DE102020216319A1 - Process for demand-oriented speed increase of a drive element - Google Patents

Abstract

Method for demand-oriented speed increase of a drive element in a drive train of a work machine with a transmission and a control device, at least one upper and one lower speed curve (I, II) being specified for the drive element, characterized in that when there is a maximum driving request in response to a external load by the control device a speed increase is initiated on a boost curve (IV), wherein the boost curve (IV) is above the upper speed curve (I).

Description

The present invention relates to a method for demand-oriented speed increase of a drive element, for example an internal combustion engine, in a drive train of a machine. The working machine can be designed in particular as a construction, agricultural or forestry machine. Construction machinery includes in particular, but not exclusively, wheel loaders, graders and/or dumpers. In the operation of such a work machine, driving situations can occur in which a maximum tractive force of the transmission, a maximum speed and/or a maximum climbing ability are to be achieved.

Out of EP 2 902 551 A1 control of the drive of a work machine with a drive motor and a hydraulic transmission is known, in which the driver can select the engine speed in a low, medium or high range depending on the operating situation and can thus set a specific speed level.

The object of the present invention is to be seen as providing an improved method for demand-oriented speed increase.

The object is achieved with the method according to the invention. In this case, a drive train of a working machine has a transmission, a drive element and a control device. If there is a maximum driving requirement in response to an external load, the control device initiates a speed increase of the drive element on a boost curve. The external load can result, for example, from the topography (e.g. an incline), the ground, a loading condition, a power requirement from a working hydraulic system or a position of a mast (shovel, front loader). The driving request can also be in the form of a required acceleration or speed change. Accordingly, the driving request can be requested by a manual input from the operator or by an automatic/autonomous driving function.

Typically, at least one upper and one lower speed curve are specified for the drive element, which enable consumption-optimized operation under different environmental and driving conditions. When the maximum driving request is present, the control device initiates a speed increase, in which case the drive element is not operated in accordance with the upper speed curve, but rather in accordance with an increase curve. The boost curve, or the speed values of the drive element mapped with it, are above the upper speed curve. The speed curves (upper, lower, increase curve) can be stored in a memory element of a control device, in particular the control device. The control device can be designed as a transmission or engine control unit, or as a higher-level computing unit (vehicle management computer) and have a suitable memory element.

In one possible embodiment of the method according to the invention, the maximum driving requirement is requested by a defined accelerator pedal position. This can be 90%, for example, which means that when the accelerator pedal is actuated with 90% or more of the pedal travel, the increase is triggered. Alternatively or additionally, it can also be provided that a defined change in the accelerator pedal position within a short time interval triggers the increase in the engine speed. This can sometimes also apply to accelerator pedal positions below 90%.

In a development of the method according to the invention, in addition to an accelerator pedal position, one or more other parameters are taken into account in order to initiate the increase in the speed of the drive element to the increase curve. These are in particular parameters that characterize the external loads mentioned above. This also includes, for example, pressure utilization in the transmission, exceeding a difference between a current speed at the output of the transmission and a target speed at the output of the transmission, or falling below a threshold value of the gradient of the speed at the output. The pressure utilization in the transmission is to be used in particular in transmissions that are designed as hydrostatic-mechanical power-split continuously variable transmissions (CVT). As part of the implementation of the method described, it can be provided that one of the conditions must be present individually or a combination of triggering criteria of the type mentioned above. Depending on the application or characteristics of the work machine, prioritization can also be defined in relation to a ranking of the triggering parameters/criteria. The other parameters can either be determined indirectly using other operating variables or provided by suitable sensors (inclination sensor, barometric height sensor, position sensors for lifting frame and/or shovel, other load sensors in relation to attachments).

According to a development of the method, it is provided that a first threshold value in relation to the gradient of the rotational speed at the output is defined as a triggering criterion, when it is reached with a negative increase or undershoot ten the speed increase is triggered. Furthermore, a termination criterion can be defined, which for example relates to a second threshold value for the gradient of the rotational speed at the output, and/or implements a temporal debounce. As a result, when the second threshold value with a positive gradient is reached, the speed increase that was triggered is terminated. When a timed debounce is implemented, the speed increase is deactivated when a specified time interval has elapsed when the speed increase was triggered.

In a further development of the invention, it is provided that the speed increase is modulated as a function of the driving request. This means that a number of boost curves can be provided, the relevant boost curve being selected based on the severity of the driving requirement. In this way, the relevant boost curve can be selected step by step according to the cumulation of triggering criteria or on the basis of their characteristics. Each boost curve lies, at least in part, above the upper speed curve.

