Six-speed automatics are standard transmissions on most cars and trucks, with 8-, 9-, and 10-speed options becoming increasingly common. When you add the complexity of continuously variable transmissions (CVT), dual-clutch transmissions (DCT), and specialty systems for electric vehicles; the options for getting power from a vehicle’s engines to its wheels are expanding.
That variety creates a challenge – how to make unfamiliar, fuel-efficient transmission systems feel comfortable to drivers. Several automakers have received customer complaints from powertrains that just don’t feel right. General Motors (GM) abandoned the CVT on the since-discontinued Saturn Vue because of service problems. Several reviewers criticized Nissan’s first-generation Murano crossover because of its CVT. More recently, Ford’s received numerous complaints and even a lawsuit because of the DCT used in its Fiesta subcompact and Focus compact cars. At lower speeds, the transmission can jump rapidly between gears, causing the cars to sputter and jerk.
Paul Goossens, vice president of engineering solutions at Maplesoft, a provider of software tools for engineering, science, and mathematics, says the key to avoiding such complaints is using digital simulation tools to predict how engine-transmission combinations will operate in hundreds of real-world driving scenarios. A software supplier to automakers and transmission suppliers such as Japan’s Aisin Seiki, Maplesoft found its niche in recent years by mapping out shift patterns that engineers can use to program transmission controllers. Goossens recently sat down with Today’s Motor Vehicles to discuss the importance of simulation and the advances in that technology.
Today’s Motor Vehicles: How do engineers use MapleSim software?
Paul Goossens: It’s a way to allow designers to get a sense of if their design is going to work, from a dynamics perspective. Is this powertrain, with this engine and transmission, going into this vehicle’s chassis, taking it through its required drive cycles – is that going to fulfill the design goals of this project?
You gain a lot of insight on how all of the various subsystems interact with each other. We don’t go into the details of finite-element analysis (FEA), but our tools can visualize what’s going on in the system at a higher level.
TMV: Do engineers use it throughout the powertrain design process?
PG: Our software is primarily used for transmission modeling. Engine modeling tends to be a domain unto itself. There are some deeply entrenched tools in that market. But we can take the results from those analyses to create a torque speed map to simulate driveline performance.
In the transmission, we can simulate everything from setting gear ratios for normal operation to a very detailed mechanical/hydraulic model to study gear-to-gear shifts.
The control engineers can develop the control codes for the transmission control unit (TCU) based on those simulations and can then test the TCU against the virtual representative simulation in a hardware-in-the-loop scenario.
TMV: With that data, do engineers often redesign mechanical systems?
PG: In the initial design stages, the use of our tools for early design verification does help to identify inherent design issues that can be fed back to the designers.
Once you get to the prototype or late-stage development, design issues are a lot more expensive to address. Where we see minor anomalies in performance, the fix is typically in the control algorithms for the gear shifts.
TMV: Do you have an example of a company changing controls instead of redesigning a mechanical system?
PG: I do, but not from the automotive market. We have a manufacturing-machine customer that was having a problem with a system. At the design level, and in factory testing, the machine was working perfectly, but on the production line, the motors kept burning out.
When they used our simulation tools, they identified some massive transient spikes in the load on the motor, due to the complex tasks the machines were performing. They could have addressed that by adding a bigger motor, requiring them to retrofit every machine in use with a different design.
Instead, they adjusted the controller speed-profile to slow the motor down a slightly when those transient spikes came, and that solved the problem. Instead of major retrofits, they simply updated the control software, and the machines have been working reliably since.
TMV: Some of the current crop of advanced transmissions have had more customer complaints. Why do you think that’s happening?
PG: You can lose sight of the fact that you still have a driver behind the wheel of the vehicle. You may be providing the most optimal fuel efficiency, but it may not be the most comfortable ride. It’s those things that can get adjusted in the controls as you simulate each scenario.
CVTs are a great example of that. Everything in a CVT is handled by the controller. You’re trying to keep the engine running at its sweet spot, then use the gear ratios to get the vehicle to operate the way you want it to operate in terms of speed and torque. To a driver, used to the transmission running through a series of discrete gear-shifts, this can often feel somewhat alien or weird.
TMV: CVTs don’t have the traditional rpm run-up, followed by a gear shift that most drivers expect, so some designers have introduced artificial shift points to give them the feel of traditional transmissions.
PG: Those sorts of things can be easily tested in simulation, very early in the control-design process. The transmission is very important to how a car feels, so getting the controls right is critical to offering a comfortable driving experience.
TMV: Maplesoft has worked on several simulation projects for electric-car power transmissions. But the highest-profile electric cars on the market, Tesla’s Model S and Model X, don’t use geared transmissions, controlling power output entirely through the electric motors. Do you expect designers to adopt more-traditional transmission technologies in the future?
PG: The goal for a lot of electric vehicle designers is to keep the motor operating away from its saturation point. They can reduce the size of the motors if they can ensure that the operating load stays lower, and that gives them advantages in weight, energy efficiency, and cost.
We’ve been working with one Formula E electric vehicle racing team. They’re using their motors to the extreme. They typically have a 3- to 5-speed transmissions to maximize output. As electric vehicle technology advances, I think we’re going to see a lot of effort put into transmissions. Getting the right-sized electric motor is really important for efficiency, and transmission technology can really influence that.
About the author: Robert Schoenberger is the editor of TMV and can be reached at 216.393.0271 or firstname.lastname@example.org.