Method for neutral switching of a hydrostatic travel drive

Abstract

The invention relates to a method for controlling a travel drive of a work machine, the travel drive being provided with a hydrostatic transmission (4), the hydrostatic transmission (4) being provided with a first hydraulic machine (8), the displacement of which can be adjusted. Wherein the first hydraulic machine (8) is coupled to the drive machine (2) and is responsible for the pressure medium supply of a second hydraulic machine (14) of the travel drive, which is coupled to the output and can be adjusted with respect to the displacement thereof, and wherein the first hydraulic machine (8) is connected to the second hydraulic machine (14) by means of a first and a second working line (10, 12), wherein a power transmission from the work machine to an output (26) can be carried out by means of a first hydraulic machine (8) and a second hydraulic machine (14), said method comprising the following steps: a. Detecting a travel speed gradient of the work machine and / or a load of the work machine or an operating variable that can be used to ascertain the load; b, obtaining an instruction for deactivating the power transmission; c. Ascertaining a desired characteristic of the displacement change of the first hydraulic machine (8) and the second hydraulic machine (14) on the basis of the travel speed gradient, the load or the operating variable detected in step a. While the power transmission is deactivated; d. The power transfer is deactivated by a change in the displacement of the first hydraulic machine (8) and the second hydraulic machine (14) on the basis of the desired characteristics ascertained in step c.

Description

Technical Field

[0001] The invention relates to a method for shifting a hydrostatic drive into neutral. Background Art

[0002] Hydrostatic travel drives for mobile working machines are known, in which a hydraulic pump and one or more hydraulic motors are connected to one another in a closed hydraulic circuit to form a hydrostatic transmission. The hydraulic pump is driven by an internal combustion engine, such as a diesel engine, and the hydraulic motors ultimately drive the mobile working machine, for example via corresponding wheels.

[0003] The hydraulic pumps of such travel drives are usually adjustable in their delivery capacity. Thus, for example, at a constant rotational speed of the internal combustion engine, the volume flow delivered by the hydraulic pump can be varied in a closed circuit and the output rotational speed of the hydraulic motor or its wheels, i.e. the travel speed of the movable driven machine, can thus be adjusted. It is also known that the hydraulic motors are also adjustable in their fluid intake per revolution.

[0004] In order to increase the transmission options, hydrostatic transmissions are often provided with a series-coupled mechanical shifting mechanism. Automation allows the transmission ratios of the shifting mechanism of such transmissions to be switched even during driving.

[0005] To this end, the torque between the hydraulic motor of the hydrostatic transmission and the transmission input of the shift transmission is reduced to zero. This is done by reducing the displacement of the hydraulic motor to zero ("zero vibration"). When the displacement reaches zero, the old transmission stage is disengaged and the new transmission stage is engaged by mechanical synchronization.

[0006] Previous solutions only allow for the time-controlled regulation of hydraulic pumps and hydraulic motors, but not for physical state variables (such as pressure) or system parameters (such as transmission ratio).

[0007] Disadvantages of previous solutions are the large parameter space required to reproduce the necessary performance, the limited performance due to the worst-case parameterization (slow ramp to avoid high pressures) and the resulting very long transition phase to the neutral state. In addition, the known solutions have limited robustness due to state independence, since the fixed parameterization is only conditionally robust. In addition, there is limited performance during the transition to normal driving, since the load state is not taken into account. Summary of the invention

[0008] It is therefore an object of the present invention to provide a method for conversion with which the above-mentioned problems can be overcome. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention is described with reference to the accompanying drawings, wherein the same reference numerals refer to the same components and / or similar components and / or corresponding components of the system. With respect to the drawings:

[0010] Figure 1 The circuit diagram of the travel drive is schematically shown;

[0011] Figure 2 The circuit diagram of the hydraulic pump is shown schematically. DETAILED DESCRIPTION

[0012] The present invention is described below with reference to specific embodiments as shown in the accompanying drawings. However, the present invention is not limited to the specific embodiments described in the following detailed description and shown in the accompanying drawings, but the described embodiments only illustrate some aspects of the present invention, and its protection scope is limited by the claims.

