ELEC­TRIC POW­ER­TRAINS

Dr Tim talks us through the in­tri­ca­cies and le­gal­i­ties of elec­tric ve­hi­cles

Street Machine - - CONTENTS -

THE pop­u­lar­ity of elec­tric ve­hi­cles (EVS) continues to in­crease, with a va­ri­ety of man­u­fac­tur­ers pre­sent­ing elec­tric cars to a market still learning how to choose one. You can also build an EV and, sure enough, I’ve now been asked by a client to en­gi­neer my first one: an ICV (In­di­vid­u­ally Con­structed Ve­hi­cle) trike. So I had to deal with three en­gi­neer­ing as­pects at the same time: an ICV, a trike and an EV all in the one project.

The only part that I was not ex­pe­ri­enced in was the EV as­pect, so I had to learn the cur­rent reg­u­la­tions. Luck­ily I had a good client who knew his stuff, and the re­sult of our co­op­er­a­tive ef­forts is an EV trike called T-rev, reg­is­tered and on the road. For my part, I read ev­ery­thing avail­able to be able to as­sist him and en­sure that the ve­hi­cle met the Na­tional Guide­lines for the In­stal­la­tion of Elec­tric Drives in Mo­tor Ve­hi­cles. This is avail­able for any­one to down­load for those in­ter­ested in go­ing a sim­i­lar route.

So this month I wanted to give you an over­view of what you need to con­sider when con­struct­ing an elec­tric ve­hi­cle. Af­ter all, it won’t be long be­fore we start see­ing EV street ma­chines!

CUR­RENT MAT­TERS

NEED­LESS to say, build­ing an EV is com­pletely dif­fer­ent to build­ing a car with a reg­u­lar in­ter­nal com­bus­tion en­gine, but there plenty of rules to guide EV builders down the right path.

Most EVS will be haz­ardous volt­age (HAZV) rated, which means they will op­er­ate above 60V DC; this is nec­es­sary to get higher power lev­els. Con­versely, ex­tra-low volt­age (ELV) ve­hi­cles op­er­ate below 60V DC. Most will use bat­ter­ies with non-spill­able liq­uids and with­out dis­charge gas (e.g. lithium or NIMH) so that full seal­ing of the bat­tery com­part­ment can be avoided.

EV bat­ter­ies are heavy, so they have to be re­strained. The mount­ings must be able to with­stand a 20 g-force frontal im­pact, 15 g side im­pact, 10 g from the rear and a ver­ti­cal rollover im­pact of 10 g. For this rea­son, it is ad­vis­able to mount bat­ter­ies in a coun­ter­sunk tray within the ve­hi­cle. There must also be an im­pact­sens­ing g-force switch to cut trac­tion power in an ac­ci­dent.

Bat­tery com­part­ments must have hazard mark­ing; the size of these warn­ing la­bels is dic­tated in the Code. Com­part­ments must be suit­ably sealed and can only be opened with the use of a tool.

All wiring con­nected to the HAZV bat­tery pack must be orange, whether it is pos­i­tive or neg­a­tive and re­gard­less of if it is con­tained within orange con­duit. It is ac­cept­able to have a short amount of red or black heat shrink at each ca­ble end to mark po­lar­ity. There must be no ground ter­mi­na­tions in the HAZV bat­tery-pack wiring.

The 12V loom within such EVS can have nor­mal colour cod­ing. For ELV ve­hi­cles, stan­dard wiring codes ap­ply. In HAZV ve­hi­cles, no con­tact must be pos­si­ble with the bat­tery pack wiring; such wiring should be out­side the pas­sen­ger or load ar­eas.

The power-on process must be ac­ti­vated by a key that can­not be re­moved ex­cept when the ve­hi­cle is de­ac­ti­vated.

There must also be over-cur­rent pro­tec­tion; there is sub­stan­tial elec­tri­cal en­gi­neer­ing around this point that will need to be con­sid­ered. Bat­tery con­di­tion mon­i­tor­ing is also re­quired.

If safety equip­ment such as lights, brakes and wind­screen wipers use the same power source as the trac­tion mo­tor, these ser­vices must be sup­plied in pref­er­ence to the trac­tion cir­cuit. The de­sign of any an­cil­lary equip­ment sup­ply should be such that sat­is­fac­tory op­er­a­tion of all equip­ment, par­tic­u­larly brake lights and head­lights, is avail­able through­out the dis­charge cy­cle of the trac­tion bat­ter­ies. This is log­i­cal!

Ve­hi­cles not fit­ted with a con­ven­tional gear­box must have a two-ac­tion switch (such as a tog­gle switch with­out a cover) to move be­tween for­ward and re­verse func­tions. The ve­hi­cle must also be con­fig­ured so that trac­tion can­not be en­gaged dur­ing the charg­ing process.

As you can see, there’s a lot to think about, and I’ve only hit the high­lights here.

