Electrical gas pedal

The safety monitoring of an electrical gas-pedal system having a desired-value transmitter (2), a controller unit (3), a controlling element (4) and safety contacts (8 and 9 respectively) associated with the desired-value transmitter and the controlling element includes the possibility of checking the safety contact (9) of the controlling element even if, as a result of an increased idling-speed-of-rotation control position or a mechanical limitation, the control position of the controlling element lies above the switch point of the safety contact. For this purpose, when the engine speed of rotation exceeds a given threshold value (ns) which results from the increased idling speed of rotation plus a safety margin, in the absence of a corresponding signal from the desired-value transmitter push operation is recognized by the controller unit (3), and the controlling element (3) is moved back to such an extent that the safety contact (9) must have switched. If a switching of the safety contact (9) does not take place then an error response is brought about.

FIELD AND BACKGROUND OF THE INVENTION 
The invention relates to an electrical gas pedal. 
In particular, it relates to an electrical gas pedal for automotive 
vehicles having a desired-value transmitter from which an electric 
desired-value signal can be fed to an electronic controller unit with 
speed-of-rotation measurement, with a controlling element which can be 
controlled by electric signals of the controller unit and can be displaced 
within a maximum possible desired setting range limited by first and 
second end positions, by which controlling element, via a transmission 
unit, a displacement device which is displaceable in an actual-place range 
which is limited by a first and a second end position can be mechanically 
actuated to control the engine output, having at least one additional 
controlling unit for increasing the idling speed of rotation, with a 
desired-value-transmitter safety contact which closes after a given path 
of displacement of the desired-value transmitter, and with a 
controlling-element safety contact which opens after a given adjustment 
path of the controlling element, and with a safety-contact monitoring 
circuit which monitors the manner of operation of the safety contacts and, 
in the event of an error on the part of one of the safety contacts, 
triggers an error reaction. 
In one known system of this type, the safety contacts are so adjusted, in 
order to permit as early as possible a recognition of errors, that they 
switch already upon the smallest possible displacement paths. By 
increasing of the idling speed of rotation as a function of certain 
factors, such as, for instance, the temperature of the engine at low 
temperatures, or on basis of the switching on of additional load consumers 
such as, for instance, an air conditioner, the idling speed control 
position lies above the switch point of the controlling-element safety 
contact. When the desired-value transmitter is not actuated and when, 
therefore, an idling desired-value transmitter signal is present, both 
safety contacts are unactuated and the safety circuit would respond. In 
such a case, proper operation of the internal combustion engine would not 
be possible. This occurs, for instance, in internal combustion engines 
having injection pumps with separate engine stop. In the case of internal 
combustion engine having injection pumps with engine stop via an injection 
pump lever, the position of the controlling element when the engine stop 
function is not actuated lies in a position above the switch point of the 
controlling-element safety contact upon an increase in the idling speed of 
rotation as a result of the above-indicated factors or in the event of a 
large limiting of the adjustment range. When the desired-value transmitter 
is not actuated, both switch contacts again are unactuated, i.e. they are 
disconnected and the safety circuit responds again. 
The result hereof is, once again, that, due to the error reaction of the 
safety circuit operation of the internal combustion engine, in the case of 
an increase of the idling speed of rotation above the switch point of the 
controlling-element safety contacts as a result of additional loads or as 
a function of the temperature of the engine, operation of the internal 
combustion engine is always impossible when the signal of the 
desired-value transmitter corresponds to a desired value which lies below 
the switch contact of the desired-value transmitter safety contact. 
SUMMARY OF THE INVENTION 
It is an object of the invention to make operation of the internal 
combustion engine possible within all operating ranges and to assure a 
safety monitoring of the safety contacts despite the limiting of the 
setting range or the increase in the idling speed of rotation above the 
switch point. 
Accordingly, by the invention, in case of the presence of an increase in 
the idling speed of rotation, the controller unit (3) bridges over the 
desired-value-transmitter safety contact (8) up to a speed-of-rotation 
threshold value (ns) and, at a speed of rotation above this, does away 
with the bridging (12) and in the case of the exceeding of this threshold 
value (ns) and the absence of a correspondingly associated desired-value 
transmitter signal, the controller unit (3) moves the controlling element 
(4) back into a position in which the controlling element safety contact 
(9) must be switched. 
By this formation, assurance is had that, even upon a limiting of the 
setting range which is effected for the reasons set forth above, an error 
response coming from the safety circuit is avoided. 
The basic idea of the present invention consists essentially in the 
bridging over the safety contacts up to a threshold value of the speed of 
rotation which lies above the desired value of the idling speed of 
rotation control, increased by a slight safety margin, in the operating 
conditions under which an error reaction would occur in the previously 
known development, so that the safety circuit does not trigger an error 
reaction. At speeds which lie above this threshold value and which are 
noted by the controller unit, the checking of the safety contact of the 
controlling element is effected when a desired-value transmitter signal is 
present corresponding to the idling speed of rotation and therefore at an 
engine speed of rotation which is actually higher than corresponds to the 
safety contact. For this purpose, the controlling element is briefly 
returned by the controller unit to such an extent back along its 
displacement path that the safety contact must have switched. This is 
customarily possible in pushing operation, but can also be carried out 
when the injection-pump lever is moved into the engine stop position as 
the result of an actuation of the engine-off key. 
