What is the function of the 'Torsion Bar' in a vehicle's steering rack assembly on power-assisted rack and pinion systems?

1. To twist slightly under steering force, aligning spool valve ports to direct hydraulic assist
2. To act as a safety link to steer the car manually if the steering column breaks
3. To absorb vibrations from the road before they reach the driver's hands
4. To adjust the tension on the rack guide yoke to prevent backlash play