 hydraulic braking system shown; and Fig. 3: one within the scope of Fig. 2 Simplified circuit diagram of a braking system of a wheel loader according to the invention in an alternative embodiment.

[0030] In Fig. 1 and Fig. Figure 2 shows a simplified and a more simplified circuit diagram of a hydraulic system for controlling a service brake of a wheel loader according to the invention in one embodiment.

[0031] The braking system comprises two redundant hydraulic circuits 100a and 100b, each with separate hydraulic supplies, preferably separate hydraulic accumulator groups. The use of hydraulic pumps 105a and 105b, or other hydraulic supplies, acting on separate brake actuators 106a and 106b, is also conceivable.

[0032] The essentially functionally identical redundant hydraulic circuits 100a and 100b are explained below using the example of the first hydraulic circuit 100a.

[0033] The first hydraulic circuit 100a can itself be divided into two sections: an electrically controlled section 110a and a mechanically controlled section 120a. The working lines of the two sections 110a and 120a join at the changeover valve 130a, which transmits the pressure of the higher-pressured working line to the brake actuator 106a.

[0034] In the working line of the electrically controlled section 110a, a release valve 111a and a control valve 112a are connected in series downstream of the pressure source 105a. Both of these valves 111a and 112a are electrically actuated and signal-connected to the central control unit 50 of the wheel loader.

[0035] The release valve 111a is an electrically actuated, normally closed directional control valve with two switching positions: open and closed. In the open position, the pressure source 105a and the control valve 112a are hydraulically connected. In the closed position, the connection between the pressure source 105a and the control valve 112a is interrupted. Instead, a return flow connection from the control valve 112a to the manifold 99 is enabled.

[0036] Valve 112a is an electrically adjustable pressure reducing valve, where the output pressure increases with the current applied, or, in the case of a pedal, with the actuation angle and / or force. The hydraulic pressure, or output pressure, at control valve 112a increases with increasing current. In the at least partially open switching position, provided the release valve 111a is also open, the pressure source 105a and the changeover valve 130a are hydraulically connected. In the closed switching position, this connection is interrupted. Instead, a return flow connection from the changeover valve 130a to the manifold 99 is opened.

[0037] When the release valve 111a and the control valve 112a are actuated by the central control unit 50 of the wheel loader, the pressure source 105a and the changeover valve 130a are hydraulically connected via the working line of the electrically controlled section 110a. The hydraulic pressure acting on the changeover valve 130a from the electrically controlled section 110a depends on the current applied to the control valve 112a by the central control unit 50 of the wheel loader.

[0038] A brake valve is arranged on the working line of the mechanically controlled section 120a between the pressure source 105a and the changeover valve 130a. The brake valve is a pressure reducing valve actuated mechanically or mechanically-hydraulically by a brake pedal 121, and is closed, for example, in the initial position of the brake pedal 121. The output pressure of the pressure reducing valve increases with the energization or, in the case of the pedal, with the actuation angle and / or force. In the closed switching position, a return flow connection to the collector 99 is opened.

[0039] When the brake pedal 121 is pressed, the pressure source 105a and the changeover valve 130a are hydraulically connected via the working line of the mechanically controlled section 120a. The hydraulic pressure acting on the changeover valve 130a from the mechanically controlled section 120a depends on the force exerted on the brake pedal 121 by the operator of the wheel loader.

[0040] The second hydraulic circuit 100b can also be divided into an electrically controlled section 110b and a mechanically controlled section 120b. The working lines of the two sections 110b and 120b also join at a changeover valve 130b, which transmits the pressure of the higher-pressure working line to the brake actuator 106b. A release valve 111b and a control valve 112b are connected in series downstream of the pressure source 105b on the working line of the electrically controlled section 110b. A brake valve – actuated by the same brake pedal 121 as the brake valve of the first hydraulic circuit 100a – is arranged between the pressure source 105b and the changeover valve 130b on the working line of the mechanically controlled section 120b.For the function, reference can be made to the description of the second hydraulic circuit 100b, with the sole exception that the release valve 111b and the control valve 112b of the second hydraulic circuit 100b are not controlled by the central control unit 50 of the wheel loader, but by a separate and autonomous additional control electronics 60.

[0041] The central control unit 50 and the electrical components of the first hydraulic circuit 100a are connected to the central power supply 53 of the wheel loader. The auxiliary control electronics 60 and the electrical components of the second hydraulic circuit 100b are connected to an autonomous auxiliary power supply 63 of the wheel loader, which includes, for example, a separate battery and remains operational even in the event of a malfunction or failure of the central power supply 53.

