DETAILED REVIEW ABOUT THE BMW M5
ENGINE SPECIFICATION
Figure
1.1 The BMW M5
|
• Cylinder
Configuration |
- V type |
|
• Cylinders |
- 8 Cylinders |
|
• Valves Per Cylinder
|
- 4 Valves |
|
• Engine
Displacement |
- 4395 CC |
|
• Power |
- 625 hp @6000 rpm |
|
• Torque |
- 750Nm @ 1800-5860 rpm |
|
• Compression Ratio |
- 10.0: 1 |
|
• Engine Location |
- Front, Longitudinal |
|
• Fuel System |
- GDI |
|
• Fuel Type |
- Petrol |
|
• Certified Mileage |
- 9.8 km/litre |
|
• Emission Norm |
- BS 6 |
|
• Acceleration
0-100 km/h |
- 3.3 Sec |
|
• Drive type |
- AWD |
|
• Top Speed |
- 305 Km/hr (with electronic speed regulator) |
The mighty M5 have a 4.4 litre
Twin turbo V-8 engine under the hood. In the base from the engine puts out a
maximum power of 627 hp @ 6000 rpm with a peak torque of 720 Nm @ 1800-5860
rpm. The new M5 has a power increase from 617 hp to 625 hp than the previous
generations of M5. The BMW M5 could reach from 0-100 km/h in just 3.3 seconds,
thanks to two TwinScroll Turbocharges, High-Precision Injection and Valvetronic
fully variable valve control. Figure 1.2show the BMW M5 engine
Figure
1.2 BMW M5 engine
The BMW TwinScroll turbo
technology is also called The BMW TwinPower Turbo technology. The BMW
TwinScroll Turbo technology is based on the twin-scroll principle and has been
actively installed in BMW petrol and diesel engines since 2011. BMW achieved to
downsize their engine all thanks to the TwinScroll Turbo technology. The
engines have been showing superior in terms of performance, efficiency,
response and pulling power. In the TwinScroll turbocharger, the exhaust
manifold is evenly split into two headers based off of firing order. The TwinPower
Turbo (also called twin scroll turbo) is a single turbo powered from pairs of
cylinders in an alternating sequence from two exhaust down tubes. The Twin
Turbo Power has two turbos, each fed by one of the two exhausts down tubes. The
Figure 1.3 show the TwinScroll Turbocharger from the 4-cylinder engine;
however, the same principle is applied in the V6, V8 and V12 engines
Figure
1.3 TwinScroll Turbocharger from the 4-cylinder engine
The Twin Turbo system can reduce the turbo
lag. The main downside of the previous generation of BMW M5 were, the vehicle
could deliver excellent torque at higher RPM but the vehicle has a significant
drop in the torque at lower RPM, Thanks to the Twin Turbo BMW could able to
solve this problem. BMW could able to achieve a significant increase in the
power of the M5. The figure 1.4 show the TwinScroll turbo
Figure
1.4 TwinScroll Turbo
FUEL SYSTEM
An innovation in the new BMW engines, including the
S63top in the F10 M5, is "Gasoline Direct Injection" (GDI). In GDI,
fuel is injected directly into the cylinder. The figure 2.1 show an GDI fuel
injector.
Figure
2.1 GDI fuel injector
The N63 and
S63 engines without variable valve lift use newer single nozzle piezoelectric
injectors. These injectors, rather than using a solenoid, use a stack of
crystals that grow when an electric charge is supplied. This allows for
extremely quick opening and closing. BMW calls that system HPI (High-Precision
Injection).
The S63top introduced variable valve lift, and the piezo style fuel
injectors were too big to fit alongside the mechanism for controlling valve
lift, so smaller injectors were required. Thus, a new system with variable
valve lift (which BMW calls Valvetronic) and turbocharging was required. This
is called TVDI, for Turbocharged Valvetronic Direct Injection. TVDI
goes back to using solenoid electromagnetic technology, but an advanced version
(called HDE) that leverages the new Bosch HDEV5.2 injectors shown in figure
2.2.
Figure
2.2 Bosch HDEV5.2
HDE injectors operate at very
high pressure, have multiple holes in the nozzle, and are optimized for fast
and short opening times. The advantages of GDI in general, and HDE in
particular, is finer atomization of the fuel due to the higher pressures, less accumulated
fuel on the intake valves and manifold, and a cylinder cooling effect which
allows for a very high 10:1 compression ratio for a car turbocharged with over
1.5 bar of boost.
