Monday, 9 September 2013

Rules Corner: FSAE2014 Changelog, Part EV

This is the second part of my FSAE2014 rules changelog. This time it is about the EV rules. Due to the many changes I decided to give the EV part its own post.
The first post about the FSAE2014 rule parts A, T, AF and IC can be found here.
A third post containing the changes in parts S and D will follow soon.

I have thoroughly compiled the changed rules, but there is no guarantee that these are complete or that there won't be another release which might make this compilation obsolete. So make sure to keep up to date when new rules are released. Although I will probably post another blog entry, if there is an update to the rules.

For the impatient, these are the rules you have to check out:

  • EV1.1.2
  • EV2.1.2
  • EV2.2
  • EV2.2.6
  • EV2.4.4
  • EV2.5
  • EV3.2.4
  • EV3.3.3
  • EV3.3.8
  • EV3.3.11
  • EV3.4.8
  • EV3.6.3
  • EV3.6.4
  • EV3.6.7
  • EV4.3.1
  • EV4.6.7
  • EV4.6.11
  • EV4.6.12
  • EV4.8.1
  • EV4.12.2
  • EV5.1.9
  • EV5.2.4
  • EV5.3.4
  • EV8.3

For the patient readers who are interested in the details:

Change: There is no change, but Formula Student Austria's max. voltage limit is missing. They will probably stick to 600VDC like all other competitions despite the North and South American competitions.
Impact: None.

Change: A minimum strength/thickness requirement for motor housings has been added.
Impact: Many teams may have to re-design their motor housings or at least check whether it fulfils the new requirements. This rule has been added due to lots of discussions this year at scrutineering about the necessary thickness of motor housings.

Change: It has been clarified how overvoltage situations will be evaluated. Basically it is the same filtering as applied to the power measurement.
Impact: There is no real impact on the design, since, before the clarification, everyone had to stay below the max voltage limit anyway.

Change: Clarification that non-availability of EM data due to the team's fault will be treated as a violation.
Impact: This has been clarified due to discussions following up situations in which a violation would have been unlikely, but the EM was not connected properly by the team such that there was no data at all.

Change: The sentence that a brake sensor failure has to be treated like an implausibility has been removed.
Impact: None, as the information removed was redundant.

Change: The rule now references the mechanical brakes and it also specifies that this function will be tested under load.
Impact: Both changes are clarifications, but the first part certainly helps teams that rely heavily on regenerative braking.

Change: Each accumulator container must now be removable from the car while still remaining rules compliant.
Impact: This is a rather big change for some teams. It means that you cannot design your accumulator containers in a way that they are interconnected without additional AIRs and are thus forming one big accumulator container. It also means that you cannot use a hollow structure in a monocoque as an accumulator container any more. This rule has been added for safety reasons. It ensures that the accumulator container can always be safely removed from the car for maintenance without working in live high-voltage potentials.

EV3.3.3 and EV4.6.12:
Change: Maintenance plugs and screwed HV connections in general must now include a positive locking feature which prevents the plug/connection from unintentionally becoming loose.
Impact: Some teams might have to change their designs due to this rule. It was included, because there were lots of discussions about the possibility of HV connections coming loose due to vibration etc.

Change: Every wire used in an accumulator container, no matter whether it is part of the GLV or tractive system, must be rated to the maximum tractive system voltage.
Impact: This is just a safety measure, but some teams might have to reconsider their wire choice. This issue lead to discussions during the ESF review.

Change: Clarification that the AIL must also work, if it was disconnected from the GLV system.
Impact: No team should have to change their AIL design, if their ESF reviewer has been thorough. However, make sure to meet this rule. It will be hard to fix at the event.

Change: It has been clarified that the contained energy of a stack is calculated by multiplying the maximum stack voltage with the nominal capacity of the used cell(s).
Impact: Some teams with lazy ESF reviewers might have to change their firewall setup within the accumulator container due to this clarification as the contained energy certainly increases, if you use the maximum stack voltage instead of the nominal stack voltage.

Change: Temperature sensors must be directly in contact with the cells.
Impact: This will make quite some teams using indirect temperature measurement change their designs. It is just hard to predict or prove that indirect temperature measurement is as accurate as direct temperature measurement. Therefore now there has to be direct contact.

Change: It has been clarified that fuses may be used instead of fusible link wires and that fuses or fusible link wires must be placed in the wire or pcb trace which is directly connected to the cell tab.
Impact: This is also one of the bigger changes. Make sure to adhere to this requirement, it will be hard to fix, even when caught in the ESF review as it usually means many changes in the accumulator container and/or BMS setup. The reason behind is that we have seen connectors in between cells and pcbs failing with a short circuit. The high current burned the insulation of the wire and the now uninsulated wire created further short circuits.

Change: Clarification that the shutdown values have to incorporate the inaccuracy of the measurement system. 
Impact: This leads to an earlier shutdown of the BMS as no measurement system is perfect. The rule has been introduced due to discussions with teams that used temperature sensors with an accuracy of +-5°C.

Change: Clarification that HV wire must also be separated by a firewall from the driver.
Impact: Some teams missed that HV wires are also tractive system components. Therefore it has now been clarified and should hopefully keep some teams from having to fix this at scrutineering.

Change: Clarification that not all requirements regarding HV wiring protection must be met, if the wiring runs within an enclosure.
Impact: There should be no impact as the rule weakens the requirements for HV wiring protection.

Change: Using orange coloured wires for LV wiring is now prohibited.
Impact: Just make sure to not use orange wires for your LV wiring harness.

Change: The HVD must be above 350mm from the ground and easily visible when standing behind the vehicle.
Impact: There have been issues with the accessibility of the HVD in the past. This rule hopefully solves these. The good thing is that I do not remember that we ever had to use this in an emergency situation at an event *knocking on wood*

EV4.12.2 and EV5.2.4:
Change: Any pre-charge circuitry must be supplied directly from the TSMS.
Impact: This rule is a follows from the weakened requirement that the TSMS must be the last switch prior the AIRs (EV5.2.4) except for the pre-charge circuitry. This should make things easier with respect to designing a rules compliant shutdown circuit as the requirement of the 2013 FSAE rules was hard to meet. It means that the power supply driving the pre-charge circuitry must be directly switched with the TSMS (no relays/transistors etc.).

Change: It must be possible to demonstrate that all features of the Shutdown circuit function correctly. It should be noted that this includes all interlocks.
Impact: There were teams this year which just used wires as interlocks to inner-wheel motors such that these would break, if the wheel assembly breaks off the car. These teams had to cut these wires in scrutineering to demonstrate that the interlocks work. So make sure to add connectors, if you intend to build interlocks like this. 

Change: The international electrical symbol consisting of a red spark on a white-edged blue triangle must be affixed in close proximity to this button.
Impact: Just put these stickers on your shutdown buttons and you are good to go.

Change: A complete paragraph about requirements for chargers has been added.
Impact: Chargers were not really regulated since the beginning of the Electric class. This year we saw some dangerous designs and we had to do something about that, so here it is. Please resist to just put a CE sticker on your team-built charger, no scrutineer will buy that.

Please note:
If you think that any content in this post is worth discussing, please do so in the forum and not in the comment section of this blog, to make sure that everyone can benefit from the contents of the discussion, even if he/she is not reading this blog.

1 comment:

  1. Are perforations allowed in the motor casing (EV2.1.2)?