Hill Assist Control Seminar

Hill assist is an automatic system that operates brakes to stop rolling back when it is starting on steep hill. When hill assist system senses vehicle is starting from rest on slope, it automatically keeps footbrake even after you release the pedal by accelerated vehicle using parking brake /hand brake. The hill start assist control helps to increase control on steep grades and prevents from locking. In this hill stop mechanism is also described to prevent car from rolling back.

1. A seminar on “Study of hill assist control feature used in vehicle on steep grade” Sinhgad Technical Education Society RMD Sinhgad School of Engineering, Pune-411058 Name of the student : Amey Ekbote (T121020876) Name of Guide: Mr. Y . D . Sonawane

2. Contents Introduction Literature review Hill Start Assist Control Hill Hold Control Comparison with HAC and without HAC Slope Calculations Advantages Disadvantages Applications Conclusion

3. Introduction In Cars there has been development in technology in last few decades. Day by day numbers of vehicles are increasing . Many times breakdown of vehicles takes place on hill roads while driving So hill assist control is technology which helps in driving vehicle on hill roads safely. It helps vehicle to stop rolling back from its position . Hill-Start Assist Control (HAC) is the new mechatronic technology as a safety features that detect the backward motion of the vehicle on hill or slope, that electronically controls and increases brake pressure at each wheel . Downhill Assist Control (DAC) automatically controls the brakes to maintain a constant low speed when descending slopes, helping reduce wheel lock and keeps good traction to maintain vehicle control.

4. Literature Review Mohammad Tamimi et al [2] investigated that while driving vehicle on Hill a typical problem that is encountered by drivers of vehicles with manual transmissions is rollback on an incline. This occurs when the driver is trying to coordinate the release of the brakepedal with the release of the clutch pedal and application of the accelerator all at the same time. Jiang Xuefeng [3] carried out experiment on starting and stopping vehicle on inclined road . The vehicle will start with jerk if it fails on inclined road. Therefore it is necessary to have a system like hill assist control . Cook George [4] suggested a hill holder mechanism holds the vehicle in slope for 2 seconds by using the brake pressure. A device operable in a transmission of a vehicle for substantially preventing vehicular rollback on an incline, comprising: a shaft rotatable which is supported in transmission housing; a gear selectively connected for common rotation with the shaft, wherein the gear is rotatable in a first rotary direction and a second rotary direction .

5. A.Arunkumar et al [1] found that while waiting in the traffic, the cars have to move on step by step very slowly, this situation is a difficult one for the drivers to make their car not to roll back in the slope. So the mechanism has to be developed to stop the vehicle from rolling back and it should not stop the vehicle in accelerating forwards. This function can beachieved by using the ratchet and pawl mechanism. Zhang L [6] investigated that a Hill Start Control uses a sensor to monitor the wheel state . If the wheel begins to roll backwards, the ECU controls the brake the system to engage the brake on the wheel. There have been some experiments with hill-start control strategy .

6. Hill Start Assist Control There may be unexpected cases for the driver where the vehicles may slide when starting on sudden hills or slippery surfaces. HAC minimizes vehicle roll-back by controlling brake fluid pressure as the driver's foot is removed from the brake to the accelerator on such steep incline. The HAC system is designed to help prevent the vehicle from rolling backward or slipping sideways during transition from a stopped position to climbing an upgrade . It also helps to start vehicle smoothly without any failure or jerk

7. Hill Start Assist Control Diagram

8. Working The hill start function has been activated as follows: T he driver lets up the brake pedal completely T he driver operates the accelerator pedal but not sufficiently to correspond to said minimum engine torque and minimum engine speed required in order to activate the clutch T he control unit maintains the brake pressure and the car remains stationary A fter this first time period, the control unit will release the braking device gradually over a second predetermined time period . The above takes place automatically without intervention by the driver in so far as the later does not interrupt the process by reapplying the braking device using the brake pedal Thus vehicle will start without jerk or rolling back

9. Hill Hold Control The Hill Hold function is a highly desirable feature in manual transmission vehicles, it also enhances the driving experience in automatic transmission vehicle. The Hill Hold feature supports the Stop and Go performance by holding the vehicle on an incline and preventing undesired motion. It prevents rolling back of vehicle and also provides descent control on slope .

