Pneumatic suspension assembly

A pneumatic suspension assembly is provided with an air spring chamber that changes its volume as a function of suspension travel, as well as a pneumatically controlled shock absorber whose pneumatic control input can be connected with the air spring chamber and with a compressed air source or compressed air supply chamber. In this manner, increased damping during critical driving states can be ensured, in addition to a shock absorber control that is independent of the load.

BACKGROUND AND SUMMARY OF THE INVENTION 
The invention relates to a pneumatic suspension assembly, especially for 
motor vehicles, with air spring chambers which change their volumes as a 
function of suspension travel, and pneumatically controlled shock 
absorbers whose pneumatic control input is connected with the air spring 
chamber. 
Pneumatic suspension systems are already in relatively frequent use in 
motor vehicles, especially trucks. In these systems, as a rule, level 
regulation is provided which makes it possible to drive the vehicle as 
required with a low clearance in order for example to increase the 
possible load height or to set the clearance to higher levels in order for 
example to permit improved comfort or special protection of the load on 
poor roads. 
In conjunction with pneumatic suspension systems, shock absorbers have 
already been used that operate as a function of the load. These are 
pneumatically controllable shock absorbers whose pneumatic control input 
is connected with an air spring chamber of the pneumatic suspension system 
associated with the shock absorber. Since the pneumatic pressure in the 
air spring chamber changes as a function of the load, this parameter can 
be basically used for load-dependent shock absorber control. 
In addition, air spring systems have already been tested in which the 
pneumatic control input of the shock absorbers can be connected by a 
control valve either with the compressed air source or the compressed air 
supply of the pneumatic suspension, or with the atmosphere. The valve can 
be controlled by means of electronics connected on the input side with 
sensors to record the movements of the body relative to the axle. In this 
manner, the shock absorber can be switched to firm damping during critical 
body movements. 
In addition, it is basically known to control electrically controllable 
shock absorbers by means of electronics connected on the input side with 
sensors for recording various parameters, for example with sensors for 
body movements as well as additional sensors for the load status of the 
vehicle. 
An object of the invention, in an air suspension assembly of the type 
recited at the outset, is to be able to take into account without 
excessive construction expense, parameters in addition to the load for 
controlling the shock absorbers. 
This object is achieved according to the invention by virtue of the fact 
that the connection between the pneumatic control input of the shock 
absorber and the air spring chamber can be shut off and the control input 
can be connected with a source of compressed air or a compressed air 
supply chamber of the suspension assembly. 
The invention is based on the general idea of controlling the basic setting 
of the shock absorber by the air pressure from the air spring chamber and 
thus taking the load of the vehicle into account without special load 
sensors being required. On the other hand, sharply increased damping can 
be set if necessary by connecting the control input of the shock absorber 
with the pneumatic pressure source or compressed air supply chamber. 
According to one preferred embodiment of the invention, a throttle is 
located in the blockable connection between the air spring chamber and the 
control input in order to decouple the control input from rapid dynamic 
pressure variations in the pneumatic pressure in the air spring chamber. 
It has proven advantageous in this regard to provide a check valve in 
parallel with the throttle, said valve opening in the direction of the air 
spring chamber and, in an especially preferred manner, being loaded with a 
preset force in the closing direction. With this arrangement, the 
pneumatic control input of the shock absorber, following connection with 
the pneumatic pressure source or compressed air supply chamber, when a 
transition to normal operation is made, i.e. when the control input is 
connected with the air spring chamber, can be rapidly vented into the air 
spring chamber until a pneumatic pressure is established at the pneumatic 
control input that corresponds to an average of the pneumatic pressure in 
the air spring chamber. 
If, upon said venting of the pneumatic control input and the resultant 
supply of compressed air into the air spring chamber, a (slight) elevation 
of the clearance of the vehicle is intended to occur, this change is 
compensated by the level regulation regularly assigned to the air 
suspension.

DETAILED DESCRIPTION OF THE DRAWINGS 
Between a chassis (not shown) of a motor vehicle (likewise not shown) and a 
vehicle axle (not shown), an air spring bellows 1 and, parallel thereto, a 
pneumatically controllable shock absorber 2 are arranged in a basically 
known manner. 
Shock absorber 2 has a pneumatic control input 3 connectable by means of a 
control valve 4, designed in the manner of a 3/2-way valve, either with 
the interior of air spring bellows 1 or with a compressed air supply 
chamber 5 or another pneumatic pressure source. 
In the air line between control valve 4 and air spring bellows 1, a 
throttle 6 and, parallel to it, a check valve 7 loaded in the closed 
position by a spring, are provided which can be traversed by the flow only 
in the direction of air spring bellows 1. 
In addition, compressed air supply chamber 5 is connected with air spring 
bellows 1 by level control valves 8 and 9 which allow connecting air 
spring bellows 1 with the atmosphere for venting or with compressed air 
supply chamber 5 for introducing compressed air, or closing it off from 
the outside. 
Valves 4, 8, and 9 are normally held in the switch positions shown by 
return springs or the like, in which positions air spring bellows 1 is 
connected with control input 3 of the shock absorber and in addition is 
shut off from the atmosphere and from compressed air supply chamber 5. 
These valves 4, 8, and 9 can be controlled by means of an electronic 
control circuit 10 as a function of sensors 11 connected on the input side 
of control circuit 10, said sensors for example recording the distance 
between the axles and the body and from whose signals the movement of the 
axle relative to the body can then be determined in terms of both 
direction and speed. 
If the electronics "notices" that the distance between the axles and the 
body is changing excessively with respect to a set value, level control 
valves 8 and 9 are controlled in order to increase or decrease this 
distance, with air spring bellows 1 being connected briefly either with 
compressed air supply chamber 5 or atmosphere. 
If control circuit 10 "determines" that excessive vigorous axle movements 
are occurring relative to the body of the vehicle, because for example the 
so-called body resonance or the so-called axle or wheel resonance of the 
suspension system is being excited, control valve 4 is switched to the 
other position in order to bring control input 3 of shock absorber 2 to a 
high air pressure and to set shock absorber 2 for increased damping. 
As soon as the critical driving state no longer exists, control circuit 10 
allows control valve 4 to return to its normal position, whereupon the air 
pressure present at control input 3 decreases through check valve 7 in a 
short time, with compressed air being introduced into air spring bellows 
1. When air spring bellows 1 is excessively "inflated" and the distance 
between the axle and body increases, control circuit 10 operates level 
control valves 8 and 9 in order to release air from air spring bellows 1. 
The special advantage of the arrangement according to the invention is that 
in the normal case there is always a setting of shock absorber 2 that 
depends upon the load in the vehicle since the average air pressure in air 
spring bellows 1 represents an analog measure of the load. Nevertheless no 
sensors of any kind are required to determine the state of the load. To 
determine critical driving states in which shock absorbers 2 should be set 
to maximum damping, sensors 11 which are provided in any case will suffice 
for controlling level control valves 8 and 9, said sensors reacting to the 
travel position of the vehicle wheels or axles relative to the body, with 
both the respective direction of motion of the axles relative to the body 
and also the speeds of movement and accelerations of the axles possibly 
being determined from the sensor signals by formation of time difference 
quotients, for example. For this purpose, the signals of sensors 11 need 
only be evaluated accordingly by control circuit 10. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.