Toyota Land Cruiser Prado. Air suspension control system description
Many Toyota Land Cruiser Prado models have rear air suspension. This type of suspension uses rubber pneumatic cylinders instead of the rear springs. The main difference of this suspension is that it works on compressed air compared to the Land Cruiser 100, working on a special working fluid.
Using two body height sensors, the air suspension automatically adjusts the height, depending on the number of passengers and the mass of the cargo. In addition to automatic adjustment, you can manually set three modes of operation of this system, which significantly increases the controllability and patency of the car.
| ||Arrangement of components of the air suspension control system. |
1 – pressure modulator / ABS control unit (models without VSC),
2 – end sensors of the side doors,
3 – front wheel speed sensors,
4 – relay “AIR SUS”,
5 – pneumatic cylinder,
6 – body height control sensor,
7 – solenoid valve pressure relief in the pneumatic cylinder,
8 – control valve,
9 – bypass valve,
10 – exhaust valve,
11 – air filter housing,
12 – rear door limit switch.
| ||Arrangement of components of the air suspension control system (instrument panel). |
1 – suspension mode indicator,
2 – air suspension “OFF” indicator,
3 – air suspension control unit,
4 – control unit for improved vehicle controllability systems (models with VSC),
5 – diagnostic connector,
6 – brake light switch,
7 – suspension mode switch,
8 – switch for automatically changing the operating mode of the air suspension (switch “OFF” air suspension).
The following components are components of the rear air suspension:
1) Air suspension mode switch block
It includes a switch for automatic control of the height of the body (“OFF”) and a switch for the modes of operation of the air suspension. There are three options for the suspension operation mode: “HI” mode (high), necessary for off-road driving, “Normal” (medium) and “LO” (low) to facilitate the entry / exit of passengers and when loading / unloading a car.
When selecting the “HI” mode, the car body rises by about 30-40 mm (depending on modifications) within 15-20 seconds. When choosing the “LO” mode, the car lowers by 30 mm relative to the normal state (within 10 – 15 seconds).
Also, in addition to manual mode switching, there is an automatic mode switching:
a) If, when the car is moving in the “Normal” mode, the speed is reduced to 12 km / h or less, the suspension will automatically switch to the “LO” position, and vice versa.
b) If you reduce the vehicle speed to 50 km / h (in the “Normal” mode), the system will switch to the “HI” mode. And if, when driving on the “HI” range, it accelerates to 50 km / h, the system will automatically return to its middle position.
2) Air suspension control indicators
The suspension mode indicator informs the driver about the selected system mode.
The “OFF” indicator of the control system is on if the automatic control of the air suspension is switched off by pressing the corresponding switch. If the indicator blinks, then there is a malfunction in the air suspension system. Using this indicator, diagnostic trouble codes are also read..
3) Air filter assembly
It consists of the filter itself, which is necessary for cleaning dust and sand taken in by the air suspension, and an expansion chamber, which serves to reduce noise during air intake. An air filter draws air from the passenger compartment. He does not understand. If necessary, replace the filter itself; replace its entire housing.
4) Compressor assembly
Includes compressor itself, exhaust valve and dehumidifier.
a) The compressor delivers compressed air to the pneumatic cylinders needed to lift the body. To avoid battery discharge, the compressor only works when the engine is running.
b) The exhaust valve is necessary for rarefying the pneumatic cylinders while reducing the height of the body.
c) A dehumidifier is necessary to remove moisture from the compressed air pumped by the compressor, and when the valve releases air from the pneumatic cylinders into the atmosphere.
5) Pneumatic cylinder
The pneumatic cylinder consists of a separate air chamber filled with high pressure compressed air to ensure a better ride. Needed to support the body and change its height.
6) Air suspension receiver
Consists of an additional tank and a block of solenoid valves.
An additional tank temporarily accumulates the air leaving the pneumatic cylinder, which helps to reduce the time required to reduce the height of the body.
The electromagnetic valve block includes: a bypass valve (bypasses compressed air between the left and right pneumatic cylinders), a control valve used to connect the compressor and the pneumatic cylinder, and a pressure relief valve (to bleed air from the pneumatic cylinder into an additional tank).
7) Body height sensors
Sensors determine the height of the body and are located on the left and right sides of the rear axle.
The sensor consists of a brush connected to the shaft, which slides along the resistor forming the base plate. Because the resistance value between the brush and the resistor changes depending on the angle of rotation of the sensor shaft, the output voltage also changes due to the rotation of the brush.
In addition to the above components, the body height change system uses elements such as:
a) End sensors of the side doors (determine the closing of the doors);
b) Limit sensor of the rear door (determines the closing of the rear door);
c) The body electrical control unit (receives a signal from the end sensors and sends information to the air suspension control unit);
d) Relay “AIR SUS” (supplies current to the receiver of the air suspension control system);
e) Front wheel speed sensors (determine vehicle speed);
f) ABS control unit (sends a signal received from the wheel speed sensors to the air suspension control unit);
g) air suspension control unit.
Features of operation of cars with air suspension
At various forums, the problem of the roll of the car during its operation is quite often discussed. In most cases, the essence of the problem is not in any malfunction, but in the features of the system settings. The problem is the roll of the car at stops when the engine is running. Many owners, turning to service workshops with this problem, get quite interesting answers, and sometimes bills.
When carrying out work requiring jacking the car, as well as before parking on uneven areas (curbs, snowdrifts, pits), it is necessary to turn off the automatic mode switching.
If this rule is not followed, then one side of the car will constantly fall during the subsequent parking of the car. This is due to the fact that when the engine starts, the air suspension control system takes the position in which the car is located, for horizontal. In order to fix this problem, you must perform the following operations:
a) Stop the car on a flat surface.
b) Turn off the automatic mode switching system by pressing the “OFF” switch (the corresponding indicator should light up).
c) Stop the engine.
d) Start the engine and turn on the automatic mode switching system, again by pressing the corresponding switch.
When towing a car, you must set the average height of the body and disable automatic mode switching.
When driving on very rough roads or when crossing a ford, it is necessary to set the “HI” mode and turn off the automatic mode switching.
Toyota also does not recommend using the air suspension control system at temperatures below -30 ° C. If you operate the car at these temperatures, set the average height of the body and disable automatic mode switching.
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