The Advantages And Disadvantages Of Leaf Springs | News

Nearly every car review out there will at some point mention something about the damping and suspension setup. Shock absorbers, springs, coilovers, upmarket stuff like Ohlins dampers; you&#;ve probably heard it all before. However, you don&#;t need to look back too far to find mass produced cars from the Western World that featured the leaf spring suspension. I first came across them on my Dad&#;s MGC GT and Austin Princess and always found them rusty, dirty and seemingly not up to the job.

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Leaf springs as an entity date back to the Romans who decided that their chariots needed some damping for when riding on rough surfaces. Leaf springs barely changed for centuries after right up until the early s when the first shock absorber (as we now it) was invented and then mass produced with the Ford Model A in .

What are leaf springs?

Leaf springs are a basic form of suspension made up of layers of steel of varying sizes sandwiched one upon the other. Most leaf spring setups are formed into an elliptical shape through the use of spring steel which has properties that allow it to flex as pressure is added at either end, but then returning to its original position through a damping process. The steel is generally cut into rectangular sections and then once held together by metal clips at either end and a large bolt through the centre of the leafs. It is then mounted to the axle of the vehicle using large U-bolts, securing the suspension in place.

The elasticity of the spring steel allows for a pliancy within the suspension for comfort and control of a car while moving, and a leaf spring setup has been proven as a viable option for cars for many decades, despite only really being found on HGVs and Military vehicles these days.

What are the advantages?

Due to the sheer amount of metal layered together, leaf springs offer a large amount of support between the wheels, axles and the car&#;s chassis. They can take huge vertical loads being applied to them due to their tight-knit structure, hence why heavy duty industries still use them. Vertical loading is also distributed throughout the length of the leaf spring rather than acutely through a small spring and damper, which can potentially create a concentrated force too large for the suspension to handle.

In a car, damping can be an extremely important characteristic. If the suspension is under-damped, the car will wallow and bounce around well after hitting any bump or pot hole in the road. This was a significant characteristic in cars that used helical springs before the dawn of the shock absorber and was disadvantageous to cars when driven at any real pace. Leaf springs coped much better with vehicle damping due to the friction between each plate of steel which made the response time after a vertical flex in the suspension much quicker, thus making for a much more controllable car.

FEA analysis of a monoleaf spring showing the distribution of stress

Leaf springs were simple in design and cheap to produce in comparison with the early springs and dampers therefore it was the go-to setup once cars were being fully mass produced to ensure reliability while keeping costs low. Monoleaf springs were the simplest design of the lot, using only one leaf of spring steel which tapered from thick in the middle to thin at the edges (known as parabolic leaf springs) to distribute the vertical loads appropriately. A single leaf setup could only however be used on extremely lightweight vehicles due to the lack of strength within the bar.

What are the disadvantages?

A big downside of leaf setups is they aren&#;t brilliant when it comes to suspension tuning. In racing and performance car applications, it is vital to be able to manipulate a suspension setup for the driving conditions and for different driving styles, something that is much easier nowadays through adjustable coilovers. This lack of adjustability of leaf setups is emphasised by the fact that the ends of the leaf springs are attached to the chassis, which leaves very little scope for shortening or lengthening of the leafs. Adjustments can therefore only really be made through the strength and flexibility of the material used to make up the leaf springs.

Leafs also allow very few directions of motion and are only really designed to move vertically, while a spring and damper combination can be manipulated into a much larger range of motion. Leaf springs are firmly clamped together and bolted to the chassis as well as clipped to the axle, thus giving little to no scope for any other direction of motion which can lead to heavy wear on the joints and connections holding the setup together.

This connection with a live rear axle can cause comical dynamic characteristics in a car when compared to a more modern independent suspension setup, something that older Mustangs are famous for. The rear axle will simply bounce around high speed corners as the suspension and axle are forced to move around together, when a modern damped system would add much more composure to the driving experience.

In comparison with a helical spring, leaf springs are generally much stiffer simply down to the steel construction and the tight package that they are bolted and clamped into. Ride comfort is therefore not a feature of vehicles that use leaf springs which made their popularity decrease dramatically after proper dampers were introduced in the s to everyday cars in a cost-effective manner.

But doesn't the Corvette use leaf springs?

The Corvette has often been laughed at for holding on to the old-school leaf spring technology, but there is genuine reason for Chevy to keep using them. A transverse leaf spring is placed along the rear axle and is simply kept as a design due to the fact that it works well and is a much cheaper alternative to coilovers. The &#;Vette has always been a &#;bang for your buck&#; car and with Chevrolet still claiming satisfactory handling dynamics, it sees no reason to change it up.

