Controlling GM’s electrified herd

  • 19-Feb-2016 10:48 EST
TimGrewe GM SAE Hybrids2016.JPG

Tim Grewe: “We’re not really hardware-limited or bandwidth-limited on our local area networks.”

As General Motors proliferates electrified powertrain applications among its brands, it is also rapidly commonizing those systems as much as possible. Witness the 2016 Chevrolet Volt and Malibu Hybrid; both systems were developed in parallel and share key design, engineering and certain component elements. And the 2017 Cadillac CT6 plug-in hybrid’s sophisticated propulsion system marries aspects of the latest Volt and those of GM’s earlier 2-Mode hybrid system. At the recent 2016 SAE Hybrid & EV Symposium in California, Automotive Engineering talked with Tim Grewe, GM’s Director of General Electrification, about the role of controls in the electrified vehicle space.

It seems that going forward it’s the controls, not hardware, that will separate a Volt from a Bolt from a CT6—and a Cadillac PHEV from a Mercedes or Audi.

Controls are fundamental to vehicle high performance and efficiency. And it’s truly multidisciplinary, getting engineers who normally don’t work together trading off the optimizations. If you take a classic control theory that’s engine-centric and just about BSFC (brake specific fuel consumption), that might not be so good because the motor control is less efficient in those operating points. You’ve got to tie them all together.

We’ve got about a dozen controllers, real time, on the same network with an optimizer and security processers running all the time. Consider all the linear transformations that we do in order to deliver the most efficient propulsion solution for a given driving moment. The controllers are communicating: What’s the best thing to do? How much regen did you get last time? Where’s the ‘free’ energy from that regen from the battery – oh, I don’t have enough energy from the battery from the last regen, so I want to leverage into an IC engine-type efficiency point. The controls make all that happen.

An ‘efficiency point’ meaning optimizing the powertrain so that it’s in the sweet spot of BSFC?

Yes. It’s one of those neat things where on the consumption chart of the engine, we’re on the BSFC ‘island’ and we want to use the electrification to stay there.

In terms of your hybrid system development teams, what sort of challenges are there now in bringing the formerly independent but now increasingly dependent domains together?

That’s my group’s role within Electrification. We’re very strong on the integration aspects. We have experts in the various component areas — motors, batteries, etc. — but it’s our job to do what’s best for the customer. So I have large teams working all those details. We’re not motor designers, but we know how to use motors. And we know how to talk to them [the motors] to say we’ve got ‘chuggle’ in EVT Low and we need to change something to get rid of the torque ripple—and we can’t dampen it out by slipping a clutch because that’s less efficient. So we find the root cause and fix it in the teeth of the motor’s stator! That’s what my team does - collaborate with the experts to make the best balance in the vehicle.

Now that GM is developing a new global electrical architecture, is this creating the need to rethink the electrical pathways and networks in vehicles going forward?

My perspective on it: We’re not really hardware-limited or bandwidth-limited on our local area networks. So while there’s a lot to do and a lot of communication, the bandwidth is there today and I don’t have problems with it. A lot of the strategy you have as to how you partition your controls and different controllers, though, enables that.

As in a multi-domain controller environment?

Yes. So while the engine controller is still doing all the optimization on the engine, there is a literal engine-to-hybrid-system, torque-based control method where we can still let them co-process and do all the heavy math and not load down the bus. We don’t have this mentality of one single controller in all the bus traffic; we distribute the processing. It’s very similar to the distributed-processing Internet stuff where you crunch all the math and only talk where you need to talk to each other.

So in order to make the hybrid functionality more seamless to the vehicle driver, you’re not overloading the CAN buses. Or looking for a technology to replace buses?

No. I’m not in trouble on any bus! In fact, what’s loading the bus is the customer-facing stuff—all the adaptive cruise control and other ADAS features. Right now we’re set. We’re just iterating and combining. The very natural thing you’ll see in the next-generation product is just more electrical and electronics integration. The parts are being reduced in size and are now getting small enough that I can still fit the APM and TPM [control modules] on the transaxle.

So just like we got rid of the big ugly orange high-voltage cables on the Gen-2 Volt, now we’re getting rid of the little orange cables to the APM. And that process of iterating and combining will continue along with Moore’s Law. As you know, the industry is converging on similar-sized batteries, similar power numbers, etc. The nice thing is, the converging is creating a focus on the technology - to make it as tiny as you can make it.

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