Generally, a hill start in a car with an automatic gearbox is easier because the vehicle controls the automatic clutch or torque converter. This allows the driver to move away at the optimum point simply by controlling the accelerator. Models fitted with electronic parking brakes ensure that all the driver has to do is begin the process of driving off on a hill is find the clutch's biting point and drive away.
The brake and hill start assist automatically disengaging at the same time. Some cars — Volkswagen Group vehicles in particular have a very effective system — feature an additional Auto Hold system for the brakes. By simply prodding firmly on the brake pedal when the driver comes to a standstill, the electronic parking brake — and consequently the hill-start assist — are automatically engaged. Electronic Control Unit ECU : This is the vehicle's embedded computer system that receives signals from the various sensors.
The ECU decides when the brakes need to be applied based on that input. The ECU can also calculate the traveling resistance, which is a function of the car's weight determined by the pressure sensors and the slope of the hill that the car is on determined by the angle sensors. Traveling resistance is used to calculate how much engine torque will be necessary to move the vehicle uphill. Brake actuator : An actuator is a device that converts an electrical signal into a physical movement. The brake actuator receives a signal from the ECU telling it to trigger the brakes.
It then activates brake valves, sending brake fluid to the brakes to hold the vehicle in place, which keeps it from rolling back down the hill.
In the case of a hybrid vehicle, the electric motor may be used in place of the brake to apply sufficient forward motion to the vehicle to keep it from rolling backward. Once the driver starts to accelerate, the torque sensors help the ECU to determine if the engine's torque is sufficient to overcome the traveling resistance already calculated by the ECU.
If it is, then the ECU sends a signal to the brake actuator telling it to turn off the brakes and let the car move. Ideally, the driver should be aware of none of this.
The release of the brakes should be so smooth that the driver is unaware that brake force was still being applied after the brake had been released. Only later will the driver realize that he or she never once had to worry that the vehicle was going to slide back down the hill and collide with the car behind it. Driving safety is rarely this painless.
Is the safety advantage supplied by hill-start control worth the extra cost of buying a car that comes equipped with it? We'll consider that question on the next page. The major benefits of hill-start control should be obvious. It makes driving easier in certain situations and it can promote driving safety, too. After all, nobody wants his or her car to roll backwards down a hill.
There are just too many possibilities for damage in that scenario. But hill-start control isn't just for the benefit of the driver of the car that that's equipped with the hill-start system. It's also for the benefit of the traffic behind it. For that reason, there may eventually come a day when all cars come with hill-start control and similar safety and regulatory devices as standard equipment simply as a matter of public safety.
Driving safety is important to everyone. Another way that hill-start control helps out is that it means less wear and tear on other parts of the car, such as the handbrake, that you might use to do the same job manually. And in a manual transmission-equipped car you don't have to ride the clutch when starting out on a hill, meaning there's less wear on the clutch.
And by preventing the car from rolling backwards, hill-start control puts less strain on the engine and drive train, which would otherwise have to counteract the backward momentum of the car in order to bring it up to speed. This feature can prevent rollback on an incline by holding the brakes while you switch between the brake and acceleration pedals. Some versions can also prevent your car from rolling forward on a decline. Sensors in the vehicle are used to detect when a vehicle is on an incline.
The hill start assist maintains the brake pressure for a set period of time as you switch from the brakes to the gas pedal. Once you press the accelerator, it releases the brake. In cars with manual transmission that have this feature, the hill start assist will also maintain brake pressure until the driver lets up on the clutch.
During this transition period, as the driver takes his foot off the brake pedal, the brake system releases the pressure applied to the wheels. So, the vehicle starts to descend again. This may prove dangerous in two ways. Firstly, it endangers the life of the people traveling in that particular car. Secondly, such a descending vehicle may strike the vehicle standing exactly at the back.
Hill start assist helps to avoid such a dangerous situation. This system resists the vehicle descend in such a situation.
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