Control unit and method for optimized charging of a secondary battery

Abstract

Method for charging a secondary battery (2) of a special means of transport (10) with a primary battery (1) and a secondary battery (2), comprising the steps: - Determining (100) a voltage of the secondary battery (2), - Determining (100) a usage history of the secondary battery (2), - determining (100) an outside temperature of the means of transport (10), - Detecting (200) a charging requirement of the secondary battery (2) based on the determined voltage, the determined usage history and the determined outside temperature, and when the primary battery (1) is in a state where it does not require charging - preventing (300) a stop operating state, and / or - Preventing (300) a recuperation function for charging the secondary battery (2).

Description

State of the art

[0001] The present invention relates to a method for charging a secondary battery of a special means of transport having a primary battery and a secondary battery. In particular, the present invention relates to a method for improved control of a charging function for the secondary battery with low technical hardware expenditure. In the prior art, in vehicles which can switch between an operating and a standby state of an internal combustion engine using a start / stop process and are intended to save fuel, the starter battery (primary battery) is diagnosed by a battery sensor. If a second battery is installed, insufficient recharging of the second battery during driving with start / stop and recuperation (e.g.Recovery of kinetic vehicle energy can result in the consumers supplied by the second battery (secondary battery) only being able to operate for an insufficiently long period of time. In particular, after a journey (i.e., during a parking phase), the consumers can only be powered by the energy stored in the secondary battery.

[0002] DE 101 16 311 A1 discloses a control device for hybrid vehicles, in which the presence of an auxiliary battery in the vehicle electrical system is discussed. The auxiliary battery can be charged by an alternator via an auxiliary battery charging line. The auxiliary battery is a conventional 12-V vehicle battery, the voltage of which is monitored by an auxiliary battery voltage detection device.

[0003] DE 10 2008 034 461 A1 addresses the temperature dependence of a vehicle battery's charging performance. Among other things, it suggests waiting until a battery refresh cycle is initiated if the battery temperature is too low (poor charge acceptance).

[0004] DE 10 2004 023 618 A1 discloses a method and a device for charging an energy storage device. A first energy storage device and a second energy storage device are charged via a generator, which in turn is driven by an internal combustion engine. Since the energy storage devices have different charging voltages, a parallel connection of both energy storage devices is varied depending on the current charging voltage. The second energy storage device is "slower" in terms of power output and consumption than the first energy storage device. A control unit determines the state of charge of the second energy storage device and controls the charging power accordingly. The charging power is additionally determined depending on the battery temperature and / or the battery aging (SOH). Furthermore, it is proposed to deactivate an automatic start / stop function during the charging process to avoid unnecessarily delaying the charging process.

[0005] DE 10 2010 032 280 A1 relates to a measuring unit for measuring the impedance of an energy storage device in the energy system or on-board electrical system, for example, of a vehicle. Furthermore, the invention relates to an energy system or on-board electrical system with a measuring unit according to the invention. Generic measuring units are used particularly in vehicle on-board electrical systems. Energy storage devices integrated into a vehicle's on-board electrical system must be regularly tested for the permissible impedance, i.e., internal resistance (Equivalent Serial Resistance ESR, also called equivalent series resistance or intrinsic resistance). The aim of this impedance measurement is to diagnose the relevant line branches for contact problems, open connections, or exceedance of the permissible limits of the resistance or capacity of the energy storage devices themselves.This diagnostic is particularly important for vehicle start / stop systems and on-board power system stabilization systems, because the impedance of energy storage devices and their supply lines determines their restart capability. If the impedance of optionally switchable energy storage devices exceeds a certain level, the start / stop function is deactivated. In many applications, this impedance diagnostic even contributes to the functional safety of the vehicle.

[0006] US 2006 / 0 097 577 A1 discloses a main power source, which is, for example, a conventional lead-acid battery, and generates a voltage of 12-13 V. When the engine is started, the main power source supplies the starter motor with power. The main power source has higher priority than an auxiliary power source when supplying loads. The auxiliary power source is a high-performance battery (e.g., a lithium-ion battery) with a higher charging capacity and better condition detection than the main power source. Furthermore, the auxiliary power source has a lower internal resistance per capacity and generates a voltage of 9-12 V. A generator is directly connected to the auxiliary power source. The auxiliary power source stores the regenerative energy generated by the generator when the vehicle decelerates and serves as a redundant power source for the main power source.The main power source and the auxiliary power source are connected to each other via a supply circuit comprising a DC / DC converter and a second supply circuit comprising a switch.

