EP2542787A1

EP2542787A1 - Hydraulic drive and method for controlling such a hydraulic drive

Info

Publication number: EP2542787A1
Application number: EP10798020A
Authority: EP
Inventors: Peter Dengler
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2010-03-01
Filing date: 2010-12-29
Publication date: 2013-01-09
Also published as: CN102782338B; KR20130012579A; JP5623556B2; CN102782338A; WO2011107135A1; US20130213024A1; US9140275B2; DE102010009704A1; JP2013521444A

Abstract

The invention relates to a hydraulic drive and method for controlling such a drive, wherein two drive motors can be controlled by means of at least one continuously adjustable distribution valve. According to the invention, the two drive motors are designed as adjustable hydraulic machines.

Description

description

Hydraulic travel drive and

Method for controlling such a travel drive

The invention relates to a hydraulic traction drive according to the preamble of claim 1 and a method for driving a traction drive.

Such hydraulic traction drives are running in mobile work equipment, such as compact and mini excavators, in which each wheel or each chain is associated with a hydraulic motor, which are individually controlled to change the motion parameters, such as the direction of travel and driving speed.

In DE 43 25 703 A1 discloses a hydrostatic drive is disclosed, in each of which a wheel of a wheeled vehicle associated hydraulic motors via continuously adjustable directional control valves with a hydraulic motor associated pump are hydraulically connected. This pump is designed as an over zero pivotable axial piston pump, wherein the pressure medium flow rate and the pressure fluid flow direction to the respective associated hydraulic machine by individually controlling the continuously adjustable directional control valves is adjustable.

Such a travel drive can be used, for example, in a hydraulic system of a mobile implement, in which not only the hydrostatic drive and all or some work functions are supplied via the variable displacement. Such hydraulic control arrangements are designed as LUDV system, as described for example in DE 10 2006 002 920 A1 of the applicant. Each work function, such as differential cylinders for adjusting a boom, a handle, a spoon or a hydraulic motor for adjusting the slewing gear each associated with a continuously adjustable directional control valve with downstream LUDV pressure balance. The latter is acted upon in the sense of reducing a throttle cross-section of the highest load pressure of all consumers and in the sense of increasing a throttle cross-section of the pressure downstream of a metering orifice formed by the associated directional control valve. In the control position of each LUDV pressure compensator corresponds to the pressure in the pressure fluid flow path between the associated metering orifice and the respective LUDV pressure compensator the highest load pressure, which is then throttled over this to the individual load pressure of each consumer. By means of this LUDV pressure compensator, the pressure drop across the metering plates load pressure is kept constant independently, whereby in the case of undersaturation the pressure medium volume flow to all actuated consumers of a circuit is proportionally reduced. The variable displacement pump is preferably also controlled depending on the highest load pressure of all connected consumers such that the pump pressure is above this maximum load pressure by a predetermined pressure difference.

When cornering, the load torque on the outside hydraulic motor increases and decreases at the inside of the curve accordingly. The resulting large pressure difference is compensated by the LUDV pressure compensator of the directional control valve, which supplies the inside drive motor. On the one hand, high hydraulic losses occur, on the other hand, it may happen that the power regulator of the variable displacement pump reduces the volume flow due to the high load pressure on the outside drive motor, which leads to a significant reduction in the cornering speed. Another disadvantage of such conventional solutions is that due to manufacturing tolerances, the maximum pressure medium volume flows to the two traction motors can not be set exactly to the same value, so that additional measures to support a straight line run must be taken.

In the publication "Hydrostatic drives with secondary control", the hydraulic trainer Volume 6, Vogel-book publishing, Würzburg, 1989 a traction drive for a shovel with secondary control is shown, each traction drive and the additional work functions are supplied via a variable displacement pump assembly with pressure medium and each chain of the The system is designed with a secondary control, in which the variable speed traction motors are connected to a pressure network and are thus subjected to an impressed pressure, ie in this solution, the speed of the traction motors is controlled so that they are independent of respective load pressure is achieved at the impressed network pressure. Such a secondary control requires a considerable regulatory effort. Another disadvantage of this known solution is that failure of the control unit, the traction motors fail, so that the mobile implement is movable only with great effort.

In contrast, the invention has for its object to provide a simple design and operable with low hydraulic losses hydrostatic drive with improved reliability. The invention is also based on the object to provide a method for driving such a hydrostatic drive.

This object is achieved with regard to the hydrostatic drive by the features of claim 1 and in terms of the method by the features of the independent claim 12.

