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What is Electric Power Steering Rack and How it Works?

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An electric power steering rack with an intense thunderstorm background. It is a graphical play on the word "electric".
The whole automotive industry is moving towards electric power steering rack!

Electric power steering rack is a type of power assisted steering rack that uses electric current and electronics to make it easier for us to steer our car.

With virtually everything advancing towards digital and electric, so did our cars! It is one of the technology that have been gaining a lot of attention in the automotive world since early 2000’s.

Don’t get me wrong, the older technology – hydraulic power steering is still widely used on the road and I love my first generation Perodua Myvi the way it is.

But –

If you followed the automotive news in early 2010’s, you’ll see that majority of the car manufacturer have already started to adopt electric power steering due to the numerous benefits that it offers compared to the hydraulic power steering.

Soon enough, we’ll start to see every car equipped with this fancy new technology.

“The future is now.”

This article will give you a glimpse of the latest gadgets in our car steering system. We will be looking at…

What is electric power steering rack?

This is a electric power steering rack. Visually, you can also spot the electric motor attached to it.
This my friend, is an electric power steering rack. You can even see the electric motor attached to it.

Electric – power – steering rack. Let’s break it down one by one.

“Steering rack” is a set of rack and pinion gears that is connected to both front wheels. When we turn the steering wheel, the rack and pinion gears engage in a way that shifts the car wheels to the left or right, which steers the car.

“Power” is short for power assisted. It makes steering our car easier by providing additional support that help us turn the steering rack.

“Electric” refers to the fact that the steering rack uses electronics to provide the additional power.

And there we have it. All in all, electric power steering rack is just like any other steering rack, except that it provides additional power through the means of electric components.

If you are not familiar with how car steering system works, I highly recommend this article about How Car Steering Works. It describes car steering system from top to bottom (from how you turn the steering wheel to actually steering the car). It will help tremendously.

What are the components of a electric power steering rack?

Now that we have the foundation in place, let’s talk electric power steering.

Here are the four components of an electric power steering that a regular steering rack do not have.

Part #1: Engine Control Unit (ECU)

This is basically the brains of our electric power steering. It collects information from his fellow sensors, evaluate the situation and barks out orders to the other components.

Engine control unit is a series of green circuit board and a ton of tiny electrical components - very much like the board in our computers.
Engine Control Unit (ECU) is like a brain – it receives and interprets information.

Part #2: Sensors

These people are the scouts. They keep an eye on how we are driving and report it back to the mastermind (the ECU) so it can decide what action to take.

  • Torque Sensor – Tells how hard we are turning our steering wheel.
  • Steering Angle Sensor – Tells the current position of our steering wheel.
  • Vehicle Speed Sensor – Tells the speed of our car (Like the odometer).
The sensor is a tiny electrical component and each sensors are different in the way they look, and the parameters they monitor.
Sensors are great scouts. They monitors and feed the information to the ECU.


Image by Joao Paulo Chagas (CC BY 4.0).


Part #3: Motor

“HULK SMASH!” (Well in this case, it turns.)

This guy is the brawn of electric power steering. The only thing it knows how to do is provide turning power to a gear.

The ECU controls the motor.

Based from the inputs from the sensors, the ECU will make a decision and let the motor know how fast to turn and when to turn.

When the ECU tells it to turn, it turns.

Electric motor have a solenoid in the center, wrapped with wires and the entire thing rotates. The outer ring is a magnet.
The electric motor is the muscles. It help us turns our steering rack.


Animation by Abnormaal (CC BY-SA 3.0).


Part #4: Reduction Gear

Reduction gears are a set of gears that amplifies the torque.

In another words, it takes the turning power from the motor, and make it even stronger.

We call them reduction gear because it is a literally gear reduced in size.

When you turns a smaller gear, and use that smaller gear to drive a bigger gear, what happens? The bigger gear moves slower, but stronger. From there, the extra torque makes it easier for us to steer our heavy car.

Example 101 – Bikes have gears too!

If you are lucky enough to own a bicycle with adjustable gears, you’ll understand this better.

  • When you shift to a higher gear (gear multiplier), it’s harder to pedal but every revolution moves your bike a lot more.
  • When you shift to a lower gear (gear reduction), it becomes very easy to pedal but you have to pedal a lot more revolutions to get it moving.

This is exactly why we need to turn our steering wheel 2 revolutions to move our car wheels so little.

A reduction gear is just a larger gear connected to a smaller gear.
A reduction gear is essentially just a larger gear connected to a smaller gear.

How does electric power steering works?

It starts with the sensors. A car that runs on electric power steering comes with a steering angle sensor and torque sensor attached to the steering column, and a vehicle speed sensor attached to the transmission housing.

As we drive, each sensor monitors a specific parameter. For example,

  • Torque Sensor – Monitors how hard we are turning our steering wheel.
  • Steering Angle Sensor – Monitors the current position of our steering wheel.
  • Vehicle Speed Sensor – Monitors the speed of our car (Like the odometer).

Then, they constantly feedback these information back to the brain of our car – the Engine Control Unit (ECU). As the ECU receives the data, it starts to evaluate how much you are turning and how much power assist you would need – all within a split second.

If the ECU thinks you are doing fine and don’t need any power assist, life goes on.

But, if the ECU thinks you need power assist, it will send a current down to the motor.

The motor is just a straightforward DC current motor. When it receives a current, it starts to rotate. Subsequently, this moves a set of reduction gear attached to your steering column, which turns the steering column itself. This motion is what gives you the power assist. The steering wheel will start to feel lighter because the motor turns the steering wheel in the direction that you want to go.

