A METHOD AND DEVICE FOR CHARGING AN ELECTRIC ENERGY STORAGE SYSTEM IN A VEHICLE

Abstract

A device/method for the control of a charge operation and the State Of Charge (SOC) of an electrical Energy Storage System (ESS), e.g. a battery, that includes a multitude of cells is provided. The ESS is electrically connected to a propulsion system of a vehicle in order to power an Electric Motor. The method includes charging the ESS from an electrical power source, e.g., the grid, when the vehicle is at standstill, stopping the charging when the SOC level of the ESS is above a maintenance limit for the SOC level of the ESS, monitoring the battery and/or performing a service operation of the ESS after the ESS has been charged to a SOC level above the maintenance limit for the SOC level of the ESS, deliberately discharging the ESS to lower the SOC level. The SOC level of the ESS is reduced to a take-off limit for the SOC level of the ESS which is set in order to allow the vehicle to be controlled to use regenerative braking for charging of the ESS under subsequent driving when the vehicle is restarted and takes off.

Claims

1. A method for the control of a charge operation and the State Of Charge (SOC) of an electrical Energy Storage System (ESS), e.g. a battery, comprising a multitude of cells, said ESS electrically connected to a propulsion system (2) of a vehicle (1) in order to power an Electric Motor (EM), said method comprising the steps of: Charging the ESS from an electrical power source, e.g. the grid, when the vehicle (1) is at standstill, Stop the charging when the SOC level of the ESS (SOC.sub.ESS) is above a maintenance limit for the SOC level of the ESS (SOC.sub.ML), Monitoring the battery and/or performing a service operation of the ESS after the ESS has been charged to a SOC level above said maintenance limit for the SOC level of the ESS (SOC.sub.ML), Deliberately discharge the ESS to lower the SOC level, characterized in that the SOC level of the ESS (SOC.sub.ESS) is reduced to a take-off limit for the SOC level of the ESS (SOC.sub.TOL) which is set in order to allow the vehicle to be controlled to use regenerative braking for charging of the ESS under subsequent driving when the vehicle (1) is restarted and takes off.

2. A method according to claim 1, characterized in that the method further comprises the features of: Setting the take-off limit for the SOC level of the ESS (SOC.sub.TOL) such that it allows the EM to be decelerated while the braking energy from deceleration of the EM is used in order to charge the ESS without reaching a driving limit for the SOC level of the ESS (SOC.sub.DL) under subsequent driving when the vehicle is used according to a predicted driving sequence.

3. A method according to claim 1 or 2, characterized in that the method further comprises the features of: Discharging the ESS to be below the take-off limit for the SOC level of the ESS (SOC.sub.TOL) before there is an upshift from the starting gear when the vehicle is started and driven after the charging, said take-off limit for the SOC level of the ESS (.sub.SOCTOL) being set such that the increase of SOC level of the ESS (SOC.sub.ESS) due to charging of the ESS by regenerative braking of the EM during the upshift not causes the SOC level of the ESS (SOC.sub.ESS) to reach a driving limit for the SOC level of the ESS (SOC.sub.DL).

4. A method according to claim 1 or 2, characterized in that the method further comprises the features of: Setting the take-off limit for the SOC level of the ESS (SOC.sub.TOL) in dependence of a predicted charging and discharging sequence of the ESS for a known or predicted route to be driven by the vehicle and controlling the SOC level of the ESS (SOC.sub.ESS) to be below the take-off limit for the SOC level of the ESS (SOC.sub.TOL) when the vehicle is started and driven after the charging in order to avoid the SOC level of the ESS (SOC.sub.ESS) to reach a driving limit for the SOC level of the ESS (SOC.sub.DL) due to charging of the ESS by regenerative braking.

5. A method according to any previous claims, characterized in that the method further comprises the features of: Balancing of the cells is performed as a service operation of the ESS after the ESS has been charged to a SOC level above said maintenance limit for the SOC level of the ESS (SOC.sub.ML).

6. A method according to any previous claims, characterized in that the method further comprises the features of: Using electrical energy from the discharge of the ESS, in which the SOC level of the ESS (SOC.sub.ESS) is lowered from being above said maintenance limit for the SOC level of the ESS (SOC.sub.ML) to be below a take-off limit for the SOC level of the ESS (SOC.sub.TOL), to charge a starter battery.

7. A method according to any previous claims, characterized in that the method further comprises the feature of: Discharging of the ESS to lower the SOC level of the ESS (SOC.sub.ESS) to be below a take-off limit for the SOC level of the ESS (SOC.sub.TOL) is performed before the vehicle is restarted, e.g. by discharging the ESS right after the monitoring and/or service operation of the ESS above said maintenance limit for the SOC level of the ESS (SOC.sub.ML).

