11: 03DAF description (electrical, pneumatic diagrams) of RAS-EC system part 1
RAS-EC stands for Rear Axle Steering Electronically Controlled.
RAS-EC DAF system
Location of hydraulic units
Location of electrical components
General diagram of the hydraulic drive
DESCRIPTION OF THE SYSTEM
Electrical equipment of the RAS-EC system
Hydraulic drive system RAS-EC
DESCRIPTION OF ASSEMBLIES
The electronic unit
Wheel Angle Sensors
Rear support axle control
Isolation Valve Verification Test
Overheating protection of hydraulic fluid
INSPECTION AND ADJUSTMENT
Points requiring special attention when checking the system
Contact terminals of the electronic unit
Explanations for the block diagram
Electrical equipment check
Checking and adjusting the power cylinder
Checking and adjusting the center position of the wheel angle sensor of the supporting rear axle
Checking and adjusting the center position of the front axle wheel angle sensor
Checking and adjusting the position of the front axle wheel angle sensor holder
REMOVAL AND INSTALLATION
Removal and installation of the valve block
Removal and installation of the power cylinder
Removal and installation of the high pressure filter
Removal and installation of the filter element of the tank
Removal and installation of the distribution block
Removal and installation of damper valves
Removal and installation of the electronic unit
Removal and installation of the front axle wheel angle sensor
Removing and installing the front axle wheel angle sensor holder
Removal and installation of the wheel angle sensor of the supporting rear axle
CHANGE OF LIQUIDS
Changing the fluid in the hydraulic circuit of the RAS-EC system
Bleeding the hydraulic circuit of the RAS-EC system
This system operation manual describes the layout, operation and adjustment of the RAS-EC system. RAS-EC stands for Rear Axle Steering Electronically Controlled.
LOCATION OF HYDRAULIC UNITS
LOCATION OF ELECTRICAL COMPONENTS
GENERAL DIAGRAM OF THE HYDRAULIC DRIVE
1. Tank with the level sensor of the working fluid (F116)
2. Power steering pump
3. Overflow valve
4. Shut-off valve
5. Control valve
6. Damper valve
7. Power cylinder
8. Damper valve
9. Steering gear with front axle wheel angle sensor (F696)
10. Distribution block
11. High pressure filter
DESCRIPTION OF THE SYSTEM
ELECTRICAL EQUIPMENT OF RAS-EC SYSTEM
Electronic unit (D940)
The electronic unit provides control and supervision over the execution of the RAS-EC system management functions. These management functions include:
- Steering wheel steering support rear axle
- Isolation Valve Verification Tests
- Protection against overheating of the working fluid in the hydraulic system
Front axle wheel angle sensor (F696)
The front axle wheel angle sensor, receiving voltage from the RAS-EC electronic unit, shows the angle through which the front axle wheels are turned.
Rear axle steering angle sensor (F695)
The steering angle sensor of the supporting rear axle, receiving voltage from the RAS-EC electronic unit, shows the true angle to which the wheels of the supporting rear axle are turned.
The RAS-EC electronic unit requires a vehicle speed signal to determine if the wheels of the supporting rear axle can be steered.
Wheel speed sensor (F705)
The wheel speed sensor transmits vehicle speed data to the RAS-EC electronic unit. In combination with the vehicle speed signal MTSO, the RAS-EC electronic unit can detect an incorrect speed signal.
Working fluid level sensor (F116)
The working fluid level sensor provides a signal to the RAS-EC electronic unit if the working fluid level falls below the minimum level.
Valve block (V381)
The valve block regulates the pressure and fluid flow to the power cylinder. The valve block contains three valves, two of which are controlled by the RAS-EC electronic unit.
VIC / DIP (D900 / D899)
VIC / DIP, by means of the dashboard informs the driver about the occurrence of:
- not very serious malfunction (yellow signal symbol RAS-EC)
- serious malfunction (red signal symbol RAS-EC)
Communication with a diagnostic scanner for diagnostic purposes.
