2011 FORD KUGA ALL

Rear Drive Axle and Differential – System Operation andComponent Description
System Operation
General Information
The powertrain with all-wheel drive consists of the
following main components:
• engine
• transaxle with front axle differential
• transfer box
• halfshafts and driveshafts
• Haldex clutch
• rear axle differential
The Haldex clutch guarantees continuous variable
torque transmission to the rear axle under all
driving conditions. The Haldex clutch reacts
immediately and equally quickly with slow or fast
wheel slip.
A difference in angle of rotation of 90° between the
input and output shafts is required to build up
maximum pressure at the multi-plate clutch or to
transmit maximum torque.
The advantage of vehicles with all-wheel drive is
that they distribute the drive between all four
wheels. They therefore have a higher tractive
power. They feature improved cornering behaviour,
as the grip at all four wheels can be better utilised.
Thus, the wheels contribute to a greater degree
towards cornering stability.
The engine torque is transmitted from the transfer
box to the rear axle via a driveshaft. The driveshaft
is flange-mounted to the input side of the Haldex
clutch.
Driving situations
Pulling away and accelerating
• When pulling away and accelerating, as muchall-wheel drive as necessary must be available
immediately in the short-term. During
acceleration, the electronic system detects slip
at the front axle. This slip is counter-controlled
and thus the propulsive force optimally
distributed to the two axes.
Cornering • A sporty driving style, in particular dynamic
cornering, demands stable cornering behaviour.
The all-wheel system distributes the propulsive
force to all four wheels and by so doing boosts
the high cornering forces so that the vehicle
makes optimum contact with the road surface.
Snow and black ice
• Snow and black ice require particularly high grip. Under these conditions, the Haldex clutch
always distributes the propulsive force to the
axle with the better traction. The all-wheel
system reacts intelligently and quickly to all
driving situations.
Trailer operation
• When driving with a trailer, the trailer weight (support load) is transmitted to the rear axle via
the towbar. This reduces the load on the front
wheels, which means they can slip. The
electronic system detects this difference and
distributes most of the propulsive force to the
rear axle.
Haldex clutch
E100642
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General overview
Haldex clutches of the 3rd and 4th generations are
used in the Ford Kuga.
The development of the third generation Haldex
clutch represents a big step forward in modern
all-wheel technology. The Haldex clutch is
electro-hydraulically controlled. Additional
information is taken into consideration during
control tasks via the all-wheel drive control unit.
Slip alone is no longer decisive for the distribution
of the propulsive forces; the vehicle's driving
dynamics are also taken into consideration. The
control unit accesses the driving-related data via
the data bus. With this data, the control unit has
all the essential information about speed, cornering,
coasting or traction operation, and can optimally
react to every driving situation.
Compared with the previous generation, the 4th
generation Haldex clutches operate with higher
pressure and achieve shorter response times when
distributing the drive forces.
Advantages of the Haldex clutch:
• Permanent all-wheel drive withelectronically-controlled multi-plate clutch
• Fast response
• No straining when parking and manoeuvring
• Compatible with different tyres (e.g. emergency spare wheel)
• Fully combinable with driving dynamic control systems
The driveshaft is connected to the input shaft of
the Haldex clutch. Within the Haldex clutch, the
input shaft is separated from the output shaft to
the rear axle differential by means of a multi-plate
clutch. Torque is only transmitted to the rear axle
differential when the plate assembly of the Haldex
clutch is closed.
The multi-plate clutch is electro-hydraulically
controlled via the all-wheel drive control unit. For
ecological driving, the torque to the rear axle is reduced to a minimum up to a throttle position of
approx. 50%. A prerequisite for this is that there is
no difference in speed in the Haldex clutch between
the input and output shafts.
Operation
E100645
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Description
Item
Output shaft
1
Working piston
2
Plates
3
Ring piston pump
4
Control Valve
5
Input shaft
6
Within the Haldex clutch is a plate assembly and
a so-called ring piston pump with a pump plunger
and a working piston.
Fluid supply is started if there is a speed difference
between the input and output shafts.
This fluid pressure is transmitted to the working
piston and in this way the plate assembly is
compressed.
Design of the 3rd generation Haldex
clutch
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E100664
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Description
Item
Multiplate clutch
1
Ring piston pump
2
All-wheel drive control unit
3
Pressure relief valve (high pressure)
4
Input shaft
5Description
Item
Electric feed pump
6
Fluid filter
7
Pressure accumulator
8
Pressure relief valve (low pressure)
9
Preload valve
10
High-pressure valves
11
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The Haldex clutch is based on the principle of a
simple wet clutch that distributes the torque variably
between the front and rear axles.
Three components are linked within the Haldex
clutch:• A mechanical component, comprising input and
output shafts, the plate assembly (clutch) as
well as the cam plate and the roller bearing.
• A hydraulic component, essentially comprising pressure valves, a pressure accumulator, the
control valve, the ring pistons and a fluid filter.
• The electronic control comprises the electric fluid pump and the all-wheel drive control unit
with integrated pressure/temperature sensor
and an actuator motor for the control valve.
