METHOD FOR IMPLEMENTING A POWER-LIMITED TORQUE AND SPEED INTERFACE FOR HYDROSTATIC DRIVES

Description

TECHNICAL AREA

[0001] The invention relates to a method for limiting the power output of a hydrostatic drive, wherein the drive is equipped with a hydraulic pump for supplying pressure medium to a hydraulic motor of the drive which can be coupled to an output, wherein the pressure and volume flow generated by the hydraulic pump can be controlled by influencing a control pressure. STATE OF THE ART

[0002] Hydrostatic drive systems for mobile machinery are known, in which a hydraulic pump and one or more hydraulic motors are connected in a closed hydraulic circuit. The hydraulic pump is driven by an internal combustion engine – e.g., a diesel engine – and the hydraulic motors ultimately drive the mobile machinery – e.g., via a wheel.

[0003] The hydraulic pump in such drive systems often has an adjustable delivery volume. This allows, for example, the flow rate delivered by the hydraulic pump in a closed circuit to be changed while the combustion engine is running at a constant speed, thereby adjusting the output speed of the hydraulic motors or the wheels – and thus the driving speed of the mobile machine.

[0004] A hydrostatic drive system according to the state of the art is disclosed in DE 10 2014 224337 A1.

[0005] Hydrostatic axial piston pumps are used, among other things, in the drive systems of construction machinery. One of the functions of these pumps is to limit the maximum permissible pressure. This is necessary to limit torques as well as the maximum permissible pressures of the components.

[0006] In addition to the use of lossy pressure relief valves (where the pump's flow rate is diverted into the tank), hydromechanical pressure control valves are also used. These valves limit the high pressure by reducing the pump's operating pressure, thereby reducing the pump's displacement volume.

[0007] The adjustment characteristics of the hydrostatic components define how the hydrostatic drive achieves a target speed or rotational speed. The acceleration behavior is only indirectly determined by the dynamic setting of the target speed. The power consumption itself cannot be directly reduced, but must be achieved indirectly through angular limitations in the drive system, which then lead to a reduction in power consumption.

[0008] Depending on the system configuration, the control of a hydrostatic transmission can have one degree of freedom, for example in system designs with a variable displacement pump and a constant displacement motor, or up to n+1 degrees of freedom in configurations with n variable displacement hydraulic motors.

[0009] The object of the invention is the successive analytical determination of these degrees of freedom for realizing a target output torque, as well as the consideration of an additional power limitation. Furthermore, the invention should also be able to realize a speed specification instead of a target output torque. Here, too, a power limitation must be taken into account.

[0010] Torque-based driving (specifying a target output torque) and speed-based driving (specifying a target output speed) should be able to be combined seamlessly. This means that no mode switch is necessary for the transition from speed-based driving to torque-based driving. A smooth or continuous switch can be achieved via the target signals. SUMMARY

[0011] The present invention is based on the idea that the hydrostatic drive can be controlled alternately by a target output torque or a target output speed. Furthermore, the present invention is based on the idea that a power limit is implemented for both target output torque control and target output speed control.

[0012] According to one embodiment of the present invention, a method for limiting the power of a hydrostatic drive is provided, wherein the drive is equipped with a hydraulic pump for supplying pressure medium to a hydraulic motor of the drive which can be coupled to an output, wherein the pressure generated by the hydraulic pump (and preferably the swivel angle of the hydraulic motor) is controllable, wherein the hydrostatic drive is alternately controlled by a target output torque or a target output speed, wherein the method comprises the following steps: a. Receiving the command to control the hydrostatic drive by means of a target output torque or a target output speed; b. If the hydrostatic drive is to be controlled by means of a target output torque, calculating a target pressure generated by the hydraulic pump that can provide the desired target output torque, taking into account the displacement volume of the hydraulic motor; if the hydrostatic drive is to be controlled by means of a target output speed, calculating a target swashplate angle of the hydraulic pump that can provide the desired target output speed, taking into account the displacement volume of the hydraulic motor; c. Receiving information about a maximum input power of the hydraulic pump; d. If the hydrostatic drive is to be controlled by means of a target output torque, processing the data from step b.Calculated target pressure, taking into account the maximum input power, if the hydrostatic drive is to be controlled by means of a target output speed; calculation of a maximum pressure that may be generated by the hydraulic pump, taking into account the target swivel angle of the hydraulic pump calculated in step b and the maximum input power, whereby if the hydrostatic drive is to be controlled by means of a target output speed, the hydraulic pump is controlled so that the maximum pressure that may be generated by the hydraulic pump is not exceeded.

