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:
• The driver lets up the brake pedal completely
• The 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
• The control unit maintains the brake pressure and the car remains
stationary
• After 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
i. Basic level system
ii. Mid level system
iii. 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

17. Slope Calculation

18. 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 = Fr + Ft
• F =µmgcosƟ + 0.5CdAV2 + mgsinƟ
• Where Ft is the driving force on the vehicle, Fr 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.

19. 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

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

21. 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

22. 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.

23. 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 2nd 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