Level control arrangement for vehicles having air springs

A level control arrangement for motor vehicles having air springs which are functionally responsive to the vehicle load. A predetermined distance of the vehicle frame from the vehicle axis can be maintained by charging or discharging the air springs. The control arrangement includes a safety valve which can be controlled by the pressure in the air springs. When the vehicle is overloaded, or if a malfunction occurs in the control apparatus of the level control arrangement, the safety valve limits the pressure in the air springs to a preselected maximum safe pressure.

FIELD OF THE INVENTION 
This invention relates to a level control arrangement for vehicles having 
air springs, and more particularly to a self-leveling vehicle 
height-adjusting system for maintaining the distance between the vehicle 
frame and the vehicle axle by charging and discharging the air suspension 
springs in accordance with the load sustained by the vehicle and including 
a safety valve for relieving the pressure in the air springs when it 
exceeds a predetermined value. 
BACKGROUND OF THE INVENTION 
On vehicles with air suspensions, a load-dependent level control system is 
generally used. The amount of air in the pneumatic bellows of the air 
spring suspension system is thereby regulated as a function of the vehicle 
load so that a predetermined distance between the vehicle frame and the 
vehicle axle is always maintained. 
A previous vehicle height control system of the present type is shown and 
described in U.S. Pat. No. 4,354,693. Such a prior system consists 
essentially of the following parts: 
A distance measurement device measures the distance between the vehicle 
frame and the vehicle axle which varies as the vehicle is loaded or 
unloaded. The measure data is compared by means of an electronic 
evaluation circuit having a command value which is equivalent to the 
standard level of distance. When a deviation occurs, the standard level is 
re-established by pressurizing or evacuating the air springs. To fill up 
the air springs, the electronic system switches an air spring valve 
between the pressure supply source and the air springs to the open 
position, and the pressure supply source causes air to be conveyed into 
the air springs until the electronic system recognizes the standard level 
reported by the distance measurement device. The air pressure is then shut 
off and the air spring valve closed. The discharging of the air springs 
takes place so that the electronic system opens the air spring valve and 
causes a second evaluation valve to open to the atmosphere. The air 
springs are then discharged to the atmosphere until the electronic system 
closes both valves when it recognizes the standard level. 
However, the systems of these previous types have the disadvantage that 
even when the vehicle frame descends as the result of an excessive 
overload, i.e., an overload of the vehicle, the pressure supply source is 
activated by the distance measurement device and the electronic system to 
re-establish the standard level. Thus, the pressure supply source 
continues to convey air into the bellows of the air springs, on account of 
the overloading of the vehicle, even though the air springs already 
exhibit a correspondingly excessively high air pressure. Accordingly, the 
air springs are filled to this extent with excess pressure and are also 
loaded during operation by dynamic pressure peaks, which can lead to 
damages to the air spring bellows. A switching malfunction caused, for 
example, by a defective distance measurement device and/or failure of the 
electronic system, is capable of causing the pressure supply source not to 
be shut off, which can also lead to an uncontrolled pressure increase in 
the air spring bellows, and thus result in the above-mentioned damage. 
OBJECTS AND SUMMARY OF THE INVENTION 
An object of this invention, therefore, is to improve a system of the type 
described above, so that during any load status of the vehicle, and/or 
when a switching malfunction occurs in the level control equipment, a 
preselected maximum pressure in the bellows of the air springs cannot be 
exceeded. 
A further object of the present invention is to provide a new and improved 
vehicle height control system in which air springs vary the distance 
between the frame and axle of the vehicle by causing a pressure supply 
source to charge the air springs when the distance is less than a 
preselected amount and for causing the air springs to be discharged when 
the distance exceeds the preselected amount and when the air spring 
pressure exceeds a predetermined value due to a malfunction in the system. 
The invention has the advantage that, when the vehicle is overloaded, the 
vehicle frame can come into contact with a fixed stop on the vehicle 
frame, and in this state, a "low level" is recognized by the distance 
measurement device to cause a subsequent pressure supply source switching 
so that a specified preselected maximum pressure in the bellows of the air 
spring is not exceeded. 
