Part 1: FMS Interface as door opener for a condition-based maintenance for Bus fleets.
The increasing complexity of the electronic architecture of a bus and a lack of trained personnel for maintenance and service is a growing challenge for bus operators in public transport. This applies already for conventional buses and this will emerge with transition to eMobility.
It is not only the cost for maintenance and service itself – which is quite a big part of the total cost – it is that service and maintenance have a great impact on availability and therefore will influence operational cost as well. More and more operators are working to install strategies for predictive maintenance and service – to achieve lower cost, higher efficiency in their workshops and last but not least higher customer satisfaction through less failures. The FMS interface opens the door to condition-based maintenance as a first step in this direction.
Traditionally, in a bus, the world of ITCS (Intelligent Transport Control Systems) is strictly separated from the world of service and maintenance. The data being relevant for service is available on the driveline CAN but due to safety reasons the access to these data is strictly regulated. For non-authorized participants, the FMS interface offers a read-only access to these data, enabled for example by the ITxPT service “FMS to IP”, see picture 1.
The FMS Standard
The FMS interface goes back to a common initiative by some major truck OEMs but has been extended to bus specific parameters as well. According to the standard FMS.04 and as minimum scope, the FMS as interface to a SAE J1939 CAN bus today provides data like:
- Engine and ambient temperature
- Air supply pressure
- Door status
- Alternator speed
- FMS TellTales
This scope can be extended on individual settings by the bus manufacturer.
Based on data as e.g. the temperature data in combination with data from other components like the transmission an early-warning logic for failure or malfunction of the cooling circuit of the bus can be realized. Another example is the electric system of a bus including the batteries, the generator etc. where repeated voltage drops indicate e.g. an upcoming breakdown of the battery – which would lead to a breakdown of the complete bus.
Even more supportive are the “TellTales”. These TellTales control the warning lights on the driver’s dashboard. If the TellTales are directly forwarded to the back-office respective the workshop, the maintenance personnel are always up to date about the status of a bus and are able to plan counter measures without delay. Returning to a depot, a bus with a malfunction is already scheduled for maintenance, necessary parts are prepared and off-time can be reduced to a minimum without any setup or waiting time.
Application of Data from the FMS
A vehicle gateway already uses data from the FMS interface as position of load and brake pedal, fuel consumption etc, for applications being installed like e.g. a driver assist system to improve the fuel economy. In addition to this, other data usable for predictive maintenance can be forwarded by a separate application (“FMS service”) to the Cloud, see picture 2.
As such an application uses the same input signals from the FMS, hence on the vehicle side there is no additional installation effort. On the back office side the data from the FMS are forwarded to the operator via an API.
Data Storage and Analysis in the Cloud
Picture 2 shows the FMS application (“FMS Service”) in the vehicle gateway and the connectivity to an arbitrary Cloud. All data are forwarded and stored in JSON Line Format (JSONL) with each line containing a data entry / a valid JSON object. This approach also implies that the amount of data is quite manageable. So, a bus with a typical set-up of the FMS will consume circa 50 MBytes/month.
Having the data available in the Cloud, the monitoring of the data from all buses itself is to be handled by analytic systems and appropriate tools. Such tools allow to deploy e.g. physical rules to the time series and so to enable arbitrary analyses. It also allows to define e.g. thresholds and in case of exceeding the levels to trigger event or warning messages. Therefore the workshop manager can reduce his attention to predefined divergences. He will just get an alert if one vehicle reaches the critical value to trigger the necessary actions. This approach as “Management by Exception” helps to focus the workshop manager’s attention to the really critical items and not to be overflowed with a tremendous amount of data – just another contribution to increase the efficiency in daily work.
Example: Maintenance of the Coolant Circuit
A quite easy detectable malfunction is the overheating of the coolant circuit of the engine. Reasons for this are manifold as e.g. bad maintenance of the heat exchanger or an insufficient level of the coolant fluid. Overheating can lead to severe damages of engine and transmission and in the end even a source for fire in the engine department.
The most appropriate data to monitor the coolant circuit are the temperature of the coolant fluid and the ambient temperature. The difference between both reflects the efficiency of the heat exchanger and its state of maintenance. Picture 4 shows a heat exchanger of a bus in a very bad condition. The heat exchanger is widely blocked by dust and dirt caused by an insufficient maintenance and cleaning. Dust and dirt are not only blocking the air flow through the heat exchanger, it is also like an “insulating layer” hindering the energy flow from the coolant fluid to the ambient air.
The reduced efficiency of the heat exchanger can easily be detected by means of the mentioned values from the FMS, the coolant temperature in combination with the ambient temperature, see picture 5.
As shown in picture 5, after an efficient and careful cleaning, the temperature of the coolant fluid was reduced significantly. The difference to the ambient temperature dropped down by 27 degrees and the reduction of the coolant temperature was reflected in the oil temperature of the transmission, too. The temperature in the oil sump of the transmission was reduced by about 26 degrees.
Knowing that a reduction of the oil temperature by 10 degrees doubles the lifetime of the oil, the reduction by 26 degrees is equivalent to increase the life of the transmission oil by a factor 6 – an important aspect how to reduce cost and also to reduce the environmental impact of less oil usage.
Disclaimer: The content of this blog post is the author’s opinion and doesn’t reflect the opinion of any other person or organization.