Electro-hydraulic steering system, method for functional testing of such an electro-hydraulic steering system, steering system and mobile working machine

Abstract

Electro-hydraulic steering system with at least one control unit comprising at least one hydraulic branch having at least one hydraulic primary circuit and at least one hydraulic secondary circuit, wherein the hydraulic primary circuit comprises at least one main valve (6) for hydraulic control of the steering system (L) in normal operation, and wherein the hydraulic secondary circuit comprises at least one emergency valve (4) for hydraulic control of the steering system (L) in emergency operation, characterized by the fact that both the pilot circuit of the main valve (6) and the pilot circuit of the emergency valve (4) each have at least one pressure reducing valve (DMV1, DMV2), at least one valve (2) is provided which simultaneously affects both the primary circuit and the secondary circuit in the sense of switching from primary circuit to secondary circuit or vice versa, and depending on the state of at least one valve (2) the steering system can be operated either via the primary circuit or the secondary circuit, wherein the emergency valve (5) is smaller than the main valve (6).

Description

[0001] The present invention relates to an electro-hydraulic steering system according to the preamble of claim 1, two methods for functional testing of such an electro-hydraulic steering system, a steering system according to the preamble of claim 14 and a mobile working machine with such an electro-hydraulic steering system or such a steering system.

[0002] Due to the inherent hazards, it is particularly important for the steering systems of construction machinery to ensure their functionality at all times. This requirement applies to all components within the steering system's control chain, regardless of the technology used. This means that the functionality of mechanical, electrical, and hydraulic components in a construction machinery steering system must be guaranteed.

[0003] For many machine functions, it may be sufficient to detect a fault and shut down the function by completely switching it off. Such a procedure is not possible with a steering system, as switching off the steering system cannot be considered a safe state. Rather, a steering system must be capable of assuming a safe state. The vehicle must be able to be brought to a standstill, and steerability must be guaranteed at least until it comes to a complete stop. The functionality of the steering system must therefore be maintained even in the event of a fault.

[0004] The electro-hydraulic steering system according to Fig. Figure 4, which is essentially known from DE 10 2013 018 237 A1, which discloses the features from the preamble of claim 1, shows, with reference numeral L, a steering system of a mobile work machine, in particular a wheel loader. The steering system is operated by a steering wheel or by a joystick; in principle, other steering devices are also conceivable within the scope of the present invention and are included in the invention, so that the term "joystick" used below stands as a placeholder for a steering wheel or for other steering devices. The hydraulic supply of the steering system L is provided by the pump P, the return line has reference numeral Tauf.

[0005] The steering system has a main valve 6 in a hydraulic primary circuit (main circuit), which is preferably of spool design. The main valve 6 is controlled by the vehicle control computer or similar device via the PWM1 and PWM2 signals according to the steering signal. Under normal operating conditions, in which no fault is present, the entire oil quantity from pump P to the steering system L or its steering cylinders is routed through the main valve 6. The pressure sensor p / U is located in the line between pump P and the main valve 6.

[0006] If the main valve 6 malfunctions, for example because it becomes stuck in an open or partially open position, this will result in a dangerous fault. The machine would become unsteerable or at least its steerability would be severely restricted.

[0007] To ensure continued steerability of the machine even in the event of a malfunction of the main valve 6, the steering system has a hydraulic secondary circuit (emergency circuit) containing an emergency valve 4. This emergency valve is preferably smaller, preferably significantly smaller, than the main valve 6, as it only needs to handle the (smaller) volume of oil required during emergency operation. If a malfunction occurs in the hydraulic primary circuit, this is detected by the vehicle control computer, and the secondary circuit is activated by de-energizing the electric valve 2, which is preferably designed as an electrically actuated 3 / 2-way valve and to which the pressure reducing valve DMV is connected. The shut-off valve 7 located between the steering system L and the main valve 6 is then closed.

[0008] In Fig. Figure 4 shows a single shut-off valve 7, designed as a 4 / 2-way valve. The invention also encompasses the use of multiple shut-off valves, which may be designed, for example, as poppet or cartridge valves. However, the arrangement shown in Figure 4 proves to be particularly advantageous. Fig. 4, in which the shut-off stage is designed in the form of a single shut-off valve 7. The advantage over the use of multiple valves lies in the improved diagnostic capabilities and functionality.

[0009] The reference symbol S denotes a hydraulic accumulator that supplies the pilot circuit of the emergency valve with control pressure for a functional check when the drive of the working machine is switched off.