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Chevrolet uses fibre reinforced plastic (FRP) instead of steel as it can handle around five times as much strain energy than a standard spring steel setup along with being a third of the weight. Suspension testing is generally governed by the number of cycles or oscillations that the springs can handle. The FRP monoleaf system can handle ten times as many cycles as the steel equivalent and the lack of interaction between leafs that occurs in a multileaf spring means that the suspension stays pliant, upholding the levels of handling and ride comfort.

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With only commercial vehicles still using leaf springs for suspension for the most part, you&#;ll have to hark back a few decades to find &#;performance&#; cars with that kind of suspension - Corvette aside, of course. From a gladiator&#;s chariot to a Ford Mustang GT, the leaf spring certainly had its time at the forefront of vehicle damping but despite its simple design, the age of the spring and damper is well and truly in full swing.

Components

Coupling Hub &#; A coupling hub adapts the pump shaft to the coupling. Usually this is a disc coupling or a gear coupling rated for high speeds.

Input Shaft &#; The pump shaft runs the length of the entire pump and is what all the impellers are attached to, as well as the coupling hub. The entire rotating assembly is suspended between the drive end and the non-drive end bearings.

Radial Bearings &#; Radial bearings support the pump shaft radially. In this case, the bearings are axially split sleeve bearings.

Thrust Bearing &#; Thrust bearings support the pump shaft axially. Although this pump is primarily hydraulically balanced, there are still axial forces as the pump operates at different speeds and pressures. In this case, the thrust bearing is a set of ball bearings. In some cases, a pivot shoe bearing (sometimes referred to as a tilt shoe bearing), such as a Kingsbury Thrust Bearing, is used.

Drive End Bearing Housing &#; This bearing housing supports the radial bearing closest to the coupling hub on the drive end of the pump.

Non-Drive End Bearing Housing &#; This bearing housing supports the radial bearing and thrust bearing on the thrust end (non-drive end) of the pump. This is often referred to as the thrust end bearing housing.

Mechanical Seal &#; The mechanical seal isolates the pressurized fluid from the atmosphere. The design consists of two very smooth surfaces gliding on each other which are held together with springs. One surface rotates with the shaft, and the other is stationary. In some cases, when leakage is not an issue, (such as when pumping potable water) rope packing is used instead of a mechanical seal.

Impellers &#; Fluid is drawn in the center of the impeller in an axial direction. Then, as the impeller rotates, the fluid is forced outward, in the radial direction, due to centrifugal force.

Casing Eye Wear Rings &#; Each impeller has a casing eye ring that is built to have a very tight clearance (0.001&#; to 0.020&#; depending on the fluid being pumped) with the outside of the impeller eye. This is because there is a pressure differential between the eye of the impeller and the outside of the impeller, and the casing ring limits the leakage of the fluid back to a lower pressure zone.

Casing Hub Wear Rings &#; Like the Casing Eye Wear Ring, the Casing Hub Wear Ring serves the same purpose, but on the hub side of the impeller.

Flow Diverters &#; These help direct the fluid into the eye of the impeller. Often, these are built into the Casing Eye Wear Ring.

Throat Bushings &#; The throat bushings are made to maintain positive pressure in the seal chamber and keep contaminants away from the mechanical seal surfaces.

Throttle Bushing &#; The throttle bushing is only required on the higher-pressure side of the pump. Its purpose is to isolate the mechanical seal from the pressure of the mid stage impeller. A balance line is usually used between the two seal chambers to make both mechanical seals operate at the same pressure, even though the drive end seal is on stage 1 and the non-drive end seal is on stage 4 (in the example above). The throttle bushing is also designed to help hydraulically balance the axial thrust load of the pump.

Center Bushing &#; The center bushing is positioned between stage 3 impeller and stage 6 impeller. This means that the pressure differential between one side of the center bushing and the other can be quite high. The center bushing is designed to help hydraulically balance the axial thrust load of the rotating assembly.

Pump Case &#; What is shown in this photo is only the bottom half of the pump case. An axially split centrifugal pump has a bottom half and a top half, clamped together by large studs and nuts with a gasket in the middle.

Clamping Studs &#; Attached to the bottom half and the top half of the pump case are clamping studs. These studs and nuts are torqued up to 10,000 ft lbs on large pumps to contain the pressure in the pump case.

Suction Port & Discharge Port &#; In a multistage, horizontal, axially split volute pump, the suction connection will always be in one of the four corners of the pump, and the discharge flange will always be in the middle (on either side).

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