Control system for influencing the speed of a motor vehicle

A control system for influencing the speed of a motor vehicle. The invention is characterized in that the retarder controller and the pertaining servomechanism already available in a vehicle with an installed retarder is in traction operation additionally utilized for throttling the drive engine down when a presettable allowed maximum value of the speed is exceeded.

BACKGROUND OF THE INVENTION 
The invention concerns a control system for influencing the speed of a 
motor vehicle. 
It is known that trucks may be equipped with the two systems: 
retarder with additional function "constant speed"--RCS (regulation to 
constant speed by means of retarder control), and 
automatic speed limitation--ASL (the internal combustion is throttled down 
as a presettable maximum value is exceeded). 
The employment of both systems is such that both operate autarchically--RCS 
for downhill travel and ASL in traction operation. With appropriate 
setpoint selection by the operator, notably on more severe grades, 
activating the retarder with the function "constant speed" causes the 
maintenance of the speed desired by the operator. 
In traction operation (=engine operation), i.e., at level, uphill travel or 
also a light grade with the engine preferably idling and thus displaying a 
slight engine braking action and natural retardation, the automatic speed 
limitation (ASL) causes the maintenance of a fixed or variable preset 
maximum speed. 
The system for automatic speed limitation in traction operation is 
comprised of a regulator and a servomechanism acting on the internal 
combustion engine, notably on the fuel dosing device (throttle plate or 
fuel injection). A limit value prescribed by law or other speed value 
meant not to be exceeded (maximum speed allowed) is either stored fixed in 
the regulator or freely selectable by the operator and storable in the 
regulator. The actual value input of the regulator is coupled to a 
measuring device that measures the actual speed of the vehicle, 
respectively the speed of rotation of the wheels. A continual comparison 
takes place between the current actual value and the speed value which is 
not to be exceeded (preset maximum speed). As long as the current actual 
speed remains below the preset maximum speed, a call for a higher speed 
made by the operator, for instance on the gas pedal, is converted to a 
control signal for the fuel dosing system. However, when the current 
actual speed is higher than the selected preset maximum speed, a 
regulating system for maintaining the preset maximum speed is activated, 
and the regulation enjoys a greater priority than the speed control by 
means of gas pedal input. In this case, the variation between actual and 
preset maximum speed is converted to a control signal for the 
servomechanism, which acts directly on the fuel dosing system of the 
internal combustion engine. The latter is throttled down until the limit 
value of the preset maximum speed is no longer exceeded. In downhill 
travel, the system of automatic speed limitation can be effective until 
the control range, which normally covers the working range of the internal 
combustion engine, is exhausted. 
Components required for realization of the ASL function are a controller, 
respectively a regulator, and a pertaining servomember, respectively a 
servomechanism, for adjustment of the fuel dosing system of the internal 
combustion engine or, more generally, of the power output member of a 
drive engine. The servomechanism is either of strictly electromechanical 
design, for instance an electric servomotor, or of electropneumatic 
design, that is, in the form of an electropneumatic valve with pertaining 
servocylinder. 
The retarder system with the function "constant speed" allows only manual 
activation by operator intervention. For realization of this task, a 
controller and a servomechanism in the form of a proportional valve are 
coordinated with the retarder. However, the controller and servomechanism 
are also required for realization of further control tasks that can be 
realized by means of the retarder and employed as well in a motor vehicle 
with ASL system. These tasks include the setting of a specific braking 
moment, the setting of a constant braking moment, and of a constant 
retardation. 
Both systems serve to influence the travel speed, but they may be effective 
in different states of operation of the vehicle. Owing to the existence of 
two control, respectively regulating, systems--one for throttling the 
engine down as a presettable maximum speed value is exceeded, and a second 
one for control of the retarder--a large number of necessary system 
components are involved, translating to high linkage expense and requiring 
installation space. The great number of system components entails a very 
high probability of failure of one of the two systems by failure of system 
components. 
