ORLANDO – The BRAKE Report recently sat down with Chris McCormick, chief engineer, brake design engineering at ZF’s Active Safety Division in Livonia, Mich. McCormick has worked with the ZF Group and its predecessor companies for more than 30 years in the brake engineering field. In his present role, he oversees all aspects of Foundation brake design engineering working with such products as the Colette caliper, the world’s leading caliper design with more than one billion in the field. This is the second part of the interview.
TBR –“One billion served,” so to speak, on a world-wide basis. How long has it taken ZF to achieve that, and are we talking just the U.S. or worldwide?
CM- When we talk about the typical Colette-type caliper, which is the most prolific caliper design in history, the number is probably well over a billion world-wide [since introduction in the mid-70s]. This caliper type is found on probably 80-90 percent of passenger car and light-truck applications.
Electric park brakes were introduced in 2002 and we’ve sold well over 100 million of them.
The electric park brake provides some interesting possibilities that you can’t do with a traditional parking brake. There’s no more hand-brake lever, there’s no more foot pedal, it’s just a button [to operate].
One interesting thing about EPB, electric park brake, is that in the U.S. we made the mistake of trying for the first couple years (while it took off in Europe first) to get customer brake engineers, the group we usually worked with, interested in it. They were saying: “I don’t get it; I don’t have any interest in this. It’s a parking brake; nobody here uses their parking brake – it just has to meet legal requirements. Why would I spend more time or money on an electric park brake?” And it was that way for a couple years; and from brake engineers’ perspective, they were right.
Later on, the vehicle chief engineers got wind of this product and said: “this has nothing to do with the parking brake, this has to do with getting rid of the parking-brake cables so we can make the HVAC ducts to the backseat bigger; getting rid of the handle and the pedal which are a challenge for crash performance, located where my customer would rather have another cupholder or two.” It was all about packaging.
And since it has software and electronics, you can get creative. So, if you have a manual transmission . . . there’s that hill with the traffic light at the top, and it turns red and you wish you had a third leg to operate the clutch and the brake and the gas. With the EPB, just pull the button and it holds you stationary on the hill. When the light turns green, just put it in gear and when it detects the throttle, you let out the clutch and the EPB releases as you pull away. It’s just brilliant. Engineers are creative when you allow them to use the software.
The EPB is also the emergency brake in addition to functioning as the parking brake. If your primary brake fails, you have that to slow you down controllably.
TBR-Are EPBs disc brakes or drum?
CM – You can do either, but they’re very predominately disc brake. There is a type of drum brake for parking called a Drum-In-Hat, and you can convert that to an eDrum-In-Hat by the addition of an electrical actuator. There are certain segments where a Drum-In-Hat still makes sense; maybe five-10 percent of the market. Most vehicles we work on have what’s often called motor-on-caliper EPB. There’s a caliper with a piston, and that piston is actuated hydraulically when you step on the brake pedal or electrically via the motor and gearbox for the parking function.
TBR – Where do you see the industry heading in terms of braking systems with all the other vehicle system changes?
CM – The first thing that’s happening right now is this migration to so-called one box or two-box systems. We refer to our one-box system as IBC – Integrated Brake Control. It was launched on a domestic pickup recently. Instead of vacuum, it uses a motor driven plunger that provides the boosted brake pressure to the calipers. This unit is the power source, so instead of a vacuum booster, it’s the motor. In addition, slip control is integrated into it so it’s at once the power source and the wheel-slip control unit.
TBR – Does that mean you can put it anywhere in the vehicle, away from the firewall? Does the driver press on the brake pedal to move a plunger (as in a traditional brake-system actuation)?
CM – The current product is mounted to the front of the dash with the brake pedal attached, similar to a conventional booster/master cylinder, but a remote mounted version may be possible in the future. The driver steps on the brake pedal, but all he’s really doing is pushing into a simulator with a sensor that provides the driver’s intent to the software control. There is a hydraulic connection, so if the [electric]boost part fails, the driver’s foot is connected hydraulically to the brakes. It’s called push-through mode. The driver can still stop the car, but it’s going take more pedal effort and/or a longer stopping distance – similar to today’s systems.
TBR – What do you see as the major challenges facing the braking industry and opportunities?
CM – Regarding opportunities, I think the one of the coolest things is [regenerative braking]. If you just zoom out and say, “All right, we’re engineers, how would we like to slow this car?”, you would never say, “let’s take 100 percent of the mv2 energy of a moving car, convert it to heat, and lose it to the atmosphere.” Instead, you’d want to recover as much of that energy as possible; so, turn the motor into a generator, recycle energy back to the battery, and extend the EV’s range. It’s a more elegant engineering solution.
TBR – To stay with this theme: regenerative braking is going to change the brake industry as autos gravitate to electrification. What impact do you think this will have on companies like ZF?
CM – We’re seeing that these changes are still taking shape, but because the battery can be full or in various states of charge, and due to power and torque considerations, you still need to retain the hydraulic friction brake to share the load with the regen braking. The piston sizes might not reduce much, since you still need the ability to generate a lot of clamp force if the regen system fails. But depending on the vehicle’s motor configuration, it’s possible for regen braking to provide most of the braking energy. So, you still need a big piston, but you could have thin pads and a thin disc because they’re doing less work and running at lower temperatures. There are a lot of discussions across the industry about the possibility that pads could last the lifetime of the vehicle, which has huge ramifications if you are an aftermarket friction supplier.
TBR – Does a ZF because of its global footprint have an advantage because you’d be developing region by region, so when the time comes here, say a much higher BEV penetration, you will already have worked on this for other regions?
CM – Sure. Market experience is always worth its weight in gold or however you want to say it, and deep experience in one region can greatly accelerate later adoption in other regions. By the time we started EPB projects in North America and China, we’d had dozens of launches and many years of experience in Europe. That European head start really boosted our growth in the other regions.
TBR – And the challenges for the future?
CM – As much as challenges, it’s opportunity and excitement.
There is a lot of change going on, with vacuum-less
and the march towards autonomous driving.
The move to autonomous will bring the most change, of course. But as ZF we have sensor technology, as well as braking and steering products in our portfolio in order to provide innovative system solutions.
Regen to me is a positive, emerging trend, with the brake and tire particulates discussion being a possible future catalyst. It’s happened before – for instance, the change to low- and no-copper pads over just a few years. With today’s tailpipe emissions so clean, tires and brakes are now the highest sources of auto emissions – so it’s not surprising that the focus there increases.
TBR – Are you working on finding solutions before it becomes law?
CM – Yes, and we know some technologies with potential. Some, like regen, or disc coatings & pad formulations with new tribology, aim to avoid generating particulates. Others, like vacuum and filter systems, aim to collect it for disposal. There’s also high focus on developing a global standard dynomometer test to measure and analyze particulates, to avoid that measurement differences inhibit progressing to solutions. Engineers are clever and we usually rise to the challenge and figure it out. It’s more exciting than challenging, I’d say.