DE202020107297U1 - Control system for a hydrostatic drive - Google Patents

Abstract

Control system for a hydrostatic drive train, comprising a primary variable displacement pump (4) and a secondary displacement motor (8) which are connected to one another, the secondary displacement motor (8) being connected to a transmission system (14) having at least a first and a second gear stage wherein the secondary displacement motor (8) is selectively coupled to the first gear stage and the second gear stage, the control system being characterized in that it comprises: a shift control unit (30) configured to accommodate a shift request between the first and to receive the second gear stage, and to regulate a swivel angle of the secondary displacement motor (8) so that the torque at a transmission system input of the transmission system (14) is regulated based on the shift request, the control system being configured so that the amount of the primary displacement pump ( 4) pressure generated is regulated up to a predetermined value is after the shift control unit (30) has detected that the pivot angle of the secondary displacement motor (8) has reached a predetermined position.

Description

TECHNICAL AREA

The present invention relates to the technical field of hydrostatic drive train control systems that include a primary variable displacement pump and a secondary displacement motor connected together, the control system being configured to provide torque control of the hydrostatic drive train based on that provided by the primary variable displacement pump Print.

STATE OF THE ART

The combination of hydrostatic and mechanical transmissions can not only improve system efficiency, but also the usability of mobile machines.

1 shows the hydrostatic-mechanical drive train solution according to the prior art.

In the in 1 The system shown is a synchronized transmission 103 between a hydraulic motor 102 and a vehicle axle 104 built-in. With such a drive train system, mobile machines with only one hydraulic motor can have two different drive ranges, such as a torque range and a speed range.

Due to the low costs compared to multi-motor solutions, hydrostatics with synchromesh drives dominate 103 the market for medium-sized mobile machines with a high speed of up to 40 km / h.

The prior art solution is a speed-based shifting concept. If the speed is higher than a certain value, the machine shifts up. On the other hand, when the speed is lower than a certain speed, the vehicle downshifts. In order to avoid the machine switching continuously in a short time, as the speed can fluctuate, two adjustment areas are provided.

The main reason for the success of this drive train is that it can shift gear without stopping the mobile machines. The synchronized gearbox differs slightly from the standard manual gearboxes in cars: it has no neutral position. This means that either first or second gear is engaged. If an active torque is still acting on the input shaft during the shifting process, the synchronization process may be destroyed. The consequence of this is that the pulling force for shifting must be reduced to zero.

The hydrostatic-mechanical drive solution according to the prior art uses a flow-based control concept when switching. The accelerator pedal controls the engine speed and the pump swivel angle, which results in the volume flow delivered by the hydraulic pump. In the meantime, the hydraulic motor is set to a certain angle depending on the engine speed. The accelerator pedal thus determines the vehicle speed individually when the mechanical transmission is not shifting. A disadvantage is that the desired speed is set to different values for different gears, which can cause the vehicle to jolt when shifting with a constant pedal position. The effect can be compensated by additional software functionality. However, this leads to a significantly higher calibration effort and more complicated control algorithms.

The problem to be solved by the present invention is to produce a simple but efficient control algorithm for switching that requires little calibration effort and at the same time has better switching behavior.

Figure list

• 1 schematisch einen hydrostatischen Antriebsstrang gemäß dem Stand der Technik;
• 2 einen als Fahrantrieb ausgestalteten hydrostatischen Antrieb gemäß einem Ausführungsbeispiel,
• 3 ein vereinfachtes Blockdiagramm einer Hydropumpe des Antriebes gemäß 2 mit ihren Einrichtungen zur Trajektorienplanung, Vorsteuerung und Regelung,
• 4 einen Kontrollfluss eines druckbasierten Regelalgorithmus beim Umschalten gemäß einer Ausführungsform der vorliegenden Erfindung.

The present invention is described with reference to the accompanying figures, wherein like reference numbers refer to like parts and / or like parts and / or corresponding parts of the system. In the figures show:

• 1 schematically a hydrostatic drive train according to the prior art;
• 2 a hydrostatic drive designed as a travel drive according to an embodiment,
• 3 a simplified block diagram of a hydraulic pump of the drive according to 2 with their facilities for trajectory planning, precontrol and regulation,
• 4th a control flow of a pressure-based control algorithm when switching according to an embodiment of the present invention.