[0010] A stuck main valve 6 is a dangerous fault in the primary circuit. In this case, the pressure applied to the downstream hydraulically actuated shut-off valve in the pilot circuit closes off the L and R ports, preventing the steering system L from being controlled by main valve 6. Similarly, a malfunction of the vehicle control unit itself shuts down the primary circuit by de-energizing the electrically actuated 3 / 2-way valve in the pilot circuit. Failure of the vehicle control unit means that the proportional pressure reducing valves on main valve 6 can no longer be controlled.

[0011] The emergency valve 4 is located in the Fig. In the embodiment shown in Figure 4, the steering system is controlled via pilot valves or stages, which in turn are electrically actuated by the signals PWM3 and PWM4. If the emergency valve 4 is not required because the steering system is operating in normal mode, a normally closed contact can interrupt the power supply to the output stages of the external electronics (i.e., those not integrated into the vehicle control computer). The normally closed contact prevents the deflection of the spool valve 4. In normal operation, it remains in a closed position, thus preventing a connection between pump P and the steering system L via the emergency valve 4.

[0012] In accordance with the order Fig. 4. The steering orbitrol, which is schematically represented in the figure at the top left by the connections L and R, takes over the reduction of pressure peaks caused by external influences (for example, when a wheel loader drives against an obstacle and a large counterforce is generated against the steering force).

[0013] According to Fig. 4. When valve 2 is de-energized, the emergency valve 4 is always supplied with control pressure, regardless of whether the malfunction or fault originates from the hydraulic or electrical branch of the steering system. According to Fig. 4. The control pressure interruption of the emergency valve 4 is achieved via valve 2, which is open when de-energized and closed when energized. Valve 2 is controlled via connection DO1.

[0014] According to Fig. 4. The proportional pressure reducing valves of the emergency valve 4 are not controlled by the vehicle control computer, but by output stages of an external electronics unit. These stages directly output pulse-width modulated signals PWM 3 and PWM 4 proportional to the position of the steering device and operate completely autonomously. The steering device can be either an electric steering wheel or an electric control lever (joystick), whereby the two output stages for controlling the emergency valve 4 can be integrated into the steering device's electronics.

[0015] The in Fig. The setup shown in Figure 4 has the advantage that, in the event of a fault, the control of the emergency valve 4 requires no information from the steering circuit and can be implemented very simply and cost-effectively instead of a duplicate vehicle control computer. While steering position control is not possible in emergency mode, the steering can be controlled in emergency mode, which is acceptable since emergency operation is not the norm and the secondary circuit is only used sporadically anyway, namely when there is a fault in the primary circuit.

[0016] The steering system has a number of sensors, which serve both for control purposes and for diagnosing faults. For example, feedback of the steering angle is required for both the position control of the primary circuit and for its monitoring during operation, in order to activate the emergency steering if necessary. To check the functionality of the emergency valve 4, which is not in operation during normal steering system operation and is in its locked position, functional tests are carried out at regular intervals. The emergency valve 4, like the main valve 6, is position-monitored.

[0017] Thus, the arrangement is characterized according to Fig. 4. characterized by a high degree of fault tolerance or availability in the event of a single fault.

[0018] As this is shown Fig. As can be seen in Figure 4, the pressure reducing valve (DMV) supplies both the main valve and the emergency valve with control pressure. Therefore, a general exclusion of faults cannot be applied, as the pressure reducing valve is a common component of both pilot circuits. Since the pressure reducing valve can become stuck, particularly due to contamination, the problem arises that in this case, the proper functioning of the valves controlled via the pilot circuit is not guaranteed.

[0019] WO 93 / 04 905 A1 as well as DE 103 51 769 A1 show further steering systems from the state of the art.

[0020] The present invention is therefore based on the objective of further developing an electro-hydraulic steering system of the type mentioned at the outset in such a way that the probability that steering capability is maintained in the event of a fault is increased compared to known steering systems.

[0021] This problem is solved by an electro-hydraulic steering system having the features of claim 1, by a method according to claim 10 or claim 11, or by a mobile working machine according to claim 19.

[0022] Furthermore, the present invention is based on the objective of preventing the occurrence of a fault, which is achieved by a steering system having the features of claim 14.