The problem underlying the invention is to avoid the existing drawbacks 
when both systems are present, such as by integrating both systems in the 
vehicle in such a way that a reduction in the total number of system 
components is accomplished, thereby lowering the failure probability of 
the systems, and also precluding error sources. 
SUMMARY OF THE INVENTION 
The inventional solution to the problem consists of utilizing the retarder 
controller and pertaining servomechanism, which in a vehicle with an 
installed retarder are already available, in traction operation 
additionally for throttling the engine down as a presettable allowed 
maximum speed value is exceeded. 
The overall system is thereby rendered more compact; with only one 
controller and one servomechanism still being used, installation space in 
the vehicle is gained. The failure probability diminishes due to the 
reduction in the number of system components. 
The control system is comprised of a controller, a servomechanism and a 
switching system. The controller has at least two inputs--a first input 
for a speed signal and a second input for a signal from a retarder switch. 
Moreover, there are at least two outputs provided--a first output for a 
control signal and a second output for a switching signal. The first input 
is coupled to a measuring system that measures the actual speed of the 
vehicle, or the speed of rotation of the wheels. The second input is 
coupled to the retarder switch. 
The first output is coupled to the servomechanism and the second output to 
the switching system. The latter has at least two switching positions; a 
first one for connecting the servomechanism with the retarder and a second 
one in which the servomechanism is coupled to the power output member of 
the engine. Means are provided which compare the current actual speed with 
a presettable allowed maximum speed and which, as the maximum speed is 
exceeded and with the retarder switch set to zero, effect a coupling of 
the servomechanism to the engine and, in the event that the maximum speed 
is exceeded and a signal from the retarder switch is present, the 
servomechanism is coupled to the retarder. 
Input signals from the retarder switch may be braking stages (BS), a 
desired braking moment (M.sub.brake) or a preselectable value for a speed 
to be kept constant (v.sub.const). In the first case, the controller 
issues on the first output the appropriate control signal for the 
servomechanism, while in the second case a regulating system subordinate 
to the control system is activated. Analogous thereto, further control and 
regulating functions may also be preset on the retarder switch, for 
instance a desired constant retardation. 
Further favorable embodiment options are also set forth. Utilized as a 
common servomechanism is the proportional valve, which is already required 
for retarder control. The power output member is then provided with a 
servocylinder which can be acted upon by the output pressure of the 
proportional valve. 
The switching device establishing the connection between servomechanism and 
retarder or drive engine in accordance with the possible switching 
positions, dependent on the signals prevailing on the input of the 
controller, is preferably fashioned as a switching valve in the form of a 
multiple-way valve. 
In a further aspect of the invention, the control system can be advanced 
and expanded to the effect that additional favorable functions can be 
carried out with it. A first option consists in specifying priorities in 
order to render erroneous actions by the operating personnel ineffective, 
for instance a simultaneous activation of the retarder by adjustment of 
the retarder switch and actuation of a foot pedal or gas pedal, that is, 
adjustment on the power output member of the engine such that a speed 
increase will be obtained. In this case, the retarder and engine would 
counteract each other. In keeping with the retarder preselection and the 
intensity of gas pedal actuation, only unsatisfactory results are achieved 
for both systems, viewed individually, due to their counteractions. 
Therefore, establishing priorities applicable to specific cases of 
application for the individual systems is appropriate. In the cited case, 
the retarder is preferably given priority. 
In case of simultaneous actuation of retarder and gas pedal as the maximum 
speed is exceeded, the retarder preferably always has priority. As an 
alternative, there is also the option that the function chosen last by the 
operator--gas pedal or retarder switch--becomes effective. 
When activating the constant speed function of the retarder, it may be 
appropriate to adjust the power output member of the engine in such a way 
that the idling position will be obtained. This will avoid a conflict 
between drive engine and retarder. Realization of this requires either the 
provision of an additional switching valve or using the switching valve in 
the form of a suitable multiple-way switching valve which meets this 
objective. 
