Mileage accumulation facilities
As a direct result of emissions regulations and the practice of homologation, it has become necessary for manufacturers to check on the change and probable deterioration in emissions performance after the vehicle has been driven for up to 80 000 km. One current legislative trend is to increase the length of this certified ‘useful life’ of the vehicles emission control system from 50 000 to 100 000 miles or greater.
The cost and the physical strain of using human drivers on test tracks or public roads for driving vehicles the prescribed distances in as little time as possible are high so special chassis dynamometer systems have been developed for running the specified sequences under automatic control, commonly for a period extending to 12 weeks.
Mileage accumulation dynamometers comprise a single large roll, of 48 inches or larger diameter, directly coupled to a d.c. or a.c. motor having sufficient power to run the required repetitive test sequence; for the average saloon car a motor capacity of 150 kW is sufficient.
In order to fully automate the process, the test vehicle is usually fitted with a robot driver. A bewildering range of these devices is available on the world market: for this particular application reliability must be the prime consideration. Some devices can be mounted on the driver’s seat and some are capable of also operating the footbrake and engaging reverse gear, but these refinements are not required by current legislative drive cycles. The set-up time of the robot may be appreciable but should be assessed against a test duration of 12 weeks or more. If wear or deterioration takes place in the robot mechanism or in the vehicle controls, for example by change in the clutch ‘bite’ position, the control system should be capable of automatic rectification, usually by means of periodic ‘relearn’ and adjustment cycles.
Due to the obvious problems of ventilating such a facility it is invariably located outside, under a simple roof. The control room housing the computerized control and safety systems can occupy a small building at one end of the facility, which in some cases may comprise up to 10 chassis dynamometers.
As the vehicle’s own cooling system is stationary, a motorized cooling fan, facing the front grill, is essential. The fan will be fitted with a duct to give a reasonable simulation of air flow under road conditions, and must be firmly anchored. The fan speed is usually controlled to match apparent vehicle speed up to about 130 km/h; above that speed noise and fan power requirements become an increasing problem. Since mileage accumulation facilities usually run 24 h a day, they must be suitably shielded to prevent noise nuisance.
Automatic refuelling systems may be fitted in the facility for each chassis dynamometer unit.
Mileage accumulation facilities
As a direct result of emissions regulations and the practice of homologation, it has become necessary for manufacturers to check on the change and probable deterioration in emissions performance after the vehicle has been driven for up to 80 000 km. One current legislative trend is to increase the length of this certified ‘useful life’ of the vehicles emission control system from 50 000 to 100 000 miles or greater.
The cost and the physical strain of using human drivers on test tracks or public roads for driving vehicles the prescribed distances in as little time as possible are high so special chassis dynamometer systems have been developed for running the specified sequences under automatic control, commonly for a period extending to 12 weeks.
Mileage accumulation dynamometers comprise a single large roll, of 48 inches or larger diameter, directly coupled to a d.c. or a.c. motor having sufficient power to run the required repetitive test sequence; for the average saloon car a motor capacity of 150 kW is sufficient.
In order to fully automate the process, the test vehicle is usually fitted with a robot driver. A bewildering range of these devices is available on the world market: for this particular application reliability must be the prime consideration. Some devices can be mounted on the driver’s seat and some are capable of also operating the footbrake and engaging reverse gear, but these refinements are not required by current legislative drive cycles. The set-up time of the robot may be appreciable but should be assessed against a test duration of 12 weeks or more. If wear or deterioration takes place in the robot mechanism or in the vehicle controls, for example by change in the clutch ‘bite’ position, the control system should be capable of automatic rectification, usually by means of periodic ‘relearn’ and adjustment cycles.
Due to the obvious problems of ventilating such a facility it is invariably located outside, under a simple roof. The control room housing the computerized control and safety systems can occupy a small building at one end of the facility, which in some cases may comprise up to 10 chassis dynamometers.
As the vehicle’s own cooling system is stationary, a motorized cooling fan, facing the front grill, is essential. The fan will be fitted with a duct to give a reasonable simulation of air flow under road conditions, and must be firmly anchored. The fan speed is usually controlled to match apparent vehicle speed up to about 130 km/h; above that speed noise and fan power requirements become an increasing problem. Since mileage accumulation facilities usually run 24 h a day, they must be suitably shielded to prevent noise nuisance.
Automatic refuelling systems may be fitted in the facility for each chassis dynamometer unit.
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