GB/T 12549-2013Terms and definitions for vehicle controllability and stability (English PDF)

3.1 Angles in steering system

3.1.1

Steer angle

deltas

The angle, BETWEEN the vehicle's longitudinal symmetry plane (see 6.1.6) and the center plane of the steering wheel (see 4.1.1) AND the intersection of the pavement (see Figure 1).

3.1.2

Steering wheel angle

deltasw

Steering wheel's angular displacement, which is measured based on the position of the steering wheel, when the vehicle is going straight.

4.1 Suspension geometry

4.1.1

Wheel plane

For a single wheel, the wheel plane is the plane, which is equidistant from the inner edge of the wheel rim, on both sides.

4.1.6

Caster angle

The angle, between the projection of the centerline of the steering kingpin on the longitudinal plane of symmetry of the vehicle (see 6.1.6) AND the plumb line. If the upper end of the steering kingpin is inclined backward, this angle is positive; if the upper end of the steering kingpin is inclined forward, the angle is negative (see

Figure 3).

4.1.10

Kingpin offset

The length of the projection of the line, which connects the intersection of the kingpin's extension line and the pavement AND the center of tire contact (see 5.1.1), on the Y'-axis (see 5.1.2). If the center of tire contact is outside the intersection of the kingpin's extension line and the pavement relative to the vehicle body, the kingpin offset is positive; otherwise, it is negative.

4.1.11

Lateral slip

The lateral slip value of the straight-running tire, per unit travel distance, which is measured on the lateral slip test bench. It is expressed in m/km, mm/m.

4.1.12

Wheelbase

The distance, between two planes that pass through point A or (B) of two adjacent wheels on the same side of the vehicle AND are perpendicular to the Y and X planes, respectively.

4.2 Suspension system mechanics

4.2.1

Suspension vertical stiffness

Under a certain load state, the change in the vertical load of the wheel, which is corresponding to the unit displacement of the sprung center of mass, as relative to the center of the wheel, in the vertical direction.

4.2.2

Suspension longitudinal stiffness

The change in longitudinal force at the wheel center, which is corresponding to a unit displacement of the wheel center, as relative to the sprung center of mass, in the longitudinal [x-axis (see 6.1.3) direction].

4.2.10

Roll axis

A line, which connects the front and rear roll centers.

4.2.11

Suspension compliance

Reciprocal of suspension stiffness.

4.2.12

Damping force characteristic

The relationship between the damping force of a shock absorber and its piston speed.

4.2.13

Overturning couple

Moment of the force acting on the vehicle, relative to the longitudinal axis of the vehicle on the pavement, due to the effects of lateral acceleration (see 6.4.16) and roll angular acceleration.

5.1 Tire axis system and variables

5.1.1

Center of tire contact

The intersection, BETWEEN the intersection line of wheel plane and the ground

AND the projection of the wheel rotation center line on the ground (see Figure 1,

Figure 4).

5.1.2

Tire axis system (X', Y', Z')

A right-handed rectangular axis system, which uses the center of tire contact as the origin. The X' axis is the intersection of the wheel plane and the road plane, wherein the travel direction of the wheel plane is positive

5.1.3

Slip angle of tire

The angle, between the traveling direction of the center of tire contact and the X' axis of the tire axis system (see Figure 4 and Figure 5).

5.4.6

Cornering stiffness

The increment of lateral force, which is corresponding to a unit increment of tire slip angle (usually refers to the measured value, when the tire slip angle is zero).

5.4.9

Aligning stiffness (aligning torque stiffness)

The increment of the aligning torque, which is corresponding to the unit increment of the tire slip angle (usually refers to the measured value, when the tire slip angle is zero).

5.4.10

Cornering stiffness coefficient

The ratio of cornering stiffness to vertical load, for a free-rolling wheel.

5.4.11

Camber stiffness coefficient

The ratio of camber stiffness to vertical load, for a free-rolling wheel.

5.5.5

Slipping braking adhesion coefficient

At a given trim, the braking force coefficient, when the wheels are locked.

6.1 Axis system

6.1.1

Earth-fixed axis system (X, Y, Z)

A right-handed Cartesian axis system, which is fixed to the ground. The origin is a point on the ground; the X and Y axes lie in the horizontal plane; the Z axis points upward. The trajectory of the vehicle's motion is described by this axis system (see

Figure 6).

6.1.7

Roll

Rotation of the vehicle's sprung mass (see 6.2.2) about the x0 axis.

6.1.8

Pitch

Rotation of the vehicle's sprung mass (see 6.2.2) about the y0 axis.

6.1.9

Yaw

Rotation of the vehicle's sprung mass (see 6.2.2) about the z0 axis.

6.1.10

Pitch axis

Axis, which passes through the fixed point of pitch vibration AND is parallel to the

Y axis.

6.2 Mass and center of mass

6.2.1

Mass of vehicle

The mass of the vehicle, under any load state.

6.2.2

Sprung mass

The mass of the load above the elastic element of the suspension, that is, the mass of the part of the load, which is carried by the suspension.

6.4 Kinematic variables

6.4.1

Velocity vector at center of mass

The 3D velocity vector of the vehicle's center of mass (or sprung center of mass).

6.4.2

Vehicle speed

The horizontal component of the velocity vector of the vehicle's center of mass (or sprung center of mass) (see Figure 6).