According to a further aspect of the present invention, a control device is also included, which is suitable and set up to carry out the method and to generate signals for controlling the drive element, in particular for increasing the rotational speed, and to send them to the drive element. Furthermore, the invention relates to a work machine with a drive element, a transmission and a control device according to the invention.

• 1: in einem Diagramm eine Betriebspunktverschiebung aufgrund der Drehzahlanhebung;
• 2a: in einem Diagramm die Funktionsweise der Drehzahlanhebung;
• 2b: einen Verlauf des Gradienten der Drehzahl am Abtrieb des Getriebes und der korrespondierenden Schwellwerte für die Aktivierung/Deaktivierung der Drehzahlanhebung;
• 2c: einen Verlauf der korrespondierenden Fahrpedalstellung.

The method according to the invention is described in more detail with reference to the following figures. show:

• 1 : in a diagram, an operating point shift due to the speed increase;
• 2a : in a diagram, how the speed increase works;
• 2 B : a course of the gradient of the speed at the output of the transmission and the corresponding threshold values for the activation/deactivation of the speed increase;
• 2c : a course of the corresponding accelerator pedal position.

1 shows a diagram of an operating point shift due to a speed increase in a schematic representation. A reciprocal transmission ratio irez of the transmission is shown on the abscissa of the diagram, while a speed n of a drive element is plotted on the left ordinate and a traction force F of the transmission or an output is plotted on the right ordinate.

Furthermore, an upper and a lower speed curve I, II of the drive element are shown, as well as two operating points B1 and B2 on the upper speed curve I. The operating point B1 is at the reciprocal ratio irez = 1.0 and the operating point B2 at the reciprocal ratio irez = 0 ,4. In the operating point B1, the drive element is operated at a speed nB1=1590 rpm and at the operating point B2 at a speed nB2=1510 rpm. This results in an output speed nab1=nB1=1590 rpm for the first operating point B1 and an output speed nab2=604 rpm for the second operating point B2. The associated traction F1, F2 of the two operating points B1, B2 results at an intersection of the course of the traction F with the relevant reciprocal transmission ratio irez.

Starting from the operating point B1, the operating point B2 is reached in that the reciprocal transmission ratio irez is reduced in the manner described above. This is done in response to an external load, such as driving up an incline or a steeper climb in an incline, particularly to prevent the high pressure in the transmission from rising above a maximum value. As a result, not only does the reciprocal transmission ratio irez of the transmission decrease, but also the speed n of the drive element. As a rule, this is also accompanied by a drop in the power generated or provided by the drive element. As a result, the work machine becomes significantly slower and sometimes the maximum performance potential of the drive element is not exhausted. Also, the response of the powertrain (reduced engine speed and reduced ground speed) is sometimes different or even contrary to the response expected by an operator (increase in speed of the drive element due to the maximum driving demand).

In order to increase the performance of the working machine and to increase its productivity, the speed of the drive element is increased as required by shifting the operating point from the operating point B2 to an operating point B3. In the present example, this corresponds to an increase in speed n to the value nB3 = 1800 rpm. With the same reciprocal ratio irez = 0.4, this results in an output speed nab3 = 720 rpm instead of nab2 = 604 rpm. In this way, an output speed increased by approx. 20% can be achieved.

2a shows in a diagram how the speed increase works. The time t is plotted on the abscissa and a speed n on the ordinate Ren speed curve I, an increase curve IV, an output speed curve V shown without a speed increase and an output speed curve VI taking into account the speed increase.

A driving specification is commanded at a time t0. As a result, the target output speed curve III experiences a sharp (linear) rise and reaches its maximum value a short time later, and well before a point in time t1. From then on, this value is kept constant over time t. The target output speed curve III thus results, for example, from actuation of an accelerator pedal. The target output speed curve III correlates with an accelerator pedal position FPS, which 2c is shown. The upper speed curve I shows a moderate increase from time t0, through time t1 to a time t2. In an interval between time t2 and a time t3, the upper speed curve I experiences a slight decrease, persisting until just before a time t4 this level before a further increase occurs up to a point in time t5 or beyond.

The output speed curve V without speed increase runs almost parabolic between times t0 to t3, a first maximum being reached at time t2, and the output speed curve V then falling until time t3. The output speed curve V falls back to a value below the value at time t1. The previously reached value is retained until just before time t4, before there is a further increase up to a second maximum value at time t5. The value at time t5 is significantly greater than that at time t2.

