What Does a Solid Axel Mean?
#2
10-19-2009, 02:21 PM
Solid-axle, leaf-spring
This system was favoured by the Americans for years because it was dead simple and cheap to build. The ride quality is decidedly questionable though. The drive axle is clamped to the leaf springs and the shock absorbers normally bolt directly to the axle. The ends of the leaf springs are attached directly to the chassis, as are the tops of the shock absorbers. Simple, not particularly elegant, but cheap. The main drawback with this arrangement is the lack of lateral location for the axle, meaning it has a lot of side-to-side slop in it.
Solid-axle, coil-spring
This is a variation and update on the system described above. The basic idea is the same, but the leaf springs have been removed in favour of either 'coil-over-oil' spring and shock combos, or as shown here, separate coil springs and shock absorbers. Because the leaf springs have been removed, the axle now needs to have lateral support from a pair control arms. The front ends of these are attached to the chassis, the rear ends to the axle. The variation shown here is more compact than the coil-over-oil type, and it means you can have smaller or shorter springs. This in turn allows the system to fit in a smaller area under the car.
And just for kicks and grins....
Beam Axle
This system is used in front wheel drive cars, where the rear axle isn't driven. (hence it's full description as a "dead beam"). Again, it is a relatively simple system. The beam runs across under the car with the wheels attached to either end of it. Spring / shock units or struts are bolted to either end and seat up into suspension wells in the car body or chassis. The beam has two integral trailing arms built in instead of the separate control arms required by the solid-axle coil-spring system. Variations on this system can have either separate springs and shocks, or the combined 'coil-over-oil' variety as shown here. One notable feature of this system is the track bar (or panhard rod). This is a diagonal bar which runs from one end the beam to a point either just in front of the opposite control arm (as here) or sometimes diagonally up to the top of the opposite spring mount (which takes up more room). This is to prevent side-to-side movement in the beam which would cause all manner of nasty handling problems. A variation on this them is the twist axle which is identical with the exception of the panhard rod. In a twist axle, the axle is designed to twist slightly. This gives, in effect, a semi-independent system whereby a bump on one wheel is partially soaked up by the twisting action of the beam. Yet another variation on this system does away with the springs and replaces them with torsion bars running across the chassis, and attached to the leading edge of the control arms. These beam types are currently very popular because of their simplicity and low cost.
4-Bar
4-bar suspension can be used on the front and rear of vehicles - I've chosen to show it in the "rear" section of this page because that's where it's normally found. 4-bar suspension comes in two varieties. Triangulated, shown on the right here, and parallel, shown on the left.
The parallel design operates on the principal of a "constant motion parallelogram". The design of the 4-bar is such that the rear end housing is always perpendicular to the ground, and the pinion angle never changes. This, combined with the lateral stability of the Panhard Bar, does an excellent job of locating the rear end and keeping it in proper alignment. If you were to compare this suspension system on a truck with a 4-link or ladder-bar setup, you'd notice that the rear frame "kick up" of the 4-bar setup is far less severe. This, combined with the relatively compact installation design means that it's ideal for cars and trucks where space is at a premium. You'll find this setup on a lot of street rods and American style classic hot rods.
The triangulated design operates on the same principle, but the top two bars are skewed inwards and joined to the rear end housing much closer to the centre. This eliminates the need for the separate panhard bar, which in turn means the whole setup is even more compact.
Derivatives of the 4-Bar system
There are many variations on the 4-bar systems I've illustrated above. For example, if the four angled bars go from the axle outboard to the chassis near the centreline, this is called a "Satchell link". (Satchell is a US designer, who used the above linkage on some of Paul Newmans Datsun road racers some years back.) It has certain advantages over the above examples. Both of the these angled linkages can be reversed to have the angled links below the axle and the parallel links above. The roll centre will be lowered with the angled bars under the axle, a function which is difficult to accomplish without this design. The other variation on the "four bars" not shown are the Watts and Jacobs bar linkages to replace the Panhard rod for lateral positioning. Another linkage is the two parallel bars above the axle and a triangulated link underneath - a design you will find on the Lotus 7 - where the lower link has its base on the chassis and the apex under the differential. Then there is the Mallock Woblink, which could be described as half way between a Jacobs ladder and a Watts link, and makes it possible to place the rear roll centre quite low without sacrificing ground clearance.
Watts links are pretty popular with the hydraulic lowrider/truck bed dancer types. The Jacobs ladder is used almost exclusively on US midget and sprintcar dirt track rear ends. The Mallock Woblink is used mostly on the Mallock U2 Clubman cars in Great Britain.
de Dion suspension, or the de Dion tube
The de Dion tube - not part of the London underground, but rather a semi-independent rear suspension system designed to combat the twin evils of unsprung weight and poor ride quality in live axle systems. de Dion suspension is a weird bastardisation of live-axle solid-beam suspension and fully independent trailing-arm suspension. It's neither one, but at the same time it's both. Weird! With this system, the wheels are interconnected by a de Dion Tube, which is essentially a laterally-telescoping part of the suspension designed to allow the wheel track to vary during suspension movement. This is necessary because the wheels are always kept parallel to each other, and thus perpendicular to the road surface regardless of what the car body is doing. This setup means that when the wheels rebound, there is also no camber change which is great for traction, and that's the first advantage of a de Dion Tube. The second advantage is that it contributes to reduced unsprung weight in the vehicle because the transfer case / differential is attached to the chassis of the car rather than the suspension itself.
