GF42.45-P-0001-02D Electronic stability program (ESP), location of hydraulic components  

P42.45-2198-09

1 Tandem master brake cylinder
5a Front right brake caliper
5b Front left brake caliper
  6a Rear right brake caliper
6b Rear left brake caliper
  A7/3 Traction systems hydraulic unit
A7/7 BAS brake booster

GF42.45-P-0001B
GF42.45-P-0001B Electronic stability program (ESP), function 11.5.99

MODEL  129 with ENGINE 112, 113 with CODE (472a) Electronic Stability Program (ESP)
MODEL  170, 202, 203, 208, 215, 220 with CODE (472a) Electronic Stability Program (ESP)
MODEL  210 with ENGINE 111, 112, 113, 605, 606, 611, 612, 613 with CODE (472a) Electronic Stability Program (ESP)


The "Electronic Stability Program" (ESP) is an active safety system which improves vehicle stability in all driving situations.

It functions by applying braking force to one or more wheels on the front or rear axle. ESP stabilizes the vehicle when cornering, braking, or during non-driven coasting to keep it on the road and in the desired lane.

ESP complements the familiar functions of the anti-lock brake system (ABS), acceleration slip regulation (ASR) and engine braking regulation (EBR).

The stability regulation function is superordinate to the ABS and ASR control systems. As well as actively intervening with the brakes, ESP also has an influence on engine / transmission management.

The Electronic Stability Program (ESP) includes the following system interplay.

ABS prevents the wheels from locking when the brakes are applied so that the vehicle remains steerable and stable as it decelerates.
  ASR prevents the powered wheels from spinning when the vehicle is being driven. It also improves directional stability and road adhesion and increases traction potential across the entire vehicle speed range.

EBR reduces brake slip at the drive wheels during deceleration and ensures directional control.

ESP prevents the vehicle from breaking away when it is oversteered or understeered. In all situations it ensures that the vehicle does not deviate from the course specified by the driver (within the bounds of physical limits). Brake forces are produced selectively at the individual wheels to correct this.



System interplay
The engine electronics (ME) is used to adjust the drive torque. This system controls the engine by adjusting the position of the throttle valve and by altering the ignition timing.

The gear setting is also evaluated by the electronic transmission control (EATC) to calculate the ESP drive torque control.

The ABS and ASR functions are integrated in the ESP electronics of the brake control loop. In the following vehicles it also includes the BAS function (as of 3/99):
Model 129 with engines 112, 113
Model 202 with engines 111, 112, 113, 605, 611
Model 203
Model 210 with engines 112, 113, 605, 606, 611, 612, 613
Model 210 with engine 111 as of 08/99
Model 170, 208, 215, 220
The basic ABS and ASR components are also combined in the ESP hydraulic unit.

The function for the electronic gas pedal (EGP) and cruise control is contained in the engine control unit.

Data is exchanged between the ESP control module, the engine control unit and (if fitted) with the transmission control module and BAS control module via a CAN data line.

Advantages of ESP
Improves moving-off and acceleration capabilities by increasing traction; especially useful on road surfaces with different levels of grip and when cornering.

Increases the level of active driving safety since only non-spinning wheels provide optimum traction without impairing side stability.
  Automatically adapts the engine torque to the respective wheel-to-road-surface traction possibilities if the driver accelerates too heavily.

Reduces the risk of skidding under all road conditions by automatically stabilizing the vehicle when braking, accelerating or coasting smoothly.

Significantly improves the directional stability of the vehicle when cornering - up to the limit range.

Reduces the braking distance in corners or on roads with a smooth surface.

A flashing warning lamp in the speedometer notifies the driver of ESP control and informs him that his vehicle is approaching the physical limits.

The ESP or ASR can be deactivated via an ESP OFF switch. The deactivated status is indicated by a permanently lit warning lamp in the speedometer. Deactivation can help to improve traction ("cutting" effect) in deep snow or when snow chains are fitted.




Function overview
Essentially, all the forces acting on a vehicle from outside attempt to rotate the vehicle about its center of gravity, regardless of whether these are one-sided braking or drive forces or lateral forces.
 
The Electronic Stability Program (ESP) analyzes the vehicle behavior and applies specific braking force to individual wheels to correct any instability.

Example A: Vehicle understeering (on left-hand bend)
The vehicle pushes outwards over the front wheels.
Precisely calculated braking force is applied to the left rear wheel.