DETAILED DESCRIPTION

In the following, the present invention will be described with reference to specific embodiments as shown in the accompanying figures. Nonetheless, the present one is The invention is not limited to the particular embodiments described in the following detailed description and shown in the figures, but the described embodiments simply illustrate various aspects of the present invention, the scope of which is defined by the claims.

Further modifications and variations of the present invention will be apparent to those skilled in the art. The present description thus includes all cited modifications and / or variations of the present invention, the scope of which is defined by the claims.

In the present invention with the wording “first gear step” and “second gear step” two general gear steps are meant which cause a general translation. The translation of the first gear can either be smaller or greater than the translation of the second gear.

According to 2 has a hydrostatic drive 1 a prime mover 2 (eg a diesel engine), a first hydraulic machine, coupled to this, designed as an axial piston pump in swash plate design with adjustable delivery volume or pivot angle 4th (hereinafter hydraulic pump 4th ) and one with one output 6th coupled second hydraulic machine designed as an axial piston motor in bent axis construction with adjustable delivery volume or swivel angle 8th (hereinafter hydraulic motor 8th ). Hydraulic pump 4th and hydraulic motor 8th are in the illustrated embodiment in a closed, hydraulic circuit via working lines 10 , 12 fluidically connected. The hydraulic motor 8th is via a transmission system 14th with the downforce 6th coupled. In the exemplary embodiment shown, the output is an axle with wheels 16 .

The drive 1 has a means 18th for recording the delivery volume of the hydraulic pump 4th determining geometric size. In the design mentioned, this variable is, for example, the swivel angle α of the swash plate of the hydraulic pump 4th .

In addition, is a means 20th to detect the pressure p of the hydraulic pump 4th , more precisely a pressure difference Δp across the hydraulic machine 4th between the working lines 10 , 12 intended. The pressure p falls due to the arrangement in the hydraulic circuit and neglecting flow losses with the same amount of the pressure difference Δp over the hydraulic motor 8th from. Furthermore, the hydraulic pump 4th an adjustment device 22nd to adjust their swivel angle α _P and thus the delivery volume. The hydraulic motor also has 8th an adjustment device 23 to adjust their swivel angle α _M and thus the delivery volume.

In the exemplary embodiment shown, the adjusting device is formed by an electromagnetically actuated hydraulic valve (not shown in detail) and an actuator designed as a double-acting hydraulic cylinder (also not shown in detail), which can be acted upon with actuating pressure medium.

The adjustment is known in particular as electrical direct adjustment or ET adjustment. A pressure medium volume flow of the hydraulic pump 4th is steplessly adjustable as a function of a control current i _des with which the hydraulic valve is controlled. It can be used for each adjustment direction, especially if the hydraulic pump 4th is pivotable or reversible due to its zero delivery volume, a valve, in particular a pressure reducing valve, is provided. The actuator is acted upon with actuating pressure medium in proportion to the control current i _des. The swivel angle that occurs at a specific control current i _des and the delivery volume determined by it is according to a characteristic map of the hydraulic pump 4th on a speed n _P , and the pressure difference Δp dependent.

The hydraulic pump is with a control unit 24 with facilities for trajectory planning of the pressure difference and its time derivatives, for pilot control of the hydraulic pump 4th Depending on the trajectory planning, it is connected to a disturbance variable feed of the hydraulic motor and to regulate the pressure. The control unit 24 is with a control unit 26th the prime mover 2 signal connected.

3 Fig. 10 shows a structure of the control unit 24 and an overview of their signal flows.

Accordingly, the control unit has 24 an entrance 28 , which can be connected, for example, to an interface of an HMI, via the to the control unit 24 the specification of a requested pressure difference Δp _des , briefly formulated below as requested pressure Δp _des , can be transferred. The pressure Δp _des represents the intensive state variable of a tensile force F of _the or a requested output torque M _{des of} the travel drive requested by an operator via the HMI 1 or, in the case of a shift request from the transmission system 14th , can be a value of pressure that allows switching between a first gear stage and a second gear stage. It is therefore the command or control variable that is controlled by the control unit 24 is to be set as precisely as possible.