Different
fuel pressure is required according to the operating conditions. Maximum
pressure (p) of 200 bar (2900 psi) is only required at high engine load and low
engine speed. The fuel rail diagram of BMW M5 is shown in figure 2.3 The high
pressures in the fuel rail are achieved using two single-piston pumps (2 &
7) driven from the exhaust camshafts by threelobed cams. In the S63 there is a
pump for each rail to ensure that sufficient pressure is generated under all
operating conditions. Fuel is fed to these pumps via (8 & 1) from an
enlarged (80L) steel gas tank by a 5-bar electric fuel pump adapted for the
increased demands of the engine.
Figure
2.3 Fuel Rail Diagram of BMW M5
The Figure 2.4 shows the
high-pressure fuel pump. The piston (4) compresses the fuel, directing it
through a high-pressure non-return valve (2) to the fuel rail via the
high-pressure connector (B). In case of over-pressure (245 bar), the pressure
relief valve (3) will open. Because the piston is constantly operating, the
pressure is electronically controlled by the volume of fuel allowed to enter
the high-pressure system by the volume control valve (5) controlled by the DME
via electrical connection (6).
Figure
2.4 High pressure fuel pump
The engine has equipped with
"anti-knock" sensors, which are simply microphones mounted on the
outside of the cylinder walls that listen for explosions that occur at
inopportune times. These signals are relayed to the DME computer, which can
modify the valve and fuel timing to bring the vehicle to a halt. However, if it
must do so, combustion is no longer ideally efficient, and exhaust gases rise,
fuel economy suffers, power is lost, and the engine can overheat, potentially
destroying the valves and turbo bearings, both of which are susceptible to
severe heat.
LUBRICATION SYSTEM
Lubrication is the lifeblood of an engine. We often
don't think about it, but the only way all those incredibly fast-moving parts
keep moving is because there is a constant supply of oil pumped and sprayed at
them. As with everything in the M5, the lubrication system needs to be beefed
up to keep up with the power output.
The M5 uses low viscosity oils
0W-30 or 0W-40. "Viscosity" is a measure of how "thick" a
liquid is. Molasses is viscous, water is not. It is actually a measure of a
liquid's resistance to being deformed when under stress. In "0W-30"
oil, the "30" part means that is the viscosity of the oil when tested
at 100 C according to SAE (Society for Automobile Engineering) standards.
Higher numbers indicate thicker oil. The "0W" means that at low
starting temperatures, the oil viscosity is like that for oil that tests at
viscosity 0 at high temperature (100 C).
The purpose of the oil is to
mainly lubricate but also cool fast moving engine parts and in certain cases to
also act as a hydraulic fluid (for the variable valve timing VANOS in the case
of the M5). Lubrication is specifically directed at the crankshaft, timing
chains, camshafts, VANOS wheels (particularly oil hungry), valves,
turbochargers, and piston crowns. Other parts of the engine, such as the
Valvetronic worm gear, and the pistons are lubricated via carefully designed
oil splash from the camshafts and crankshaft respectively.
The Figure 3.1 shows the oil pan
and the oil cooler. The oil collects in the oil pan at the bottom of the
engine. A lot of the oil is pumped through holes in the engine block onto the
crankshaft at the bearing and simply falls down into oil pan. It is cooled
using an oil-air heat exchanger (3) located under the front bumper as shown in
the figure 3.2, under control of a thermostat (1) that allows the oil to flow
to the radiator through connection (2) only after the oil hits 100 C.
Figure
3.1 The oil pan and the oil cooler
Figure
3.2 The oil-air heat exchanger located under the front bumper
The oil pump
is driven by a roller chain off the rear of the engine near the flywheel, it is
shown in the figure 3.3. The oil pump is responsible for a considerable amount
of leeching of engine power. Moreover, the VANOS system uses hydraulic oil
pressure to advance and retard timing, and is quite oil hungry as a result.
However, VANOS only needs the oil when it is adjusting, and not in cruising
situations, therefore the oil pump is of a new design that adapts to the oil
requirements of the engine. There is also a second oil pump in the front of the
oil pan that sucks fluid back to the sump when braking and cornering hard.
Figure
3.3 The oil pump driven by a roller chain
The
oil pump is shown in the figure 3.4 below. The oil pump is a volumetric
flowcontrolled sliding-vane positive displacement pump, and only supplies as
much oil as is required by the engine at any given time. The rotor (8)
pivots around the pump shaft (2) on pivot pin (10) against the tension of the
compression spring (3). When demand for oil pressure is high, this creates lack
of oil and hence lack of pressure in the oil chamber (7) which causes the rotor
(8) to drop off centre When off-centre, the difference in volume between the
chambers formed by the lower vanes and the upper ones force more oil to pump.
