METHOD FOR CONTROLLING A CHANGE OF DIRECTION OF TRAVEL OF A WORK VEHICLE BETWEEN FORWARD AND REVERSE TRAVEL OR VARY

Description

[0001] The invention relates to a method for controlling a change of direction of travel of a work vehicle between forward and reverse travel or vice versa, wherein the work vehicle has an electronically controllable hydrostatic drive, an externally operated braking system with at least one electronically controllable brake circuit and an electronic brake control unit for controlling the drive and the at least one electronically controllable brake circuit of the braking system, and wherein, during travel in a first direction of travel, a change of direction of travel in the opposite direction of travel is triggered by switching the hydrostatic drive by means of an associated manual control element.

[0002] A hydrostatic drive system of a work vehicle, such as a wheel loader, tractor, or forklift, comprises a hydrostatic drive train with at least one hydrostatic pump and one hydrostatic motor, which may be connected in a closed or open fluidic circuit. At least the hydrostatic pump is adjustable so that its delivery volume can be variably controlled. The hydrostatic drive system can consist solely of the hydrostatic drive train (DE 101 45 996 A1) or, for example, be formed from a power-split transmission with a hydrostatic drive train and a parallel mechanical drive train (DE 101 22 823 B4). EP 3 315 370 A1 discloses a tractor equipped with a reversing device capable of automatically reversing the tractor's direction of travel or movement.

[0003] It is assumed here that a change in the direction of travel, which is effected by switching the high-pressure and low-pressure lines leading to the hydrostatic motor, is achieved in a closed circuit by a corresponding reversing of the hydrostatic pump or in an open circuit by switching a changeover valve arranged between the hydrostatic pump and the hydrostatic motor.

[0004] In a work vehicle with such a hydrostatic drive and a loading shovel or fork mounted at the front, a change of direction can be initiated while driving by switching a control element, such as a direction lever or switch, to the opposite direction. This can occur, for example, in the following situations: when picking up cargo at a loading position from forward to reverse, at a turning position with cargo picked up to change from reverse to forward, and at an unloading position to unload the previously picked-up cargo from forward to reverse.

[0005] The driver of a work vehicle must perform several tasks when loading cargo, such as steering the vehicle, alternately operating the accelerator and brake pedals, operating the levers for raising, lowering, and tilting the loading shovel or forks during loading and unloading, and observing the surroundings to avoid collisions with other vehicles, people, and stationary obstacles. By switching the control element to the opposite direction of travel while driving, the delivery volume of the hydrostatic pump is first continuously reduced to zero and then increased again with the reverse flow direction or with the changeover valve switched.If the driver does not actively assist the deceleration of the work vehicle by releasing the accelerator pedal and applying the brake pedal, but instead keeps their foot on the accelerator pedal, the deceleration of the work vehicle occurs solely via the hydrostatic drivetrain, which is associated with a detrimentally high mechanical stress on the relevant components. This stress is naturally higher when the vehicle is loaded due to its increased mass than when it is unloaded.

[0006] The present invention is therefore based on the objective of presenting a method for controlling a change of direction of travel of a generic work vehicle between forward travel and reverse travel or vice versa, the use of which can reduce the mechanical stress on the components of the hydrostatic drive train in the described operating mode.

[0007] This problem is solved by a method that has the features of claim 1. Advantageous further developments of this method are defined in the dependent claims.

[0008] Accordingly, the invention relates to a method for controlling a change of direction of travel of a work vehicle between forward and reverse travel or vice versa, wherein the work vehicle has an electronically controllable hydrostatic drive, an externally operated braking system with at least one electronically controllable brake circuit and an electronic brake control unit for controlling the drive and the at least one electronically controllable brake circuit of the braking system, and wherein, during travel in a first direction of travel, a change of direction of travel in the opposite direction of travel is triggered by switching the hydrostatic drive by means of an associated manual control element.

[0009] To solve the task at hand, this method provides that when changing direction from forward to reverse or vice versa, the deceleration of the work vehicle is supported by automatic actuation of the brakes of the electronically controlled brake circuit of the braking system, whereby these brakes are actuated by switching the manual control element and are released again at the latest when the vehicle comes to a standstill.

[0010] The invention therefore relates to a work vehicle known per se, such as a wheel loader, a tractor or a forklift, which has an electronically controlled hydrostatic drive, an externally operated braking system with at least one electronically controlled brake circuit and an electronic brake control unit for controlling the drive and the electronically controlled brake circuit of the braking system.

[0011] If the operator of this vehicle switches the aforementioned manual control during forward or reverse travel to initiate a change of direction, the delivery volume of the hydrostatic pump in the hydrostatic drivetrain is first continuously reduced to zero and then increased again with the reversed delivery direction or with the changeover valve switched. If the operator does not actively assist the deceleration of the machine by applying the brake pedal, this results in an undesirably high mechanical load on the components of the hydrostatic drivetrain.

