How ADAS Systems Perform

How ADAS Systems Perform

When new technologies are applied to driver safety, a higher level of scrutiny and service is required.

New automotive technologies might work great when they roll off the dealer’s lots, but independent shops know that some technologies do not age well. It could be an LCD digital dash now blank or a variable valve timing actuator damaged internally due to a lack of oil changes. However, when new technologies are applied to driver safety, a higher level of scrutiny and service is required.

Automatic driver assistance systems (ADAS) have been on the market for almost two decades. ADAS was first used on luxury vehicles, and then many of the technologies found their way onto every vehicle in an automaker’s lineup. 

This proliferation of new technologies like lane keeping, blind spot detection and automatic emergency braking systems offer new levels of safety for the driver and new levels of frustration for shops. But, the thing to remember is that most of these systems require brakes and steering to be effective.

What do ABS and ESC have to do with ADAS?

ABS has been around since the 1980s. Early systems were called anti-lock braking and allowed the driver to maintain steering control while panic braking. Electronic stability control (ESC) also went by another name when it was first introduced – roll-over mitigation. This was because since people could now steer during a braking maneuver, rolling the vehicle became more common. Both technologies are now standard equipment.

Both ABS and ESC use the same module to carry out corrections, the ABS hydraulic control module, or HCU. This module has three parts: the electronic module, hydraulic modulator and pump. These three parts work together to control the braking at the four corners. Many ADAS features like lane keeping, automatic emergency braking and blind spot detection use the ABS HCU to make corrections.

What Sensors are Involved?

Both ABS and ESC use similar sensors. In the early days of ABS, the system was only concerned with wheel speeds and the pressure levels inside the hydraulic modulator. ESC sensors then started to look at not only the wheel speeds but also:

  • Steering angle
  • Lateral acceleration
  • Yaw
  • Brake pedal position

These sensors can tell the ESC system what the driver wants to do and what the vehicle is actually doing.  

Let’s examine what happens during an understeer condition where the wheel turns, but the vehicle travels in a straight line. The driver will continue increasing the steering angle, but the lack of traction keeps the vehicle straight.

The ESC computer sees the understeer event via the sensors long before the driver realizes it. The ESC computer also sees that the driver’s steering angle is greater than the actual path measured by the yaw and lateral accelerometers.

The ESC system intervenes to make the vehicle turn using the brakes. The first action might be to close the throttle to transfer weight to the front so the tires can gain traction. The next action might be to increase braking force on the inside front and/or outside rear tire to get the vehicle to rotate. All this time, the sensors are monitoring what the driver is doing and the effectiveness of the correction. This happens in nanoseconds.

Let’s say a steering position sensor gives a false reading of an extra 50° when the car travels in a straight line. The ESC might perform a correction by activating the brakes to get the yaw and steering angle to match the desired specifications. 

What happens if the vehicle is aligned and the steering angle sensor is not calibrated? The incorrect angle could mean the system might think it is experiencing an under- or over-steer condition. This may cause a false activation of the ESC system.

Another false activation scenario can be caused by an excessive thrust angle. The thrust angle is an imaginary line drawn perpendicular to the rear axle’s centerline. It compares the direction the rear axle is aimed at with the vehicle’s centerline. Excessive thrust angle can cause the vehicle to go down the road at an angle with the steering wheel turned to one side.

The ESC system can experience the effects of an excessive thrust angle but can’t see the thrust angle. The yaw sensor shows that the vehicle is not traveling in a straight line, and the accelerometers and the steering angle indicate that the driver might be trying to correct it. The accelerometers tell the system that nothing is happening.

The ESC system might read this as the rear end starting to step out, which could be interpreted as an oversteer. The ESC system might try to correct the condition by pulsing the inside rear brake.

ABS and ESC systems are essentially blind. They can sense what is occurring with vehicle dynamics and interpret the driver’s inputs. ADAS systems can sense what is happening outside the vehicle, like lane markings and other objects around the vehicle. ADAS does this using cameras, lasers and radar. The three systems control the vehicle’s dynamics and calculate an effective correction for the given circumstances and environment.

False activations can range from the automatic braking system stopping a vehicle when pulling out of a garage, to activating a lane-keeping system when the customer does not expect a warning or steering correction. The secret to resolving these complaints is to treat them like a drivability problem with a condition, cause and correction.

The condition caused by an ADAS activation might be completely normal. The correction might be a warning or the activation of the brakes or steering. The key to understanding the condition is to know the criteria for activation of the system. 

Many ADAS functions and corrections operate with a similar strategy as an emissions monitor. Like an oxygen sensor or misfire monitor, specific criteria must be met for the system to activate. 

The other keys to know are the ADAS outputs during a dangerous situation. For some early systems, it was just an audio or visual alert. Some newer systems will shake the driver’s seat to alert the driver. More advanced systems can build up brake pressure and apply the brakes if a collision is imminent. Some systems will take further steps with the steering and even close the windows.

