DE102019206220A1 - Method for comparing an electrical current of an electrochemical energy store with a target current - Google Patents

Abstract

Method for comparing a detected electrical current Iact of an electrochemical energy store of an electrically drivable vehicle with a desired electrical current Iset of the electrochemical energy store.

Description

The invention is based on a method for comparing an electrical current of an electrochemical energy store of an electrically drivable vehicle with a target electrical current of the electrochemical energy store, an electrical drive system with at least one electrochemical energy store, a computer program product and a computer-readable medium according to the preamble of the independent claims.

State of the art

In contrast to vehicles with conventional drives, vehicles with an electric drive offer the option of recovering energy during deceleration by means of recuperation. In the case of high recuperation power, high negative wheel torques sometimes arise, which can lead to instability of the vehicle, especially when cornering. Just like the recuperation torque, a high drive torque while cornering can endanger the stability of the vehicle.

In order to reliably detect and avoid an undesirably low drive torque as well as an undesirably high drive torque, according to the current status, a high level of accuracy and reliability of the sensors as well as precise safeguarding of the development process in accordance with ISO standard 26262 are necessary.

The document DE 10 2017 204 132 A1 discloses a method for operating a drive of a vehicle, wherein a target torque is calculated from at least a driver's desired torque, a permissible torque is calculated at least from the driver's desired torque, the target torque being compared with the permissible torque and the target torque being passed on to at least one drive control unit of the drive if a deviation of the nominal torque from the permissible torque is below a threshold value.

It is the object of the present invention to further improve the state of the art. This object is achieved by the features of the independent claims.

Disclosure of the invention

Advantages of the invention

1. a) Erfassen einer Drehzahlgröße n_act, die eine Drehzahl eines elektrischen Motors des Fahrzeugs repräsentiert;
2. b) Ermitteln einer Fahrerwunschmomentgröße M, die ein Fahrerwunschmoment in Abhängigkeit einer Fahrpedalstellung APP_act (108) des Fahrzeugs repräsentiert;
3. c) Erfassen einer Spannungsgröße U_act, die eine elektrische Spannung des elektrochemischen Energiespeichers repräsentiert;
4. d) Bestimmen des elektrischen Sollstroms I_set gemäß I_set $I_{set}=\frac{2\ast \pi \ast M\ast n_{act}}{U_{act}};$
   
5. e) Vorgeben eines zulässigen Stromintervalls I_Hi, I_Lo zumindest teilweise in Abhängigkeit des elektrischen Sollstroms I_set;
6. f) Erzeugen einer Plausibilitätsinformation in Abhängigkeit eines Vergleichs des elektrischen Stroms I_act mit dem Stromintervall I_Hi, I_Lo.

The procedure according to the invention with the characterizing features of the independent claims has the advantage that the method comprises the following steps:

1. a) detecting a speed variable n _act which represents a speed of an electric motor of the vehicle;
2. b) determining a driver's desired torque quantity M, which represents a driver's desired torque as a function of an accelerator pedal position APP _act (108) of the vehicle;
3. c) detecting a voltage _variable U _act , which represents an electrical voltage of the electrochemical energy store;
4. d) determining the electrical setpoint current I _set according to I _set ${\mathrm{I.}}_{set}=\frac{2\ast \pi \ast \mathrm{M.}\ast n_{act}}{U_{act}};$
   
5. e) specifying a permissible current interval I _Hi , I _Lo, at least partially as a function of the nominal electrical current I _set ;
6. f) Generating plausibility information as a function of a comparison of the electrical current I _act with the current interval I _Hi , I _Lo .

A correlation of the converted drive torque with the current current is advantageously used to identify an incorrect torque position. As a result, undesirably high drive and recuperation torques due to an incorrect torque calculation in the torque path, for example due to a sensor error, actuator error and / or calculation error, can be detected and avoided in electrically driven vehicles.

ergibt.In step d) in an advantageous embodiment, in addition to the drive power, further power losses P ₁ , for example due to electrical lines, efficiency losses P ₂ , for example of an electric motor and / or inverter, and / or power from auxiliary consumers P ₃ , such as air conditioning, heating and / or DC / DC converter. This is done in particular by adding the other electrical powers to the drive power P ₀ = 2 * π * M * n _act , so that the desired electrical current ${\mathrm{I.}}_{set}=\frac{\left(2\ast \pi \ast \mathrm{M.}\ast n_{act}\right)+{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="DE102019206220A1\_0004.png"\; state="\{\{state\}\}">P</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="DE102019206220A1\_0004.png"\; state="\{\{state\}\}">P</figure-callout>}}_2+P_3}{U_{act}}$

results.