[0013] Other changes and variations of the present invention are clear to those skilled in the art. Therefore, this specification covers all changes and / or variations of the present invention, and its protection scope is defined by the claims.

[0014] according to Figure 1 A travel drive 1, for example a travel drive of a movable working machine, has a transmission 3 with a drive engine 2, preferably in the form of a diesel engine, a hydrostatic transmission 4 and, preferably in the present embodiment, a two-stage shifting transmission 6. As explained in the course of the description, the present invention can be used in travel drives with or without a shifting transmission 6. However, it is important that a hydrostatic transmission 4 is present.

[0015] The hydrostatic transmission 4 has a first hydraulic machine 8 constructed as an axial piston pump in the form of a swash plate structure, which is fluidically connected to a second hydraulic machine 14 constructed as an axial piston motor in the form of a slanted shaft structure in a closed hydraulic circuit via two working lines 10, 12. The first hydraulic machine 8 is coupled to the drive machine 2 via a drive shaft 16. The drive shaft 18 of the second hydraulic machine 14 is coupled to the input shaft 20 of the gearshift transmission 6 in this embodiment. The output shaft 22 of the gearshift transmission 6 is coupled to the differential 24 of the shaft 26 of the two wheels of the travel drive 1. The two hydraulic machines 8, 14 each have an adjustable displacement. The first hydraulic machine 8 is constructed so that it can work not only as a hydraulic pump but also as a hydraulic motor in all four quadrants along two torque directions.

[0016] The transmission 3 further comprises a control device 28, in particular for controlling the torque of the drive shaft 18. A shift request device 30, a gear selection device 32, a driving direction selection device 34, an accelerator pedal 36, a crawler gear selection device 38, a brake pedal 40 and an automatic device selection device 42 are connected to the control device 28 by signals. All of the aforementioned devices 30 to 42 are connected to the control device 28 by signals on the one hand and to at least the drive machine 2 on the other hand via a CAN bus 44.

[0017] The shifting mechanism 6 has a first transmission stage 46 with a small transmission ratio and a second transmission stage 48 with a larger transmission ratio, which is the ratio of the rotational speed of the output shaft 23 to the rotational speed of the input shaft 18. In addition, the shifting mechanism 6 has a claw clutch 50, which is designed without a synchronizer ring (however, a synchronizer can of course be provided within the scope of the present invention). The actuator 52 of the claw clutch 50 is rigidly coupled to the piston 54 of the control cylinder 56. The last-mentioned control cylinder has two identical pressure medium chambers 58, 60 separated from the piston 54, which are connected to the electromagnetically actuated 4 / 3-way switching valve 66 via control lines 62, 64. The last-mentioned switching valve has a first switching position 66a, in which the first pressure chamber 58 is connected to the pressure medium line 68 and the second pressure chamber 60 is connected to the tank line 70. In the second switching position 66b, the second pressure medium chamber 60 is connected to the pressure medium line 68 and the first pressure medium chamber 58 is connected to the tank line 70. In this case, the first shift position 66 a causes a displacement of the piston 54 , so that the first transmission ratio 46 is engaged via the claw clutch 50 , and the second shift position 66 b causes the second transmission ratio 48 to be engaged via the piston 54 and the claw clutch 50 .

[0018] The 4 / 3-way switching valve 66 and the control cylinder 56 are combined into one unit. In addition, this unit has two end position switches 72, 74, by which the successful switching of the corresponding transmission stage 46, 48 can be detected according to the position of the piston 54. The two end position switches 72, 74 are each connected to the control device 28 via a signal line. The 4 / 3-way switching valve 66 is connected to the feed pump 76 via a pressure medium line 68.

[0019] The hydrostatic transmission 4 has a variable, continuously adjustable transmission ratio range. The gearshift transmission 6 connected downstream thereof is used to cover the required speed range of the driving drive 1. The transmission 3 is designed in this case so that the gearshift transmission 6 can be switched during driving operation.

[0020] The switching or changeover of the transmission stages 46, 48 can be automatically controlled by the control device 28. For this purpose, the transmission 3 has a rotational speed sensor 76, by which the rotational speed of the output shaft 22 can be detected. In addition, the transmission has a rotational speed sensor 78 for detecting the rotational speed of the input shaft 18.

