The front wheels of the car are installed with their tops tilted outward or inward. This is called “camber” and is measured in degrees of tilt from the vertical. When the top of a wheel is tilted outward, it is called “positive camber”. Conversely, inward inclination is called “negative camber”. In early automobiles, the wheels were given positive camber in order to improve the durability of the front axle, and to cause the tires to contact the road surface at right angles to prevent uneven tire wear on roads where the center of the road is higher than the edge. In modern automobiles, the suspension and axles are stronger than in the past and road surfaces are flat, so there is less need for positive camber. As a result, tires are being adjusted more toward zero camber (and there are some vehicles with zero camber). In fact, negative camber is now commonly employed in passenger cars to improve cornering performance.

SERVICE HINT:

If the wheels are given excessive positive or negative camber, this causes uneven tire wear. If the wheels are given excessive negative camber, the tires wear quicker on the inside; if the wheels are given excessive positive camber, the tires wear quicker on the outside.

Negative Camber

When a vertical load is applied to a cambered tire, force is generated in the horizontal direction. This force is called “camber thrust” and operates to the inside of the vehicle for negative camber and the outside of the vehicle for positive camber. During cornering, because the vehicle leans to the outside, the tire camber becomes more positive, the camber thrust to the inside of the vehicle is reduced, and cornering force is reduced. The negative camber suppresses the positive camber of the tires during cornering and helps maintain proper cornering force.

Camber During Cornering

When a vehicle turns a corner, the camber thrust on the outside tires acts to reduce the cornering force due to the increase in positive camber. Centrifugal force tilts the turning vehicle due to the action of the suspension springs, changing the camber.

HINT:

Cornering is always accompanied by centrifugal force, which tires to force the vehicle to turn in a larger arc than intended by the driver unless the vehicle can generate a sufficient counterforce – that is, centripetal force – to balance this. This centripetal force is generated by the deformation and side-slipping of the tread that occurs due to friction between the tire and the road surface. This called cornering force.

Camber During Cornering

When a vehicle turns a corner, the camber thrust on the outside tires acts to reduce the cornering force due to the increase in positive camber. Centrifugal force tilts the turning vehicle due to the action of the suspension springs, changing the camber.

HINT:

Cornering is always accompanied by centrifugal force, which tires to force the vehicle to turn in a larger arc than intended by the driver unless the vehicle can generate a sufficient counterforce – that is, centripetal force – to balance this. This centripetal force is generated by the deformation and side-slipping of the tread that occurs due to friction between the tire and the road surface. This called cornering force.

The axis around which the wheel rotates as it turns to the right or left is called the “steering axis”. This axis is found by drawing an imaginary line between the top of the shock absorber’s upper support bearing and the lower suspension arm ball joint (in the case of strut type suspensions). This line is tilted inward as viewed from the front of the car and is called “steering axis inclination”( S.A.I) or “kingpin angle”. This angle is measured in degrees. Furthermore, the distance “L” from the intersection of the steering axis with the ground to the intersection of the wheel centerline with the ground is called the “offset”, “kingpin offset” or “scrub radius”.

Roles of Steering Axis Inclination

1. Reduction of steering effort Since the wheel turns to the right or left with the steering axis as its center and the offset as the radius, a large offset will generate a great moment around the steering axis due to the rolling resistance of the tire, thus increasing steering effort. This offset can be reduced in order to reduce the steering effort. Either of the following two methods can be used to make the offset small:

(1) Give the tires positive camber

(2) Incline the steering axis.

2. Reduction of kick-back and pulling to one side If the offset is excessively large, the force due to driving or braking generates a moment around the steering axis whose magnitude is proportional to the amount of offset. Also, any road shock applied to a wheel will cause the steering wheel to jerk or kick-back. These phenomena can be improved by reducing the amount of offset. If there is a difference between the left and right steering axis inclination angles, the vehicle will typically pull to the side of the smaller angle (having the larger offset).

3. Improvement straight-line stability The steering axis inclination causes the wheels to automatically return to the straight-ahead position after the completion of turning.