The method according to the invention is not restricted to the illustrated sequence of the embodiment. Rather, steps a) to c) can take place in any order, repeatedly, successively in time and / or simultaneously.

Further advantageous embodiments are the subject of the subclaims.

The plausibility information represents an implausible electrical current I _act , if the electrical current I _{act is} outside the current interval I _Hi , I _Lo .

On the basis of the plausibility information, undesirably high drive and recuperation torques can be detected early and without additional safeguarding measures.

• g) Einleiten von Maßnahmen, insbesondere Reduzierung eines maximal zulässigen elektrischen Stroms, um ein ungewolltes Drehmoment zu vermeiden, in Abhängigkeit der Plausibilitätsinformation.

The method according to the invention further comprises the advantageous step:

• g) initiating measures, in particular reducing a maximum permissible electrical current, in order to avoid an undesired torque, depending on the plausibility information.

This can prevent unstable driving situations in the electrically driven vehicle and possible personal injury. In an advantageous embodiment, the measures introduced separate the electrical connection between the electrochemical energy store and the vehicle. This maintains the driving stability of the electrically driven vehicle.

The accelerator pedal position APP _{act of} the vehicle includes a plausibility check of raw values APP _{1, rαw} . APP _{2, rαw} the accelerator pedal position.

The electrical drive system according to the invention comprises at least one electrochemical energy store, at least one voltage sensor, at least one current sensor and means which are suitable for carrying out the steps of the method according to the invention. The accuracy and the redundancy of the sensors and thus the system costs can advantageously be reduced. Likewise, the security measures previously required can be reduced, thus reducing the development effort.

The computer program product according to the invention comprises commands which cause the device to carry out the method steps according to the invention.

The computer program is advantageously stored on a computer-readable medium.

Figure list

Exemplary embodiments of the invention are shown in the drawing and explained in more detail in the description below.

• 1 eine beispielhafte Darstellung einer Ausführungsform eines erfindungsgemäßen elektrischen Antriebssystems eines Fahrzeugs; und
• 2 eine schematische Darstellung eines Stromverlaufs einer ersten Ausführungsform des erfindungsgemäßen Verfahrens; und
• 3 eine schematische Darstellung eines Stromverlaufs einer zweiten Ausführungsform des erfindungsgemäßen Verfahrens.

Show it:

• 1 an exemplary representation of an embodiment of an electric drive system according to the invention of a vehicle; and
• 2 a schematic representation of a current profile of a first embodiment of the method according to the invention; and
• 3 a schematic representation of a current profile of a second embodiment of the method according to the invention.

Detailed description of the exemplary embodiments

The same reference symbols denote the same device components in all figures.

1 shows an exemplary representation of an embodiment of an electric drive system according to the invention 100 of a vehicle. The electric drive system 100 includes a battery management system 101 and a control unit 103 ("Vehicle Control Unit"). The control unit 103 detects variables 102 (1), 102 (2), the accelerator pedal position of the accelerator pedal 102 represent.

One unity 107 plausibility checks raw values 104 (1), 104 (2) of the recorded variables 102 (1), 102 (2) of the accelerator pedal position and transmits a plausible accelerator pedal position 108 to a unit 111 .

The unit 111 also detects a speed variable 106 showing a speed of an electric motor 105 of the vehicle, as well as a voltage quantity 110 , which represents an electrical voltage of the electrochemical energy store of the vehicle, the electrical voltage by means of a voltage sensor 109 is captured. Furthermore, a driver desired torque variable is determined, which is a driver desired torque as a function of the accelerator pedal position 108 of the vehicle.

Based on the speed size 106 , the voltage magnitude 110 As well as the driver's desired torque, an electrical target current is determined and limits 112 (1) , 112 (2) predetermined for a permissible current interval at least partially as a function of the nominal electrical current.

The limits 112 (1) , 112 (2) the permissible current interval are system-dependent and can be dynamically specified as a function of other operating variables, for example an operating time, a state of charge (SOC) and / or a state of health (SOH) of the electrochemical energy store, a temperature, an ambient pressure and / or as a function of performance requirements and / or efficiency of electrical consumers.

Furthermore, at least one of the limits can be provided 112 (1) , 112 (2) to be statically specified.

One unity 115 generates plausibility information 116 depending on a comparison of an electric current 114 , the electric current 114 by means of a current sensor 113 is captured. The plausibility information 116 represents an implausible electrical current if the detected electrical current is outside the current interval.