10. Hill Hold Components Brake pedal travel sensor Master cylinder pressure sensor Wheel speed sensors Throttle position sensor Clutch sensor Longitudinal acceleration sensor Gear position sensor

11. Working The hill hold control consists of three systems Basic level system Mid level system Up level system

12. Basic level system A Hill Hold apply takes place after the driver comes to a full stop with their foot on the brake. A desired Hill Hold torque output level is calculated based on the torque / pressure level used to stop the vehicle or keep it stationary Once the brake pedal is released , Hill Hold will continue to command the same level of torque / pressure calculated above . The limitation of this approach is that the system will not know the percent grade that the vehicle is on. Therefore, Hill Hold will be engaged on every grade, even zero percent. Furthermore, the vehicle will not know the difference between a positive slope and a negative slope.

13. Mid level system The vehicle is stopped on an incline, the clutch is pressed and the Reverse gear is engaged The vehicle is stopped on a decline (negative slope) and the clutch is released. A brake apply by the driver in any of these cases would be a clear indication that the driver has a desire to let the vehicle roll down in the direction of the slope. Once one of the above criteria is met, the latching mechanism in the electric brake module is de-latched if it was engaged and the torque output level is released at a rate proportional to the slope .

14. Up level System The addition of a Hill Descent feature that would take control of the vehicle to assist the driver in rolling down an incline (positive slope) once the reverse gear is engaged. The brake system would release and apply torque/pressure to the wheels to control the descent of the vehicle at very low speeds. This would assist the driver carefully down the hill on such an awkward condition where rear visibility is restricted and seating position is uncomfortable. Active wheel speed sensors would provide a major advantage to make the control of the Hill Descent at such low speeds comfortable.

15. Comparison with HAC and without HAC

16. Slope Calculation

17. Slope calculation The longitudinal vehicle road load includes the rolling resistance, aerodynamic resistance, and uphill resistance. The vehicle model can be described as follows: ma = F r + F t F = µ mgcosƟ + 0.5C d AV 2 + mgsinƟ   Where F t is the driving force on the vehicle, F r is the total resistance, m is the mass of the vehicle, a is the acceleration ,α is the grade angle, µ is the friction coeffient of the wheel ,C d is the air drag coefficient that depends on the body style and dimension and A is the frontal area of the vehicle .

18. Advantages Prevents accidents while starting the vehicle on slopes Cost effective solution Stress free driving Longer clutch life It is an advantage for heavily loaded vehicles

19. Disadvantages Holding the vehicle on the footbrake can lead to warping of the discs. Maintenance cost high.

20. Applications These are cars given below having hill assist control feature in existence below : Honda CR-V Honda CR-Z Toyota Fortuner Toyota Prius Toyota Land Cruiser Toyota RAV4 Chevrolet Trax Volkswagen Touareg Opel Mokka

21. Conclusion The Hill Hold feature itself has proven to be very beneficial to manual transmission drivers that find themselves on grades that would normally make driving difficult . In addition to manual transmission vehicles, the driving experience of vehicles with automatic transmissions can be enhanced . The choice of which method of Hill Hold (basic level, mid-level, or up-level) to implement is influenced by many factors: desired performance, system cost and vehicle powertrain. When implemented correctly, the functionality of the Hill Hold feature seamlessly matches the driver's normal driving habits and instincts . Hill Hold function makes the driving experience as comfortable and natural as possible while keeping the system commercially feasible. By using this feature we can drive vehicle easily.

22. References   A.Arunkumar , T. Muthumani , V. Balasubramani – Design and Fabrication of Anti- rollbackSystem in Vehicles Using Ratchet and Pawl Mechanism. International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE) ,ISSN: 0976-1353 Volume 12 Issue 3 –JANUARY 2015 . Mohammad Tamimi , Deron Littlejohn, Mark Kopka and Gordon Seeley –Hill Hold Moding 2005 SAE International ISSN: 2005-05-0786 Jiang Xuefeng , Xu Xian, Jin Guodong , Chen Wei – Research on Hill Start, The 2 nd international conference (2012 ) ISSN:435562 Cook George -Anti creep and hill holderbrake system (US 2938611 A) Ge A., Lei Y., Gao Y., Zhang H. & Fan J.- A Research on Hill Starting Control of AMT System of Vehicle, Automotive Engineering, 1998, 3