Source: Electric Vehicle Resource Network
REVIEW: In recent years, the development of new energy vehicles is very rapid, whether it is the urgent need to transform the traditional car prices, or capital blessing industry new army, we are actively layout of the new energy vehicles, "outlet", hoping to become the industry leader.
In recent years, the development of new energy vehicles is very rapid, whether it is the urgent need to transform the traditional car prices, or capital blessing of the industry's new army, we are actively layout of the "new energy vehicles," the outlet, hoping to become the industry leader. According to incomplete statistics, there are more than 50 vehicle manufacturers in mainland China and new energy vehicles alone. While fierce competition among enterprises, the state subsidies for new energy vehicles have shown a decreasing trend year by year. How to reduce costs, most car companies to take measures to reduce (such as reducing the number of relays and the use of capacity).
The author as a new energy automotive industry for many years practitioners, for this phenomenon is very worried. Industry experts believe that the "lifeline" of new energy vehicles should be prioritized in terms of safety, quality, and cost, rather than simply paying attention to the proportion of BOM-based parts based on parts costs, and thus cost down each year. At present, new energy vehicles is still in its infancy, every practitioner should strive to think about our car is really safe?
From a security perspective, I believe that the current new energy vehicles is not the amount of relays, but less. For example, in the high-voltage, high-current battery pack module, except for a few manufacturers, most new energy vehicles only install passive components such as fuses. Chat here, I thought of a story, 2014, I travel 4S shop, and maintenance personnel in the exchange, understand that most of their concerns for new energy vehicles is in the maintenance process, the battery pack will be high Piezoelectricity to. After three years, I once again went to 4S shop for understanding, maintenance staff is still the most worried about the problem. Professional maintenance personnel are so talk about "electricity" color change, you can imagine ordinary consumers in the new energy vehicles any anomalies, it must be hope "electricity" sigh, helpless. If the battery pack body module to increase the partial pressure relay, when the car is turned off, the successful electric vehicle voltage from 300-800V, split into several smaller than 100V battery pack module, which is safer for the human body . At the same time, the driving safety factor of the electric vehicle with the relay installed will be improved compared with the passive safety strategy such as merely installing the fuse; at present, the mainstream design of the fuse in the battery pack often only adds 1 ~ 2pcs fuses in the main circuit, If the short circuit generated by the collision is outside the selection range of the fuse, there is a big risk that the fuse will not be disconnected; the fuse needs to be replaced after being blown, and the relay can be used repeatedly, thus effectively improving the safety performance of the new energy vehicle.
SAE J2929 Battery System Safety Standards for Electric Vehicles and Hybrid Electric Vehicles - As mentioned in lithium-ion batteries, the voltage on the external terminals of the battery system must not exceed 60V within 5 seconds after the battery system is automatically disconnected. In the event of a battery system auto-disconnect failure (such as relay firing), one of the following options should be provided to prevent inadvertent contact with the open terminals (1) Manual switch to reduce the voltage across the positive and negative terminals to within 5 seconds 60V or (2) to prevent finger from entering.
ISO6469-3 "Safety Technical Codes for Electric Vehicles" Part 3: Insulation resistance is required in the protection of personnel from electrical injuries, requiring 100 ohms per volt DC. Therefore, the international electric vehicle safety standards also require the addition of partial pressure in the battery pack relay.
In practical application, there are some benefits to increase the partial pressure relay as follows:
1, due to multiple relays, battery system failure probability of failure will be reduced. The probability of three or more relays sintering at the same time is much lower than the probability of one relay sintering.
2, the open terminal of the battery system (including the manual switch terminal) in the event of a single point of failure may appear high pressure failure conditions include: battery positive insulation failure, battery insulation failure, battery negative insulation failure, positive relay sintering, Negative relay sintering; and the presence of multiple partial pressure relays can open the terminal to reduce the probability of high pressure.
3, the partial pressure relay voltage cut off, reducing the voltage between open terminals under failure conditions, reducing the pressure on the insulation protection.
So if the battery pack body to increase the partial pressure relay, the relay has some special requirements? According to the author's past experience, at least so few battery pack designer needs to be considered.
1, the relay forward and reverse electrical life and other electrical properties need to be consistent, or can be said to be non-polar, weak polarity relays.
2, because the relay installation location close to the battery pack, the battery pack for the temperature rise higher, so the relay temperature needs to be as low as possible.
3, because the smaller space within the battery pack, designers will be limited space for battery core installation. Therefore, the design of the relay needs to meet various structural requirements of the battery pack, and the performance index also requires a high level. The design requirements of the relay are high (see Table 1 below).
4, because a package body needs to install more than 3pcs relay, relay action consistency requirements higher.
5, an effective match with the fuse.
