Issue: Sep 2011


Modularization concepts of automotive front-ends



by Tony Davison

Modularization concepts of automotive front-ends 

Front-end modules have been around since the early 1990s, with Volkswagen implementing them in their VWs and Audis, and they have proved to be a significant improvement over earlier automobile assembly methods. A number of European manufacturers have adopted modularization, but it has been slow in coming to North America. Because of higher fuel costs, there has been a need to reduce weight. In order to see what in an automotive front-end can be modularized, we should review front-end systems and assemblies, themselves.

What is an automotive front-end? 

When you go to a shop and ask the mechanic to check your car’s front end, they place the car on a lift or jack stands and proceed to inspect the suspension, steering, and alignment. If you want to have the brakes checked, normally you specifically have to say “brakes”. If want to have your cooling system checked, you need to say so. Mechanics normally don’t think of these as “the front-end” but as separate systems.

However, automotive designers consider all of these, and more as part of the “front-end”, or front-end module (FEM), literally meaning everything in front of the windshield, save for the power train [1]. That means frame, body parts, and electrical system, as well as the other well-known systems, such as suspension.

Historically and for conceptual purposes, we think of systems that respond to a function. For front ends, we consider:

• Brakes
• Steering
• Electrical
• Cooling
• Frame
• Suspension
• Mobility - Wheels, axles, and bearings

Let’s identify the main systems found in the typical automotive front-end. At such point, we can discuss modularization.

Basic construction of automotive front-end 

An automotive front-end consists of suspension steering, part of the braking system, wheel/bearing assembly, electrical, cooling, air conditioning, and frame. Overlaid onto these are accessory items and systems, such as V belts, fans, tensioners, and the window washer system (wipers, pump, and reservoir). We present a brief overview of these systems and their weight considerations in order to assess what can be modularized and made less heavy.

Suspension 

Any part that is involved in holding the car body up and easing its up and down or sidewise motion is referred to as suspension. Depending upon the type of suspension, there are springs - usually coil or air, motor mounts, ball joints (upper and lower), stabilizer bar, bushings, knuckle, infrastructure (such as yokes and housings), McPherson struts or shock absorbers, torsion bars, and control arms. This is one of the heaviest systems in the front end and a candidate for design with lightweight materials.

Steering 

The steering system is everything in between the steering wheel to the wheel being turned. Depending upon the system, this includes the steering wheel, of course, power assist mechanism (if any), Pitman arm, standard, rack and pinion, and linkage (tie rod ends, tie rods, idler arm, etc.).

There are two major areas: linkage and steering mechanism. Arrangements will vary, but most linkage systems consist of ball-type joints (tie rod ends, control arms), intermediate links (Pitman arm – also called “steering arm”, drag link), threaded adjuster sleeves, and links.

There are two basic steering assemblies: recirculating ball bearings, and rack and pinion. The recirculating ball bearing system contains an “endless belt” of ball bearings that serve to reduce friction between the steering wheel shaft and the main linkage – through the Pitman arm - to the linkage assembly and then to the wheels. Rack and pinion consists of a gear rolling against a toothed rack which goes back and forth, in turn, directing the wheels. A part of most modern steering systems is the power assist unit system, either hydraulic or electrical. The hydraulic one is made up of a pump, and hydraulic unit attached directly to the steering gear box, or gear, at the end of the steering column or attached to the rack and pinion assembly. Active front steering (AFS), technology designed to make the front wheels
turn a certain number of degrees in accordance with the speed of the vehicle, is more
involved and, of course adds more weight.

Brakes 

We are talking about 60% of the braking power being done by this half of a system located in the front-end. This system includes the master cylinder with booster, lines, calipers, shoes with pads, and rotors (or drums in older cars). For an automatic braking system (ABS), we add an electric motor and planetary gear set, which are not light components. Rotors and drums – made of dense steel - can be considered candidates for weight reduction.