[0007] Common to the solutions known in the prior art is that the condition of the second battery (secondary battery) is either not monitored at all or requires complex sensors and expensive evaluation hardware. Therefore, it is an object of the present invention to resolve this conflicting objectives as effectively as possible. Disclosure of the invention

[0008] The above-mentioned object is achieved according to the invention by a method for charging a secondary battery and a corresponding control unit. The method is particularly suitable for charging a secondary battery of a special means of transport comprising a primary battery and a secondary battery. In the context of the present invention, a "special means of transport" is understood to mean a vehicle which, due to the presence of additional electrical consumers, requires increased storage capacity in the form of an additional electrochemical energy storage device (secondary battery). Examples of such special means of transport are ambulances, police vehicles, fire engines, camping vehicles, and cars with auxiliary heating.A secondary battery is therefore understood to be, in particular, an electrochemical storage device that does not contribute, or only contributes to a limited extent, the provision of energy needed to start a combustion engine installed in a vehicle. In the prior art, such batteries are therefore also referred to as "slow" energy storage devices. Structurally, this property is reflected in the fact that the electrical connections / infrastructure of the secondary battery are designed for significantly lower power (or current) than the connections / infrastructure of the primary battery. The method for charging the secondary battery initially comprises the step of determining various values. First, the voltage of the secondary battery is determined. This does not require complex and costly evaluation electronics.For example, the voltage measurement of the secondary battery can be carried out by a two-wire line, which feeds the voltage signal to a control unit in the means of transport. The control unit can, for example, be a special control unit specific to the means of transport, which is also referred to as a "special control unit" (e.g. in the form of a so-called authority module). In other words, this special control unit is not included in all examples of a production series of the means of transport, if it is, for example, a passenger car. In addition, according to the invention, the usage history of the secondary battery is determined at least for a predefined period in the past. The usage history can, for example, include a terminal status of the means of transport over time, through which the usage history of the means of transport can be determined in a certain respect (e.g.regarding the electrical energy balance of the on-board network). Such parameters are already determined and stored by engine control units or similar devices. In addition, the usage history for the same period can include parameters for the operating states of electrical consumers that are supplied with electrical energy from the secondary battery. For example, a data memory of an auxiliary heater can be queried, in which the last operating cycle of the auxiliary heater is stored. In the case of special emergency vehicles, information about the operating status of installed radio devices, special signaling devices, or similar can be queried. In the case of camping vehicles, for example, it is possible to determine whether lights, cooling units, entertainment systems, or pumps have been used recently. In particular, the usage history can also include information regarding the energy supply to the secondary battery (i.e., any charging processes).In other words, the aforementioned information can be countered by how much energy was fed into the secondary battery within the same period. Such a value can, for example, also be estimated based on the usage history of an internal combustion engine and / or an alternator (generator) connected to it. "Usage history" within the meaning of the present invention is not understood to mean an actual analysis of the secondary battery parameters (apart from the voltage of the secondary battery), as they are recorded in the prior art using battery data modules (BDM) in a complex and costly manner. A state of charge (SOC), a measurement of the internal resistance of the secondary battery (SOH), etc., are in particular not understood under the term "usage history" and are therefore neither determined nor used according to the invention.In addition, the method according to the invention proposes determining an outside temperature of the means of transport. This can be determined, for example, by an already existing temperature sensor and provided via a bus system. Based on the information determined, a charging requirement of the secondary battery is determined. In doing so, according to the invention and in the interests of cost-effective implementation, a certain probability is accepted that the charging requirement of the secondary battery determined according to the invention does not (exactly) correspond to reality. In other words, the method according to the invention proposes determining a certain probability for a current operating state (charging requirement) of the secondary battery and, in response to the probability value, taking measures to improve the charging state of the secondary battery.According to the invention, an automatic switch to a stop operating state is prevented when the primary battery is not requiring charging. In other words, in a state in which the primary battery would allow a stop operating state with a corresponding on-board electrical system load, a switch to the stop operating state in order to charge the secondary battery is prevented due to the charging requirement of the secondary battery detected according to the invention. In the context of the invention, a "stop operating state" is understood to mean a standby state in which the internal combustion engine of the means of transport is temporarily not required, but a resumption of its operation within a short period of time, e.g., a maximum of 3 minutes (e.g., "traffic light stop") is foreseeable.Since several consumers of the means of transport usually continue to run during such a stopped operating state, a certain load on the energy storage devices of the means of transport is accepted. If the method according to the invention determines during a stopped operating state that energy should be supplied to the secondary battery, a restart of the internal combustion engine is initiated when the primary battery is no longer in need of charging. Alternatively or additionally, a recuperation function can be prevented in order to meet the charging requirements of the secondary battery. A recuperation function can in particular be understood as locomotion using electrical energy without the operation of the internal combustion engine. A recuperation function can, for example, also comprise the controlled lowering of an on-board voltage by reducing the power output of an electrical generator.According to the invention, the aforementioned measures enable charging of the secondary battery. In this way, the present invention realizes a cost-effective improvement in energy management in conjunction with a secondary battery.