The increase curve IV can be seen from time t1, here it still has the same value as the upper speed curve, increases significantly up to time t2 or shortly thereafter and then remains at the level reached until time t4. In the interval between times t4 and t5, the increase curve IV undergoes a reduction until, at time t5, it assumes the same value as the upper speed curve I before it.

The output speed curve VI, taking into account the speed increase, is particularly evident in the time interval between times t2 and t4. Here the curve deviates from the output speed curve V, in particular the output speed curve VI lies above the output speed curve V. The output speed curve VI shows an almost straight course in the interval mentioned. In particular, it becomes clear that the dip in the output speed curve V is significantly reduced or almost eliminated between the times t2 to t4. This is the result of the speed increase due to the increase curve IV.

In 2 B a course of the gradient G of the speed at the output of the transmission and the corresponding threshold values S1, S2 for the activation/deactivation of the speed increase are shown. The times t0 to t5 agree with those in 2a match, i.e. depict the respective states at the same point in time t0 to t5.

Beginning at time t0, the gradient initially experiences a sharp rise, with an almost parabolic curve presenting itself up to time t2. In this case, the gradient G in the interval from t0 to t1 initially exceeds a first threshold value S1 and then a second threshold value S2 before a maximum value is reached. The second threshold value S2 is greater than the first threshold value S1. In this state, exceeding the first and second threshold value S1, S2 is just as irrelevant as falling below the second threshold value S2. Only when the first threshold value S1 is reached and then fallen below at the point in time t1 is used as the triggering criterion for the speed increase. This is also evident when looking at the 2a and the course of the increase curve IV shown there. As a result, the gradient G decreases further, remains in the time interval between the times t3 and t4 initially close to G=0 before shortly before the time t4 a new increase begins, which also runs almost parabolic and lasts until shortly after time t5. At the time t4, the second threshold value S2 is again exceeded, which is now interpreted as a termination criterion when the speed increase is activated. When the speed falls below the first threshold value S1 at or shortly after the point in time t5, the conditions are met for a new speed increase to be initiated. However, this is not shown here.

2c depicts a course of the corresponding accelerator pedal position FPS. The times t0 to t5 agree with those in 2a and 2 B match, i.e. depict the respective states at the same point in time t0 to t5. At time t0 a drive request is commanded or entered. This can be seen from the (here linear) increase in the accelerator pedal position FPS. Shortly after point in time t0, and well before point in time t1, the accelerator pedal position FPS reaches its maximum value, which is kept constant in the further course. This value can correspond, for example, to an actuation of 100%, that is to say to a maximally actuated accelerator pedal, or else to a lower value. However, the lower value corresponds to a triggering criterion for the speed increase, for example an actuation of 90%.

Reference List

I

upper speed curve

II

lower speed curve

III

target output speed curve

IV

boost curve

v, vi

output speed curve

B1, B2, B3

operating point

F, F1, F2

traction

FPS

accelerator pedal position

G

gradient

irez

Reciprocal gearing

n

rotational speed

nab1, nab2, nab3

output speed

nB1, nB2, nB3

speed at the operating point

S1, S2

threshold

t

time

t0 - t5

time

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 2902551 A1 [0002]

Claims (7)

Method for demand-oriented speed increase of a drive element in a drive train of a work machine with a transmission and a control device, at least one upper and one lower speed curve (I, II) being specified for the drive element, characterized in that when there is a maximum driving request in response to a external load by the control device a speed increase is initiated on a boost curve (IV), wherein the boost curve (IV) is above the upper speed curve (I). Method according to Claim 1, characterized in that a maximum driving requirement is requested by a defined accelerator pedal position (FPS). Method according to one of the preceding claims, characterized in that one or more other parameters are taken into account in addition to an accelerator pedal position (FPS). Method according to one of the preceding claims, characterized in that a first threshold value (S1) for a gradient (G) of the speed at the output is defined as a triggering criterion, the speed increase being triggered when this gradient is reached with a negative gradient, while a second threshold value is also used as a termination criterion (S2) is defined for the gradient (G) of the speed at the output, when this is reached the triggered speed increase is ended. Method according to one of the preceding claims, characterized in that the speed increase is modulated as a function of the driving requirement. Control device which is suitable and set up to carry out the method according to one of the preceding claims. Working machine with a drive element, a transmission and a control device claim 6 .

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