# Question on Electric Vehicle speed control

I have a very limited knowledge on Automobiles. Now, Imagine a ICE car on a straight road at constant speed. Suppose the engine rpm is 1000. Suddenly the car has to climb a steep hill. Now the driver does not change the accelerator or the gear. The vehicle speed and engine rpm naturally lowers and inorder to increase speed one has to increase throttle.

Let's put this on an electric car. Do you have to hit accelerator to increase speed? Or the closed loop control of the motor automatically adjusts the motor rpm?

• Can you define what you mean by throttle in both types of car. Many ICE cars don't have a literal throttle mechanism. Commented Jan 14, 2020 at 14:31
• I am sorry I meant the accelerator
– User
Commented Jan 14, 2020 at 14:33
• Irrespective of hill or not, you will have to hit the accelerator to increase speed at any time. Commented Jan 14, 2020 at 16:37
• @SteveMatthewas Uhmm...It is a well known fact. It does not answer the question.
– User
Commented Jan 14, 2020 at 17:04
• Set the cruise control and you will see it increase the power output to keep the speed constant until you run out of power... Commented Jan 14, 2020 at 18:02

There isn't going to be a definitive answer to this, since, as you suggest, the behavior is entirely down to the programming of the control loop. You wouldn't want to have the speed directly tied to accelerator position, since the driver would have very poor control over how fast you'd change speed, resulting in jerky acceleration, so typically there's a load component in the demand signal to the loop such that it will respond in exactly the same way that an ICE car would. Since it's entirely down to programming, it's possible to have multiple throttle responses programmed in e.g. for sport or economy modes.

Typically it is constant power for constant accelerator depression. The torque is power divided by speed, so once the speed becomes lower, torque is going to increase. So, if you press the accelerator with constant depression, the speed is going to adapt to the grade of the hill.

At least that's the case on my RAV4 which is not fully electric but rather a hybrid electric vehicle. I assume Teslas etc. work in a similar way, but do not yet own a Tesla.

• My e-Golf behaves the same way. The accelerator "selects" a certain engine power as shown on the power meter (adjustable though various modes and regen settings), and that power is then held constant.
– towe
Commented Jan 15, 2020 at 14:47

If the accelerator pedal became a speed pedal as I believe you are asking, I would imagine that driving could become a bit uncomfortable. If you pressed a little harder on the pedal to increase your speed, the car wouldn’t know how quickly you wanted to accelerate to that speed and therefore could by default try to reach your selected speed as quickly as it could, accompanied by being pushed back hard in your seat. If the default acceleration was a bit more graceful, how would you then indicate that you wanted to accelerate more quickly to the selected speed?

• So accelerator pedal normally only sets the level of acceleration and not the speed.?
– User
Commented Jan 15, 2020 at 2:00

## It's going to slow down

I mean, it could be set up any way you please to configure it. The motor controller treats the accelerator rheostat as a "call" to do something. It could mean

• A particular amount of motor current (amps).
• A particular amount of power (V x A)
• Something complicated to make the EV drive feel more car-like, or to improve handling characteristics.
• A constant motor speed (which would translate to vehicle speed).

All of these would slow the car down upon reaching a hill, except the last one.

However, it wouldn't be the last one. That function would be the cruise control. Making the accelerator do that would be fatiguing to the driver, and make the accelerator pedal "jumpy" - a bad UX.