[0009] The subclaims show preferred developments of the invention.

[0010] Preferably, determining the usage history further includes determining an operating time during which the secondary battery was discharged. This can, for example, be a predefined time interval, over which the periods with a negative charge balance are compared with the total time interval. In other words, a ratio of the operating time with a negative charge balance to the corresponding total operating time of the means of transport can be determined.

[0011] Preferably, the beginning of this immediately past time interval is chosen at a starting point at which the state of charge of the secondary battery is known exactly or approximately exactly. For example, after several hours of motorway travel, it can be assumed that the secondary battery is fully charged. At a later point in time, the aforementioned ratio can be determined from the end of this motorway journey, and the current state of charge of the secondary battery can be estimated from this.

[0012] If available, quantitative values ​​for the charging balance (“how much power was drawn during which intervals”) can also be determined to improve the accuracy of the method.

[0013] Further preferably, both the intervals in which the secondary battery was charged and those in which the secondary battery was discharged can be compared. A starting point at which the secondary battery had a known (with high probability) state of charge is also suitable for this method. Taking the charging currents into account further improves the method in this development.

[0014] According to a further aspect of the present invention, a control unit for improving the readiness of a secondary battery in a special vehicle having a secondary battery and a primary battery is proposed. The control unit comprises an input unit for receiving a voltage of the secondary battery and an external temperature of the vehicle. In other words, a bus controller can be provided, for example, for receiving corresponding measured values. Alternatively or additionally, proprietary lines (sensor lines, probes) can be provided for connection to the control unit according to the invention. Furthermore, the control unit comprises an output unit for sending control commands to a unit for monitoring the on-board power supply. In other words, the control unit is configured to output control commands to the periphery.An evaluation unit within the control unit further configures the control unit to determine a usage history of the battery's performance and to detect a charging requirement of the secondary battery based on the determined voltage, the determined usage history, and the determined outside temperature. Regarding the terms "usage history" and "charging requirement" of the secondary battery, reference can be made to the above explanations of the method according to the invention. The control unit according to the invention offers the advantage of essentially relying on existing hardware while still enabling an improvement in the detection of the charging requirement of the secondary battery.

[0015] Preferably, the control unit is configured to perform one of the methods mentioned above. As a special control unit, the control unit can also perform additional functions that distinguish the means of transport as a special means of transport compared to predominantly identically constructed means of transport.

[0016] Further preferably, the control unit can be configured to measure a (resting) voltage of the secondary battery at predetermined times. According to the invention, this is achieved without using a costly battery data module. Instead, a cost-effective, mass- and space-saving two-wire cable can be used to measure the voltage of the secondary battery while the vehicle is not in driving mode. In particular, the control unit can be configured to wake up (i.e., start operation independently) at predetermined times to measure a resting voltage of the secondary battery and then go back to sleep. In this way, operation of the control unit can also be used during the parking phases of the vehicle to improve monitoring of the secondary battery without placing unnecessary strain on the vehicle electrical system.

