E.P.A.S. Electric Power Assisted Steering ELECTRIC POWER
Electro Hydraulic Power Steering (EPAS) Systems
ASSISTED STEERING
The first version of Electric Power Assisted Steering was the changing of the power source for the traditional hydraulic power steering from a mechanical pump , driven off the engine via a belt drive Issue driven 16/2017pump. arrangement to an electrically
E.P.A.S. Electric Power Assisted Steering
Electro Hydraulic Power Steering (EPAS)
SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS Systems
Electro Hydraulic Power Steering Systems The first version of Electric Power Assisted Steering was the changing of the power source for the The first version of Electric Assisted (EPAS) pump was the, driven changing theengine power source for drive the traditional traditional hydraulic powerPower steering fromSteering a mechanical offofthe via a belt hydraulic power steering from a mechanical pump , driven off the engine via a belt drive arrangement to an arrangement to an electrically driven pump. electrically driven pump.
Electric Power Assist Mechanism Operation • According to the steering action of the driver, the P/S angle sensor detects the steering speed, and then outputs a steering speed signal to the EPAS control module. The EPAS control module uses the steering speed signal, vehicle speed signal, and other vehicle conditions, to determine the proper motor speed. • Based on the motor speed determined by the Electro Electric Power Mechanism Electric Power AssistAssist Mechanism OperationOperation Hydraulic Power Steering Systems (EHPAS) control
• on According to the steering action ofby thethe driver, the control module, • Based the motor determined EHPAS the current from the motor drive circuit module, the current from the motor drive circuit to the • According to theseed steering action of the the driver, the P/S angle sensor detects the steering speed, and then outputs a to the Power Steering angle sensor detects steering EHPAS motor is controlled to within the target current EHPASsteering motor isand controlled within the target current andmodule the oil pump operates speed signaloutputs toto the EPAS control module. The EPAS control uses the steering accordingly. speed signal, vehicle speed, then a steering speed signal to amount the amount and the oil pump operates accordingly.
EPAS control The EPAS control module uses the proper motor speed. speed signal, andmodule. other vehicle conditions, to determine
• Thethe hydraulic pressure createdDue by the oil pump • The hydraulic pressure by thespeed oil pump is used shaft to turn axially. to this, the issteering the steering speedcreated signal, vehicle signal, and to assist used to assist the shaft to turn axially. Due to this, other vehicle conditions, to determine the proper motor • Based onon thethe motor seed tothe the operation load driver is determined reduced. by the EHPAS control module, the current from the motor drive circuit speed.
steering operation load on the driver is reduced.
EHPAS motor is controlled to within the target current amount and the oil pump operates accordingly.
• The hydraulic pressure created by the oil pump is used to assist the shaft to turn axially. Due to this, the steering operation load on the driver is reduced.
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ELECTRIC POWER
ASSISTED STEERING Issue 16/2017
Electric Power Assisted Steering (E.P.A.S.) System SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS
Electric Power Steering (EPAS) hasAND replaced hydraulic power steering in many new vehicles today. One of WHEEL ALIGNMENT SPECIALISTS the advantages of electric power steering is that it eliminates the power steering pump, which can use as much asAssisted 8 to 10 horsepower load. This improves fuel economy while also eliminating the weight and Electric Power Steering under (EPAS) Systems bulkAssisted of the power steering and hoses. Gettingpower rid ofsteering the hydraulics awaytoday. with fluid leaks Electric Power Steering (EPAS)pump has replaced hydraulic in manyalso newdoes vehicles One of and the need to check the power steering fluid. Electric power steering is also quieter than hydraulic the advantages of EPAS is that it eliminates the power steering pump, which can use as much as 8 to 10 horsepower because there is no pump noiseeliminating and no fluid valves. But pump the most under load.systems This improves fuel economy while also theflowing weight through and bulk hoses of the and power steering and noticeable difference is also in handling and with steering hoses. Getting rid of the hydraulics does away fluid refinement. leaks and the need to check the power steering fluid. Electric power steering is also quieter than hydraulic systems because there is no pump noise and no fluid flowing through hoses and valves. But the most noticeable is in handling andeliminates steering refinement. Electrically assisted steering or EPAS, is difference a power-assist system that the connection between the
and steering system. or direct system electricthat power steeringthe takes the technology stepengine further by Electrically engine assisted steering or EPAS, is aEPAS power-assist eliminates connection betweena the completely eliminating fluid and the accompanying hardware from the system, becoming a full and steering system. EPAS or directhydraulic electric power steering takes the technology a step further by completely eliminating“electric hydraulicpower fluid and the accompanying hardware from the system, becoming a full “electric power assisted assisted steering system” or EPAS. steering system” or EPAS. An EPAS Direct electric steering uses motor an electric motor attached to rack the steering rack via a gear An EPAS Direct electric steering system usessystem an electric attached to the steering via a gear mechanism and torquemechanism sensor. A microprocessor or electronic control unit,orand diagnostic software steeringsoftware dynamics and torque sensor. A microprocessor electronic control unit,controls and diagnostic and driver effort. Inputs include vehicleand speed andeffort. steering, wheel torque, angular position turning rate.torque, controls steering dynamics driver Inputs include vehicle speed and and steering, wheel angular position and turning rate.
