DE102020208249A1 - Method for operating a drive train of a vehicle - Google Patents

Abstract

A method for operating a drive train of a vehicle, wherein during a vehicle standstill, if a direction of travel is specified and the direction of travel switching element is open, a start-up process is prevented without an explicit driving request, in that the drive train is transferred to a safe state if cumulative activation criteria are met, one for setting a driving range or a gear stage, a first activation criterion when this shift element is in a closed state, with exceeding a threshold value of a differential speed of the travel direction switching element represents a second activation criterion, falling below a threshold value of a vehicle speed represents a third activation criterion, a specific signal of the travel direction switching element represents a fourth activation criterion.

Description

The present invention relates to a method for actuating a switching element, in particular in a drive train of a vehicle. The switching element is a non-positive switching element, for example a clutch or a brake. A non-rotatable, non-positive connection between two rotatable components of a drive train can be established or released by means of a coupling. Analogously to this, a brake describes a switching element by means of which a non-positive connection between a rotatable component and a stationary component can be established or released. Corresponding shifting elements can in particular be used as direction of travel and / or range clutches. In this case, the direction of travel clutches are used to change between a forward and a reverse (opposite to this) driving operation or drive of the vehicle. On the other hand, different gears or driving ranges with different gear ratios of a transmission can be realized by driving range clutches.

Methods are known from the prior art which, if defined criteria are present, establish a safe state of a transmission or a drive train in order to prevent an undesirable degree of torque transmission from a shifting element. So revealed DE 199 26 697 B4 A similar method in which the vehicle is prevented from moving off even if, for example, there is a fault in the control unit or the energization of a hydraulic valve for actuating a clutch. For this purpose, a switch is made to a neutral state and the clutch is closed if the service or parking brake of the vehicle has been actuated continuously for a predetermined period of time since the vehicle came to a standstill.

The object of the present invention is to provide an improved method for operating a drive train which prevents a start-up process without an explicit driving specification.

The object is achieved with the method according to the invention according to claim 1. The vehicle is initially at a standstill, with a direction of travel specification being present. This is to be understood as meaning that a direction of travel has already been preselected or determined in which a future approach process is to take place. This can be done by the operator or, in the case of autonomous vehicles, by a corresponding control. The direction of travel specification also defines which of the travel direction switching elements (forwards / backwards) is to be closed during a start-up process.

The vehicle is, for example, a motor vehicle, in particular a utility vehicle or a work machine. The vehicle has a drive train with a drive element, for example an internal combustion engine, which is operatively connected to a transmission. The drive element introduces a rotary movement or torque into the transmission, translates it according to the selected gear stage or the driving range and sends it to an output. This can be operatively connected, for example, to drive wheels of the vehicle in order to drive them.

A start-up process without an explicit driving request is to be understood as meaning, for example, that the relevant direction-of-travel switching element is (sometimes partially) closed without a driving request in the form of an actuation of the accelerator pedal being present. This could be caused by a faulty control, a defect in a component in the control, faulty software or some other imprint (e.g. unwanted electrical or electromagnetic interference from other devices - EMC), a wrong current for the actuation of a proportional valve for Control of the relevant switching element is provided. There could also be an electrical fault, for example in the form of a short circuit that leads to actuation of the proportional valve.

According to the invention, the drive train is transferred to a safe state if the corresponding activation criteria are cumulatively met. The safe state can be established, for example, in that, in addition to the direction of travel switching elements, one or all of the switching elements for setting a driving range or a gear step are also opened. As far as technically feasible, the transmission can be brought into a neutral position. Alternatively or in addition, a parking and / or service brake can also be activated, the drive element can be switched off and / or an optical and / or acoustic indication can be output to the operator. A first activation criterion is met when a shift element required for setting a driving range or a gear step is in a closed state. Depending on the design of the transmission, it can also be provided that several shift elements are simultaneously in a closed state for setting a driving range or a gear step. Accordingly, this should be summarized under the first activation criterion.

A second activation criterion represents exceeding a threshold value of a differential speed of the travel direction switching element. In this case, a differential speed is to be understood as the difference which the clutch halves form with respect to one another in the open state. A vehicle speed falling below a threshold value represents a third activation criterion. The reason for this is that a start-up process without an explicit driving specification can no longer be assumed if a defined vehicle speed has already been reached or exceeded. A fourth activation criterion is a specific signal for the direction of travel clutch. The specific signal can be, for example, the presence of an electrical fault in the direction of travel switching element or an impermissible change in current in a control signal for this same direction of travel switching element. In principle, these features can also be combined with one another to form a fourth activation criterion. In addition, further activation criteria, for example the actuation state of further switching elements in the drive train, a motor signal, etc., can be used as activation criteria.

