DE102011006395A1 - Method for operating electrical system in event of failure of e.g. voltage sensors of monitoring system of high-volt lithium-ion battery in electric car, involves not-disconnecting battery from onboard network during discharging process - Google Patents

Abstract

The method involves checking whether a traction battery is completely in a charging process or discharging process (10) after a failure of elements of a monitoring system and before possible disconnection of the traction battery from an onboard network of a vehicle. The traction battery is disconnected (15) from the onboard network of the vehicle in a presence of the charging process when energy stored in the traction battery drops below a threshold value. The traction battery is not disconnected (20) from the onboard network of the vehicle in a presence of the discharging process. The traction battery is selected from a group consisting of a lithium-polymer battery, a lithium metal battery, a lithium manganese battery, a lithium iron phosphate battery and a lithium titanate battery. An independent claim is also included for a device for performing a method for operating an electrical system in an event of failure of elements of a monitoring system of a traction battery of a hybrid vehicle or electric vehicle.

Description

The present invention relates to a method for operating the electrical system in hybrid or electric vehicles during a failure of one or more elements of monitoring the traction battery and a device comprising means for performing the method.

State of the art

For the power supply of electric drives in electric or hybrid vehicles usually high voltage batteries are used, so-called traction batteries. Such traction batteries have by their structure or their ingredients on a potential hazard. In particular, when operating limits are exceeded, it can lead to a battery burn or leakage of hazardous substances. In order to avoid or reduce the risk to the environment and the vehicle occupants, methods and devices are usually provided which disconnect the traction battery immediately from the electrical system, as soon as a safety-relevant operating limit is exceeded. To control the traction battery usually a monitoring system of several elements is used, which detect the safety-related parameters of the traction battery during operation and monitor for exceeding operating limits.

Traction batteries with such a monitoring system, in particular lithium-ion high-voltage batteries, which are used as energy source in electric or hybrid vehicles, usually have devices such. B. a battery management system (BMS), with which the safety-related operating variables of the traction battery such as cell voltages, total battery voltage, total battery current and cell or battery temperature can be detected and monitored. These operating variables are detected by means of elements of the monitoring system, such as, for example, specific sensors and monitored by means of the BMS for the exceeding of limit or threshold values. The limit or threshold values are chosen such that when these limit or threshold values are exceeded, chemical reactions in the cells can be set in motion (so-called "thermal runaway"), which endangers persons as well as the vehicle or the vehicle Environment can lead. Especially with overvoltage and / or undervoltage is expected to increase the risk situation.

In case of failure of one or more elements of the monitoring system such. B. one or more safety-related sensors, such as a failure of voltage sensors or temperature sensors of the traction battery, no plausibility of the measured values and thus no sufficiently safe monitoring of the traction battery for compliance with the operating limits is no longer possible. In such a case, the traction battery is transferred to a safe state in which it is disconnected from the electrical system. As a result, however, the power supply of the electric drive of the vehicle is interrupted, so that it comes to failure of the electric drive in hybrid vehicles or even to a complete "lying" of the electric vehicle.

The invention will be explained in more detail below with reference to FIG. It shows:

• – Ausfall eines oder mehrerer Elemente des Überwachungssystems 5,
• – Prüfung, ob sich die Traktionsbatterie insgesamt in einem Lade- oder einem Entladevorgang befindet 10,
• – Abtrennung der Traktionsbatterie vom Traktionsnetz des Fahrzeugs beim Vorliegen eines Ladevorgangs 15; oder
• – zumindest vorläufig keine Abtrennung der Traktionsbatterie vom Traktionsnetz des Fahrzeugs beim Vorliegen eines Entladevorgangs 20.

The single figure illustrates the method according to the invention with the steps:

• - Failure of one or more elements of the monitoring system 5 .
• - Checking whether the traction battery as a whole is in a loading or unloading process 10 .
• - Separation of the traction battery from the traction network of the vehicle in the presence of a charging process 15 ; or
• - At least for the time being no separation of the traction battery from the traction network of the vehicle in the presence of a discharge 20 ,

Disclosure of the invention

According to the invention, a method is provided for operating the vehicle electrical system in hybrid or electric vehicles in the event of failure of elements of the monitoring system of the traction battery, which is characterized in that after the failure of one or more elements of the monitoring system and before disconnecting the traction battery from the electrical system of Vehicle is checked whether the traction battery is in a total charge or discharge, the traction battery is separated in the presence of a charging operation of the traction network of the vehicle, while the traction battery is not disconnected in the presence of a discharge. Thus, the method can be provided in particular as a method for emergency operation of the vehicle electrical system.