In order to prevent a stalling of the engine in the case of engines with 
engine stop via injection-pump lever, which would lead to a considerable 
impairment in safety in the case of vehicles with power-booster-units say, 
for instance, if power steering and brakes were to fail, in a further 
development of the invention the controller unit (3) prevents a return of 
the controlling element (4) by the control at engine speeds of rotation 
which are only slightly above the idling speed of rotation but are below 
the threshold value (ns1) and at speeds of rotation above this permits 
only a brief return by the control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As seen in FIG. 1, the overall arrangement comprises a gas pedal 1, a 
desired-value transmitter 2, a controller unit 3 comprising multiple 
controller functions, a controlling element 4, a transfer unit 5, a 
displacement device 6 of an injection pump 7, a safety contact 8 of the 
desired-value transmitter which can be actuated by the gas pedal 1, and a 
safety contact 9 which can be actuated by the controlling element 4. The 
controller unit 3 comprises various additional functions and is capable of 
shifting the position of the controlling element 4, for instance upon a 
cold start, on basis of a desired speed of an automatic temperature device 
or as a function of an additional load 10 by increasing the idling speed 
of rotation, as a result of which it can possibly lie above the safety 
control switch point. 
In order fully to assure the inherent security of the system, for instance 
upon a short circuit, the safety contacts 8 and 9 are provided. The safety 
contact 8, which is associated with the desired-value transmitter, closes 
after a given displacement path, i.e. at a given angular position of the 
gas pedal and therefore at a given desired-value position. The safety 
contact 9, which operates as a function of the displacement path of the 
controlling element and therefore as a function of the angular position of 
the controlling element 4, is closed commencing from the stop up to its 
switch point, designated 11 in FIG. 2, and opens upon further displacement 
of the controlling element beyond this switch point. Both switches perform 
an "OR operation" and have the result that a command from the controller 
unit 3 is only transmitted to the controlling element when one of the two 
safety contacts is connected. 
If now, on basis of a change in control position, the control position for 
the idling speed of rotation lies above the safety switch point, as is the 
case when the idling speed of rotation must be increased due to a low 
engine temperature or additional loads or when a mechanical limitation is 
present, then no possibility is present for the corresponding safety 
circuit within the controller unit to check the correct manner of 
operation of the safety contacts since in this operating state the idling 
speed control lies above this switch point. This new idling speed control 
position is designated LLE2 in FIG. 2. With the normal, unrestricted 
adjustment range or non-increased idling-speed control position, the 
idling speed of rotation control position would be at a lower value, 
designated LLE2 in FIG. 2. If now, with a cold engine or due to the 
connecting of additional units, the required idling speed control position 
is set above the safety switch point 11 then, with the desired-value 
transmitter not actuated, both safety contacts would be disconnected and 
the safety monitoring would lead to a corresponding error response. 
In order not to permit this condition to occur, the safety contact is 
bridged over up to a given threshold value of a speed of rotation which 
lies above the increased speed of rotation control desired value by a 
small safety margin, in which connection the controller unit continuously 
establishes the speed of rotation. This bridging is indicated in FIG. 2 by 
a thin line 12. If a speed of rotation which lies above this threshold 
value is measured by the controller unit without a corresponding 
desired-value signal ns of the desired-value transmitter being present, 
then this bridging 12 is eliminated and an error is assumed by the safety 
circuit. 
In order to acquire certainty as to whether an error is actually present, 
one proceeds in accordance with the function logic of FIG. 3. 
The monitoring step 13 in accordance with FIG. 3 represents the customary 
monitoring of the safety contact. In this connection it is determined by 
the safety circuit whether a desired-value signal from the desired-value 
transmitter is present and whether the corresponding safety contact has 
switched, which is shown in the monitoring step 13 by SWGSK=1. 
If, upon further testing in accordance with test step 14 it is found that 
the actual speed of rotation lies below the threshold value designated ns, 
then the manner of operation will be recognized to be correct and the 
desired-value signal will be forwarded further to the controller unit for 
leveling out. On the other hand, if the speed of rotation actually noted 
lies above the threshold value ns and if no switching of the safety 
contact 8 has been noted, then a further measure in accordance with 
testing step 15 is carried out. 
This further measure for the carrying out of the safety monitoring consists 
therein that with an engine speed of rotation lying above the threshold 
value and in the absence of a corresponding signal from the desired-value 
transmitter, the controller unit recognizes that there is push operation 
since the controller unit has regulated down. The controlling element is 
thereupon returned to a position in which the safety contact 9 must 
switch. If, in this connection, switching of the safety contact 9 is noted 
corresponding to the testing step 16, then the desired-value signal is 
forwarded to the controller unit. If this is not the case then there is an 
error response, in which connection either an intervention into the 
transmission or return to the idling speed of rotation can take place. An 
engine stop function is not carried out here in order not to impair the 
further manner of operation of servo-units. This step is designated 17 in 
FIG. 3.