Ultimate Diesel Builder's Guide - - Contents -

The In­side Scoop on GM’S Baby Diesel

We Get Gory De­tails About GM’S Lat­est North Amer­i­can Diesel En­gine

We weren’t ex­pect­ing a diesel an­nounce­ment from GM when in­vited to the press launch of the new GMC Ter­rain, but there it was—a new 1.6-liter, state-of-art diesel four-cylin­der. With some quick foot­work we were able to spend time with Mike Siegrist, As­sis­tant Chief En­gi­neer for North Amer­i­can diesel pas­sen­ger cars at General Mo­tors. You may remember him from our Cruze diesel story a cou­ple of years ago. When it deals with small diesels at GM, the buck stops at Mike’s desk.

Of course, we nor­mally are not all that ex­cited about small en­gines, but this pocket rocket packs a se­ri­ous punch for a light­weight with an Sae-cer­ti­fied 137 horse­power and 240 lb-ft of torque while pass­ing strin­gent new U.S. en­vi­ron­men­tal stan­dards. It was also re­cently an­nounced that when cou­pled with the 6-speed man­ual trans­mis­sion in the Cruze Diesel Sedan that it fea­tures an Epa-es­ti­mated 52 mpg high­way fuel econ­omy rat­ing, or 47 mpg when cou­pled with the new 9-speed au­to­matic (see side­bar be­low).

Since we had less than an hour our ques­tions were a bit rushed, and we may have missed some de­tails, but we now know a lot more about GM’S new “Whis­per Diesel” than we did be­fore. We are work­ing on bring­ing you a full re­view of the new Cruze Diesel Sedan as soon as we can; un­til then here’s a slightly edited tran­script of our ex­clu­sive in­ter­view.

UDBG: Mike, is this en­gine go­ing into all three ve­hi­cles, Ter­rain and its sib­ling Chevro­let Equinox as well as Cruze? Mike Siegrist: The en­gine that goes into Cruze is very sim­i­lar. The last generation had a 2.0-liter. The en­gine we’re talk­ing about now is a 1.6-liter that goes into Cruze, Equinox, and Ter­rain. The 2.0-liter en­gine in Cruze was only on sale for model years 2014 and 2015. It served its pur­pose. It la­beled at 46 mpg, bet­ter than any non-hy­brid in all North Amer­ica.

UDBG: Pre­tend we're com­pletely ignorant; tell us ev­ery­thing about this mo­tor, one we’ll be able to buy later this year. MS: Would you like to talk Tech first? This is a com­plex en­gi­neer­ing pro­ject to put into pro­duc­tion. Our (General Mo­tors) cen­ter of ex­per­tise for small diesel en­gines is in Torino, Italy. They do all the en­gine hard­ware as well as the (en­gine) con­troller and soft­ware. Then we bring that en­gine from Europe‚ and it is in a bunch of Euro­pean ap­pli­ca­tions I can share with you‚ and de­velop the prod­uct for North Amer­ica here in Michi­gan.

UDBG: What does that mean, what sauce do you add to the meat? MS: It means dy­namome­ter development, dura­bil­ity development on dy­namome­ters, cal­i­bra­tion and driv­abil­ity en­gi­neer­ing, and fi­nally in­te­gra­tion into the ve­hi­cles to­gether with our ve­hi­cle col­leagues. We do all that development here in North Amer­ica. It’s a part­ner­ship with the guys that are in Europe. The chief en­gi­neer for this pro­ject resided in Torino, Italy.

UDBG: Why do it that way, why add the ad­di­tional geo­graph­i­cal com­plex­ity? MS: We do it be­cause we in North Amer­ica are very well versed in re­quire­ments for North Amer­ica. We took an en­gine that ex­ists as a prod­uct for As­tra, In­signia, Zafira, Meriva, Mokka (all Opel ve­hi­cles), and in Korea Chevro­let Or­lando and Trax. So this same ba­sic en­gine is in pro­duc­tion in those re­gions. We take the base en­gine and de­velop it here, as the base re­quire­ments are dif­fer­ent.

There are three ba­sic stan­dards we have to meet in North Amer­ica that are dif­fer­ent. One is our emis­sions stan­dards are dif­fer­ent, and tougher. The cy­cles are a lot tougher. Sec­ond, we have the most ex­ten­sive di­ag­nos­tic rules in the world, dic­tated by the Cal­i­for­nia Air Re­sources Board. So di­ag­nos­tics are con­sid­er­ably dif­fer­ent from those of any other coun­try or re­gion.

