What is hill hold control in cars?
Hill hold control refers to a driver assistance feature that prevents the car from rolling backwards on an incline or uphill road when driving the vehicle from a stationary position. Typically, when moving the car uphill from a standstill position, the car will roll back once you release the brake and clutch and step on the accelerator.
The problem becomes pronounced with inexperienced drivers. During such scenarios, the hill hold control or hill assist control applies the brakes for a brief period to provide that extra time required to move the vehicle. The system eliminates the chances of the car rolling backwards due to the inclination.
How hill assist control works
Hill assist control works with the help of several sensors onboard the vehicle. There are different ways to implement the technology. Here are the most common techniques used to implement hill start assist in cars.
1. Clutch detection
It is one of the most common methods that is predominantly used in manual gearbox cars.
As the name suggests, the system detects the application of clutch to engage hill start assist.
It is necessary to press the clutch pedal to start a manual transmission car. Doing so disengages the engine from the gearbox.
The car can roll freely when the clutch is engaged, as there is no engine braking.
When you accelerate the car, you have to disengage the brake and slowly release the clutch.
The car can roll backwards on an incline during that brief period of releasing the brake and clutch.
The system detects the application and release of the clutch pedal to activate hill hold control.
2. Incline detection
If the car is stopped at an incline, even with the engine running, it may roll back when you move the vehicle ahead.
In an incline detection system, a sensor measures the incline.
If the inclination is beyond a certain degree, it sends a signal to activate the hill assist control as the vehicle may start rolling due to the uphill surface.
One of the disadvantages of this system is that the hill start assist may activate at times when there is no need for it. For example, if the wheel dips into a pothole, there is no need for any driver assistance.
3. Engine torque detection
In this system, the sensors monitor the engine torque.
The sensor’s job is to detect whether the engine produces enough torque to propel the vehicle forward.
If there’s not enough torque, the car can roll backwards. During such situations, the hill start assist will be engaged.
The hill hold control will be disabled if the engine produces sufficient torque.
4. Brake detection
In this system, the sensors detect if the brakes are applied.
When the brakes are engaged, the sensors also monitor the brake force.
If there’s insufficient brake force to hold the car in place, the hill start assist will be activated.
5. Backward roll detection
As the name suggests, the system detects if the vehicle is rolling backwards through sensors.
When the vehicle starts rolling backwards due to insufficient brake force, the sensors send a signal to the ECU (Electronic Control Unit) to activate the hill hold control.
6. Forward roll detection
This system comes into the picture if you try to reverse the vehicle on an uphill road.
When you slot the reverse gear, the system understands that you are moving the vehicle backwards.
If the vehicle rolls forward when you release the brakes and clutch, the hill start assist will hold the brakes for a few seconds so that you can smoothly accelerate.
Hill start control components
Hill hold control makes use of several components to work seamlessly. In this section, let's look at the system's essential components.
Angle sensor: It detects the incline angle when the car is on an uphill road. In other words, it measures how steep the incline is.
Pressure sensor: It is a sensor that measures the vehicle's weight, including the weight of the occupants and cargo. The sensor is part of the suspension system. The sensor works by producing an electrical signal that is proportional to the vehicle's weight.
Torque sensor: It detects how much torque the wheels receive from the drivetrain. Torque is responsible for propelling the vehicle. Hence, it's one of the crucial components of the system.
Wheel-speed sensor: It monitors the wheels' speed and direction of rotation. It is typically installed on the vehicle's axles.
Brake actuator: It's an actuator device that receives a signal from the ECU to engage the brakes. Once the actuator gets a signal from the ECU, it activates the brake valves to engage the brakes. In a hybrid vehicle, the system may also use the electric motor to apply the stopping power to prevent the car from rolling backwards.
ECU (Electronic Control Unit): ECU can be referred to as the brain of a vehicle. It receives data from various sensors and controls the car's critical components. It also decides when to engage the hill hold assist after receiving information from the sensors. It can compute data like the vehicle's weight, rolling resistance, and inclination angle to decide whether to engage or disable hill hold control.
Benefits of hill-hold control
Here are the advantages of hill start assist in cars.
It makes driving easier in tricky situations, such as moving the car uphill. Hence, it creates a safe driving environment, especially for beginner drivers who drive a manual transmission car.
The hill hold control is helpful for the driver and other motorists on the road. The traffic behind your car will be safe as your vehicle will not roll backwards on an uphill road.
The hill assist system also reduces the wear and tear of specific components such as the handbrake, brakes, and clutch plates. Since the driver assistance system works efficiently, there will be no unnecessary load on certain car parts.
How do you use hill assist in a car?
To use hill start assist in your car, you need not follow any special procedure as the system functions automatically. Generally, the hill hold control will be an automatic function. However, some cars may have a button to toggle the system on or off. In that case, you may have to ensure that you switch on the system for it to work. Otherwise, it’s pretty straightforward, and you can continue driving as you normally do.
There’s a slight difference between driving a manual car and an automatic car with hill assist. The following section explains the same.
With a manual transmission
Here are the steps to drive your manual car with hill assist control while stopped on an incline.
Step 1: Press the brake pedal and engage the clutch simultaneously.
Step 2: Shift to 1st gear if the transmission is in the “Neutral” position.
Step 3: Lift off your foot from the brake pedal. Gradually release the clutch while accelerating steadily.
Step 4: With the hill hold control, the car shouldn’t roll back until you accelerate.
Manual cars with hill assist in India
Here are the manual cars that come with the hill hold control function in India.
Tata Nexon
Hyundai i20
Honda City
With an automatic transmission
Here are the steps you can follow if you drive an automatic transmission car.
Step 1: Press the brake pedal and start the car.
Step 2: Shift the gear knob to the “Drive” or D position.
Step 3: Release the brake and step on the accelerator to drive ahead.
Step 4: The car shouldn’t roll back until you accelerate, as the hill start assist will hold the brakes for a few seconds.
Automatic cars with hill assist in India
Here’s the list of automatic cars in India with hill hold control.
Maruti Suzuki Celerio
Maruti Suzuki Dzire
Maruti Suzuki Swift
Hyundai Venue
Maruti Suzuki Ertiga
How do you make a hill start going downhill?
To make a hill start going downhill, you can follow the same steps as for an uphill star;. the only difference is you need not apply too much throttle as the car will start rolling automatically due to the slope. Ensure that you are in the right gear. The engine braking will control the speed. There’s a lot less risk of stalling the car when going downhill, and it’s much easier than driving on an uphill road.
Does the hill-start assist work on every hill?
The hill start assist should work on every incline, provided the system is working correctly. However, in some extreme conditions, such as a very steep inclination, the hill hold control may fail to stop the vehicle from rolling back. But that may happen if the gradient is too extreme.
Is auto hold the same as hill start assist?
Auto hold and hill start assist are two different safety features in a car. As far as hill hold control is concerned, it will hold the brakes for only a few seconds. Once you release the brake and clutch, you only have a few seconds to accelerate before the brake releases.
On the other hand, the auto-hold function holds the brake automatically for an unlimited time. The auto-hold will release the brakes only when you step on the accelerator pedal.