6.4.3

Longitudinal velocity

The component of the velocity vector of vehicle's center of mass (or sprung center of mass), along the x-axis (see Figure 6).

6.6.2

Pitching moment

The component of the moment vector, which acts on the vehicle, to rotate the vehicle around the y-axis.

6.6.3

Yawing moment

The component of the moment vector, which acts on the vehicle, to rotate the vehicle around the z-axis.

7.1 Control modes

7.1.1

Position control

Vehicle control, when displacement inputs (or limits) are applied to certain control points, in the steering system (steering wheels, steering arm, handwheel), independent of the required force.

7.2 Response

7.2.1

Steering response

The motion of the vehicle, which is caused by inputs, which are applied to operating (steering) components. It includes the steering response, which is caused by the driver's input on the brake and accelerator pedals.

7.2.2

Disturbance response

The motion of the vehicle, which is caused by the external disturbance (force or displacement), acting on the vehicle.

Example. Vehicle movement, which is caused by wind, uneven pavement.

7.3 Steering characteristics

7.3.1

Neutral steer

When the vehicle speed is constant AND the lateral acceleration is changed, if the slope of the nominal steering angle (see 3.1.4) is equal to the slope of the Ackermann angle (see 3.1.6), the steering characteristic of the vehicle is neutral steer. This characteristic is roughly equivalent to a zero value for the static margin (see 7.3.6).

It is shortly referred to as NS (see Figure 8).

7.4.5

Asymptotic stability

For the specified trim, when there is any small and brief change in disturbance or control input, the vehicle will approach the motion state, which is specified by the trim.

7.4.6

Neutral stability

For the specified operating point, the vehicle will remain in a state of motion close to but not reaching the specified trim, when disturbances or brief changes in control input occur.

7.4.7

Driver viewing distance

During driving, the horizontal distance from the driver's eyes to the fixation point.

7.4.8

Quantification of on-center handling

A description of steering feel and precision, when a vehicle is traveling at high speed and with small lateral acceleration, in an approximately straight line and through large diameter curves.

8.1 Characteristics of limit maneuver

8.1.1

Maximum centripetal acceleration

The maximum value of the centripetal acceleration, which is achieved by the vehicle in a curved motion, under manual control or fixed control conditions.

8.1.6

Overturning limit angle

The acute angle, between the roll test bench and the horizontal plane, in the state of the kerb weight of the whole vehicle, when using the roll test bench to tilt the vehicle to the left (or right), until all the wheels on the unloaded side leave the roll bench or the wheels start to slip,

8.2 Abnormal motion

8.2.1

Break away

The lateral slip of the vehicle, when the resultant force on the tread surface of the tire contact is greater than the adhesion force. Rear wheel sideslip is called 'tail flick' (a sharp increase in yaw velocity and rear wheel's slip angle); front wheel slip is called 'float' (increase in turning radius and decrease in yaw velocity).

8.2.2

Tuck in

In the slewing motion, the phenomenon that the vehicle turns inward, when the accelerator pedal is suddenly retracted OR the clutch is rapidly disengaged.

8.2.3

Wheel lift

Under the action of centrifugal force, the front wheel or rear wheel inside the vehicle steering leaves the pavement.

9.1 Normal tests

9.1.1

Steady static circular test

It is a test to evaluate the understeer and oversteer characteristics, roll characteristics, maximum lateral acceleration, steering wheel torque, etc., of the vehicles, by changing the lateral acceleration and allowing the vehicle to run, at a certain speed, along an arc which has a fixed radius.

9.1.2

Minimum turning diameter test

The test, which is used to measure the diameter of the trajectory circle, which is formed by the movement of the vehicle, by keeping the steering wheel angle at the maximum position AND allowing the vehicle to drive at a very low speed.

9.1.3

Test of effect of sudden power change

A test, which is used to evaluate the stability of the vehicle, when the vehicle is suddenly accelerated or decelerated, during cornering, by controlling the acceleration pedal.

9.1.9

Test of braking stability

It is a test, to evaluate whether the vehicle deviates, sideslips and loses steering ability, when braking while driving.

Note. Use lateral displacement, yaw angle, etc. for evaluation.

9.1.10

Kick-back test

A test, which is used to evaluate the steering wheel torque and steering wheel kick- back, when the vehicle is running on bad roads or uneven pavements.

9.1.11

Response test of tire burst

A test to evaluate how easy it is for the driver to control the vehicle, after the tire bursts while driving.

9.3 Evaluation

9.3.1

Relative steering wheel displacement

The steering wheel's angle increment, when the vehicle turns at a very low speed

AND the turning radius of the center of mass is 10 m.

9.3.2

Coefficient of centripetal acceleration effect

The ratio -- of the steering wheel's angle increment TO the centripetal acceleration increment, when the vehicle turns at a fixed turning radius.

9.3.3

Coefficient of centripetal acceleration on steering force

The ratio -- of the steering force increment to the centripetal acceleration increment,

-- when the vehicle turns at a fixed turning radius.

9.3.15

Degree of understeer

The average slope, at the lateral acceleration value of 2 m/s2 (the ordinate value divided by the abscissa value), on the relationship curve, BETWEEN the side slip angle difference between the front and rear axles AND the lateral acceleration.

9.3.16

Roll rate of body

The average slope, at the lateral acceleration value of 2 m/s2 (the ordinate value divided by the abscissa value), on the curve of the relationship, between the vehicle roll angle and the lateral acceleration.

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