Advantageous developments of the invention are the subject of the dependent claims.

According to the invention, the hydraulic traction drive with at least two traction motors and at least one, for adjusting movement parameters continuously adjustable directional control valve via which the pressure medium supply and removal to or from the traction motors in response to the actuation of an actuator, such as a joystick or foot pedals or the like is adjustable. According to the invention, the two hydraulic motors are designed adjustable and controlled by a control unit in response to the actuation of the actuator.

Accordingly, it is a kind of mixed solution, in which the advantages of the conventional solution described above with a control of the pressure fluid supply and - are discharged via a directional control valve with the advantages of a secondary control, in which the hydraulic motors of the traction drive are made adjustable. Such a solution thus makes it possible to influence the pressure medium supply to the hydraulic machines via the directional control valve and make any corrections by adjusting the hydraulic motors. This variability is exploited in the process according to the invention. In this case, the setpoint values for the traction motors are initially set via the named actuator, and control signals for the at least one directional control valve are determined from the desired values and a desired speed ratio calculated therefrom by a control unit. In a further method step, this setpoint speed ratio is compared with the actually present actual speed ratio of the traction motors and, depending on the result of this comparison, the traction motors are adjusted until the desired speed ratio is reached. In this way, it is ensured that a desired state of motion, for example, an exact straight ahead or cornering with a predetermined cornering speed can be maintained even under unfavorable operating conditions. Another advantage is that in case of failure of the electronic control for the traction motors by adjusting the directional control valve at least a slow forward or reverse drive of the mobile implement is guaranteed to move it out of a hazardous area out.

In a preferred embodiment of the invention, the continuously adjustable directional control valve is associated with a LUDV pressure compensator via which the pressure medium volume flow can be kept constant, independent of the load pressure, via the directional control valve.

In a simply constructed variant, a single directional control valve is assigned to both traction motors. According to the invention, it is preferred if the one or more continuously variable directional control valves are actuated as a function of the control unit, via which the drive motors are also actuated. In one embodiment, each traction motor is associated with a continuously adjustable directional control valve of the type described above, so that in case of failure of the control electronics for traction motors, the functionality of a conventional system is maintained, so that the mobile implement is still maneuverable. It may be advantageous to provide in the drain lines of the traction motors, a pressure equalizing diaphragm, which improves the straight-ahead running independently of the control of the traction motors.

In one embodiment of the invention, each traction motor is assigned its own actuator. This actuator can be designed as an electronic actuator (Drive by Wire). In principle, however, a hydraulic actuator can be used, the adjustment detected by suitable sensors and converted into control signals for the control unit.

The driving safety is further improved when the traction motors are set in a basic position in the direction of the maximum absorption volume.

To detect the actual state, speed sensors are preferably used.

The control for the travel drive described is preferably carried out as a directional control valve section of a mobile control block, via the other directional valve sections, the other work functions of the mobile implement are controlled.

In the following preferred embodiments of the invention will be explained in more detail with reference to schematic drawings. Show it:

Figure 1 is a circuit diagram of a hydraulic control arrangement of a mobile working device;

FIG. 2 shows a hydraulic travel drive of the control arrangement from FIG. 1; Figure 3 is a flowchart of the control of the traction drive and

FIG. 4 shows a variant of a travel drive for a hydraulic control arrangement according to FIG. 1.

1 shows a circuit diagram of a hydraulic control arrangement 1 of a compact excavator for operating a boom 2, a handle 4, a spoon 6, a slewing gear 8 and a traction drive 10. The boom 2, the handle 4 and the bucket 6 are each a differential cylinder 12th , 14, 16 pressed. The slewing gear 8 has a hydraulic motor 18 and the traction drive 10 is provided with a differential speed control executed, in each of which a traction motor 20, 22 is assigned to a left and a right chain. The pressure medium supply of these hydraulic units via a variable displacement pump 26, which is adjustable via an unillustrated LS control valve in response to the highest load pressure of the driven loads so that the pump pressure is a predetermined Δρ above this highest load pressure. Instead of a variable displacement pump 26, it is also possible to use a constant-displacement pump with an associated LS pressure compensator, via which an excess flow conveyed by the pump flows out to the tank.

