Active Height Control & Adaptive Variable Suspension: Other Lexus LX J100

Control Switches

The height select switch, height control switch and damping mode select switch are located in front of shift lever. (Scheme 158)

1. Height Select Switch - A rocker type momentary switch has been adopted for height select switch that is used for selecting desired height. Pressing the up side of the switch once raises vehicle height and pressing down side once lowers vehicle height.
2. Height Control Switch - Pressing this switch prevents height control function. Pressing it again cancels prevention. Prevention cancels automatically when vehicle speed exceeds 50 MPH at normal vehicle height, or 19 MPH at any other vehicle height. The state of height control prevention is stored in memory even after ignition switch has been turned off.
3. Damping Mode Select Switch - This switch enables the driver to select a desired damping force from 4 modes. (Scheme 159)

Scheme 158

Scheme 159

Front Speed Sensors

The front speed sensors detect individual speeds of front wheels. The wheel speed sensors are then input into suspension control ECU via ABS & hydraulic brake booster ECU.

Gas Chamber & Damping Force Control Actuator

A gas chamber (substituting for gas chamber in a conventional shock absorber) and an actuator to switch damping force have been integrated. The housing is provided with heat dissipating fins to improve dissipation of heat that is generated by actuator. (Scheme 160)

1. Gas Chamber - The gas chamber uses a bladder type hydro-pneumatic accumulator. A resin membrane is sandwiched between rubber layers for gas penetration resistance. Internal pressure of gas chamber is varied by allowing fluid to flow in and out of gas chamber in order to raise or lower vehicle height.
2. Damping Force Control Actuator - Pressure resistance performance of damping force control actuator has been improved over that available on electric modulated suspension of other models. This actuator consists of a 16 steps step motor, a screw mechanism (which converts rotational movement to linear movement), a spool valve, a soft damping force valve and hard damping force valve. Signals from suspension control ECU activate actuator causing spool valve to switch oil passage. This causes the volume of oil that passes through each valve to be varied in order to control damping force in 16 steps. (Scheme 161)

Scheme 160

Scheme 161

Height Control Accumulator

The height control accumulator is a free piston type which provides a large gas chamber capacity. The height control accumulator consists of a cylinder, free piston and solenoid valve. When raising vehicle height, accumulator discharges stored fluid to accelerate raising speed. Normally the solenoid valve remains closed. When vehicle height is being raised or fluid is being stored in main accumulator, the solenoid valve opens in accordance with signal received from suspension control ECU. (Scheme 162)

Scheme 162

Height Control Sensors

A total of 3 sliding resistance type height control sensors are provided. There is one in each right and left front wheel housing and one in center of cross member located above rear axle. Each sensor consists of a brush that is integrated with a shaft which slides on resistor that is formed on a substrate. Because resistance value between brush and resistor terminal varies in proportion to shaft's rotational angle, a prescribed amount of voltage is applied to resistor so that a change in rotational angle can be detected by a voltage change. (Scheme 163)

Scheme 163

Pump & Motor

The pump, pump motor, reservoir tank, return valve, pressure sensor and temperature sensor are integrated. (Scheme 164)

1. Pump - An external gear pump that contains less parts has been adopted. Pump is a pressure-loading type in which discharge pressure of pump is utilized and routed via gear case to push on side of pump gear in order to reduce internal leakage, thus making high pressure discharge possible. (Scheme 165)
2. Motor - A DC motor with 4-pole brushes is used for durability and high torque.
3. Return Valve - The return valve opens and closes oil passage between control valve assembly and reservoir tank. The return valve has been simplified by adopting a construction in which the valve is closed by flow of discharged fluid. Normally, a spring force is applied to return valve to maintain oil passage between control valve assembly and reservoir tank open. When pump operates to raise vehicle height, pressure of fluid that is discharged by pump causes return valve to move. Accordingly, oil passage between control valve assembly and reservoir tank closes, and fluid that is discharged from pump flows toward control valve assembly. (Scheme 166)

Scheme 164

Scheme 165

Scheme 166

Pump Attenuator

The pump attenuator dampens hydraulic pulsation of fluid that is discharged by pump. A bellows type accumulator that is made of stainless steel, which offers gas penetration resistance and pulsation absorption performance, has been adopted. (Scheme 167)

Scheme 167

Shock Absorber

The shock absorber has dual construction using a high-pressure main seal made of fluoroethylene resin and a high-pressure oil seal made of nitrile rubber. It is provided with a backup ring in order to ensure sealing performance and reduce friction. (Scheme 168)

Scheme 168

Steering Angle Sensor

The steering angle sensor is fitted to turn signal switch assembly and detects steering direction and angle. The sensor contains 2 photo interrupters with phases. A slotted disc interrupts the light to turn photo transistor on and off to detect steering direction and angle.