Third, and the most im­por­tant to the cus­tomer, is the en­vi­ron­ment the prod­uct op­er­ates in. In North Amer­ica we have roads that are higher; I’ve driven many times to the top of Mt. Evans in Colorado’s Rocky Moun­tains at 14,300 feet. We drive at 130° F down into Death Val­ley and need to prop­erly drive the ve­hi­cle out! We also get colder than else­where and the en­gine has to start prop­erly; it’s all those en­vi­ron­men­tal con­di­tions that

we have to meet while meet­ing strict emis­sions stan­dards. They’re the most im­por­tant to our cus­tomers.

UDBG: So let’s do a walk around the en­gine! MS: The en­gine is a brand-new en­gine fam­ily. We de­signed it at our Torino fa­cil­ity from the ground up to be the lat­est in diesel tech­nol­ogy start­ing about seven years ago. It’s been in pro­duc­tion for about three years prior to its North Amer­i­can in­tro­duc­tion. It’s not a legacy from any­thing. Our development fo­cused on three things; one, great fuel econ­omy; two, very high power den­sity‚ be­ing pow­er­ful for a 1.6-liter mo­tor; third, of ut­most im­por­tance was its noise and vi­bra­tion char­ac­ter­is­tics. From the be­gin­ning, NVH was a fo­cus.

UDBG: Mike, doesn’t this en­gine have a solid rep­u­ta­tion in Europe? MS: The Euro­pean press has named this the “flus­tern” diesel, the whis­per diesel, be­cause it is the bench­mark for noise and vi­bra­tion char­ac­ter­is­tics for a small diesel en­gine. (That’s ver­sus Volk­swa­gen, Audi, Peu­geot, Ford, Fiat and oth­ers.) When you drive this in a Cruze, Ter­rain, or Equinox it is trans­par­ent to the ve­hi­cle, you al­most can­not de­tect that it is a diesel. Other than the fun part, the torque. The en­gine is SAE cer­ti­fied at 137 hp, 230 lb-ft, and the torque band­width is the fun part. It makes 219 lb-ft from 1,500-3,250 rpm, a large-big-wide torque band.

UDBG: May we have the nitty-gritty de­tails please? MS: The block is alu­minum with cast-in iron cylin­der lin­ers and an alu­minum bed­plate. The turbo is a Vari­able Ge­om­e­try Turbo-style; the scrolls shape the torque curve. If you were to have a fixed-scroll turbo the torque curve would look con­sid­er­ably dif­fer­ent than with VGT. You could shape that curve to fo­cus on torque or horse­power, not both. That’s the ad­van­tage we get from the Vgt-style turbo.

We have me­chan­i­cal solenoid in­jec­tors run­ning at 2,000 bar (29,000 psi—ed.). It’s a very so­phis­ti­cated in­jec­tion sys­tem, and we have a very ad­vanced com­bus­tion sys­tem.

UDBG: What do you mean by ad­vanced com­bus­tion? MS: Our com­bus­tion anal­y­sis, per­formed to op­ti­mize the burn process be­tween fuel econ­omy, emis­sions and power was a lot of work. Orig­i­nally, and from a de­sign stand­point, we wanted an en­gine that was very well bal­anced and was op­ti­mized for global re­quire­ments. To be able to use this en­gine in Korea, Europe or North Amer­ica, well, if you start with a poor com­bus­tion process it is not pos­si­ble to meet the emis­sions re­quire­ments we have (in North Amer­ica) or the fuel econ­omy. It took many com­puter sim­u­la­tions, many it­er­a­tions or rep­e­ti­tions in or­der to achieve this.

That’s a big state­ment. And of course most of the work was done in math­e­mat­i­cal anal­y­sis and sim­u­la­tion of com­bus­tion. We’re very good; I’d say the guy we have doing this is one of the best in the world, very very good.

UDBG: It’s said get­ting air in, air out is a key to every en­gine’s per­for­mance. What have you done here? MS: We have an in­take man­i­fold with vari­able swirl. Each cylin­der has two ports en­ter­ing the head, one open and one with a valve in it. We open or close the valve to cre­ate or re­duce mix­ture mo­tion. There’s a com­mon open/close shaft used to cre­ate the mix­ture mo­tion and change the com­bus­tion process. It looks just like a lit­tle throt­tle valve.

MS: Re­ally, for this en­gine it’s mostly swirl, not tum­ble. On a diesel you want great mix­ture mo­tion since when you in­ject the fuel, eight to ten times per com­bus­tion event, you need the mix­ture to have lots of mo­tion.