[0042] The central control unit 50 of the wheel loader and the auxiliary control electronics 60 each include a built-in receiver unit to independently receive a brake signal 51 or 61, respectively. Each receiver unit is designed to receive the brake signals 51 and 61 from a transmitter, either wired or wirelessly, and is configured to receive different signal types. The receiver unit of the central control unit 50 is designed to receive a digital radio signal, while the receiver unit of the auxiliary control electronics 60 is designed to receive an analog radio signal. The brake signal can thus be transmitted redundantly via two different channels to both the central control unit 50 and the auxiliary control electronics 60.The central control unit 50 and the additional control electronics 60 are also interconnected via signals, for example by means of a wired CAN bus connection 55.

[0043] Preferably, the 51 and 61 are wired signal paths or wired transmitted signals to a higher-level automation control computer and / or remote control receiving unit.

[0044] Alternatively, the brake signal can be received directly and wirelessly at the primary and secondary control units. The entire embodiment applies to both of these signal transmission variants (wired and wireless), regardless of the specific description.

[0045] In normal operation, the central control unit 50 receives a digital brake signal 51 remotely from a transmitter installed in the wheel loader or from an external transmitter and applies this signal directly to the first hydraulic circuit 100a. It also applies this signal to the second hydraulic circuit 100a by forwarding a command to the auxiliary control electronics 60. The analog brake signal 61 received in parallel by the auxiliary control electronics 60 is not processed by the auxiliary control electronics 60 in this case. If the central control unit 50 or the central power supply 53 of the wheel loader fails due to a malfunction, the analog brake signal 61 received in parallel by the auxiliary control electronics 60 is applied directly to the second hydraulic circuit 100a, which corresponds to an emergency function of the service brake.

[0046] The braking concept thus allows for the selective implementation of electrical and mechanical braking commands, namely, on the one hand, the implementation of wired or wireless brake signals 51 or 61, and on the other hand, the implementation of actuations of a brake pedal 121. It also features redundancy with regard to the implementation of both electrical and mechanical braking commands. It is particularly suitable for optionally self-propelled or remotely controlled wheel loaders. Unintentional activation of the brakes is prevented by the normally closed release valves 111a and 111b.

[0047] Beyond the changeover valves 130a and 130b, branch lines extend from the two working lines of the first and second hydraulic circuits 100a and 100b, converging at another changeover valve 140. This second changeover valve 140 supplies the higher pressure to a pressure switch 141 of a brake light and to a pressure sensor 142. The pressure sensor 142 is connected to the central control unit 50 of the wheel loader and can be used, for example, to perform a functional check of the release valves 111a and 111b as well as the control valves 112a and 112b. Such a functional check can be performed, for example, when the wheel loader is put into operation, i.e., when the engine is started.

[0048] In Fig. Figure 3 shows a highly simplified circuit diagram of a hydraulic system for controlling a service brake of a wheel loader according to the invention in an alternative embodiment. Already in the hydraulic system of the Fig. 1 and Fig. Two installed elements are marked with corresponding reference symbols.

[0049] This hydraulic system of Fig. 3 differs from the hydraulic system of the Fig. 1 and Fig. 2. This is achieved by the fact that in both hydraulic circuits 100a and 100b, the mechanically controlled sections 120a and 120b, including brake valves, are completely absent, and instead the brake pedal 121 is equipped with sensors whose signals 52 and 62, respectively, are transmitted, in particular via wired connections, to the central control unit 50 and the auxiliary control electronics 60. The sensors are designed redundantly, with a first complete sensor set connected to the central power supply 53 of the wheel loader and signal-connected to the central control unit 50 via line 54, and with a second complete sensor set connected to the auxiliary power supply 63 of the wheel loader and signal-connected to the auxiliary control electronics 60 via line 64. Each sensor set includes electrical sensors for detecting a linear or angular position of the brake pedal 121.

[0050] The processing of signals 52 and 62 at the control elements 50 and 60 respectively is analogous to the processing of signals 51 and 61, as described in the exemplary embodiment of the Fig. 1 and Fig. 2. Describe.

[0051] In this version, mechanical brake actuation is completely dispensed with, and braking commands from either a transmitter, possibly a remote control, or a brake pedal are implemented purely electronically. In any case, regardless of the type of braking command, two completely autonomous systems exist side by side.

[0052] Preferably, the following sequence occurs during normal operation: Signal 51 - Control unit 50 - Communication via 55 with control unit 60. In emergency operation, signaling occurs without the vehicle control computer 50. In emergency operation, only signal 61 is present, which is read into the control unit 60, which then directly controls the second brake circuit via valves 111b and 112b.

[0053] Preferably, the controllers 50 and 60 are configured differently (design and / or dimensions and / or hardware and / or software), with the communication link 55 serving as the sole signal connection between the controllers. In emergency operation, defined communication is established, for example, with only the second hydraulic circuit. Access by controller 60 to the first control circuit, e.g., of a valve(s), is preferably not provided. Thus, the controller's functionality is simplified in terms of hardware and software and serves as an alternative to pure functional redundancy with mirrored identical components for the first and second hydraulic circuits or hydraulic brake circuit.

