Tài liệu đào tạo kĩ thuật viên HYUNDAI - hệ thống lái trợ lực điện( EPS- MDPS)

Tài liệu đào tạo kĩ thuật viên HYUNDAI - hệ thống lái trợ lực điện( EPS- MDPS) A typical power rack-and-pinion steering assembly is used on many cars. This rack-and-pinion assembly is a hydraulic-mechanical unit with an integral pis

POWER RACK AND PINION STEERING

A typical power rack-and-pinion steering assembly is used on many

cars This rack-and-pinion assembly is a hydraulic-mechanical unit with an integral piston and rack assembly An internal rotary valve direct power steering fluid flow and controls pressure to reduce steering effort

When the steering wheel is turned, resistance created by the weight of the car and tires-to-road friction causes a torsion bar in the rotary valve to

deflect This changes the position of the valve spool and sleeve, thereby directing fluid under pressure to the proper end of the power cylinder

The difference in pressure on either side of the piston (attached to rack) helps move the rack to reduce turning effort The fluid in the opposite end

of the power cylinder is forced to the control valve and back to the pump reservoir When the steering efforts stops, the control valve is centered by the twisting force of the torsion bar, pressure is equalized on both sides of the piston, and the front wheels return to the straight ahead position

POWER RACK AND PINION STEERING

Steering Column

Power Steering Pump

Power Steering Gear

POWER RACK AND PINION STEERING

System construction

POWER RACK AND PINION STEERING

The rack-and-pinion power steering system consists of:

- Rack and pinion steering gear box

- Power steering oil pump

- Oil reservoir

- Tubes

The power steering system uses a hydraulic pressure which is generated

by the power steering pump to reduce the effort required to turn the

steering wheel The power steering pump is mounted on the front of the engine The pump has a vane-type design, and is driven by the

crankshaft through a drive belt

The power steering fluid is drawn into the pump from the reservoir when the engine is running The fluid is pressurized by a power steering switch and a control valve located in the power steering pump

System construction

POWER RACK AND PINION STEERING

Rack-and-pinion steering linkage

Rack-and-pinion linkage connects the gear to the steering knuckles The construction of the Rack-and-pinion linkage is tie rod ends, Lock nut,

Boot, Inner ball joint, Rack, Pinion shaft assembly, Steering gear

housing, Oil pipe, Bearings, Seals, Bushings, O-rings

One end of the inner tie rod is inside the steering gear and is connected with the inner ball joint The inner tie rod is protected from the elements

by a rubber boots The outer part of the inner tie rod is a threaded shaft and the outer tie rod is threaded onto this shaft and held in place by a

locknut Toe adjustment is made by loosening the locknut and turning the inner rod to shorten or lengthen the tie rod assembly

POWER RACK AND PINION STEERING

1 Tie rod end

Rack-and-pinion steering assembly

POWER RACK AND PINION STEERING

In Out

Left Turn

Right Turn

Right Turn Oil Flow Left TurnOil Flow

Cutaway of a Rack-and-Pinion steering gear

POWER RACK AND PINION STEERING

Cutaway of a Rack-and-Pinion steering gear

POWER RACK AND PINION STEERING

Torsion bar Bearing Input shaft

Yoke spring

Rack Pinion gear

From oil pump

To oil reservoir

B Rotary valve

Bearing [Section A-A]

Cutaway of a Rack-and-Pinion

steering gear

Cutaway of a Rack-and-Pinion steering gear

POWER RACK AND PINION STEERING

To cylinder tube right chamber

To cylinder tube left chamber

Torsion bar

Rotary valve

Input shaft

To oil reservoir From oil pump

[Section B-B]

Operation of the pinion and valve assembly (at the center position)

POWER RACK AND PINION STEERING

Chamber “A”

Port a

Port d

To the left cylinder tube

From the oil pump

To the right cylinder tube Port c

Port b

Operation of the pinion and valve assembly (at the center position)

POWER RACK AND PINION STEERING

Oil pump Oil reservoir

R’ Oil passage-way ROil passage-way L

L’

