Rack and pinion steering gear consists of steering wheel, steering shaft, steering gear, tie rod, steering trapezoid arm and steering wheel (front wheel). The steering gear is flexibly connected with the steering wheel. The driver applies the steering torque to the steering wheel, drives the steering gear to rotate through the steering shaft, and converts it into linear motion through the rack. The rack drives the tie rod to reciprocate and the steering knuckle to rotate, so as to realize the steering of the car.
1.Build virtual prototype model
In order to improve the design efficiency, this paper mainly analyzes the simulation of the gear rack, neglects the parts which have little influence on the simulation results when building the steering gear model. According to the rack and pinion steering gear template provided in ADAMS / car module, the virtual prototype model of the steering gear is created, as shown in the figure.
1.Steering wheel (steering column) 2. Steering column 3. Upper steering shaft 4. Lower steering shaft 5. Rack and pinion steering gear 6. Steering tie rod 7. Steering trapezoid arm 8. Steering wheel
2.Define constraints
Before using ADAMS software to simulate, it is necessary to define the constraints of components to determine the relative motion relationship between system parts. According to the actual movement of the rack and pinion steering gear, constraints are added between parts. Apply rotating pair to steering wheel 1 and steering column 2; apply fixed pair to steering column 2 and ground; apply universal joint pair to steering wheel column 1 and upper steering shaft 3; apply universal joint pair to upper steering shaft 3 and lower steering shaft 4; apply cylindrical pair to lower steering shaft 4 and body; apply rotating pair, sliding pair and gear rack pair to gear rack steering gear 5; A spherical pair is applied between the rack and pinion steering gear 5 and the steering tie rod 6; a spherical pair is applied between the steering tie rod 6 and the steering trapezoid arm 7; a fixed pair is applied between the steering trapezoid arm 7 and the steering wheel 8; a plane pair is applied between the steering wheel 8 and the ground, and friction is defined.
3.Apply force and get simulation results
In order to calculate the strength of steering gear rack and pinion, the limit force acting on it must be determined. The wheel steering force is the steering output force caused by the manual steering torque applied by the driver to the steering wheel. The force applied by the driver to the steering wheel must overcome the resistance of the steering wheel to rotate around the kingpin, the resistance of wheel stability, the resistance of tire deformation and the resistance of internal friction in the steering system, etc. the parameters required for the simulation of the steering gear are shown.
The in-situ steering resistance moment MR is calculated by semi empirical formula as follows:
ΜR=μ3G13/p=394625.6Ν·mm (1)
Since the rack and pinion steering gear has no steering arm and knuckle arm, the steering wheel hand force FH is:
Fh=2MR/ (DiWη) =160.2N (2)
For a given vehicle, the force calculated by formula (2) is the maximum value. The force is applied to the steering wheel of virtual prototype, and the dynamic simulation function of Adams is used to analyze the force on the rack and output the simulation curve. When the steering wheel hand force increases from 50N to 160.2n in 1s, the change curve of rack tangential force is shown in Figure 2. When the steering wheel hand force is the maximum, the maximum tangential force of the rack Fmax = 2952.2n. According to the force analysis, the maximum tangential force ft of the gear is:
Ft=Fmaxcosα=2952.2cos20°=3141.67Ν (3)
Where: α is the installation angle of gear rack.