HINT:

In front engine, front-wheel-drive cars, the offset is generally kept small (zero or negative) to prevent the transmission to the steering wheel of shock from the tires generated during braking or by striking an obstruction, and to minimize the moment created around the steering axis by the driving force at the time of quick starting or acceleration.

SERVICE HINT:

If there is a difference between the steering angle on the left and right, there will also be a difference between the moments around the steering axis on the left and right during braking and the braking force will be greater on the side with the smaller steering angle. Also, any difference between the left and right offsets generates a difference in the drive reaction force (torque steer) on the left and right. In either case, a force acts that attempts to turn the vehicle.

1. Description

EPS (Electric Power Steering) generates the assist torque by the motor for steering operation and reduces the steering effort. Hydraulic power steering uses the power of the engine to generate the hydraulic pressure and obtain the assist torque. Since EPS uses a motor, it does not require the power of the engine and improves fuel economy.

2. Construction & Operation

(1) EPS ECU

The EPS ECU receives signals from various sensors, judges the current vehicle condition, and determines the assist current to be applied to the DC motor accordingly.

(2) Torque sensor

When the driver operates the steering wheel, the steering torque is applied to the torque sensor input shaft via the steering main shaft. Detection rings 1 and 2 are positioned on the input shaft (steering wheel side) and detection ring 3 is positioned on the output shaft (steering gear side). The input shaft and output shaft are connected via a torsion bar. Also, the detection rings have non-contact detection coils on their outer circumferences in order to form an excitation circuit. When the steering torque is generated, the torsion bar is twisted, generating a phase difference between detection rings 2 and 3. Based on this phase difference, a signal proportional to the input torque is output to the ECU. Based on this signal, the ECU calculates the motor assist torque for the vehicle speed and drives the motor.

(3) DC motor & Reduction mechanism

The DC motor consists of the rotor, stator, and motor shaft. The reduction mechanism consists of a worm gear and a wheel gear. The torque that is generated by the rotor is transmitted to the reduction mechanism. Then, this torque is transmitted to the steering shaft. The worm gear is supported by the bearings in order to reduce noise. Even if the DC motor breaks down, the rotation of the steering main shaft and the reduction mechanism is not fixed therefore the steering wheel can be steered. (4) ABS ECU Vehicle speed signal is outputted to EPS ECU. (5) Engine ECU Engine speed signal is outputted to EPS ECU. (6) Combination meter In case of a malfunction in the system, turns on the warning light. (7) Relay Supplies power to DC motor and EPS ECU.

1. Description

To improve driving comfort, most modern automobiles have wide, lowpressure tires which increase the tire-to-road surface contact area. As a result of this, more steering effort is required. Steering effort can be decreased by increasing the gear ratio of the steering gear. However, this will cause a larger rotary motion of the steering wheel when the vehicle is turning, making sharp turns impossible. Therefore, to keep the steering agile and, at the same time the steering effort small, some sort of a steering assist device became necessary. In other words, power steering, which had been chiefly used on larger vehicles, is now also used on compact passenger cars.

2. Type of power steering

There are hydraulic type and electric type power steering. Currently, hydraulic power steering is used on almost all models. The three main components of hydraulic power steering are the vane pump, control valve, and power cylinder.

3. Operation of hydraulic power steering

The power steering system uses the power of the engine to drive the vane pump that generates the hydraulic pressure. When the steering wheel is turned, an oil circuit is switched at the control valve. As oil pressure is applied to the power piston in the power cylinder, the power needed to operate the steering wheel is reduced. It is necessary to inspect for leakage of power steering fluid periodically.

Vane Pump

Power steering is a type of hydraulic device requiring a very high pressure. It uses the power of the engine to drive the vane pump uses that generates this hydraulic pressure. Vanes are used in this pump, so this name is used for this type of power steering.

1. Elasticity

If a force (load) is applied to an object made of a material such as rubber, it will create stress (deformation) in that object. When that force is released, the object will return to its original shape. We call this characteristic ÅgelasticityÅh. The springs of a vehicle use the principle of elasticity to cushion the body and occupants of a vehicle from road shock. The steel springs use bending or twisting elasticity.