Operation of the pinion and valve assembly (at the center position)

POWER RACK AND PINION STEERING

Sleeve a

Operation of the pinion and valve assembly (turning left)

POWER RACK AND PINION STEERING

Chamber “A”

Port c

Port d

To the left cylinder tube

From the oil pump

From the right cylinder tube Port b

Port a

Operation of the pinion and valve assembly (turning left)

POWER RACK AND PINION STEERING

Oil pump

Oil reservoir

R’ Oil passage-way ROil passage-way L

L’

Operation of the pinion and valve assembly (turning left)

POWER RACK AND PINION STEERING

Operation of the pinion and valve assembly (turning right)

POWER RACK AND PINION STEERING

Operation of the pinion and valve assembly (turning right)

POWER RACK AND PINION STEERING

Oil pump Oil reservoir

R’ Oil passage-way ROil passage-way L L’

Cylinder tube left chamber

Cylinder tube right chamber

Operation of the pinion and valve assembly (turning right)

POWER RACK AND PINION STEERING

Oil reservoir

Oil pump

Port c Port d

Cylinder tube

left chamber

Cylinder tube right chamber

Chamber “A” Torsion bar

Port b

Sleeve b Rotary valve

Sleeve a Sleeve c

Port a

POWER STEERING PUMP

Oil pump construction

Oil pump construction

POWER STEERING PUMP

Operation of the oil pump

POWER STEERING PUMP

Flow control valve

As the discharge rate of the power steering pump increases in

proportioning to the pump revolution speed, a flow control valve is added

to control it so that the optimum amount of fluid for steering operation is supplied according to the engine speed (driving condition)

Described below is its operation at different engine speeds

POWER STEERING PUMP

Flow control valve (when idling)

The fluid discharged from the pump is supplied through the clearance around the rod in orifice A1 to the gear box

POWER STEERING PUMP

Flow control valve (when running at Low Speed)

POWER STEERING PUMP

1 Flow control valve

2 Flow control spring

(Increase in engine speed)

As the engine speed rises, the pump discharge rate increases and causes

a pressure difference to occur between both ends of the orifice (P1 – P2) Thus the pressure exceeding the flow control spring force pushes the flow valve to the right in figure, making the opening in the orifice narrower

through which only a necessary amount of fluid is fed to the gear box and the excess fluid is returned to the pump

Flow control valve (when running at High Speed)

POWER STEERING PUMP

As the engine speed rises higher, opening in the orifice is made narrower and fluid flow to the gear box reduces As a result, hydraulic pressure

application is slow at the start of the steering wheel turn This provides straight-ahead stability to suit the driving condition with the steering wheel operated near its neutral position

The steel ball in the relief valve is under the hydraulic pressure in the circui

t coming through orifice A2 When the steering wheel is turned and the hydraulic pressure increases higher than 75-82kg/cm2 (1060-1160 psi), it compresses the relief spring to push the steel ball which then allows the fluid to flow to the power steering pump

Such relief valve operation causes a pressure difference to occur between chamber A and B.

Then the flow valve moves to the right to make opening in orifice A1,

maintaining the hydraulic pressure constant

Relief Valve

POWER STEERING PUMP

ELECTRONIC POWER

STEERING (EPS)

STEERING G/BOX EPSCM

EPS GENERAL

System Layout

EPS Gear box

EPS COMPONENTS

(1) Provides a light steering effort when the vehicle is stationary or

running at low speeds

(2) Controls the steering effort according to the vehicle speeds

(3) During intermediate and high speed operation, the steering effort

linearly increases with respect to the steering angle, offering stable

steering feeling

EPS FEATURES

(4) During intermediate and high speed operation, when the steering

wheel is at or near the neutral position, the function of the reactionary plunger increases the steering effort to give you a stable feeling

(5) When the vehicle is running on a rough road at intermediate and high speeds, even if there is a large force from the road surface, it does not affect directional control, as the output hydraulic pressure for the steering effort becomes high as in the conventional power steering

