Merritt Morris - Writer | Jan. 20, 2023
When It Comes to Driving EVs, You’ll Need to Adapt
We outline several key differences to know about how EVs are designed and operated.
During a recent neighborhood picnic, my neighbor excitedly approached me to boast about his brand-new Rivian R1S, which was due to arrive any minute at the hands of his partner. They’d gotten in very early on the reservation list, and after years of waiting, they finally had their SUV. He marked off a parking space for its arrival and stated I had full rights to judge his partner’s self-proclaimed high-level parallel parking skills.
In my head, I knew what was coming. The R1S was the first electric vehicle either one had owned or regularly driven, so when I saw the forest green Rivian pull up, I wasn’t surprised to see it lurching and jerking while maneuvering into its parking spot. I got behind the wheel next, dug into the settings to confirm, then remarked that they were rather ambitious to jump headfirst into one-pedal driving right off the bat rather than stick with standard drive mode, which more closely mimicked internal combustion engine systems.
Learning How to Drive an EV
Aggressive regenerative and one-pedal drive modes are typically buried as choices in an EV’s settings menu. The experience of a vehicle decelerating at a high rate without touching the brake pedal (a setup unique to strong hybrids and most EVs) can be off-putting to unfamiliar drivers used to internal combustion propulsion and automatic transmissions. One-pedal mode will pull a vehicle to a complete stop and hold it there until the driver taps the accelerator pedal again—no brake pedal use required. There’s a learning curve to adapt to rolling out of the regenerative torque as vehicle speed decreases so as to not experience a jerking behavior when lifting the foot off the pedal.
Additionally, a fast on-off accelerator pedal application common in most gas-powered vehicles can cause an EV to act like a bucking bronco due to the near instantaneous torque supplied by the electric motors until the driver unlearns the habit. For most individuals it only takes a couple of days to adjust to a particular EV and its pedal mapping, but it can be difficult to compare the drivability from one all-electric vehicle to another for someone who hasn’t experienced one before.
In EVs, drive mode options often change the percentage of accelerator pedal travel applied in relation to the torque curve of the motor or motors. For instance, in an EV’s high-regeneration mode, a portion of the pedal angle when traveling with enough speed becomes reverse torque in essence, causing a braking effect. The tuning of this transition is up to the automaker, lending each vehicle’s high-regen mode a different feel.
What Makes EVs Different from One Another?
When comparing EV models, it’s worthwhile to focus on the comfort of the foot angle at the torque inflection point of the pedal travel, as it will feel the most natural when the foot sits in a position with good ankle mobility. It will make tight parking lot maneuverability more controllable, especially when you’re talking about a vehicle with four motors and 908 lb-ft of torque like the Rivian R1S. Regen also tapers off from high to low speed, so drivers should evaluate where their ideal seating position rests their foot for easy regen braking control in both highway conditions and stop-and-go traffic.
When it comes to how EVs normally slow down, most use drive-by-wire braking systems that allow for blended braking, a way to cover for the occasional loss of regeneration energy that can also add a level of control to the vehicle’s high-regen drive modes. For instance, when an EV has a fully charged battery, its ability to take on any further input current is limited. In this condition, its regen braking may be reduced, which can lead to varying levels of brake pedal feel for the driver. Other EVs use the capability of braking actuation without the need for driver pedal input, so the brakes take over when full regen isn’t available to still apply the same stopping torque to the wheels. Regen issues can also be a factor in cold weather climates. If consistent vehicle behavior is desired in all temperature conditions, drivers in areas that see frigid temperatures should note whether an EV’s brakes are blended.
Frequent snowy streets also usually come with the territory in regions with sub-zero temperatures. When driving an EV in the snow, consistent vehicle deceleration behavior when a driver takes their foot off the accelerator pedal also helps it handle more predictably. An EV in a high regen setting can easily become upset if a driver suddenly steps their foot off the accelerator pedal with too much input in the steering wheel. In this instance, stability and traction control interventions will pull out regenerative torque and balance the vehicle with strategic brake actuation at each wheel that needs it, depending on
the system.