Another advantage of this invention is to provide a level control system 
which is equipped with an air dryer, which, when the air springs are 
filled, is operated in the drying phase and when the air springs are 
discharged, i.e., when the vehicle frame descends, is operated in the 
regeneration phase. 
The air which flows out of the air springs when the vehicle is overloaded 
can then also be conducted to the air dryer for regeneration of the air 
dryer. This results in a maximum utilization of the air flowing out of the 
air springs for the regeneration of the air dryer when the vehicle frame 
descends or when the vehicle is overloaded. 
In accordance with the present invention, there is provided a level control 
arrangement for vehicles having air springs by which a vehicle frame is 
suspended in relation to at least one vehicle axis, comprising a control 
device connected between a pressure supply source and a valve means to 
raise and lower the vehicle frame by charging and exhausting the air 
spring, the valve means includes a safety valve which is controlled by 
pressure corresponding to the pressure of the air spring so that the 
pressure in the air spring can be reduced.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, and particularly to FIG. 1, an air spring 15 
is schematically illustrated and symbolically represents all the other air 
springs of the vehicle. The air spring 15 is shown connected to a suitable 
pressure supply source 5 which supplys compressed air to the spring 
bellows. The air springs are connected by a first pneumatically-controlled 
multi-way valve 19 which may be exhausted into the atmosphere. The first 
multi-way valve 19 has a pneumatic-control input portion 18 which is 
controlled by a second multi-way valve 8. The first multi-way valve 8 
functions as the air spring valve and can be pressurized with a control 
pressure which is determined by the pressure in the air spring 15. A 
biasing spring 22 provides a return force which acts in the opposite 
direction to the pressure conveyed to the pneumatic control input 18. 
It will be noted that a suitable air dryer 11 is connected via a first 
check valve 13 which permits the flow of compressed air to the air spring 
15, but blocks the flow of air from the air spring 15. A second check 
valve 23 permits the flow of air from the air spring 15 to the air dryer 
11 via the second multi-way valve 8. Upstream of the second check valve 
23, there is provided a choke or a throttle valve 21. The second check 
valve 23 is connected with a pressure supply output port 34 of the second 
multi-way valve 8. 
The pneumatic control input portion 18 of the first multi-way valve 19 is 
connected to the throttle 21 via a line 20 and is connected to the 
pressure supply output port 34 of the second multi-way valve 8. 
A height or distance measuring device 1 senses and measures the distance or 
the level of the vehicle frame from the vehicle axis. The measuring device 
1 is connected by means of an electrical lead or line 26 to an integrated 
electronic control unit 2. The electronic control unit 2 includes an 
evaluation circuit having a desired stored value which corresponds to a 
preselected standard level. The height or level which is measured by the 
distance measuring device 1 is compared with the standard level stored in 
the evaluation circuit. Thus, the actual height or given distance between 
the sprung and unsprung portions of the vehicle can be varied as 
necessary. The electronic control unit 2 conveys electrical control 
signals corresponding to the results of the level comparison over an 
electrical line 3 which is connected to an electric control terminal 4 of 
the pressure supply source 5. The electrical control signals are also 
conveyed to line 6 which is connected to an electric control terminal 7 of 
the multi-way valve 8. 
If the actual measured level value is less than the preselected stored 
standard level value, then the pressure supply source 5 is switched on or 
activated by the electronic control unit 2. Thus, compressed air is 
conducted to the air spring 15 over pressure lines 9 and 10, through the 
air dryer 11, over a pressure line 12, through the check valve 13, and 
over a pressure line 14. The compressed air is conveyed to the air spring 
15 until the standard level is reached, at which time the electronic 
control unit 2 turns off or deactivates the pressure supply source 5. 