Many ADAS features do not become active until the vehicle reaches a specific speed. Depending on the OEM, pre-collision systems might start working between 5-10 mph. Lane departure might not begin to work above 25 mph. The takeaway from this is that a test drive is required after calibration is performed. Simply pulling out of the bay and parking the vehicle in a spot will not allow the vehicle to activate or run a self-diagnosis routine.

Knowing the speed range limits of these systems is critical if you try to perform a dynamic calibration on the road or diagnose a concern. The logic behind most ADAS warnings or corrections is to examine the plausibility of the situation. For example, if the camera classifies an object as another vehicle, it will also use the radar sensor to confirm the vehicle’s path. If only one sensor detects an object, it might just decide the camera has made a false identification, and the plausibility that it is another vehicle is low.

Before you start a calibration procedure, you need to prepare the vehicle. Missing a step can cause the calibration process to be aborted or calibration to be off. In addition, something as simple as a weak battery can cause problems.

Inspecting the sensors and the vehicle for damage is the first step. Damage to the short- and long-range sensor behind the bumper covers or front air dam might not be seen during the initial inspection, but minor collisions can disturb the sensor and damage the mounting points. It could be from hitting a snowbank or parking block.

You might have to remove the bumper cover to inspect the sensor. The most common symptom is false or delayed activation of the system. If the front radar sensor is pointed up or down, it might detect another vehicle too late, and the correction might be more severe than expected. If the sensor is pointed too far left, it could think it is oncoming traffic in the vehicle’s path.

The other key inspection point is to look at the dash for any lights or messages. Never assume a check engine light is only for engine issues; many codes indicate a loss of communication with the different modules on the vehicle. ADAS systems communicate with many modules on the vehicle. Any problems with missing data could cause problems for ADAS calibrations. If the light is on, pull all the codes from the modules.

What is AEB?

There has been a lot of talk about automatic emergency braking systems (AEB). Starting in 2025, these systems will be mandatory for cars and trucks under 8,000 lbs. The National Highway Traffic Safety Administration (NHTSA) estimates that AEB will prevent 28,000 crashes and 12,000 injuries by next year. This is great for the new car buyer, but what about the car owner who needs to maintain the vehicle five or 10 years from now?

As sophisticated as AEB, ABS and ESC systems can be, they still require 60-year-old disc brake technology to work. This technology works great when the car rolls off the production line. But in the field, when the car is on its second or third pad slap with bargain parts, it is unclear how the AEB will perform.

Brake failure is easy to spot with the naked eye in the form of leaking brake fluid, glazed brake pads and a pedal that goes to the floor. What is difficult to identify by a technician, driver or crash investigator is a brake system that is compromised due to mechanical problems or low-quality parts.

Mechanical problems like worn friction material, seized guide pins or rotors below specifications won’t cause the vehicle to stop working and a driver might be able to nurse the brakes along until their next paycheck. But, during that one moment when they need the brakes to perform during a human or autonomous panic stop, it may take longer to brake. Even if the vehicle has ABS and AEB, the systems can’t compensate for bad brakes.

When a crash occurs, compromised brakes are hardly ever investigated. The condition of the brakes (outside of the parts being there) and the hydraulic system’s integrity are never taken into account. Ninety-nine percent of the time a crash is usually chalked up to driver’s error if the vehicle slams into the back of another car.

But what about the AEB system? No AEB system can diagnose the condition of the pads, rotors and calipers. It is difficult to test the caliper clamping force, friction levels, and even the ABS system’s operation on a vehicle. Even finding baseline distances for a vehicle based on the result of a government test is impossible.

Driver error is easy to prove. It has always been a driver’s responsibility to operate their vehicle safely. This includes knowing how their brakes will perform and how much pressure should be applied to bring the car to a safe stop. In most traffic courts, it is the driver who is accountable, not the vehicle. This is kind of scary to technicians because most drivers have no idea how their brakes work, much less an AEB system.

A distracted driver can add seconds to reaction times and feet to stopping distances. Even if the driver is not distracted, if the brakes are not functioning as engineered, a crash can occur. But who is to blame? The car? The driver? AEB systems? Or, the pads you just installed?

Why is Brake Inspection Critical for ADAS?

Chances are you have seen how some vehicle owners maintain their vehicles. They take the chance that a brake noise, pedal pulsation or warning light will go away without their intervention. Also, some will not use the highest quality brake pads or other brake parts. What they don’t realize is that the ABS, ESC and ADAS all need brakes that perform as expected when they perform a correction. It all comes down to friction.

At the corners, there are two types of friction. There is the friction that is generated by the brake pads on the brake rotor. The other type of friction is between the tires and road. Both work together to control the dynamics of a vehicle. 

The friction generated by the brakes needs the friction supplied tires to perform a correction. The vehicle can’t measure friction; it can only measure the results of the friction. The sensor that observes the results of the friction generated are the wheel speed sensors. 

If the friction generated by the brake pads is not within a specific range, it might assume the vehicle is on a low- or high-friction surface and then perform a correction to bring the vehicle back under control. Without the proper friction levels, a correction might take longer, or not be effective.

When you hear all of the talk about cameras, radar sensors and calibrations, remember that even the most advanced system can’t work to its full potential with out brakes.

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