Suspension Control ECU

The suspension control ECU is located in driver's side instrument panel. Based on signals received from sensors and switches, suspension control ECU detects vehicle height and conditions and outputs control signals to actuators and pump. (Scheme 169)

Scheme 169

Float & Pitch Control

Float and pitch control affects independent front/rear control of damping force to achieve an optimal damping force depending on roughness of road surface. The suspension control ECU calculates relative speed between body and wheels based on signals received from height control sensor, and controls actuators to maintain a flat and stable vehicle posture in various road conditions. These are independent between front and rear wheels in order to stabilize vehicle to a flat posture.

Thumping Sensitive Control

When road surface condition does not require damping force, thumping sensitive function controls actuators so their damping force will not increase. As a result, both flatness and a soft ride are achieved.

Speed Sensitive Control

Speed sensitive control balances vehicle's riding comfort and road-holding performance. Damping force is increased with increase in vehicle speed to ensure stability during high-speed driving.

Anti-Roll Control

During cornering anti-roll control makes damping force firmer, thus restraining body roll to provide stability and control.

Anti-Dive Control

Anti-dive control makes damping force firmer during braking to restrain body dive.

Anti-Squat Control

Anti-squat control makes damping force firmer during acceleration to minimize changes in vehicle body posture.

Damping Force Control

The damping force control actuator uses a 16 step motor to generate a continually variable damping force. This provides a wide selection of damping force and enables a smooth transition of damping force. As a result, a minutely controlled damping force that accommodates various types of driving conditions has been made possible.

FUNCTION OF COMPONENTS

To identify function of components (Scheme 170)

Scheme 170

RIGHT-LEFT WHEEL COMMUNICATING FORCE

Normally, an oil passage remains open between shock absorbers for right and left wheels. This enables the suspension to contract and elongate smoothly when right and left wheels move gradually at opposite phases, and provides road-holding performance while driving on a winding road. When driver operates steering wheel, oil passage between right and left shock absorbers closes according to that condition. This restrains increase of vehicle body roll during cornering and increases vehicle stability and control.

VEHICLE HEIGHT CONTROL FUNCTION

Note. Occasionally, set vehicle height may not be maintained when vehicle is carrying a load that is heavier than a prescribed amount. At these times, it might not be possible to raise vehicle height even by operating switch. For maximum load see MAXIMUM LOAD table.

MAXIMUM LOAD

Vehicle Height Selection Function

There are three types of vehicle heights which can be selected by operating switch: normal vehicle height (N), low vehicle height (Lo) and high vehicle height (Hi). (Scheme 171)

Scheme 171

Automatic Leveling Function

Automatic leveling function maintains vehicle height constant regardless of load conditions such as number of occupants or weight of cargo under prescribed loading condition. It effects constant control so vehicle height is maintained at a prescribed value when normal vehicle height is selected.

Vehicle Speed Sensing Function

Vehicle speed sensing function automatically adjusts vehicle height in accordance with vehicle speed in order to ensure stability and riding comfort while driving. (Scheme 172)

Scheme 172

Extra High Mode

If one wheel freewheels while driving on an unpaved road with transfer shifted in low range and vehicle height set to high, vehicle height raises automatically by approximately 1.2 inches in front and .8 inches in rear.

Normal Driving (Straightline Driving)

High pressure in gas chamber and shock absorber is shut off with leveling valve. Gate valve remains open, and right and left shock absorbers remain connected. Damping force is controlled in accordance with road surface conditions. (Scheme 173)

Scheme 173

Cornering

High pressure in gas chamber and shock absorber is shut off with leveling valve. Gate valve is closed and left and right shock absorbers are shut off from each other. Damping force is controlled in accordance with road surface conditions and operating condition of steering wheel. (Scheme 174)

Scheme 174

Raising Vehicle Height

Operating height select switch to raise vehicle height activates pump motor, which rotates pump. Fluid that is discharged by pump is sent to gas chambers and shock absorbers to raise vehicle height.

Scheme 175

1. Vehicle Stopped - Solenoid valve of height control accumulator is opened to use fluid that is stored in height control accumulator, which accelerates raising of vehicle height. To use fluid stored in accumulator, front and rear leveling valves are opened simultaneously to raise all 4 wheels. When stored fluid has been depleted, front and rear leveling valves are opened alternately to raise suspension of front wheels and rear wheels alternately.
2. Vehicle In Motion - When vehicle speed is less than approximately 16 MPH, fluid that is stored in height control accumulator is used in the same way as when vehicle is stopped. When vehicle speed is higher than approximately 16 MPH, vehicle height is raised using only fluid that is discharged by pump without using height control accumulator. At this time, front and rear leveling valves are opened alternately to raise suspension of front and rear wheels. When vehicle height is at low, it is automatically raised to normal when vehicle speed reaches approximately 3 MPH. At this time fluid that is stored in height control accumulator is also used. (Scheme 175)

BLEEDING

Note. If any work is done on AHC system or if air is suspected in AHC lines, bleed system of air.