[0021] The first transmission stage 46 has a gear wheel 80 that is fixedly coupled to the input shaft and that permanently meshes with an idler gear wheel 82 that can be coupled to the output shaft 22 via a dog clutch 50. The second transmission stage 48 accordingly has a gear wheel 84 that is fixedly coupled to the input shaft 18 and an idler gear wheel 86 that is permanently meshed with the gear wheel and that can be coupled to the output shaft 22 via a dog clutch 50.

[0022] according to Figure 1 , the first hydraulic machine 8 has a regulating unit 88 for regulating its first displacement, and the second hydraulic machine 14 has a regulating mechanism 90 for regulating its second displacement, wherein the regulating mechanism 90 is completed in an electrically proportional manner. For this purpose, the regulating mechanism 90 has a hydraulic regulating cylinder, and the pressure medium can be supplied to the interacting pressure chambers of the regulating cylinders respectively through pressure regulating valves that can be adjusted electrically proportionally. The electrically proportional regulation enables stepless regulation of the displacement. Here, the regulation is proportional to the applied regulating current. The regulating pressure is usually obtained from the working pipelines 10, 12 and supplied to the pressure chambers through pressure regulating valves that can be adjusted electrically proportionally. The regulation of the second hydraulic machine is preferably independent of the load pressure. This means that due to the return of the regulating position (displacement) of the regulating mechanism 90, the regulation can be corrected, so that a specific displacement can be reliably achieved without depending on the load pressure. In contrast, the first hydraulic machine 8 is a load-sensing pump, wherein the regulation of the displacement in the load-sensing hydraulic machine depends on the pressure in the first working pipeline and / or the second working pipeline.

[0023] According to the invention, the pressure difference is regulated by the first hydraulic machine 8. The already mentioned regulation concept based on the control pressure to be regulated is explained in detail below. The working lines 10, 12 are protected against overload by corresponding pressure limiting valves 92 with supplementary suction function. In addition, each first hydraulic machine 8 has a control pressure port G, at which a constant control pressure is present.

[0024] according to Figure 2 , the regulating mechanism 88 of the first hydraulic machine 8 has a pressure reducing valve 106. The pressure reducing valve can be connected to the pressure medium chamber of the regulating cylinder 98 via the 4 / 3-way switching valve 96, and the piston 100 of the regulating cylinder is coupled to the cradle of the first hydraulic machine 8 to adjust the first displacement of the first hydraulic machine. The pressure reducing valve 106 can be electromagnetically actuated in the case of direct electrical control and is connected to the pressure medium chamber of the regulating cylinder 98 via the signal line 44a according to Figure 128 of the control device 24. The control pressure provided by the connection G is present at the control pressure inlet 104 of the pressure reducing valve 106 via the control pressure line 102. The valve body of the pressure reducing valve 106 is preloaded by a spring into an end position in which the control pressure outlet of the pressure reducing valve 106 is connected to the tank T in a pressure medium connection. The electromagnet 109, which can be energized via the signal line 44a, counteracts the spring force. When energized, the valve body of the pressure reducing valve 106 moves from the mentioned end position (connection of the control pressure outlet to the tank T) toward an intermediate position in which the other end position that causes the fluid connection of the control pressure inlet 104 to the control pressure outlet is increasingly influenced.

[0025] Correspondingly, as the energization level of the electromagnet 109 increases, the control pressure at the control pressure outlet 106 increases. The control pressure outlet 106 is connected to the 4 / 3-way switching valve 96 via a control pressure line. Then, depending on its switching position 96a or 96b, either one or the other pressure medium chamber of the regulating cylinder 98 is loaded with pressure medium. Thus, the 4 / 3-way switching valve 96 serves as a valve for determining the travel direction. As an alternative, two different pressure reducing valves can be used to supply control pressure to the two pressure medium chambers independently of each other.

[0026] In order to change the gear stage from the first gear stage 46 to the second gear stage 48, as already mentioned, the input shaft 20, that is, the drive shaft 18, should be adjusted to be torque-free. This is achieved by adjusting the displacement of the first and second hydraulic machines 8, 14. After the drive shaft 18 is torque-free, the gear stage change can be performed.