HYDRAULIC DRIVE SYSTEM RAS-EC
The hydraulic component of the RAS-EC system includes:
1.tank with hydraulic fluid level sensor (F116)
2.pump for power steering
9.steering gear with front axle wheel angle sensor
11.High pressure filter
The hydraulic power required to steer the wheels of the front axle and trailing axle is provided by the power steering pump (2). The pump draws in the working fluid from the reservoir (1). In the distribution block (10), the fluid flow is distributed between the steering mechanisms of the front axle and the supporting rear axle. The working fluid is cleaned by means of a filter in the reservoir (1) and a high pressure filter (9).
Valve block (V381)
The valve block contains three valves: a bypass valve (3), an isolation valve (4) and a control valve (5). The shut-off valve and control valve are electronically actuated.
If the pressure in the system becomes too high, the bypass valve opens against the spring force. As a result, the P inlet terminal and the T drain terminal are directly connected. In this case, the liquid flow is directed directly into the tank.
When not activated, the check valve (4) connects the inlet port P to the drain port T. No fluid is supplied to the control valve (5). In the activated state, the shut-off valve (4) separates the inlet port P from the drain port T. This ensures that the power cylinder (7) is actuated and its operation is controlled by the control valve.
The control valve has a double electrical action. The position of the control valve determines the direction of movement of the piston inward or outward of the actuator.
The power cylinder connections are fitted with damper valves (4) and (6). Damper valves are used to provide precise and smooth steering performance.
The power cylinder (5) is a double-acting cylinder and is constantly monitored by a control valve.
Straight line movement of the car
When the vehicle is moving in a straight line, the electronic unit actuates the shut-off valve (4), thus blocking the connection between the inlet port P and the drain port T. The control valve (5) constantly corrects the operation of the power cylinder (7), keeping the wheels of the supporting rear axle position "straight".
The electronic unit actuates the isolation valve (4), thus blocking the connection between the inlet P and the drain terminal T. The electronic unit energizes the coil (b) of the control valve (5). As a result, the fluid flow from the inlet port P enters the port A and, through the damper valve (6), is directed to the power cylinder (7). The piston of the power cylinder moves into the cylinder, thus setting the wheels of the supporting rear axle in the desired position.
The electronic unit actuates the isolation valve (4), thus blocking the connection between the inlet P and the drain terminal T. The electronic unit energizes the coil (a) of the control valve (5). As a result, the fluid flow from the inlet port P enters the port B and, through the damper valve (8), is directed to the power cylinder (7). The piston of the power cylinder moves outward, thus setting the wheels of the supporting rear axle in the desired position.
DESCRIPTION OF ASSEMBLIES
THE ELECTRONIC UNIT
The electronic unit continuously processes all input signals from various sensors and other systems.
All these data are compared with the parameters (control programs and control variables) stored in the memory of the electronic unit.
Based on this data, the electronic unit calculates the steering angle of the rear axle wheels. The electronic unit constantly actuates the control valve, ensuring that the actual steering angle matches the calculated value. The electronic unit is mounted on a mounting bracket between the two cross members of the vehicle frame.
The working fluid supplied by the power steering pump is divided into two equal parts by the distributor block. From the distribution block, one part of the fluid enters the steering gear of the front axle, and the other part goes into the steering gear of the rear axle.
The distribution block allows the use of only one power steering pump.
The valve block has three valves: a control valve, a shut-off valve and a bypass valve.
The liquid flow from the distribution block enters the outlet P. The liquid flow returns to the tank through the drain outlet T.
Conclusions A and B are connected to the power cylinder.
Control valve (1)
It is a type 4/3 valve with double electrical proportional action and a spring return center position.
When the vehicle is moving in a straight line, both electromagnets (a) and (b) are constantly energized, keeping the rear axle in the center position. If voltage is only applied to electromagnet (a), terminal P is connected to terminal B. Terminal A is connected to drain terminal T.
If only electromagnet (b) is energized, P is connected to A and B is connected to T.
Shut-off valve (2)
It is a type 2/2 valve with an indirect electric actuator and a spring return.