[0012] By automatically braking the work vehicle using the brakes of the electronically controlled braking system, the hydrostatic drivetrain is supported and relieved of stress during deceleration, thus reducing the mechanical load on the relevant components and extending the service life of the hydrostatic drivetrain. The electronically controlled braking system can, for example, actuate the brake actuators on the front axle, the rear axle, or both axles.

[0013] According to the invention, for metering the brake pressure p B introduced into the brake cylinders of the electronically controlled brake circuit, the driving speed of the work vehicle and at least one operating parameter characterizing the mechanical load of the hydrostatic drive train are sensorially detected and their values ​​are transmitted to the associated control unit, and the brake pressure p B to be introduced into the brake cylinders of the electronically controlled brake circuit is determined in this control unit as a function of the driving speed v F of the work vehicle and of the value of the at least one operating parameter characterizing the mechanical load of the hydrostatic drive train.

[0014] Operating parameters that characterize the mechanical load of the hydrostatic drive train include, for example, the input torque M HA_E, the output torque M HA_A and the gear ratio i HA of the hydrostatic drive train, as well as the working pressure p A in a high-pressure line of the hydrostatic drive train.

[0015] Since additional braking of the work vehicle using the brakes of the electronically controlled braking circuit is only useful at higher driving speeds v F, it can be provided that the brakes of the electronically controlled braking circuit are only activated if the driving speed v F of the work vehicle has reached or exceeds a predefined minimum driving speed v F_min at the time the manual control element is switched | v F | ≥ V F_min . This minimum driving speed v F_min can, for example, be set to a value of 5 km / h (v F_min = 5 km / h).

[0016] It can also be advantageous to release the brakes prematurely before the vehicle comes to a complete stop (vehicle speed vF = 0), because the brake release after the pressure release of the associated brake cylinders typically occurs with a certain time delay. To prevent the subsequent acceleration of the work vehicle from being hindered by the brakes still engaged, the brakes of the electronically controlled brake circuit can be released before the vehicle comes to a complete stop (vF = 0) if the vehicle's vehicle speed vF reaches or falls below a minimum speed vF_min* close to zero (|vF| ≤ vF_min*). This minimum speed vF_min* can, for example, be set to a value of 0.5 km / h (vF_min* = 0.5 km / h).

[0017] The brakes of the electronically controlled brake circuit are preferably also released as soon as the actuation of a foot brake valve is registered, whereby the brake pressure p B already controlled in the relevant brake cylinders is continuously converted into the brake pressure controlled via the foot brake valve or determined by means of a brake pressure sensor or position sensor arranged on the foot brake valve.

[0018] The level of the brake pressure p B applied to the brake cylinders of the electronically controlled brake circuit is determined, for example, proportionally to the driving speed v F of the work vehicle at the time of switching the control element, since the load on the components of the hydrostatic drive train increases with the driving speed v F when the work vehicle is braked.

[0019] Additionally or alternatively, the level of the brake pressure p B applied to the brake cylinders of the electronically controlled brake circuit can also be determined proportionally to the input torque M HA_E present at the time of switching the control element, the working pressure p A in the high-pressure line and the output torque M HA_A or the transmission ratio i HA of the hydrostatic drive train, which are characteristic of the load on the components of the hydrostatic drive train.

[0020] The brake pressure p B applied to the brake cylinders of the electronically controlled brake circuit after switching the control element can be kept constant until the brakes are released.

[0021] However, it is also possible that the brake pressure p B, which is applied to the brake cylinders of the electronically controlled brake circuit after the control element has been switched, is continuously reduced until the brakes are released, for example proportionally to the decreasing driving speed v F.

[0022] Another possibility is that the brake pressure p B, which is applied to the brake cylinders of the electronically controlled brake circuit after the switching of the control element, is regulated in such a way that a predetermined braking deceleration a F_set is maintained.

[0023] Depending on the design of the work vehicle's braking system, the brake pressure in the brake cylinders of the electronically controlled brake circuit can be adjusted in different ways. For example, the brake pressure pB in the brake cylinders of the electronically controlled brake circuit can be adjusted by means of an electronically controlled proportional valve, to which a pressurized supply line is connected on the inlet side and a main brake line leading to the brake cylinders is connected on the outlet side.

[0024] Alternatively, the brake pressure pB in the brake cylinders of the electronically controlled brake circuit on each side of the vehicle can be adjusted by means of an ABS control unit. The ABS control units have inlet and outlet valves and are components of a known anti-lock braking system. An ABS control unit enables the implementation of an anti-lock braking process at the vehicle wheels in a known manner. Each of the two ABS control units has an input section of a front axle brake line branching off from an axle brake line serving as the main brake line. Each of the two ABS control units has an output section of the front axle brake line leading to a brake cylinder of the corresponding brake.