(6) The system has a fail-safe function so that even if the electrical

system, including the control unit and sensors fails, the steering

characteristics of a vehicle with normal power steering will be retained

EPS FEATURES

Relation between steering effort and output hydraulic pressure

EPS FEATURES

Vehicle speed vs steering effort characteristics

• At low vehicle speed or when steered at standstill, the hydraulic pressu

re to the reaction plunger is kept at such low level that the EPS is steere

d with minimum steering effort

• As vehicle speed increases, the hydraulic pressure to the counter-force plunger is raised by closing the solenoid valve, then the reaction force increases accordingly and the steering force becomes large In other word

s, the steering characteristics are desirable in that the steering effort increases in proportion to the increment of torsional rigidity of the steering input shaft

EPS FEATURES

Vehicle speed vs steering effort characteristics

EPS FEATURES

Steering angle vs steering effort characteristics

• In this system, the assist pressure ge

nerated during steering is also applied

to the reaction plunger through the hyd

raulic pressure control valve under the

condition that the vehicle speed is high

and the solenoid valve is closed In thi

s manner, the reaction from the road s

urface also contributes to the variation

in torsional rigidity of the system, and t

he “direct” steering feeling is thus obtai

ned, which is realized by proportional s

teering effort characteristics to the stee

ring angle

EPS CONSTRUCTION

1 Parking, At low vehicle speed

1) EPSCM supplies the maximum current (around 1A) to the PCV solenoid 2) PCV solenoid is energized and solenoid rod pushes PCV spool to the right 3) Pump oil pressure cannot flow to the reaction chamber because PCV spool

blocks the orifice from the oil pump on the PCV spool guide

4) Reaction plunger does not move allowing a light steering effort.

PCV OPERATING PRINCIPLE

REACTION CHAMPER FROM OIL PUMP (CLOSED)

1) Output current from EPSCM to the PCV Solenoid reduces Pushing force by a solenoid rod also decreases And return spring force pushes a PCV spool back 2) Pump pressure via the orifice on the PCV spool guide is delivered to the

reaction plunger pressing the steering input shaft

3) This time, reaction force by a reaction plunger is delivered to the input shaft This resists a steering allowing its heavy steering effort

PCV OPERATING PRINCIPLE

REACTION CHAMPER

Pushing force reduces

and a PCV spool

moves small amount

FROM OIL PUMP

(OPEN)

2 Medium, High vehicle speed

EPS CONSTRUCTION

ROTARY VALVE

The rotary valve is of

double construction with the valve body rotating inside the valve case

This makes it unnecessary

to seal the rotating portion (valve body) of the valve, so less steering friction assures smoother steering

The rotary valve operates to direct the oil to the power cylinder of steering gear box

as in the conventional power steering

COUNTER-FORCE PLUNGER

The counter-force plunger consists of four plungers The force pressing the input shaft varies according to the hydraulic pressure (which varies with the vehicles speed) acting on the chambers behind the plungers The higher the hydraulic pressure on the chambers, the more tightly the input shaft is pressed So the steering effort increases according to the vehicle speed as shown in the vehicle speed vs steering effort

characteristics, diagram

EPS CONSTRUCTION

Vehicle speed sensor

EPS OPERATING PRINCIPLE

EPS CONSTRUCTION

Pump

TPS (XG)

EPSCM INPUT & OUTPUT

TARGET CURENT CALCULATION

SOLENOID VALVE

VEHICLE SPEED CALCULATION

EPSCM LOCATION & PIN LAYOUT

3 2 1

8 7 6 5 4

6 Sensor signal from vehicle speed sensor

-Solenoid(-)