The pressure medium supply to and from the consumers is controlled by a mobile control block 28, the directional valves described in more detail below are controlled via suitable actuators, for example via joysticks 30, 32 shown in FIG. 1, wherein the joystick 30 is connected to the boom 2 and the handle 4 and the joystick 32 is associated with the bucket 6 and the slewing gear 8. Via each joystick 30, 32, a hydraulic pilot control device is actuated with pressure reducing valves, via which a control pressure provided by a control pressure source control pressure is reduced to a control pressure difference for actuating the respective control valves. The construction of such hydraulic control devices is known, so that further explanations are unnecessary.

The control of the traction motors 22, 24 via a respective electronic foot pedal 34, 36, the control signals are converted via a control unit 38 into corresponding control signals for the traction drive.

The mobile control block 28 has a basic structure, as described in the aforementioned DE 10 2006 002 920 A1 and consists of a plurality of valve disks, here directional valve sections 40, 42, 44, 46, 48 called an input element 50 and an output element 52nd The directional control valve section 40, 42, 44 are the differential cylinders 12, 14, 16, the directional valve section 46 to the hydraulic motor 18 and the directional valve section 48 associated with the traction drive 10. The input element 50 has an LS connection, via which the load pressure for adjusting the LS pump 26 is tapped.

In the input element 50, an LS pressure relief valve arrangement 54 is provided, via which the LS pressure can be limited and, by means of an orifice, directed to a tank T. can be built. Furthermore, a pressure port P connected to the delivery port of the variable displacement pump 26 and a tank port T connected to a tank 56 are formed on the input element 50. Each directional valve section 40, 42, 44 has two working ports A, B connected to the respective pressure chambers of the differential cylinders 12, 14, 16, and further two control ports a, b connected to the output ports of the above-described pilot devices, so that the respective control pressure difference can be applied.

The mobile control block 28 is designed as a LUDV control block, wherein each directional control valve section 40, 42, 44, 46 with a continuously variable directional control valve 58, 60, 62, 64 is executed. Each of these directional control valves 58, 60, 62, 64 has a speed part formed by a metering orifice 66 and a directional part 68 for adjusting the pressure fluid flow direction to and from the associated consumer 12, 14, 16, 18. For the sake of clarity, only the directional part 68 is shown in FIG and the metering orifice 66 of the directional control valve 58 of the directional valve section 40. With regard to the concrete structure of such directional valves, reference is made by way of example to DE 10 2006 002 920 A1 or corresponding LUDV solutions.

Downstream of each metering orifice 66, a LUDV pressure compensator 70, 72, 74, 76 is arranged, which in the closing direction is driven by the highest load pressure of all

Consumers is charged, which is tapped via a shuttle valve cascade, not shown. In the opening direction acts on the LUDV pressure compensator 70, 72, 74, 76 respectively, the pressure downstream of the associated metering orifice 66. As explained above, via the LUDV-pressure compensator 70, 72, 74, 76 of the downstream of the metering orifices 66 applied highest load pressure throttled the individual load pressure of each associated consumer 12, 14, 16, 18. Depending on the setting of the directional part 68 then pressure medium flows from the associated LUDV pressure compensator 70, 72, 74, 76 to the associated working port A, B, so that the corresponding

Consumers are moved or driven in a predetermined direction at a predetermined speed.

In order to avoid cavitations when the load is drawn, at the directional control valve sections 40, 42, 44, any additional working lines 78, 80 with pressure control are still associated with each working line. limit function provided over the pulling load of increasing pressure chamber with the tank is connected, so that pressure medium can be sucked. About this Nachsaugventile 78, 80 and the pressure in the respective working lines is limited to a maximum pressure. The construction of such Nachsaugventile is also known, so that further explanations are unnecessary.

The structure of the directional control valve section 48 associated with the traction drive 10 will be explained with reference to the enlarged illustration in FIG. Also in this directional valve section 48, a continuously adjustable directional control valve 82 is provided, which has a speed part formed by a metering orifice 84 and a direction part 86 for adjusting the pressure fluid flow direction to the terminals B5, A5.

Downstream of the metering orifice 84, in turn, a LUDV pressure compensator 88 is provided which is acted upon in the closing direction by the highest load pressure of the load in an LS line 90 and in the opening direction by the pressure downstream of the metering orifice 84, which flows from a pressure medium flow path between the metering orifice 84 and the LUDV pressure compensator 88 forming connecting channel 92 is tapped.