[0013] According to one embodiment of the present invention, a method is provided wherein the hydraulic motor is a radial piston motor, wherein the displacement volume of the hydraulic motor depends on a hydraulic motor swivel angle, wherein the calculation of the hydraulic motor swivel angle is carried out using a volume flow balance and taking into account the current speed of the hydraulic motor and the hydraulic pump.

[0014] According to one embodiment of the present invention, a method is provided wherein the hydrostatic drive comprises at least two hydraulic motors.

[0015] According to one embodiment of the present invention, a method is provided wherein, when the hydrostatic drive is to be controlled by means of a target output torque, the target pressure calculated in step b. is limited in step d by adding an estimated or detected hydraulic pump swivel angle and the maximum input power.

[0016] According to one embodiment of the present invention, a method is provided wherein the pressure limited in step d. is implemented by a pressure regulator at the hydraulic pump.

[0017] According to one embodiment of the present invention, a method is provided wherein the hydraulic pump swivel angle is estimated by means of a volumetric flow balance, wherein a leakage volumetric flow rate is taken into account in said volumetric flow balance. According to one embodiment of the present invention, a method is provided wherein the leakage volumetric flow rate is estimated by this formula: Q Leak = k off + Δ p kl wobei Q Leak the leakage volume flow rate, k off an offset factor kl pressure-dependent leakage factor and Δ p The pressure generated by the hydraulic pump. BRIEF DESCRIPTION OF THE FIGURES

[0018] The present invention is described with reference to the accompanying figures, where identical reference numerals refer to identical parts and / or to similar parts and / or to corresponding parts of the system. Regarding the figures: Fig. 1 shows a hydraulic circuit diagram of a hydrostatic drive system according to the state of the art, Fig. 2 shows the method for controlling the hydrostatic drive to realize a target output torque T Drv according to an embodiment of the present invention; Fig. 3 The method for controlling the hydrostatic drive to achieve a target output speed n is shown according to an embodiment of the present invention. Fig. 4 shows a way to adjust the translation of a hydrostatic variator consisting of a pump and motor (a sequential adjustment) according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The present invention is described below with reference to certain embodiments as shown in the accompanying figures. However, the present invention is not limited to the specific embodiments described in the following detailed description and shown in the figures; rather, the described embodiments merely illustrate some aspects of the present invention, the scope of which is defined by the claims.

[0020] Further modifications and variations of the present invention are obvious to a person skilled in the art. The present description therefore encompasses all modifications and / or variations of the present invention whose scope of protection is defined by the claims.

[0021] According to Fig. 1 A drive system 1 has a hydrostatic transmission 2 with a hydraulic machine 4 that functions as a hydraulic pump during traction operation of the drive system 1, and two hydraulic machines 6 and 8 that function as hydraulic motors during said traction operation. Both hydraulic motors 6 and 8 are fluidically connected to the hydraulic pump 4 in a closed hydraulic circuit via working lines 10 and 12 on one side and 14 and 16 on the other. The hydraulic machines 4, 6, and 8 are adjustable in their displacement volume and are each designed as an axial piston machine in a swashplate or swashplate configuration.

[0022] The hydraulic pump 4 is connected via its drive shaft 18 to a drive motor 20 designed as a diesel engine. One of the two hydraulic motors 6, 8 has a first drive shaft 22, and the second hydraulic motor 8 has a second drive shaft 24. A summing gearbox 26 with two input shafts 28 and 30 is connected downstream of the hydrostatic transmission 2 as a mechanical transmission. The first input shaft 28 is rotationally fixed to the first drive shaft 22, and the second input shaft 30 is rotationally fixed to the second drive shaft 24. An output shaft 32 of the summing gearbox 26 is rotationally fixed to a differential 34 of a drive axle 36.

