The Nivomat shock absorber is a self-leveling monotube shock
absorber developed by Sachs. Nivomat is a contraction of two French
words, niveau and automatique, that when translated to English would be
"level automatic" or "automatic level."
The
Nivomat is like an ordinary monotube shock absorber with a hydraulic
piston, tube and accumulator. There are two different configurations of
the shock: diaphragm type (shown above as the left unit of each pair)
and piston type (right).
Nivomat shocks are used by Chrysler, Ford, General Motors, Jaguar, Kia,
Mitsubishi, Saab and Volvo, among other OEMs. The system is also
available on the GM Suburban and Tahoe as part of ZW7 Premium Smooth
Ride Suspension.
Replacement units are available from Monroe, ZF Sachs and OE suppliers.
The system makes use of the mechanical energy generated during the first
meters of driving from the relative movement between the axle and
vehicle body.
An unlevel vehicle can create many problems. Extra weight on the rear
axle shifts the center of gravity, which has a major impact on ride
characteristics. In critical situations, the vehicle can be very
difficult to control. Under these conditions, a “floaty” ride
characteristic cannot be considered as comfort anymore.
Other effects are increasing expenses: The tires wear unevenly and
faster. Bad aerodynamics causes a higher fuel consumption. Greater
strain is also placed on the axle.
In place of conventional shock absorbers, this unique system is
installed on the rear axle. While providing additional roll stability
without requiring any additional electronics, the Nivomat adjusts the
vehicle to the optimum ride height for every load condition, thus
ensuring a safe and comfortable ride.
The Nivomat system does more than just level the vehicle under load. As
the load increases, the pressure inside the shock increases as oil is
displaced from the reservoir to the inside of the unit, compressing the
gas volume. This creates a progressive increase in spring rate and
damping with little or no change to ride frequency.
The Nivomat is like an ordinary monotube shock absorber with a hydraulic
piston, tube and accumulator. There are two different configurations of
the shock. The first looks like a conventional twin tube air shock with
a dust cover. What appears as a dust cover houses the high pressure
accumulator and low pressure oil reservoir.
The second configuration has its high pressure accumulator at the top of
the shock, reducing the overall diameter of the shock. This allows the
shock to be installed in a more confined space, like an independent rear
wheel drive suspension, and can be mounted in a shaft up or down
configuration as designed by the manufacturer. The normal application
for this shock absorber is for the rear suspension of a passenger car or
SUV.
What gives the shock its leveling capability is a pump mechanism and oil
reservoir that can increase the accumulator pressure, which increases
the shock’s lifting capability. It is used in combination with springs
matched to the load capacity of the shock to reduce suspension travel
while utilizing more of the piston and shaft travel of the shock.
This maintains the ride quality whether the vehicle is operated with a
driver only or to compensate for passengers and luggage. The big
advantage to the Nivomat is the shock absorber requires no plumbing,
compressor and height sensing device to level the vehicle. The normal
movement of the suspension over a regular road surface provides enough
pumping action to level the vehicle.
Leveling Components
As
the load increases, the pressure inside the shock increases as oil is
displaced from the reservoir to the inside of the unit, compressing the
gas volume. This creates a progressive increase in spring rate and
damping with little or no change to ride frequency.
The accumulator can be a diaphragm or piston. The normal pressure
contained in the accumulator ranges from 20 bar (290 psi) to 50 bar (725
psi). The pump can increase the accumulator pressure from 90 bar (1,305
psi) to 130 bar (1,885 psi). Under driving conditions, pressure can
reach 350 bar (4,424 psi).
The control sleeve is fixed in the shaft and controls oil flow through
the spiral cut and release bore in the pump rod. The inlet valve is a
one-way check valve located at the end of the spiral cut in the hollow
pump rod.
The low pressure oil reservoir contains the oil used to charge the pump
mechanism. The pump is located at the end of the control sleeve and uses
a pump cup and balance spring.
Leveling Operation
The Nivomat shaft and piston provide the same damping as a normal
monotube shock, the difference being that the shaft is hollow and
contains the pump mechanism. The pump is operated by the displacement of
oil caused by the movement of the shaft in and out of the shock. When
the piston shaft moves out of the shock, oil is drawn from the low
pressure oil reservoir through the hollow pump rod and inlet valve into
the pump chamber.
Since Nivomat is mechanical, the vehicle needs to be moving before the
pump starts to work; it takes about a mile to a mile and a half of
travel before the vehicle reaches its optimal level point.
When the piston shaft moves into the shock, the oil is compressed,
collapsing the pump spring and expanding the balance spring to fill the
pump cup. When the shaft moves out of the shock, the control sleeve
opens the spiral cut in the pump rod, and the oil is forced into the
main chamber of the shock. The pump and balance spring return the pump
cup to its level position. This increases the pressure in the
accumulator, creating more lift to return the piston and shaft to the
level position. In the level position, the control sleeve closes the
spiral cut and the shock operates normally until the next inlet and pump
action.
The release bore is used to return the shock to the level position when
the load is removed from the vehicle. When the shaft and control sleeve
is extended out of the shock past the release bore, the oil that was
pumped to increase the accumulator pressure and lift is returned to the
low pressure reservoir.
Installation
When replacing a load leveling shock absorber, it is necessary to
inspect both mounting points for damage and stress cracks. All mounting
hardware should also be replaced. All fasteners should be tightened to
their proper torque specifications.
The diameter of a conventional shock absorber is 54 mm (2-1/8 inch). The
diameter of a Nivomat shock can range from 60 mm (2-5/8 inch) to 72 mm
(2-7/8 inch). Make sure the shock is properly mounted to provide
adequate clearance. It is recommended to test the operation of the
shocks by loading and driving the vehicle.
Disposal
Take the following steps, making sure to comply with local safety and
environmental protection regulations to recover and dispose of the oil
before scrapping the shock.
Diaphragm Type (except Mercedes Benz M Class):
1. Clamp the shock in a horizontal position using a vice with the shaft fully extended.
2. Center punch a mark 50 mm (2 inches) from the top of the tube.
3. Drill a 5 mm (3/16 inch) hole to exhaust the gas and oil from the low pressure reservoir.
4. Center punch a mark 25 mm (1 inch) from the bottom of the shock’s tube.
5. Drill a 5mm (3/16 inch) hole to exhaust the gas from the high pressure accumulator.
6. Remove the remaining oil in the shock by pumping the shaft in and out of the tube.
7. The shock can now be scrapped.
Piston Type (Mercedes Benz M Class):
1. Clamp the shock in a horizontal position using a vice with the shaft fully extended.
2. Center punch a mark 50 mm (2 inches) from the bottom of the tube.
3. Drill a 5 mm (3/16 inch) hole to exhaust the gas and oil from the low pressure reservoir.
4. Center punch a mark 10mm (3/8 inch) from the top of the tube.
5. Drill a 5 mm (3/16 inch) hole to exhaust the gas from the high pressure accumulator.
6. Remove the remaining oil by pumping the shaft in and out of the tube.
7. The shock can now be scrapped.
anaheim, fullerton, villa park, brea, placentia, la Habra,
orange, santa ana, garden grove, anaheim hills, yorba linda, whitter, orange
county,