REFERENCE: Even if an object has elasticity, if the force that is applied to it is excessively large, the elasticity limit will be exceeded, thus preventing the object from completely returning to its original shape. This is referred to as “plasticity”.

2. Spring rate (constant)

The deflection of a spring varies in proportion to the force (load) applied to it. That is, the value obtained by dividing the force (w) by the amount of deflection (a) is constant. This constant value (k) is called the “spring rate” or “spring constant”. A spring with a low spring constant is said to be “soft”, while a spring with a high spring constant is said to be “firm”.

3. Spring oscillation

When the wheels of a vehicle strike a bump, the vehicle’s springs will be rapidly compressed. Since each spring will immediately attempt to return to its original length, in order to release the compressed energy it will extend beyond its original length. Then the spring will respond to the rebound by attempting to return to its original length and will contract to less than its original length. This process, which is called spring oscillation, is repeated many times until the spring eventually returns to its original length. If spring oscillation was left uncontrolled, it would cause not only an uncomfortable ride, but would also lead to handling stability. To prevent this, shock absorbers are also provided.

The vehicle must have proper straightline performance for stable driving, cornering performance for driving around curves, recovery force for returning to the straight-line condition, the capacity to soften the shock transmitted to the suspension when the tires are impacted, etc. Therefore, the wheels of a vehicle are mounted at specific angles to the ground and specific suspensions for each purpose. This is called wheel alignment. The wheel alignment has the following five factors:

• Camber
• Caster
• Steering axis inclination (kingpin inclination)
• Toe (toe-angle, toe-in and toe-out)
• Turning radius (wheel angle, turning angle) If even one of these elements is incorrect, the following problems can occur:
• Difficult steering
• Poor steering stability
• Poor recovery on curves
• Shortened tire life

1. Diagnosis

If the EMS/air suspension ECU detects a malfunction in this system, it blinks the damping mode or vehicle height indicator light to alert the driver of the malfunction. The ECU will also store the codes of the malfunctions.

Reading DTC The DTCs can be read by connecting the hand-held tester to the DLC3 to communicate with the ECU directly or causing a short between TC and CG terminals of the DLC3 and observing the blinking pattern.

Clearing DTC The DTCs can be cleared by connecting the hand-held tester to the DLC3 or causing a short between TC and CG terminals of the check connector and depressing the brake pedal 8 or more times within 5 seconds.

2. Fail-safe

If the ECU detects a malfunction in any of the sensors or actuator, the ECU prohibits the vehicle height control and/or the damping force control.

3. Input signal check (test mode)

The input signal check is to see whether signals from the steering sensor and stop light switch, etc. are being input normally to the ECU. By connecting the TS and CG of the DLC3 with the SST and carrying out the prescribed operation, you can read the input signal from the pattern with which the indicator light flashes. Alternatively, you can connect a hand-held tester and read the input signals on it. This depends on the model. For details, refer to Repair Manual.

4. Damping force controlling condition check

With the DLC3 TS and CG connected with the SST, you can check the change in the shock absorber damping force by operating the absorber control switch or pressing the brake pedal. This depends on the model. For details, refer to Repair Manual.

The suspension improves the riding comfort and driving performance of the vehicle. EMS (Electronically-Modulated Suspension) and air suspension electronically control the damping force of the shock absorbers and air springs to further improve riding comfort and driving performance.

EMS

EMS is an abbreviation which stands for “Electronically- Modulated Suspension”. The size of the shock absorber orifice is changed so that the amount of oil flow is adjusted, causing the damping force to vary. The damping force is automatically controlled by the EMS ECU (electronic control unit) according to the selector switch condition and the driving condition. This ensures increased driving comfort and provided excellent driving stability. Diagnostic functions and a fail-safe function are also provided.

Air Suspension

The air suspension uses an ECU to electronically control the suspension which uses air springs that utilize the elasticity of compressed air. There are also models that combine air suspension with EMS. The air suspension has the following features.

• The damping force can be changed.
• The spring rate and vehicle height can be changed by adjusting the air volume.
• Diagnostic functions and a fail-safe function are also provided.

Characteristics

The EMS & air suspension have the following features.