Example B: Vehicle oversteering (on left-hand bend)
The tail of the vehicle breaks away.
Precisely calculated braking force is applied to the right front wheel.

a Desired travel direction
b Braked wheel
c Generated compensating moment of vehicle
d Understeering vehicle motion
e Oversteering vehicle motion
   
    P42.45-0203-02   P42.45-0204-02

ESP operates:
when cornering (vehicle under- or oversteered)
when driving straight ahead (vehicle deviates off course due to uneven road conditions)

To be able to perform these extremely precise control interventions, an expanded system of sensors is required compared with ASR.
A distinction is made between:
1.) sensors which register driver requirements
Steering angle sensor
Accelerator pedal position (throttle valve actuator)

2.) sensors which measure the actual vehicle behavior
Yaw rate sensor
Lateral acceleration sensor
Brake pressure sensor
Wheel speed sensor

The ESP control module (N47-5) records and processes the wheel speeds, the steering angle, the yaw rate of the vehicle, the lateral acceleration and the brake pressure at the front axle.
The ESP control module (N47-5) is linked to the control modules of the engine/transmission management system over a CAN data bus. This digital link permits fast data exchange between the ESP control module, engine control unit,
  and transmission control module.
The ESP control module (N47-5) is continuously supplied with current data on engine torque, accelerator pedal position and transmission ratio.
The forces attempting to rotate the vehicle about its center of gravity are detected via the yaw rate and lateral acceleration sensors.
The longitudinal and lateral forces acting on the wheels can be calculated by this data acquisition.
If these values exceed certain control thresholds, the appropriate solenoids as well as the high-pressure/return-flow pump in the hydraulic unit are actuated via the ESP control module (N47-5) in order to apply precisely defined brake pressure to one or more wheels.
At the same time, commands are sent to the engine and transmission control module via the CAN data bus. Calculated values for throttle valve position and ignition timing are predefined and downshifting is suppressed in order to reduce driving torque.

The precise and accurately proportioned intervention is completed within a few fractions of a second.

Active brake intervention and driving torque reduction by the ESP ensure optimum vehicle stability.

The following control functions are performed during this process:

ESP braking moment control circuit
ABS control
If, for example, a wheel has a tendency to lock, the brake pressure in this wheel brake is regulated. The ESP hydraulic unit (A7/3) is actuated in three control phases (pressure build-up, pressure hold and pressure reduction) by the solenoids.

ESP braking moment control circuit
ASR control
To brake the spinning wheel , the brake pressure is fed to the rear brake caliper via a pressure system in the hydraulic unit (pressure build-up).
The other wheel can then transmit optimum driving power (locking differential effect).
Solenoid valves in the ESP hydraulic unit (A7/3) regulate the braking torque with pressure build-up, pressure hold and pressure reduction phases.

ESP drive torque control circuit
ASR control
In order to reduce an excessive drive torque and thereby obtain optimum traction, the drive torque is reduced over the CAN data bus between the ESP control module and the engine control module.
  The ESP control module continuously checks whether the control functions can be canceled owing to, for example, a sudden improvement in road grip so that the drive torque requested by the driver via the gas pedal can then be made available again.

ESP drive torque control circuit
EBR control (except engines with fuel shutoff)

If wheel slip at the drive wheels occurs when the gas pedal is released, this is also detected in the ESP control module. The signal is sent to the engine control module over the CAN data bus. On the basis of this information, the wheel slip is reduced by increasing the drive torque, and the side stability of the vehicle is thus increased. This process occurs without notifying the driver (ESP warning lamp).

ESP brake moment and drive torque control circuit
ESP control
If over- or understeering is detected, calculated braking force is applied to the front or rear axle via the ESP control module and the hydraulic unit. This brake intervention counteracts the undesired driving behavior.
A signal sent to the engine control unit via the CAN data bus triggers the demand-based reduction in drive torque by decreasing engine torque.

GF42.45-P-2000D
GF42.45-P-2000D ESP braking moment control circuit, function 17.5.99

MODEL  170 with ENGINE 111, 112 with CODE (472a) Electronic Stability Program (ESP)
MODEL  202 with ENGINE 111, 605, 611 with CODE (472a) Electronic Stability Program (ESP)
MODEL  208 with ENGINE 111 with CODE (472a) Electronic Stability Program (ESP)
MODEL  203.0 up to 31.7.01 with CODE (472a) Electronic Stability Program (ESP)


The functions of the braking moment control circuit are controlled using the components of the electric/electronic system.

The ESP control module (N47-5) is supplied with power via the fuse and relay module (K40/2).

