Torsion beam rear suspension - lateral location of the wheel/axle. How its done?

Sankar · 14th January 2011, 18:44

3 Link rigid axle rear suspension: Two trailing arms from both sides of the vehicle with wheels at their ends and both wheels are connected together with a rigid axle. A panhard bar drops from above the body(aka monocoque) of the car and is connected to the rigid axle. This panhard bar's job is to provide lateral location of the axle.

Torsion beam rear suspension: Two trailing arms from both sides of the vehicle with rear wheels at their ends. Both wheels are not connected together, but a C section metal beam connects the trailing arms on both ends together. The torsion beam flexes allowing for a slight independent movement at both ends, ie., movement at one side is not completely transferred to the other side.

The above explanation provides for a basic idea of how these two suspension systems are. Both are kind of similar due to the fact that both uses two trailing arms and piece of metal connecting both sides, yet they're different when it comes to the details.

What i'm interested to know is how is the lateral location of the rear axle done in the torsion beam setup, because in the torsion beam setup the whole rear suspension unit is anchored to the body (monocoque) only at two places at the trailing arms. In the 3 link rigid axle system the anchoring is done at 3 points. So how is the lateral location acheived in torsion beam rear suspension?

In 3 link rigid axle setup as found in small hatches like 800, Alto, AStar, Zen, WagonR, Matiz etc etc the trailing arm mount is parallel to the direction of travel.

In torsion beam rear suspension the trailing arm mount is not parallel to the direction of travel. So is this angled mounting providing for the lateral location of the wheel/axle?

Please help me understand because i've been wondering about the same ever since i came to know about the torsion beam setup.

Mpower · 14th January 2011, 19:20

Quote:

Originally Posted by Sankar

In torsion beam rear suspension the trailing arm mount is not parallel to the direction of travel. So is this angled mounting providing for the lateral location of the wheel/axle?.

Its a combination of the angled pivot plus the use of a stiff bushing that gives it lateral location. It is however not the perfect solution as the bushing transmits to road noise.

Sankar · 14th January 2011, 19:51

But is the bushing hard enough to do the jaob of lateral location along with the angle mount? Also does the two point mounting of the torsion beam rear axle make it less durable than a 3 link rigid axle setup?

Mpower · 14th January 2011, 21:04

The bushing rate is a compromise between NVH and lateral stiffness. That's the Achilles heel of the twist beam. Lateral is taken by both LH and RH bushings.

On the 2011 Opel Astra rear..uses a twist beam with soft bushing and adds a watts link to control lateral compliance. But the compromise here is that its takes up packaging space that is used for the fuel tank volume.

14th January 2011, 18:44	#1
Sankar Senior - BHPian Join Date: May 2005 Location: Location Posts: 5,766 Thanked: 9,054 Times	Torsion beam rear suspension - lateral location of the wheel/axle. How its done? 3 Link rigid axle rear suspension: Two trailing arms from both sides of the vehicle with wheels at their ends and both wheels are connected together with a rigid axle. A panhard bar drops from above the body(aka monocoque) of the car and is connected to the rigid axle. This panhard bar's job is to provide lateral location of the axle. Torsion beam rear suspension: Two trailing arms from both sides of the vehicle with rear wheels at their ends. Both wheels are not connected together, but a C section metal beam connects the trailing arms on both ends together. The torsion beam flexes allowing for a slight independent movement at both ends, ie., movement at one side is not completely transferred to the other side. The above explanation provides for a basic idea of how these two suspension systems are. Both are kind of similar due to the fact that both uses two trailing arms and piece of metal connecting both sides, yet they're different when it comes to the details. What i'm interested to know is how is the lateral location of the rear axle done in the torsion beam setup, because in the torsion beam setup the whole rear suspension unit is anchored to the body (monocoque) only at two places at the trailing arms. In the 3 link rigid axle system the anchoring is done at 3 points. So how is the lateral location acheived in torsion beam rear suspension? In 3 link rigid axle setup as found in small hatches like 800, Alto, AStar, Zen, WagonR, Matiz etc etc the trailing arm mount is parallel to the direction of travel. In torsion beam rear suspension the trailing arm mount is not parallel to the direction of travel. So is this angled mounting providing for the lateral location of the wheel/axle? Please help me understand because i've been wondering about the same ever since i came to know about the torsion beam setup.
	() Thanks

14th January 2011, 19:51	#3
Sankar Senior - BHPian Join Date: May 2005 Location: Location Posts: 5,766 Thanked: 9,054 Times	Re: Torsion beam rear suspension - lateral location of the wheel/axle. How its done? But is the bushing hard enough to do the jaob of lateral location along with the angle mount? Also does the two point mounting of the torsion beam rear axle make it less durable than a 3 link rigid axle setup?
	() Thanks

14th January 2011, 21:04	#4
Mpower Senior - BHPian Join Date: Mar 2005 Location: Bangalore Posts: 10,409 Thanked: 1,730 Times View My Garage	Re: Torsion beam rear suspension - lateral location of the wheel/axle. How its done? The bushing rate is a compromise between NVH and lateral stiffness. That's the Achilles heel of the twist beam. Lateral is taken by both LH and RH bushings. On the 2011 Opel Astra rear..uses a twist beam with soft bushing and adds a watts link to control lateral compliance. But the compromise here is that its takes up packaging space that is used for the fuel tank volume.
	() Thanks