Instead of the traction battery in case of failure of an element of the monitoring system such. B. to transfer a voltage or temperature sensor immediately in the safe state and separate the traction battery from the electrical system, a discharge of the traction battery is still allowed, so that a temporary continued operation of the electric drive and possibly other electronic components of the vehicle is possible. The electrical system of the vehicle can therefore in particular in a so-called emergency operation continue to be operated. This allows the driver to move the vehicle even after the failure of elements of the monitoring system of the traction battery to a workshop or at least to a secure parking space.

The method according to the invention makes use of the knowledge that only the overcharging of the traction battery or of a cell thereof leads directly to a fire or thermal runaway of the cell or of the battery. The condition of overcharging must therefore be avoided or prevented. In contrast, undercharging the traction battery or a cell thereof does not immediately lead to fire or thermal runaway. The risk of fire arises in this case only when recharging the battery after the underload. It is therefore sufficient in this case to prevent recharging of the traction battery to safely avoid danger to the environment and the occupants of the vehicle.

The method according to the invention serves to operate the on-board network in electric or hybrid vehicles in the event of failure of elements of the monitoring of the traction battery. This operating state can be provided for example in an emergency operation. Under an emergency operation is understood a temporary limited continued operation of the electrical system until the error that has led to emergency operation, has been eliminated or the traction battery has been disconnected from the electrical system of the vehicle. The emergency operation can be configured such that at least the electric drive of the vehicle is still supplied with energy from the traction battery. It is also possible to design the emergency operation such that in addition further electronic components of the vehicle continue to operate. Basically, the emergency operation can also be designed such that the electrical system is essentially operated unchanged. Preferably, during emergency operation, the electrical supply of components that are not directly involved in or necessary for the safe use of the vehicle in traffic may be excluded in order to minimize the energy consumption during emergency operation.

It should be explicitly noted here that in the context of the present description, many technical features are described by way of example in connection with an emergency operation. All described features can also be provided without the presence of an emergency operation.

Under the vehicle electrical system of the vehicle is understood the network of the vehicle, with which the electronic components of the vehicle are supplied with electrical energy. The electrical system comprises at least the supply of the electrical drive of the vehicle with power from the traction battery of the vehicle. In addition, the electrical system may include the supply of other or all electronic components of the vehicle.

The traction battery is the battery of the vehicle, which supplies the electrical drive of the vehicle with electrical energy. In addition, the traction battery can supply other or all electrical consumers of the vehicle with electrical energy. The traction battery preferably has a plurality of battery cells, which may be combined to form a functional unit. The traction battery may comprise one or more individual battery cells or one or more battery modules, wherein the modules each comprise a plurality of battery cells which are suitably connected. For this purpose, the individual battery cells of the traction battery can be electrically connected to one another in such a way that they are connected to desired battery module or battery architectures.

A battery cell is understood to mean an electrochemical energy store which can store an energy by means of electrochemical processes and can provide it again if necessary. Basically, battery cells of any accumulator or battery cell type can be used in the traction battery. Preferably, the traction battery battery cells of the type of lithium-ion cells, in particular of the type Li-ion lithium-ion battery, LiPo-lithium-polymer battery, LiFe-lithium-metal battery, Li-Mn-lithium-manganese Battery, LiFePO ₄ lithium iron phosphate battery, LiTi lithium titanate battery.

The traction battery is preferably a lithium-ion battery, in particular a high-capacity lithium-ion battery, particularly preferably a battery, for. As a lithium-ion battery, with a nominal capacity of ≥ 2 Ah, preferably of ≥ 3 Ah.

The traction battery has elements of a monitoring system. Such elements may be understood to mean all components of a battery monitoring system or battery management system that serve to capture, store and / or analyze safety-related data of the traction battery or are suitable for this purpose. Examples of such elements are sensors, connections, lines or arithmetic or memory units. Preferred elements of the monitoring system are voltage and / or temperature sensors. For this purpose, the traction battery, for example, voltage and / or temperature sensors having the voltage or temperature in detect individual cells, modules and / or the entire traction battery and provide the measured values for monitoring the traction battery. The monitoring of the voltage or temperature of the traction battery can be done for example by comparison with a limit or threshold. This comparison can z. B. in a battery management system (BMS) of the vehicle.

