Torque Steer - Revision history

Emilyanthony: add categories

2024-05-30T21:54:30Z

add categories

SpookySimon: disclaimer

2023-01-23T18:04:03Z

disclaimer

SpookySimon: /* Example Calculation */

2023-01-23T16:42:05Z

Example Calculation

SpookySimon: /* Example Calculation */ snetence struicture

2023-01-23T16:39:54Z

Example Calculation: snetence struicture

SpookySimon: links to remove dead-end

2023-01-23T16:38:56Z

links to remove dead-end

SpookySimon: /* Assumptions */ shaft hardening assumnpmtion

2023-01-23T16:22:22Z

Assumptions: shaft hardening assumnpmtion

SpookySimon: Listing assumptions

2023-01-23T16:19:03Z

Listing assumptions

SpookySimon: /* Example Calculation */ finishing example calculation

2023-01-23T16:12:48Z

Example Calculation: finishing example calculation

SpookySimon: /* Example Calculation */ step 2&3

2023-01-23T16:00:35Z

Example Calculation: step 2&3

SpookySimon: step1

2023-01-23T15:51:20Z

step1

← Older revision		Revision as of 21:54, 30 May 2024
Line 93:		Line 93:
	* Tire circumference is equivalent to 2 * dynamic radius * π		* Tire circumference is equivalent to 2 * dynamic radius * π
	* Shaft hardening does not impact stiffness		* Shaft hardening does not impact stiffness
		+
		+	[[Category:Vehicle_Dynamics]] [[Category:Drivetrain]]

← Older revision		Revision as of 18:04, 23 January 2023
Line 1:		Line 1:
−	'''Torque Steer''' is a yawing effect caused by unequal stiffness [[Drivetrain#Driveshafts\|driveshafts]], most frequently due to unequal length. A stiffer shaft will turn the wheel further than a softer shaft for the same input torque.	+	'''Torque Steer''' is a yawing effect caused by unequal stiffness [[Drivetrain#Driveshafts\|driveshafts]], most frequently due to unequal length. A stiffer shaft will turn the wheel further than a softer shaft for the same input torque. Despite it's relevance to the discussion of torque steer, the calculation shown here is only an example and should not be copied for use in the design event. There are many points not covered here, and the assumptions are not justified.

	=Example Calculation=		=Example Calculation=

@@ Line 54: / Line 54: @@
 :&phi; = T / k
-Left Shaft Twist (phi<sub>L</sub>): 3.704 degrees
+Left Shaft Twist (&phi;<sub>L</sub>): 3.704 degrees
-Right Shaft Twist (phi<sub>R</sub>): 4.692 degrees
+Right Shaft Twist (&phi;<sub>R</sub>): 4.692 degrees
 It is important to note that shaft twist indicates how far each wheel has <em>not</em> rotated compared to the engine.
@@ Line 64: / Line 64: @@
 If both shafts were perfectly stiff, one rotation of the driven sprocket would equal one rotation of the wheels, driving the car forward the distance equal to 2 * &pi; * the tire's dynamic radius. Because the shafts twist, the wheels/tires will move less than one full rotation. Because the shafts have different stiffnesses, they will travel different distances under the same load. We will find the distance <em>not</em> rotated to compute vehicle yaw, as we are looking for magnitude, not direction.
-: Tire travel (T) = Shaft twist/360 * Tire Circumference
+: Tire travel (T) = &phi;<sub>shaft</sub>/360 * Tire Circumference
 : Yaw = sin<sup>-1</sup>(T<sub>max</sub>-T<sub>min</sub> / Track Width)

@@ Line 22: / Line 22: @@
 '''Step 2: Calculate Torsional Stiffness'''
-We will use 4130 chromoly [[Steel|steel]] as our half-shaft material, most steels have a very similar shear modulus (G) so this choice is not a driving factor in the result. The torsional stiffness (k) of the shaft will be found using the following formula and values:
+We will use 4130 chromoly [[Steel|steel]] as our half-shaft material. Most steels have a very similar shear modulus (G) so this choice is not a driving factor in the result. The torsional stiffness (k) of the shaft will be found using the following formula and values:
 :k = G*J / L

@@ Line 1: / Line 1: @@
-'''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.
+'''Torque Steer''' is a yawing effect caused by unequal stiffness [[Drivetrain#Driveshafts|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=
@@ Line 22: / Line 22: @@
 '''Step 2: Calculate Torsional Stiffness'''
-We will use 4130 chromoly steel as our half-shaft material, most steels have a very similar shear modulus (G) so this choice is not a driving factor in the result. The torsional stiffness (k) of the shaft will be found using the following formula and values:
+We will use 4130 chromoly [[Steel|steel]] as our half-shaft material, most steels have a very similar shear modulus (G) so this choice is not a driving factor in the result. The torsional stiffness (k) of the shaft will be found using the following formula and values:
 :k = G*J / L