The inadmissibility of a change in current results either from its magnitude, its gradient, its duration or its number in a time interval. A combination of magnitude, gradient, duration and number can also result in the current change being inadmissible. Accordingly, an absolute and / or a dynamic threshold value is specified for the amount, the gradient, the duration and the number of current changes. The absolute threshold value is understood to mean that it specifies a maximum value for the respective parameter (amount, gradient, duration, number of current changes). A dynamic threshold value is accordingly to be understood as meaning that the threshold value for one of the parameters can vary as a function of the other parameters, in particular can deviate from the absolute threshold value. Furthermore, limit values can be defined below which current changes are not taken into account. In particular, these are to be understood as current changes which are not suitable for initiating a start-up process for the vehicle without an explicit driving request.

According to a further aspect of the present invention, actual values of the change in current, that is to say the actual values of the parameters, are recorded cyclically and compared with the absolute and / or dynamic threshold values. The number of cycles to be taken into account for assessing the inadmissibility of a change in current can vary depending on the threshold value or parameter. This is to be understood as meaning that a change in the gradient is considered and used as a basis, for example over 5 cycles, while 10 cycles are taken into account for the number of current changes.

In an advantageous development, the absolute and / or dynamic threshold values are specified in the form of a parameterizable map. This means that the map can be adapted to the respective vehicle, the operating conditions, legal requirements or personal preferences of an operator. Wear of components in the drive train can also be taken into account. The map can be designed in two or more dimensions. The parameterization is carried out by the operator of the vehicle himself using a suitable interface or input device, or via a diagnostic interface by service personnel on site, in a workshop or by remote maintenance. Updates can also be installed accordingly.

According to a further aspect of the present invention, the invention also includes a control device with a computing unit, an input interface and an output interface. In addition to specifying the direction of travel and a driving request, the input interface also transmits or communicates the presence of the activation criteria to the computing unit. The computing unit is suitable and set up to carry out the method according to the invention and to output a signal via the output interface, as a result of which the drive train is transferred to a safe state.

The invention further comprises a vehicle with a control device of the above-mentioned type and a drive train, the drive train including a drive element, a transmission and an output.

• 1: eine schematische Darstellung der Verfahrenslogik,
• 2: eine erste schematische Darstellung eines Stromverlaufs,
• 3: eine zweite schematische Darstellung eines Stromverlaufs,
• 4: eine schematische Darstellung eines parametrierbaren Kennfelds.

The invention is explained further on the basis of the following figures. Show it:

• 1 : a schematic representation of the procedural logic,
• 2 : a first schematic representation of a current curve,
• 3 : a second schematic representation of a current curve,
• 4th : a schematic representation of a parameterizable map.

1 shows the method according to the invention, or the processing of input signals to bring about a safe state of a drive train, in particular in a greatly simplified manner a transmission of a vehicle. In this case, signal information from activation criteria 1, 2, 3, 4 is fed to a computing unit R, which processes it in accordance with the method according to the invention.

The method is used when the vehicle is at a standstill and the direction of travel is specified. Accordingly, an input has already been made as to whether the vehicle should accelerate in the forward or reverse direction during a start-up process. However, the direction switching element is still in an open state. Furthermore, there is also a specification with regard to a driving range or a gear step. This can either be commanded by an operator or specified by a corresponding gearshift program of the transmission or a vehicle control computer. As a result, shift elements that are required for setting the selected gear are in a closed state. This represents the first activation criterion 1. Depending on the design of the transmission, it may be necessary to close one or more shift elements in order to set a gear or a driving range.

In addition, a threshold value with regard to a differential speed of the travel direction switching element to be closed is specified. This can be stored in the processing unit or in a separate control unit or some other storage element. Exceeding this threshold value of the differential speed represents the second activation criterion 2. In addition, a threshold value with regard to a vehicle speed is specified, with the third activation criterion 3 falling below this threshold value. The fourth activation criterion 4 is also provided as an input variable or signal input of the computing unit R. This is in the form of a specific signal from the relevant direction-of-travel switching element. This can be, for example, an indication of an electrical fault or an impermissible change in current a. A comparison with regard to the presence of the activation criteria 1, 2, 3, 4 takes place in the arithmetic unit R. Insofar as this is the case, a signal S is output, as a result of which the drive train of the vehicle or the transmission of the drive train is brought into a safe state. In other words, the presence of activation criteria 1, 2, 3, 4 is processed in accordance with a logical AND link.

2 shows a greatly simplified first schematic representation of a current curve for the control of a proportional valve of a switching element, for example a travel direction switching element. A time curve t is shown on the abscissa, a current I on the ordinate. Starting at time t0, current I has the value 10 or fluctuates by a small amount around this value up to time t1. In particular, the value of the current I deviates downwards from the value 10 in the mentioned interval and does not exceed it. For example, the value 10 represents a current I below which insufficient torque is transmitted via the relevant switching element, so that this does not result in a start-up process or a vehicle movement.