8. A method according to any of claims 1-6, characterized in that the method further comprises the features of: Discharging of the ESS to lower the SOC level of the ESS (SOC.sub.ESS) to be below a take-off limit for the SOC level of the ESS (SOC.sub.TOL) is performed when the vehicle is restarted during vehicle start-up.

9. A method according to any previous claims, characterized in that the method further comprises the features of: Only said electrical propulsion system, electrically connected to said ESS, is used when the vehicle is restarted after the charging.

10. A computer program comprising program code means for performing the steps of any of claims 1 to 9 when said program is run on a computer.

11. A computer readable medium carrying a computer program comprising program code means for performing the steps of any of claims 1 to 9 when said program product is run on a computer.

12. A control unit for controlling an electrical Energy Storage System (ESS), the control unit being configured to perform the steps of the method according to any of claims 1 to 9.

13. A control system for a vehicle provided with an electrical propulsion system comprising an Electric Motor (EM) electrically connected to an electrical Energy Storage System (ESS) and a control unit connected to the electrical propulsion system, characterized in that it comprises a control unit according claim 12.

14. A vehicle, characterized in that it comprises a control system according to claim 13.

15. A vehicle according to claim 13, characterized in that the vehicle is a Hybrid Electrical Vehicle (HEV), e.g. a heavy duty vehicle such as a truck or bus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0026] In the drawings:

[0027] FIG. 1 is a schematic view of an Electric Vehicle (EV) suitable for the present invention,

[0028] FIG. 2 is a schematic view of a Hybrid Electric Vehicle (HEV) suitable for the present invention,

[0029] FIG. 3a is a flow chart for a charging control method for an electric Energy Storage System (ESS) according to an embodiment of the present invention,

[0030] FIG. 3b is a flow chart of a modified version of the charging control method in FIG. 3a

DETAILED DESCRIPTION

[0031] In FIG. 1 is shown a vehicle I comprising an electric propulsion system 2. The electric propulsion system 2 comprises a pair of driven wheels 3 attached to a driven axle 4 which is drivingly connected to an output shaft 5 of an Electric Motor (EM). The Electric Motor (EM) is electrically connected to an electric Energy Storage System (ESS) for powering the electric motor (EM). The electric propulsion system 2 further comprises an Electronic Control Unit (ECU) connected to the electric Energy Storage System (ESS) and the Electric Motor (EM) in order to monitor and/or control the ESS and EM. The vehicle I further comprises a second pair of wheels 3′ connected to a second axle 4′ which wheels 3′ not are driven.

[0032] The above described vehicle is only intended to serve as an example of an Electric Vehicle (EV) suitable for the control system according to the invention. The system may be modified, e.g. may the Electric Motor (EM) also be drivingly connected to the second axle 4′ such that both wheel pairs 3, 3′ are driven by the EM. Alternatively, still another electric motor may be included to provide a propulsion force to the second axle 4′. A second electric motor may thus be electrically connected to either the existing electrical Energy Storage System (ESS) or to another, separate electrical energy storage system. If desired, electric motors designed to be drivingly connected to a driven axle could be replaced for electrical motors designed to work directly on a wheel, e.g. replacing an electric motor drivingly connected to a driven axle with a wheel hub electric motor for each driven wheel on the axle. Hence, the electric propulsion system for the EV intended to be used for the control system may have a wide variety of different design as long as there is an electrical Energy Storage System (ESS) on board the vehicle intended to function as a power source for an Electric Motor (EM).

[0033] In FIG. 2 is shown a vehicle 1 having an Internal Combustion Engine (ICE) in addition to the Electrical Motor (EM). The same reference numbers have been used for the same features as described in FIG. 1. Compared to FIG. 1 has thus the Internal Combustion Engine (ICE) been added and is drivingly connected to the second axle 4′ via an ICE output shaft 5′. The ICE is also connected to the ECU in order to receive control signals. The vehicle 1 in FIG. 2 thus represents a Hybrid Electric Vehicle (HEV).

[0034] The above described vehicle is only intended to serve as an example of an Hybrid Electric Vehicle (HEV) suitable for the control system according to the invention. The HEV could for example instead be a parallel hybrid, a series hybrid or a series/parallel hybrid. Hence, the hybrid propulsion system for the HEV intended to be used for the control system may have a wide variety of different designs as long as there is an electrical Energy Storage System (ESS) on board the vehicle intended to function as a power source for an Electric Motor (EM).

[0035] In FIG. 3a is a flow chart for the control method for an electrical Energy Storage System (ESS) according to an embodiment of the invention.