According to 2 he goes to a facility for trajectory planning 30th a, which has a target trajectory of the pressure Δp _{des, filt} as flat, linearized outputs and whose two time derivatives Δṗ _{des, filt} , Δp̈ _{des, filt} . The three target trajectories Δp _{des, filt} , Δṗ _{des, filt} , Δp̈ _{des, filt} go to a device for precontrol 32 a, where the highest of the time derivatives Δp̈ _{des, filt} previously by a device for regulation 34 can be changed, which is explained in more detail below.

The device for pilot control 32 contains an inverse model of the hydraulic pump 4th including their adjustment device 22nd with valve and actuator according to 1 . The device for precontrol is used as disturbance variables 32 the pressure medium volume flow of the hydraulic motor 8th and its time derivative switched on. An exit 36 the pilot control supplies a control current i _des , with which the valve of the adjusting device 22nd is controlled and thus the actuator is acted upon with control pressure medium and a pivot angle α of the hydraulic pump 4th represents.

The resulting pressure .DELTA.p is recorded and sent to a first comparison element 38 returned as a subtrahend, where it is offset against _{the target trajectory of the pressure Δp des, filt.}

The deviation determined in this way is sent to the control device designed as a PID controller 34 on. Their output is in turn as a subtrahend with a second comparison element 40 connected and is offset there with the target trajectory of the highest time derivative Δp̈ _{des, filt of} the pressure. The result of this then goes to the device for precontrol as a changed target trajectory of the highest time derivative of the pressure 32 a and leads to a changed control current i _des , with which the valve of the adjustment device 22nd is controlled. A new pressure Δp then results from this.

As mentioned in the introduction of this patent application, the tractive force during switching, in particular during the synchronization process, must be reduced to zero (no active torque may be generated during switching) so that switching can be carried out successfully.

wobei T_m das Ausgangsdrehmoment des Hydraulikmotors ist, V_g,max das maximale Verdrängungsvolumen des Hydraulikmotors, am der Schwenkwinkel des Hydraulikmotors, Δp die tatsächliche Druckdifferenz im geschlossenen Kreislauf, η_me der mechanische Verlustkoeffizient. Dabei muss entweder der Schwenkwinkel am oder der Druck Δp gleich Null sein, um den Schaltvorgang zu ermöglichen. Basierend auf diesen beiden Konzepten wurden zwei Regelalgorithmen untersucht: schwenkwinkelbasierter Regelalgorithmus (ABCA) und druckbasierter Regelalgorithmus (PBCA).Formally, the torque can be calculated as follows: $${\text{T}}_m=\frac{V_{G,max}\cdot {\alpha }_m\cdot {\Delta }_p\cdot {\mathrm{\eta }}_{me}}{2\pi }$$

where T _{m is} the output torque of the hydraulic motor, V _{g, max is} the maximum displacement of the hydraulic motor, am is the swivel angle of the hydraulic motor, Δp is the actual pressure difference in the closed circuit, η _{me is} the mechanical loss coefficient. Either the swivel angle at or the pressure Δp must be zero in order to enable the switching process. Based on these two concepts, two control algorithms were investigated: swivel angle-based control algorithm (ABCA) and pressure-based control algorithm (PBCA).

The basic idea of the pressure-based control algorithm (PBCA) is to adjust the pressure inside the closed circuit to zero so that the swivel angle of the motor can keep the same angle as before the shift. Due to the relatively higher dynamics, the switching time is potentially shorter when using the pressure-based control algorithm (PBCA) than with the swivel angle-based control algorithm (ABCA).

Since the speed of the hydraulic motor is higher in first gear than in second gear at the same speed, the motor is accelerated by downshifting during the synchronization process. However, the swivel angle of the pump cannot always go up to compensate for the change in pressure.

Therefore, a preparation step for the downshift should be added to the entire shift. Specifically, the swivel angle of the motor is reduced to a certain low level before the synchronization process, so that the swivel angle of the pump is also set to a lower level.

4th shows the control sequence of the shift process between a first and a second gear stage with this algorithm. The following sections describe how to switch between the first and second gear stages (right-hand side of 4th ). It is clear to the person skilled in the art that in the switching process between the second and the first gear stage (left side of 4th ) the same steps can be performed in reverse order.