[0025] In certain cases, the operation of vehicle combinations consisting of a towing vehicle and an attached trailer also involves frequent changes of direction. For example, a tractor with an attached single-axle sprayer must make two U-turns at the end of a field if leaving the field for the maneuver is not possible, for example, due to bushes or trees.

[0026] To prevent the vehicle combination from jackknifing around the trailer hitch, it can be designed so that, in a vehicle combination consisting of a towing vehicle and a trailer, only the brakes of at least one electronically controlled brake circuit of the braking system of the rearmost vehicle (as viewed in the direction of travel) are applied. Accordingly, only the trailer is braked when forward travel is coming to an end, and only the towing vehicle is braked when reverse travel is coming to an end.

[0027] Alternatively, for the same purpose, it can be provided that, in a vehicle combination consisting of a towing vehicle and a trailer, the brakes of at least one electronically controlled brake circuit of the braking system of the rearmost vehicle (in the current direction of travel) are applied more strongly than the brakes of at least one electronically controlled brake circuit of the braking system of the front vehicle (in the direction of travel). Thus, when traveling forward, the trailer is braked more strongly than the towing vehicle, and when traveling in reverse, the towing vehicle is braked more strongly than the trailer.

[0028] Finally, it may be provided that, after activation of the manual control element to assist the deceleration of the work vehicle, towing vehicle, or trailer, the brakes on the front axle, the rear axle, and / or both the front and rear axles of this vehicle are electronically controlled. Accordingly, depending on the vehicle's design and / or operation, the wheels of the axle optimal for the task at hand and the vehicle's general operation can be braked.

[0029] The invention is explained in more detail below with reference to an embodiment illustrated in the accompanying drawing. The drawing shows Fig. 1 a view from above of a loading area where a work vehicle is loading a trailer of a towing vehicle with cargo, wherein the method according to the invention is used to control a change of direction of travel of the work vehicle from forward travel to reverse travel and vice versa, Fig. 2a the switching state of a manual control element of the work vehicle when in Fig. 1 depicted driving scenario in a time diagram, Fig. 2b the speed and direction of travel of the work vehicle at the Fig. 1 depicted driving scenario in another time diagram, Fig. 3 the control of the braking processes in the driving scenario according to the Figuren 1 , 2a und 2b in a functional diagram, and Fig. 4 a braking system of a work vehicle for the application of the procedure according to the Figuren 1 bis 3 in a schematic illustration.

[0030] The method according to the invention serves to control a change of direction from forward to reverse travel or vice versa in a work vehicle 2, which has an electronically controllable hydrostatic drive 3, a power-operated braking system 22 with at least one electronically controllable brake circuit 106, and an electronic brake control unit 40 for controlling the drive 3 and the electronically controllable brake circuit 106 of the braking system 22. This method is explained below by way of example using a driving scenario, which is shown in a top view in the Fig. 1 is shown.

[0031] A work vehicle 2, in this case a tractor equipped with a front loader bucket 4, is to pick up loose material 8 from a larger pile 6 and unload it onto the loading platform of a trailer 14 of a vehicle combination 10. In this example, the material 8 is sand, grain, or silage. The vehicle combination 10 consists of another tractor 12 and the trailer 14 attached to it.

[0032] To carry out this loading operation, the work vehicle 2 travels forward from a starting position A along a first travel path 16 to loading position B, where the pile 6 containing the load 8 is located, in order to pick up the load 8 with the front loader bucket 4. The work vehicle 2 then travels backward approximately along the first travel path 16 to the first turning position C, which is located near the starting position A. From the first turning position C, the work vehicle 2 travels forward along a second travel path 18 to an unloading position D, which is located directly next to the trailer vehicle 14. Once there, the front loader bucket 4 tips the load 8 it has picked up onto the loading platform of the trailer vehicle 14. The work vehicle 2 then travels backward approximately along the second travel path 18 to a second turning position E, which is located close to the starting position A and the first turning position C.This driving cycle is repeated several times until the trailer vehicle 14 is sufficiently loaded with the cargo 8.

[0033] It can be seen that at loading position B and unloading position D, the direction of travel changes from forward to reverse, while at the two turning positions C and E, the direction of travel changes from reverse to forward.

[0034] The aforementioned changes of direction can be made while driving by actuating a manual control element 69 70 (see Fig. 4 ), i.e., a direction lever or a direction switch, which are triggered in the opposite direction of travel. In the hydrostatic drive train 3.1, the delivery volume of a hydrostatic pump (not shown) is first continuously reduced to zero or at least close to zero and then increased again with the opposite delivery direction or with a switched reversing valve (also not shown). This causes an undesirably high mechanical load on the components of the hydrostatic drive train 3.1.

