History of BMW

BMW came out of a merger between an airplane maker and an engine maker. Leading up to and during the world wars, BMW made airplanes. Immediately after each war, they were shut down and had to shift to motorcycles first, and then cars.

The roots of the airplane maker side of BMW go back to Gustav Otto, the son of the inventor of the four stroke internal combustion engine and a pioneer aviator in Bavaria in 1910.

Otto's airplane manufacturing company "Otto Flug Maschinen Fabrik" was plagued with production problems, and was taken over by the German government and then reorganized as Bayerische Flugzeug Werke AG (BFW) in 1916 in the midst of WWI (1914-1918). They managed to solve the quality problems and were a major contributor to the war effort.

The company was hit hard after WWI, as it was forced to shut down airplane production by the allies. To survive, BFW moved into furniture and fitted kitchens using their advanced joinery factories developed to build the wooden aircraft of the time.

By 1922, taking advantage of BFW's hard times, Viennese financier Camillo Castiglioni

had acquired all the shares. At this time it also branched out into designing and building "Flink" and "Helios" brand motorcycles, with the engines supplied by a company called Bayerische Motoren Werke (BMW), for whom Castiglioni was a shareholder. 

In that same year, Castiglioni bought the rights to the name BMW, its engine designs, and its engine manufacturing capabilities and merged that with his wholly-owned aircraft manufacturing company, BFW, renaming the whole to BMW and moving it to the same buildings as previously occupied by Otto Flugzeug Werke on Lerchenauer Strasse 76, where BMW HQ has been ever since. 

Meanwhile, Rapp Motoren Werke, established in 1913, supplied Otto with his four cylinder aircraft engines. They were also subcontracted by Austro-Daimler to produce their V12 aircraft engines, a deal brokered by Castiglioni. The Austrian sent to oversee the contract, Franz Popp, became actively involved in company management, changed the name of the company to Bayerische Motoren Werke GmbH in 1916, and brought on Max Friz as the chief designer to replace Rapp. Friz designed an excellent aircraft engine, the BMW IIIa.

Not willing to continue financing the company itself anymore, The Bavarian and Prussian ministries of war encouraged BMW to be taken public in August of 1918. It was to be one third owned by Bavarian Banks, one third by Bavarian industrialist Fritz Neumeyer, and one third by Castiglioni.

At the end of WWI in November of 1918, BMW was no longer allowed to make aircraft engines by the terms of the armistice, yet the BMW IIIa was its only product. At this time, Castiglioni bought all outstanding shares, the other shareholders having lost confidence in the future of the company.

When allowed to reopen in 1919, under the guidance of Popp and Friz, BWM shifted to motorcycle and boat engines. This alone could not sustain them and Castiglioni maneuvered a contract from Knorr-Bremse of Berlin to manufacture pneumatic railway brakes (having arranged for the Bavarian government to buy their trains in exchange for having the brakes made in Bavaria). The brake building part of the venture quickly overshadowed the engine part of the business. Castiglioni sold BMW to Knorr-Bremse at a considerable profit. Under Knorr-Bremse, the company rapidly grew.

In 1922, Castiglioni offered to buy back BMW's engine-building business (including Popp as GM, Friz as Chief Designer, and all their engine-related intellectual property), and all rights to the BMW name from Knorr-Bremse, who agreed, being only interested in trains, not airplanes. This company was merged into Castiglioni's other company, Bayerische Flugzeug Werke in 1922, under the BMW name.

In the early 1920's, the modestly sized BMW Company produced motorcycles, small engines, and spare parts, and did not do very well, having not gotten back into the airplane building business since the end of WWI. However, Castiglioni had bought BMW back from Knorr-Bremse for a reason, and had in his back pocket a deal with the Czech government for the BMW IIIa and IV aircraft engines to be manufactured under license by the Walter Company of Prague. The considerable proceeds of the licensing deal went straight into Castiglioni's pocket through unscrupulous accounting practices. Consummating this deal was his true goal in acquiring back the engine division from Knorr-Bremse.