As demand drops the rotor returns to a more central position and less oil is
pumped.
Figure 3.4 The oil pump
Figure 3.5 illustrates the oil
pimp in the oil pan. The
intake pipe (9) is positioned deep in the rear area of the oil pan sump to
ensure a good oil supply under even "dynamic driving conditions" (i.e., driving like a maniac). The oil
return line (1,2,3) returns oil into the rotor pump (4) where it drains into
the sump. Pressurized oil flows out through the outlet (6) into the oil filter,
the radiator if above 100 C, and then onto the engine. When less oil is
required by the engine, it accumulates in the sump. The oil filter has a valve that bypasses the filter if
the pressure differential on either side of the filter is more than 2.5 bar.
This is for cold start situations when the oil is too viscous to flow properly
through the filter. There
are spray nozzles placed in strategic locations near cylinder heads, chain
drives, and bearings, to direct oil where it is needed, it is shown in the
figure 3.6
Figure
3.5 The oil pimp in the oil pan
Figure
3.6 Spray nozzles
COOLING SYSTEM
A critical aspect of the BMW F10 M5 engine is its
cooling. Because of the high RPM's and boost pressures, considerable heat is
thrown off in spirited driving that must be controlled. When the engine is
generating as much power as does the M5's, cooling is not something you want to
treat as an afterthought. If the cooling system fails, it is quite possible to
melt the engine very thoroughly. If it is even a bit off, heat can accumulate
at sensitive places and cause a lot of damage, shortening the longevity of the
engine. It is clear from the Figure 4.1 that, BMW does not include the fog
lamps so as to provide an extra air vent to feed more air to cool the massive
4.4L V8.
Figure
4.1 Front view of BMW M5
The engine and turbo water
coolant circuit are shown in the figure 4.2. The coolant is circulated
through the radiator (1) by a belt-driven pump. From there, it flows to an
electric pump (5) which drives coolant through the engine block. On exit it is
monitored by the coolant temperature sensor (11). At this point the thermostat
(4) either sends it back into the engine during warmup, or directs it back to
the radiator to get cooled down. An electric motor (10) directs heated coolant
through a valve (8) to the cabin heat exchanger (7). Electric motor (9) sends
coolant through to the turbos (6). As the pressure gets higher, coolant is bled
off into two expansion tanks (3 & 12) where it can be recycled when needed.
Figure
4.2 The engine and turbo water coolant circuit diagram
The main pump has a modified
design that achieves a higher coolant flow rate through different impeller
geometry. As well, the cylinder head cooling has been optimized. After
the engine is shut down, there is an auxiliary electric coolant pump that can
run for up to 30 minutes, with the electric fan running for up to 11 minutes to
improve cooling.
The turbochargers are also liquid
cooled. This is not critical during operation, as the intake airflow and the
oil lubrication keep the turbo within acceptable operating temperature ranges.
However, after the engine is shut down and no further airflow or oil flow
occurs, the exhaust manifold retains heat which will be absorbed into the turbo
bearings which can cause damage. Figure 4.3 shows the sectioned view of a
turbo. For
this reason, there is an electric motor (3) driven cooling circuit for the
turbocharger bearings as shown below. Its coolant flows in after it has already
exited the engine so as not to detract from engine cooling during operation.
After the engine shuts down is when the turbo bearings need cooling. Electric
motor driven cooling circuit is shown in Figure 4.4.
Figure
4.3 The sectioned view of a Turbo
Figure
4.4 Electric motor driven cooling circuit
In addition, there is a second
"low temperature" cooling circuit shown in figure 4.5 dedicated to
the charge air coolers (aka "turbo intercoolers") (D, H) and the DME
computers (F, G). There are three radiators (A, B, J) located beneath and to
the sides of the main radiator. These cooling circuits are driven off two
electric pumps (C, I) and the circuit has its own reservoir (E).
Figure
4.5 Low temperature Cooling circuit
The low temperature cooling
circuit diagram is shown in figure 4.6. It cools the DME's (F, G) and the
charge air (D, H) using radiators (A, B, J) and electric pumps (C, I). It also
has its own expansion tank (E). This circuit has the two air-to-water charge
air coolers and the three radiators, for a total of five coolers. Add to this
the main engine radiator, a radiator for the engine oil, one for the
transmission oil, one for the power steering, and the air conditioner's
condenser, and that's the total of 10. In addition, there are cooling fins on
the rear diff under its aluminium oil tray
Figure
4.6 The low temperature cooling circuit diagram
TRANSMISSION SYSTEM
The drivetrain is shown in figure 5.1. The gearbox is mounted
longitudinally, in line with the engine crankshaft and connected via a
driveshaft to the rear differential which directs torque to the wheels, tires,
and road.