[0027] The object of the invention is in fact to develop a method for achieving a torque-free state of a drive shaft.

[0028] It is clear to a person skilled in the art that this goal can also be achieved in the case of a travel drive without a gearshift transmission. In the agricultural and construction machinery market, hydrodynamic drives are increasingly being replaced by hydrostatic drives. In order to facilitate the switching, it is partly required to simulate the characteristics of the hydrodynamic drive with a hydrostatic device during neutral shifting (disconnecting the clutch and thus "freewheeling" the drive train). There are no known solutions on the market that switch to neutral when neutral is required and redirect the hydrostatic device back to the normal drive mode when the direction of travel is required. Therefore, it will be clear to a person skilled in the art that the method described in this patent application can also be used in a travel drive without a gearshift transmission.

[0029] In the course of the description a method is therefore described by which a torque-free state of the drive shaft 18 can be achieved.

[0030] In a first step, a command is given to deactivate the power transmission between the first and second hydraulic machines, so that the drive shaft will no longer receive torque from the drive machine 2 .

[0031] After receiving this command, the speed gradient of the driven machine and / or the load of the driven machine or an operating variable that can be used to determine the load is detected. Of course, this detection can also be performed continuously, so that the control device already knows this variable when receiving the command. The operating variable can be the pressure in the first and / or second working line 10, 12, wherein the load is determined by the detected pressure.

[0032] The command can be generated either manually via the shift request mechanism 30 or automatically via the control mechanism 28. For example, the control mechanism 28 can recognize that a gear change is required to achieve the driving desire that can be recognized by the accelerator pedal 36. In another example, when the movable working machine is traveling downhill, it can be recognized by the control mechanism that the power of the drive machine is not required, so that the power transmission should be stopped in order to save energy. It should be pointed out that in this specific application, a gearshift transmission mechanism is not required in the driving drive (that is, the present invention can also be used in a drive without a gearshift transmission mechanism).

[0033] During the deactivation of the power transmission, the desired behavior of the displacement change of the first and second hydraulic machines 8, 14 is determined based on the detected driving speed gradient, load or operating variable. The reason is that the greater the load or the driving speed gradient, the faster the power deactivation should be carried out (i.e. the faster the adjustment speed of the two hydraulic machines) in order to supply the power of the drive machine to the output end again. On the other hand, if a lower gradient is observed, the deactivation can be carried out significantly slower, making it more comfortable.

[0034] The desired characteristic is determined based on a function, wherein the function determines the displacement gradient for the first hydraulic machine 8 and the second hydraulic machine 14 based on the detected driving speed gradient, load or operating variable, wherein the higher the detected driving speed gradient and / or load, the greater the displacement gradient.

[0035] In a further step, based on the ascertained desired properties, the power transmission is deactivated by changing the displacement of the first and second hydraulic machines, wherein in this step both hydraulic machines are steered in the direction of zero displacement.

[0036] During this step, the pressure in the first and / or second working lines 10, 12 is detected, wherein, in the case where the detected pressure exceeds a first value or falls below a second value, the desired characteristics of the second hydraulic machine 14 and / or the first hydraulic machine 8 are adjusted in such a way that the pressure in the first and / or second working lines 10, 12 will again fall below the first value or again exceed the second value.

[0037] The reason for this is that, due to the dynamic differences between the motor (second hydraulic machine) and the pump (first hydraulic machine), a pressure increase may occur in the hydrostatic circuit. In order to counteract this pressure increase, the adjustment speed of at least one of the two hydraulic machines is reduced in proportion to the pressure increase. For example, if the pressure exceeds a first value, the adjustment of the motor is slowed down, because otherwise a higher pressure would still appear in the working line. In addition, since the adjustment speed of the second hydraulic machine is too slow, the pressure in the working line will also drop significantly. However, the second value ensures that there is sufficient adjustment pressure to supply the second hydraulic machine 14, because it does not have an additional pump to deliver the adjustment pressure.