In the neutral position, the shut-off valve connects terminal P to drain terminal T. When the ignition is switched on, voltage is applied to the valve, the valve is triggered and disconnects the inlet terminal P from the drain terminal T. After that, it becomes possible to control the wheels of the supporting rear axle.
In the event of a serious malfunction, the electronic unit stops supplying voltage to the shutoff valve.
The inlet terminal is directly connected to the drain terminal, the steering of the wheels of the supporting rear axle becomes impossible, instead they begin to turn in response to the rotation of the wheels of the front axle.
Overflow valve (3)
The overflow valve protects the hydraulic system from excessive pressure. When the pressure exceeds a certain value, the bypass valve opens and the inlet port is connected to the drain port.
WHEEL STEERING ANGLE SENSORS
Principle of operation
The wheel steering angle sensor includes two potentiometers.
The output signals of both potentiometers are linear and opposite to each other. When the vehicle is moving in a straight line, both signals are equal. When turned, the signal of one potentiometer decreases, while the signal of the other increases.
Using two opposite signals allows the electronics to detect incorrect signals.
The potentiometers are spring loaded. When the connection between the steering gear and the wheel angle sensor is broken, a spring pushes the potentiometers to their end positions. The electronic unit receives signals that are outside the normal range.
Rear axle steering angle sensor
The wheel angle sensor is installed on the rear axle and is connected to the steering knuckle by means of a rod. Each time the wheel is turned, the sensor transmits information about the actual steering angle to the electronic unit.
Front axle steering angle sensor
The wheel angle sensor is mounted directly on the steering gear. With each turn of the wheels, the sensor transmits information about the steering angle to the electronic unit.
The mechanical range of the potentiometers is 110 °. The maximum steering angle is 96 °. If the steering angle sensor is installed incorrectly, there is a great risk of damage to the steering angle sensor.
The double-acting power cylinder is attached to the frame and to the left steering knuckle of the supporting rear axle with ball joints.
Outlets of the power cylinder are equipped with damper valves. The power cylinder is connected to the valve block by means of flexible oil lines.
The damper valve consists of a check valve, a calibrated orifice and a relief valve.
The working fluid enters the power cylinder cavity through a check valve and a calibrated hole. The piston is displaced to the side, as a result of which the volume of the cavity increases.
The movement of the piston reduces the volume of the other cavity.
Fluid in this other cavity is pushed out through the calibrated hole in the damper valve. The resistance encountered by the fluid ensures a controlled and smooth operation of the power cylinder.
To ensure equality of the magnitude of the resistance that the piston encounters, both on the left and on the right, it is necessary that the back pressure on both sides is different. This difference in back pressure is provided by the difference in surface area on the left and right side of the piston.
Backpressure values are controlled by damper valves.
If the damper valves are reversed, the resistance encountered by the piston on the left and right will be different. The outward movement of the piston in the cylinder will occur much faster than inward.
In the event of a self-deactivation of the system due to a serious malfunction, the steering of the wheels of the supporting rear axle becomes impossible, instead they begin to turn in response to the rotation of the wheels of the front axle. Without damper valves, the rear wheels would rotate when the car is turning until they stop against the locking bolts. The vehicle's turning trajectory would be significantly steeper than expected. Damper valves prevent the rear wheels from moving quickly or too quickly towards the stop bolts.
If the damper valves are reversed, the forced steering effect of the rear wheels when the car is turning left and right will be different, which will negatively affect the car's handling characteristics.
It is forbidden to change the damper valves in some places. Such a replacement will negatively affect the handling characteristics of the vehicle.
The tank is equipped with a filter element that filters the oil at the drain.
The filter is not installed in the fluid supply line, as this would increase the filtering resistance of the element and, as a result, the tank would be too large.
When working on the steering gear, do not allow dirt to enter the reservoir. The working fluid is not filtered during the intake, which makes it possible for dirt to freely penetrate into the steering mechanism.
The filter element (6) is held in place by the holder (5). If the resistance of the filter becomes excessive, for example, due to low oil temperature or a dirty filter, the filter element is partially pushed out of its seat. In this case, part of the working fluid passes under the lower part of the filter element directly into the tank. This passage of liquid is made possible by a spring fitted between the filter element and the filter holder.