Naturally, the advantages are equalled by disadvantages, and in the case of de Dion systems, the disadvantages would seem to win out. First off, it needs two CV joints per axle instead of only one. That adds complexity and weight. Well one of the advantages of not having the differential as part of the suspension is a reduction in weight, so adding more weight back into the system to compensate for the design is a definite distadvantage. Second, the brakes are mounted inboard with the calipers attached to the transfer case, which means to change a brake disc, you need to dismantle the entire suspension system to get the driveshaft out. (Working on the brake calipers is no walk in the park either.) Finally, de Dion units can be used with a leaf-spring or coil-spring arrangement. With coil spring (as shown here) it needs extra lateral location links, such as a panhard rod, wishbones or trailing links. Again - more weight and complexity.
de Dion suspension was used mostly used from the mid 60's to the late 70's and could be found on some Rovers, the Alfa Romeo Alfettas (including the sedans and the GTV) and the GTV6, one or two Lancias a smattering of exotic racing cars and budget sports cars or coupes.
More recently deDion suspension has had somewhat of a renaissance in the specialist sports car and kit car market such as those from Caterham, Westfield and Dax. These all uniformly now use outboard brake setups for ease-of-use, and a non-telescoping tube, usually with trailing links and an A-bar for lateral location (rather than a Watts linkage or Panhard rod.) Whilst a properly setup independent suspension system will always win hands-down on poorly maintained roads, when you get on to the track, the advantage is not so clear cut and a well set up deDion system can often match it turn-for-turn now, espeically for flyweight cars.
Source
This system was favoured by the Americans for years because it was dead simple and cheap to build. The ride quality is decidedly questionable though. The drive axle is clamped to the leaf springs and the shock absorbers normally bolt directly to the axle. The ends of the leaf springs are attached directly to the chassis, as are the tops of the shock absorbers. Simple, not particularly elegant, but cheap. The main drawback with this arrangement is the lack of lateral location for the axle, meaning it has a lot of side-to-side slop in it.
Solid-axle, coil-spring
This is a variation and update on the system described above. The basic idea is the same, but the leaf springs have been removed in favour of either 'coil-over-oil' spring and shock combos, or as shown here, separate coil springs and shock absorbers. Because the leaf springs have been removed, the axle now needs to have lateral support from a pair control arms. The front ends of these are attached to the chassis, the rear ends to the axle. The variation shown here is more compact than the coil-over-oil type, and it means you can have smaller or shorter springs. This in turn allows the system to fit in a smaller area under the car.
And just for kicks and grins....
Beam Axle
This system is used in front wheel drive cars, where the rear axle isn't driven. (hence it's full description as a "dead beam"). Again, it is a relatively simple system. The beam runs across under the car with the wheels attached to either end of it. Spring / shock units or struts are bolted to either end and seat up into suspension wells in the car body or chassis. The beam has two integral trailing arms built in instead of the separate control arms required by the solid-axle coil-spring system. Variations on this system can have either separate springs and shocks, or the combined 'coil-over-oil' variety as shown here. One notable feature of this system is the track bar (or panhard rod). This is a diagonal bar which runs from one end the beam to a point either just in front of the opposite control arm (as here) or sometimes diagonally up to the top of the opposite spring mount (which takes up more room). This is to prevent side-to-side movement in the beam which would cause all manner of nasty handling problems. A variation on this them is the twist axle which is identical with the exception of the panhard rod. In a twist axle, the axle is designed to twist slightly. This gives, in effect, a semi-independent system whereby a bump on one wheel is partially soaked up by the twisting action of the beam. Yet another variation on this system does away with the springs and replaces them with torsion bars running across the chassis, and attached to the leading edge of the control arms. These beam types are currently very popular because of their simplicity and low cost.
4-Bar
4-bar suspension can be used on the front and rear of vehicles - I've chosen to show it in the "rear" section of this page because that's where it's normally found. 4-bar suspension comes in two varieties. Triangulated, shown on the right here, and parallel, shown on the left.
The parallel design operates on the principal of a "constant motion parallelogram". The design of the 4-bar is such that the rear end housing is always perpendicular to the ground, and the pinion angle never changes. This, combined with the lateral stability of the Panhard Bar, does an excellent job of locating the rear end and keeping it in proper alignment. If you were to compare this suspension system on a truck with a 4-link or ladder-bar setup, you'd notice that the rear frame "kick up" of the 4-bar setup is far less severe. This, combined with the relatively compact installation design means that it's ideal for cars and trucks where space is at a premium. You'll find this setup on a lot of street rods and American style classic hot rods.