In the method according to the invention is after a failure 5 one or more elements of the monitoring system of the traction battery first checked 10 whether the traction battery is in a total charge or discharge process. This check shall be carried out after the failure of elements of the monitoring system has been detected and before any disconnection of the traction battery from the vehicle electrical system. Preferably, the failure includes or consists of 5 of elements of the monitoring system of the traction battery from the failure of one or more voltage and / or temperature sensors. Will in this exam 10 found that the traction battery is in total in a charging process, the traction battery is disconnected directly from the electrical system 15 and thus transferred to a safe state. If, on the other hand, it is determined during the test that the traction battery as a whole is in a discharge process, then the traction battery is initially not disconnected from the vehicle electrical system 20 , And it is an emergency operation of the electrical system ensured. Thus, the vehicle can still be moved by means of the electric drive to a workshop or at least to a secure parking space.

The method according to the invention can be configured in such a way that the check as to whether the traction battery as a whole is in a charging or discharging process is carried out by determining the voltage at the traction battery or at a suitable location in the connected electrical system of the vehicle. Alternatively or additionally, as an additional safety measure, the check for the presence of a charging or discharging process on the traction battery by determining the flow of current to the traction battery (ie by monitoring the battery current) or at a suitable location in the electrical system.

The safety can be further increased during emergency operation, in which the check whether the traction battery during emergency operation continues to be in a total unloading or not, during the emergency operation is recurring or even continuous. If it is found in this repeated or continuous test that the traction battery is in total in a state of charge, so the traction battery can be disconnected directly from the electrical system and thus the emergency operation be terminated.

Preferably, the traction battery is then in a total charging process when the amount of energy stored in the traction battery increases in a sum in a predetermined time interval.

Preferably, the traction battery is then in a total unloading process, when the energy stored in the traction battery in a predetermined time interval in the sum decreases or remains substantially unchanged. In this case, the time interval may in particular be selected so that short-term charging operations, which may for example result from the operation or from the movement of the vehicle, for. As a recuperation from the brake system, are harmless for the detection of a discharge, provided that the amount of energy stored in the traction battery decreases over the entire considered time interval in total or remains essentially unchanged. The advantage of such a regulation is that the possible operating period of the traction battery can be further increased during emergency operation, in which short-term charging processes are permitted within a certain range and do not lead directly to the separation of the traction battery from the vehicle electrical system.

In a particular embodiment of the method according to the invention can be provided that the traction battery is only then in a total charging and thus not in a discharge when the energy stored in the traction battery in the sum exceeds a limit or threshold or the increase of in the energy stored in the traction battery exceeds a limit or threshold value in a predetermined time interval. The limit or threshold values are chosen to be exceeded before there is an imminent danger of battery burn or thermal runaway of the traction battery. The absolute value for such a limit or threshold depends on the type of battery used and can be easily determined and determined by the skilled person without undue burden.

The method according to the invention can additionally be designed such that the traction battery is disconnected from the electrical system of the vehicle at least when the energy stored in the traction battery falls below a limit value or the energy quantity discharged from the traction battery since the failure of voltage sensors exceeds a limit value or the decrease the amount of energy stored in the traction battery in a predetermined time interval, ie the decrease rate exceeds a threshold or threshold. In any case, the limit value should be chosen so that the traction battery is disconnected from the electrical system before the traction battery due to excessive discharge permanent damage. In particular, the limit value can be set such that a permanent undershooting of the limit value can lead to damage of the traction battery. An advantage of this variant of the method is that it prevents the entire traction battery from having to be replaced because an excessive discharge has occurred during emergency operation.

In the method according to the invention it can be provided that as soon as the vehicle is in emergency operation, an alarm function is triggered, which informs the driver of the vehicle about the failure of elements of the monitoring system and / or about the existence of an emergency operation. In addition, the driver may be requested to visit a workshop or to park the vehicle safely.

Additionally or alternatively, it may be provided in the method according to the invention that the failure of elements of the monitoring system and possibly the presence of an emergency operation is entered into a non-volatile fault memory. This fault memory can be designed such that the fault memory is read out during an initialization and the re-commissioning of the traction battery remains suppressed until the fault entry has been removed from the fault memory. In particular, the error memory can be designed such that a deletion of the defect entry can only be done by means of a special tool and thus preferably exclusively in a workshop.