[0035] The method according to the invention counteracts this by supporting the deceleration of the work vehicle 2 by means of the hydrostatic drive train 3.1 through automatic braking with the brakes 113a, 113b of at least one electronically controlled brake circuit 106 of the brake system 22. The respective wheel brakes 113a, 113b are actuated by switching 69 of the manual control element 70 against the current forward direction 15, V or reverse direction 17, R and are released again at the latest when the vehicle comes to a standstill (v F = 0). This is shown in the two diagrams of the Figuren 2a und 2b for the in Fig. 1 The depicted driving scenario illustrates the driving scenario shown. In the first diagram according to Fig. 2a The solid line represents the switching state S BE of the manual control element 70 between forward travel V and reverse travel R over time t, while the diagram according to Fig. 2b The driving speed v F of the work vehicle 2 is shown over time t when driving forwards and backwards.

[0036] Like the two Figuren 2a und 2b In summary, the driving operation begins at starting position A according to Fig. 1 at time t0 with an acceleration of the work vehicle 2 in forward travel, whereby the aforementioned manual control element 70 is initially in the switching position S BE = V for forward travel.

[0037] At time t1, the driver of the work vehicle 2 switches the manual control element 70 to the switching position S BE = R for reverse travel. The work vehicle 2 is then decelerated in a first braking phase B1, firstly by reversing the hydrostatic drive 3 and secondly by applying the brakes 113a and 113b of the aforementioned electronically controlled brake circuit 106 of the braking system 22. At the latest when the vehicle comes to a standstill (v F = 0) at time t1', which ideally coincides with reaching the loading position B, the brakes 113a and 113b of the electronically controlled brake circuit 106 are released.

[0038] The work vehicle 2 is then accelerated in reverse, as shown by the curve v F (t). At time t2, the driver switches the manual control element 70 to the forward driving position S BE = V. The work vehicle 2 is then decelerated in a second braking phase B2 by reversing the hydrostatic drive train 3.1 and additionally by applying brakes 113a and 113b of the electronically controlled brake circuit 106. At the latest when the vehicle comes to a standstill (v F = 0) at time t2', which coincides with reaching the first turning position C, the brakes 113a and 113b of the electronically controlled brake circuit 106 are released.

[0039] The work vehicle 2 is then accelerated forwards. At time t3, the driver switches the manual control element 70 to position S BE = R for reverse travel R. The work vehicle 2 is then decelerated in a third braking phase B3 by reversing the hydrostatic drive train 3.1 and additionally by applying brakes 113a and 113b of the electronically controlled brake circuit 106. At the latest when the vehicle comes to a standstill (v F = 0) at time t3', which ideally coincides with reaching the unloading position D, the brakes 113a and 113b of the electronically controlled brake circuit 106 are released.

[0040] The work vehicle 2 is then accelerated in reverse. At time t4, the driver switches the manual control element 70 to position S BE = V for forward travel. The work vehicle 2 is then decelerated in the fourth braking phase B4 by reversing the hydrostatic drive train 3.1 and additionally by applying brakes 113a and 113b of the electronically controlled brake circuit 106. At the latest when the vehicle comes to a standstill (v F = 0) at time t4', which coincides with reaching the second turning position E, the brakes 113a and 113b of the electronically controlled brake circuit are released.

[0041] Since precise adherence to the respective positions is not critical at the two turning positions C and E, the control according to the inventive method is unproblematic during the two braking phases B2 and B4. In contrast, largely precise adherence to the loading position B and the unloading position D is necessary to enable the loading of the cargo 8 at loading position B and the unloading of the cargo 8 at unloading position D, as well as to avoid a collision with the trailer 14 of the vehicle combination 10 near the unloading position D. Therefore, a skilled driver is required when approaching loading position B and unloading position D so that these two positions B and D can be reached with considerable accuracy without the driver having to operate the brake pedal and / or the accelerator pedal.

[0042] In the functional diagram according to Fig. 3 is the determination of the braking phases B1, B2, B3, B4 mentioned above according to Fig. 2a und Fig. 2b The brake pressure pB applied to the brake cylinders of the electronic brake circuit 106 of the brake system 22 is illustrated. Accordingly, the switching position SBE of the manual control element 70, the driving speed vF of the work vehicle 2, the desired braking deceleration aF_set of the work vehicle 2, and the input torque MHA_E and / or the output torque MHA_A of the hydrostatic drive train 3.1 are measured by sensors and fed to an electronic control unit 20. In this control unit 20, these sensor data are processed, and the brake pressure pB to be applied to the brake cylinders 114a, 114b of the electronic brake circuit 106 is determined. This electronic control unit 20 can be a component of a central electronic control unit 60, or it can be integrated with it as shown in Fig. 4 The system is connected via a data line. The brake pressure pB to be controlled is then set either by means of an electronically controlled proportional valve or by means of the electronic ABS control units 130, 132.