The triangulated design operates on the same principle, but the top two bars are skewed inwards and joined to the rear end housing much closer to the centre. This eliminates the need for the separate panhard bar, which in turn means the whole setup is even more compact.
Derivatives of the 4-Bar system
There are many variations on the 4-bar systems I've illustrated above. For example, if the four angled bars go from the axle outboard to the chassis near the centreline, this is called a "Satchell link". (Satchell is a US designer, who used the above linkage on some of Paul Newmans Datsun road racers some years back.) It has certain advantages over the above examples. Both of the these angled linkages can be reversed to have the angled links below the axle and the parallel links above. The roll centre will be lowered with the angled bars under the axle, a function which is difficult to accomplish without this design. The other variation on the "four bars" not shown are the Watts and Jacobs bar linkages to replace the Panhard rod for lateral positioning. Another linkage is the two parallel bars above the axle and a triangulated link underneath - a design you will find on the Lotus 7 - where the lower link has its base on the chassis and the apex under the differential. Then there is the Mallock Woblink, which could be described as half way between a Jacobs ladder and a Watts link, and makes it possible to place the rear roll centre quite low without sacrificing ground clearance.
Watts links are pretty popular with the hydraulic lowrider/truck bed dancer types. The Jacobs ladder is used almost exclusively on US midget and sprintcar dirt track rear ends. The Mallock Woblink is used mostly on the Mallock U2 Clubman cars in Great Britain.
de Dion suspension, or the de Dion tube
The de Dion tube - not part of the London underground, but rather a semi-independent rear suspension system designed to combat the twin evils of unsprung weight and poor ride quality in live axle systems. de Dion suspension is a weird bastardisation of live-axle solid-beam suspension and fully independent trailing-arm suspension. It's neither one, but at the same time it's both. Weird! With this system, the wheels are interconnected by a de Dion Tube, which is essentially a laterally-telescoping part of the suspension designed to allow the wheel track to vary during suspension movement. This is necessary because the wheels are always kept parallel to each other, and thus perpendicular to the road surface regardless of what the car body is doing. This setup means that when the wheels rebound, there is also no camber change which is great for traction, and that's the first advantage of a de Dion Tube. The second advantage is that it contributes to reduced unsprung weight in the vehicle because the transfer case / differential is attached to the chassis of the car rather than the suspension itself.
Naturally, the advantages are equalled by disadvantages, and in the case of de Dion systems, the disadvantages would seem to win out. First off, it needs two CV joints per axle instead of only one. That adds complexity and weight. Well one of the advantages of not having the differential as part of the suspension is a reduction in weight, so adding more weight back into the system to compensate for the design is a definite distadvantage. Second, the brakes are mounted inboard with the calipers attached to the transfer case, which means to change a brake disc, you need to dismantle the entire suspension system to get the driveshaft out. (Working on the brake calipers is no walk in the park either.) Finally, de Dion units can be used with a leaf-spring or coil-spring arrangement. With coil spring (as shown here) it needs extra lateral location links, such as a panhard rod, wishbones or trailing links. Again - more weight and complexity.
de Dion suspension was used mostly used from the mid 60's to the late 70's and could be found on some Rovers, the Alfa Romeo Alfettas (including the sedans and the GTV) and the GTV6, one or two Lancias a smattering of exotic racing cars and budget sports cars or coupes.
More recently deDion suspension has had somewhat of a renaissance in the specialist sports car and kit car market such as those from Caterham, Westfield and Dax. These all uniformly now use outboard brake setups for ease-of-use, and a non-telescoping tube, usually with trailing links and an A-bar for lateral location (rather than a Watts linkage or Panhard rod.) Whilst a properly setup independent suspension system will always win hands-down on poorly maintained roads, when you get on to the track, the advantage is not so clear cut and a well set up deDion system can often match it turn-for-turn now, espeically for flyweight cars.
Source
Last edited by okvortec; 10-19-2009 at 02:24 PM. Reason: pics
#3
10-19-2009, 02:22 PM
^^ Yep, that about covers it. ^^
I was going to post pictures from our applications. The term typically gets used for front axle arrangements. The s-series trucks have an independent front suspension from the factory. These setups can be restrictive in terms of the amount of lift that can be attained without major surgery. A solid front axle on the other hand is just a spring swap, longer driveshaft, and a drop pitman arm away from much higher lifts.
I was going to post pictures from our applications. The term typically gets used for front axle arrangements. The s-series trucks have an independent front suspension from the factory. These setups can be restrictive in terms of the amount of lift that can be attained without major surgery. A solid front axle on the other hand is just a spring swap, longer driveshaft, and a drop pitman arm away from much higher lifts.
