K24912512

Solution K24912512
Wednesday, December 4, 2019 10:23:23 PM CET
** SOLUTION **
Title
Volvo Chassis - Volvo Hill Start Assist System Information
Volvo Models
Volvo Model
VN
** SOLUTION **
Cause
Limited information in Trucks Dealer Portal ( TDP )
Volvo Hill Start Assist HILLSTA2
Solution
Hill start assist, function description
Impact Meta Data
Valid From
04.07.2019
Valid To
01.01.2099
PD string
VN, HILLSTA2
Hill start assist component location, dashboard
1
Instrument cluster (A03)
2
Hill start assist switch (S212)
3
Brake control unit (A12B)
4
VECU (Vehicle Electronic Control Unit) (A17)
5
GLU (Gear Lever Unit) switch (S171)
6
Accelerator pedal sensor (B25A)
7
Brake pedal valve switch (S59)
Control units, chassis
1
ECM (Engine Control Module) (A14)
2
TECU (Transmission Electronic Control Unit) (A13)
Function behavior
General information
Hill start assist variants
Variant symbol
Variant description
HILLSTA2
Hill start assist, all wheels and trailer
UHILLST
Without hill start assist
Description
Hill start assist is safety feature in the truck which helps the driver to avoid rolling back
while truck taking a gradient.This feature allows the truck to hold in a uphill with a
forward gear or in a down hill with reverse gear when the service brake is released. The
hill start assist program is activated when the driver releases the brake pedal and the
brake pressure being hold for 3 seconds until the truck is sufficient to move on without
roll back.
The brake pressure in the brake chambers being held by the hill start pneumatic solenoid
valve via brake control unit. The TECU calculates the required engine torque with load
dependency and releases the hill start assist program while truck starts move on without
rolling back.
The hill start assist program activates automatically in the truck with predefined
conditions.If the driver wants to deactivate the program by selecting the dashboard
disable switch.The program will re-enables when the ignition key covers a cycle of OFF–
ON or else the driver can chose the disable switch again to re-enable the program.
Functionality conditions
Conditions to hill start assist activation
Key switch in the ignition position and engine rpm is present
Vehicle speed is equal to 0 km/h
Vehicle is in a forward gear on an incline equal to or greater than 2%
Vehicle is in a reverse gear on an decline equal to or greater than 2%
The brake pressure should not below at 10 psi
Service brake is activated
Hill start assist disable switch is not selected
No brake failures with active J1939 communication faults
System is not in a downgraded mode
Conditions to hill start assist deactivation
Vehicle Speed is greater than 20 km/h (12 mph)
Hill start assist disable switch is in ON position
Note:
Hill start assist will not works (applies brake) when the system attains low brake
pressure. It
will activates when the brake pressure is at 10 psi or greater.
Pneumatic diagram
1
Primary tank
2
Secondary tank
3
Treadle valve (foot brake valve)
4
Central pressure control ATR-6 relay valve
5
Central pressure control ATR-3 relay valve for Hill start assist
6
Quick release valve for front brakes
7
Quick release valve for rear brakes
8
Relay valve for rear brakes
9
Trailer hand control valve
10
ABS Solenoid valves
11
Brake chamber, rear
12
Brake chamber, front
13
Trailer protection valve
14
Park control valve
15
Pedal plate bulkhead
Activation scenario, truck is stopped
1. The brake pedal is released and the brake pedal response information send via
foot brake valve switch (S59) and the signal received by brake control unit
(A12B).
2. The brake control unit (A12B) receives wheel rotation information via speed
sensor (B1).
3. The brake control unit (A12B) receives steering angle position via steering angle
sensor (S49) and lateral acceleration via yaw rate sensor (S50).
4. The VECU (A17) analyses the pre conditions of the truck via brake control unit
(A12B) to activate hill start assist.
5. The VECU (A17) send information to brake control unit (A12B) to activate hill
start assist.
6. The brake control unit (A12B) pulses the solenoid valve (Y106) to hold the
brake pressure for the set time.
7. The brake control unit (A12B) sends the status information to instrument cluster
(A03) about hill start assist program activation.
Deactivation scenario, truck is driving off
1. The accelerator pedal is depresses and the information send via accelerator
position sensor (B25A) and the signal received by VECU (A17) or when
deactivation switch (S212) is in ON position.
2. The VECU (A17) calculates the available engine torque as well as the driveline
torque from ECM (A14) and from TECU (A13) .
3. The TECU (A13) calculates the engine torque available from ECM (A14)
4. The VECU (A17) send the information to brake control unit (A12B) to release
the brake pressure from brake chambers via solenoid valve (Y106).
5. The VECU (A17) commands the TECU (A13) to move the truck with available
engine torque via ECM (A14).
6. The brake control unit (A12B) sends the status information to instrument cluster
(A03) about hill start assist program deactivation.
7. If the brake pressure is below 10 psi , the brake control unit (A12B) calculate the
brake pressure value and sends information to VECU (A17) and send
deactivation status to instrument cluster (A03).
Solution visibility
Dealer distribution
Function(s)/component(s) affected
Function affected
VECU , EECU , MID 128 – EMS , MID 130 – TECU , MID 144 – VECU , Braking
/Auxiliary Pneumatic Circuits , Diagnostic tool
Function Group
Function Group
5 brake
Customer effect
Main customer effect
efficiency/abnormal behavior , stop/start
Conditions
Vehicle operating mode
on start-up , uphill
Road conditions
very hilly
Administration
Author
A044013
Dealer ID
A044013
Last modified by
RU4469V
Creation date
21-10-2019 13:10
Date of last update
14-11-2019 14:11
Status
Published
UNCONTROLLED COPY. Printed document is for temporary use only and should not be retained.