But Castiglioni was not done yet. Soon after this deal, in 1923, BMW began again producing aircraft engines, and won a major contract with the Russian Red Army brokered by Castiglioni. An illicit 10% commission on each engine sold went back into Castiglioni's pocket though shadow companies.

In 1926, Castiglioni ran into unrelated financial problems with Deutsche Bank, and had to relinquish some shares in BMW. As part owner, he was then investigated by the bank for his shady business dealings, and got into further financial difficulty, and was forced to pay back BMW for the illicit commissions which resulted in all his shares going to Deutsche Bank. The Soviets argued they had been overcharged the illicit 10% and settled for a perpetual license to the BMW VI engine design, and then ceased doing business with BMW by 1931.

As the writing was on the wall, under Popp's leadership BMW diversified into motorcycles and then cars in 1928. The Dixi Company of Eisenach licensed the British Austin Seven and began selling it in 1927. In 1928, BMW bought the Dixi Company and renamed the car to be the BMW Dixi, and then the BMW 3/15.

Wishing to wean themselves from the Austin license that was set to expire in 1932, BMW began designing and producing its own cars in 1933, with the BMW 3/20.

The successor, the BMW 303 produced in 1933, was the first BMW to sport the iconic "kidney grill" that continues to be used as a BMW design cue today.

A number of cars and motorcycles were built up to and into WWII. During the war, BWM was increasingly pressured to exclusively build aircraft engines for the Nazi's, which Popp thought a bad business to be so tied to the Nazis. By the end of the war, BMW was forced to use concentration camp labour to build jet and aircraft engines.

After the war, the company was again shut down and only emerged with its first post-war automobile in 1952. Meanwhile, an English company, Bristol, took plans for BMW's cars as war reparations, and started building Bristol Cars which were knockoffs of BMW's. BMW also had its car manufacturing in Eisenach, which was in Soviet territory. The Soviets used the plans, machinery, factories, and workforce to manufacture "BMWs" for state officials. Later on they even started exporting the cars under the BMW marque to try to get hard currency. BMW's first post-war car was the BMW 501, a luxury car costing 4x the average annual salary (in today's terms, $200,000).

These cars and the likes of the acclaimed sports car, the BMW 507 (below) were too expensive to produce, and were not commercial successes.

The company was saved in 1955 by the tiny and affordable bubble car, the Isetta, of Italian design, which married BMW's motorcycle and automobile work.

This car was popular with city dwellers, and in 1957 BMW tried to expand on the appeal of the Isetta with the unusual BMW 600.

This car was not a commercial success, but it did lay the engineering groundwork for the popular 1959 BMW 700 economy car whose success saved the company from being acquired.

This car inherited the 600's rear mounted 2 cylinder four stroke "flat-twin" engine and was BMW's last economy car until it acquired Mini.

The financial success of the 700 made up for the expensive money losing 500 series cars, but the company was still in trouble. In a famous shareholders meeting in 1959 management stressed that the 700 and their next development, the "New Class", would lead to success. Another faction wanted to essentially sell to Mercedes. In the end, a wealthy German, Herbert Quandt, acquired shares from a disgruntled shareholder and blocked the sale of the company to Mercedes. The Quandts remain as the most important shareholder to this day.

Herbert Quandt

With the new leadership at the Board, BMW was able to pursue the development of the New Class, starting with the BMW 1500 in 1962.

This car was targeted at neither the super-rich (as were the 501 and 507), nor the budget minded (as were the 600 and 700), but somewhere in between, for the affluent middle class, a market niche the BMW brand has occupied ever since. It was followed by the 1800, 1600, and 2000. All the '00' cars were four-door, and were the pre-cursors of the 5-Series. 2-door variants of these models ending in '02' were also introduced.

The new class cars used the BMW M10 engine line in production from 1962 until 1988. In its original form it was an inline 4 cylinder single overhead camshaft engine designed by former race car driver Baron Alex von Falkenhausen, displacing 1.5L and producing 80HP. In the 1500 it went from 0-60mph in 15s.

The New Class was a commercial success and established BMW as a maker of sporty, upper scale automobiles.

