hill-start assist (hac) & downhill assist (dac) REPORT

Hill-Start Assist & Downhill Assist Control

Dept of Mechanical Engineering, AIT Chikmagalur. 1

ACKNOWLEDGEMENT

We express our sincere and humble Pranamas to their holiness

BHAIRAVAIKYA JAGADGURU PADMABUSHANA SRI SRI SRI Dr.

BALAGANGADHARANATHA MAHASWAMIJI and PARAMA POOJYA SRI

SRI SRI NIRMALANANDANATHA MAHASWAMIJI and seek their blessings.

My heartiest gratitude to our honorable Principal Dr. C.K.SUBBARAYA for

creating the right kind of Milieu.

I express sincere thanks to our beloved H.O.D, Professor T.N.KRISHNAIAH,

for his moral support during the Seminar work.

I would like to express my heartfelt thanks to Guide Mr. PRASHANTH N, Asst.

Professor, Dept. of Mechanical Engineering Department for their constructive

suggestions and constant help throughout.

I also thank everybody wholeheartedly who has rendered their help directly or

indirectly in preparation of seminar report.

It’s a great pleasure to thank our subject seminar coordinator Dr. G M

SATHYANARAYANA and Mr. BASAVA PRABHU K M for giving this golden

opportunity.

Last but not least I am grateful to my parents and family members for their

constant support, without which I may have not achieved whatever little I have achieved.

PRATHAM PRAKASH

(4AI13ME416)



ABSTRACT

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. When the Hill Start Assist system

senses that the vehicle is starting from rest on a steep slope, it automatically keeps the

foot brake applied even after you have released the pedal. You can accelerate away as

slowly or as quickly as you wish, without needing to use the parking brake and with no

concerns about the vehicle rolling back. The brakes are smoothly released, entirely

automatically, as the vehicle pulls away. If the driver aborts a hill climb by releasing

pressure on the accelerator, Hill Start Assist controls the speed at which the vehicle rolls

back down the slope until the driver applies the brakes.

HAC (Hill-start Assist Control)

Without the HAC system, backward rolling or slippage occurs in steep inclines.

The HAC system helps increase control on steep upgrades and prevents individual wheels

from locking.

DAC (Downhill Assist Control)

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.



CONTENTS

CHAPTER 1 INTRODUCTION Page

1.1 Introduction 5

1.2 Break Control Systems 5

1.3 HAC & DAC 5

CHAPTER 2 HILL-STARTS ASSIST CONTROL (HAC)

2.1 Outline of HAC 5

2.2 Technology Functionality 6

CHAPTER 3 DOWNHILL ASSIST CONTROL (DAC)

3.1 Outline of DAC 9

3.2 Technology Functionality 9

3.3 Target Vehicle Speed 10

CHAPTER 4 CONCLUSIONS

4.1 Applications 12

4.11 HAC

4.12 DAC

4.2 Advantages 12

4.3 Conclusion 13



LIST OF FIGURES

Figure no. Title Page

2.1 Smoother start on steep & slippery surface 6

With HAC

2.2 Comparison with & without HAC 8

2.3 Driver effort with & without HAC 8

3.1 Comparison with & without DAC 10

4.2 Driver effort with & without DAC 11



CHAPTER 1

1.1 Introduction

Once reserved for high-end luxury vehicles, electronic brake control systems are

now required standard equipment on even the most inexpensive cars and trucks. Today,

nearly every new vehicle benefits from the optimized braking, enhanced acceleration, or

improved stability that these systems provide.

1.2 Brake control Systems:

Some of the brake control systems are,

1. Hill-start Assist control (HAC)

2. Downhill Assist control (DAC)

3. Anti-lock Brake System (ABS)

4. Electronic Brake force Distribution (EBD)

5. Brake Assist

6. Active Traction control (A-TRC)

7. Vehicle Stability Control (VSC)

1.3 HAC (Hill-start Assist Control) & DAC (Downhill Assist Control)

It is the new mechatronic technology in brake control system as a safety feature &

improves their off-road capability.

HAC detect the backward motion of the vehicle on hill or slope, and

electronically controls and increases brake pressure at each wheel. It applies brakes

for approximately three seconds when starting off on an incline. Smoothly reducing

backward movement hence the problem of braking by foot or handbrake ends-up by the

use of such intelligent technology.

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.