[0036] In a first step, S1, is the electrical Energy Storage System (ESS) charged. The State Of Charge of the ESS (SOCEss) is compared with a maintenance limit for the State Of Charge (SOC L) above which a monitoring or service operation may be performed. Hence, the ESS is charged until it has reached a SOC level which is above the maintenance limit for the State Of Charge, i.e. until SOCESs>SOCML. When the desired SOCEss has been reached continue the method with the next step, S2

[0037] In a second step, S2, is there a monitoring or service operation performed of the ESS. For certain monitoring or service operation is it desired to have a rather high SOC level, e.g. when deciding if a balance operation is desired as well as when performing a balance operation. The operation may thus for example be balancing of cells in the ESS. This monitoring and/or service operation may include further charging and/or discharging of the ESS while being at a high SOC level. This maintenance step is followed by the third step, S3.

[0038] In a third step, S3, is the SOC level of the ESS (SOCESS) lowered by discharging the ESS. The SOC level of the ESS is compared with a desired take off limit of the SOC level of the ESS (SOCJOL) below which the vehicle is having a SOC level considered suitable for starting the vehicle and take off. The ESS is thus discharged until the SOC level has reached a value below the desired take off limit (SOCJOL) where after step 4, S4 follows.

[0039] In step 4 is the vehicle started and takes off having its SOC level below the take-off limit (SOCJOL)—This limit, SOCTOL, may be set to a default value below which the driving operations when a vehicle is restarted in general may control the EM to perform braking operations as desired without reaching a driving limit of the SOC of the ESS (SOCDL)—This driving limit (SOCDL) is a SOC level up to which the ESS may be recharged by regenerative braking of the EM without causing any significant deterioration of the ESS. The default value of the take-off limit may for example be set to be able to use the EM as a generator during regenerative braking for recharging of the ESS during a first gear up-shift without reaching the driving limit (SOCDL). Of course could also further actions which in general are performed at start causing a regenerative braking of the EM also be included in the estimation of a default take-off limit. The take-off limit (SOCTOL) could also be set in dependence of an expected regenerative braking of the EM to be used for recharging of the ESS from a predicted route or certain starting position of the vehicle. The lowering of the SOC level in the ESS is thus in general made in order to be able to use the EM as predicted for regenerative braking without causing the SOC level to rise above the driving limit of the SOC of the ESS (SOCDL)—In FIG. 3a is the SOC level of the ESS reduced in step S3 to a level below the take-off limit of the SOC level of the ESS (SOCTOL)—It is herein not specified at which time point, or by which trigger actions, the SOC level is reduced to be below the take-off limit. In case it is considered appropriate, the SOC level may be controlled to be below the take-off limit of the SOC level (SOCJOL) right after the monitoring or servicing sequence. However, it is also possible that the lowering of the SOC level to be below the SOCTOL not is made until there is an indication the vehicle is restarted for take-off, e.g. a key on indication.

[0040] In FIG. 3b has the step 3, S3, from FIG. 3a been divided into three sub steps, step S3a, S3b and S3c in order to further specify how the SOC level may be controlled after the monitoring and/or servicing step S2 and before the vehicle is started to take off in step S4.

[0041] In step S3a is disclosed that the SOC level of the ESS (SOCEss) is lowered to be below the storage limit of the SOC of the ESS (SOCSL). AS previously discussed, there may be a desire to tower the SOC level of the ESS after the monitoring/servicing action in order to reduce the storage limit after charging, i.e. the ESS is discharged directly following the charging (S1) and monitoring/servicing (S2) routine to have a SOC level below the storage limit (SOCSL)—When storage limit has been reached step S3b follows.

[0042] In step S3b is the ESS controlled to be maintained at the storage limit of the SOC of the ESS (SOCSL)—The SOC level will maintain at this level until there is an indication the vehicle is or soon will be restarted for take-off, e.g. a key-on indication. There is thus no lowering of the SOC level to be below the SOCTOL made until there is an indication the vehicle is restarted. The reason for waiting could for example be that the predicted future use of the vehicle not is known. If waiting until the vehicle is restarted, or until there is an start-up indication, is it possible there may be a better chance to know how the vehicle is expected to be used in the near future and the SOCTOL may be set more accurately and the SOCEss level controlled accordingly. This could for example be the case for a vehicle in a vehicle fleet which is assigned a certain route at, or slightly before, start up in the morning where after the SOC level is controlled to a desired take off level. Another reason for not lowering the SOC level more than necessary may be that it is unsure for how long time the vehicle not will be used and there may be a desire to have some extra electric power saved for maintenance operation if the vehicle happens to be parked for a longer tithe, e.g. a week or more. When the vehicle receives a start-up indication follows step S3c.

[0043] In step 3c is the SOC level controlled in dependence of the start-up indication to be below the take-off limit. The start-up indication could be a key on indication where after a soon take-off is expected. However, it could also be a remote signal indicating the vehicle will be used at a certain time point (and possibly for a certain use) such that the SOC-level will be set to an appropriate take-off limit for the expected purpose at a convenient time. When the SOC level is below the take-off limit follows step S4 and the vehicle is ready to be started and take off.

[0044] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.