In 1970, Eberhard von Kuenheim was installed by the Quandts as the top manager within BMW, a position he held for nearly 25 years. von Kuenheim is credited with the idea of the "3-5-7", "small-medium-large", basic model lines which continue to exist today.

In 1972 the E12 5-Series was introduced, the "5" denoting BMW's fifth "New Class" platform.

The car was sold in various trims using inline 4 and inline 6 cylinder engines.

There followed by the E28 in 1981,

the E34 in 1988,

the E39 in 1995,

the E60 in 2003,

and finally, the latest in the series, the F10 model in 2010.

Steering

The steering on the M5 uses the traditional rack and pinion method with computer-controlled hydraulic power assist.

"Rack and pinion" describes the main mechanism for moving the tie rods that themselves steer the front wheels.

The steering has a variable ratio, meaning that the rack teeth are placed closer together towards the centre and farther apart towards the outside. This means that movements of the steering wheel are "amplified" as the wheel is turned more towards lock.

All the linkages are mechanical so that the driver can feel the road through his or her hands. There is, however, a power assist that enables less effort to be put in to turn the wheel.

The basic way power steering works is that as the wheel is turned this way or that, pressurized hydraulic fluid pushes on one side of a cylinder or the other, giving the rack an extra push. The system used by BMW is from ZF Lenksystem and is called Servotronic. It provides greater steering assistance at lower speeds by using a computer.

The F10 M5 uses a new type of power steering pump called a VARIOSERV power steering pump from ZF for increased efficiency.

This uses an offset rotor, much like for the oil pump in the car, to vary the amount of oil pumped through the system depending upon need.

This means that less drag is placed on the engine when the power steering is not operating as strongly.

The Servotronic is called "M Servotronic" because the electronics are tuned specifically for the M5 and there is a button that adjusts the degree of assistance (Comfort, Sport, and SportPlus).

The complete system is shown below.

There is a dedicated hydraulic fluid cooling system for the power steering with radiator (1). The fluid reservoir is (2), the Varioserv pump (3), the Servotronic valve (4) which understands the motion of the steering wheel, and the "M" rack with its power assist cylinders (5).

Suspension

The suspension of a car is what holds the wheels to the chassis, and is critical to good handling.

The front features an M Double Wishbone suspension.

"Double-Wishbone" means that that there are two main supports for the wheel, each of which looks like a wishbone. In the illustration above these as (2) and (5). There is also a "trailing link" (8) for additional support. The car is steered by means of the track rod (7) hooked up to the steering box (11).

In the F10, but all components are M-specific. There is also a 2.45 cm anti-roll bar (10) and a stiffening plate (12). The axle is attached in a more rigid fashion to the chassis than is usual, promoting increased torsional stiffness for better handling. It is made mostly from Aluminium to save weight.

The double wishbone in the F10 is an improvement over the McPherson strut system in most other cars, and also the E60 5-Series. With the MacPherson strut, the springs and dampers hold the weight of the car. With the double wishbone, they do not, and the springs and dampers are therefore more able to do their jobs. The MacPherson strut cannot allow vertical movement of the wheel without changing geometry relative to the road surface. The double wishbone is inherently superior in this regard. The MacPherson strut also transmits road noise and vibrations to a greater extent than does the double wishbone. Finally, the double wishbone allows for more freedom in the setting of camber and roll centre  thus allowing the engineers to provide a better setup for handling purposes. The double wishbone tends to be more expensive and complex than the MacPherson strut, and it also can handle a heavier car.

The rear axle is also mainly made of Aluminium and is as follows.

It is an M Integral IV multi-link suspension with a 2.15 cm roll-bar (2), stiffening plate (1), and is directly attached (without rubber bushings) to the chassis for increased stiffness. Attaching the axle to the chassis without rubber bushings is uncommon in street cars, but standard for race cars. It is possible in the M5 because the base F10 starts with a very stiff chassis to being with.

This suspension incorporates “elastokinematics” that allow each wheel to move and flex individually without loads and forces through the subframe to the opposing wheel. It has been in use since the E39 5-Series, and the one in the F10 M5 was taken virtually unchanged from the E60 M5.