Conversely, when the actual measured value is above the preselected stored 
standard level value and with the pressure medium source 5 turned off, the 
air spring 15 is vented into the atmosphere until the standard pressure 
level is reached. Under this condition, the electronic control unit 2 then 
shifts the second multi-way air spring valve 8 from a closed position as 
shown in FIG. 1 to the open position. The air pressure in the air spring 
15 flows through the pressure lines 14, 16, 17 to the pneumatic control 
input 18 of the first multi-way valve 19. Thus, the valve 19 is shifted 
from its closed position to its opened position to vent air spring 
pressure to the atmosphere. 
It will be seen that the pressure line 20 is connected to the air dryer 11 
and the second multi-way valve 8 so that the air spring 15 is then 
connected via the pressure lines 10.9 and the first multi-way valve 19 to 
the atmosphere. Now when the distance measurement device 1 signals that 
the standard level has been attained, electronic control unit 2 switches 
the multi-way valve 8 back to its closed position. 
Thus, the pressure line 9 is closed during the discharge of air from the 
spring 15 and shuts off the outlet of pressure supply source 5. The 
pressure at the control input 18 of the multi-way valve 19 is then 
equalized via the connection lines 17, 20, the filter and lines 11, 10, 9 
and the multi-way valve 19 to the atmospheric pressure until the biasing 
force of tension of the spring 22 causes the multi-way valve 19 to move to 
its closed position. 
It will be seen that, during the charging phase, the check valve 23, which 
is located in the line 20 between the throttle 21 and the air dryer 11, 
closes the flow to the control connection terminal 18 of the multi-way 
valve 19. The multi-way valve 19 is prevented from being switched into the 
position in which the pressure line 9 is connected with the atmosphere 
during the charging operational phase. 
It will be observed that there is a line connection such as a tee joint 24 
which is interposed between the pressure line 12 and the pressure line 20. 
The pressure lines 12, 14, 16 are connected to one another by means of a 
line connection fitting or tee joint 25. 
As shown, the check valve 13 is located in the line 12 between the tee 
pipes 24, 25 and is adapted to close the connection from the air spring 15 
to the air dryer 11 during the exhaust phase. 
The air dryer 11 dries the air during the charging or filling of the air 
spring 15 and purges the dessicant of moisture during the discharging or 
exhausting of the air spring 15, namely, in regeneration mode. An air 
dryer which is suitable for this purpose is shown and described in U.S. 
Pat. No. 3,592,563. 
It will be seen that the choke 21 is located in the pressure line 20 and is 
effective during the exhaust phase to throttle or reduce the pressure of 
the air which flows to the air dryer 11, but unthrottled or full control 
pressure is fed to the control input 18 of valve 19. 
The valve arrangement to exhaust the air spring 15 into the atmosphere 
advantageously includes a third or ancillary multi-way valve 27 which acts 
as a safety valve against an overpressure in the air spring. The multi-way 
valve 27 may preferably be controlled with the pressure which corresponds 
to the pressure in the air spring 15. The exhausting of the air spring 15 
via the third multi-way valve 27 occurs as soon as pressure in the air 
spring 15 has reached a predetermined or preselected critical pressure 
level which is above a normal maximum operating pressure. 
Such excessive or critical pressure level which is above the normal maximum 
operating pressure can occur when the vehicle is overloaded. The overload 
condition, like the normal loading process, within the specified allowable 
load limits, causes a descent of the vehicle frame. The distance 
measurement device 1 records this change of the level, but does not 
recognize that this level change is due to an overloading of the vehicle. 
The distance measurement device 1 consequently triggers the electronic 
system 2 and causes compressed air to flow from the pressure supply source 
5 into the air spring 15 to re-establish the standard or normal level of 
the vehicle frame. The air pressure in the air springs 15 caused by 
overloading of the vehicle is thereby increased even further. 
Depending on the degree or relative intensity of overloading, a 
predetermined critical pressure level can be reached in the air spring 15 
which can lead to the damage of the bellows of the air spring 15. This 
critical pressure level can specifically be reached during vehicle 
operation if, on account of overloading, the pressure in the air spring 
15, already increased above the maximum operating pressure, is increased 
even further by short-term dynamic pressure peaks. 