[0017] The control unit can further preferably be configured to determine a total electrical power of consumers connected to the secondary battery. In particular, for simplification, a maximum possible power consumption of consumers in operation that are connected to the secondary battery can be determined. In response to an assigned limit value for the electrical power being exceeded and / or in response to a limit value for a corresponding energy (amount) drawn from the secondary battery being exceeded, a start-up process can be initiated during an operating state without use of an internal combustion engine of the means of transport. In other words, under the aforementioned conditions, the control unit issues a so-called “restart recommendation”. Alternatively or additionally, a recuperation function can be prevented orAn energy recovery process can be initiated even though the primary battery indicates a state that does not require charging. For example, braking energy recovery is performed, which charges the secondary battery. Alternatively or additionally, during an operating state using an internal combustion engine of the vehicle, a stopping process can be prevented and / or a (braking) energy recovery process (as described above) can be initiated. This enables energy management for the secondary battery that is largely independent of the charge state of the primary battery.

[0018] As indicated at the beginning, the primary battery can be a starter battery of the means of transport, and the secondary battery, in particular, can not be a starter battery of the means of transport. In particular, it can be provided that the secondary battery is electrically separated from the primary battery or the starter of the means of transport to avoid impermissibly high currents during a starting process. In particular, the secondary battery can be provided to supply energy to a consumer that distinguishes the means of transport from standard vehicles. In this case, the control unit can also be designed in the form of a so-called authority module, which is not offered to every customer. Authority modules, for example, allow the engine to continue running even if the ignition key of the means of transport has been removed and the vehicle has been locked.The method according to the invention can thus be implemented as software code within the authority module (or the control unit according to the invention). This offers the advantage that the additional functionality only needs to be provided if the relevant secondary battery is also installed in the vehicle.

[0019] In general, the invention comprises a special control unit which, according to the prior art, operates the additional consumers during stationary phases, provides deep discharge protection for the auxiliary battery by switching off the auxiliary battery, and additionally controls the recharging mechanism while driving. According to the invention, the recuperation and start / stop behavior of a vehicle are additionally influenced to improve energy management. For example, the special control unit can determine its own operating time without the combustion engine running. Since the consumers connected to the special control unit, along with their (maximum) energy consumption, are known, the amount of energy in the secondary battery that has already been used and therefore needs to be recharged can be determined based on the operating time.While the engine is running, if a predefined limit for the energy quota to be recharged is exceeded, a stop prohibition is issued. This limit remains in effect until a corresponding energy quota has been charged with the generator partially loaded, taking into account the decreasing current consumption. A certain hysteresis can be provided to return the secondary battery to a sufficiently "filled" charge state. A falling outside temperature extends the recharging time, as it is assumed that the secondary battery will not be able to absorb the charge properly. In other words, the secondary battery's ability to charge is reduced at lower temperatures.In addition, an undervoltage protection shutdown that occurred during a previous stationary phase of the vehicle can be taken into account in the usage history so that a very long stop ban is issued for a subsequent operating cycle of the combustion engine in order to at least return the secondary battery to a "healthy" state of charge (SOC). In addition, electrical load management measures can lead to a stop ban being issued due to an electrical energy deficit. In other words, a signal to switch off a (low-priority) consumer connected to the secondary battery for the purpose of saving electrical energy will result in the secondary battery being charged quickly using the combustion engine.By agreeing on a corresponding message in the communication protocol) to the recuperation coordinator (energy-monitoring control unit in the vehicle network), the recuperation function can then also be prevented in the above cases. Short description of the drawings

[0020] Embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawings: Fig. 1 is a schematic view of a means of transport comprising components for carrying out an embodiment of a method according to the invention; and Fig. 2 a flowchart illustrating steps of an embodiment of a method according to the invention. Embodiments of the invention

[0021] Fig. 1 shows a passenger car 10 as a means of transport, which is driven by an internal combustion engine 5. The internal combustion engine 5 is connected via a generator 4 to a Body Control Module (BCM) 40 as a unit for monitoring the on-board electrical system energy. On the output side, the BCM 40 is connected to a primary battery 1, which supplies electrical consumers 6 with electrical energy. In addition, the generator 4 is connected to a multifunction control unit 3 as a control unit according to the invention. The multifunction control unit 3 has an input unit 30, by means of which it can measure a voltage or open-circuit voltage of a secondary battery 2 via a two-wire line 34. The secondary battery 2 is in turn electrically connected to a plurality of electrical consumers 7. The multifunction control unit 3 further has an output unit 31, by means of which it can send control signals to the BCM 40.Using the control signals, the multifunction control unit 3 is configured to influence the energy management of the vehicle electrical system in response to a respective operating state of the secondary battery 2. A further input unit 32 is configured to receive CAN bus signals and forward them to an evaluation unit 33. Symbolically, a thermometer 11 is connected to the multifunction control unit 3 as a temperature sensor, by means of which an outside temperature of the passenger vehicle 10 can be determined. The information available to the multifunction control unit 3 is compiled, interpreted, and used by an evaluation unit 33 to influence the vehicle electrical system's energy management.

