Case Study
Daimler Chrysler Commercial Bus

The challenge: Take a conventionally wired bus and convert it into a fully multiplexed bus.

In today’s competitive market place engineers are seldom afforded the luxury of being able to completely redesign a product. More often than not all engineering time is spent in support of existing product, designing customer specified options and putting out the day-to-day fires. At Class 1 we realized that this was just the case at Daimler Chrysler Commercial Busses (DCCB). So we offered the unprecedented service of taking one of their conventionally wired SLF 235 Super Low Floor Busses and multiplexing it. Since their engineering time was at a premium and Class 1 wanted to tap into new industries, the joint project was a perfect match.

After receiving the SLF 235 at our facility we went right to work. We identified the inputs and outputs on the bus and insured that we understood the functionality. Once the input output list was established, we divided the vehicle into zones; the front power panel, the dash, the drivers’ side panel, the left front overhead, the right front overhead, the rear door area and the rear overhead. At the request of DCCB engineering we located all ES-Key nodes in the interior of the bus.

The front power panel zone is located just inside the entry door. It is provided to DCCB as a completed sub-assembly that allows them to simply install and plug it in. In addition to handling both 12 and 24-volt power distribution for the front half of the vehicle, it is also responsible for headlamp control (with DRL), ramp and kneeling functions.

The dash area contains the USM and several input and output nodes. The kneel and ramp controls and all lighting switches are in the dash as well as important operator indicators such as “check engine” and “door open”.

The drivers’ side panel zone contains the transmission ECU the ABS computer and three ES-key nodes. The ES-Key nodes receive inputs from and give outputs to the transmission ECU and the ABS computer as well as receive inputs from the door control switch. This is also an intricate sub-assembly provided by class 1.

The left front overhead zone houses two power distribution modules (PDM), the Es-Key information center and the data logger. The PDM’s control such functions as the left side interior lights the stop request sign and the left side marker lights.

The right front overhead zone has two more ES-Key PDM’s. They control right side interior and exterior lighting as well as the front entry door. The ES-Key system provides complete entry door control eliminating the necessity to purchase a separate controller.

The rear door area zone has only one ES-Key PDM dedicated to rear door control and lighting. The rear door control is complete with sensitive edge operation that will automatically open the rear door if an obstruction is sensed during closure. The door remains open until the operator intervenes by cycling the door control switch.

The rear overhead zone has several ES-Key nodes and the rear bus 12/24-volt power distribution. This is also provided to DCCB as a drop in sub-assembly. The rear overhead zone is where the ES-Key system interfaces with the engine and where all of the rear exterior lighting is controlled. The engine interface even includes a starter lockout feature that will not allow the engine to be started unless all safety interlocks are met.

The end results were fantastic! We were able to successfully multiplex the SLF 235, saving the customer valuable engineering time and money. Besides the obvious benefits of multiplexing, such as onboard diagnostics, fewer light duty mechanical parts, and many less electrical connections, DCCB realized a weight reduction of over 150 pounds. That’s enough weight to add another passenger.

At the time of this writing we are approaching 200 “fielded units” with outstanding customer satisfaction. Class1 would like to thank the people at Daimler Chrysler Commercial Busses for the opportunity to work with them. Their co-operation and commitment to quality have proven them to be a force in the transit bus industry.