[0043] According to this, Fig. 4 It is provided that the brake pressure p B in the brake cylinders 114a, 114b of the two brakes 113a, 113b of the electronically controlled brake circuit 106 is set by means of ABS control units 130, 132. A section 112a, 112b of the front axle brake line 112, branching off from the axle brake line 110 which serves as the main brake line, is connected to each of these ABS control units 130, 132 at the input side, and a section 115a, 115b of the front axle brake line 112, leading to a brake cylinder 114a, 114b of the associated brake 113a, 113b, is connected at the output side.

[0044] As a further operating parameter for determining the brake pressure pB to be applied, the working pressure pA in a high-pressure line 77 of the hydrostatic drive train 3.1 can be measured by a sensor and transmitted to the control unit 20. Instead of measuring the output torque MHA_A by a sensor, the gear ratio iHA of the hydrostatic drive train 3.1 can be measured by a sensor and transmitted to the control unit 20, with which the output torque MHA_A can be calculated from the input torque MHA_E.

[0045] In the schematic diagram of the Fig. 4 Figure 22 shows a brake system 22 of a work vehicle 2 designed as a tractor, which is known per se and in which the method according to the invention can be applied. The work vehicle 2 has a non-driven front axle 24 with two front wheels 26a, 26b arranged on either side and a rear axle 28 designed as a drive axle with two rear wheels 30a, 30b arranged on either side. A wheel speed sensor 32a, 32b, 36a, 36b is arranged on each of the wheels 26a, 26b, 30a, 30b of both vehicle axles 24, 26, which are connected to the electronic brake control unit 40 via sensor lines 34a, 34b, 38a, 38b. The driving speed v F of the work vehicle 2 can be determined from the sensor signals of the wheel speed sensors 32a, 32b, 36a, 35b in the brake control unit 40.

[0046] The braking system 22 comprises a hydraulic primary braking system 72, a hydraulic secondary braking system designed as the electronically controlled brake circuit 106, and a pneumatic trailer control valve 88. A hydraulic pressure medium source 42 includes an oil pump 46, from which hydraulic oil can be pumped from a hydraulic reservoir 44 via a relay valve 48 into a hydraulic pressure medium preparation unit 50. In the pressure medium preparation unit 50, the pumped hydraulic oil is cleaned, cooled, and directed to two supply lines 52, 62. An electro-hydraulic pressure sensor 54, 64 and a hydraulic pressure accumulator 58, 68 are each connected to the two supply lines 52, 62. The two pressure sensors 54, 64 are connected via electrical sensor lines 56, 66 to a central electronic control unit 60 of the work vehicle 2.A manually operable control element 70, designed as a direction lever, is also connected to this control unit 60, by means of which the direction of travel of the work vehicle 2 can be selected.

[0047] The primary brake system 72 can be used as both a service brake system and a steering brake system and, in this example, has two brake circuits, each assigned to one side of the vehicle. The primary brake system 72 comprises the first supply line 52 with the associated hydraulic first pressure accumulator 58, two foot brake valves 74a, 74b, each mechanically actuated by the driver via a brake pedal, an axle relay valve 76, and two wheel brake lines 78a, 78b. The two foot brake valves 74a, 74b are connected on the inlet side to the first supply line 52 and on the outlet side to the axle relay valve 76. The axle relay valve 76 is also connected to the supply line 52. The two wheel brake lines 78a, 78b are routed from the axle relay valve 76 to a rear brake cylinder 80a, 80b, respectively.The rear brake cylinders 80a, 80b are designed as actively acting diaphragm or piston brake cylinders and are arranged on the wheel brakes of the rear wheels 30a, 30b, which are known per se and not shown here.

[0048] In its function as a service brake system, the brake pedals of the two foot brake valves 74a, 74b are mechanically coupled, so that when one of the two brake pedals is actuated, both assigned rear brake cylinders 80a, 80b are synchronously applied with the same brake pressure, thus ensuring the vehicle 2 is braked in a directionally stable manner. In its function as a steering brake system, the brake pedals are mechanically separated, so that when one of the brake pedals is actuated, only the assigned rear brake cylinder 80a, 80b is applied with brake pressure, thereby assisting a turning or maneuvering of the vehicle 2 in the respective direction.