The means determining or specifying all of the relations between the input 
and output variables of the controller may be fashioned, e.g., as an 
internal switching logic or may be programmable routines with the 
controller fashioned as a microprocessor. Consequently, the tasks of a 
regulator can also be performed within the controller.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows a controller 1 for realization of control and regulating tasks 
on a retarder 2 and a drive engine 3, the latter fashioned for instance as 
an internal combustion engine. 
Realizing a desired braking moment depends on changing the filling degree 
of the retarder 2. Control of the filling degree of the retarder is 
normally effected by compressed air. The required pressure is furnished by 
an actuator 4, normally a proportional pressure valve. The magnitude of 
the pneumatic output pressure of the proportional pressure valve 
determines the change in filling degree of the retarder. 
The internal combustion engine 3 features a fuel dosing system 5. Upon 
exceeding a preselectable value for a maximum allowable speed v.sub.lim, a 
servoelement, presently a pneumatic servocylinder 6, becomes effective on 
system 5. To effect an appropriate adjustment on the fuel dosing system 5, 
a servomechanism allows the required pressure to act on the servocylinder 
6. Employed as the servomechanism is presently the proportional valve 4, 
which is already required for retarder control. 
Also acting on fuel dosing mechanism 5 is a mechanism, not illustrated 
herein, which effects an adjustment of the fuel dosing mechanism 5 in 
accordance with a call for higher speed or acceleration effected by the 
operator, for instance by actuation of a foot pedal. This direct control 
between foot pedal and fuel dosing mechanism 5 is ineffective upon 
activation, or exceeding, of the preselected value for the maximum 
allowable speed v.sub.lim. 
The controller features at least two inputs--a first input and a second 
input--and at least two outputs--a first output and a second output. 
Arranged after the controller are the proportional valve 4 and a switching 
mechanism 7 for coordinating the proportional valve 4 with the retarder 2 
or the internal combustion engine 3, that is, for connecting the 
servomechanism 4 with the retarder or the fuel dosing mechanism of the 
internal combustion engine. For that purpose, the output of the 
proportional valve connects, via working line 8, to the switching 
mechanism 7 and, according to the latter's switching position, with the 
retarder or the fuel dosing mechanism. The switching mechanism 7 is 
structured and fashioned such that in keeping with the input variables of 
the controller and the desired function it is able to establish at least 
two switching positions. A first switching position SI serves to establish 
the connection between servomechanism 4 and retarder 2. A second switching 
position SII serves to connect the servomechanism 4 with the internal 
combustion engine 3. With the servomechanism fashioned as a proportional 
valve, the output pressure of the proportional valve is in the first 
switching position SI effective on the retarder 2, while in the second 
switching position SII it acts on the servocylinder 6 of the fuel dosing 
mechanism. Decisive for the individual switching positions are also the 
sequences which are internally provided in the controller. 
A presettable signal for a desired braking moment M.sub.brake, a braking 
stage BS or also, if possible, a desired value for a speed v.sub.const to 
be kept constant etc. is fed to the first input on the retarder switch 9. 
A signal for the actual speed value v.sub.act, which value is continually 
determined by means of a measuring device not shown here, is passed to the 
second input. 
A control signal Y for the proportional valve 4 is issued at the first 
output, while on the second output a signal S for coordination of the 
output pressure of the proportional valve with the retarder 2 or the 
internal combustion engine 3 is issued. 
As regards the signals prevailing on the inputs, a differentiation is 
required between various cases: 
1) First input: tachometer signal for v.sub.act ; second input: retarder 
switch in zero position v.sub.act &lt;v.sub.lim. 
2) First: input: tachometer signal for v.sub.act ; second input: retarder 
switch in zero position v.sub.act &gt;v.sub.lim. 
3) First: input: tachometer signal for v.sub.act ; second input: retarder 
switch signal for M.sub.brake, or v.sub.const, v.sub.act &lt;V.sub.lim. 
4) First input: tachometer signal for v.sub.act ; second input: retarder 
switch signal for M.sub.brake or v.sub.const, v.sub.act &gt;v.sub.lim. 
