Standard Bus Procurement Guidelines - APTAStandards.com

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Standard Bus Procurement Guidelines Exhaust gases and waste heat shall be discharged from the roadside rear corner of the roof. The exhaust pipe shall be of sufficient height to prevent exhaust gases and waste heat from discoloring or causing heat deformation to the bus roof. The entire exhaust system shall be adequately shielded to prevent heat damage to any bus component. The exhaust outlet shall be designed to prevent rain, snow or water generated from high-pressure washing systems from entering into the exhaust pipe and causing damage to the catalyst. 5.3 CHASSIS 5.3.1 SUSPENSION 5.3.1.1 GENERAL REQUIREMENTS Both the front and rear suspensions shall be pneumatic type. The basic suspension system shall last the service life of the bus without major overhaul or replacement. Items such as one suspension bushing or air spring shall be replaceable by a 3M mechanic in 30 minutes or less. Adjustment points shall be minimized and shall not be subject to a loss of adjustment in service. Necessary adjustments shall be easily accomplished without removing or disconnecting the components. 5.3.1.2 SPRINGS AND SHOCK ABSORBERS 5.3.1.2.1 TRAVEL The suspension system shall permit a minimum wheel travel of 3.5 inches jounce-upward travel of a wheel when the bus hits a bump (higher than street surface), and 3 inches rebound-downward travel when the bus comes off a bump and the wheels fall relative to the body. Elastomeric bumpers shall be provided at the limit of jounce travel. Rebound travel may be limited by elastomeric bumpers or hydraulically within the shock absorbers. Suspensions shall incorporate appropriate devices for automatic height control so that regardless of load the bus height relative to the centerline of the wheels does not change more than + 1/2 inch at any point from the height required in Section 5.1.5.1.3. 5.3.1.2.2 DAMPING Vertical damping of the suspension system shall be accomplished by hydraulic shock absorbers mounted to the suspension arms or axles and attached to an appropriate location on the chassis. Damping shall be sufficient to control coach motion to 3 cycles or less after hitting road perturbations. Shock absorbers shall maintain their effectiveness for at least 50,000 miles of the service life of the bus. Each unit shall be replaceable by a 2M mechanic in less than 15 minutes. The shock absorber bushing shall be made of elastomeric material that will last the life of the shock absorber. 5.3.1.2.3 LUBRICATION All elements of steering, suspension, and drive systems requiring scheduled lubrication shall be provided with grease fittings conforming to SAE Standard J534. These fittings shall be located for ease of inspection, and shall be accessible with a standard grease gun without flexible hose end from a pit or Technical Specifications 142 10/18/07
Standard Bus Procurement Guidelines with the bus on a hoist. Each element requiring lubrication shall have its own grease fitting with a relief path. Lubricant specified shall be standard for all elements on the bus serviced by standard fittings. 5.3.1.2.4 KNEELING A kneeling system shall lower the bus a minimum of 3 inches during loading or unloading operations regardless of load up to GVWR, measured at the longitudinal centerline of the front door, by the driver using a three position, spring loaded to center switch. Downward direction will lower the bus. Release of switch at anytime will completely stop lowering motion and hold height of the bus at that position. Upward direction of the switch will allow the system to go to floor height without the driver having to hold the switch up. Brake and Throttle interlock shall prevent movement when the bus is kneeled. The kneel control shall be disabled when the bus is in motion. The bus shall kneel at a maximum rate of 1.25 inches per second at essentially a constant rate. After kneeling, the bus shall rise within 2 seconds to a height permitting the bus to resume service and shall rise to the correct operating height within 7 seconds regardless of load up to GVWR. During the lowering and raising operation, the maximum acceleration shall not exceed 0.2g and the jerk shall not exceed 0.3g/sec measured on the front door step tread. An indicator visible to the driver shall be illuminated until the bus is raised to a height adequate for safe street travel. An audible warning alarm will sound simultaneously with the operation of the kneeler to alert passengers and bystanders. A warning light mounted near the curbside of the front door, minimum 3" diameter, amber lens shall be provided that will blink when kneel feature activated and throughout operation. Kneeling shall not be operational while the wheelchair lift is deployed. 5.3.1.3 WHEELS AND TIRES 5.3.1.3.1 WHEELS Wheels and rims shall be (procuring agency to specify hub or stud piloted, and whether with aluminum rims) and shall be integral formed steel drop center construction. All wheels shall be interchangeable and shall be removable without a puller. Wheels shall be compatible with tires in size and load-carrying capacity. Front wheels and tires shall be balanced as an assembly per SAE J1986. 5.3.1.3.2 TIRES Tires shall be suitable for the conditions of transit service and sustained operation at the maximum speed capability of the bus. Load on any tire at GVWR shall not exceed the tire supplier's rating. (Procuring agency to describe arrangements for furnishing tires from lessor or supplier.) 5.3.2 STEERING 5.3.2.1 FRONT AXLE The front axle shall be non-driving with a load rating sufficient for the bus loaded to GVWR and shall be equipped with grease type front wheel bearings and seals. All friction points on the front axle shall be Technical Specifications 143 10/18/07
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American Public Transit Association
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Standard Bus Procurement Guidelines - APTAStandards.com

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