Making an EV Feel More Like a Traditional Car
Due to their higher weight, instability in EVs can occur when high regenerative braking causes a sudden shift of a vehicle’s mass towards the front of the vehicle when a driver removes their foot from the accelerator pedal. On the flip side, the low center of gravity found in EVs due to the location of most battery packs helps fight front-end dive and aids in overall vehicle stability. Regardless, the weight and placement of an EV’s battery pack have added new challenges for vehicle dynamics engineers to tackle.
Fast on-off accelerator pedal events not only need to be addressed in suspension response but can also lead to reverberations through the driveline. In an EV, oscillations through driveline components can be especially pronounced since the wheels are more directly connected to the drive motor shaft. The high torque output of electric motors leads to a torsional wind up through the motor shaft, gear shafts, and axle shafts. Internal combustion vehicles have flywheel dampers and torque converters within their transmissions to combat the shuttering and clunking effect of torque fluctuations. Developers of electric vehicle controls specifically target the tuning of a vehicle’s driveline response to minimize such negative effects.
A favorite test among engineers is to evaluate an EV in stop-and-go maneuvers on a steep driveway grade. The steep grade increases the torque required to move a vehicle from a stop, and such increased initial command torque requests can result in a more pronounced overshoot in oscillation control. A quiet and smooth ride means the controls are well adjusted. When the tune is not quite in sync, the gearbox may bump and shudder. Events like low-speed driving over speed bumps can also be jarring without good driveline damping. The joy of instantaneous high torque in an EV does not have to come with a literal kick in the pants every time the pedal hits the floor.
Even with all the potential control methods and drive mode possibilities that EV powertrains allow, they don’t have to feel different from a typical internal combustion vehicle with an automatic transmission. The standard drive mode in some EVs features creep torque to maintain the typical forward motion that occurs with an automatic transmission when the brake pedal is released. Creep torque aids in the navigation of tight spaces and reverse maneuvering. Standard mode also typically tunes in some regenerative braking to achieve a similar level of vehicle deceleration compared to internal combustion engine driveline drag. It is a design to keep EVs feeling familiar. It makes swapping between vehicles with different propulsion systems comfortable and easy. Driving an EV can be a customizable experience, as my neighbors with the Rivian are finding out, so it’s best to evaluate all the features and not just stick with the standard modes. It might be surprising how quickly the body can adjust.
When it comes to vehicle replacement parts, there are two camps of people who will argue ad nauseum on the internet. One side believes original equipment manufacturer (OEM) parts direct from the automaker are the only way to go. The other thinks aftermarket parts are the more sensible option―one that doesn’t come with a premium tacked on to cover the cost of the satellite TV and Keurig coffee machine in the dealership service department lounge.
Both arguments have their merits, but the OEM part is the design intent and fully validated component, which spent months undergoing robustness testing and other validation before being released to production. That kind of rigor adds cost to a part. But no matter what side of the debate you’re on, it’s one that will potentially come to an end with the rise of fully autonomous vehicles. Because as vehicles begin to drive us, today’s traditional vehicle ownership model will almost assuredly become a thing of the past.
Merritt Morris - Writer
Tim Marrs - illustrations | Nov 4, 2022
Why You Won’t Own an Autonomous Car
The challenges of a self-driving future will put a huge emphasis on vehicle safety and stability, possibly meaning an end to today’s ownership model.
Traditionally, an individual’s choice about how they maintain their vehicle has only impacted themselves or those who directly interact with it. For example, they might find that although an aftermarket alternator won’t last as long as the original, the economics make sense because multiple aftermarket alternators could be purchased for the price of one OEM replacement. By the time the car needs another, it will be on to a second owner anyway.