Mobility 

“Mobility” consists of the parts that allow the car to actually roll on the ground. Although this is not a standard term in automotive textbooks, such as Stockel [5], it, nevertheless can be identified as a separate system and with one specific purpose – to allow the vehicle rolling movement. Constant velocity (CV) joints, axles and axle tube, wheels and wheel bearings, spindle, and hub are included in the mobility part of the front-end. Overall, the mobility system is just as heavy as the suspension or steering systems. CV joints replace what was before the universal joint (UJ), the difference being that the CV joint, as the name indicates, permits the drive shaft to turn at a constant rotational speed, while the UJ has a varied angular velocity. Variations of the CV include Rzeppa and tripod joints, double cardan, and Thompson couplings. Wheels on which the tire is mounted and, in turn, are mounted on the axle (drive axle for front wheel drive, and driven axle for rear wheel drive cars) are, with the axle, itself sources of medium weight. The spindle, which some consider part of the suspension [6] is what the brake rotor or hub mounts. The wheel, hub and its bearings, and spindle is often called the “wheel-hub assembly”, and the hub, being solid steel, is quite dense, hence quite heavy. In the CV joint, the spindle is a part of the assembly. In older models, the spindle is a separate part mounted between the upper and lower control arms.


Electrical 

The wiring harness, computer modules, such as for the engine, brakes, and steering, fuse box, lights, and battery are part of the front end. The alternator (with its internal regulator) and starter usually are mounted on the petroleum-fueled engine. For electric cars, configurations vary, and what is considered as a part of the front-end should be considered on a case-by-case basis. With electric cars, only the batteries as the main part normally are in the back of the vehicle.

Cooling 

The cooling system has a radiator, water pump, fans – direct mount and separate (usually electric), low pressure reservoir, thermostat for the fan, and hoses, but usually, only the radiator, external fan, reservoir, and hoses would be considered as part of the front end, since the water pump and internal thermostat normally are part of the engine. In electric vehicles, only the fan is needed.

Air conditioning 

This system comprises the compressor (quite heavy), condenser, drier, tubing, hoses, ducts, and squirrel cage fans. Usually, this system is scattered throughout the front-end, condenser being in front, drier on one side and the compressor on the other. The blowers are attached to the fire wall, pointing inward to the inside compartment.

Frame 

The frame includes support members (I-beam, or sheet metal fabricated with a built-in geometry as a support structure), sheet metal or plastic, fenders, bumper, attachment point and hardware for attaching, glass, and doors. A central focus of applying new materials has been on the frame. 

Want to learn more about current technologies and developments in automotive front-end?

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References(Subject is indicated by URL – accessed 22 August 2011)

[1] A Survey of Front-End Modularity, http://www.just-auto.com/analysis/review-of-front-end-modules_id104743.aspx
[2] http://мбмастер.рф/SsangYongRexton/files/2C.pdf
[3] http://autorepair.about.com/library/bl244lib.htm
[4] Willy Klier, Gerd Reimann and Wolfgang Reinelt, Concept and Functionality of the Active Front Steering System, ZF Lenksysteme GmbH, Schwäbisch Gmünd, Germany, No. 2004-21-0073, 2003 SAE International (2003), pp. 1-3
[5] http://www.goodreads.com/author/show/617260.Martin_T_Stockel
[6] http://en.wikipedia.org/wiki/Spindle_%28automobile%29
http://www.secondchancegarage.com/public/140.cfm
http://www.paulstravelpictures.com/GM-Wheel-Bearing-Hub-Assembly-Replacement/index.html and http://www.getusedparts.com/auto_parts_guide/S/used_spindle.html
[7] Potentials and Limitations of Pre-Crash Systems for Pedestrian Protection

Resources (Subject is indicated by URL – accessed 22 August 2011)

http://en.wikipedia.org/wiki/Caster_angle
http://www.automotive-frontend.com/Event.aspx?id=578242
http://www.broadwaytrans.com/resources/car-care-articles/brakes - smaller sized brake system
http://www.stjoesauto.com/course_support/Unit%201%20Introduction%20to%20Brakes.PDF
http://www.stjoesauto.com/course_support/
http://www.iqpc.com/Event.aspx?id=578750
http://www.a-sp.org/database/publicationmain.asp
http://en.wikipedia.org/wiki/Constant-velocity_joint
http://wardsautoworld.com/ar/auto_frontend_module_demand_2/
http://www.faurecia.com/expertise-innovation/automotive-equipment/Pages/car-exterior.aspx
http://wardsauto.com/ar/module_supplier_future_100907/

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