The ESP control module (N47-5) receives input signals from the following components:

4 wheel speed sensors
Steering angle sensor
Lateral acceleration sensor
Yaw rate sensor
ESP brake pressure sensors
Stop lamp switch
Parking brake switch
ME-SFI control module over CAN data line
ETC control module over CAN data line
ESP OFF switch
BAS release switch
BAS diaphragm travel sensor




  The input signals are processed in the ESP control module ESP to form output signals for the following components:

BAS solenoid valve
Solenoid valves in the hydraulic unit
High-pressure and return-flow pump
Stop lamp suppression relay
Engine control unit via CAN data line
EATC control module over CAN data line
ESP warning lamp over CAN data line
ABS indicator lamp over CAN data line
BAS/ESP indicator lamp over CAN data line

On the basis of the input signals, the ESP control module (N47-5) decides which of the 7 operating modes

Normal mode
ABS control mode
ASR control mode
EBR control mode
ESP control mode
ESP OFF mode
BAS mode

must be activated.

Normal mode
This is the case when the driving state requires no control mode. All solenoid valves in the ESP hydraulic unit (A7/3) are in the basic position, i.e. de-energized. The system is ready for braking.
This mode also exists when there is a malfunction in the ESP, BAS or ABS system. Drive torque control is not activated.

ABS control mode
The ESP control module (N47-5) uses the wheel speed signals to determine whether the criteria for ABS control exist. The appropriate solenoids in the hydraulic unit are then actuated.
The solenoids for front and rear axle in the ESP hydraulic unit (A7/3) are actuated individually (4-channel control).

ASR control mode
As soon as a driving wheel shows a tendency to spin, the ESP control module (N47-5) actuates the high-pressure and return-flow pump (A7/3m1), switchover solenoid (rear axle), inlet solenoid (rear axle), and rear-axle solenoids. The solenoids for the left and right-hand side of the rear axle are actuated separately.
  ESP control mode
A status controller in the ESP control module (N47-5) receives and processes the signals for the wheel speeds, the steer angle, the yaw rate of the vehicle, the lateral acceleration and the brake pressure in the front and rear axle circuit. After evaluating the input signals, the BAS solenoid valve (A7/7y1), the inlet solenoid valves, the switchover valves, the high-pressure and return-flow pump (A7/3m1) and the necessary solenoid valves are actuated to regulate the brake pressure in the individual wheel brakes.

ESP OFF mode
When the ESP OFF switch (S76/6) is pressed, the ASR drive torque control function is deactivated and the ESP stability function for acceleration and coasting is canceled. The ESP stability function remains operational during braking. EBR control is deactivated.
With the switch in this position, braking force is applied to one spinning drive wheel via the braking moment control circuit at vehicle speeds of up to 40 km/h. If activation conditions continue to exist, brake intervention continues up to max. 60 km/h. The braking torque is, however, reduced continuously.

BAS mode
From the speed of the brake pedal the ESP control module (N47-5) recognizes that emergency braking is in progress and initiates BAS mode (see Brake Assist (BAS), function).

GF42.45-P-3000D
GF42.45-P-3000D ABS control mode, function 10.5.99

MODEL  170 with ENGINE 111, 112 with CODE (472a) Electronic Stability Program (ESP)
MODEL  202 / with ENGINES 111, 605, 611 with CODE (472a) Electronic Stability Program (ESP)
MODEL  208 with ENGINE 111 with CODE (472a) Electronic Stability Program (ESP)
MODEL  203 with CODE (472a) Electronic Stability Program (ESP)


Brake application under normal operating conditions
ABS control mode - pressure build-up
Each ABS control phase begins with normal application of the brakes when the driver presses the brake pedal.

The ESP control module recognizes the braking procedure by the drop in wheel speeds.

The brake pressure is built up via the two change-over solenoid valves (y18 and y19) and the solenoid valves (y6, y8, y10 and y12).
During an ABS control procedure, this pressure build-up phase can occur individually at each wheel.

During the braking procedure under normal operating conditions, the pressure is built up via the same solenoid valves.

b Brake pressure
 
    P42.45-2181-76

ABS control mode, pressure hold
The control procedure and valve positions shown in the example relate to the front right brake.

If a wheel shows a tendency to lock during brake application, the ABS prevents a further build-up of pressure. The ESP control module initiates the pressure holding phase using the slip values of the braked wheels.