Figure
5.1 Drive Train
The gearbox on the M5 is the Getrag GS7D36BG M Double-Clutch
Transmission (DCT) with Drivelogic. The "Drivelogic" is marketing
speak for the computer that controls the gearbox: BorgWarner's DualTronic
clutch module (also called the "mechatronics" as a hybrid of
mechanical and electronic in one package). It is classified as an
"Automatic Manual" because it uses clutch plates and a clutch
mechanism to connect and disconnect the engine from the geartrain as for a
manual transmission, but is has no clutch pedal and the gears can be made to
shift automatically as for an automatic. It does not use a fluid-coupled torque
converter as would a traditional automatic
transmission, instead using hydraulically controlled wet clutches.
It is a "Dual-Clutch"
because it has two set of clutch plates, one for the even gears and one for the
odd ones. This creates two sub-transmissions. As one is driving along in a
certain gear using sub-transmission A, the electronics know if you are
accelerating or decelerating, and will automatically engage the next gear in
advance on sub-transmission B. This subtransmission B free-wheels until the one
clutch is disengaged and the other engaged. This allows extremely rapid gear
changes with no interruption of power to the wheels. This type of transmission
was first used on a BMW in the M3. The Getrag BG used in the M5 is a beefedup
version of the SG used in the M3, and shown in figure 5.2 in a partial cut-away
view.
Figure
5.2 Partial cut-away view of the Getrag BG
The principle of operation is as shown in figure 5.3. The
engine (A) inputs torque to two clutch assemblies (1,3) within the transmission
(B). Depending upon which clutch is engaged, torque flows to either the top
transmission sub-assembly (2) or the bottom one (4). These gears engage the
propeller shaft which drives the rear wheels through a differential (C).
Figure
5.3 The principle of operation of DCT
The dual-clutch assembly pulled away from the gear trains is
shown in figure 5.4. It is a wet clutch, meaning that it is bathed in oil for
smoother operation and longer life, and uses multiple clutch plates to
compensate for any resulting slip. The two clutches are concentric, and the two
transmission sub-assembly shafts nest one inside the other (observe the nested
toothed gears towards the middle right, each drives its own subassembly).
Figure
5.4 The dual-clutch assembly pulled away from the gear trains
The illustration in Figure 5.5 represents the inside of the
M5 gearbox. The gear train on the bottom is called the countershaft. It is
permanently rotating and meshed with the constant gear on the output shaft.
There is an additional small gear train sticking out the side for reverse gear.
The various gears are always meshed with one another. Some are permanently
rotating with their shaft, others are free-wheeling on their shaft until a dog
clutch pushed in place by the shift mechanism meshes them to their shaft. The
dog clutch uses a synchromesh mechanism to match RPMs before locking the gear
to the shaft. The main shaft is actually two entirely separately rotating
shafts, one nested inside the other. Some of the dog clutches mesh the gear to
the inner shaft, others to the outer shaft, and some of the gears are
permanently rotating with either the inner or outer shaft.
Figure 5.5 inside of the M5 gearbox
The system predicts what gear it
will likely go to next depending on if the car is accelerating or decelerating.
It will then pre-engage the appropriate dog clutch. The next gear is always on
the other shaft which is not yet clutched to the drive shaft, so its shaft can
freewheel. The engaged clutch can then start decreasing and the other clutch
can start increasing in pressure to match RPMs. The Figure 5.6 shows the entire
Transmission system. The transmission (2) is lubricated and cooled by oil
via the air/transmission oil cooler (1). The
transmission has its own integral
oil pump driven from the centre input shaft. Therefore, the engine must be
running for the oil pressure to build up. It is connected by wires to the gear
selector level.
Figure
5.6 The Transmission System
The "mechatronics"
(electronics + hydraulics) module plugs into the side of the transmission,
receiving input from the various position, rotation, temperature, and pressure
sensors within, and effecting via hydraulics the shifting and clutching
functions. The mechatronics plugs are shown in
Figure 5.7 The mechatronics communicate with DME-1 via the PT-CAN
computer bus to get pertinent information and to "blip" the throttle
on shifts. Blipping means bringing the engine revs up to match the wheel speed
at the next lower gear down during down-shifts. The gearbox blips in all
shifting modes.
