Electronic power steering (EPS) has enabled benefits to the automotive world such as light-weighting of technologies, increasing efficiency and reducing complexity and cost. A key component to operating the EPS system is the torsion bar, otherwise known as the torque sensor or quill shaft. When the vehicle operator turns the steering wheel, the torsion bar twists and this displacement is used to determine the level of input torque. The electronic control unit (ECU) then uses this information to ensure the correct output torque is applied. A schematic of this system can be seen in Figure 1.
Figure 1: A Schematic diagram of where the torsion bar is used in an EPS system. The bearing highlighted in red is where the bushing sits.
Commonly, needle bearings are used in this application. The torsion bar twists inside the needle bearing and if vibrations are present in the system, the interface between the needle bearings and the torsion bar will cause a buzzing feeling in the steering wheel.
Noise Free Engineered Benefits for Steering Feel (Torsion Bar)
Figure 2 shows how the sound pressure level (SPL) of the “buzz” caused vibrations between the torsion bar and the needle bearing can be reduced by using a single NORGLIDE® bearing. The overall level has been reduced from 40.3 dB(A) for needle bearings to 36.2 dB(A) for a NORGLIDE® bearing. Figure 2: Sound pressure levels (SPL) for the current solution and the NORGLIDE® solution during radial excitation of the torsion bar at 15 Hz and 2.3 m/s2. Overall levels; current solution = 40.3 dB(A), NORLGIDE® = 36.2dB(A).
Figure 3 shows how the sound pressure level (SPL) of the rotational rattle noise can also be reduced by the use of a single NORGLIDE® bearing. The overall level has been reduced from 40.3 dB(A) for needle bearings to 36.2 dB(A) for a NORGLIDE® bearing.
Figure 3: Sound pressure levels (SPL) for the current solution and the NORGLIDE® solution for rotational excitation at 15 Hz and 2.3 m/s2 of the constrained torsion bar resulting in a backlash test for the gear teeth. Overall levels; current solution = 33.0 dB(A), NORLGIDE® = 25.7 dB(A).