FEATURE AUTOMOTIVE ELECTRONICS
Improving the automotive power distribution architecture
The ongoing electrification of vehicles is impacted by three major forces: The “connected car” model, new powertrains and regulations, and the globalisation and consolidation of platforms. In this article, Philippe Dupuy Ph.D., advanced R&D smart relays and smart grid manager at NXP considers two aspects: relay replacement and fuse alternatives along with some of the available methods for improving distribution architechture
C
onnected cars require a vehicle’s power network to connect to the
external power source of a fixed structure. Connecting a 48V mild hybrid car to a fixed structure also requires communication between the 48V port in the garage or external 48V source and the vehicle. Many new features will come with 48V capabilities, such as X-by-wire, that require high quality and a high level of
safety.The trend being discussed is classifying the wiring harness as an ISO 26262 element for critical areas such as steer-by-wire and brake-by-wire. As a result, the wiring needs to be considered as a safety-critical aspect compliant with ISO 2626. The real driving force for power distribution architecture replacement will come from new functions of the connected car for which relays are not adequate. For example, the stop and start function embraced by many manufacturers dramatically increases the switching cycles, far beyond the capability of any common relay. As a result, the relay is no longer adequate to perform as expected over the lifetime of the vehicle. The same applies to relays in other applications such as pumps and the HVAC system.
POWERTRAIN AND REGULATION REQUIREMENTS The cost savings behind wiring harness optimisation and vehicle weight reduction drive the second argument for overhauling automotive power distribution architecture via electrification. For example, in the European Union (EU) communities, the
cost per gram of over-limit CO2 emissions will increase in 2019 to 95 euros for the first gram that exceeds the EU limit. Avoiding these costly penalties should motivate OEMs to optimise and trim wiring harness weight, to lower the 30kg average weight.
8 MARCH 2017 | ELECTRONICS The replacement of mechanical relays
with semiconductor technology has been proposed for over 30 years and the capability to replace fuses has been possible for almost 20 years. However, significant reductions from existing alternatives are required to make the
Figure 2:
Several high voltage spikes with 100µs of activating the contacts of a mechanical relay
GLOBALISATION With mega-platform approaches, OEMs can minimise engineering time and the associated cost and reduce the overall time-to-market for new vehicles. A single platform provides commonality for a range of vehicles at a minimum of engineering effort and expense. For semiconductor suppliers, the wiring harness including power distribution must be as flexible as possible to be compatible with low- to high-end cars.
Figure 1:
Relay replacement has occurred at different rates in various areas of the car
transition compelling enough to reject the status quo. Today, some OEMs still need to initiate the design activity required to make this transition. One incentive for replacing mechanical relays is a safety regulation that requires anti-pinch diagnostics/protection. For a mechanical relay, meeting this regulation requires many additional components that make the mechanical design much more expensive. These expensive elements add even more justification to increased system requirements (e.g., the increased mission profile from the stop-start system and quality related issues that require oversizing the relay to handle the inrush current). With 48V, mechanical relays will have severe challenges to be compliant. A high-end vehicle can easily have 100 fuses and four fuse boxes that need to be accessible for servicing and fuse replacement. The cost of this space and access in the passenger compartment is very expensive because it detracts from passenger comfort. Since a solid-state protected device (an electronic or eFuse) does not have to be replaced after a short circuit occurs, it can be placed in less important areas. In contrast to the mechanical fuse that
is designed for a single value and is not programmable, an eFuse can be programmed for 10, 15, 20 Amps or beyond. This flexibility makes the electronic fuse fully compliant with mega-platform vehicle designs. Mechanical fuses, have inaccurate
minimum and maximum values that require the wiring to be oversized for a sufficient safety margin under all extremes. Additionally, fuses do not provide diagnostic and monitoring safety features, whereas an electronic fuse can frequently report a dynamic operation status that complies with connected-car trends. An electronic fuse also adds safety for the wiring harness through the diagnostic and health monitoring that it can provide. Today, the main driving force for
electronic replacement comes from carmakers and not the semiconductor industry. While the silicon solution is more expensive, the carmakers’ calculations have led them to conclude that there will be cost savings at the system and vehicle levels.
NXP
www.nxp.com T: 020 3510 0690
/ ELECTRONICS
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56