The standard F10 has moved on to the Integral Link V, as it supports rear wheel steering that assists in parking and in stability control. The M5 eschewed rear wheel steering as being not worth the weight.

As with any suspension, there are springs and shock absorbers at all four wheels. The springs allow the wheels to bounce up and back down when hitting bumps, the shocks prevent them from continuing to bounce.

The shocks in the F10 M5 are under electronic control, and can be stiffened or loosened very quickly in response to changing situations in order to optimize both comfort and handling.

The system is called M VDM (for M-Specific Vertical Dynamics Management). The shock absorbers were developed with ZF Sachs and adapted to the M5. This is the VDC II (Vertical Dynamics Control System II) system that uses independent extension (A) and compression (B) adjustment via two sets of valves and works on the frequency at which the body of the car is oscillating to damp it.

The M VDM control unit gets signals from ride height sensors. The Electronics Damper Control (EDC) works with infinitely variable valves in the dampers. The hydraulic oil flow is regulated by the electromagnetic control valves. Control variables such as the ride height, front wheel speeds, steering angle, body movements and damper piston speed are used. Vertical acceleration between the suspension and body is monitored by the ride height sensors of the headlights. There is one ride height sensor installed at the front left and one at the rear left. They are hard wired to the Integrated Chassis Management control unit which sends these signals over FlexRay to the M VDM control unit.

The fundamental control principle is known as the “Skyhook system”, because the primary objective is to hold the vehicle stationary in a vertical direction. An overall analysis is performed of the ride height data, z-axis acceleration rates, and steering inputs (e.g. transition from straight-ahead travel to cornering). If M VDC detects a rapid increase in the steering angle, the controller infers that the vehicle is entering a bend and can preventively adjust the dampers on the outside of the bend to a harder setting in advance. Moreover, VDC is able to detect the braking operations by the driver based on the brake pressure information supplied by DSC. A high brake pressure normally results in pitching of the vehicle body; VDC counteracts that effect by setting the front dampers to higher damping forces. This also results in an improvement in the front/rear brake force distribution, which in turn reduces the braking distance.

The driver can set the system to Comfort, Sport, and Sport+ for increasing levels of stiffness.

This set by means of the shock absorber symbol near the gear shift lever (third from the top on the left).

Chassis

The chassis of the car has dimensions in millimetres as follows.

The incoming F10 is slightly larger than the E60 in all dimensions.

The body is made from lightweight materials including aluminium, multiphase steels and very high strength press-hardened hot-formed steels. The average strength of all body materials has increased by 55% as compared to the E60.

The monocoque metal shell is shown above. The body struts in the engine compartment are all of die-cast lightweight aluminium as opposed to a conventional steel shell structure.

Here we see the distribution of materials. Aluminium (green 3) is used for hood and door panels. Multiphase steels with tensile yield strength >300MPa (44,000psi) (1) are used in many parts, and super-high-strength hot-formed manganese-boron steels with a strength >900MPa (2) are used in certain critical location. The rest (4) are other steels <300MPa.

The unit of strength MPa is a Mega-Pascal which is millions of Newtons per square meter. For comparison, Titanium alloy starts breaking at 940 MPa, Aluminium alloy at 414 MPa.

The goal of the choice of materials for the chassis is structural integrity, stiffness of the chassis (for cornering purposes), light weight, and getting as close as possible to a 50-50 weight distribution, front and rear, which also promotes better handling.

Tires and Wheels

The tires on a car are a critical factor in its performance. Having bad tires on a great car would be analogous to having crummy speakers hooked up to a fantastic sound system.

The wheels on the M5 are forged alloy and are either 19" (1) or 20" (2). This dimension refers to the diameter of the wheel itself, not the wheel+tire diameter. On my M5 I have 19" wheels for the winter tires, and 20" for the summer tires.

It is important that the wheels be as lightweight as possible, because they act like a gyroscope and resist turning if too heavy. Also, they are part of the so-called "unsprung" mass of the car, that part of the car which is isolated from the heavier chassis. Lighter unsprung mass means that the wheels will more readily conform to the road surface, promoting better traction.