Column Type
Pinion Type
Dual Pinion
Active Rack
Advantages:
Electric power assist steering can be fine tuned with a precision that is hard to match with hydraulic controls. • Small compact units, requiring only a battery By monitoring the driver’s steering inputs, vehicle speed, connection work.compact units, requiring only a battery • toSmall connection to work.dynamics, the system can provide and other suspension the right amount of steering feel and effort to match • No messy•hydraulic connections systems to bleed. No messy hydraulicorconnections or systemsjust to bleed. rapidly • Weight saving advantage hydraulic systems. changing driving conditions. EPS can deliver • Weight saving advantage over hydraulicover systems. extra effort when you need it, and reduce steering effort • Reduced mechanical drag on engine compared to hydraulic engine driven pumps. when you do not need it. It can even provide steering • Reduced mechanical drag on engine compared to • Built-in fail-safe revertwhen to conventional in the unlikely event of a the engine issteering off. hydraulic engine driven pumps.which allows the system toassist
Advantages:
fault occurring.
• Built-in fail-safe which allows the system to revert to conventional steering in the unlikely event of a fault occurring.Electric power assist steering can be fine tuned with a precision that is hard to match with hydraulic
controls. By monitoring the driver's steering inputs, vehicle speed, and other suspension dynamics, the system can provide just the right amount of steering feel and effort to match rapidly changing driving conditions. EPS can deliver extra effort when you need it, and reduce steering effort when you do not need it. It can even provide steering assist when the engine is off.
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ELECTRIC POWER
ASSISTED STEERING Issue 16/2017 SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS
AND WHEEL ALIGNMENT SPECIALISTS In current-day systems, there is always a mechanical connection between the steering wheel and the steering gear. For safety reasons, it is important that a failure in the electronics never result in a situation where the motor In current-day theresteering is always a mechanical While it fail-safe has been used in electric forklifts and some prevents systems, the driver from the vehicle. EPS systems incorporate mechanisms that disconnect power connection between the steering wheel and the steering tractors, as well as a handful of concept cars, the from the motor in the event that a problem with the ECU is detected.
gear. For safety reasons, it is important that a failure 2014 Infinity Q50 was the first commercial vehicle to in the electronics result steering in a situation where implement steer-by-wire. Although there is normally no The next stepnever in electronic is to remove thethe mechanical linkage to the steering wheel and convert to pure motor prevents the driver from steering the vehicle. direct mechanical linkage, the Q50 has a mechanical electronically controlled steering, which is referred to as steer-by-wire. This functions by transmitting digital signals EPAS systems incorporate fail-safe mechanisms that back-up. In the event that a problem is detected to one or more remote electric motors instead of a rack and pinion assembly, which in-turn steers the vehicle. While with disconnect from the motor in the that a as well the electronic controls, clutch to was restore it has power been used in electric forklifts andevent some tractors, as a handful of concept cars,a the 2014engages Infinity Q50 problem with the ECU is detected. the driver’s mechanical control. As with throttle control the first commercial vehicle to implement steer-by-wire. Although there is normally no direct mechanical linkage, systems, it is likely that steer-by-wire will become the The next in electronic steering remove thea problem is detected with the electronic controls, a clutch thestep Q50 has a mechanical back-up.isIntothe event that standard once the electronic controls prove to be safer mechanical linkage to the steering wheel and convert to throttle control systems, it is likely that steer-by-wire will engages to restore the driver's mechanical control. As with and more reliable than the current hybrid systems. pure electronically controlled which is referred become the standard once steering, the electronic controls prove to be safer and more reliable than the current hybrid to as steer-by-wire. This functions by transmitting digital At this point in time E.P.A.S. racks are not repairable systems. signals to one or more remote electric motors instead or serviceable, therefore if they fail internally a new At and this point in time E.P.A.S. which racks are not repairable or serviceable, therefore rack if theywill failbe internally a new of a rack pinion assembly, in-turn steers the replacement required. vehicle.replacement rack will be required.
Driver Input
Steering Angle Sensor
Steering Column Steering Column
Torque Sensor
Electric Drive Motor
Control Module Control Module
Steering Rack
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ELECTRIC POWER
ASSISTED STEERING Issue 16/2017 AND WHEEL ALIGNMENT Direct Adaptive Steering (DAS) or SPECIALISTS Steering by Wire (SBW) SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS
Direct Adaptive Steering (DAS) or Steering by Wire (SBW)
1. Steering Force Sensor and Steering Angle Sensor This plays two roles, the unit sends commands to the So-called “by-wire” controls, which replace a mechanical between driver control modules and acts as connection the driver’s feedback So-called “fly-by-wire” controls, which replace a source by varying resistance to the wheel. electronic signal, have become commonplace. Steering systems haven’t gone com mechanical an connection between driver and automobile 2. Clutch - Most of the time it’s open. If a fault occurs in with an electronic signal, have become commonplace. good reason: It’s a little scary to imagine front wheels that orand may nota respond t the electronics, the clutch will may activate create Steering systems have not gone completely by-wire for solid link between the steering wheel and the rack. good reason: It is a little scary front wheels depending ontoaimagine computer’s whim. that may or may not respond to the driver’s inputs, 3. Control Modules – This trio controls the electic-assist depending on a computer’s whim. motors and the steering force sensor.