[0023] The summing transmission 26 comprises a clutch 38 designed as a multi-plate clutch. This clutch has a first clutch section 40, which is rotationally fixed to the first input shaft 28. It also has a second clutch section 42, which is rotationally fixed to the second input shaft 30 of the summing transmission 26 via a gear arrangement 44 (shown only schematically). By actuating the clutch 38, which engages the second clutch section 42, the two input shafts 28 and 30, and thus the two output shafts 22 and 24, can be rotationally fixed to each other.

[0024] For actuating the clutch 38, an actuating element 46 designed as a hydraulic cylinder is provided. Its piston 48 is coupled to the second clutch section 42 via a piston rod in a tensile and shear-resistant manner. The hydraulic cylinder 46 has a piston chamber in which a compression spring 50 is arranged. The piston chamber is permanently connected to a tank T via a tank line. On the piston rod side, the hydraulic cylinder 46 has an annular chamber 52, which is connected via a control pressure line 54 to a port S of a control device 56 designed as a pressure regulating valve. The latter has a pressure port P, which is connected via a pressure line 58 to a feed pump 61, which, together with the hydraulic pump 4, is driven by the drive shaft 18. The feed pump 61 draws hydraulic fluid from the tank T. Furthermore, the pressure regulating valve 56 has a tank port T, which is connected to the tank T.The pressure regulating valve 56 is continuously adjustable and has two end positions a and b. In the first end position a, in which the valve body is pre-loaded by a spring 60, the pressure port P is connected to the control pressure port S, and port T is closed off from port S. In the second end position b, the pressure regulating valve 56, or more precisely its valve body, can be actuated by an electromagnet 62. When the electromagnet is energized, and provided the second position b is fully engaged, the control pressure port S is connected to the tank port T, and the pressure port P is closed off. In the first end position a, the annular space 52 is exclusively filled with hydraulic fluid, whereas in the second end position b, hydraulic fluid is exclusively discharged from the annular space 52.Between the two end positions a and b, control positions of the valve body are possible in which the ports P, S and T are in respective pressure medium connection to each other. To return the control pressure to be regulated, which is present at the control pressure port S, to the annular space 52, the annular space 52 is fluidically connected via a control line or a control channel to a control surface of the valve body of the pressure control valve 56, which acts in concert with the spring 60.

[0025] The mechanical transmission 26 further comprises a first speed detection unit 64, via which the speed of the first input shaft 28, and thus of the first clutch section 40 and the first output shaft 22, can be detected. Via a second speed detection unit 66 of the mechanical transmission 26, the speed of the second clutch section 42, and thus indirectly, given the gear ratio of the gear arrangement 44, the speed of the second input shaft 30 and the second output shaft 24, can be detected.

[0026] A control device 70 is associated with the hydraulic pump 4 and interacts with an adjusting device 72 to adjust the displacement volume of the hydraulic pump 4. The first hydraulic motor 6 and the second hydraulic motor 8 each have a control device 74 and 78, respectively, and an adjusting device 76 and 80, respectively. The adjusting device 72 can influence the swivel angle of the hydraulic pump 4 by affecting a control pressure. Similarly, the adjusting devices 76 and 78 can influence the swivel angle of the hydraulic motors 6 and 8 by affecting a control pressure. An example of an adjusting device that controls the swivel angle of the hydraulic pump by affecting a control pressure is disclosed in DE 10 2018 211 586 A1. Alternatively, one or more of the adjusting devices can be electrically actuated units. The present invention is not limited to hydraulic motors 6 and 8 that can be adjusted.In other embodiments, the hydraulic motors can also be constant-speed motors.

[0027] The drive machine 20, the control devices 70, 74 and 78, the electromagnet 62 and the speed detection units 64, 66 are each connected to the control unit 68 via a signal line.

[0028] The following refers to Figuren 2 and 3 The procedure for limiting the power output of the hydrostatic drive is briefly described. The individual steps of the procedure are then described in more detail.