The pressure holding phase is initiated by actuation of the solenoid valve (y8). In this control phase, the solenoids (y8 and y9) remain closed; the pressure in the front right brake caliper thus remains constant.


b Brake pressure
 
    P42.45-2182-76

ABS control mode, pressure reduction
The control procedure and valve positions shown in the example relate to the front right brake.
The ESP control module initiates the pressure reducing phase using the slip values of the braked wheels.
The pressure reduction phase is initiated by actuation (opening) of the solenoid valve (y9). The solenoid valve (y8) remains actuated (closed) in this control phase.
During the pressure reduction phase, brake fluid flows through the reservoir (11) and back into the high-pressure and return-flow pump (p1). From there the high-pressure and return-flow pump in the front-axle brake circuit pumps the brake fluid against the existing pressure back into the master brake cylinder. Each brake circuit has a muffler (12) to dampen the pumping sound.

b Brake pressure
e Reduced pressure
 
    P42.45-2183-76

GF42.45-P-3700B
GF42.45-P-3700B ESP control mode, function 17.5.99

MODEL  129 with ENGINE 112, 113 with CODE (472a) Electronic Stability Program (ESP)
MODEL  202 with ENGINE 112, 113, 604 with CODE (472a) Electronic Stability Program (ESP)
MODEL  208 with ENGINE 112, 113 with CODE (472a) Electronic Stability Program (ESP)
MODEL  210 with ENGINE 111, 112, 113, 604, 605, 606, 611, 612, 613 with CODE (472a) Electronic Stability Program (ESP)
MODEL  215, 220 with CODE (472a) Electronic Stability Program (ESP)


ESP pressure build-up control mode
The control process and valve positions shown in the example relate to the FR brake.

f High pressure
g Pilot pressure
 
    P42.45-0266-76

A brake intervention to stabilize the vehicle is introduced by the ESP control module.
At the start of ESP control the switchover solenoid valves (y18 and y19) are switched to the "shut-off position" (closed) and the high pressure and return pump (m1) is actuated. The BAS solenoid valve (A7/7y1) in the brake booster (A7/7) is actuated (opened) from a speed of > 20 km/h (starting off range). Atmospheric pressure is led to the back of the diaphragms in the brake booster, generating pressure of approx. 5 bar in the brake circuits which is applied as pilot pressure at the suction side of the high pressure and return pumps.
  The inlet solenoid valve (y22) is only opened during the pressure build-up phases. In the process the self-priming high pressure and return pump (p1) draws in brake fluid from the reservoir via the inlet solenoid valve (y22) and master brake cylinder.

The pressure limiting valve integrated in the switchover solenoid valve (y18) serves to limit high pressure (approx. 170 bar).

ESP pressure holding control mode
The control process and valve positions shown in the example relate to the FR brake.
The ESP pressure holding control mode starts if a major brake intervention is no longer required for stabilization.
The inlet solenoid valve (y22) is closed. As a result the pressure in the brake caliper cannot be increased via the high pressure and return pump (p1).

a Suction line
b Brake pressure
g Pilot pressure
 
    P42.45-0267-76

ESP pressure reduction control mode
The control process and valve positions shown in the example relate to the FR brake.
The ESP pressure reduction control mode starts if the brake pressure required for stabilization is too high.

The pressure reduction phase is introduced by opening the switchover solenoid valve (y18). The solenoid valve (y8) remains open and the solenoid valve (y9) remains closed.
The returning brake fluid flows back via the high pressure and return pump (p1) through the switchover solenoid valve (y18) to the brake fluid reservoir via the master brake cylinder.

The self-priming high pressure and return pump (p1) is also actuated in these control phases.

a Suction line
e Reduced pressure
 
    P42.45-0268-76

GF42.45-P-3700D
GF42.45-P-3700D ESP control mode, function 15.3.99

MODEL  170 with ENGINE 111, 112 with CODE (472a) Electronic Stability Program (ESP)
MODEL  202 with ENGINE 111, 605, 611 with CODE (472a) Electronic Stability Program (ESP)
MODEL  208 with ENGINE 111 with CODE (472a) Electronic Stability Program (ESP)
MODEL  203 with CODE (472a) Electronic Stability Program (ESP)


a Suction pipe
f High pressure



ESP control mode, pressure build-up
The control procedure and valve positions shown in the example relate to the front right brake.

The ESP control module (N47-5) initiates brake intervention at the front right wheel in order to stabilize the vehicle.

At the beginning of the ESP control phase under normal operating conditions, the solenoid (y8) is opened, the switchover solenoid (y18) is switched to the "lock position" (closed), and the high-pressure and return-flow pump (p1) is actuated.