[0054] In a preferred embodiment, the control systems are physically separated from each other, and the emergency circuit is operated by a largely self-contained control unit with a completely different hardware and software structure.

[0055] Preferably, the braking request is transmitted from higher-level control units to a largely autonomous small control unit via technologically diverse signal paths. The signal connection preferably exists only in the form of the bus link between the vehicle's main computer and the emergency control unit, with otherwise minimal interconnection.

Claims

[1] Working machine with a hydraulic system for controlling a service brake of the working machine, wherein the hydraulic system comprises two redundant hydraulic circuits (100a, 100b) acting on different brake actuators (106a, 106b), wherein the working machine has a primary control unit connected to a first power source and a secondary control unit connected to a second power source, wherein the primary control unit acts on a first of the hydraulic circuits (100a, 100b) and the secondary control unit acts on a second of the hydraulic circuits (100a, 100b), characterized by, that the working machine is designed to transmit a received brake signal (51, 61) from the primary control unit to the secondary control unit in normal operation and, in emergency operation, to transmit a received brake signal (51, 61) to the secondary control unit, bypassing the primary control unit, which is designed to convert this signal on the second hydraulic circuit. [2] Working machine according to claim 1, characterized by , that the hydraulic circuits have separate hydraulic supplies, wherein in the case of a supply by electrically driven hydraulic pumps (105a, 105b), the hydraulic pump of the first hydraulic circuit is connected to the first power source and the hydraulic pump of the second hydraulic circuit is connected to the second power source. [3] Working machine according to any one of the preceding claims, characterized by, that the primary control unit and the secondary control unit each have a receiving unit in order to be able to receive a braking signal (51, 61) independently of each other. [4] Working machine according to claim 3, characterized by that the two receiving units are designed to receive different types of signals. [5] Working machine according to any one of the preceding claims, characterized by , that the primary control unit and the secondary control unit are interconnected via signals. [6] Working machine according to claim 5, characterized by , that the primary control unit is designed to transmit a received brake signal (51, 61) to the secondary control unit and the secondary control unit is designed to convert this signal to the second hydraulic circuit. [7] Working machine according to any one of the preceding claims, characterized by, that the secondary control unit is designed to implement the braking request on a brake circuit using the redundant signal path in the event of failure of the primary control unit. [8] Working machine according to any one of the preceding claims, characterized by , that the two hydraulic circuits (100a, 100b) each have an electrically controlled section (110a, 110b) with a working line on which an electrically actuated release valve (111a, 111b) and an electrically actuated control valve (112a, 112b) are arranged in series one after the other. [9] Working machine according to claim 8, characterized by , that the release valves (111a, 111b) are normally closed directional control valves which, in the open switching position, release a hydraulic connection of the respective control valve (112a, 112b) with a pressure source (105a, 105b). [10] Working machine according to claim 8 or 9, characterized by, that the control valves (112a, 112b) are electrically adjustable pressure reducing valves that are normally closed and / or in which the output pressure increases with the current applied and / or in the case of the pedal with the actuation angle and / or force [11] Working machine according to any one of the preceding claims, characterized by that the two hydraulic circuits each have a mechanically controlled section with a working line, on which a brake valve is arranged which is mechanically and / or mechanically-hydraulically actuated by means of a preferably common brake pedal. [12] Working machine according to one of claims 8-10 and according to claim 11, characterized by, that the working lines of the electrically controlled (110a, 110b) and mechanically controlled (120a, 120b) sections of the two hydraulic circuits (100a, 100b) each join at a changeover valve (130a, 130b), which transmits the pressure of the higher-pressured working line to the brake actuator (106a, 106b). [13] Working machine according to one of claims 1-10, characterized by , that in the working machine a brake pedal (121) is arranged with a sensor system for detecting the pedal position, wherein the sensor system is connected to the primary and the secondary control unit via a signal. [14] Working machine according to claim 13, characterized by , that the sensor system is redundantly designed, wherein a first sensor system for detecting the pedal position is signal-connected to the primary control unit and wherein a second sensor system for detecting the pedal position is signal-connected to the secondary control unit. [15] Working machine according to claim 14, characterized by , that the first sensor is connected to the first power source and the second sensor is connected to the second power source. [16] Working machine according to any one of the preceding claims, characterized by , that at the final sections of the working lines of the two hydraulic circuits (100a, 100b), in which the pressure acting on the brake actuator (106a, 106b) prevails, branch lines branch off, which converge at a further changeover valve (140), which directs the respective higher pressure to a hydraulic switch of a brake light and / or to a pressure sensor (142). [17] Working machine according to any one of the preceding claims, characterized by that the machine in question is a wheel loader.

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