The summer tires are Michelin Pilot Super Sports. The front tires are 265/35R20 at the front, and 295/30R20 at the rear. The "295" part is the width of the tire in millimetres, or 11.6" wide. The "30" part is the ratio of tire width to tire sidewall height. So the sidewalls are 295 * 30% = 88.5mm = 3.5". Therefore the diameter of the tire and wheel together is 27". The summer tires are rated for very high speed, and the tire has been customized by Michelin specifically for the F10 M5. The tires would be extremely poor for winter driving, as the grippy rubber compound becomes hard like a hockey puck when too cold.

The tire has two types of tread rubber. The outboard shoulder features a track-type compound to withstand the stresses of high performance cornering while the notched centre ribs and inboard shoulder feature a compound designed for superior performance at very high speeds and in wet conditions. The tire's internal structure has twin steel belts reinforced by a spirally wound Twaron cord. Twaron is a polyamide cord that offers a lightweight, high-strength reinforcement above the steel belts.

The winter tires are Pirelli Winter 240 Sottozer Series 2.

They are 255/40R19 all around. The narrower tire is better for traction in the snow. It concentrates the weight of the car onto a smaller patch to allow for better grip in the snow. However traction on dry pavement is less good due to the smaller contact patch with the road. The rubber, however, stays soft even in the cold. The tire is optimized for winter driving, high speeds, and great handling.

Unlike on most BMWs, the tires are not "run-flat" models.  The very stiff sidewall on a run-flat compromises grip and handling, and so is not deemed suitable for an "M" car. However, neither is there a spare tire in the trunk due to space and weight considerations. Instead we get a "kit" that attempts to seal and re-inflate a punctured tire.

Hmmmm....

Brakes

The F10 M5 is fitted with very large and efficient brakes for bringing its 4000+ lbs quickly from high speed to a standstill, or for dropping the speed quickly for corner entry.

The front brakes are M specific and use a large 15.7" ventilated and cross-drilled compound brake disk (aluminium centre, steel disk) combined with six-piston fixed calipers.

The rear brakes use the same type of disks (but a touch smaller at 15.5"), and have a single-piston floating calliper which includes the electromechanical parking brake. The rear is taken from the base 550i, but painted racy blue!

The front brakes do more work than the rears as the weight of the car shifts towards the front during hard braking and therefore there is more traction available at the front and more braking force needed there.

The steel outer ring is completely symmetrical, so when it expands due to heat it does so uniformly without introducing any bends or kinks that can rub against the brake callipers  As the brakes cool you hear them "ping ping ping" as the outer disk collapses back onto the inner aluminium ring via the pins.

The disks are ventilated, meaning that they are hollow with a plate on each side. They are also cross-drilled, which provides more ventilation and a lighter weight.

The front brakes are six-piston fixed callipers and the rear brakes are single piston floating calliper. 

Disk brakes have brake pads that squeeze against a brake rotor to slow the car door. There are two types of brake callipers at the wheels: fixed and floating. 

The floating calliper system is shown below.

It uses only a single piston that pushes against one side of the brake disk that then pulls the calliper over to make contact with the other (bottom left).

The fixed calliper system is as follows.

There are pairs of pistons that squeeze down on the brake pad from both sides simultaneously. the M5 has three such pairs, hence it is a six-calliper brake. Fixed calliper systems are more effective than floating, but more complex and expensive.

The brakes are power-assisted using the traditional time-honoured approach. Brakes use hydraulic lines to transfer force from the brake pedal to the pistons and callipers.

Leverage combined with hydraulic force multiplication translate a relatively longer travel on the brake pedal into a shorter travel at the brake pistons at a much higher force. The diagram above illustrates the basic mechanisms at work. In this example, the force at the brake pedal is multiplied by a factor of 3 by the leverage and by a further factor of 3 by the hydraulics.

By law, all brakes have two isolated subsystems, one for the front brakes and one for the rear, in case a brake line fails.

The master cylinder is a clever arrangement that ensures the system does not empty of hydraulic pressure and keeps functioning even when one or the other of the sub-systems leak.

