Accelerated reliability tests of EVs are performed to provide several years of vehicle performance information in a short time—within a year. The tests are based on standard guidelines and the results of the tests provide a better understanding of EV performance.
These tests are conducted by operating the EVs in accelerated mileage modes that simulate typical fleet missions with the intent to obtain and analyze vehicle operation experiences within a relatively short period of one year. While these tests are conducted in an accelerated mode, they are always performed within the EV manufacturer’s guidelines and do not void the manufacturer’s warranty under any circumstances. In case the vehicle battery pack cannot be charged using a fast charge mode, the tests will be performed in accordance with no fast charging.
Each vehicle under the reliability test is tested for a period of one year.
The vehicle is required to maintain the original components for the entire 25,000 miles testing period. The accelerated reliability tests may be carried out beyond the one-year period to gain additional vehicle knowledge.
The miles driven during the trip should be approximately 100 miles per day. Each driving cycle should be balanced with respect to the time required to charge so that the vehicle can be ready for the next test trip.
The battery pack should not be discharged beyond 80% DOD unless rec- ommended by the battery manufacturer. During the test, it is important to maintain the battery pack at 80% DOD.
The data gathered during the tests include:
• Average miles/charge by vehicle model (including potential range)
• Miles/charge by vehicle model (on a monthly or quarterly basis)
• Cumulative fleet mileage (on a monthly basis)
The charging pattern indicates when the vehicle is charged (time of the day), the duration of the charge (hours), and the magnitude of the charge (kWhr). In addition, the charging pattern also provides an ACCELERATED RELIABILITY TESTING OF ELECTRIC VEHICLES 167
assessment of the EV’s impact on the utility system. If the time-of-use tariffs are available, the charging pattern also provides an accurate cal- culation of the cost of the energy consumed by the EV.
The charging data gathered during the accelerated tests includes:
• Number of charges per month
• Miles per charge
• Average charge time
• Energy consumed at on-peak rates
• Energy consumed at off-peak rates
This charge data obtained from the vehicle tests provides important vehicle information including:
• Miles/charge per month by vehicle and model
• Average recharge time by vehicle and model
• Average daily charging load profile by vehicle
• Average AC kWhr/mile by vehicle and by model
As part of the vehicle profiling data, it is useful to also determine the servicing man-hours by the vehicle model (both scheduled and unscheduled), vehicle availability, and downtime. The downtime of the vehicle may be further attributed to waiting for parts or downtime for maintenance.
The vehicle breakdown can also be attributed to on-road failure inci- dents. These will be breakdowns due to the vehicle failure while it is under test. On-road failure incidents also provide an estimate of repair costs per vehicle model down to the component level. Some the com- ponents that should be monitored are:
• Battery Pack
• Charging System
• Auxiliary System
• Traction Motor System
• Brakes and ABS System
• Tires
• Drivetrain and/or Transmission
• HVAC
In addition, the number of incidents/1,000 vehicle miles/per com- ponent is a good estimate of vehicle downtime. The inverse of the vehicle component downtime provides an estimate of the vehicle com- ponent reliability.
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For the EV battery system, the following components should be monitored:
• Traction Battery
• Battery Modules
• High Voltage Battery Wiring
• Battery Pack Fan Filter
• Battery Fuse
• Battery Pack Disconnect Switch
• SOC Charge Gauge
• Battery Tray
• Battery Pack Fan
• Battery Pack Thermal System
• Battery Current Sensor
• Battery Temperature Sensor
For the EV charging system, the following components should be monitored:
• Onboard Battery Charger
• Onboard Charging Wiring
• Charger Unit Fan
• Charging Algorithm Interface Card
• Onboard Charging Port
• Charger Unit Fuse
For the vehicle traction motor system, the following components should be monitored:
• Traction Motor
• Traction Motor Filter
• Traction Motor Seal
• Traction Motor Throttle System
• Traction Motor Fan
• Traction Motor Cable
• Traction Motor Controller Connectors
• Traction Motor Mounting
• Traction Motor Hose
• Traction Motor Controller
• Traction Motor Wiring Harness
• Traction Motor System Cooling
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For the vehicle drive train, the following components should be monitored:
• Axle
• CV Joint
• Differential/Rear Axle
• Rear Axle Seal
• Differential Mounting
• Parking Pawl
• Transmission/Transaxle
• Transmission/Transaxle Seal
• Transmission/Transaxle Mount
• Transmission/Transaxle Shifter
For the vehicle auxiliary system, the following components should be monitored:
• DC/DC Converter
• Auxiliary Battery
• Auxiliary Battery Fuse
• Backup Alarm
• Miscellaneous Belt System
• Heating System (Resistance/Fuel Fired)
• Miscellaneous Gages
• Power Steering Motor
• Power Steering Controller
• Power Steering Module
• Relay
• Warning Light
• HVAC
• Cooling System
• A/C Hose
• A/C Compressor
• Cooling System
• A/C Valve
• Heat Pump Reversing Valve
• A/C Motor Controller
• Ground Fault
For the vehicle brake system, the following components should be monitored:
170 TESTING AND MODELING OF ELECTRIC VEHICLE BATTERIES
• Brake Controller
• Power Brake Module
• Brake Rotor
• Brake Pads
• Regenerative Module
• Brake Drum
• Tire
• Wheel
• Tire Inflation Pressure Sensor
• ABS Sensor
Battery amortization costs should also be factored into the reliability test data. If the batteries in the battery pack are replaced during the period of the test, the battery replacement cost shall be divided for the miles traveled by the EV. This is to account for the vehicle cost per mile.
This will provide a summary of the EV operating cost in $/mile or cents/mile based versus the energy consumed, maintenance, compo- nents, battery costs.