But the steer-by-wire (SBW) system includes a fail-safe clutch in its column. In norma
But the steer-by-wire (SBW) system includes a fail-safe 4. Steering Assist Motors. clutch in its column. In ¬normal driving situations, thisif one of the three control modules detects a fault, the this clutch is disengaged, but The Direct Adaptive Steering can transmit the driver’s clutch is disengaged, but if one of the three control intentions to the assisted wheels faster than a mechanical system. The the steering acts snaps as a conventional, electrically rack-and-pinion modules detects a fault, the clutch shut and the system. It also enables four different settings that allow steering acts as a conventional, electrically assisted drivers to customize steering effort/response suit their when the engine shuts off, so if the SBW-equipped car fails to start,tothe owner can rack-and-pinion system. The clutch also engages when preference or road conditions. Those settings include, in the engine shuts off, soit. if the SBW-equipped car fails to pushing increasing order of driver engagement: standard/casual; start, the owner can still steer the car while pushing it. standard/standard; heavy/standard; and heavy/quick.
1. Steering Force This plays two ro commands to the acts as the driver varying resistanc
2. Clutch - Most a fault occurs in t clutch will activa link between the the rack.
3. Control Modul the electic-assist steering force se
4. Steering Assist
The Direct Adaptive Steering can transmit the driver’s intentions to the wheels faste system. It also enables different settings allow drivers Straightfour advice, specialists youthat understand and... to customize steering suit their preference or road conditions. Those settings include, in increasing order o standard/casual; standard/standard; heavy/standard; and heavy/quick.
ELECTRIC POWER
ASSISTED STEERING HINTS
Issue 16/2017 Description:
SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS
VF Commodore Electric Power Steering
Techstop Hints One of the new features incorporated into the new VF Commodore is an Electric Power Steering system. Caution must be exercised, when turning the steering back and forth wheels steering assistance to the driver by the means of an electric motor rather than a high Theusing EPASthe provides When a vehicle has been raised so the steering wheels are clear of pressure hydraulic system. the ramps or ground, it is stressed that the use of the wheels to turn the steering from lock to lock to the point of engaging the steering Service CAUTION stops with any force, may cause internal damage to the steering rack.
The following precautions should be observed if the vehicle is on a hoist or the front wheels are OFF the ground. Failure to observe these precautions may result in steering rack damage. (These racks are not The following precautions should be observed if the vehicle is on a hoist or the front wheels are OFF the ground. serviceable and the unit will have to be replaced) Failure to observe these precautions may result in steering rack damage. E.P.A.S. racks are not serviceable and the Service CAUTION
unit will have to be replaced.
•
The front wheels should NOT be turned to full lock by manually moving the rack by hand at the
• The front wheels should NOT be turned to full lock by manually moving the rack by hand at the road wheels with road or wheels. any great velocity force.
• The front wheels should NOT be turned to full lock by using the steering wheel. If the wheels need to be turned towards full lock for service work, they should be turned GENTLY and care • If the wheels need to be turned towards full lock for service work, they should be turned GENTLY and care must be must be taken to avoid hitting the steering lock stops with any force. • The front wheels should NOT be turned to full lock by using the steering wheel with any great velocity or force. taken to avoid hitting the steering lock stops with any force.
This only applies to vehicles where the wheels are OFF theOFF ground. This does not does applynot in normal This only applies to vehicles where the wheels are the ground. This apply operation in normalwhilst operation driving. The above procedure should be applied to EVERY E.P.A.S. rack.
whilst driving.
1. Rack and Pinion Gear 2. Power Steering Control Module 3. Electric Drive Motor 4. Drive Belt 5. Steering Torque Sensor
This is a typical belt drive E.P.A.S. rack
DANGER
DON’T FORGET about the S.A.S.:
The above procedure should be applied to EVERY EPAS rack. But, this does not stop you from using the
Every time a front suspension repair has taken place and a wheel alignment is required, the Steering Angle Sensor wheels when the vehicle is raised to go from lock to lock, BUT ( there is always a but) always use a gentle (SAS) is to be checked using a scan tool and re – calibrated as required. This process is not an option, it is a must do. slow movement, as soonmay as drift you or become over enthusiastic, problems may occur. If not performed the vehicle steer left or right.
DON”T FORGET about the S.A.S.: Every time a front suspension repair has taken place and a wheel alignment is required, the Steering Angle advice, specialists you understand and... Sensor (SAS) is to be checkedStraight using a scan tool and re – calibrated as required. This process is not an option, it is a must do. If not performed the vehicle may drift or steer left or right.