Design of the multi-plate clutch
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6
10911
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A
B12
5
E100662
Description
Item
Pump plunger assembly
A
Working piston assembly
B
Output shaft
1
Inner plates
2
Outer plates
3
Disc drum
4
Contact plate
5Description
Item
Input shaft
6
Cam disc
7
Springs
8
Pump plunger roller
9
Pump plunger roller
10
Pump plunger
11
Working piston roller
12
Working piston
13
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All-wheel drive control unit
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Description
Item
Electronic Control Unit
1
Control valve
2
Pressure/temperature sensor
3
Electrical connection CAN (controller area
network) databus
4
Electric feed pump connection
5
The all-wheel drive control unit is bolted directly to
the housing of the Haldex clutch.
It forms one unit made up of the control valve, a
pressure/temperature sensor, and a control
module. It receives signals from the PCM and from
the ABS control module via the CAN data bus. The
control module in the control unit uses these
signals to determine the fluid pressure that is
needed to actuate the clutch plates depending on
the requirement. This determines how much torque
should be transmitted to the rear wheels. All-wheel
drive is deactivated if a fault occurs in the all-wheel
drive control unit.
A preload of approx. 80 Nm is always present at
the Haldex clutch. The temperature sensor of the Haldex clutch is
installed near the control valve in the control unit
and is surrounded by the hydraulic fluid. The
temperature is transmitted to the control module
and is used for adaptation to the changing viscosity
of the hydraulic fluid. If the hydraulic fluid is cold,
the control valve has to be opened slightly more
than requested. This allowance has to be reduced
as the temperature increases. The normal working
temperature of the hydraulic fluid is between +40
°C and +60 °C. If the temperature rises above 100
°C, the clutch is depressurised; if the temperature
falls below 95 °C, the clutch is pressurised again.
All-wheel drive is deactivated and a diagnostic
trouble code set if a fault occurs in the temperature
sensor.
With Haldex Generations I and II, the control valve
was actuated via a stepper motor. With Haldex
Generation III, the stepper motor has been omitted.
The control valve is now actuated via a solenoid
valve. The solenoid valve is actuated by the control
module in the all-wheel drive control unit by means
of pulse width modulation. The pulse width
modulation determines the position of the
adjustment spindle and thus the opening cross
section of the return hole. This is how the pressure
at the working piston of the plates is determined.
If the return hole is fully closed, maximum pressure
is applied to the plates. If the return hole is fully
open, the plates are unpressurized.
Electric feed pump
The electric feed pump is installed in the clutch
unit. It works according to the gerotor principle.
The main purpose of the feed pump is to fill the
pressure accumulator and the space behind the
pump plunger with hydraulic fluid, thereby ensuring
a fast response time of the Haldex clutch. The feed
pump used in the third generation is designed to
achieve an even higher pressure than the base
pressure of 4 bar. It is supplied with current by the
control module in the all-wheel drive control unit
when the engine is running above approx. 400 rpm.
Pressure control - 3rd generation
Haldex clutch
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E100542
Description
Item
Barometric Pressure
A
Base pressure
BDescription
Item
Increased base pressure (preload)
C
Operating pressure
Drive
The pump plungers generate the operating
pressure that is controlled by the control valve as
a function of the difference in speed between the
input and output shafts. The control valve works
progressively from fully open to fully closed. The
fluid pressure can be approx. 67 bar when the
control valve is fully open. The maximum pressure is mechanically controlled by means of the
pressure relief valve.
Design of the 4th generation Haldex
clutch
General overview
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1
2
3
4
E115887
Description
Item
Fluid filter
1
All-wheel drive control unit
2Description
Item
Electric feed pump
3
Pressure accumulator
4
The electric feed pump is an axial piston pump
which is more robustly designed than the gerotor
pump in the 3rd generation Haldex. The higher
feed pressure means that the ring piston pump at
the clutch plate assembly, the pressure relief
valves, preload valve and the high pressure valves
are no longer necessary.
The pressure accumulator on the 4th generation
Haldex is larger and is designed for the higher
pressure. The 4th generation Haldex has a larger fluid filter
which contains a non-return valve.
The all-wheel drive control unit no longer contains
a pressure sensor in the 4th generation Haldex.
Pressure control - 4th generation Haldex
clutch
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E114914
Description
Item
Haldex clutch fluid
1
Inlet filter
2
Electric feed pump
3
Filters4
Pressure accumulator
5Description
Item
Control valve
6
Dished washer
7
Ring piston
8
Clutch plate pack
9
Return pressure accumulator
10
Return control valve
11
Full torque is available at any time on the 4th
generation Haldex clutch because the pressure is
not dependent on the difference in the speeds of
rotation. This is used for instance to activate the
Haldex clutch for better traction when moving off.
On the 4th generation Haldex clutch, the preload
function which applied 80 Nm to the plates in the
3rd generation is no longer required.
On request from the control unit and at engine
speeds above 400 rpm, the electric feed pump runs
and maintains the storage pressure at about 30
bar.
A pressure reducing valve acts as a control valve,
allowing the all-wheel drive control unit to control
the pressure with much greater precision. The
all-wheel drive control unit monitors the position and function of the control valve. The control valve
distributes the pressure, depending on the
requirements, across its three outlet openings
(storage pressure, working pressure, return).
From the storage pressure (30 bar) and depending
on the requirements, the control valve regulates a
working pressure of 0 - 17 bar, which is applied to
the ring piston. At 17 bar working pressure, the
maximum torque of 1000 Nm is transferred to the
rear wheels. The all-wheel drive control unit
ensures the best possible performance under all
driving conditions, for all road conditions and
independent of the speed.
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Rear Drive Axle/Differential
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