[0049] Each of the two foot brake valves 74a, 74b has a position sensor 82a, 82b that measures the position of the respective valve piston and transmits this information via an electrical sensor line 84a, 84b to the central control unit 60, where a brake signal can be generated from the position signal. The central control unit 60 communicates with the brake control unit 40 via a data bus 86, such as a CAN bus, for information transmission. The brake control unit 40 also communicates with the hydrostatic drive 3 via a control line 122.

[0050] The trailer control valve 88 is connected on the input side via a pneumatic supply line 92 to a compressed air source 90 and via a hydraulic brake control line 94 to the axle relay valve 76 of the primary brake system 72. In addition, the trailer control valve 88 is connected to the brake control unit 40 via an electrical control line 96.

[0051] In normal operation, the incoming pneumatic supply pressure is reduced as needed and passed through the trailer control valve 88. On the outgoing side, it is routed via a pneumatic supply line 98 to a coupling head "Supply" (red) 100 of the work vehicle 2. Additionally, depending on the brake pressure present in the hydraulic brake control line 94 and / or a control signal transmitted via the control line 96, a pneumatic brake control pressure is set in the trailer control valve 88. This pressure is routed via a brake control line 102 to a coupling head "Brake" (yellow) 104 of the work vehicle 2. When a trailer 14 is coupled, its pneumatically operated brake system 22 is supplied with the supply pressure present at the coupling head "Supply" 100 and controlled depending on the brake control pressure present at the coupling head "Brake" 104.

[0052] The secondary braking system, i.e., the electronic brake circuit 106, can be used at least as an auxiliary braking system, enabling the work vehicle 2 to be safely braked in the event of a failure of the primary braking system 72. The secondary braking system has only one electronically controlled brake circuit 106 and comprises the second supply line 62 with the associated second hydraulic pressure accumulator 68, a brake control valve 108, an axle brake line 110 branching into two axle brake lines 112a, 112b and serving as the main brake line, and two front brake cylinders 114a, 114b, each connected to one of the two branched brake lines 112a, 112b. The two front brake cylinders 114a, 114b are designed as actively acting diaphragm or piston brake cylinders and are arranged on the wheel brakes 113a, 113b of the front wheels 26a, 26b of the front axle 24, which are known per se and not shown in detail here.

[0053] The brake control valve 108 is designed as a 3 / 3-way proportional solenoid valve with a hydraulic fluid inlet, a hydraulic fluid outlet, and a working port, by means of which the working port can be continuously adjusted between a connection to the hydraulic fluid outlet and the hydraulic fluid inlet. The hydraulic fluid inlet is connected to the hydraulic fluid source 42 via the supply line 62, the hydraulic fluid outlet to a pressureless hydraulic reservoir, and the working port to the two front brake cylinders 114a and 114b via the aforementioned axle brake line 110 and the brake lines 112a and 112b branching off from it.By appropriately controlling the brake control valve 108, the brake pressure p B in the axle brake line 110 and the front brake cylinders 114a, 114b connected to it can be continuously adjusted between a minimum pressure corresponding to the ambient pressure and a maximum pressure corresponding to the supply pressure in the supply line 62.

[0054] The electromagnet of the brake control valve 108 is connected to the brake control unit 40 via an electrical control line 116 and can be controlled by it. In the de-energized state, the working port of the brake control valve 108 is connected to the hydraulic fluid outlet, and in the fully energized state, it is connected without any restriction to the hydraulic fluid inlet. To detect and monitor the brake pressure pB introduced into the axle brake line 110 via the brake control valve 108, a third electro-hydraulic pressure sensor 118 is connected to this axle brake line 110 and is connected to the brake control unit 40 via an electrical sensor line 120. The secondary brake system 106 is thus purely electronically controllable.The brake pressure p B in the axle brake line 110 and the front brake cylinders 114a, 114b connected to it is thus adjustable independently of the primary brake system 72 depending on a brake value signal, which can be determined in the brake control unit 40 from the sensor signals of the position sensors 82a, 82b or in another way.

[0055] For the application of the present method, it is provided that the secondary braking system or the electronically controlled brake circuit 106 is used for the mechanical relief of the hydrostatic drive train 3.1 by controlling the brake control valve 108 by the brake control unit 40 in such a way that the two brake cylinders 114a, 114b on the front axle 24 in the braking phases B1, B2, B3, B4 according to Fig. 2each is subjected to a brake pressure p B, which was previously determined as a function of the driving speed v F of the work vehicle 2 and at least one operating parameter characterizing the mechanical load of the hydrostatic drive train 3.1. Reference symbol list (part of the description)