[0023] According to claim 1, both the control circuit of the main valve and the control circuit of the emergency valve each have at least one pressure reducing valve. The disadvantage of the risk of steering system failure due to the failure of a pressure reducing valve supplying both pilot circuits is eliminated according to the invention by the fact that, compared to the circuit according to Fig. 4 at least one second pressure reducing valve is used, so that the pilot control of the main and auxiliary valves is carried out by one or more independent pressure reducing valves.

[0024] Both the main valve and the emergency valve are electro-hydraulically pilot-operated. Each pilot circuit contains at least one pressure-reducing valve.

[0025] In a preferred embodiment of the invention, at least one shut-off valve is provided between the main valve and the steering system, wherein the shut-off valve is arranged in the pilot circuit of the emergency valve, i.e., it is controlled via the pilot circuit of the emergency valve. Thus, there is a common pilot circuit for the emergency valve and for the aforementioned shut-off valve. In a closed position, the shut-off valve isolates the steering system from the main valve, so that when the shut-off valve is functioning and closed, actuation of the steering mechanism does not result in any movement of the steering system.

[0026] Preferably, it is provided that during normal operation, i.e., when there is no malfunction of the steering system, the entire quantity of oil delivered by one or more pumps flows via the main valve to the steering cylinder(s) of the steering system. Furthermore, it is preferably provided that, in the event of a malfunction of the steering system, the entire quantity of oil delivered by one or more pumps flows via the emergency valve to the steering cylinder(s) of the steering system, i.e., the main valve is "switched off".

[0027] It should be noted here that the terms “control” and “control” within the scope of the present invention encompass both control and regulation, and that the terms “electrical”, “electrical”, “electronic” and “electronics” each relate to the field of electrical engineering and / or the field of electronics.

[0028] In a further preferred embodiment of the invention, at least one accumulator is provided in the control circuit of the emergency valve for maintaining the control pressure when the drive of the working machine is stationary. Thus, a functional test of the emergency valve can be carried out when the drive of the working machine is stationary. The hydraulic accumulator supplies the required control pressure for this test.

[0029] Preferably, the pilot circuit of the main valve does not include a pressure accumulator for maintaining the control pressure. The independent pilot circuit for the main valve does not require a pressure accumulator connection, as an extended functional test of the main circuit can be performed while the drive of the machine is running. Closing the shut-off valve prevents any reaction at the steering system caused by the opening of the main valve. This process allows for a functional test of the shut-off valve while the drive is running, ensuring reliable closure of the shut-off valve in the event of a fault as soon as the emergency circuit is activated. Since there is preferably no shut-off valve between the emergency valve and the steering system in the hydraulic secondary circuit, the drive of the machine is switched off for the functional test of the hydraulic secondary circuit.

[0030] At least one emergency steering pump may be provided, arranged in such a way that the storage tank is charged by the emergency steering pump.

[0031] It is conceivable that the hydraulic accumulator is arranged in such a way that it is filled by an electric emergency steering pump or another type of pump before the engine, preferably the diesel engine, of the mobile machine is started. This allows it to be checked, with the diesel engine off, whether the components active in emergency mode are functioning correctly, before the operator starts the engine and puts the electro-hydraulic steering system into operation.

[0032] Furthermore, at least one valve can be provided which is arranged such that, in emergency operation, it supplies the emergency valve with control pressure and / or closes the shut-off valve between the main valve and the steering system, preferably being arranged between the pressure reducing valve of the emergency valve's control circuit and the emergency valve itself. Preferably, this valve is normally open and, in this position, supplies the emergency valve and the shut-off valve with control pressure. In the event of a fault, this valve opens.

[0033] Preferably, exactly one such valve is provided. This is preferably a 3 / 2-way valve. The shut-off valve is preferably a 4 / 2-way valve.

[0034] In a further embodiment of the invention, the emergency valve and / or the main valve is designed with position feedback. This allows for a reliable functional test of the emergency valve or the main valve, as well as a functional test of the position feedback itself.

[0035] The electro-hydraulic steering system can have at least one shock valve in the hydraulic secondary circuit, which opens when a certain threshold value for the pressure of the hydraulic fluid in a line of the secondary circuit is exceeded, in order to be able to cushion pressure surges in the line concerned, wherein it is preferably provided that the shock valve is arranged between the emergency valve and the steering system.

[0036] In a further embodiment of the invention, at least one main steering pump and / or at least one emergency steering pump are provided, which serve to supply the hydraulic primary circuit and / or the hydraulic secondary circuit, wherein according to the invention it is provided that the control pressure for the primary and secondary circuits is supplied via a pressure reducing valve, which can be supplied by the main and emergency steering pumps.