At the time t1, the current I rises suddenly with a high gradient, the value 10 being reached at the time t1 or exceeded shortly thereafter. The strong increase in current continues until time t2, in which case the value 11 is reached. Between the times t2 and t3, the current I drops with a large negative gradient, with the value 10 being reached at the time t3 and then even being clearly undershot. The short-term but strong increase in current represents a permissible curve, since this would lead to a jerky torque transmission in the drive train, which on the one hand can be recognized by a control unit and appropriate countermeasures can be initiated. Furthermore, the jerky start-up process can be perceived by an operator, so that suitable measures can be initiated immediately by him. This could include the actuation of the service and / or parking brake. Accordingly, the in 2 to classify the current change described as a permissible current change β.

3 shows a greatly simplified second schematic representation of a current curve, as was already shown in FIG 2 shown. However, the curves of the current I differ, starting at the point in time t0 to the point in time t1, the current I assumes the value 10 or fluctuates around this by a small amount. At time t1, the current I increases steadily until it assumes the value 11 at time t2. Thus, there is a constant current increase between t1 and t2, the gradient being significantly lower than in the illustration in 2 is. This could result in a constant but almost imperceptible closing of the relevant shift element, so that a start-up process without a driving specification would sometimes be recognized poorly or late. In the same way, the representation could also depict constant closing of the relevant switching element, which results in long-lasting strong acceleration of the vehicle. Since both of these must be avoided, the current change shown here must be classified as an impermissible current change a. If this progression occurs, this information is fed to the computing device R as fourth activation criterion 4. Consequently, the signal S can be used to establish the safe State triggered or the transmission or the drive train transferred to the safe state.

It should be noted that the scaling of the time profiles t in 2 and 3 are not to scale, so that a delta between t1 and t2 in 2 may have a value other than a delta between t1 and t2 in 3 .

4th shows a schematic representation of a parameterizable map. In the present case, this is designed in two dimensions. In the diagram shown here, a frequency A of the change in current is plotted on the abscissa and a characteristic B of the change in current is plotted on the ordinate. A characteristic curve K divides the spanned area into impermissible current changes a and permissible current changes β. The impermissible current changes a are hatched and the permissible current changes β are shown dotted. The permissible change in current β according to 2 is therefore assigned to the area below the characteristic curve K, while the impermissible change in current a according to 3 is to be assigned to the area above the characteristic curve K.

The characteristic B of the change in current can be expressed in particular in the value of the current I reached (amount), a gradient of the change in current or the duration of the change in current or the value of the current I reached. In other words, permissible current changes β correlate with a low accumulation A and a high level B, while inadmissible current changes a correlate with a high level A and a low level B. Since the map can be parameterized, it can be adapted in the manner mentioned above. Correspondingly, this results in a changed course of the characteristic curve K.

List of reference symbols

A.

frequency

B.

Expression

1, 2, 3, 4

Activation criterion

I, 10, 11

electricity

K

curve

R.

Arithmetic unit

S.

Safe state signal

t

Temporal course

t0, t1, t2, t3

time

a

impermissible change in current

β

permissible change in current

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed 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

• DE 19926697 B4 [0002]

Claims (9)

Method for operating a drive train of a vehicle, whereby during a vehicle standstill, if a direction of travel is specified and the direction of travel switching element is open, a start-up process is prevented without an explicit drive request, in that the drive train is transferred to a safe state if the cumulative activation criteria (1, 2, 3, 4) are met are, where - a shift element required for setting a driving range or a gear stage represents a first activation criterion (1) when this shift element is in a closed state, - Exceeding a threshold value of a differential speed of the travel direction switching element represents a second activation criterion (2), - A third activation criterion (3) if a vehicle speed falls below a threshold value, - A specific signal of the direction switching element represents a fourth activation criterion (4). Procedure according to Claim 1 , characterized in that the specific signal indicates the presence of an electrical fault in the direction switching element. Procedure according to Claim 1 , characterized in that the specific signal indicates the presence of an impermissible change in current (a) of a control signal for the direction switching element. Procedure according to Claim 3 , characterized in that an inadmissibility of a current change (α, β) results from an amount, a gradient, a duration and a number of the current changes (α, β), with the amount, the gradient, the duration and the number of Current change (α, β) an absolute threshold value and / or a dynamic threshold value is given. Procedure according to Claim 4 , characterized in that actual values of the current change (α, β) are recorded cyclically and compared with the absolute and / or dynamic threshold values, a number of cycles varying depending on the threshold value for assessing the inadmissibility of a current change (α, β). Method according to one of the Claims 4 or 5 , characterized in that the absolute and / or dynamic threshold values are specified in the form of a parameterizable map. Procedure according to Claim 6 , characterized in that the parameterization of the map is adapted by an operator of the vehicle and / or a suitable interface via remote maintenance. Control device comprising a computing unit (R), an input interface and an output interface, the input interface not only indicating the direction of travel and a driving request, but also indicating the presence of activation criteria (1, 2, 3, 4) to the computing unit (R), the computing unit ( R) is set up to carry out the inventive method according to one of the Claims 1 until 7th and to output a signal (S) via the output interface, whereby the drive train is brought into a safe state. Vehicle with a control device according to Claim 8 and with a drive train, the drive train comprising an input element, a transmission and an output.

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