1. Mode change

(1) Damping mode select The damping force of the shock absorber can be changed from soft to firm.

(2) Height control (Air suspension only) The vehicle height setting can be changed from low to high. There are indicator lights that show the status for both the damping mode and the height control.

2. Damping force and spring rate control

(1) Anti-squat control

Changes damping force to firmer. This suppresses squatting during acceleration, thus minimizing changes in vehicle posture.

(2) Anti-roll control

Changes damping force to firmer. This suppresses rolling, thus minimizing changes in vehicle posture, providing excellent controllability.

(3) Anti-dive control

Changes damping force to firmer. This suppresses nose-diving during braking, thus minimizing changes in vehicle posture.

(4) High-speed control (normal mode only)

Changes damping force to firmer. This control provides the excellent driving stability and controllability at high speed.

(5) Shift-squat control (A/T vehicles only)

This limits the amount of rear-end squat when a vehicle with an automatic transmission first starts out. When the transmission shifted from the “N” or “P” range, the damping force is set to firm.

(6) Semi-active control

Smoothly changes the damping force to a target value in accordance with the changes in the road surface or driving conditions. Thus, excellent ride comfort has been realized while ensuring a high level of vibration damping performance.

Sky-hook EMS:

Putting the vehicle in the sky-hook state constantly achieves a stable vehicle attitude in relation to the change of the road condition. In sky-hook EMS using this theory, the up and down motion of the body is sensed and a computer finely controls and adjusts the movement of the shock absorbers. This system greatly improves ride comfort and driving stability. In the latest models, such as the LS430, the semiactive control of the damping force control has been changed from sky-hook control to non-linear H_ control in order to effect even more fine control. As a result, excellent ride comfort has been realized.

3. Vehicle height control

(1) Auto-leveling control

Maintain vehicle height at a constant level regardless of the passenger and luggage weights. Operation of the height control switch changes the target vehicle height to “normal” or “high” level.

(2) High-speed control

Controls vehicle height to a lower side than the height selected by the height control switch (to lower position if “normal” is selected or to normal if “high” is selected) when the vehicle is driven at a prescribed speed or higher. This provides aerodynamics and excellent stability at high speed.

(3) Ignition switch-off control

Lowers vehicle height to target height when vehicle height becomes higher than target height due to a reduction in weight of passengers or luggage after ignition switch is turned off. This improves vehicle posture during parking.

HINT:

Method to cancel the vehicle height control:

Before jacking up the vehicle or raising it on a hoist, make sure that the ignition switch is turned OFF.

If the vehicle must be raised with its engine running, jump terminals TD and EI of the TDCL or OPB and CG of the DLC3 (Data Link Connector 3) to stop the vehicle height control operation of the air suspension ECU.

For the vehicle with the height control ON/OFF switch, the switch is turned OFF.

4. Torsion bar springs

A torsion bar spring (usually simply called a torsion bar) is a spring-steel rod that uses its torsional elasticity to resist twisting. One end of the torsion- bar is anchored to the frame or other structural member of the body, and the other end to a component that is subjected a torsional load. Torsion bar springs are also used to make stabilizer bars. Characteristics:

• Since the energy absorption rate per unit of weight is great as compared to other springs, the suspension can be lightened.
• The layout of the suspension system is simplified.
• As with coil springs, torsion bar springs do not control oscillation, so it is necessary to use shock absorbers along with them.

5. Rubber springs

Rubber springs absorb oscillations through the generation of internal friction when they are deformed by an external force. Characteristics:

• They can be made in any shape.
• They are silent during use
• They are not appropriate for use in supporting heavy loads. Therefore, rubber springs are used mainly as auxiliary springs or as bushings, spacers, cushions, stoppers and other supports for the suspension components.

6. Air springs

Air springs make use of the fact that air has elasticity or “springiness” when compressed. Characteristics:

• They are extremely soft when the vehicle is not loaded, but their spring constant can be increased as the load is increased by increasing the air pressure inside the chamber. This provides optimum riding comfort both when the vehicle is lightly loaded, and when it is fully loaded.
• The height of the vehicle can be kept constant, even if the load changes, by adjusting the air pressure. However, in air suspensions using air springs, devices for controlling the air pressure and compressors for compressing air, etc., are necessary, so the suspension becomes complex. Currently, the electronically-modulated air suspension, which incorporates this type of air spring, is offered as an option in some models.