[0037] The steering system can include at least one electric steering device in the form of a steering wheel or joystick, which operates the electro-hydraulic steering system and acts as a secondary control unit for the emergency valve. It is conceivable, for example, that the vehicle control computer takes over the control of the main valve. Furthermore, it can be provided that, in emergency operation, the steering device takes over the control of the emergency valve, thus operating independently of the vehicle control computer and ensuring steerability.

[0038] Furthermore, it is conceivable that the steering system has at least one electrical circuit which only allows the power supply to control the emergency valve through a release signal from the vehicle control computer, in order to put the emergency valve into a standby mode.

[0039] The present invention further relates to a method for functional testing of an electro-hydraulic steering system according to the invention, wherein the method comprises the step of supplying the emergency valve with control pressure, wherein the emergency valve is deflected depending on the applied control pressure, and wherein the method comprises the step of detecting the position feedback of the emergency valve.

[0040] As explained above, the procedure preferably takes place with the drive of the working machine stationary, i.e., switched off.

[0041] Alternatively or additionally, to check the function of the valve, it may be provided that the supply of control pressure to the emergency valve by the aforementioned valve is interrupted, the actuating valve(s) or pressure reducing valve(s) of the emergency valve are energized, and the position feedback of the emergency valve is recorded.

[0042] The present invention further relates to a method for functional testing of an electro-hydraulic steering system according to the invention, wherein the method comprises the step of closing the shut-off valve of the hydraulic primary circuit, the step of supplying the main valve with control pressure, wherein the main valve is deflected depending on the applied control pressure, and the step of detecting a movement of the steering and / or the articulated joint and / or the position feedback of the main valve.

[0043] Preferably, the procedure is carried out while the machine is running and the control pressure for actuating the main valve is transmitted via the pressure reducing valve of the main valve's control circuit. This allows for a functional test of the pressure reducing valve in the pilot circuit of the main valve in the case of the hydraulic main circuit.

[0044] The present invention further relates to a mobile working machine, in particular a wheel loader, with at least one electro-hydraulic steering system according to the invention.

[0045] Preferably, the functionality of the components operating in emergency mode is checked and ensured at regular intervals. These include, in addition to the pressure reducing valves, in particular the emergency valve, the electrically actuated valve (preferably a 3 / 2-way valve), and the shut-off valve (preferably a 4 / 2-way valve) which can be shut off by the 3 / 2-way valve.

[0046] The vehicle control system of the work machine can initiate a functional test at regular intervals.

[0047] It is conceivable that this test is carried out automatically during vehicle commissioning, with the time interval corresponding to at least 1 / 100th of the time between the occurrence of a hazardous fault in the main circuit and its recurrence. In other words, this means that the functional test is performed 100 times more frequently than the safety function is required (EN ISO 13849-1 from 2008).

[0048] It is conceivable that the functional check is carried out more frequently than required by the standard, at least every 8 hours (BGIA Report 2 / 2008).

[0049] The present invention further relates to a steering system, in particular an electro-hydraulic steering system with the features of claim 14. This steering system is distinguished in that it has at least one flushing circuit which is decoupled from the hydraulic circuit in which the spool valves are located and which is connected to the housing of the spool valve(s) in such a way that the housing can be heated by a flushing medium, in particular by a hydraulic medium, which flows through the flushing circuit.

[0050] This aspect of the invention thus relates to a steering valve arrangement with spool valves and at least one further, vehicle-side hydraulic oil circuit or other flushing circuit, independent of the steering, which, after starting the diesel engine of the working machine, brings the valve housing to temperature via one or more flushing channels.

[0051] Thus, one or more flushing channels are added to the valve housing to bring the valve housing(s) up to operating temperature immediately after starting the combustion engine, especially the diesel engine of the machine, using hydraulic oil, for example. This offers the following advantages:

[0052] Regarding the functional test of an emergency valve, the following advantage arises: Under unfavorable cold-start conditions, there is a risk that the functional test of the emergency valve cannot be carried out successfully due to insufficient temperatures. This would result in the electro-hydraulic steering not being able to be activated after the diesel engine has started, as a failed test sequence would be interpreted as a fault in the secondary circuit of the steering system, thus preventing the steering from operating.

[0053] The at least one flushing channel allows hydraulic oil or other suitable flushing medium at a higher temperature to be quickly routed through the housing after a cold start and the subsequent warm-up phase, thus heating up the valve unit.