[0022] Fig.2 shows a flowchart illustrating steps according to an exemplary embodiment of the present invention. In step 100, a voltage and a usage history of the secondary battery 2 and an outside temperature of the passenger vehicle 10 are determined. In step 200, the determined variables are then evaluated to identify a charging requirement for the secondary battery. Even if the primary battery is not in a state requiring charging, a stop operating state is prevented in step 300 and, alternatively or additionally, a recuperation function is suspended to enable charging of the secondary battery. Possible embodiments of the method and the associated advantages arise from the above explanations regarding the method according to the invention and the control unit according to the invention.

[0023] Even if the aspects and advantageous embodiments of the invention have been described in detail with reference to the exemplary embodiments explained in conjunction with the attached drawing figures, modifications and combinations of features of the illustrated exemplary embodiments are possible for those skilled in the art without departing from the scope of the present invention, the scope of protection of which is defined by the attached claims.

Claims

[1] Method for charging a secondary battery (2) of a special means of transport (10) with a primary battery (1) and a secondary battery (2), comprising the steps: - Determining (100) a voltage of the secondary battery (2), - Determining (100) a usage history of the secondary battery (2), - determining (100) an outside temperature of the means of transport (10), - Detecting (200) a charging requirement of the secondary battery (2) based on the determined voltage, the determined usage history and the determined outside temperature, and when the primary battery (1) is in a state where it does not require charging - preventing (300) a stop operating state, and / or - Preventing (300) a recuperation function for charging the secondary battery (2). [2] The method of claim 1, wherein determining the usage history further comprises - Determining an operating time during which the secondary battery (2) was discharged, and in particular - Determining a ratio of the operating time to a corresponding total operating time of the means of transport (10). [3] Method according to one of the preceding claims, wherein the usage history further comprises a charging current balance of a predefined period of time. [4] Control device (3) for improving the readiness of a secondary battery (2) in a special means of transport (10) with the secondary battery (2) and a primary battery (1) comprising - an input unit (30) for receiving a voltage of the secondary battery (2) and an outside temperature of the means of transport (10), - an output unit (31) for sending control commands to a unit (40) for monitoring an on-board power supply, and - an evaluation unit (33) by means of which the control device (3) is set up, - to determine a usage history of the secondary battery (2), and - to detect a charging requirement of the secondary battery (2) based on the determined voltage as well as the determined usage history and the determined outside temperature. [5] Control device according to claim 4, wherein the control device (3) is further configured to carry out a method according to one of the preceding claims 1 to 3. [6] Control device according to one of claims 4 or 5, wherein the control device (3) is configured to measure a rest voltage of the secondary battery (2) at predetermined times and in particular to wake up for this purpose. [7] Control device according to one of claims 4 to 6, wherein the control device (3) is set up to determine a, in particular maximum possible, total electrical power of consumers (7) connected to the secondary battery (2) and in response to exceeding a limit value of the electrical power and / or a limit value of a corresponding energy drawn from the secondary battery (2), - to initiate a starting process and / or a recuperation process during an operating state without the use of an internal combustion engine (5) of the means of transport (10), and / or - to prevent a stopping process and / or to initiate a recuperation process during an operating state using an internal combustion engine (5) of the means of transport (10). [8] Control device according to one of claims 4 to 7, wherein the input unit (30) is arranged to be connected to the secondary battery (2) via a two-wire line (34) to receive the voltage. [9] Control device according to one of claims 4 to 8, wherein the primary battery (1) is a starter battery of the means of transport (10) and in particular the secondary battery (2) is not a starter battery of the means of transport (10), wherein further in particular the secondary battery (2) is provided for supplying energy to a consumer (7) which distinguishes the means of transport (10) from standard means of transport. [10] Method according to one of claims 1 to 3 or control device (3) according to one of claims 4 to 9, wherein the special means of transport (10) is an ambulance, a police vehicle, a fire engine, a camping vehicle, a vehicle with an auxiliary heater.

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