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Imagine a driving situation where you have stopped while moving up an inclined road and want to move uphill again. A few seconds are required to switch from the brake pedal to the accelerator pedal. As soon as you release the brake pedal, gravity does its job and the vehicle starts rolling backwards. Starting your car up a hill isn’t always easy.
Here’s a technology that has come to our rescue. It's called the Hill Start Assist System (HSA), and it holds the brake for a few seconds after the driver releases the brake pedal. In the meantime, the driver can switch between the brake and the gas pedals and move uphill without rolling backwards, sorry gravity! In short, the Hill Start Assist keeps the brake activated even after you release the brake pedal, but only in an uphill climb situation. Under normal driving conditions, prolonged brake activation shouldn’t happen. How does your car distinguish between normal driving and an uphill start condition? Let’s explore this intelligent controller in detail.
Let’s design a simple hill holding system using the fewest essential components.
Here, the driver wants to start his car on a hill. The driver has pressed the brake pedal sufficiently to hold it on the hill. A pressure sensor in the master cylinder measures the fluid pressure and transfers this data to the HSA controller; clearly, it’s an electronic system. This pressure value is important because this is the exact pressure the HSA has to maintain after the driver releases the brake pedal. Now things are easy; as soon as the driver releases his foot from the brake pedal, the HSA goes into action. Using electronic controllers, the HSA maintains the same pressure even when the foot is released. Now the driver presses the accelerator pedal. HSA detects the accelerator pedal pressing as well. At this time, the controller gives the order to gradually release the brake pressure.
This is a very simple system, but it can't distinguish between an inclined road and a plane road. It also doesn't know whether the driver wants to move uphill or downhill. It will continue the prolonged brake activation even if the vehicle starts on a plane road. This can lead to accidents. With such a simple system, the driver would have to activate the HSA manually only when he has to climb uphill. This is a tedious task.
Let’s improve this design so that the driver doesn’t have to operate a switch. A longitudinal acceleration sensor is also used in the design. The longitudinal acceleration sensor is used to estimate the road’s inclination. This sensor works based on the Hall effect. We can obtain the gear position information from another sensor called a transmission position sensor. With the road inclination and gear position information, the HSA can behave intelligently. Let’s see how.
Here’s a technology that has come to our rescue. It's called the Hill Start Assist System (HSA), and it holds the brake for a few seconds after the driver releases the brake pedal. In the meantime, the driver can switch between the brake and the gas pedals and move uphill without rolling backwards, sorry gravity! In short, the Hill Start Assist keeps the brake activated even after you release the brake pedal, but only in an uphill climb situation. Under normal driving conditions, prolonged brake activation shouldn’t happen. How does your car distinguish between normal driving and an uphill start condition? Let’s explore this intelligent controller in detail.
Let’s design a simple hill holding system using the fewest essential components.
Here, the driver wants to start his car on a hill. The driver has pressed the brake pedal sufficiently to hold it on the hill. A pressure sensor in the master cylinder measures the fluid pressure and transfers this data to the HSA controller; clearly, it’s an electronic system. This pressure value is important because this is the exact pressure the HSA has to maintain after the driver releases the brake pedal. Now things are easy; as soon as the driver releases his foot from the brake pedal, the HSA goes into action. Using electronic controllers, the HSA maintains the same pressure even when the foot is released. Now the driver presses the accelerator pedal. HSA detects the accelerator pedal pressing as well. At this time, the controller gives the order to gradually release the brake pressure.
This is a very simple system, but it can't distinguish between an inclined road and a plane road. It also doesn't know whether the driver wants to move uphill or downhill. It will continue the prolonged brake activation even if the vehicle starts on a plane road. This can lead to accidents. With such a simple system, the driver would have to activate the HSA manually only when he has to climb uphill. This is a tedious task.
Let’s improve this design so that the driver doesn’t have to operate a switch. A longitudinal acceleration sensor is also used in the design. The longitudinal acceleration sensor is used to estimate the road’s inclination. This sensor works based on the Hall effect. We can obtain the gear position information from another sensor called a transmission position sensor. With the road inclination and gear position information, the HSA can behave intelligently. Let’s see how.
If the inclination is more than a predetermined value and the vehicle is in drive mode, it activates the HSA, which means it will hold the brake like it did in the previous case. Here comes the interesting part. As the driver hits the acceleration pedal, the HSA doesn’t release the brake suddenly, but rather releases the brake proportional to the slope of the hill. The controller even calculates the rate of brake release based on the slope of the hill, which feels natural to the driver.
What we have seen in these examples are quite a basic model of the modern HSA. The actual HSA of the modern vehicles are far more complicated than these.
We saw how the HSA helps the driver in the uphill start condition. In addition to this common scenario, the HSA needs to work in one more scenario. Consider this situation: here, the driver wants to go in reverse when the vehicle is stopped on a downhill slope.
Moving in the reverse direction while going downhill is more difficult than moving forward while going uphill because in addition to the brake and acceleration pedal switching, you also need to consider the back view. Here, HSA will hold the brake for you while you look in the rearview mirror. HSA will hold the brake until you apply a specific level of pressure on the throttle pedal. When sufficient torque is generated, the HSA will be deactivated.
We have seen two scenarios in which the HSA will be activated, but in the remaining two cases the HSA need not be activated. In short, the HSA will help you when gravity is working against your wishes. See you soon with another video. Thank you!
What we have seen in these examples are quite a basic model of the modern HSA. The actual HSA of the modern vehicles are far more complicated than these.
We saw how the HSA helps the driver in the uphill start condition. In addition to this common scenario, the HSA needs to work in one more scenario. Consider this situation: here, the driver wants to go in reverse when the vehicle is stopped on a downhill slope.
Moving in the reverse direction while going downhill is more difficult than moving forward while going uphill because in addition to the brake and acceleration pedal switching, you also need to consider the back view. Here, HSA will hold the brake for you while you look in the rearview mirror. HSA will hold the brake until you apply a specific level of pressure on the throttle pedal. When sufficient torque is generated, the HSA will be deactivated.
We have seen two scenarios in which the HSA will be activated, but in the remaining two cases the HSA need not be activated. In short, the HSA will help you when gravity is working against your wishes. See you soon with another video. Thank you!