Method for maintaining the charge capacity of traction battery modules of a hybrid electric vehicle

• US 5,828,201 A
• Filed: 10/30/1997
• Issued: 10/27/1998
• Est. Priority Date: 10/30/1997
• Status: Expired due to Term

• Current Assignee: BAE Systems Controls Incorporated (BAE Systems Plc)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Grewe, Timothy Michael, Hoffman, David William Jr.
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US08/961,573
• Time in Patent Office: 362 Days
• Field of Search: 320/104, 320/118, 320/119, 320/120, 320/121, 320/122, 320/123, 320/132, 320/134, 320/136, 320/111, 320/114, 320/156, 310/67 R, 310/67 A, 310/74, 322/4
• US Class Current: 320/104
• CPC Class Codes: B60K 6/28 characterised by the electric energy storing means, e.g. batteries or capacitors
• CPC Class Codes: B60K 6/46 Series type
• CPC Class Codes: B60L 2220/20 DC electrical machines
• CPC Class Codes: B60L 2240/36 Temperature of vehicle components or parts
• CPC Class Codes: B60L 3/0046 relating to electric energy storage systems, e.g. batteries or capacitors
• CPC Class Codes: B60L 50/62 charged by low-power generators primarily intended to support the batteries, e.g. range extenders
• CPC Class Codes: B60L 58/14 Preventing excessive discharging
• CPC Class Codes: B60L 58/15 Preventing overcharging
• CPC Class Codes: B60L 58/18 of two or more battery modules
• CPC Class Codes: B60L 58/20 having different nominal voltages
• CPC Class Codes: B60L 58/21 having the same nominal voltage
• CPC Class Codes: B60L 58/22 Balancing the charge of battery modules
• CPC Class Codes: B60W 10/26 for electrical energy, e.g. batteries or capacitors
• CPC Class Codes: H01M 10/06 Lead-acid accumulators semi-lead accumulators H01M10/20
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H02J 7/0069 Charging or discharging for charge maintenance, battery initiation or rejuvenation
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02T 10/62 Hybrid vehicles
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 10/7072 Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
• CPC Class Codes: Y10S 903/903 : having energy storing means, e.g. battery, capacitor
• CPC Class Codes: Y10S 903/907 : Electricity storage, e.g. battery, capacitor

Abstract

A hybrid electric vehicle includes a lead-acid traction battery made up of a plurality of series-connected modules. During operation of the vehicle, the traction battery is discharged for acceleration, and charged by an ancillary power source. The traction battery is desirably not fully charged at the beginning of a day'"'"'s operation, so that overcharging cannot occur, so the battery spends long periods of time in a partially charged condition. When not fully charged for long periods of time, sulfation may reduce the charge storage capacity of the battery. A maintenance procedure takes place when the vehicle is not operating, in which one or more modules of the traction battery, but less than all the modules, are fully charged, then partially discharged. The full charging tends to reduce sulfation in the particular module being maintained, and the partial discharge restores its charge condition to that prior to the full charge. Each of the modules is eventually maintained by a programmed controller. The charging energy comes from an auxiliary battery, and the discharge energy is returned to the auxiliary battery, so there is little net loss of energy. If maintenance procedure is interrupted before full charge of a module, that module is scheduled for the next maintenance. If the maintenance is interrupted before partial discharge, the partial discharge is accomplished by equalizing the voltage of the battery modules.

Claims

1. A method for maintaining the modules of a traction battery of a hybrid electric vehicle, which traction battery is made up of a plurality of series-connected modules, which vehicle, when operating, tends to charge said traction battery at a rate which may at times exceed the discharge rate for powering said vehicle so that said traction battery tends to receive a net charge, each of said modules of said traction battery having a nominal voltage when fully charged, and each of said modules of said traction battery having a characteristic which includes degradation when overcharged, and which experiences a reduction of charge capacity when discharged without prompt full recharging, said method comprising the recurrent steps of:

while said vehicle is not operating, and under control of a programmed processor, fully charging at least one module of said traction battery, but not charging any of the remaining modules of said traction battery simultaneously with charging of said one module of said traction battery;

under said control of said programmed processor, and after said step of fully charging said at least one module, intentionally partially discharging said at least one module, but not said remaining modules, of said battery; and

operating said vehicle for a period of time.

2. A method according to claim 1, wherein said battery is a lead-sulfuric-acid battery comprising plates, and said reduction of charge capacity results from at least one of sulfation of said plates of said battery and reduction in the specific gravity of said acid.

3. A method according to claim 1, wherein said step of partially discharging said at least one module includes the steps of:

prior to said step of fully charging, determining the charge state of said at least one module;

storing a representation of said charge state in a temporary memory store; and

while said vehicle is not operating, discharging said at least one module until its charge state equals the value of charge state stored in said temporary memory store.

