Difference between revisions of "Torque Steer"
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| + | '''Torque Steer''' is a yawing effect caused by unequal stiffness driveshafts, most frequently due to unequal length. A stiffer shaft will turn the wheel further than a softer shaft for the same input torque. | ||
| + | |||
=Example Calculation= | =Example Calculation= | ||
| − | Step 1: | + | Using ballpark values, we can calculate an approximate torque steer value for a generalized FSAE car. |
| + | |||
| + | '''Step 1: Polar Moment of Inertia''' | ||
| − | + | The moment of inertia (J) for a hollow shaft is found using the formula π/32 * (D<sup>4</sup>-d<sup>4</sup>). Using values from an RCV axle below, we can find J. | |
| − | Shaft ID | + | {| class="wikitable" |
| + | | Shaft OD (D) || 0.8" | ||
| + | |- | ||
| + | | Shaft ID (d) || 0.5" | ||
| + | |} | ||
| − | Shaft Area of Inertia | + | Shaft Area of Inertia = 0.034076in2 |
| − | Step 2: Calculate Torsional Stiffness | + | '''Step 2: Calculate Torsional Stiffness''' |
Shaft Material: 4130 Steel | Shaft Material: 4130 Steel | ||
Revision as of 11:51, 23 January 2023
Torque Steer is a yawing effect caused by unequal stiffness driveshafts, most frequently due to unequal length. A stiffer shaft will turn the wheel further than a softer shaft for the same input torque.
Example Calculation
Using ballpark values, we can calculate an approximate torque steer value for a generalized FSAE car.
Step 1: Polar Moment of Inertia
The moment of inertia (J) for a hollow shaft is found using the formula π/32 * (D4-d4). Using values from an RCV axle below, we can find J.
| Shaft OD (D) | 0.8" |
| Shaft ID (d) | 0.5" |
Shaft Area of Inertia = 0.034076in2
Step 2: Calculate Torsional Stiffness
Shaft Material: 4130 Steel
4130 Shear Modulus: 80 Gpa or 1.16e+7 psi
Left Shaft Length: 15 in
Right Shaft Length: 19 in
k = G*J / L
Left Torsional Stiffness (kL): 38.3379023 lb-ft / degree
Right Torsional Stiffness (kR): 30.26401 lb-ft / degree
Step3: Find Torque
Max Torque from Engine (Launch): 40 lb-ft
Final Drive Ratio: 3.55
Torque Seen by Driveshaft: 142 lb-ft
Step 4: Find Shaft Twist
phi = T / k
Left Shaft Twist (phiL): 3.704 degrees
Right Shaft Twist (phiR): 4.692 degrees
Step 5: Find Vehicle Yaw
Tire travel (T) = Shaft twist/360 * Tire Circumference
Yaw = arcsin(Tmax-Tmin / Track Width)
Circumference of Tire: 56.52 in
Left Tire Travel: 0.582 in
Right Tire Travel: 0.737 in
Rear Track: 36 in
Yaw: 0.247 degrees
