Traction Control System (TCS, ASC + T, ASR, EDS ….): Traction control has several acronyms to designate the same function. With different systems, the purpose is always the same: to avoid sliding of the driving wheels at the moment of acceleration.
The EDS system uses the brake system and takes advantage of the ABS system for its operation. These systems seek the best motricity of the vehicle to avoid the skid of the tires on firm sliding or under a strong acceleration, being considered the system EDS like a self-locking differential.
The traction control, as well as the ESP stability control, uses the anti-lock brake sensors to operate. But unlike the second system, the traction controls only prevent motor losses due to excess acceleration, and are not able to recover the vehicle’s trajectory in case of excessive understeer or oversteer.
There are those that only act on the engine (ASR Anti Slip Regulation), reducing the power, although the driver keeps the accelerator pedestrian to the bottom, (either by the control of the ignition, the injection or, in some cases, even temporarily disconnecting some cylinder). Others act on the brakes (EDS), as a self-locking differential, because they break the wheel that skids to reach the power to which it has more adhesion. There are also traction control systems that combine performance on engine and brakes, also called ASR or EDS per the manufacturer of the vehicle.
The differential in the transmission of the vehicle is used to compensate as its own name indicates the difference between the numbers of revolutions between the driving wheels of the same axis. The operation of the differential is especially noticeable in the curves, avoiding lateral slips of the tire (due to the traction), but the problem comes due to its conception since it is not an appropriate system for a distribution of correct motive force in phase of acceleration on a slippery road. The differential would cause the wheel that skates receives all the driving force, while the wheel that can pull is almost completely eliminated this force. The consequence of this is the sliding of one of the wheels at high speed while the other wheel, which can pull, stands still.
If the two drive wheels of a vehicle turn at the same speed, the power distribution is the same with which the traction is very favorable. Achieving the equal speed of both drive wheels is the goal of the traction control system. This system is also known as TCS when mounted on vehicles equipped with an ABS Teves MK II system.
The EDS uses the clear majority of the original elements of ABS and only needs a few additional elements:
- Additional solenoid valve block TC
- Safety interlocks in the amplification chamber
- Witnesses of TCS and TCS CONTROL
- Simultaneous EDS and ABS control center.
The goal of the ESD is to match the speed of rotation of the two drive wheels. When a wheel rotates faster than its opposite, wheel sensors (common to ABS and EDS) report such a situation. The control unit elaborates the following operation process:
- Activate a TC solenoid valve to communicate the high pressure of the system with the main solenoid valve of the ABS.
- Activate the main solenoid valve to have high tension on the clamps through the conventional brake pump seals.
- It closes the solenoid valve of the wheel that does not want to brake to avoid the arrival of the liquid until its clamp.
The high pressure reaches the clamp of the wheel that skids and it stops. By equalizing its turn with the other wheel, the braking pressure is released to prevent an excessive speed decrease. The process is repeated from the beginning to get equal the speed of rotation of the two wheels.
There are two valves:
Normally open: allows the arrival of high pressure from the pump-accumulator assembly to the main valve. This happens in the conventional and ABS braking phases, as in a normal ABS system without traction control. It closes when the ABS enter to avoid the arrival of high pressure to the amplification chamber.
Normally closed: only open to communicate EDS running high pressure to the main valve without this pressure passes through the amplification chamber.
In the TC block we have a presocontact; its mission is to detect the arrival of pressure to the amplification chamber during the operation of the ESD. The arrival of high pressure to the amplification chamber means that the driver has stepped on the brake and therefore the EDS must be disconnected.
The braking system is preferred on the traction control? The presock completes the braking detection function performed by the brake pedal switch as an additional safety measure.
In the instrumentation table four ABS / EDS related controls are used:
- BRAKE ALERT indicator: low level of liquid at low pressure.
- ABS warning: indicates the test of the system to the contact. The brake light indicates brake malfunction.
- EDS LED: Illuminates when the anti-patched system comes into operation. It is normal for it to light up when it is abruptly accelerated over firm sliding to indicate to the driver that the system is operating properly.
- EDS CONTROL indicator: lights up when there is a fault in the traction control.
The EDS system is complemented with the control of the operation of the vehicle’s engine via the ETS or electronic throttle. The ETS isolates the vehicle throttle from the throttle control on the throttle. This butterfly is governed by a servomotor controlled by a control unit. When the driver presses the accelerator pedal, the movement is detected by a potentiometer that in turn sends an electrical signal to the control panel to move the throttle accordingly.
This system is necessary because the TCS can only match the speed of rotation of the wheels of the same axis. If you are trying to prevent both wheels from skidding (higher front wheel speeds compared to rear wheels) the EDS will not be able to do this. When both front wheels skid, the ETS or electronic butterfly goes into operation to cut power to the engine and prevent slippage. One can say that the EDS seek to match the speed of the drive wheels on the same axle, while the ETS seeks to match the rotational speed of the front axle compared to the rear. Of course, the ETS will also receive information from the wheel spin sensors to be able to detect the speed differences.
Finally, there is no possibility of causing dangerous overheating of the brake pads under the action of the TCS because the control unit will cut the operation of the antipattern over a certain time to avoid these problems.
In the operation phase of the EDS the braking pressure is not generated by the driver since it does not press the brake pedal so that the electric pump located in the hydro group will be responsible for generating the necessary pressure that will be applied to the brake caliper of the wheel that is skidding to slow down its speed.
The start-up of the electric pump causes the braking pressure to be created. Differential pressure valves reduce the pressure created by the pump to about 60 bar to avoid blocking the wheel. The EDS valves are activated by cutting the brake communication towards the rear wheels.
The EDS system has a potentiometer connected to the brake booster membrane which indicates the travel of the brake pedal. The signal from this potentiometer is used to detect braking by the driver. With the potentiometer, it is also possible to inform the control of the intensity with which the driver presses the pedal.
Detecting braking through this potentiometer also causes the EDS to be switched off if the system is in operation.