[0056] 2Work vehicle, tractor 3Hydrostatic drive 3.1Hydrostatic drivetrain 3aFirst rear drive axle 3bSecond rear drive axle 4Front loader bucket 6Hill 8Load 10Vehicle combination 12Towing vehicle, tractor, front section 14Trailer, trailer, rear section 15First direction of travel 16First path 17Second direction of travel 18Second path 20Electronic control unit 22Externally operated braking system 24Front axle 26a, 26bFront wheels 28Rear axle, drive axle 30a, 30bRear wheels 32a, 32bWheel speed sensors 34a, 34bSensor lines 36a, 36bWheel speed sensors 38a, 38bSensor lines 40Brake control unit, control unit for brakes and the drive 42 Hydraulic pressure medium source 44 Collection tank 46 Oil pump 48 Relay valve 50 Pressure medium conditioning unit 52 First supply line 54 First pressure sensor 56 Sensor line 58 First pressure accumulator 60 Central control unit 62 Second supply line 64 Second pressure sensor 66 Sensor line 68 SecondPressure accumulator 69 Switching of the control element 70 70 Control element, direction lever 72 Primary brake system 74a, 74b Foot brake valves 76 Axle relay valve 77 High-pressure line of the hydrostatic drive train 78a, 78b Wheel brake lines on the rear axle 80a, 80b Two brake cylinders on the rear axle 82a, 82b Two brake force sensors or travel sensors on the two foot brake valves 84a, 84b Sensor lines 86 Data bus, CAN bus 88 Trailer control valve 90 Compressed air source 92 Supply line (compressed air) 94 Brake control line (hydraulic) 96 Control line 98 Supply line (compressed air) to coupling head "Supply" (red) 100 Coupling head "Supply" (red) 102 Brake control line 104 Coupling head "Brake" (yellow) 106 Electronically controlled brake circuit; secondary brake system 108 Brake control valve 110 Axle brake line serving as main brake line 112 Front axle brake line branching off from axle brake line 110 112a First section branching off from front axle brake line 112 112b From the frontAxle brake line 112 branching second section 113a First brake of the electronically controlled brake circuit 106 113b Second brake of the electronically controlled brake circuit 106 114a First brake cylinder of the electronically controlled brake circuit 106 114b Second brake cylinder of the electronically controlled brake circuit 106 115a Section of the front axle brake line 112 between the first ABS control unit 130 and the first brake cylinder 114a 115b Section of the front axle brake line 112 between the second ABS control unit 132 and the second brake cylinder 114b 116 Control line 118 Third pressure sensor 120 Sensor line 122 Control line for the drive 130 First ABS control unit with inlet and outlet valve 132 Second ABS control unit with inlet and outlet valve a F_target operating parameter, target braking deceleration AStart position BLoading position B1First braking phase B2Second braking phase B3Third braking phase B4Fourth braking phase CFirst reversing position DUnloading position ESecondReversing position i HA Operating parameter, translation M HA_A Operating parameter, output torque M HA_E Operating parameter, input torque p A Operating parameter, working pressure p B brake pressure R Reverse S BE Operating parameter, switching position t time t0 time point t1, t1' time points t2, t2' time points t3, t3' time points t4, t4' time points v F travel speed v F_min minimum travel speed v F_min* minimum travel speed V forward travel

Claims

1. A method for controlling a change in the direction of travel of a working vehicle (2) between forward travel and rearward travel or vice versa, wherein the working vehicle (2) has an electronically controllable hydrostatic travel drive (3), a power-operated brake system (22) with at least one electronically controllable brake circuit (106), and an electronic brake control unit (40) for controlling the travel drive (3) and the at least one electronically controllable brake circuit (106) of the brake system (22), and in which, during travel in a first direction of travel (15), a change in the direction of travel in the opposite direction of travel (17) is triggered by switching (69) the hydrostatic travel drive (3) by means of an assigned manual operating element (70), wherein, when performing the change in the direction of travel from forward travel to rearward travel or vice versa, decelerating of the working vehicle (2) is supported by automatically actuating the brakes (113a, 113b) of the electronically controllable brake circuit (106) of the brake system (22), wherein these brakes (113a, 113b) are actuated by being triggered by switching (69) the operating element (70) and are re-released when standstill of the vehicle (v F =0) is reached at the latest, characterised in that the speed of travel (vF) of the working vehicle (2) and at least one operating parameter (aF_soll, iHA, MHA_A, MHA_E, pA, SBE) characterising the mechanical load of the hydrostatic drive train (3.1) are sensor-recorded and their values are being transmitted to the brake control unit (40), and in that the brake pressure (pB) that is to be set for the brake cylinders (114a, 114b) of the brakes (113a, 113b) of the electronically controllable brake circuit (106) is determined in the brake control unit (40) depending on the speed of travel (vF) of the working vehicle (2) and the value of the at least one operating parameter (aF_soll, iHA, MHA_A, MHA_E, pA, SBE) characterising the mechanical load of the hydrostatic drive train (3.1).

