Apta (Draft) Specification For: 30-ft, 35-ft, 40-ft, 45-ft, 60-foot (articulated) Transit Buses

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IP 12.Retarder

The powertrain shall be equipped with a retarder designed to extend brake lining service life. The application of the retarder shall cause a smooth blending of both retarder and service brake function.

Actuation of ABS and/or Automatic Traction Control (ATC) shall override the operation of the brake retarder.


Brake lights shall illuminate when the retarder is activated.


Standard requirement for retarder activation

The retarder shall be adjustable within the limits of the powertrain and activated when the brake pedal is depressed. The procuring agency will work with the OEM/drive system manufacturer to determine retarder performance settings.


Throttle pedal activation of the retarder

The retarder shall become partially engaged (approximately one-third of its total application, with a resulting deceleration of no greater than 0.077g) when the throttle pedal is completely released. Maximum retarder shall be achieved when brake pedal is depressed prior to engagement of service brakes, with a maximum resulting deceleration of approximately 0.20g in an empty bus. The resulting decelerations specified include the effects of engine braking, wind resistance and rolling resistance.

The thermostatically controlled cooling fan shall be activated when the retarder is engaged and the coolant temperature reaches the maximum operating temperature established by the engine and transmission manufacturers.


Accessible retarder disable switch

The retarder disable switch shall be accessible to the seated driver.


Retarder disable switch not accessible

The retarder disable switch is not required to be accessible to the seated driver.


Disabling retarder shall be recorded for procuring agency data collection

IP 13.Mounting

All power plant mounting shall be mechanically isolated to minimize transfer of vibration to the body structure and provide a minimum clearance of 0.75 in. (20 mm). Mounts shall control the movement of the power plant so as not to affect performance of belt-driven accessories or cause strain in piping and wiring connections to the power plant.


The propulsion system shall be arranged for ease of access and maintenance. The contractor shall list all special tools, fixtures or facility requirements recommended for servicing. The muffler, exhaust system, air cleaner, air compressor, starter, alternator, radiator, all accessories and any other component requiring service or replacement shall be easily removable and independent of the engine and transmission removal. An engine oil pressure gauge and coolant temperature gauge shall be provided in the engine compartment. These gauges shall be easily read during service and mounted in an area where they shall not be damaged during minor or major repairs.

Engine oil and the radiator filler caps shall be hinged to the filler neck and closed with spring pressure or positive locks to prevent leakage. All fluid fill locations shall be properly labeled to help ensure that correct fluid is added. All fillers shall be easily accessible with standard funnels, pour spouts and automatic dispensing equipment. All lubricant sumps shall be fitted with magnetic-type drain plugs.


Unique fluid (lubricant) fillers

The engine, transmission and hydraulic reservoir shall each incorporate a unique lubricant fill fitting to prevent cross-contamination of lubricant types. Fitting types shall be specified by the procuring agency.

The engine and transmission shall be equipped with sufficient heavy-duty fuel and oil filters for efficient operation and to protect the engine and transmission between scheduled filter changes. All filters shall be easily accessible and the filter bases shall be plumbed to ensure correct reinstallation.


No engine bypass oil filter

Centrifugal, non-disposable engine bypass oil filter

An air cleaner with a dry filter element and a graduated air filter restriction indicator shall be provided. The location of the air intake system shall be designed to minimize the entry of dust and debris and to maximize the life of the air filter. The engine air duct shall be designed to minimize the entry of water into the air intake system. Drainage provisions shall be included to allow any water/moisture to drain prior to entry into air filter.


Oil pressure and coolant temperature gauges

No engine oil pressure and coolant temperature gauges required in engine compartment.


Engine-driven accessories shall be mounted for quick removal and repair. Accessory drive systems shall be maintained in accordance with the manufacturer’s requirements. These accessories shall be driven at speeds sufficient to ensure adequate system performance during extended periods of idle operation and low route speed portions of the design operating profile. Belt guards shall be provided as required for safety and shall be sturdy in design and installation and easily removable. Accessories may be driven directly by the engine, electrically or hydraulically.


Direct-driven engine accessories

Electrically powered accessories

Electrically powered accessories shall be provided. Contractor shall provide a list of these accessories to the procuring agency.

IP 14.Hydraulic systems

Hydraulic system service tasks shall be minimized and scheduled no more frequently than those of other major coach systems. All elements of the hydraulic system shall be easily accessible for service or unit replacement. Critical points in the hydraulic system shall be fitted with service ports so that portable diagnostic equipment may be connected or sensors for an off-board diagnostic system permanently attached to monitor system operation when applicable. A tamper-proof priority system shall prevent the loss of power steering during operation of the bus if other devices are also powered by the hydraulic system.

The hydraulic system shall operate within the allowable temperature range as specified by the lubricant manufacturer.


No requirement for hydraulic system sensors

Hydraulic system sensors

Sensors in the main hydraulic system, excluding those in the power steering system, shall indicate on the driver’s on-board diagnostic panel conditions of low hydraulic fluid level.

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