Method for determining the heat capacity of a battery

Abstract

The present invention relates to a method for determining the thermal capacity (C-thermisch) of a battery, in particular a battery in a vehicle, the method having the following steps: - determining the weight of the acid, the weight of the water and the weight of the lead of the battery, - calculating the thermal capacity (C-thermisch) of the battery based on the determined weights of the acid, water and lead of the battery and based on the specific heat capacities of the acid, water and lead.

Description

Field of the Invention

[0001] The present invention relates to a method for determining the heat capacity of a battery, in particular a vehicle battery. Background Art

[0002] To diagnose a battery, it is necessary to know the battery temperature. However, directly measuring the battery temperature is very costly technically. For this reason, the battery temperature is usually calculated with the aid of a calculation model.

[0003] These calculation models are based on: detecting the temperature near the battery, for example, by means of a temperature sensor arranged above the battery sensor. The battery sensor is mounted on the battery electrode and detects other battery parameters, such as the battery voltage or the battery current.

[0004] The current flowing through the battery causes heat power losses, resulting in an increase in the battery temperature. The battery exchanges heat with the environment, in particular the ambient temperature. Therefore, the increase in the battery temperature leads to an increase in the temperature of the battery environment. This increase in temperature can be detected by means of the temperature sensor of the battery sensor. The greater the temperature difference between the battery and the environment, the greater the heat compensation power.

[0005] Therefore, the battery temperature can be obtained or calculated by measuring the temperature in the environment of the vehicle battery.

[0006] The heat power losses depend to a large extent on the battery size, in particular on the heat capacity of the vehicle battery. Therefore, in order to be able to calculate the battery temperature as accurately as possible, it is necessary to know the heat capacity of the battery.

[0007] Usually, the battery is calibrated during production, and the heat capacity of the battery is also determined. The heat capacity is stored in the vehicle software so that it can be taken into account when calculating the battery temperature.

[0008] However, the calibration of vehicle batteries is very complex. Summary of the Invention

[0009] The object of the present invention is to provide a method for determining the heat capacity of a battery, in particular a battery in a vehicle, such that simple and rapid calibration of the vehicle battery can be achieved.

[0010] To achieve this object, a method for determining the heat capacity of a battery, in particular a battery in a vehicle, is provided, the method having the following steps:

[0011] - Determining the weight of the acid, the weight of the water, and the weight of the lead of the battery,

[0012] - Calculating the heat capacity of the battery based on the determined weights of the acid, water, and lead of the battery and the specific heat capacities of the acid, water, and lead.

[0013] The concept underlying the present invention is to determine the heat capacity based on values or measured values that can be obtained or determined in a simple manner, so that it is not necessary to calibrate the vehicle battery at high cost. In particular, these values can already be determined during the production of the vehicle battery and transmitted to the control device of the vehicle during the installation of the vehicle battery.

[0014] In principle, the amounts of acid, water, and lead in the battery are determined computationally and / or by measurement. Since the specific heat capacities of these components are known, the heat capacity of the battery can be calculated in a simple manner therefrom.

[0015] The heat capacity of the battery also depends in particular on the state of charge of the battery. To improve the accuracy of determining the heat capacity, it is therefore preferred to additionally determine the state of charge of the battery and take this state of charge into account when calculating the heat capacity. In particular, two different states of charge can also be considered in order to improve the accuracy of the calculation.

[0016] To determine the amounts of water, acid, and lead, the method can have the following steps:

[0017] - Determine the ratio of acid to water in the battery in a first state of charge of the battery,

[0018] - Determine the ratio of acid to water in the battery in a second state of charge of the battery,

[0019] - Determine the amount of charge between the first state of charge and the second state of charge,

[0020] - Determine the weight of the battery

[0021] - Calculate the weight of the acid and the weight of the water in the charged battery based on the obtained ratio of acid to water and the amount of charge of the charged battery.

[0022] Based on the amount of charge between the first state and the second state and the ratio of acid to water in the first state and the second state, the absolute amounts of acid and water in the battery in the first state can be determined.

[0023] When the battery is discharged, one acid molecule is converted into one water molecule for each electron provided. Therefore, the ratio of acid to water changes. Since the amount of charge between the first state and the second state is known and the charge of an electron is also known, the amounts of water and acid in the battery are determined based on these amounts of charge. In addition, the masses of acid and water molecules are also known, so that the weights of acid and water in the battery in the first state can be calculated very accurately. The amount or weight of lead can be determined in a simple manner, namely, by subtracting the determined weights of acid and water from the total weight of the battery.

[0024] Preferably, the battery has more charge in the first state of charge than in the second state of charge. The amount of charge between the first state of charge and the second state of charge is preferably at least 50% of the total charge of the battery, in particular at least 70%.

[0025] For the above method, it is not necessary to fully charge or fully discharge the battery. For example, the amount of charge of the battery in the first state of charge is at least 70%, in particular at least 80%.

[0026] However, the battery can also be fully charged in the first state.

[0027] Preferably, the battery is charged to less than 30%, in particular less than 20% in the second state of charge.

[0028] Alternatively, the battery is fully discharged in the second state of charge. Description of the Drawings

[0029] Other advantages and features are derived from the following description in conjunction with the accompanying drawings. Figure 1 A flowchart showing the method according to the invention is shown. Detailed Description

[0030] During the operation of a vehicle, it is necessary to perform diagnostics on the vehicle battery. In addition to the state of charge of the battery, this diagnosis includes additional parameters such as the battery temperature. Directly measuring the temperature of the battery is very costly. For this reason, the temperature of the battery cannot be directly measured, but is obtained by means of a measurement model or a calculation model.