[0054] The flushing circuit can be directly or indirectly connected to the housing(s) of the spool valve(s). It is essential that the flushing circuit is arranged in such a way that both flows of heated flushing medium, in particular hydraulic oil, result in heating in the area of ​​the spool valve(s).

[0055] After the warm-up phase is completed, the diesel engine is switched off by the driver and, upon restarting, the warming of the valve housing creates the conditions necessary to successfully complete the emergency valve function test and thus activate the electro-hydraulic steering.

[0056] With regard to a stuck valve, the flushing circuit offers the following advantages: Preheating the valve body helps manage situations where operating-temperature hydraulic oil encounters a relatively cold valve or main valve. This can cause the valve piston to heat up and expand significantly faster than the surrounding valve body. If this occurs, the main valve or a downstream shut-off valve can become blocked because the piston gets stuck in the housing, resulting in a loss of steering capability.

[0057] To avoid this, it's conceivable that the driver would only engage the electro-hydraulic steering system once the rest of the vehicle has already reached operating temperature. In the case of an electro-hydraulic auxiliary steering system, this fault could occur if the driver initially steers the machine with the steering wheel, for example, while driving on the road, and only later switches to the auxiliary steering.

[0058] If the electro-hydraulic steering were the primary steering system, the driver could bring the machine up to temperature by operating the working hydraulics, even while stationary and with the diesel engine running, and then immediately start driving and steering.

[0059] The steering system according to claim 14 can be further developed by comprising a main steering system and / or an auxiliary steering system with or without an emergency valve. Thus, an arrangement of one or more purge channels for a main or auxiliary steering system with a main and emergency valve arrangement is conceivable. An arrangement on one or more purge channels for an electro-hydraulic main or auxiliary steering system without an emergency valve as support for the conventional hydraulic steering system (comfort steering) is also conceivable.

[0060] In a further embodiment of the invention, the flushing circuit itself does not have any valves. Preferably, the housing preheating of the spool valves is achieved by the arrangement of one or more flushing panels, particularly with an external flushing medium supply, especially an external oil supply that is not part of the hydraulic oil supply of the steering system. This arrangement of flushing panels preferably does not include any additional valves in the steering valve architecture. This has the advantage that no monitoring of creeping faults in the area of ​​housing preheating by the flushing medium is required.

[0061] In a further embodiment of the invention, the flushing circuit is supplied by an external source, i.e., a source outside the system boundaries of the steering system. Preferably, the source of the flushing medium is therefore located outside the system boundaries of the steering system.

[0062] As explained above, a preferred application of the flushing channels is that jammed spool valves can be avoided, thus eliminating the common cause of failure in a redundant valve arrangement of unequal heating of the valve piston and housing.

[0063] Preferably, the valve arrangement corresponds in its design to a control category 3 or 4, with the safe condition of remaining available in case of a fault.

[0064] Further details and advantages of the invention are explained in more detail with reference to an embodiment illustrated in the drawing. The drawing shows: Fig. 1: a representation of the hydraulic circuit of a steering system with shock valves and pressure reducing valves in the pilot circuits of the main valve and the emergency valve; Fig. 2: a representation of the hydraulic circuit of a steering system according to Fig. 1 with steering orbitrol and without shock valves; Fig. 3: a representation of the hydraulic circuit of a steering system with comfort steering; Fig. 4: a representation of the hydraulic circuit of a known steering system; Fig. 5: a representation of the hydraulic circuit of a steering system according to Fig. 2 with flushing circuit.

[0065] All features and details regarding the item in Fig. The steering systems described in section 4 also apply to the present invention, so reference is made accordingly.

[0066] In the Fig. 1 to Fig. The three reference symbols used denote identical or functionally equivalent elements with the same reference symbols according to Fig. 4, so that also in this respect to Fig. 4 is referenced.

[0067] As this is shown Fig. As can be seen from Figure 1, the pressure reducing valve DMV1 is located in the pilot circuit of the main valve 6. Furthermore, there is an independent pilot circuit for the emergency valve 4, which has its own pressure reducing valve DMV2.

[0068] Both pressure reducing valves DMV1 and DMV2 are connected on their high-pressure side to the hydraulic supply P of the primary and secondary hydraulic circuits. Pressure reducing valve DMV1 is connected on its low-pressure side to the pilot valve(s) of the main valve 6. Pressure reducing valve DMV2 is connected on its low-pressure side to valve 2. This valve 2 supplies control pressure to the shut-off valve 7 of the primary hydraulic circuit and to the emergency valve 4 of the secondary hydraulic circuit.

