The present invention relates to an adaptive cruise control (ACC), specifically improving braking response when the adaptive cruise control requests braking.
Some ACCs use an electronic stability program (ESP) system to execute braking. Because the brake pads need to contact the brake disks before any braking can occur, the initial brake deceleration following a request from the ACC takes a relatively long time to execute (e.g., a delay of 200 to 500 milliseconds before a deceleration really occurs), and causes a large volume of brake fluid to be pumped. Other than limitations of how fast the pump can run, there is usually an unacceptable noise (a noise/vibration/harshness (NVH) issue) that occurs when running the pump very fast.
Thereafter, (a) either the ACC brake deceleration request catches up, or (b) the delay is kept constant throughout the entire control. The advantages of point (a) is that after the request has caught up, there are no more ‘late’ reactions due to delays, and there are less problems with oscillations that are caused by delays in reactions. The disadvantage, however, is that when catching up to the request, a jerk (rate-of-change of acceleration) that the ESP system executes is greater than the ACC demands. This jerk can be felt by the driver, and is higher on the initial braking than on subsequent reactions. Furthermore, since the jerk is higher, it may also be associated with more noise than necessary (an undesirable element of NVH). The advantage of (b) is that the jerk requested by the ACC is executed as the ACC requested, and therefore ‘feels’ right. However, this method reacts as late as the initial delay, and is susceptible to oscillations in the system (unless a significant effort is made to tune the systems to be in-line with each other).
The described effects apply to ACC and also other types of longitudinal control used for comfort functions. In addition, in the future the effects would also apply to autonomous driving.