The inlet solenoid (y22) is only opened during the pressure build-up phases.
 
    P42.45-2187-76

The self-induced high-pressure and return-flow pump (p1) draws brake fluid out of the reservoir via the inlet solenoid (y22) and master brake cylinder, and provides the high pressure required for actuating the respective wheel brake.
If extremely rapid stabilization intervention is required, the pressure build-up phase is supported by active actuation of the brake assist system. Here, atmospheric pressure is fed to the rear sides of the diaphragms in the brake booster. This generates a pressure of approx. 5 bar in the brake circuits.
The primary pressure produced in this way is directed by the switchover solenoid valve (y18) via the check valve (7) into the active brake circuit to the
  front right brake caliper until the pressure downstream of the check valve (7) is higher than the primary pressure.
At the same time, the primary pressure is applied to the suction side of the high-pressure and return-flow pump (p1) via the opened inlet solenoid valve (y22) and improves the volumetric efficiency of the pump and, therefore, its delivery rate. The primary pressure is kept away from the non-active wheel brakes by closing the solenoid valves (y6,10,12).
The high pressure is limited by the pressure relief valve integrated into the switchover solenoid valve (y19), which opens at pressures >150 bar.

ESP control mode, pressure hold
The control procedure and valve positions shown in the example relate to the front right brake.
When no more severe brake intervention is required to stabilize the vehicle, the ESP pressure hold control mode commences.
The inlet solenoid valve (y22) and the solenoid valve (y8) are closed. As a result, the pressure in the brake caliper cannot be increased via the high-pressure and return-flow pump (p1).

a Suction pipe
b Brake pressure
f High pressure
 
    P42.45-2188-76

ESP control mode, pressure reduction
The control procedure and valve positions shown in the example relates to the front right brake.
If the brake pressure required for stabilization is too high, the pressure-reduction phase of the ESP control mode begins.
The pressure reduction phase is initiated by opening of the solenoid valve (y9). The solenoid (y8) remains closed. The high-pressure and return-flow pump (p1) pumps the backflowing brake fluid through the pressure relief valve integrated in the switchover solenoid (y18), and then through the master brake cylinder back to the brake fluid reservoir.
The self-induced high-pressure and return-flow pump (p2) is clocked (according to demand) in all control phases.
Various damping components (12, 13, 14) are fitted to reduce noise further.

e Reduced pressure
f High pressure
 
    P42.45-2189-76

GF42.45-P-4550A
GF42.45-P-4550A Wheel speed sensor, location / task / design / function 13.5.96

MODEL  129,
  140, 202 as of 1.6.94,
  163, 168, 170, 208, 210
  with CODE (470a) Anti-lock brake system (ABS)
  with CODE (212a) Electronic traction system (ETS)
  with CODE (471a) Acceleration slip regulation (ASR)
MODEL  129,
  140 as of 1.6.94,
  163, 168, 170, 210 with CODE (472a) Electronic Stability Program (ESP)
MODEL  202 with ENGINE 112, 113, 604 with CODE (472a) Electronic Stability Program (ESP)
MODEL  208 with ENGINE 112, 113 with CODE (472a) Electronic Stability Program (ESP)


L6/1 Left front wheel speed sensor
L6/2 Right front wheel speed sensor

ABS only
L6 Rear axle speed sensor

ETS, ASR, ESP only
L6/3 Left rear wheel speed sensor
L6/4 Right rear wheel speed sensor
 
    P42.30-0221-06

  Wheel speed sensor, location The front wheel speed sensors (L6/1 and L6/2) are installed in the steering knuckle on the front axle.
ABS: The rear axle speed sensor (L6) is installed in the rear axle center assembly.
ETS, ASR, ESP: The rear wheel speed sensors (L6/3 and L6/4) are installed on the rear axle wheel carriers.
 
  Wheel speed sensor, task To supply the current wheel speed to the ABS, ETS, ASR or ESP control module (N47-7, N47-2, N47-1 or N47-5).  
  Wheel speed sensor, design Inductive sensor: Coil with magnetic core at a defined distance to the rotor which is attached to the front wheel hub, rear axle shafts or rear axle drive pinion.  
  Wheel speed sensor, function The magnetic field of the wheel speed sensor is intersected by the teeth of a rotor. This changes the magnetic field and the coil induces an alternating voltage. This alternating voltage changes frequency according to the wheel speed and the number of teeth, i.e. the frequency is proportional to the wheel speed.