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Active Body Height Control (AHC) – Part 1

Active Body Height Control (AHC) - Part 1 1
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The active body height control system (ANS) allows you to change the height of the car body from the road surface depending on the speed and load. This system was used on Toyota Land Cruiser 100 and Lexus LX470. It increases the permeability of the car, stability when cornering, which is necessary when driving on Russian roads. It also facilitates the entry and exit of passengers from the car and allows you to save the amount of clearance, regardless of the load on the car..

The body height control system (ANS) uses a special working fluid

“Active suspension fluid AHC”.

The main modes of the active body height control system are:

1) Forced change heights location bodywork.

There are three modes of operation of this system: “LO”, “N” and “HI”.

LO mode selected when loading the luggage compartment of the car. When choosing this mode of operation, the front of the car body lowers by approximately 50 mm, and the rear by 40 mm relative to the position of the body in the “N” mode.

N mode It is recommended to use when driving on good roads, the car height corresponds to.

HI Mode it is desirable to use when driving on bumpy roads and to overcome water obstacles.

When switching to “HI” mode, the front of the car rises by 50 mm and the rear by 40 mm.

Switching between the modes “LO” → “N” and “N” → “HI” occurs within 10 – 15 seconds and depends on the vehicle load. Switching “HI” → “N” and “N” → “LO” occurs within 3 – 8 seconds.

2) Automatic regulation heights location bodywork.

This function allows you to automatically maintain a constant height of the car body, regardless of the number of passengers and car load.

3) Automatic control pendant in addictions from speed.

This function automatically changes the height of the body depending on the speed of the car to ensure maximum stability and passenger comfort.

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If the car starts to drive at a speed of more than 5 km / h, the ANS system switches to the normal mode and fixes in it (when the speed decreases, it does not return to the “LO” mode) If the car starts to travel at a speed of more than 30 km / h, the ANS system switches to normal mode. “N” mode will not change when speed decreases If the car starts to drive at a speed of more than 50 km / h, the system goes into an intermediate position (the height of the body is 25 mm above the “N” position). When the speed decreases to 20 km / h, the “N” mode changes to “HI”

* – When driving on the “LOW” range of the transfer case.

If one of the wheels starts slipping when the car is moving on rough roads in the “HI” mode on the “LOW” range of the transfer case, the height of the car’s body automatically increases by 30 mm (front) and 20 mm (rear).

5) Prohibition adjustments heights location bodywork a car.

When jacking the car or when towing it is necessary to turn off the system for changing the height of the body by pressing the appropriate switch. The body height control system will turn on automatically when the car is moving at a speed of more than 80 km / h in the “N” mode or when driving at a speed of more than 30 km / h in the “HI” or “LO” mode.

Attention: the system may not increase the height of the body relative to the road surface if the total vehicle load exceeds 570 kg in the “N” mode or 440 kg in other modes.

6) In addition to the described operating modes, the ANS system provides hydraulic communication between the shock absorbers of the left and right wheels, which provides better stability and controllability of the car on bends.

Basically, the hydraulic circuit between the shock absorbers of the left and right wheels is open. This makes it possible to increase the smoothness of the suspension when the wheels begin to move in opposite phases, which provides better traction of tires with the surface when driving on a winding road. When the steering wheel is turned, the hydraulic circuit closes, this restrains the increase in the vehicle roll at frequent turns.

AHC system components and their purpose

The system for changing the body height is controlled not only by sensors of this system, but also by signals from sensors of other systems, such as: an axle differential lock enable sensor, a transfer case “L4” enable sensor, a brake light switch, door and door end sensors “L” generator.

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Component Location
AHC systems.
1 – pump damper,
2 – diagnostic connector,
3 – pump and fluid pressure sensor,
4 – control valve block,
5 – rear right drive AHC,
6, 8, 9 – door limit switches,
7 – rear body height control sensor,
10 – rear left drive,
11 – accumulator,
12 – front-wheel drive,
13 – pump relay,
14 – front wheel speed sensors,
15 – front sensors for controlling the height of the body,
16 – the main relay of the system,
17 – electronic control unit AHC,
18 – a combination of devices (indicators),
19 – steering wheel position sensor,
20 – brake light switch,
21 – DLC3 connector,
22 – switch block system AHC.
Component Appointment
AHC system mode indicator Shows the selected operating mode of the body height control system.