CHAPTER 2

Hill-start Assist control

2.1 Outline of HAC:

When the vehicle starts off on a steep or slippery hill, the vehicle could descend

backward while the driver switches from the pedal brake to the accelerator pedal, thus

making it difficult for the vehicle to start off. To prevent from occurring, HAC

temporarily (approximately 3 seconds at the maximum) applies the brakes to the 4 wheels

in order to reduce the backward speed of the vehicle.

Without HAC, driver must quickly & precisely switch from the brake pedal to the

accelerator pedal. With HAC however, the driver can start off easily.

Fig 2.1



2.2 Technology Functionality:

Sensors are located in each wheel. The sensor uses a rotating magnetic encoder

located in the wheel hub to detect a magnetic field. Once detected, it delivers digital

signals based on the change of magnetic poles. The detection of the magnetic fields

allows the use of magneto-resistive (MR) effects. The active wheel speed sensor is then

able to measure the vehicle’s extra low speed and rotating wheel direction.

Extra low speed detection is possible because the output signal of the active wheel

sensor is proportional to the amplitude of a magnetic field. Because the magnetic field

encoder does not depend upon the basic wheel rotation speed, the active wheel sensor can

deliver a precise signal, even if the wheel speed is extra low.

The active wheel sensors detect rotation direction through the use of two MR

elements. If the magnetic encoder detects a change in rotation, the phase between the two

MR elements is shifted upside-down. This allows the active wheel sensors to digitally

process the signals and provide wheel direction information. The sensor output is

provided in three levels of current via a two-wired interface. In the case of a forward

movement, the output is a two-level pulse signal. A three-level output pulse signal is

provided in the event of backward movement.

The basic function of the HAC system is to help increase control on steep

upgrades and stopping and starting on slippery surfaces. 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. The system is automatically activated

when the transmission is in any forward gear. The HAC system controls the brakes to

help stop the individual wheel or wheels, which helps prevent the vehicle from rolling

backward or slipping sideways.

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. When

backward rolling or slippage occurs, the HAC system is automatically activated. Upon

activation the HAC system gently applies the brakes. The HAC system measures the

necessary brake pressure of each wheel to help prevent individual wheels from locking

and causing vehicle slippage.



Fig 2.2

Fig 2.3



CHAPTER 3

Downhill Assist Control

3.1 Outline of DAC:

When the vehicle is descending a steep hill & engine brake alone cannot provide a

sufficient deceleration force while the transfer is in the low range, DAC effects the 4

wheel brakes control to maintain a constant low vehicle speed. Thus, the vehicle is able

to descend in a stable manner without causing the wheel to become locked.

When the vehicle descends a steep hill without DAC, the drives must be close

attention to the brake and accelerator pedal. However, with DAC, the driver can

concentrate on steering operation, without accelerator and brake pedals operation.

DAC enables the vehicle to realize a high level of stability because it can

descends a slippery hill at the low speeds without causing the wheels to be locked.

3.2 Technology Functionality:

The DAC system assists engine braking to help improve directional control

during descent on steep or slippery surfaces. When in 4WD low range and with DAC

activated, if any one wheel accelerates beyond or below a 5-10 km/h low-speed setting,

the DAC system will control the brakes to help ensure the vehicle continues in a straight

position when going down a hill. The DAC system is automatically de-activated if the

driver depresses the brake pedal, accelerator pedal, or the DAC button.

The skid control ECU (ENGINE CONTROL UNIT) 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. 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.



During DAC operation, Skid control ECU outputs to the stop light control relay to

cause the stop light to turn ON and combination meter causing the slip indicator light to

blink. 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.

3.3 Target Vehicle Speed:

Travel Direction Travel vehicle speed

Forward - 5-7 km/h (3-4 mph)

Backward - 3-4 km/h (2-3 mph)

Fig 3.1



Fig 3.2



CHAPTER 4

Conclusion

4.1 Applications:

4.1.1 HAC:

Honda CR-V

Honda CR-Z

Toyota Fortuner

Toyota Prius

Toyota Land Cruiser

Toyota RAV4

Chevrolet Trax

Volkswagen Touareg

Opel Mokka

4.1.2 DAC:

Toyota Fortuner

Toyota Land Cruiser

Toyota 4Runner

Toyota RAV4

Opel Mokka

4.2 Advantages:

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



4.3 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.

hill-start assist (hac) & downhill assist (dac) REPORT

Automotive

Transcript of hill-start assist (hac) & downhill assist (dac) REPORT