2. The method according to claim 1, characterised in that the brakes (113a, 113b) of the electronically controllable brake circuit (106) are only actuated if the speed of travel (vF) of the working vehicle (2) at the time of switching (69) the operating element (70) has reached or exceeds (| vF | > vF_min) a predefined minimum speed of travel (vF_min).

3. The method according to any one of claims 1 to 2, characterised in that the brakes (113a, 113b) of the electronically controllable brake circuit (106) are released already before reaching standstill of the vehicle (vF = 0) if the speed of travel (vF) of the working vehicle (2) has reached or fallen below (| vF | <vF_min*) a minimum speed of travel (vF_min*) near zero.

4. The method according to any one of claims 1 to 3, characterised in that the brakes (113a, 113b) of the electronically controllable brake circuit (106) are released as soon as actuation of a foot brake valve (74a, 74b) is detected, wherein the brake pressure (pB) already set for the brake cylinder (114a, 114b) in question is translated, in a constant progression, into the brake pressure that is set via the foot brake valve (74a, 74b) or is determined by means of a braking value generator or an actuator travel sensor (82a, 82b) arranged on the foot brake valve (74a, 74b).

5. The method according to any one of claims 1 to 4, characterised in that the level of the brake pressure (pB) set for the brake cylinders (114a, 114b) of the electronically controllable brake circuit (106) is determined in proportion to the speed of travel (vF) of the working vehicle (2) present at the time of switching (69) the operating element (70).

6. The method according to any one of claims 1 to 5, characterised in that the level of the brake pressure (pB) set for the brake cylinders (114a, 114b) of the electronically controllable brake circuit (106) is determined in proportion to the input torque (MHA_E), the working pressure (pA) in a highpressure line (77), and the output torque (MHA_A) or the transmission (iHA) of the hydrostatic drive train (3.1) at the time of switching (69) the operating element (70).

7. The method according to claim 5 or 6, characterised in that the brake pressure (pB) set for the brake cylinders (114a, 114b) of the electronically controllable brake circuit (106) after switching (69) the operating element (70) is kept constant until the brakes (113a, 113b) are released.

8. The method according to claim 5 or 6, characterised in that the brake pressure (pB) set for the brake cylinders (114a, 114b) of the brakes (113a, 113b) of the electronically controllable brake circuit (106) after switching (69) the operating element (70) is continuously lowered until the brakes (113a, 113b) are released.

9. The method according to claim 5 or 6, characterised in that the brake pressure (pB) set for the brake cylinders (114a, 114b) of the electronically controllable brake circuit (106) after switching (69) the operating element (70) is controlled such that a predetermined braking deceleration (aF_soll) is complied with.

10. The method according to any one the claims 1 to 9, characterised in that the brake pressure (pB) in the brake cylinders (114a, 114b) of the electronically controllable brake circuit (106) is set by means of an electronically drivable proportional valve (108) to which, on the input side, a pressure-containing supply line (62) and, on the output side, a main brake line (110) leading to the brake cylinders (114a, 114b) are connected.

11. The method according to any one of the claims 1 to 9, characterised in that the brake pressure (pB) in the brake cylinders (114a, 114b) of the brakes (113a, 113b) of the electronically controllable brake circuit (106) is set by means of ABS control units (130, 132), to each of which, on the input side, a portion (112a, 112b) of a front axle brake line (112) branching off an axle brake line (110), and, on the output side, a portion (115a, 115b) of the front axle brake line (112) leading to a brake cylinder (114a, 114b) of the associated brake (113a, 113b) are connected.

12. The method according to any of the claims 1 to 11, characterised in that in a vehicle combination (10) consisting of a towing vehicle (12) and a trailer vehicle (14), only the brakes (113a, 113b) of at least one electronically controllable brake circuit (106) of the brake system (22) of the in the direction of travel rear partial vehicle (14) are actuated.

13. The method according to any one of the claims 1 to 11, characterised in that in a vehicle combination (10) consisting of a towing vehicle (12) and a trailer vehicle (14) the brakes (113a, 113b) of at least one electronically controllable brake circuit of the brake system (22) of the in the direction of travel rear partial vehicle are actuated more strongly than the brakes (113a, 113b) of at least one electronically controllable brake circuit (106) of the in the direction of travel front partial vehicle (12).

14. The method according to any one of claims 1 to 13, characterised in that, after actuating (69) the manual operating element (70) to support decelerating the working vehicle (2) or the towing vehicle (12) or the trailer vehicle (14), the brakes (113a, 113b) on the front axle (24) or on the rear axle (28) and / or on the front axle (24) and on the rear axle (28) of this vehicle (2, 12, 14) are actuated electronically controlled.