Figure
5.7 The mechatronics plugs
The M5 has a very special computer controlled limited slip
differential. The purpose of the rear differential is to transfer the longitudinal
rotary torque of the prop shaft 90 degrees to the wheels, while allowing the
wheels to spin at different rates for when going around curves (the outer wheel
needs to travel further than the inner). The Figure 5.8 shows how power is
transmitted from the engine to the rear wheel.
Figure
5.8 Transmission of power to Rear Wheel.
In situations
where the tires have different traction, a regular "open"
differential as will direct all the torque to the tire with the least traction,
this satiation is dangerous as the vehicle takes a curve the weight of the
vehicle is transferred to the outer wheel leading the inner wheel to loose
traction. So just when the driver wants more torque going to the outer wheel
that has traction, it won't go there, and the torque will just spin the inner
wheel uselessly. For this reason, various "limited slip
differentials" have been invented over the years. They use clutch plates
to lock one of the axles to the cage thus preventing the gears form rotating
about their own axis. The innovation in the M5 is to have these clutch plates
operated by an electrical motor under computer control. Figure 5.9 show the LSD
of BMW
Figure
5.9 LSD of BMW
BRAKE SYSTEM
The F10 M5 is fitted with very large and efficient
brakes for bringing its 1800+ kgs 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 callipers.
Front brake callipers are shown in Figure 6.2. 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, are shown
in Figure 6.3. 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.
Figure
6.1 Side view of the BMW M5
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. The steel outer ring is shown in figure 6.4
Figure
6.4 Outer Steel Ring
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 in figure 6.5. 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.
Figure
6.5 The floating calliper system
The fixed calliper system is
shown in figure 6.6. 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.
Figure
6.6 The fixed calliper system
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. Figure 6.7 shows
the basic Hydraulic Lines
Figure
6.7 The basic Hydraulic Lines
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. Figure 6.8 shows the pictorial representation of the inside
of Master cylinder
Figure
6.8 Inside the master cylinder
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. Figure 6.9 shows the tandem brake booster in the applied position
Figure
6.9 Tandem brake booster in the applied position
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. Figure 6.10 shows 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.
Figure
6.10 Typica Arrangement of pedal to power brake booster to master cylinder
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). Figure 6.11 show
the schematic diagram of the brake system in the M5. 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.
Figure
6.11 Schematic diagram of the brake system in the M5
Additional braking functions in the M5 includes 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 pretensions 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. 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
electromechanical parking brake system is shown in figure 6.12. The
system is operated from a switch on the centre console under the gear lever,
shown in Figure 6.13. Pull up on it to apply. Push down to release. It can also
be released by pressing on the accelerator.
Figure
6.12 Electromechanical parking brake
Figure 6.13 Parking Brake Switch
Figure
6.14 Dimension of Brakes
STEERING SYSTEM
The steering on the M5 uses the traditional rack and
pinion method with computer-controlled hydraulic power assist. "Rack and
pinion" describe the main mechanism for moving the tie rods that
themselves steer the front wheels. Figure 7.1 shows the Rack and Pinion
steering system. 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.
Figure
7.1 The Rack and Pinion steering system
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. The figure 7.2 show the VARIOSERV power steering pump.
Figure
7.2 The VARIOSERV power steering pump
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 offset rotor is shown in the figure 7.3 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).
Figure
7.3 The offset rotor
The complete Steering system is
shown in figure 7.4. 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).
Figure
7.4 Steering system
SUSPENSION SYSTEM
Figure
8.1 The Suspension System
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 M Double
Wishbone suspension is shown in figure 8.2
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 M Double Wishbone suspension system lowers the center of
gravity of the car there by help the car to manuver through the corners more
quickly and with a greater stability
Figure
8.2 The M Double Wishbone suspension
The rear axle
is also mainly made of Aluminium.
It is an M Integral IV multi-link suspension as shown in figure 8.3,
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.
Figure
8.3 M Integral IV multi-link suspension
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. 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. The M VDM is shown in
figure 8.4. 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.
Figure
8.4 M VDM
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 could use the drive
selectors to choose different drive modes from various options. For each mode
the vehicle sets different stiffness for the suspensions, there by the vehicle
could deliver different drive experience to the driver. The drive selector for
BMW M5 is shown in Figure 8.5
Figure
8.5 Drive selector for BMW M5