[0038] When adjusting the displacement, the displacement of the second hydraulic machine 14 is preferably first brought to zero, wherein after the displacement of the second hydraulic machine 14 has been adjusted to zero, the displacement of the first hydraulic machine 8 can also be brought to zero. With this solution, sufficient pressure can always be effectively present in the working line, so that the second hydraulic machine can actually be adjusted until the displacement reaches zero. However, it is not necessary to also bring the displacement of the first hydraulic machine 8 to zero. The advantage is that the drag torque or friction torque of the second hydraulic machine 14 can be reduced to a minimum due to the lower pressure.

[0039] After the power transmission has been deactivated (i.e. after both the first hydraulic machine and the second hydraulic machine have reached zero displacement), an instruction is received to reactivate the power transmission, wherein after the instruction is received, the reactivation of the power transmission is performed by changing the displacement of the first hydraulic machine 12 and the second hydraulic machine 8 based on the desired characteristics determined.

[0040] In the method described, the rotational speed of the drive machine 2 is kept constant throughout the deactivation period (and preferably also during the reactivation period).

[0041] When the power transmission is reactivated, a target value is determined for the displacement of the second hydraulic machine 14 , wherein this target value is determined taking into account the displacement of the second hydraulic machine 14 before the power transmission was terminated and the transmission ratio of the shifting mechanism 6 .

[0042] In order to determine the target value for the displacement of the second hydraulic machine 14 , two intermediate steps are carried out.

[0043] In a first intermediate step, a first and a second intermediate value are determined, wherein the two values ​​are determined using two different functions. These functions can depend on whether a switch is being made from a lower transmission ratio of the gearshift mechanism to a higher transmission ratio or vice versa.

[0044] When switching from a lower transmission ratio to a higher transmission ratio of the gearshift transmission, these two functions can be used:

[0045]

[0046] Where VgL 2 A first function for a first intermediate value is described, in which the displacement for the second hydraulic machine under low load conditions, VgH, can be ascertained. 2 A second function for a second intermediate value is described, wherein the displacement for the second hydraulic machine under higher load conditions can be ascertained, Vg describes the displacement of the second hydraulic machine before the switchover, and i A and i N The gear ratios before and after the shift are described respectively.

[0047] As an alternative, when switching from a higher transmission ratio to a lower transmission ratio of the gearshift transmission, these two further functions can be used:

[0048] V L 1 =Vg

[0049]

[0050] Where VgL 1 A first function for a first intermediate value is described, in which the displacement for the second hydraulic machine under low load conditions, VgH, can be ascertained. 1 A second function for a second intermediate value is described, wherein the displacement for the second hydraulic machine under higher load conditions can be ascertained, Vg describes the displacement of the second hydraulic machine before the switchover, and i A and i N The gear ratios before and after the shift are described respectively.

[0051] The two intermediate values ​​determined using these functions are then used to determine a target value for the displacement of the second hydraulic machine. In particular, in a second intermediate step, an interpolation is performed between the first and second intermediate values, wherein this interpolation is performed based on the detected driving speed gradient and / or the detected load. The higher the load, the more meaningful the second intermediate value is, and conversely, the lower the load, the more meaningful the first intermediate value is.

[0052] In order to ensure that there is always sufficient pressure to supply the second hydraulic machine, the adjustment speed of the first hydraulic machine is reduced in proportion to the pressure drop, similar to the deactivation phase. This prevents the hydraulic motor (second hydraulic machine) from absorbing more oil than the pump (first hydraulic machine) can deliver due to its dynamic limitations.

[0053] The invention has been described with reference to the above embodiments, and it is clear to those skilled in the art that various modifications, changes and improvements of the invention can be implemented based on the above theory and within the scope of the appended claims without departing from the scope of protection of the invention.

[0054] Furthermore, areas of expertise that are well known to those skilled in the art have not been described herein in order not to unnecessarily obscure the described invention.

[0055] Accordingly, the present invention should not be limited by the specific illustrative embodiments, but should only be limited by the scope of protection of the appended claims.