EPS SOLENOID VALVE

EPS solenoid valve

Solenoid performance characteristic

1 Disconnect EPS solenoid valve connector and install the ampere-meter Notice: Do not ground solenoid terminal

2 Current value at the speed of 0 km/h should be in 0.9 ~ 1.1 A.

3 Read the output current while increasing the vehicle speed slowly

4 When increasing the vehicle speed, the ampere should be decreased.

EPS SOLENOID VALVE

EPS solenoid valve

SOLENOID VALVE

CURRENT VEHI CLE SPEED

1A

0 km/h

1) Vehicle stop or at a low speed

When a vehicle stops or at a low speed, EPSCM controls the current

of a pressure control solenoid valve as 1 ampere This time, a reaction plunger of the solenoid valve moves to the top inhibiting the oil flow The reaction plunger does not have a force to push the input shaft, therefore, a driver can steer easily

This output pressure helps a driver to get a proper steering feeling at

a mid-high speed

a torsion spring and a pinion gear are moves together resulting in a heavy steering effort like a non power steering vehicle.

Trouble symptom Trouble area Inspection item

Solenoid valve continuity By-pass valve

Blown fuse Remove the control unit connector and check the continuity in the solenoid harness (between terminal No.1 and No.2)

abnormalities in the control module power circuit Use a tester to check the stationary steering effort Check the solenoid current in relation to changes in vehicle speed

Steering gear and

Steering gear and linkages

Harness of fuse

Control module

Steering wheel movement is

heavy (when igintion key is

turned ON, no current flows

through the solenoid)

While driving at medium or

high speed, steering

remains light

TROUBLESHOOTING

EPSCM HI-SCAN PRO DATA

Output voltage of Pin No.6 (Vehicle Speed Sensor) at 30Km/h

Waveform of Pin No.5 (Diagnosis): Normal status

EPSCM HI-SCAN PRO DATA

Waveform of Pin No.5 (Diagnosis): Pin No.1 or 2(Solenoid) open

EPSCM HI-SCAN PRO DATA

Waveform of Pin No.5 (Diagnosis): Pin No.6 open

the same as normal status

▶ the same as normal status

EPSCM HI-SCAN PRO DATA

Waveform of Pin No.5 (Diagnosis): Pin No.8(Ground) open

EPSCM HI-SCAN PRO DATA

Waveform of Pin No.1 (Solenoid -): at 0 Km/h

EPSCM HI-SCAN PRO DATA

Waveform of Pin No.1 (Solenoid -): at 80 Km/h

EPSCM HI-SCAN PRO DATA

Waveform of Pin No.1 (Solenoid -): at 140 Km/h

EPSCM HI-SCAN PRO DATA

Waveform of Pin No.2 (Solenoid +): at 0 Km/h

EPSCM HI-SCAN PRO DATA

Pin No 2(Solenoid+) control current at 0 Km/h

EPSCM HI-SCAN PRO DATA

Waveform of Pin No.2 (Solenoid +): at 40 Km/h

EPSCM HI-SCAN PRO DATA

Pin No 2(Solenoid+) control current at 40 Km/h

EPSCM HI-SCAN PRO DATA

Waveform of Pin No.2 (Solenoid +): at 80 Km/h

EPSCM HI-SCAN PRO DATA

Pin No 2(Solenoid+) control current at 80 Km/h

Waveform of Pin No.2 (Solenoid +): at 120 Km/h

EPSCM HI-SCAN PRO DATA

Pin No 2(Solenoid+) control current at 120 Km/h

Waveform of Pin No.2 (Solenoid +): at 140 Km/h

EPSCM HI-SCAN PRO DATA

Pin No 2(Solenoid+) control current at 140 Km/h or more

EPSCM HI-SCAN PRO DATA

Pin No.2(Solenoid+) waveform when Pin No.8(Ground) open: IG on, 0km/h

However, the output current is 0A.

Pin No.2(Solenoid+) waveform when Pin No.5(Diagnosis) or Pin No 6(vehicle sensor) open: IG on, 0km/h , The output current is 1A.

EPSCM HI-SCAN PRO DATA

Pin No.2(Solenoid+) waveform when Pin No.6 open: 1~ 250km/h The output current is always 1A.(Failsafe- light steering effort)

EPSCM HI-SCAN PRO DATA