BY DE­SIGN

THE de­sign of the EV it­self also re­quires plenty of for­ward plan­ning. Bat­ter­ies are heavy, so the chas­sis and sus­pen­sion must be able to carry the load. The dis­tri­bu­tion of the cells is also im­por­tant for the dy­namic be­hav­iour of the ve­hi­cle. Bat­ter­ies are normally mounted low in the floor­pan area to keep the cen­tre of grav­ity as low as pos­si­ble and within the wheelbase to min­imise po­lar in­er­tia.

Con­ven­tional brakes are usu­ally used, and they have a vac­uum booster, so EVS need a vac­uum pump to make the sys­tem work. Any other vac­u­um­op­er­ated func­tions also need to be con­nected.

Power steer­ing and air con­di­tion­ing ei­ther need to be con­verted to elec­tric op­er­a­tion or driven off the main elec­tric drive mo­tor as aux­il­iaries.

EVS are qui­eter than ‘nor­mal’ ve­hi­cles, so they may need rev­ers­ing beep­ers, prox­im­ity sen­sors and closed-cir­cuit cam­era sys­tems to min­imise pedes­trian risk.

RANGE ANX­I­ETY

PEO­PLE for­get that most daily driv­ing is over short dis­tances, with park­ing time (and there­fore charg­ing time) in be­tween trips. So EV bat­tery packs should be suited to this daily range, plus a bit to spare.

How­ever, most peo­ple who buy an EV are still look­ing for very high range like they are used to with petrol ve­hi­cles. As a re­sult, most EV car man­u­fac­tur­ers are putting in very big bat­tery packs to ac­com­mo­date cus­tomers’ wishes.

Builders and mod­i­fiers should there­fore con­sider this as­pect care­fully to get the best bal­ance be­tween power and range. Lack of charg­ing in­fra­struc­ture is the main cause for con­cern, but this will im­prove with time, and can be dealt with through per­sonal in­ge­nu­ity. For ex­am­ple, my first EV client can fully charge by so­lar (free) in two hours, from a pub­lic charge point in two hours, or from a wall socket in eight hours.

Take a look at the Nis­san Leaf, the high­est­selling EV around the globe. It only has a 270km range, but that’s plenty for most peo­ple who have no am­bi­tion to drive non-stop from Syd­ney to Bris­bane. It does 0-100km/h in 7.3 sec­onds, with 110kw and 320Nm of torque from zero. It uses 14.5kwh/100km, which equates to $3.86 per 100km, based on an av­er­age tar­iff rate of 28.6 cents/kwh. In rel­a­tive terms of petrol priced at $1.50 a litre, this would trans­late to a fru­gal 2.6L/100km.

BACK TO THE FU­TURE

NOW let’s re­cap what we’ve learned and how you can use it in the fu­ture. We know the rules in­volved, and like any street ma­chine, we need a fully formed con­cept of what an EV can be and how we can use the rules to our ad­van­tage.

My trike client towed his project at 100km/h to my place in Bris­bane from the Mackay re­gion, be­hind a Toy­ota Hilux that he con­verted to elec­tric drive in 2007. The Hilux used ba­sic com­po­nents he sourced around the world. He es­ti­mates he has saved $40,000 since then in fuel, us­ing so­lar charg­ing and free charg­ing sta­tions along the Queens­land coast. On the trip to see me, he could use the trike bat­tery pack con­nected from the trailer if he needed more range in the Hilux, and if all else failed, he had a petrol gen­er­a­tor in the tray!

His uni­tary-con­struc­tion trike used a fi­bre­glass body with an in­de­pen­dent front end and a swingarm rear sus­pen­sion, with two axle-mounted elec­tric mo­tors. We checked body strength, com­po­nent strength, safety fea­tures and code com­pli­ance for the elec­tric drive, and did a lanechange and sim­u­lated brake test. We didn’t bother with a noise test. Ev­ery­thing passed, so my first EV ex­pe­ri­ence was good. I ad­mired the in­ge­nu­ity of my client and his EV R&D. Now I have two new cus­tomers who want to take all the gear out of Tes­las and put it un­der ve­hi­cles that will sur­prise.

I’m a ded­i­cated old-school petrol­head, but I’ll still get ex­cited when the first elec­tric street ma­chine creeps silently into the Top 60 Hall at Sum­mer­nats with a 350kw mo­tor! It might also fea­ture 800V elec­tri­cal ar­chi­tec­ture with the abil­ity to recharge in just 15 min­utes, like Porsche has de­vel­oped.

See you on Elec­tric Av­enue!

The elec­tric Hilux tow ve­hi­cle at a charge point

The Hilux’s 48-cell bat­tery pack, mounted un­der the tray The elec­tric Hilux’s en­gine bay. Cen­tre: EV mo­tor con­nected to a stan­dard gear­box. Top left: vac­uum pump box. Bot­tom right: stan­dard bat­tery for nor­mal func­tions. Mid-right: con­troller. Mid-left: bat­tery man­age­ment LEFT: The ICV trike’s 48-cell bat­tery com­part­ments with the cov­ers off BELOW: The trike at the test track for the lane-change test

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