[0031] For example, a temperature sensor is arranged above a battery sensor that is mounted on the battery electrodes of the vehicle battery. The temperature sensor can detect the ambient temperature, and this ambient temperature can be used to obtain the temperature of the vehicle battery.

[0032] The current flowing through the battery causes a thermal power loss P_loss, which causes the battery temperature to rise. The change in the battery temperature dT_batt over time can be expressed as the quotient of the power loss P_loss and the thermal capacity C_thermisch of the battery:

[0033] dT_batt = p_loss / C_thermisch

[0034] The battery exchanges heat with the environment. The greater the temperature difference between the ambient temperature T_env and the battery temperature T_batt, the greater the heat compensation power P_eq. The heat compensation power P_eq can be expressed as the quotient of the temperature difference and the thermal resistance R_thermisch:

[0035] P_eq = (T_env - T_batt) / R_thermisch

[0036] The thermal resistor R_thermisch depends substantially on the environment of the battery.

[0037] Therefore, the heat capacity C_thermisch of the battery is required to calculate the change in battery temperature dT_batt over time. This heat capacity depends on the battery size and the battery composition, in particular on the amount of water in the battery.

[0038] The battery is usually calibrated during production, in which the heat capacity C_thermisch is also determined, so that each battery type or each battery size is assigned a fixed heat capacity C_thermisch. This heat capacity can be stored in the vehicle software so that the vehicle control device can use this heat capacity when determining the battery temperature.

[0039] The determination of the heat capacity C_thermisch can be carried out in a simple manner by means of the following method.

[0040] The basic idea of this method is not to use a fixed, pre-determined value for the heat capacity C_thermisch, but to determine this heat capacity based on measured values known or obtainable during vehicle operation.

[0041] In principle, for this method, the composition of the battery is obtained, in particular the weight ratios of water, acid and lead. The specific heat capacities of the individual components are known. The heat capacity of an object is its specific heat capacity multiplied by its weight. Therefore, the heat capacities of the individual components of the battery can be calculated and from this the heat capacity C_thermisch of the entire battery can be calculated.

[0042] The weight ratios of water, acid and lead can be obtained in different ways. For example, for this purpose the ratio between acid and water is obtained in a first state of charge and a second state of charge of the battery. In the second state of charge, the battery is preferably less charged than in the first state of charge. In addition, the charge quantity between the first state and the second state is obtained.

[0043] When the battery is discharged, for each electron provided, one acid molecule is converted into a water molecule. Therefore, the ratio of acid to water changes. Since the charge quantity Q between the first state of charge and the second state of charge and the charge of an individual electron are known, the absolute amounts of water and acid in the battery can be determined from these values.

[0044] Since the masses of the acid molecules and water molecules are known, the weight of the acid and the weight of the water in the vehicle battery can thus be calculated very accurately. The weight of the battery minus the weight of the acid and the weight of the water equals the weight of the lead in the battery.

[0045] When producing a vehicle battery, the value of the battery capacity is obtained, that is, the charge quantity Q between a fully charged battery and a fully discharged battery. Similarly, when producing, the open-circuit voltages of the fully charged battery and the fully discharged battery are obtained, that is, the ratio between the acid and the water. Therefore, only the weight of the battery needs to be determined to determine the thermal capacity C_thermisch.

[0046] In the above method, the battery is fully charged (100%) in the first state of charge and fully discharged (0%) in the second state of charge. However, if the corresponding charge quantities between the first state of charge and the second state of charge are known or can be obtained for other states of charge values, other states of charge in the first state of charge and the second state of charge can also be used. For example, values between 70% and 100% (especially 80%) can also be used for the first state of charge and values between 0% and 30% (especially 20%) can be used for the second state of charge.

Claims

1. A method for determining the thermal capacity (C-thermisch) of a battery, the method comprising the following steps: - Determining the weight of the acid, the weight of the water, and the weight of the lead in the battery, - Calculating the thermal capacity (C-thermisch) of the battery based on the determined weights of the acid, water, and lead in the battery and the specific heat capacities of the acid, water, and lead, wherein, To determine the weight of the water, the weight of the acid, and the weight of the lead, the method comprises the following steps: - Determining the ratio of acid to water in the battery in a first state of charge, - Determining the ratio of acid to water in the battery in a second state of charge, - Determining the amount of charge between the first state of charge and the second state of charge, - Determining the weight of the battery, - Calculating the absolute amounts of acid and water in the battery based on the determined ratio of acid to water and the amount of charge of the battery, - Calculating the weight of the acid and the weight of the water in the battery based on the calculated absolute amounts of acid and water and the known masses of acid molecules and water molecules, - Determining the weight of the lead by subtracting the determined weights of the acid and water from the weight of the battery.

2. The method according to claim 1, characterized in that, the battery is a battery in a vehicle.

3. The method according to claim 1 or 2, characterized in that, the amount of charge between the first state of charge and the second state of charge is at least 50% of the total charge of the battery.

4. The method according to claim 3, characterized in that, the amount of charge between the first state of charge and the second state of charge is at least 70% of the total charge of the battery.

5. The method according to claim 1 or 2, characterized in that, the amount of charge of the battery in the first state of charge is at least 70%.

6. The method according to claim 5, characterized in that, the amount of charge of the battery in the first state of charge is at least 80%.

7. The method according to claim 6, characterized in that, the battery is fully charged in the first state of charge.

8. The method according to claim 1 or 2, characterized in that, the battery is charged to less than 30% in the second state of charge.

9. The method according to claim 8, characterized in that, the battery is charged to less than 20% in the second state of charge.

10. The method according to claim 9, characterized in that, the battery is fully discharged in the second state of charge.

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