With the tachometer signal for the travel speed v.sub.act, present, a 
comparison takes place within the controller 1, or subordinate to the 
control system, with the allowable maximum speed v.sub.lim, which must not 
be exceeded. The allowable maximum speed v.sub.lim is either a value 
stored in hardware fashion within the controller 1 or may be issued to the 
controller by the operator as a possible third input variable. 
When the actual speed v.sub.act, is lower than the allowable maximum speed 
v.sub.lim, no control and switching signals are issued for the 
servomechanism 4 and the switching mechanism 7. In case of an acceleration 
call by the operator by actuation of the gas pedal, an adjustment on the 
fuel dosing system equivalent to the desired acceleration takes place by 
means of direct control between foot pedal and fuel dosing system. 
When the current actual speed equals or exceeds the allowable maximum speed 
v.sub.lim, the regulating system for maintaining the allowable maximum 
speed v.sub.lim is activated. The signal for linking the servomechanism 4 
to the fuel dosing mechanism of the internal combustion engines prevails 
on the second output of the controller. 
The proportional valve 4 allows a pressure to act on the servocylinder 6. 
The pressure results in a displacement of the piston in the servocylinder 
6 to effect a change in the setting on the fuel dosing system. The 
required pressure is established through a signal on the first output on 
the proportional valve 4. The continual comparison of actual and allowable 
maximum speed takes place, e.g., in a regulator integrated in the 
controller. Throttling the internal combustion engine down continues until 
the allowable maximum speed v.sub.lim is no longer exceeded. 
When the current actual speed v.sub.act, is smaller than the allowable 
maximum speed v.sub.lim and a signal for a desired braking moment 
M.sub.brake, which prevails on the second input, was preset on the 
retarder switch 9, the controller issues on its second output the signal 
for connecting the proportional valve 4 to the retarder. The control 
signal for the proportional valve to make an appropriate output pressure 
available that causes a change of the filling degree prevails on the first 
output. 
At downhill travel and preselection of "constant speed" on the retarder 
switch 9, a comparison subordinate to the control system occurs between 
the preset speed v.sub.const, and the current actual speed. With a 
variation between v.sub.act and v.sub.const, the controller 1 issues on 
its second output the signal for connecting the proportional valve 4 to 
the retarder 2. Prevailing on the first output is the control signal Y to 
the proportional valve, for making available an output pressure required 
for achieving constant speed and causing a change in retarder filling 
degree, and thus producing appropriate braking moments. 
In a further aspect of the invention, the control system can be advanced 
and expanded to the effect that additional functions favorable to the 
travel performance can be fulfilled. These include: 
1. settling priorities; 
2. idling of the engine during any activation of the constant speed 
function. 
The first objective consists in not allowing erroneous operations by the 
operating personnel to become effective, for instance a simultaneous 
activation of the retarder, e.g., by selection on the retarder switch 9, 
and actuation of a foot pedal or gas pedal, that is, selection on the 
power output member 5 of the engine such that an increase in speed would 
result. In this case, retarder 2 and engine 3 counteract each other. In 
keeping with the retarder design and the foot pedal actuation, a 
satisfactory result can be achieved for none of the individual systems. It 
is appropriate to specify from the outset which of the activated systems 
takes priority--preferably the retarder. As an alternative, there is the 
option of allowing the function selected last by the operator (foot pedal 
or retarder switch 9) to become effective. 
In case of simultaneous activation of the retarder and actuation of the 
foot pedal or gas pedal at maximum speed, the retarder actuation is 
preferably assigned priority. 
Moreover, it is recommended to establish idling of the engine upon 
actuation of the retarder, or the retarder function "constant speed." 
Although not detailed herein, the use of a suitable multiple-way switching 
valve as a switching valve is possible. A further option is providing an 
additional switching valve for activation of the pneumatic servocylinder. 
These additional functions can be realized as well with the controller, but 
additional inputs and outputs need to be provided for that purpose, and 
further relations need to be established between the input and output 
variables in the controller. The controller becomes more compact because, 
for example, additional points of comparison and linkages with case 
decisions need to be provided. 
The inventional design of the basic control system can be expanded to 
include additional functions in keeping with applications.