If the level of the working fluid falls below the minimum mark, the contacts of the fluid level sensor (2) are closed.
SUPPORTING REAR AXLE CONTROL
When cornering, a wheel angle sensor (F696) on the steering box measures the steering angle of the front axle. The steering angle sensor on the steering gear sends a voltage signal to the electronic unit (D940), which corresponds to the degree of rotation of the front wheels.
In order to turn the wheels of the supporting rear axle, the electronic unit also needs vehicle speed data. The tachograph (B525) and the wheel speed sensor ring (F705) transmit information about the vehicle speed to the electronic unit.
Using this data, the electronic unit calculates the degree of wheel rotation and accordingly activates the control valve. The control valve is integrated in the valve block (B381). The control valve has a double electrical action. If voltage is applied to the control valve solenoid (s), the power cylinder piston is pushed outward. The car turns right. If voltage is applied to the solenoid (b) of the control valve, the piston of the hydraulic power cylinder moves inward. The car turns left.
The wheel angle sensor (F695), mounted on the supporting rear axle, transmits information to the electronic unit about the actual steering angle of the rear wheels. In order to keep the wheels of the supporting rear axle in the calculated position, the supporting rear axle is constantly corrected by both electromagnets (a) and (b).
Speed from 15 to 38 km / h
After the vehicle speed exceeds 15 km / h, the electronic unit gradually reduces the degree of deflection of the wheels of the supporting rear axle. When the vehicle reaches a speed of 38 km / h, the wheels of the supporting rear axle stop turning and are locked in the center position.
STOP VALVE INSPECTION TEST
A shut-off valve in the valve block (B381) determines the ability to control the wheels of the supporting rear axle. When no voltage is applied to the valve, hydraulic fluid is directed directly to the reservoir. This can happen when certain malfunctions occur or to prevent overheating of the hydraulic fluid.
The electronic unit (D940) checks the function of the shut-off valve when the ignition is turned on, as well as when the car stops after a trip that has lasted at least 15 minutes.
When the electronic unit stops receiving vehicle speed signals from the tachograph (B525) and the wheel speed sensor ring (F705) for at least 15 minutes, the voltage supply to the shutoff valve is interrupted. At the same time, voltage is applied to the solenoid (a) or (b) of the control valve. If the steering angle sensor of the supporting rear axle (F695) registers an angular rotation, this means. that the shut-off valve is not functioning properly. The electronic unit will register the malfunction and fix the supporting rear axle in the center position. The driver is warned about this by a sound signal and the illumination of the STOP lamp on the instrument panel.
PROTECTING THE HYDRAULIC OPERATING FLUID FROM OVERHEATING
In order to prevent overheating of the hydraulic fluid, under certain circumstances the hydraulic fluid is redirected directly to the reservoir.
In order to ensure the redirection of the working fluid into the tank, voltage is no longer applied to the shut-off valve in the valve block (B381).
This occurs when the electronic unit (D940) stops receiving any signals from the tachograph (B525), the wheel speed sensor ring (F705) and the wheel angle sensor (F696) on the steering gear for 20 seconds.
As soon as the vehicle moves or the steering wheel turns, the electronic unit re-energizes the shut-off valve. It is again possible to steer the wheels of the supporting rear axle.
INSPECTION AND ADJUSTMENT
ITEMS REQUIRING SPECIAL ATTENTION WHEN CHECKING THE SYSTEM
1. When connecting and disconnecting connectors, turn off the ignition.
2. When backhauling and / or measuring system parameters, use the special tool, the BOB Universal Tester (DAF No. 1329433), in combination with the BOB RAS-EC harness (DAF No. 1451996).
3. Use a fuse-protected wire for backhaul connections.
4. If a problem occurs, first of all check the power supply and ground connections. In addition, check the reliability of the contacts in the connectors (corrosion, etc.).
5. Due to the measurement error, the values obtained during the measurement process may slightly differ from those indicated in this manual.
ELECTRONIC UNIT PINS
Contact terminals of the electronic unit