As can be seen from the switching symbol of the directional control valve 82 shown on the bottom right in FIG. 2, its input connection P is connected to a supply line 93, which is connected to a pump line 94 connected to the delivery connection of the variable displacement pump 26. A tank connection T of the directional valve 82 is connected via a discharge channel 96 to a tank line 98 leading to the tank 56. The output of the LUDV pressure compensator 88 is connected via a pressure compensator channel 100 to an input P ^{* of} the directional part, while the connection channel 92 connects the input of the LUDV pressure compensator 88 with a pressure compensator connection D of the directional control valve 82. The two working ports A5, B5 are connected via lines 102, 104 to output ports A, B of the directional control valve 82. Depending on the setting of the directional part 86, these lines 102, 104 act as flow or return lines.

To actuate the directional valve 82, two pressure reducing valves 106, 108 are provided, whose input terminals connected to said control oil supply are and which are controlled via the control unit 38 in order to apply to the control sides of the directional control valve 82, a predetermined control pressure difference (a5-b5). The outputs of the pressure reducing valves 106, 108 are, as indicated in Figure 2, connected to the tank 56.

The two traction motors 24, 26 are designed as over zero pivotable hydraulic machines whose pivot angle is adjustable via the control unit 38. Both traction motors 24, 26 are connected in parallel, wherein in each case a working port A is connected via a branching working line 110 to the port A5 of the directional valve section 48 and ports B via a further branching working line 112 to the port B5 of the directional valve section 48. The actuation of the foot pedals 34, 36 is detected electronically via sensors 114, 116 and reported to the control unit 38 by means of signal lines. This converts these setpoints into control signals for adjusting the directional valve 82.

In the solution according to the invention thus takes place via the directional control valve 82, a presetting of the pressure fluid flow direction and the pressure medium flow, with a subsequent adjustment / change of these parameters (flow direction, pressure fluid flow) can be done by appropriate control of the traction motors 24, 26 so that the movement parameters of the traction drive very accurately can be adjusted.

The mode of operation of the traction drive according to the invention is explained on the basis of the greatly simplified flowchart according to FIG.

The two drive motors 24, 26 are preset to their maximum swing angle and thus the maximum displacement. First, the desired cornering speed and the curve are predetermined by the operator by pressing the accelerator pedals 34, 36. From these electronic setpoint signals, the control unit 38 determines control signals for the directional control valve, so that it is acted on by a control pressure difference (a5-b5) and the metering orifice 84 and the directional part 86 are adjusted accordingly. Furthermore, a desired speed ratio of the two traction motors 24, 26 is determined via the control unit 38 from the actuating signals, and this desired speed ratio is compared with the actual speed ratio of the traction motors 24, 26. These actual rotational speeds can be detected, for example, via rotational speed sensors, not shown, or the like.

In a subsequent process step, the actual values are compared with the desired values. In the case where the actual speed ratio corresponds to the target speed ratio, the traction motors 24, 26 are set in accordance with the target value signals, and the mobile working device moves along the predetermined movement curve. In the case in which the actual speed ratio differs from the specification, the two drive motors 26, 28 are adjusted via the control unit, and then in turn the actual speed ratio which then arises is compared with the preset desired speed ratio - this adjustment takes place as long as until the actual speed ratio corresponds to the desired speed ratio.

That is to say, if the speed ratios deviate, the control unit 38 corrects the "faster" traction motor 24, 26 by returning it until the speed ratio specified by the operator has been reached , where the value 0 corresponds to a rotation about a standing chain and the value 1 of a straight ahead driving Furthermore, the specification of negative target speed ratios to -1 allows a counter run of the chains, so that the vehicle - in accordance with the predetermined speed ratio - can turn in place This is then made possible by pivoting an engine over 0 into the negative range

In the exemplary embodiment explained with reference to FIGS. 1 and 2, two travel motors 24, 26 are assigned a common directional valve section 48 and the foot pedals 34, 36 are embodied as so-called electronic foot pedals, whose setpoint signals for the control unit 38 are generated by their actuation.