In 4th the normal switching process is shown with the white arrows (from the first step to the fifth step and vice versa). On the other hand, switching protection steps that protect the switching process are shown with the black arrows.

In a first step 50 becomes the shift control unit 30th receive a shift request, and the swivel angle am of the hydraulic motor 8th control based on the shift request so that the torque at a transmission system input of the transmission system 14th is regulated based on the switching request. In particular, the swivel angle am is regulated in such a way that a predefined position of the swivel angle is reached, the predefined position of the secondary displacement motor 8th corresponds to a future position of the second gear stage.

In a second step 51 after the shift control unit 30th detects that the swivel angle on the hydraulic motor 8th has reached the predetermined position, the shift control unit 30th a signal to the control unit 24 send in order to decrease the pressure Δp generated by the pump to a predetermined value so that no active torque is generated during the synchronization process. This predetermined value is preferably equal to 0 bar. Alternatively, the specified value is chosen so that friction losses of the secondary displacement motor 8th be minimized.

In a third step 52 after the shift control unit 30th detects that the pressure Δp generated by the pump has reached the specified value, the switching control unit 30th a signal to the transmission system 14th send to start switching between first gear and second gear. In this step, the first gear stage is decoupled.

In a fourth step 53 the synchronization process is carried out and the second gear stage is coupled.

In a fifth step 54 the swivel angle α _{m of} the hydraulic motor 8th adjusted due to the switching process.

As in 4th is shown with the black arrows when in the second step 51 the predetermined value of the pressure is not reached, the procedure becomes the first step 50 go back. In addition, if in the first step the shift control unit 30th detects that the swivel angle on the hydraulic motor 8th has not reached the specified position, a switching abort function will interrupt the switching process.

While the present invention has been described with reference to the embodiments described above, it will be apparent to those skilled in the art that it is possible to make various modifications, variations, and improvements of the present invention in light of the teaching described above and within the scope of the appended claims, without departing from the spirit and scope of the invention.

For example, it is clear that even if the transmission system 14th of the hydrostatic drive train includes only two gear stages, the invention also works with transmission systems that include more than two gear stages.

In addition, in order not to unnecessarily obscure the invention described, such areas believed to be known to those skilled in the art have not been described herein.

Accordingly, it is intended that the invention not be limited by the specific illustrative embodiments, but only by the scope of the appended claims.

Claims (6)

A control system for a hydrostatic drive train, comprising a primary variable displacement pump (4) and a secondary displacement motor (8) which are connected to one another, the secondary displacement motor (8) being connected to a transmission system (14) having at least a first and a second gear stage wherein the secondary displacement motor (8) is selectively coupled to the first gear stage and the second gear stage, the control system being characterized in that it comprises: a shift control unit (30) configured to accommodate a shift request between the first and to receive the second gear stage, and to regulate a swivel angle of the secondary displacement motor (8) so that the torque at a transmission system input of the transmission system (14) is regulated based on the shift request, the control system being configured so that the output from the primary variable displacement pump ( 4) generated pressure regulated up to a predetermined value t becomes after the shift control unit (30) has detected that the swivel angle of the secondary displacement motor (8) has reached a predetermined position. Tax system according to Claim 1 , wherein the predetermined position of the pivot angle of the secondary displacement motor (8) corresponds to a future position of the second gear stage. Tax system according to one of the Claims 1 or 2 , the predetermined value being less than 1 bar, preferably essentially equal to zero Tax system according to one of the Claims 1 or 2 , wherein the predetermined value is chosen so that friction losses of the secondary displacement motor (8) can be minimized. Tax system according to one of the Claims 1 to 4th wherein the control system is configured, after the predetermined value of the pressure generated by the primary variable displacement pump (101) has been reached, to enable switching between the first and second gear stages. Tax system according to one of the Claims 1 to 5 , wherein the switching control unit (30) further comprises a switching protection module which is configured to monitor the pressure generated by the primary variable displacement pump (4) during the switching and to cancel the switching process based on the detected pressure if the Switching protection module evaluates that switching is no longer permissible due to the pressure detected.

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