A pressure level in the air spring 15 which exceeds the specified maximum 
operating pressure can also be achieved by a malfunction or failure in the 
height or level regulation system. For example, if a malfunction occurs in 
the distance measurement device 1 and/or in the electronic system 2, the 
pressure supply source 5 will not shut or cut off in time. 
In practice, the multi-way valve 27 which is connected with the air spring 
15 has a switching point which lies below the critical damaging pressure 
level of the air spring 15 so that a reduction of the pressure in the air 
spring 15 is initiated or triggered before damage occurs to the air spring 
15 under the conditions described above. 
As shown in FIG. 1, the multi-way valve 27 is connected via the pressure 
line 14 to the air spring 15. The multi-way valve 27 has a pneumatic 
control input 28 which can be pressurized with the pressure prevailing in 
the air spring 15 via a pressure line 29. 
Referring now to another embodiment which is illustrated in FIG. 2, the 
multi-way valve 27 may include an electrical control input 30 which is 
connected via an electrical line 31 with a pressure sensor 32. The 
pressure sensor 32 responds and measures the pressure which is constantly 
present in the air spring 15. When a specified critical pressure level in 
the air spring 15 is reached, the multi-way valve 27 causes the air spring 
15 to be connected to the atmosphere. It will be appreciated that, located 
between the pressure sensor 32 and the electrical control input 30, there 
is an appropriate transducer which converts the pressure signal from the 
pressure sensor 32 into a current signal for the electrical control input 
30. 
Referring now to FIG. 3, there is shown a multi-way valve 27 which has the 
same structural features as the valve 27 of FIG. 1. As shown, valve 27 is 
connected via the line 14 to the air spring 15. The air spring 15 is also 
connected via the multi-way valve 27 and a pressure line 33 to the 
pressure line leading to the pressure output 34 of the second multi-way 
valve 8 and to the control input 18 of the first multi-way valve 19. 
Such an arrangement has the advantage that the air spring 15 can be 
connected via the first multi-way valve 19 to atmosphere by the distance 
measurement device 1 when the measured value is above the standard height 
or level. The air which flows out of the air spring 15 via the multi-way 
valve 27 is also used for regeneration of the air dryer 11. 
Referring now to FIG. 4, there is shown the multi-way valve 27 which is 
structurally equivalent to the valve 27 of FIG. 3. In place of the 
pneumatic control input 28, there is shown an electrical control input 30, 
which is connected via the electrical line 31 with the pressure sensor 32 
which measures the pressure in the air spring 15. The operation of the 
apparatus is substantially the same as that of FIG. 2. 
Another embodiment is illustrated in FIG. 5. It will be noted that the 
third multi-way valve 27 and the second multi-way valve 8 of the 
arrangement illustrated in FIG. 1 are combined to form a single or unitary 
multi-way valve 35 having an electrical control input 7 and a pneumatic 
control input 28. The air spring 15 is connected via the multi-way valve 
35 to the pneumatic control input 18 of the first multi-way valve 19 and 
via the air dryer 11 with the outlet to atmosphere of the first multi-way 
valve 19. The electrical control input 7 is activated by the vehicle 
height or control sensing apparatus which sense the descent of the vehicle 
frame by the distance measurement device 1 and the electronic control unit 
2. The pneumatic control input 26 is activated by a pressure sensed of the 
above-mentioned overload control line 29 by a pressure which corresponds 
to the pressure in the air spring 15. Both controls are independent of one 
another so that the multi-way valve 35 is switched from the closed 
position into the open position, whereupon a connection is established 
from the air spring 15 to the control input 18. Thus, the outlet of the 
multi-way valve 19 connects the air dryer 11 to the atmosphere. 
In viewing FIG. 6, it will be seen that the electrical control input 7 of 
the second multi-way valve 8 is connected via the electrical line 6 to the 
electronic control unit 2 which is activated by the distance measurement 
device 1 and is also connected via an electrical line 36 to the pressure 
sensor 32. In order to activate the control input 7 by the electronic 
control unit 2 (which is illustrated schematically) or by the pressure 
sensor 32, the multi-way valve 8 is switched from the closed position into 
the open position, whereupon the exhausting of the air spring 15 takes 
place in the manner as illustrated in FIG. 5. 