Claims

1. A method for controlling a travel drive of a driven machine, wherein the travel drive is provided with a hydrostatic transmission (4), wherein the hydrostatic transmission (4) is provided with a first hydraulic machine (8) whose displacement is adjustable, wherein the first hydraulic machine (8) is coupled to a drive machine (2) and is responsible for the pressure medium supply of a second hydraulic machine (14) of the travel drive which is coupled to an output and whose displacement is adjustable, wherein the first hydraulic machine (8) is connected to the second hydraulic machine (14) by means of a first and a second working line (10, 12), wherein power can be transmitted from the driven machine to an output (26) via the first hydraulic machine (8) and the second hydraulic machine (14), wherein the method comprises the following steps: a. detecting the speed gradient of the working machine and / or the load of the working machine or an operating parameter that can be used to ascertain the load; b. Obtaining an instruction to deactivate the power transfer; c. determining the desired characteristics of the displacement change of the first hydraulic machine (8) and the second hydraulic machine (14) based on the driving speed gradient, load or operating variable detected in step a. during the deactivation of the power transmission; d. Based on the desired characteristics ascertained in step c., the power transmission is deactivated by changing the displacement of the first hydraulic machine (8) and the second hydraulic machine (14).

2. The method according to claim 1, wherein the first hydraulic machine (8) is a load-sensing hydraulic machine, wherein the regulation of the displacement in the load-sensing hydraulic machine depends on the pressure in the first working line and / or the second working line.

3. A method according to any one of claims 1 or 2, wherein during step d. the pressure in the first working line and / or the second working line (10, 12) is detected, wherein in the case where the detected pressure exceeds a first value or is lower than a second value, the desired characteristics of the second hydraulic machine (14) and / or the first hydraulic machine (8) are adjusted so that the pressure in the first working line and / or the second working line (10, 12) is again lower than the first value or again exceeds the second value.

4. The method according to any one of claims 1 to 3, wherein in step d. the displacement of the second hydraulic machine (14) is first brought to zero, wherein after the displacement of the second hydraulic machine (14) is adjusted to zero, the displacement of the first hydraulic machine (8) is also brought to zero.

5. A method according to any one of claims 1 to 4, wherein in step c. the desired characteristic is determined based on a function, wherein the function determines the displacement change gradient for the first hydraulic machine (8) and for the second hydraulic machine (14) based on the driving speed gradient, load or operating parameters detected in step a., wherein the higher the detected driving speed gradient and / or load, the greater the displacement change gradient.

6. A method according to any one of claims 1 to 5, wherein after the power transmission is deactivated in step d., an instruction for reactivating the power transmission is obtained, wherein after obtaining the instruction, the reactivation of the power transmission is performed by changing the displacement of the first hydraulic machine (12) and the second hydraulic machine (3) based on the desired characteristics ascertained in step c.

7. The method according to any one of claims 1 to 6, wherein the travel drive further comprises a shift transmission mechanism (3) connected downstream of the hydrostatic transmission mechanism (4), wherein the command obtained in step b. is ascertained from the shifting expectation of the shift transmission mechanism (3).

8. The method according to claim 7, when dependent on claim 6, wherein a target value for the displacement of the second hydraulic machine (14) is determined when the power transmission is reactivated, wherein the target value is determined before the power transmission and the transmission of the shift transmission mechanism (3) are deactivated taking into account the displacement of the second hydraulic machine (14).

9. The method according to claim 8, wherein the following steps are performed in order to determine the target value for the displacement of the second hydraulic machine (14): i. finding the first and second intermediate values, wherein two different functions are used to find the two values; ii. interpolating between the first and second intermediate values, wherein the interpolation is performed based on the driving speed gradient detected in step a. and / or the load detected.

10. The method according to claim 1, wherein in step a. the operating variable is the pressure in the first working line and / or in the second working line (10, 12), wherein the load is determined via the detected pressure.

11. The method according to claim 1, wherein during the method the rotational speed of the drive machine (2) is kept constant during the entire method.

12. A computing unit (28) which is designed to carry out the method according to any one of the preceding claims.

13. A working machine having a travel drive (1), wherein the travel drive is provided with a first hydraulic machine (8) for supplying pressure medium to at least one second hydraulic machine (14) of the travel drive (1) which can be coupled to an output end (26), and the working machine has a calculation unit (28) according to claim 12.

14. A computer program which, when executed on a computing unit, causes the computing unit to carry out the method according to any one of claims 1 to 11.

15. A machine-readable storage medium having stored thereon the computer program according to claim 14.

Images