FIG. 4 shows a variant in which, similar to the conventional solutions described above, each travel motor 24, 26 is provided with a directional valve section 48a, 48b. is ordered, the basic structure of the directional valve section 48 corresponds to Figure 2, so that can be omitted with reference to these statements to a detailed description. A difference from the common directional valve section 48 is that the two directional control valves 82a, 82b are not designed directly with pressure reducing valves, but that the adjustment is done hydraulically via pilot control devices 114, 116, which in dependence on the operation of the footpedals 34, 36 a control pressure difference a5 Generate -b5 or a6-b6. This control pressure difference is applied via corresponding control terminals a5, b5, a6, b6 to the corresponding directional valves 82a, 82b. Each directional valve section 48a, 48b has its own working ports A5, B5 and A6, B6, which are connected via working lines 110a, 112a and 110b, 112b to the corresponding terminals A, B of the traction motors 24, 26. Their adjustment is again via the control unit 38. In this case, the control pressures generated at the pilot control devices 114, 116 are detected by pressure sensors 118 and converted into corresponding desired value signals, which are applied to the input of the control unit 38. In response to this electrical setpoint signals, the displacement of the traction motors 24, 26 is adjusted at preset metering orifices 84a, 84b according to the procedure described above, until the predetermined target speed ratio at the traction motors 24, 26 sets.

Another difference from the solution described above is that the two drain lines 96a, 96b of the two directional control valves 82a, 82b are connected to each other via a pressure equalization diaphragm 120 - this ensures, when driving straight ahead, that differences in speed resulting from manufacturing tolerances and setting tolerances occur when driving straight ahead due to the hydraulic Coupling be compensated in the process. However, such a pressure compensation diaphragm 120 has the disadvantage that when cornering, the speed differences in unbalanced load - for example when driving across the slope still enlarged - these deviations can be compensated by appropriate control of the traction motors 24, 26.

The variant shown in Figure 4 has over the embodiment according to Figures 1 and 2 has the advantage that when switched off or failed electronics for adjusting the pivot angle of the traction motors 24, 26 continue to control in conventional manner via the two-way valve sections 48a, 48b can be done. This means that even if the electronics fail, the vehicle remains fully controllable - without this development, the compact excavator would be left behind and would pose a significant obstacle on the construction site, for example. As a result, the advantages of a conventional hydraulic control are retained in the embodiment according to FIG. 4, although the advantages for improving the driving behavior can be exploited when the electronics are activated.

Disclosed are a hydraulic drive and a method for controlling such a drive, wherein two drive motors are controlled via at least one continuously adjustable directional control valve. According to the two traction motors are designed as adjustable hydraulic machines.

Claims

claims

1. Hydraulic travel drive with two drive motors (24, 26) and at least one for adjusting movement parameters via at least one actuator (34, 36) adjustable directional control valve (82), characterized in that the two drive motors (24, 26) are designed to be adjustable and in that the traction motors (24, 26) can be adjusted by a control unit (38) for adjustment as a function of the actuation of the actuator (34, 36).

2. Drive according to claim 1, wherein the directional control valve (82) is associated with a LUDV pressure balance (88).

3. Drive according to claim 1 or 2, wherein a directional control valve (82) is associated with both traction motors (24, 26).

4. Directional valve according to claim 1 or 2, wherein each drive motor (24, 26) is associated with a directional control valve (82 a, 82 b).

5. Drive according to claim 4, wherein drain lines (96a, 96b) of the directional control valves (82a, 82b) via a pressure compensating diaphragm (20) are hydraulically connected.

6. Drive according to one of the preceding claims, wherein the directional control valve (82) via the control unit (38) is adjustable.

7. Drive according to one of the preceding claims, wherein each drive (24,26) is associated with an actuator (34, 36).

8. Drive according to one of the preceding claims, wherein the actuator is an electronic actuator or a mechanical actuator, whose adjustment via sensors (118) detected and in control signals for the control unit (38) is convertible.

9. Drive according to one of the preceding claims, wherein the traction motors (24, 26) are set to maximum delivery volume in a basic setting.

10. Drive according to one of the preceding claims, with sensors for detecting the rotational speed of the traction motors (24, 26).

11. Drive according to one of the preceding claims, wherein the directional control valve (82) in a directional valve section (48) of a mobile control block (28) is designed to supply multiple hydraulic consumers, wherein a common pump (26) is associated with the drive and a plurality of consumers.

12. A method for controlling a traction drive, in particular according to one of the preceding claims, with the steps:

- Setting set values for traction motors (24, 26) via an actuator (34, 36);

- Generating actuating signals for at least one continuously adjustable directional control valve (82) from the desired values and setting the directional control valve (82) in accordance with these actuating signals;

- Determining a target speed ratio of the traction motors 24, 26;

Comparing an actual speed ratio with the desired speed ratio and

- Adjusting the traction motors (24, 26) via the control unit (38) until the desired speed ratio is reached.

13. The method of claim 12, wherein the speed ratio is in the range of -1 to +1.