Note. When reservoir tank is empty, or after AHC pump and motor is replaced or removed, starting engine may cause air to flow into AHC fluid line. In this condition, AHC system can not be operated even if fluid is poured into tank. If this happens, raise vehicle height of front or rear wheel by conducting active test and activate AHC pump and motor for about 10 seconds. See TEST D: HEIGHT CONTROL OPERATION TEST (ACTIVE TEST) under SYSTEM TESTS.

1. With engine stopped, pour suspension fluid AHC into reservoir tank.
2. Start engine and push vehicle height select switch to select "N" mode.
3. After vehicle height adjustment is completed, check that AHC pump motor is stopped.
4. Stop engine.
5. Connect bleeder hose to bleeder screw of either right or left damping force control actuator. (Scheme 176)
6. Loosen bleeder screw.
7. When emulsified fluid containing air is discharged, tighten bleeder screw to specification. See «TORQUE SPECIFICATIONS»(ref-154858-S39302085462003052900000).
8. Perform 5 and 6 for damping force control actuator in rear.
9. Repeat procedure for left and right damping force control actuators alternately.
10. Start engine on a level place. Adjust vehicle to "N" position with vehicle unloaded.
11. Check that fluid level in reservoir tank is within standard range. (Scheme 177)

Scheme 176

Scheme 177

SERVICING

The system uses a fluid called "Active Suspension Fluid AHC" LEXUS part no. 08886-01805.

TORSION BAR SPRING

Note. Perform operation with vehicle unloaded, fuel tank filled, normal temperature in engine compartment (50 to 122°) and vehicle on a level place.

SYSTEM PRE-CHECK

1. Turn ignition switch on.
2. Check that height control indicator light and height control OFF indicator light go on for 2 seconds. (Scheme 178) If indicator does not light, inspect height control OFF indicator light circuit and height control indicator light circuit. See «TEST A: HEIGHT CONTROL INDICATOR LIGHT CIRCUIT»(ref-154858-S11805980852003052900000) and «TEST B: HEIGHT CONTROL OFF INDICATOR LIGHT CIRCUIT»(ref-154858-S09761741212003052900000) under SYSTEM TESTS.

Scheme 178

Height Select Switch & Change Of Vehicle Height

1. Check tires for proper inflation pressure and check vehicle height. see scheme 29
2. Push height select switch to change from "N" to "HI" mode. After vehicle height control has been completed, wait for approximately 5 seconds until height is fixed securely. Check time required for height change and amount of change in height. See «Vehicle Height Change "N" To "HI"»(ref-154858-S36254672902003052900000).
3. Push height select switch to change from "HI" to "N" and then to "LO" mode. Check time required for height change and amount of change in height. See «VEHICLE HEIGHT CHANGE "N" TO "LO"»(ref-154858-S33039334622003052900000).

Vehicle Height Change "N" To "HI"

Vehicle Height Change "N" To "LO"

1. Start engine and push height select switch to "LO" mode.
2. Drive vehicle approximately 7 MPH or more and check indicator that vehicle height changes from "LO" to "N" position.
3. Stop vehicle and push height select switch to select "HI" mode.
4. Drive vehicle at 19 MPH or more and check indicator that vehicle height changes from "HI" to "N" position.
5. Stop vehicle and push height control switch to turn off height control.
6. Drive vehicle and check indicator that height control is activated automatically under various speeds. See «Vehicle Height Standard Values»(ref-154858-S29829737692003052900000) .

Vehicle Height Standard Values

SYSTEM TESTS

SYMPTOM INDEX

DAMPING FORCE CONTROL ACTUATOR

Note. Perform inspection 30 seconds after "HI" indicator light has changed from flashing to illuminated.

1. Check that front and rear shock absorber neutral pressures are within specified range. See «PRESSURE VALUE OF FRONT SHOCK ABSORBER»(ref-154858-S22717558312003052900000) .
2. Start engine with vehicle unloaded and a full fuel tank. Adjust vehicle height to "LO" position.
3. Record graduation level on reservoir tank.
4. Adjust vehicle height from "LO" to "HI" position.
5. Note graduations on reservoir tank. Check that change in value is 7 graduations or more. If value is not within specification, replace all gas chambers with new ones. See «DAMPING FORCE CONTROL ACTUATOR»(ref-154858-S00073482572003052900000) under REMOVAL & INSTALLATION.

PRESSURE VALUE OF FRONT SHOCK ABSORBER

Note. Perform operation with vehicle unloaded and fuel tank full.

PRESSURE VALUE OF REAR SHOCK ABSORBER

Note. Perform operation with vehicle unloaded and fuel tank full.

Note. Cylinder pressure read by hand-held tester is estimated by pump emitted pressure so pressure is approximately 171 PSI (1179 kPa) higher than pressure read by (LSPV) gauge special tool (09709-29018).