Hill Start Assist is an automatic system that operates the brakes to stop your vehicle rolling back when it is starting on a steep hill. The DAC system assists engine braking to help improve directional control during descent on steep or slippery surfaces.

1. TECHNICAL SEMINAR ON
Hill-Start Assist & Downhill Assist
Presented by,
PrathamPrakash
DEPARTMENT OF MECHANICAL
ENGINEERING
ADICHUNCHANAGIRI INSTITUTEOF TECHNOLOGY

2. HILL-START ASSIST CONTROL
&
DOWNHILL ASSIST CONTROL

3. INTRODUCTION
 Hill-Start Assist Control (HAC) is the
new mechatronic technology as a safety feature
that detect the backward motion of the vehicle
on hill or slope, that electronically controls and
increases brake pressure at each wheel.

4. •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.

5. 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.

6. The HAC system helps increase control
on steep upgrades and prevents
individual wheels from locking.
Without the HAC system, backward rolling
or slippage occurs in steep inclines.

7. How it works……
• The HAC system determines the driver’s intended
vehicle direction from the present gearshift position
of the transmission, the moving direction of the
vehicle wheels and the wheel speed of the four
wheels through the use of active wheel sensors.
• An active wheel sensor is located in each wheel.
The sensor uses a rotating magnetic encoder
located in the wheel hub to detect a magnetic field.
• The active wheel sensor is then able to detect the
rotating wheel direction.
• The active wheel sensors detect rotation direction.
This allows the active wheel sensors to digitally
process the signals and provide wheel direction
information.

8. • When backward rolling or slippage occurs, the
HAC system is automatically activated.
• Upon activation the HAC system gently applies the
brakes. The system measures the necessary
brake pressure of each wheel to help prevent
individual wheels from locking and causing vehicle
slippage.
• Without HAC, driver must quickly & precisely
switch from the brake pedal to the accelerator
pedal. With HAC however, the driver can start off
easily & operate the pedal in a relaxed manner
because HAC reduces the backward speed of the
vehicle.

11. Downhill Assist Control
• When the vehicle is descending a steep hill &
engine brake alone cannot provide a sufficient
deceleration force.
• DAC effects 4 wheel brake control to ,maintain a
constant, low speed. Thus, the vehicle is able to
descend in a stable manner without causing the
wheels to become locked.
• When the vehicle descends a steep hill without
DAC, driver must pay close attention to the brake &
accelerator pedal. However with DAC, driver can
concentrate on steering operation, without
accelerator & brake pedals operation.

12. Without the DAC system, wheels lock when
pressing the breaks in steep slopes.
The DAC system improves directional
control during descent on steep or
slippery surfaces.

13. How it works……
 The active wheel speed sensors and ECU (Engine
control unit) enable the operation of the DAC
system by determining current road conditions &
gradient of hill.
 The skid control ECU computes the vehicle speed,
travel direction, gradient of hill in accordance with
signals from speed sensor and deceleration sensor
and these effects, brake control to attain the target
vehicle speed.

14.  The DAC system will calculate the required brake
hydraulic pressure for each wheel, allowing each
individual wheel to meet the target vehicle speed.
 If the accumulator pressure drops during this
operation, the skid control ECU receives the
signals from pressure switch and actuates the
pump & pump motor to ensure the proper
accumulator pressure through solenoid valves
brake wheel cylinders of each wheel.

16. Existence…
 Hill-start Assist
Control is available
on a number of
Toyota models
including Fortuner,
Prius, Land Cruiser,
RAV4 and 4Runner,
Honda C-RV and
also in Volkswagen
Touareg.
 Downhill Assist
Control is standard
equipment on
Toyota Fortuner,
Land Cruiser,
RAV4 and
4Runner.

17. Advantages & limitations….
 Prevents accidents while starting the
vehicle on slopes
 Cost effective solution
 Stress free driving
 Longer clutch life
 It’s a advantage for heavily loaded
vehicles
 It is suitable for only manual
transmission.

18. Conclusion:
By devising a mechanism of this sort we could
make driving more easier and most importantly this
sort of technology could reach the common man
who form the majority in any economy.