4. A method according to claim 3, wherein a measure of said charge state is module voltage.

5. A method according to claim 1, wherein said step of partially discharging said at least one module includes the steps of:

prior to said step of fully charging, determining the charge state of said at least one module;

storing a representation of said charge state in a temporary memory store;

while said vehicle is not operating, discharging said at least one module toward a charge state which equals the value of charge state stored in said temporary memory store, and if said vehicle begins operation before said charge state of said at least one module reaches said value of charge state stored in said temporary store, discharging said at least one module toward a charge state which is near the average charge state of said remaining modules.

6. A method according to claim 5, wherein a measure of said charge state is module voltage.

7. A method according to claim 1, further comprising the steps of:

immediately ceasing said steps of fully charging and partially discharging when said vehicle is placed in operation, whereupon said at least one module may be left in a state with more charge than prior to commencement of said step of fully charging; and

following said step of immediately ceasing, transferring energy from said at least one module to at least some of said remaining modules in a manner which tends to equalize the charge state of said modules.

8. A method for maintaining the modules of a traction battery of a hybrid electric vehicle, which traction battery is made up of a plurality of modules, which vehicle, when operating, tends to charge said traction battery at a rate which may at times exceed the discharge rate for powering said vehicle, each of said modules of said traction battery having a nominal voltage when fully charged, and each of said modules of said traction battery having a characteristic which includes gassing when overcharged and which experiences a reduction of charge capacity when discharged without prompt full recharging, said method comprising the recurrent steps of:

under control of a programmed processor, selecting at least one module of said traction battery, but not simultaneously selecting the remaining ones of the modules of said traction battery, for maintenance;

while said vehicle is not operating, and under control of said programmed processor, fully charging the selected at least one module, but not charging any of said remaining ones of said modules simultaneously with said selected at least one module;

under control of said processor, and after said step of fully charging, intentionally partially discharging said selected at least one module, but not said remaining modules, of said battery; and

operating said vehicle for a period of time.

9. A method according to claim 8, wherein said selecting step includes the step of selecting as one of said selected modules that module which has operated for the longest time without the benefit of said step of fully charging.

10. A method for maintaining the modules of a traction battery of a hybrid electric vehicle, which traction battery is made up of a plurality of series-connected modules, which vehicle, when operating, tends to charge said traction battery at a rate which may at times exceed the discharge rate for powering said vehicle so that said traction battery tends to receive a net charge, each of said modules of said traction battery having a nominal voltage when fully charged, and each of said modules of said traction battery having a characteristic which includes degradation when overcharged, and which experiences a reduction of charge capacity when discharged without prompt full recharging, said method comprising the recurrent steps of:

while said vehicle is not operating, and under control of a programmed processor, fully charging one module of said traction battery, but not charging at least some of the remaining modules of said traction battery simultaneously with charging of said one module of said traction battery;

under said control of said programmed processor, and after said step of fully charging said one module, intentionally partially discharging said one module, but not said at least some of said remaining modules, of said battery; and

operating said vehicle for a period of time.

11. A hybrid electric vehicle, comprising:

a traction motor for driving said vehicle during operation in response to a flow of current;

a traction battery, said traction battery including a plurality of series-connected traction battery modules, each of which has a charge level above which further charging may damage the module, and each of which tends to be damaged by protracted periods of less than full charge;

a dynamic braking system for extracting energy from said traction motor during braking;

an auxiliary source of electrical energy;

an energy controller coupled to said traction motor, said traction battery, said dynamic braking system, and to said auxiliary source, for controllably discharging said traction battery to said traction motor in order to drive said traction motor, for controllably regenerating energy from said dynamic braking system to said traction battery during braking, and for maintaining charge in said traction battery by means including said auxiliary source, whereby said energy controller tends to maintain said traction battery partially charged so that charge current due to regenerative braking can be regenerated to said traction battery without damaging modules of said traction battery;

an auxiliary battery;

a programmed controller associated with said energy controller, for, while said vehicle is not operating, fully charging at least one module of said traction battery, but not charging any of the remaining modules of said battery at the same time as the full charging of said at least one module, and for intentionally partially discharging said at least one module, but not said remaining modules, of said battery.

12. A method for maintaining the modules of an electrical storage battery, which battery is made up of a plurality of series-connected modules, each of said modules of said battery having a characteristic which includes degradation when overcharged, and which experiences a reduction of charge capacity when discharged without prompt full recharging, said method comprising the recurrent steps of:

under control of a programmed processor, fully charging at least one module of said battery, but not charging any of the remaining modules of said battery simultaneously with charging of said one module of said battery;

under said control of said programmed processor, and after said step of fully charging said at least one module, intentionally partially discharging said at least one module, but not said remaining modules, of said battery.