The embodiment illustrated in FIG. 6 has an advantage over the embodiments 
illustrated in FIGS. 1 to 5 in that it is simpler and economical. It will 
be seen that the second multi-way valve 8 includes only one electrical 
control input 7 which can be activated both by the distance measurement 
device 1 and by the pressure sensor 32. 
According to the embodiments shown in FIGS. 1 to 6, the pressure supply 
source 5 is not normally turned off during an overload of the vehicle 
since the distance measurement device 1 indicates a low height level, and 
so the pressure source 5 would continue to supply compressed air to the 
air spring 15. Nevertheless, the pressure supply source 5 is protected 
against any undesirable excessive pressure in the system because the 
pressure supply source 5 and the air spring 15 are connectable to 
atmosphere via the first multi-way valve 19 which is activated by the 
excessive pressure occurring in the air spring 15. 
Referring now to the embodiment illustrated in FIG. 7, it will be seen that 
the pressure sensor 32 is connected via an electrical line 37 to the 
electronic control unit 2. In a circuit which compares the command value 
and the instantaneous value of the electronic control unit 2, the pressure 
indicated by the pressure sensor 32, which appears in the air spring 15, 
is compared with a specified command value. This command value corresponds 
to a maximum pressure that should appear in the air spring 15 during the 
overloading of the vehicle at which time the electrical control input 7 of 
the second multi-way valve 8 is activated via the electrical line 6 of the 
electronic system 2, to switch the second multi-way valve 8 from the 
closed position into the open position. 
When this command value is reached, an OR gate or logic element in the 
electronic control unit 2 causes the electrical control input 4 to 
activate the pressure supply source 5 via an electrical line 3 to turn off 
the pressure supply source 5. The signal thereby emitted by the distance 
measurement device 1 and sent to the electronic control unit 2, which 
corresponds to a low height level resulting from the overloading of the 
vehicle, is suppressed in the electronic control unit 2. 
The apparatus shown in FIG. 7 has the advantage that energy can be 
conserved by shutting off the pressure supply source 5 during an overload 
phase. 
The apparatus described above for the protection against an overload beyond 
a specified maximum pressure in the air spring 15 can also be utilized in 
level control systems which are equipped with an air dryer. The air 
flowing out of the air spring 15 is then as shown in FIGS. 1 and 2 
conducted directly into the atmosphere. 
Instead of utilizing a multi-valve 27 as illustrated in FIGS. 1 and 2 the 
air spring 15 can be protected against an undesirable pressure increase by 
using a conventional pressure limiting valve which may be inserted in the 
pressure line between the pressure supply source 5 and the air spring 15. 
Such a pressure limiting valve would shut off the pressure supply source 5 
from the air spring 15 if a specified pressure occurred on its secondary 
side which corresponds to the pressure appearing in the air spring 15. The 
pressure supply source 5 would then be connected to atmosphere for the 
duration of the overload of the air spring 15. Of course, with such an 
apparatus, the pressure in the air spring would increase in proportion to 
the overload of the vehicle, until the vehicle frame came into contact 
with a fixed stop on the vehicle frame, but a further increase in pressure 
in the air spring 15 would not be possible, because then the pressure 
supply source 5 would be switched by the pressure limiting valve to 
atmosphere. 
Thus, the present invention has been described in such full, clear, concise 
and exact terms as to enable any person skilled in the art to which it 
pertains to make and use the same, and in which the best mode contemplated 
of carrying out this invention has been set forth. We state that the 
subject matter, which we regard as being our invention, is particularly 
pointed out and distinctly claimed in what is claimed. It will be 
understood that variations, modifications, equivalents and substitutions 
for components of the above specifically-described embodiment of the 
invention may be made by those skilled in the art without departing from 
the spirit and scope of the invention as set forth in the appended claims.