AHC suspension update for Lexus LX600/LX500d

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Eugenio,77
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Dec 2021 - Jan 2022

AHC (Active Height Control) - hydropneumatic suspension with functions of height adjusting, damping force adjusting and spring rate adjusting (rigidity).

Let's note some differences in its implementation on the previous generation Land Cruiser / Lexus LX (J200) and on the new Lexus LX (J300).

J200J300
AHC was offered for both Toyota Land Cruiser (although this version was not available in all markets) and Lexus LX Initially, AHC is offered only for Lexus and is not available for Land Cruiser
Spring rate (stiffness) control was applied to the front wheels only Spring rate control with three pneumatic chambers is used for all wheels
There was a pump accumulator for a faster change in the suspension height No common accumulator
Single control valve unit was used Two valve units are installed, for the right and left side (the pressure/temperature sensor and the cut valve are in the right side unit)
Coordinated operation of the all shock absorbers was performed via central hydraulic cylinder Shock absorbers have independent electronic control
Suspension height range was +70/-60 mm for the front and +80/-40 mm for the rear Height change range is +85/-25 mm, at automatic extra-mode the lift height is increased to +105 mm


Structure

1 - shock absorber (FL), 2 - suspension control accumulator (FR), 3 - relief gas chamber, 4 - absorber control actuator, 5 - high spring rate gas chamber, 6 - suspension control valve (FR), 7 - low spring rate gas chamber, 8 - spring rate switching valve, 9 - height control valve unit #1, 10 - cut valve, 11 - oil pressure/temperature sensor, 12 - bypass valve (FR), 13 - leveling valve (FR), 14 - leveling valve (RR), 15 - bypass valve (RR), 16 - height control pump and motor module, 17 - pump attenuator, 18 - pump, 19 - motor, 20 - fluid temperature sensor, 21 - reservoir tank, 22 - return valve, 23 - suspension control valve (RR), 24 - suspension control accumulator (RR), 25 - shock absorber (RR), 26 - height control valve unit #2, 27 - bypass valve (FL), 28 - leveling valve (FL), 29 - leveling valve (RL), 30 - bypass valve (RL), 31 - shock absorber (FL), 32 - suspension control accumulator (FL), 33 - suspension control valve (FL), 34 - suspension control valve (RL), 35 - suspension control accumulator (RL), 36 - shock absorber (RL)

Height control: increase

Height control: decrease

Accumulation control

Spring rate switching control (low rate)

Spring rate switching control (high rate)

Components

AHC pump consists of pump, electric motor, fluid temperature sensor, attenuator, check valve, reservoir tank. It is located, according to tradition, in the rear body overhang.

1 - reservoir tank, 2 - fluid temperature sensor, 3 - pump attenuator, 4 - pump and motor

Height control valve unit #1 controls the right side shock absorbers, unit #2 controls the left side shock absorbers.

Height control valve unit #1. 1 - leveling valve (FR), 2 - bypass valve (FR), 3 - bypass valve (RR), 4 - leveling valve (RR), 5 - cut valve, 6 - oil pressure/temperature sensor

Height control valve unit #2. 1 - leveling valve (RL), 2 - bypass valve (RL), 3 - bypass valve (FL), 4 - leveling valve (FL)

Suspension control valve assembly consists of a low spring rate gas chamber and a spring rate switching valve. The pneumatic chamber is a balloon-type hydraulic accumulator with a polymer diaphragm. When the low spring rate gas chamber is operating (valve is open), it absorbs the pulsations of the fluid during the operation of the shock absorber and performs some of the functions of a coil spring. When the valve is closed, the gas chamber is excluded from operation.

1 - low spring rate gas spring (suspension control accumulator), 2 - spring rate switching valve. b - oil chamber, c - bladder containing resin film, d - gas chamber (nitrogen gas)

Regulator/accumulator consists of a relief gas chamber, a high spring rate gas spring, and an absorber control actuator. The chambers are hydraulic accumulators of metal bellows type. The high spring rate chamber absorbs pulsations of the fluid during operation of the shock absorber and performs part of the functions of the coil spring. The relief chamber absorbs pulsations of the fluid during operation of the shock absorber and compensates pressure increase in the hydraulic circuit.

1 - high spring rate gas spring (accumulator 2), 2 - relief gas spring (accumulator 3). b - oil chamber, c - metal bellows, d - gas chamber

Control

Height control switch allows to select the AHC operating mode: N (Normal), L (Low), H1 (High 1), H2 (High 2). In addition, the height depends on the range of the transfer case.

Height modeTransferTarget height
H2 (High 2)L4+105 mm*
H2 (High 2)L4+85 mm
H2 (High 2)H4+75 mm
H1 (High 1)L4+55 mm
H1 (High 1)H4+20 mm
N (Normal)H4/L40 mm
L (Low)H4/L4-25 mm
*Extra mode

The 'easy access' and 'AHC OFF' switches are displayed in the central information display.

1 - height select switch, 2 - integration control panel. a - front multi operation panel, b - height control off switch, c - easy access mode switch


The system sequentially reduces the height when accelerating and again increases it when decelerating.

In addition to height control, AHC is designed to reduce roll and pitch sway while driving, and to provide comfort when riding on uneven surfaces. While straight driving, all three pneumatic chambers are involved, which maintains a low spring rate. When steering, accelerating or braking, the large gas chamber is cut-off and the remaining two actuate, providing increased stiffness of the suspension springs.









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