[0029] First, a command is received to control the hydrostatic drive 1 by means of a target output torque or a target output speed.

[0030] The method for controlling the hydrostatic drive to realize a target output torque T Drv is in Figur 2 depicted.

[0031] In this process, the currently recorded speed is initially used as the basis. n m_a the hydraulic motors 6, 8 and the current detected speed n p_a The necessary swivel angles of the hydraulic pump 4 are determined by means of a volume flow balance. α M, 1 , α M, 2 is calculated for the hydraulic motors. If hydraulic motor 6, 8 is a constant hydraulic motor, this first step will be omitted.

[0032] Subsequently, based on the determined hydraulic motor swivel angle, α M, 1 , α M, 2 a target pressure generated by the hydraulic pump 4 Δp des calculated, which determines the desired target output torque T Drv provides.

[0033] In a further step, the determined target pressure is Δp des including a maximum input power P m the hydrostatic drive is limited to limiting performance. The resulting pressure Δp des _ l This is then implemented by a pressure regulator on the hydraulic pump 4.

[0034] The method for controlling the hydrostatic drive to achieve a target output speed n soll is in Figur 3 depicted.

[0035] In this process, the currently recorded speed is initially used as the basis. n m_a the hydraulic motors 6, 8 and the current detected speed n p_a The necessary swivel angles of the hydraulic pump 4 are determined by means of a volume flow balance. α M, 1 , α M, 2 is calculated for the hydraulic motors 6 and 8. If the hydraulic motor 6 or 8 is a constant hydraulic motor, this first step will be omitted.

[0036] Subsequently, based on the determined hydraulic motor swivel angle, α M, 1 , α M, 2 a target swivel angle α des calculated for the hydraulic pump 4, which is supposed to provide the desired target output speed n.

[0037] In a further step, taking into account the calculated target swivel angle, α des the hydraulic pump 4 and the maximum input power P m a maximum through the

[0038] Hydraulic pump 4 generates pressure Δp des_l calculated so that this calculated value is not exceeded and the maximum input power is not exceeded.

[0039] The resulting limited target swivel angle Δp des_l is subsequently implemented by a pressure regulator or by a swivel angle control on the hydraulic pump 4.

[0040] As already mentioned, the procedure for limiting the power output of the hydrostatic drive will now be described in detail.

[0041] As described in the preceding section, the hydraulic motor swivel angle is calculated using a volume flow balance. Preferably, leakage-related losses are not included in this volume flow balance. This volume flow balance assumes that the hydrostatic drive comprises two hydraulic motors 4 and 6. It is clear to those skilled in the art that this invention can be used with any number of hydraulic motors.

[0042] The volume flow balance is represented in Formula 1: V GP α P n P = V GM , 1 α M , 1 n M , 1 + V GM , 2 α M , 2 n M , 2

[0043] Where VGP is the maximum delivery volume of hydraulic pump 4, VGM,n are the maximum displacement volumes of the hydraulic motors (1..n). Furthermore, αP is the normalized swivel angle of hydraulic pump 4, αM,n is the normalized swivel angle of hydraulic motors 6, 8, nP is the hydraulic pump speed, and nM,n is the hydraulic motor speed.

[0044] Formula 1 is initially only solved for a hydraulic motor and results, taking into account the subsequent adjustment, which is in Figur 4 This is shown accordingly in Formula 2. α M , 1 = min V GP α P n P − V GM , 2 α M , 2 _ Old n M , 2 V GM , 1 n M , 1 1

[0045] The in Figur 4 The illustrated sequential adjustment is based on a serial adjustment of the hydraulic components, whereby first the swivel angle of the pump is utilized (solid line) and subsequently one or more hydraulic motors are reduced in their displacement volume (dashed line).

[0046] As a consequence of the "min" (minimum) function in formula 2, the displacement volume of the hydraulic motors is only reduced once the speed for the in Figur 4 has set the overlap point (L) shown.