In each mode, the corresponding indicator lights up. When changing the height, the indicator of the previously selected mode goes off and the indicator of the set mode starts flashing, indicating that there is a change in the height of the body position (at the end of the process, the indicator starts to light without blinking).

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ANS indicator “OFF” – Lights up when the ANS OFF switch is pressed.

– Blinks when a malfunction is detected in the body height control system.

– Diagnostic code output

ANS system operating mode switch The choice of the operating mode of the body height control system
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ANS OFF switch Sets a ban on changing the height of the body.

Attention: the altitude prohibition system will turn off automatically when the vehicle is moving at a speed of more than 80 km / h in the “N” mode or when driving at a speed of more than 30 km / h in the “HI” or “LO” mode.

Wheel speed sensors The speed of each wheel is determined and a signal is transmitted to the ANS control unit (via the ABS control unit)
Body height sensors Determine the height of the body
Steering wheel position sensor Determines the steering direction and angle
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ANS electric pump It creates the working fluid pressure necessary to increase the height of the body. Includes: working fluid reservoir, pump, check valve, pressure and temperature sensors.
Pump damper A gas damper (1.96 MPa) with a volume of 2 cm 3 is designed to reduce the pressure pulsation of the working fluid pumped by the electric pump
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Hydraulic accumulator of ANS system It stores hydraulic pressure to increase the rate of change in body height relative to the road surface
Control valve block Consists of control valves for adjusting the height of the body and bypass valves for controlling the hydraulic circuit between the shock absorbers of the left and right wheels
Component Appointment
ANS system drive (gas chamber) It performs the same functions as the gas chamber of a conventional shock absorber (additional shock chamber)
Shock absorbers Telescopic shock absorbers are used to damp vibrations similarly to conventional shock absorbers.
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High pressure hose Serves as a hydraulic circuit connecting the drive (gas chamber) and the shock absorber of the ANS system
ANS control unit It controls the entire system, making calculations to control the height of the body, based on signals from sensors and switches
Control relays The ANS MAIN relay supplies power to the ANS system elements, and the ANS MOTOR relay connects to the ANS electric pump

Body height sensors

The system contains three sensors: two front sensors for each of the wheels and one rear located in the central part of the transverse beam above the rear axle.

The sensor consists of a brush connected to the shaft, which slides along the resistor forming the base plate. The voltage at the output of the sensor varies in proportion to the angle of rotation of the sensor shaft.

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ANS electric pump

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The ANS system pump includes a working fluid reservoir, a pump, a check valve, pressure and temperature sensors.

– Gear pump with DC motor.

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This valve is used to open / close the hydraulic circuit between the control valve block and the working fluid reservoir. The non-return valve is designed in such a way that it closes due to the high pressure of the liquid generated by the electric pump.

In the normal state, the spring holds the non-return valve open (see figure). When the electric pump of the ANS system starts to work (when lifting the car body), the working fluid leaving it presses on the valve, moving it to the left. Thus, the circuit between the control valve block and the tank is closed, and the liquid exiting the pump starts to move to the control valve block.

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Hydraulic accumulator of ANS system

The hydraulic accumulator consists of a cylinder (volume 945 cm 3) filled with nitrogen (5.9 MPa), a free piston and an electromagnetic valve.

When lifting the body, the accumulator gives up the stored fluid under high pressure, further increasing the speed of lifting the body. In the normal state, the solenoid valve remains closed. When the height of the body starts to increase or when the liquid in the main accumulator runs out, the solenoid valve opens by a signal received from the ANS control unit.

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Control valve block

The unit consists of two control valves and two bypass valves..

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– The control valves bypass the working fluid from the pump to the ANS system drives (gas chambers) located on each wheel. Under normal conditions, the valves are closed. During operation of the ANS system, the valves open with signals from the control unit.

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– Bypass valves connect the hydraulic circuits of the left and right shock absorbers. Under normal conditions, the valves are open and close only at the command of the electronic control unit of the ANS system.

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ANS system drives (gas chambers)

The gas chamber is a pneumatic-hydraulic accumulator of membrane type, with a three-layer rubber-polymer membrane and a cavity of 400 and 500 cm 3 for the front and rear wheels, respectively, filled with nitrogen.

The gas pressure in the cavities is 2.26 MPa for front-wheel drives and 2.65 MPa for rear-wheel drive.

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Description of repair procedures, diagnostics and maintenance of vehicles on which the ANS system was installed, you can find in the following books:

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