Most power brake systems use a vacuum booster to assist braking. The brakes use a brake servo which is powered by the vacuum generated by the engine. In the M5, because it is turbocharged, vacuum is in short supply in the intake manifold, and so a special vacuum pump maintains a reservoir of vacuum in a can, ready to be used to assist breaking on demand.

When the brake pedal is depressed hard enough, an air valve is opened which allows atmospheric pressure into one side of a vacuum chamber that boosts the pressure applied to the master cylinder. 

Here we see a typical arrangement of pedal to power brake booster to master cylinder, and then off to the front and rear brakes respectively, with hydraulic fluid returning on the left.

For each brake there is also the Anti-Lock Braking system that contains electronically controlled valves and an electric pump that modules brake pressure when wheel lock-up is about to occur.

The purpose of ABS is to shorten the braking distance and to retain manoeuvring during braking so that obstacles can be avoided. When a brake is applied until it locks up, then the car starts sliding on its tires. Once the tires start sliding, they are actually less sticky. By pulsing the brakes, they are kept just on the threshold of lockup, which is the most effective for stopping. When driving without ABS, drivers must feel the point at which the brakes are just starting to lockup, and then ease off a bit to keep the wheels spinning. This is called "threshold braking", and is more effective than "pumping the brakes" but harder to master.

When brakes lock up, since there is no traction at all, there is certainly no traction for manoeuvring. The driver can turn the steering wheel round and round but the car will keep sliding in a straight line. With ABS, the car is kept on the threshold of traction, so traction is made available when the steering wheel is turned to steer the car away from obstacles during braking.

The system in the M5 pulses the brakes very quickly, can apply itself to the four wheels independently, and is completely under computer control. This system is used for a variety of additional stability control purposes in addition to the standard "Anti-Lock Braking" (ABS) function, all under the control of a sub-system calls "Dynamic Stability Control" (DSC).

Under normal braking conditions, hydraulic pressure from the master cylinder passes straight through to the brake pistons. The computer compares the wheel speeds against one another. If it detects a wheel locking it can isolate that brake from the driver's foot, and then bleed pressure off and then on again very rapidly. In order to recover pressure after the bleed, a pump is used to restore it. The operation of the pump and the valves is felt in the driver's foot as pressure pulsations when the system is regulating braking.

Additional braking functions in the M5 include the following.

• Cornering Brake Control (CBC) which applies brakes differentially when cornering with light braking;
• Dry Braking which applies 1 bar of pressure on the rotors for 1.5 s every 90s to dry the brakes when the windshield wipers are on continuous mode;
• Brake Standby which looks for a quick release of the accelerator pedal and pre-tensions the brakes with 2.5 bar of pressure for 0.5 s in anticipation of hard braking;
• Dynamic Brake Control which monitors speed and brake pedal pressure changes and goes to maximum braking pressure when warranted;
• Automatic Soft-Stop which automatically reduces pressure at the rear axle just before the vehicle comes to a stop when braking lightly;
• Fading Compensation which monitors brake effectiveness and provides additional pressure when brakes start fading;
• Drive-off Assistant which holds the brakes until sufficient torque is available when on a hill.
• The brakes are also requested to apply themselves to various wheels by the chassis dynamics system discussed later. 

The rear brakes incorporate an electromechanical parking brake that is an independent system for clamping the callipers down on the rotors. It will work when parked and when moving (as per government regulations).

A motor is used to turn a spindle that applies locking pressure. When the motor is off, the pressure is still held as it is "screwed down" tightly.

The system is operated from a switch on the centre console under the gear lever. Pull up on it to apply. Push down to release. It can also be released by pressing on the accelerator.

There is a manual release buried under the trunk.

There is an additional system in the car related to braking called "Brake Energy Regeneration". In most cars, the alternator is continuously run whenever the engine is turning over. In this car, when accelerating or coasting the alternator is disconnected leading to a smaller engine load and more efficiency.

As long as the battery stays above a certain threshold, the only time the alternator is connected and drains shaft energy is during braking, either by means of engine overrun or when applying the brakes directly.