UDBG: 8-10 events? That’s a sur­prise! So we’re be­yond the previous lim­its of solenoid-driven elec­tro-me­chan­i­cal in­jec­tors at 4-6 events, into the realm of piezo­elec­tric in­jec­tors?

MS: Oh yeah! 8-10. This is part of what makes it re­ally quiet, too. That eight, or nine, or ten in­jec­tions per (com­bus­tion) event re­ally have a huge noise ben­e­fit. It’s dra­matic, and com­mon sense. If you get a big burst of fuel it’s a dra­matic event. Spread it out (es­sen­tially feed­ing the fire) and it’s quite dif­fer­ent.

UDBG: Wouldn’t the abil­ity to spread out the fuel give you great con­trol over the com­bus­tion event, and power? MS: It re­ally does. It helps to shape the torque process, the curve. For all the at­tributes we’re look­ing for we get more con­trol.

UDBG: The en­gine also has a unique fea­ture; where does the tim­ing go? MS: Un­like a small block, its ar­chi­tec­ture places the tim­ing at the rear, not the front. This makes it much qui­eter be­cause much of the tim­ing gear is en­cap­su­lated by the trans­mis­sion. It covers and ab­sorbs the noise.

There are lots of other de­tails that make it quiet. For ex­am­ple, the way we iso­late the oil sep­a­ra­tor on top of the cylin­der head with lit­tle stand­offs to cre­ate a gap be­tween the head and the sep­a­ra­tor. We have a molded foam piece that goes over the in­jec­tors that re­ally qui­ets them down‚ since they are a pretty big noise source. All of this leads the en­gine to be the “whis­per diesel.”


Swirl ver­sus tum­ble is a topic that of­ten comes up when dis­cussing com­bus­tion cham­bers and de­sign. They’re self-de­scrip­tive about the fuel-air mix­ture as it en­ters the com­bus­tion cham­ber.

UDBG: Any other de­tails we’ve missed? MS: Two other items I’ve not men­tioned. Remember the fuel econ­omy? Con­tribut­ing to that is the en­gine’s very low fric­tion. Pis­ton rings are de­signed to min­i­mize tan­gen­tial load­ing, yet we still use con­ven­tional cylin­der hon­ing. And we don’t use poly­mer-coated bear­ings. It’s got a two-step vari­able dis­place­ment oil pump. In ad­di­tion‚ it has oil squirters at the bot­tom of each pis­ton. We con­trol those when we need them—an­other fric­tion im­prove­ment. They are con­trolled by a sep­a­rate solenoid to a gal­ley in the lubri­ca­tion sys­tem that turns them on and off.

UDBG: So, alu­minum block, alu­minum bed­plate, any other ex­otic de­tails to share? MS: The rest is pretty stan­dard. Al­loy pistons, steel rods, steel crank­shaft and an 18:1 com­pres­sion ra­tio.

UDBG: Why alu­minum for the bed­plate? Is it ro­bust enough? MS: Oh, it is. Our an­a­lyt­i­cal tools for struc­tural anal­y­sis are so ca­pa­ble that we can lighten up the en­gine sig­nif­i­cantly and still have the same struc­tural in­tegrity.

UDBG: And for emis­sions? MS: It uses SCR, of course. DOC/DPF and par­tic­u­late trap, plus SCR. The re­fill in­ter­val for the sedan urea tank should be about 4,000 miles. Our tar­get for the SUV will be about 7,500 miles as it has larger ca­pac­ity.

UDBG: Ear­lier you men­tioned GM’S abil­ity to con­trol its own soft­ware for en­gine con­trol hard­ware. Any de­tails to share? MS: Yes. An­other very im­por­tant com­po­nent is that our con­trol sys­tem (ECU) is done in­ter­nally. We write all our own soft­ware whereas we used to pur­chase it. So we have great con­trol and it is com­mon among all our en­gines. Hav­ing in­ter­nal con­trol over soft­ware is a huge en­abler for de­vel­op­ing all the diesel prod­ucts in our port­fo­lio.

Chevro­let is be­com­ing the big­gest diesel en­gine brand in North Amer­ica with the Du­ra­max they’ve had for quite a while in the Sil­ver­ado. Then we came out with the first generation Cruze (2.0-liter), and now the Canyon and Colorado and their 2.8-liter XLDE, and now the sec­ond generation Cruze and Equinox and Ter­rain. When we’re de­vel­op­ing these prod­ucts, to have stan­dard work that we do this with is im­por­tant to our cal­i­bra­tions. UDBG

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