By means of a unit 117 measures are based on the plausibility information 116 initiated, for example a maximum permissible electrical current is reduced and / or an electrical connection between the electrochemical energy store and the electric motor of the vehicle is disconnected, for example by opening contactors. This can prevent an unstable driving situation, for example due to the vehicle swerving.

2 shows a schematic representation of a current profile in a first embodiment of the method according to the invention. A curve over time is shown on the abscissa axis. A current intensity and current direction of an electric current are shown on the ordinate axis. If the electrical current is positive, an electrochemical energy store is discharged, for example in the case of a drive torque. If the electrical current is negative, the electrochemical energy store is charged, for example in the event of a recuperation torque.

A time profile of an electrical current lies between a point in time t ₀ and a point in time t ₁ 203 within a current interval which is defined by an upper limit 201 and by a lower limit 202 is given.

At the time t ₁ , the electric current exceeds 203 the upper limit 201 and is therefore outside the current interval. In this case, a violation of the permissible torque is recognized by the method according to the invention and the power supply to the electric motor is reduced or switched off by the electrochemical energy store.

In the embodiment shown, the current interval is specified continuously on the basis of the determined electrical setpoint current. In an alternative embodiment, the current interval is specified at specific times.

3 shows a schematic representation of a current profile in a second embodiment of the method according to the invention. A curve over time is shown on the abscissa axis. A current intensity and current direction of an electric current are shown on the ordinate axis. There is an electric current between times t ₀ and t ₁ 302 positive, the electrochemical energy storage of the vehicle is discharged, for example by a drive process. The electrical current is between times t ₁ and t ₂ 302 negative, the vehicle's electrochemical energy store is being charged, for example through a recuperation process. Between time t ₂ and t _3, in turn, is a discharge place and between the time points t ₃ and t _4, a charging process.

At a point in time t ₄ , the electric current falls below 302 a lower limit 301 and is therefore outside the current interval. In this case, a violation of the permissible torque is recognized and the power supply of the electric motor is reduced or switched off by the electrochemical energy store.

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 102017204132 A1 [0004]

Claims (8)

A method for comparing an electrical current I _act (114, 203, 302) of an electrochemical energy store of an electrically drivable vehicle with a nominal electrical current I _{set of} the electrochemical energy store, comprising the following steps: a) detecting a speed variable n _act (106), which represents a speed of a electric motor (105) of the vehicle; b) determining a driver's desired torque quantity M, which represents a driver's desired torque as a function of an accelerator pedal position APP _act (108) of the vehicle; c) detecting a voltage _variable U _act (110) which represents an electrical voltage of the electrochemical energy store; d) determining the electrical setpoint current I _set according to ${\mathrm{I.}}_{set}=\frac{2\ast \pi \ast \mathrm{M.}\ast n_{act}}{U_{act}};$

e) specifying a permissible current interval I _Hi , I _Lo (112 (1), 112 (2), 201, 202, 301) at least partially as a function of the electrical setpoint current I _set ; f) generating plausibility information (116) as a function of a comparison of the electrical current I _act (114, 203, 302) with the current interval I _Hi , I _Lo (112 (1), 112 (2), 201, 202, 301); Procedure according to Claim 1 , the plausibility information (116) representing an implausible electrical current I _act (114, 203, 302) if the electrical current I _act (114, 203, 302) is outside the current interval I _Hi , I _Lo (112 (1), 112 (2), 201, 202, 301). Method according to one of the preceding claims, further comprising the following step: g) initiating measures (117), in particular reducing a maximum permissible electrical current, in order to avoid an undesired torque, depending on the plausibility information (116). Procedure according to Claim 3 , wherein the initiated measures (117) disconnect the electrical connection between the electrochemical energy store and the vehicle. Method according to one of the preceding claims, wherein the accelerator pedal position APP _act (107) of the vehicle is a plausibility check of raw values APP _{1, raw} , APP _{2, raw} (104 (1), 104 (2)) of the accelerator pedal position (102 (1), 102 (2)) includes. Electrical drive system with at least one electrochemical energy store, at least one voltage sensor (109), at least one current sensor (109) and means (101) which are suitable for the steps of the method according to one of the Claims 1 to 5 execute. Computer program product comprising instructions that cause the electric drive system of the Claim 6 the process steps according to one of the Claims 1 to 5 executes. Computer-readable medium on which the computer program is based Claim 7 is stored.

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