Difference Between Open Loop and Closed Loop Control Systems Explained

Imagine that you are just starting to learn how to drive a car for the first time. Your instructor/friend might have introduced you with basic and essential controls of the vehicles such as:

1. Accelerator or Gas Pedal

2. Brake

3. Clutch

4. Gear

5. Park Brake

6. Steering wheel

These controls are bare minimum of any vehicle to drive it.

Have you ever imagined how these small components are capable of driving the car smoothly?

These control levers/pedals are attached to further mechanisms which are further connected to end components such as

1. Accelerator with carburetor (for petrol vehicle) or a diesel pump (diesel vehicle)

2. Brake pedal with brake assembly

3. Clutch pedal with clutch assembly which connects or disconnects your vehicle driveline with engine's main shaft

4. Gear shift lever with gear assembly where it can provide different torques for different driving conditions

5. Park brake lever with parking brakes that when engaged can hold vehicle's real wheels and stops it from moving when standing in parking lot.

6. Steering wheel with front axle that helps us to navigate our vehicle on roads

   
   

All above parts have one pattern in common: -

a. Driver provides input to the pedal or shifter

b. Input is processed by respective mechanism

c. Processing mechanism controls the desired quantity. (Speed or Angle of vehicle movement)

If I try to summarize above actions in one diagram that shows the concepts behind conventional controlling of the vehicle, it can be:-

but, let's take it little further and see if such a diagram can be made specific for each control.

Similarly, these kinds of diagrams can be made for other components and i want you try that once at your own.

Here, the idea is not to tell you about these components but to actually realize that this kind of system is called an Open Loop Control System, where input given by driver converts to the output without keeping track of accuracy of output.

For example, if you are pushing gas pedal continuously but you are not looking at speedometer, this means you do not have an idea of actual speed of the car, and it may crash if you don't pay much attention to its speed.

A control system is always advised to be a Closed Loop Control System. You can see an updated diagram in below image: -

Again, I want you to explore more such closed loop systems for steering, clutch, and park brake for a better understanding.

Anyways, here starts the curiosity that what if there is a machine that provide the driver input on my behalf and also check the feedback (such as reading speed on speedometer) at the same time so that I remain free from constantly controlling my vehicle speed.

When engineers started to make such machines, they came up with innovations such as

• Adaptive Cruise Control - ACC

• Lane Keep Assist - LKA

• Automatic Emergency Braking - AEB etc.

Key Takeaways:

1. There are two types of control systems, Open and Closed

2. Open systems were used conventionally in almost all vehicles till now

3. Closed systems are more practical and amazing to use when we talk about ADAS