CAN Newsletter magazine
Fleet managers expect error-free inspection, maintenance, and repair. For many businesses, an inspection and maintenance (I/M) process that meets the requirement “right at the first time” and serves the reduction of expensive downtime to a minimum is existential.
The complete article is published in the December issue of the CAN Newsletter magazine 2020. This is just an excerpt.
Be it a passenger car, a heavy-duty truck or a non-road mobile machine (figure 1), preventive maintenance (PM) is an important measure to reduce unexpected breakdowns. PM is a scheduled process, performed at regular service intervals. It includes but is not limited to inspection, cleaning, and lubrication, but also the exchange of fluids, filters, spark plugs, and drive/timing belts. Predictive maintenance is similar to preventive maintenance and performed only when necessary. It consists of measures such as the exchange of a component that still functions but became conspicuous, because specific parameters indicate that a failure is about to occur, for example a bearing that started making noise. Predictive maintenance is associated with condition monitoring and performed by the service technician only when needed – but how is the need discovered? It’s all about data - data is the new oil.
This term is credited to the British Mathematician Clive Humbry and leads to the question, what data and oil have to do with each other. The simple answer is that both have no value in their raw state.
In the context of predictive maintenance, the vehicle is one of the most important data sources. Today‘s vehicles and mobile machines are packed with E/E components. Figure 3 shows a representation of an E/E system and its most important components. Electronic control units (ECUs) such as the engine control module (ECM) and the trans- mission control module (TCM) are connected to each other by an in-vehicle network, typically CAN.
The gateway separates the in-vehicle network (and thus the in-vehicle data exchange) and the diagnostic link connector (DLC). ECUs process self-diagnostic functions, monitor their environment, and generate diagnostic data. Common examples of diagnostic data are diagnostic trouble codes (DTCs) and their associated freeze frames, and the DM1 message in a J1939 network.
For the purpose of I/M, road-vehicles are usually driven to a service workshop. A workshop tester (TST) is connected to the DLC of the E/E system. In this most common setup, a vehicle communication interface (VCI) is used for that purpose. The TST-to-VCI connection can be wired (USB) or wireless (Wi-Fi). The VCI-to-DLC connection is always wired and either CAN or Ethernet. K-Line and SAE J1850 are outdated.
The workshop tester supports the service technician in the diagnostic process and the necessary I/M measures, for example by guided fault finding sequences. To acquire diagnostic data, the tester sends a diagnostic service request and receives the associated diagnostic services response from the vehicle’s E/E system. Requests and responses are standardized as diagnostic protocols such as OBD, SAE J1939, and UDS (Unified Diagnostic Services) on CAN or IP/Ethernet (ISO 14229). A very common request is known as “mode 1” requesting the current powertrain diagnostic data from the OBD (on-board diagnose) system of the vehicle. Another common service is the ISO 14229 (UDS) request “read data by Identifier” with a 2-byte data identifier (DID) for the acquisition of theoretically more than 65 000 different values.
Table 1 shows the OBD and UDS services for data acquisition. Inspection and maintenance in the service workshop is carried out when the vehicle speed is zero. To process condition monitoring under real driving conditions, the vehicle must be equipped with a data-logging device that is connected to the in-vehicle system and becomes part of the E/E-system.
The extended telematics control unit (xTCU) has two CAN channels. One can be connected to the DLC, the other one to the powertrain CAN. The xTCU reads raw CAN signals and supports diagnostic protocols to request diagnostic data at the same time. In addition, the product comes with internal sensors for the position (GNSS), the acceleration, and the rotation (gyroscope) of the vehicle.
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