[0047] In systems with multiple motors, the displacement volumes from the previous calculation cycle are used to calculate the remaining motors. In the initial state (vehicle speed = 0 km / h), it can be assumed that all hydraulic motors have their maximum displacement volume. In this context, α M,2_Old is the normalized swivel angle of the second hydraulic motor from the previous cycle. The pump's delivery volume is assumed to be 95%, or a factor of 0.95.

[0048] The two hydraulic motors are initially set to maximum swallowing volume according to the principle of sequential adjustment.

[0049] For multi-motor drive variants, it is possible to modify Formula 2 according to the second hydraulic motor. This results in Formula 3, where α M,1 has already been determined using Formula 2. α M , 2 = min V GP α P n P − V GM , 1 α M , 1 n M , 1 V GM , 2 n M , 2 1

[0050] This first step applies to both the target output torque control and the target output speed control of the hydrostatic drive 1.

[0051] If the hydrostatic drive 1 is to be controlled by means of a target output torque, a target pressure generated by the hydraulic pump 4 is now used. Δp des calculated, which determines the desired target output torque T Drv can provide, taking into account the hydraulic motor swivel angles calculated in the previous step α M, 1 , α M, 2 .

[0052] For this purpose, a simplification (formula 4) of the formula described in German patent application number 10 2019 218901.6 is applied. Δ p des = T Drv 2 π V GM , 1 α m , 1 i 1 + V GM , 2 α m , 2 i 2

[0053] In this formula T Drv the desired target output torque and i 1 and i 2 the translation stage from the hydraulic motors to the gearbox output.

[0054] Alternatively, if the hydrostatic drive 1 is to be controlled by means of a target output speed n, a target swivel angle is now specified. α des The hydraulic pump 4, which should be able to provide the desired target output speed n, is calculated, taking into account the hydraulic motor swivel angles calculated in the previous step. α M, 1 , α M, 2 .

[0055] In particular, the target swivel angle α des The hydraulic pump 4 is calculated using a volume flow balance (see formula 5). α des = V GM , 1 α M , 1 n M , 1 + V GM , 2 α M , 2 n M , 2 + Q Leak V GP n P

[0056] Where Q Leak The leakage volume flow rate is...

[0057] The leakage volume flow rate lost due to the leakage is determined by extending the leakage estimation described in patent application DE 102013217708. Q Leak = k off + Δ p kl where k off an offset factor kl pressure-dependent leakage factor and Δ pThe pressure generated by hydraulic pump 4.

[0058] As in Figur 1 As shown, the hydraulic motors are typically mechanically coupled to each other via a gearbox. Therefore, the speed of the second hydraulic motor can be described as the product of the speed of the first hydraulic motor and a gear ratio (n M,1 = n M,2 *i M12). This allows the desired swivel angle to be calculated. α des = V GM , 1 α M , 1 n M , 1 + V GM , 2 α M , 2 n M , 1 i M 12 + k off + Δ p kl V GP n P

[0059] In the next step, the power limitation is performed. The power limitation is carried out in a similar manner for both cases, where the hydrostatic drive 1 is to be controlled by means of a target output torque or a target output speed.

[0060] In this step, formula 8 is used to calculate, taking into account a maximum input power. P m , to limit the calculated target pressure or the calculated target swivel angle.

[0061] In particular, when the hydrostatic drive 1 is powered by a target output torque T Drv The maximum pressure Δ calculated using formula 8 is to be controlled. p Lim with the calculated pressure Δp des compare and, if the calculated target pressure is greater than 0, the smaller of the two values ​​is used. Δp des and the target pressure Δ calculated using formula 8 p Lim as desired pressure Δp des_l taken (conversely, if the calculated target pressure is less than 0, the higher pressure is taken). Δ p Lim = ϑ P P m V GP α P

[0062] Where ϑ P The efficiency of the hydrostatic drive system is...

[0063] If the hydrostatic drive 1 is to be controlled by means of a target output torque, the swivel angle contained in formula 8 can be used. α P either estimated or measured.

[0064] Formula 7 can be used for the estimation, where Δ p the calculated target pressure Δp des is taken.