[0069] The electro-hydraulic steering system thus has a primary hydraulic circuit and a secondary hydraulic circuit with separate control oil supplies for the two circuits, with at least one pressure reducing valve for the respective control pressure supply being arranged in each of the separate pilot circuits. A failure of one pressure reducing valve therefore does not lead to a failure of the entire steering system.

[0070] In the Fig. In the embodiment shown in Figure 1, two shock valves 8 and 9 are arranged between the steering system L and the main valve 6 or emergency valve 4 (depending on which circuit is currently in operation), the shock valves 8 and 9 serving to reduce pressure spikes. These shock valves can, for example, take over the reduction of pressure spikes when the steering orbitrol, as in the Fig. Figure 1 is omitted. Shock valves 8 and 9 are each designed as 2 / 2-way valves that open in the direction away from the hydraulic line when a certain pressure is exceeded. For example, the valve flaps or valve bodies are spring-loaded, as shown in the Fig. Figure 1 is shown schematically. Furthermore, the opening cross-section of the pressure valves can be configured to change depending on the pressure, for example, increasing with increasing pressure. In the illustrated embodiment, each pressure valve has a bypass line in which a check valve, such as a non-return valve or a ball valve, is arranged. This allows hydraulic fluid, which has previously passed through a pressure relief valve, to flow into the hydraulic line with the lower pressure, typically the line where a pressure peak does not occur.

[0071] Preferably, the shock valve is located between the main or emergency valve and the steering system (for example, the articulated steering of a wheel loader). Preferably, the shock valve is arranged close to the steering system, i.e., it is the last valve before the steering system and protects all other valves in the respective line, which are further away from the steering system, from pressure surges.

[0072] Fig. Figure 2 shows an embodiment of the steering system according to Fig. 1, however without shock valves, but with a steering orbitrol. In the arrangement according to Fig. 2. The steering orbitrol, which is schematically represented in the figure at the top left by the connections L and R, takes over the reduction of pressure peaks caused by external influences (for example, when a wheel loader drives against an obstacle and a large counterforce is generated against the steering force).

[0073] Out of Fig. Figure 3 shows an embodiment in which only one hydraulic primary circuit is present. In this case as well, the main valve 6 is controlled via a pressure reducing valve DMV1 and the shut-off valve 7 is controlled via another pressure reducing valve DMV2. Downstream of the pressure reducing valve DMV2 is valve 2, which is normally open and in this state causes the shut-off valve 7 to close. Thus, in the embodiment according to Fig. 3 Two separate pilot control circuits are provided, each with a pressure reducing valve DMV1 or DMV2.

[0074] Furthermore, it should be noted that in Fig. 3. The reference symbols denote the same or functionally equivalent elements, as in Fig. 4, so that appropriate reference is made.

[0075] By functional testing of the emergency circuit, i.e., the hydraulic secondary circuit according to Fig. 1 or Fig. 2. With the drive of the machine, especially the wheel loader, stationary, it can be determined whether any of the components operating in the hydraulic secondary circuit have a fault. These are the components DMV2, the 3 / 2-way valve, the emergency valve 4, and its position feedback. By functionally testing the main circuit, i.e., the hydraulic primary circuit, according to Fig. 1 or Fig. 2. The function of the components DMV1, main valve 6, shut-off valve 7 and, if applicable, position feedback of the main valve 6 can take place while the drive is running.

[0076] However, for the load sensing pressure changeover valve LS, the fault exclusion can be applied.

[0077] The functional testing of the hydraulic primary and secondary circuits implicitly covers the functional testing of the upstream control components.

[0078] The functional test of the emergency circuit to ensure its availability in the event of a fault in the main circuit is preferably carried out as follows: 1. With the drive of the working machine stationary and the ignition switched on, the storage tank S is charged by the electric emergency steering pump via the pressure reducing valve DMV2, 2. Switching off the electric emergency steering pump, 3. Switching off the power to valve 2 by DO1, so that the emergency valve 4 is supplied with control pressure from the reservoir 5. 4. Deflecting the slide of the emergency valve 4 from its central position to one or both end positions using PWM3 and PWM4, checking that the end positions have been reached by observing the position feedback of the emergency valve 4, 5. Deflecting the slide of the emergency valve 4 back to the central position so that the emergency valve 4 closes, and checking that the central position has been reached by observing the position feedback. 6. If the test result is positive, the vehicle control system ensures that the DMV2, the emergency valve 4 and its position feedback are functioning.