But what happens when a vehicle is heavily automated or Level 5 fully autonomous? Will a vehicle owner get to make their own decisions about replacement options for safety-critical sensors? Specifications for cameras alone can vary wildly. Latency, field of view, vibration resistance and UV resistance are properties specific to an application and mounting location. Autonomous systems will rely on the fact that the components within the system have well-defined performance characteristics for the intended vehicle life span. Replacement with an off-the-shelf component won’t ensure optimum vehicle performance and could potentially lead to catastrophic consequences.
Validation testing for vehicle manufacturers and component suppliers takes many months and involves the passing of accelerated durability life tests with statistical significance, along with numerous individual tests to address environmental risks and system interactions. The higher the risk factor of any component failure or feature degradation, the more extensive the testing necessary from the individual component level up to the full vehicle before it is released into production.
Systems related to vehicle autonomy are carefully calibrated through life conditions as a sensor and vehicle feature package. If elements of a vehicle’s characteristics change, such as, say, a tire’s rolling radius or a brake pad’s friction surface, it can throw off the programmed parameters of those various control systems.
Freedom of Choice Will Come With Consequences
“Right to Repair” adds another complicating factor, which should also prompt an increased shift away from the traditional vehicle ownership model as levels of automation increase. From laptops to tractors, the right to repair has pushed manufacturers to be more open with diagnostic tools, software updates, and independent mechanic servicing. Mainstream automakers have continually made arguments against providing open systems, stating that maintaining explicit control is safety-critical.
Safety-critical components and systems are those that ensure occupant safety as well as operational safety and regulatory compliance. Failures or abnormalities within a safety-critical system require a vehicle to have measures such as redundant backups, operator warnings, restrictions to limited performance ranges, etc. Any potential design flaw related to safety-critical systems can also lead to extremely costly recall campaigns, such as the Takata airbag fiasco, which impacted numerous manufacturers and tragically led to the loss of lives. Even OEM and related parts can and will fail, despite all of the testing that goes into them.
The risk of compromising a safety-critical function of an autonomous vehicle—and the potential consequences—should turn off many shade-tree mechanics. The burden will fall on the OEMs to be responsible for service training, deployment, and necessary preventative maintenance campaigns.
Safety Is Too Critical to
Leave to Others
When comparing EV models, it’s worthwhile to focus on the comfort of the foot angle at the torque inflection point of the pedal travel, as it will feel the most natural when the foot sits in a position with good ankle mobility. It will make tight parking lot maneuverability more controllable, especially when you’re talking about a vehicle with four motors and 908 lb-ft of torque like the Rivian R1S. Regen also tapers off from high to low speed, so drivers should evaluate where their ideal seating position rests their foot for easy regen braking control in both highway conditions and stop-and-go traffic.
When it comes to how EVs normally slow down, most use drive-by-wire braking systems that allow for blended braking, a way to cover for the occasional loss of regeneration energy that can also add a level of control to the vehicle’s high-regen drive modes. For instance, when an EV has a fully charged battery, its ability to take on any further input current is limited. In this condition, its regen braking may be reduced, which can lead to varying levels of brake pedal feel for the driver. Other EVs use the capability of braking actuation without the need for driver pedal input, so the brakes take over when full regen isn’t available to still apply the same stopping torque to the wheels. Regen issues can also be a factor in cold weather climates. If consistent vehicle behavior is desired in all temperature conditions, drivers in areas that see frigid temperatures should note whether an EV’s brakes are blended.
Frequent snowy streets also usually come with the territory in regions with sub-zero temperatures. When driving an EV in the snow, consistent vehicle deceleration behavior when a driver takes their foot off the accelerator pedal also helps it handle more predictably. An EV in a high regen setting can easily become upset if a driver suddenly steps their foot off the accelerator pedal with too much input in the steering wheel. In this instance, stability and traction control interventions will pull out regenerative torque and balance the vehicle with strategic brake actuation at each wheel that needs it, depending on
the system.
What Makes EVs Different from One Another?