[0065] Alternatively, if the hydrostatic drive 1 is to be controlled by means of a target output speed, the calculated target swivel angle is taken into account. α des the hydraulic pump 4 and the maximum input power P m a maximum pressure Δp des_l calculated, which may be generated by the hydraulic pump 4 so that the maximum input power P m is not exceeded. In particular, the maximum pressure is calculated using this principle. Δp des_l the target swivel angle calculated using formula 7 α P used for the swivel angle included in Formula 8.

[0066] Patent application WO 15 007 465 A1 shows an example of a system for controlling the swivel angle that can be used in this invention.

[0067] While the present invention has been described with reference to the embodiments described above, it is clear to the person skilled in the art that it is possible to implement various modifications, variations and improvements of the present invention in light of the teaching described above and within the scope of the attached claims without deviating from the scope of protection of the invention.

[0068] Furthermore, the areas in which experts are likely to be knowledgeable have not been described here in order to avoid unnecessarily obscuring the described invention.

[0069] Accordingly, the invention should not be limited by the specific illustrative embodiments, but only by the scope of protection of the attached claims.

Claims

1. Method for power limitation of a hydrostatic traction drive (1), wherein the traction drive (1) is provided with a hydraulic pump (4) for the pressure medium supply of a hydraulic motor (6, 8), which can be coupled to an output, of the traction drive (1), wherein the pressure generated by the hydraulic pump (4) is controllable, wherein the hydrostatic traction drive (1) is alternately actuated by a setpoint output torque (TDrv) or a setpoint output speed (nsoll), wherein the method comprises the following steps: a. receiving the command to actuate the hydrostatic traction drive (1) by means of a setpoint output torque (TDrv) or a setpoint output speed (nsoll); b. if the hydrostatic traction drive (1) is to be actuated by means of a setpoint output torque (TDrv), calculating a setpoint pressure (Δpdes) which is generated by the hydraulic pump (4) and can provide the desired setpoint output torque (TDrv), taking into account a displacement of the hydraulic motor (6, 8); if the hydrostatic traction drive (1) is to be actuated by means of a setpoint output speed (nsoll), calculating a setpoint swash angle (αdes) of the hydraulic pump (4), which can provide the desired setpoint output speed (nsoll), taking into account the displacement of the hydraulic motor (6, 8); wherein the method is characterized by the following steps: c. receiving information about a maximum input power (Pm) of the hydraulic pump (4); d. if the hydrostatic traction drive (1) is to be actuated by means of a setpoint output torque (TDrv), limiting the setpoint pressure (Δpdes) calculated in step b., taking into account the maximum input power (Pm); if the hydrostatic traction drive (1) is to be actuated by means of a setpoint output speed (nsoll), calculating a maximum pressure (Δpdes_l) that may be generated by the hydraulic pump (4), taking into account the setpoint swash angle (αdes) calculated in step b of the hydraulic pump (4) and the maximum input power (Pm), wherein, if the hydrostatic traction drive (1) is to be actuated by means of a setpoint output speed (nsoll), the hydraulic pump (4) is controlled in such a way that the maximum pressure (Δpdes_l) that may be generated by the hydraulic pump (4) is not exceeded.

2. Method according to Claim 1, wherein the hydrostatic traction drive (1) comprises at least two hydraulic motors (6, 8).

3. Method according to either of Claims 1 and 2, wherein, if the hydrostatic traction drive (1) is to be actuated by means of a setpoint output torque (TDrv), the setpoint pressure calculated in step b. is limited in step d by adding an estimated or detected hydraulic pump swash angle and the maximum input power.

4. Method according to Claim 3, wherein the pressure limited in step d. is implemented by a pressure regulator at the hydraulic pump (4).

5. Method according to either of Claims 3 and 4, wherein the hydraulic pump swash angle is estimated by means of a volume flow balance, wherein a leakage volume flow is taken into account in the said volume flow balance.

6. Method according to Claim 5, wherein the leakage volume flow is estimated by this formula: Q Leak = k off + Δρ kl , where QLeak is the leakage volume flow, koff is an offset factor, kl is a pressure-dependent leakage factor, and Δp is the pressure generated by the hydraulic pump (4).