[0079] A functional check of valve 2, which is preferably designed as a 3 / 2-way valve, may include the following steps: 1. Energizing or closing valve 2 by DO1, so that the control pressure supply of the emergency valve 4 is interrupted, 2. Energizing the pressure reducing valve(s) at the emergency valve using PWM3 and / or PWM4, 3. Checking the deflection at the emergency valve 4, preferably by checking the position feedback of the emergency valve 4.

[0080] If valve 2 is functioning correctly, there should be no deflection of the emergency valve when the pressure reducing valves are actuated. If deflection of the emergency valve is detected, valve 2 is malfunctioning.

[0081] A functional test of the shut-off valve 7 or the hydraulic primary circuit is preferably carried out as follows. The functional test is performed with the drive of the machine running, preferably immediately after starting: 1. De-energizing valve 2 by DO1, which must result in the closing of shut-off valve 7, 2. at least minimal deflection of the slide of the main valve 6, 3. Check whether any movement occurs at the steering cylinder or the articulated joint of a wheel loader, which would indicate a malfunction of the shut-off valve 7, 4. In the event of a negative test result, the vehicle control system would, as a final step, prevent the activation of the electro-hydraulic steering.

[0082] If the main valve's slide valve optionally has a position detection function, the functional check can be extended to the main circuit as follows: 1. De-energizing valve 2 by DO1, which must result in the closing of shut-off valve 7 again. 2. Deflecting the slide of the main valve 6 from its central position to one or both end positions by means of PWM1 and PWM2, checking that the end positions have been reached by observing the position feedback of the main valve 6, 3. Deflecting the slide of the main valve 6 back to the central position so that the main valve 6 closes, and checking that the central position has been reached by observing the position feedback, 4. Ensuring, in the event of a positive test result, that the vehicle control system, even before commissioning the electro-hydraulic steering system, the DMV1, the main valve 6 and its position feedback are functioning. 5. In the event of a negative test result, the vehicle control system would, as a final step, prevent the activation of the electro-hydraulic steering.

[0083] From the perspective of the standards regulations, the functional test of the main circuit, i.e. the hydraulic primary circuit, may be omitted, since a malfunction of the main circuit would be detected immediately after switching on the electro-hydraulic steering system by the fault diagnosis processes of the vehicle control system.

[0084] Fig. Figure 5 shows a hydraulic circuit of a steering system according to Fig. 2, in contrast to Fig. Figure 2 shows an additional flushing circuit, which has connections N1 and N2. A flushing medium, in particular a hydraulic medium, can be supplied via these connections. This medium is heated and therefore, when flowing through the steering system, can be cooled according to... Fig. 5 causes the valve block, and in particular the housings of the spool valves arranged therein, to heat up. N1 can be the inlet for the heated hydraulic fluid and N2 the outlet, or vice versa, N1 the outlet and N2 the inlet for the heated hydraulic fluid. As shown in Fig. As can be seen in Figure 5, the flushing circuit within the depicted steering system is designed without valves. The source of the flushing medium is located outside the system shown. Fig. The system boundary of the steering system is shown in section 5 with a dashed line. It can be provided, for example, by an external oil supply, thereby increasing operational reliability. How this is achieved is explained below. Fig. As further shown in section 5, the flushing circuit is completely independent, i.e., it is not in fluid contact with the hydraulic circuits of the steering system.

[0085] In contrast to Fig. 2 is the storage S according to Fig.5 is displayed outside the system boundary and is connected to the system via the SP port.

