Patent ID: 12253570

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Identical reference numerals denote the same device components in all of the figures.

FIG.1shows a first schematic illustration of voltage characteristics100of electrochemical energy stores having different states of health according to a respective state of health that corresponds to a ratio of the currently maximally usable capacity to the nominal capacity of the electrochemical energy stores. Voltage characteristic101is characteristic of an electrochemical energy store having a state of health of 60%, voltage characteristic102is characteristic of an electrochemical energy store having a state of health of 80%, voltage characteristic103is characteristic of an electrochemical energy store having a state of health of 90%, and voltage characteristic104is characteristic of an electrochemical energy store having a state of health of 100%.

A predefined electric voltage105intersects voltage characteristics101,102,103,104in voltage-sensitive points106as a function of the state of health at a specified temperature.

FIG.2shows a flow diagram of an embodiment of a method according to the present invention. The method is started in step201, for instance when a diagnostic device in a workshop is connected to a diagnosis interface of an electrically drivable vehicle having an electrochemical energy store.

In addition, a voltage variable is acquired in step201, which represents an electric voltage of the electrochemical energy store, and the acquired voltage variable is compared with a predefined setpoint voltage variable.

Moreover, a temperature of the electrochemical energy store and a state of health are acquired from a control unit, e.g., a control unit of the electrochemical energy store (battery control unit, BCU) or a control unit of the electrically drivable vehicle (vehicle control unit, VCU). The determination of the state of health is preferably conducted at a defined constant temperature such as 20° C. For this purpose, the electrochemical energy store or the electrically drivable vehicle having the electrochemical energy store is able to be parked in a climate chamber or be exposed to the flow of a blower.

In step202, a signal for the charging and/or discharging of the electrochemical energy store is generated based on the result of the comparison of the acquired voltage variable with the predefined setpoint voltage variable.

In this way, the electric voltage of the electrochemical energy store is adjusted to a voltage level at which the sensitivity of the electric voltage of the electrochemical energy store is at its maximum. The sensitivity differs as a function of a cell chemistry of the electrochemical energy store, and the electric voltage does not necessarily lie at the same voltage level for all states of health but may vary as a function of the state of health.

The state of health acquired from the control unit is used as a reference value based on which the method according to the present invention is started. The setpoint voltage variable results from the acquired state of health, e.g., based on technical data of the electrical energy store stored in the diagnostic device. The electrochemical energy store is charged or discharged as a function of the comparison of the acquired voltage variable with the predefined setpoint voltage variable.

In the simplest case, the discharging of the electrochemical energy is performed by switching on consumers such as an air-conditioning or heating system if a deviation of the current voltage variable from the setpoint voltage variable is very small.

In the other case, the electrochemical energy store is connected to a buffer battery and discharged until the setpoint voltage variable is reached.

Moreover, a connection to a charge station is possible as well, in which case the excess energy of the electrochemical energy store is fed into a current network. At the end of the method, buffered or recirculated energy is conveyed to the electrochemical energy store again so that practically no energy is lost and the electrochemical energy store has the same state of charge (SOC) after the state of health has been determined.

When the predefined voltage variable is reached, the discharge process is ended and a wait for a predefined period of time takes place in step203during which the electrochemical energy store relaxes. The electric voltage of the electrochemical energy store rises as a result but still lies in a range close to the setpoint voltage variable.

In step204, the electrochemical energy store is discharged for a predefined period of time using small currents, e.g., 0.1 C to 0.5 C. If the charge station does not permit such small adjustable currents, then a small load such as a consumer or resistor is able to be connected directly to the electrochemical energy store. During the discharging operation, the voltage variable is acquired and in step205a voltage gradient is determined based on a characteristic of the acquired voltage variable for the predefined time period.

In step207, the electrochemical energy store is discharged for a further predefined time period using small electric currents. After a short measuring pause with the further discharging, steps204and205are repeated for as long as the voltage variable is still in the predefined voltage range, e.g., between 3.4 V and 3.2 V. A certain number of repetitions should be carried out for tolerance-related reasons, for which purpose the number of repetitions is compared with a predefined number of cycles in step206.

In step208, a voltage gradient is determined from a mean value of the determined voltage gradients when the predefined number of cycles is reached.

In step209, the voltage gradient is compared with a predefined setpoint voltage gradient, and the state of health of the electrochemical energy store is determined based on the result of the comparison.

In step210, the method is terminated. In a further advantageous embodiment, the state of health is validated in step210by evaluating the voltage variable during the discharge and/or the relaxation of the electrochemical energy store and/or by evaluating a voltage characteristic after a voltage jump.

In a further advantageous embodiment, a further voltage variable is acquired in step210, the acquired further voltage variable is compared with the voltage variable acquired in step201, and signals for charging and/or discharging the electrochemical energy store are generated based on the result of the comparison. The electrochemical energy store therefore has the same state of charge (SOC) as at the start of the method in step201after the state of health has been determined and the end of the method in step210.

FIG.3shows a schematic representation of a voltage characteristic300following a discharge operation of the electrochemical energy store according to step202. If the predefined setpoint voltage variable is reached, then the discharging operation of the electrochemical energy store is ended. The electrochemical energy store relaxes within a predefined time period301. The electric voltage rises slightly again during the predefined time period in step203. A measurement of the electric voltage according to step204is able to be carried out at an instant302.

FIG.4shows a second schematic illustration of voltage characteristics400of electrochemical energy stores having different states of health, according to a respective state of health that corresponds to a ratio of the currently maximally usable capacity to the nominal capacity of the electrochemical energy stores. Voltage characteristic410is characteristic of an electrochemical energy store having a state of health of 80%. Voltage characteristic420is characteristic of an electrochemical energy store having a state of health of 90%. Voltage characteristic430is characteristic of an electrochemical energy store having a state of health of 100%.

To determine the state of health of the electrochemical energy store according to the present invention, an electric voltage440is predefined, which intersects the voltage characteristics410,420,430in voltage-sensitive points413,423,433as a function of the state of health at a specified temperature. Depending on the state of health, voltage-sensitive points411,413,415,421,423,425,431,433,435may shift between predefined electric voltage limits441,442.

In step202, the electrochemical energy store is discharged to a setpoint voltage variable440such as approximately 3.3 V. The electric voltage rises slightly in response to the relaxation of the electrochemical energy store. In step204, the electrochemical energy store is discharged for a predefined period of time. In step205, a first voltage gradient412,422,432is determined. In step207, the electrochemical energy store is discharged for a further predefined period of time using small currents, which causes the electric voltage to drop. Steps204and205are now repeated and a second voltage gradient414,424,434is determined. In a third cycle, a third voltage gradient416,426,436is determined. In step208, the voltage gradient is determined from a mean value of the determined voltage gradients412,422,432,414,424,434,416,426,436. In step209, the voltage gradient is compared with a predefined setpoint voltage gradient and the state of health of the electrochemical energy store is determined based on the result of the comparison.