Anyway, the steering column is connected to the pinion gear of our steering rack. When it rotates, the pinion gear turns and the steering rack moves left and right, which also moves the car tyres to the left or right. And I guess you know the rest of the story – the car turns!

So why are we going electric?

I’m sure you’ve noticed by now. Electric power steering and hydraulic power steering, they both do the same thing, which is to reduce the effort we need to steer our car.

So, why are we replacing hydraulic with electric power steering? Here are some of the advantages of electric power steering.

Pros #1: Improves fuel economy

A traditional hydraulic power steering uses a steering pump that is driven by an engine belt.

The moment you start your car engine, the steering pump starts running regardless whether you are turning the steering wheel or not.

This drains your car engine power, which means you get less bang for your petrol bill.

As opposed to the hydraulic power steering, an electric power steering only activate when necessary.

  • When you turn, the sensors tells the ECU that you need help turning the car. The ECU will then orders the motor to turn.
  • When you are not turning, the electric power steering parts will just stay put.

Yes, you do need more electric power from your battery and your car alternator now to keep these components powered up.

But cumulatively speaking, it’s a lot less wastage compared to the old hydraulic way!

An electric power steering improves the fuel economy by up to 2% compared to their hydraulic counterpart.

This is an old school poster. A tiny man drenched in oil stands in the middle while the other people stare at him angrily for wasting precious oil.
It’s bad for the environment, and our wallet.

Pros #2: No more leaks and no more topping up steering fluids!

Because electric power steering no longer requires hydraulic to provide the power assist, we can get rid of steering pump, hoses, and steering fluid altogether. This takes away one common power steering rack problem – fluid leaks!

Gone were the days that you have to top up steering fluids too.

Ah, isn’t life great now?

Replacing leaked fluid costs both time, money, and a lot of unnecessary headaches.


Image by Robert Couse-Baker (CC BY 2.0).


Pros #3: Programmability – Limitless potential

As an electronic and computer-controlled device, we are not limited by the nature of hydraulic systems.

Theoretically, we can use electronics to monitor everything and help us make well-informed decisions. If we don’t like a certain thing, we can fine tune them through programming.

Here are two examples of things that we have achieved with electric power steering: (i) Optimizing Torque Assist and (ii) Lane Keep Assist.

Optimizing Torque Assist.

When our car is stationary, it’s harder to steer and we could use extra torque assist. Unfortunately for us, we couldn’t get that from a hydraulic power steering.

Hydraulic power steering are powered by steering pump which depends on engine speed. When our car is stationary, our engine’s RPM will be low. With that being said, the steering pump gets lesser power and in turn, we get lesser torque assist.

As you can see, there is a mismatch between the torque assist output and the torque assist that we need.

But guess what?

Electric power steering can solve that. Just like a computer, electric power steering can be programmed to provide maximum assistance at engine idle speed.

This makes manoeuvering in and out of parking bays so much easier!

It also reduces steering assist when at we are driving fast, so the car is less likely to dart around than their hydraulic counterpart.

Lane Keep Assist.

A camera or laser recognises and monitor the road markings when we are driving.

They are acting as our third eyes.

As soon as we drift out of a lane, the system detects this and turn our steering wheel to bring the car back on track. Yes, it’s that magical. But, of course it’s still a bad idea to drink and drive.

As you can see, we leave nothing off to chance. We are able to “see” everything and we can control virtually everything with an electric power steering system.

If you would like to read more about this specific technology, here’s a quick and simple article on lane keeping assist system.

There is no doubt that we’re moving towards a digital era now.

Is electric power steering all unicorns and rainbows?

As much as I love electric power steering, it still have it’s own inherent flaws. Here’s a few examples.

Cons #1: Poor steering feedback.

Many who bought a car with electric power steering have commented that the steering doesn’t give feedback of the road as good as before.

For some people, car is not just about driving from Point A to Point B. It’s the thrill, the fun. And that includes feeling the sensation of the road being reflected onto your steering wheel. It used to be raw, natural and authentic. You can feel every on and off between the tyres and the road.

Now, it just feels… flat and robotic, and that takes the fun and emotions away. You feel as if the steering wheel is disconnected from the front tyre treads.

With an electric power steering system, you won’t be able to feel the road as good as before.

Cons #2: Electronics are not 100% fail-proof!

Remember what John Connor warned us in the Terminator movie?

“Don’t trust the robots!”

He’s almost right, electronics can fail us too.

In the event that the motor goes haywire, instead of assisting us, the motor can resists our steering effort.

Now that’s a really scary thought.

But luckily, there are fail-safe mechanism to prevent that from happening.

First of all, ECU will cut off power supply to the motor when any problem is detected. This avoid any kind of unwanted “assist” from the motor that do not assist, but resist your manual steering effort.

On top of that, our steering wheel is still mechanically connected to the steering rack. So even if the electronics are not working, we can still control and steer the car (although difficult).

Without the power assist, it can be very VERY difficult to steer the car. It can lead to a car accident depending on the strength and skill of the driver.

But you know what…

Some control is better than none, right?

Electronics still fails, and they are notoriously difficult to deal with.


Image by Binarysequence (CC BY-SA 3.0)


The Bottom Line

That is the A to Z you need to know about electric power steering.

So what do you think? Does your car have hydraulic or electric power steering? Which one do you prefer?

Let us know in the comment section below.

Until then, drive safe and drive smart!

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