Claims

[1] Electro-hydraulic steering system with at least one control unit comprising at least one hydraulic branch having at least one hydraulic primary circuit and at least one hydraulic secondary circuit, wherein the hydraulic primary circuit comprises at least one main valve (6) for hydraulic control of the steering system (L) in normal operation, and wherein the hydraulic secondary circuit comprises at least one emergency valve (4) for hydraulic control of the steering system (L) in emergency operation, characterized by , that both the pilot circuit of the main valve (6) and the pilot circuit of the emergency valve (4) each have at least one pressure reducing valve (DMV1, DMV2), at least one valve (2) is provided which simultaneously affects both the primary circuit and the secondary circuit in the sense of switching from primary circuit to secondary circuit or vice versa, and depending on the state of at least one valve (2) the steering system can be operated either via the primary circuit or the secondary circuit, wherein the emergency valve (5) is smaller than the main valve (6). [2] Electro-hydraulic steering system according to claim 1, characterized by , that at least one shut-off valve (7) is provided between the main valve (6) and the steering system (L) and that the shut-off valve (7) is arranged in the pilot circuit of the emergency valve (4). [3] Electro-hydraulic steering system according to claim 1 or 2, characterized by , that in the pilot circuit of the emergency valve (4) at least one accumulator (S) is provided for maintaining the control pressure when the drive of the working machine is stationary. [4] Electro-hydraulic steering system according to one of the preceding claims 1 or 2, characterized by , that no accumulator (S) for maintaining the control pressure is provided in the pilot circuit of the main valve (6). [5] Electro-hydraulic steering system according to claim 3, characterized by , that at least one emergency steering pump is provided which is arranged in such a way that, during operation of the emergency steering pump, the storage (S) of the pilot control circuit of the emergency valve (4) is charged. [6] Electro-hydraulic steering system according to any one of the preceding claims, characterized by , that at least one valve (2) is provided which is arranged such that in emergency operation it supplies the emergency valve (4) with control pressure and / or closes the shut-off valve (7), wherein preferably it is provided that the valve (2) is arranged between the pressure reducing valve (DMV2) of the pilot circuit and the emergency valve (4). [7] Electro-hydraulic steering system according to any one of the preceding claims, characterized by that the emergency valve (4) and / or the main valve (6) is designed with position feedback. [8] Electro-hydraulic steering system according to any one of the preceding claims, characterized by, that at least one shock valve (8, 9) is provided in the hydraulic secondary circuit, which opens when a certain threshold value for the pressure of the hydraulic fluid in a line of the secondary circuit is exceeded in order to be able to cushion pressure surges in the line concerned, wherein it is preferably provided that the shock valve (8, 9) is arranged between emergency valve (4) and steering system (L). [9] Electro-hydraulic steering system according to any one of the preceding claims, characterized by , that the steering system has at least one electric steering device, which may be designed as a steering wheel or joystick, and by which the electro-hydraulic steering system (L) is operated, and which performs the function of a secondary control unit for controlling the emergency valve (4). [10] Method for functional testing of an electro-hydraulic steering system according to one of the preceding claims, wherein the method comprises the step of supplying the emergency valve (4) with control pressure, wherein the emergency valve (4) is deflected depending on the applied control pressure, and wherein the method comprises the step of detecting the position feedback of the emergency valve (4) and / or wherein the method comprises the step of interrupting the supply of the emergency valve (4) with control pressure, energizing the actuating valves of the emergency valve (4) and detecting the position feedback of the emergency valve (4). [11] Method for functional testing of an electro-hydraulic steering system according to one of the preceding claims, wherein the method comprises the step of closing the shut-off valve (7) of the hydraulic primary circuit, the step of supplying the main valve (6) with control pressure, wherein the main valve (6) is deflected depending on the applied control pressure, and the step of detecting a movement of the steering and / or the articulation joint and / or detecting the position feedback of the main valve (6). [12] Method according to one of the preceding claims 10 and / or 11, characterized by that the procedure is carried out with the drive of the working machine stationary. [13] Method according to claim 11, characterized by , that the procedure is carried out with the drive of the working machine running and the control pressure for actuating the main valve (6) is transmitted via the pressure reducing valve (DMV1) of the control circuit of the main valve (6). [14] Steering system with one or more spool valves and with at least one hydraulic circuit in which the spool valve(s) are arranged, characterized by that the steering system has at least one flushing circuit which is independent of the hydraulic circuit and which is connected to the housing of the spool valve(s) in such a way that the housing can be heated when the flushing circuit is supplied with heated flushing medium. [15] Steering system according to claim 14, characterized by that the steering system has a main and / or an auxiliary steering system with or without an emergency valve (4). [16] Steering system according to claim 14 or 15, characterized by that the flushing circuit has no valves. [17] Steering system according to any one of claims 14 to 16, characterized by that the flushing circuit is supplied by an external supply, in particular by an external hydraulic oil supply. [18] Steering system according to any one of claims 14 to 17, characterized by that the steering system is designed according to one of claims 1 to 9. [19] Mobile working machine with at least one electro-hydraulic steering system according to any one of claims 1 to 9 or with a steering system according to any one of claims 14 to 18.

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