In particular, the inventive method comprises a method for emergency operation of the electrical system in hybrid or electric vehicles in case of failure of voltage sensors of the traction battery, which is characterized in that is checked after the failure of one or more voltage sensors and before disconnecting the traction battery from the electrical system of the vehicle, whether the traction battery as a whole is in a charging or discharging process, wherein the traction battery is disconnected from the traction network of the vehicle in the presence of a charge, while the traction battery is not disconnected in the presence of a discharge and thus an emergency operation of the vehicle electrical system is ensured.

In addition, the inventive method also includes a method for emergency operation of the electrical system in hybrid or electric vehicles in case of failure of temperature sensors of the traction battery, which is characterized in that is tested after the failure of one or more temperature sensors and before disconnecting the traction battery from the electrical system of the vehicle whether the traction battery as a whole is in a charging or discharging process, wherein the traction battery is disconnected from the traction network of the vehicle in the presence of a charging operation, while the traction battery is not disconnected in the presence of a discharge and thus an emergency operation of the vehicle electrical system is ensured.

The invention also relates to a device comprising means suitable for carrying out a method according to the invention. If the on-board network of the vehicle has a battery management system (BMS), then the BMS can represent such a device according to the invention and be designed to carry out the method according to the invention. In most cases, the BMS of the traction battery is designed so that it for safety and / or life reasons, the traction battery falls below a lower voltage or charge threshold directly from the electrical system and transferred to a safe state. In the method according to the invention, it can be provided that this lower voltage or charge threshold of the traction battery is disabled during emergency operation or the threshold is correspondingly lowered further, so that an undesired interruption of the emergency operation is prevented or avoided.

The invention also relates to a vehicle comprising a device with means for carrying out the method according to the invention. The term "vehicle" is to be understood as meaning all driven vehicles which have a traction battery for supplying energy to at least one electric drive of the vehicle, regardless of whether these vehicles have a further drive and, if so, which further drive these vehicles have. In particular, the term "vehicle" includes hybrid electric vehicles (HEV), plug-in hybrid vehicles (PHEV), electric vehicles (EV), as well as all vehicles employing a traction battery for at least partially powering an electric drive.

Claims (11)

Method for operating the vehicle electrical system in hybrid or electric vehicles in the event of failure of elements of the monitoring system of the traction battery, characterized in that after the failure ( 5 ) of one or more elements of the monitoring system and before a possible disconnection of the traction battery from the electrical system of the vehicle ( 10 ), whether the traction battery as a whole is in a charging or discharging process, wherein the traction battery in the presence of a charging process from the traction network of the vehicle is disconnected ( 15 ), while the traction battery is not disconnected in the presence of a discharge ( 20 ). The method of claim 1, wherein the failure of elements of the monitoring system of the traction battery comprises or consists of the failure of one or more voltage and / or temperature sensors. A method as claimed in claim 1 or 2, wherein the check of whether the traction battery is in a total charge or discharge operation is repetitive or continuous during an emergency operation. A method according to any one of the preceding claims, wherein the traction battery is all in one discharge operation when the amount of energy stored in the traction battery decreases in a predetermined time interval in sum or remains substantially unchanged and / or wherein the traction battery is then total in a charging process is when the energy stored in the traction battery increases in a predetermined time interval in the sum. Method according to one of the preceding claims, wherein the traction battery is disconnected from the electrical system of the vehicle at least when the stored energy in the traction battery falls below a threshold value. The method of claim 5, wherein the limit value is set such that a permanent undershooting of the limit value can lead to damage of the traction battery. Method according to one of the preceding claims, wherein an alarm function is triggered, which informs the driver about the failure of elements of the monitoring system and / or the existence of an emergency operation and this possibly asks to visit a workshop or safely park the vehicle. Method according to one of the preceding claims, wherein the failure of elements of the monitoring system and optionally the presence of an emergency operation is entered in a non-volatile fault memory. The method of claim 8, wherein the error memory is read at an initialization and the re-commissioning of the traction battery is inhibited, as long as the entry is in the error memory. Device comprising means for carrying out the method according to one of claims 1 to 9. Vehicle comprising a device according to claim 10.

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