1. Outline

In automotive suspension systems, the springs used are metallic springs and non-metallic springs

• Metallic springs
• Leaf springs
• Coil springs
• Torsion bar springs
• Non-metallic springs
• Rubber springs
• Air springs

2. Leaf springs

Leaf springs are made of a number of curved bands of spring steel, called “leaves”, stacked together in order from shortest to longest. This stack of leaves is fastened together at the center with a center bolt or a rivet and to keep the leaves from slipping out of place, they are held at several places with clips. Both ends of the longest (main) leaf are bent to form spring eyes, used to attach the spring to the frame or to a structural member such as a side member. Generally, the longer a leaf spring, the softer it will be. Also, the more leaves in a leaf spring, the greater the load they will withstand, but on the other hand, the spring will become firmer and riding comfort will suffer.

Characteristics:

• Since the springs themselves have adequate rigidity to hold the axle in the proper position, it is not necessary to use linkages for this.
• They function to control their own oscillation through inter-leaf friction.
• They have sufficient durability for heavy-duty use.
• Due to inter-leaf friction, it is difficult for them to absorb the minute vibrations from the road surface. Therefore leaf springs are generally used for large commercial vehicles which carry heavy loads and for which durability is highly regarded. The curvature of each leaf is called “nip”. Since the nip of a leaf is greater the shorter the leaf, each leaf curves more sharply than the one above it in the stack. When the center bolt is tightened, the leaves flatten somewhat, as shown in the illustration in the left, causing the ends of the leaves to press very tightly against one another. The overall curvature of the leaf spring is called “camber”. However, this friction also causes a decrease in riding comfort, since it prevents the spring from flexing easily.

The purpose of nip

• When a spring is flexed, nip causes the leaves in the spring to rub together, and the friction created by this rubbing quickly damps the oscillations of the spring. This friction is called inter-leaf friction, and is one of the greatest features of the leaf spring. However, this friction also causes a decrease in riding comfort, since it prevents the spring from flexing easily. Therefore, leaf springs are mainly used on commercial vehicles.
• When the spring rebounds, nip prevents gaps from occurring between each of the leaves, thus preventing dirt and sand, etc., from penetrating between the leaves and causing wear.
• Measure to reduce inter-leaf friction Silencer pads are inserted between each of the leaves at their ends to improve the sliding of the leaves against each other. Each of the leaves is also tapered at the ends so that they exert the proper amount of pressure when they come in contact with each other. Helper springs In trucks and many other vehicles which undergo great fluctuations in their loads, helper springs are used. The helper spring is installed above the main spring. When the load is light, only the main spring operates, but when the load exceeds a certain value, both the main and helper springs come into operation

3. Coil springs

Coil springs are made from rods of special spring steel formed into the shape of a coil. When a load is placed on a coil spring, the entire rod is twisted as the spring contracts. In this way, the energy of the external force is stored, and shock is cushioned.

Characteristics:

• The energy absorption rate per unit of weight is greater in comparison with leaf springs.
• Soft springs can be made.
• Since there is no inter-leaf friction as with leaf springs, there is no control of oscillation by the spring itself, so it is necessary to use shock absorbers along with them.
• Since there is no resistance to lateral forces, linkage mechanisms to support the axle (suspension arm, lateral control rod, etc.) are necessary Progressive spring If a coil spring is made from a rod of spring steel having a uniform diameter, the entire spring will flex uniformly in proportion to changes in the load. This means that if a soft spring is used, it will not be stiff enough to handle heavy loads, while if a hard spring is used, it will give a rough ride when only lightly loaded. However, if a rod having a constantly-changing diameter is used, as shown in the left, the ends of the spring will have a lower spring rate than the center. Consequently, under light loads, the ends of the spring will contract and absorb road shock. On the other hand, the center part of the spring will be stiff enough to handle heavy loads. Unequal-pitch spring, conical springs, etc. have the same effect.