← Older revision		Revision as of 16:22, 23 January 2023
Line 92:		Line 92:
	* The tire's rolling radius does not change under loading		* The tire's rolling radius does not change under loading
	* Tire circumference is equivalent to 2 * dynamic radius * π		* Tire circumference is equivalent to 2 * dynamic radius * π
		+	* Shaft hardening does not impact stiffness

@@ Line 49: / Line 49: @@
 Torque Seen by Driveshaft: 142 lb-ft
-''''Step 4: Find Shaft Twist'''
+'''Step 4: Find Shaft Twist'''
 This step is the meat of the calculation. We can find how far each shaft has twisted using our previous results according to the equation below:
@@ Line 79: / Line 79: @@
 '''Result'''
 According to our calculations, the vehicle will yaw less than one quarter of one degree, which if even perceptible by the driver will be unlikely to force corrective action. please see further below for discussion of assumptions used and real world relevance.

@@ Line 41: / Line 41: @@
 '''Step 3: Find Torque'''
-Our last input value that we need to find is the torque experience by the driveshafts. This is the torque output by the motor and transmitted through the final drive ratio. The maximum torque applied to the driveshafts by the engine will be during launch, when the wheels are still and we can assume a perfect launch by the driver, applying the maximal engine torque for the split second we are examining.
+Our last input value that we need to find is the torque experienced by the driveshafts. This is the torque output by the motor and transmitted through the final drive ratio. The maximum torque applied to the driveshafts by the engine will be during launch, when the wheels are still and we can assume a perfect launch by the driver, applying the maximal engine torque for the split second we are examining.
 Max Torque from Engine: 40 lb-ft
@@ Line 49: / Line 49: @@
 Torque Seen by Driveshaft: 142 lb-ft
-Step 4: Find Shaft Twist
+''''Step 4: Find Shaft Twist'''
-phi = T / k
+This step is the meat of the calculation. We can find how far each shaft has twisted using our previous results according to the equation below:
 Left Shaft Twist (phi<sub>L</sub>): 3.704 degrees
@@ Line 57: / Line 58: @@
 Right Shaft Twist (phi<sub>R</sub>): 4.692 degrees
-Step 5: Find Vehicle Yaw
+It is important to note that shaft twist indicates how far each wheel has <em>not</em> rotated compared to the engine.
-Tire travel (T) = Shaft twist/360 * Tire Circumference
+'''Step 5: Find Vehicle Yaw'''
-Yaw = arcsin(T<sub>max</sub>-T<sub>min</sub> / Track Width)
+If both shafts were perfectly stiff, one rotation of the driven sprocket would equal one rotation of the wheels, driving the car forward the distance equal to 2 * &pi; * the tire's dynamic radius. Because the shafts twist, the wheels/tires will move less than one full rotation. Because the shafts have different stiffnesses, they will travel different distances under the same load. We will find the distance <em>not</em> rotated to compute vehicle yaw, as we are looking for magnitude, not direction.
 Circumference of Tire: 56.52 in
@@ Line 72: / Line 77: @@
 Yaw: 0.247 degrees

@@ Line 7: / Line 7: @@
 '''Step 1: Polar Moment of Inertia'''
-The moment of inertia (J) for a hollow shaft is found using the formula &pi;/32 * (D<sup>4</sup>-d<sup>4</sup>). Using values from an RCV axle below, we can find J.
+The moment of inertia (J) for a hollow shaft is calculated as follows:
 {| class="wikitable"
@@ Line 15: / Line 18: @@
 |}
-Shaft Area of Inertia = 0.034076in2
+Shaft Area of Inertia: 0.034076in<sup>2</sup>
 '''Step 2: Calculate Torsional Stiffness'''
-Shaft Material: 4130 Steel
+We will use 4130 chromoly steel as our half-shaft material, most steels have a very similar shear modulus (G) so this choice is not a driving factor in the result. The torsional stiffness (k) of the shaft will be found using the following formula and values:
-Shear Modulus: 80 Gpa or 1.16e+7 psi
+{| class="wikitable"
+| Shaft Material || 4130 Steel
-Left Shaft Length: 15 in
+|-
+| 4130 Shear Modulus || 1.16e+7 psi
-Right Shaft Length: 19 in
+|-
+| Left Shaft Length (L<sub>L</sub>) || 15 in
-k = G*J / L
+|-
 Left Torsional Stiffness (k<sub>L</sub>): 38.3379023 lb-ft / degree
@@ Line 33: / Line 39: @@
 Right Torsional Stiffness (k<sub>R</sub>): 30.26401 lb-ft / degree
-Step3: Find Torque
+'''Step 3: Find Torque'''
-Max Torque from Engine (Launch): 40 lb-ft
+Max Torque from Engine: 40 lb-ft
 Final Drive Ratio: 3.55