Method and arrangement for controlling the drive unit of a motor vehicle

The invention is directed to a method and an arrangement for controlling the drive unit of a motor vehicle. The maximum permissible torque or the maximum permissible power is determined and fault reactions are initiated when the limit value is exceeded by a computed actual torque value or an actual power value.

BACKGROUND OF THE INVENTION 
U.S. Pat. No. 4,603,675 discloses a method and an arrangement for 
controlling the drive unit of a motor vehicle. In this method and 
arrangement, the power of the drive unit is determined via an electric 
adjustment of the throttle flap of an engine in dependence upon the 
command of the driver pregiven by the adjustment of the accelerator pedal. 
It is especially necessary to consider operational reliability because, in 
this system, the drive power of the drive unit is adjusted only via an 
electrical path. For this reason, the method and arrangement disclosed in 
U.S. Pat. No. 4,603,675 provide that the setting of the accelerator pedal 
and therefore the driver command is compared to the position of the 
throttle flap. An erroneous operation of the equipment is assumed and a 
corresponding reaction initiated if the difference between the two values 
exceeds a predetermined limit value. If required, this difference can be 
after a pregiven filter time. This monitoring concept is predicated on a 
certain coupling between the position of the accelerator pedal and the 
position of the throttle flap. In modern engine controls, a complete 
decoupling between accelerator pedal and throttle flap for new functions 
such as lean concepts or catalytic converter heating functions can be an 
objective. If this is the case, then the known monitoring concept is 
applicable only with difficulty in at least several operating regions. 
U.S. Pat. No. 5,558,178 discloses adjusting an input value for the torque 
to be outputted by the drive unit or the power to be generated thereby. In 
this context, an estimate of this torque or this power is described and, 
if required, while also considering the internal losses as well as the 
operating state of ancillary consumers. In the engine described herein, 
the input value is adjusted by controlling the following: the air supply, 
the fuel metered and/or the ignition angle. The actual torque or the 
actual power is computed on the basis of engine rpm, motor load (air mass) 
and the actual adjustment of the ignition angle. If required, this is 
supplemented by considering the internal friction losses as well as the 
operating state of ancillary consumers. 
SUMMARY OF THE INVENTION 
In view of the foregoing, it is an object of the invention to provide 
measures for monitoring the control of a drive unit which is easily 
applied even when there is a complete decoupling between driver command 
and the actuating element or elements which adjust the drive power. 
The method of the invention is for controlling the drive unit of a vehicle. 
The method includes the steps of: adjusting the torque and output power of 
the drive unit via an electrical path in dependence upon a first operating 
variable defining the position of an operator-actuated element actuated by 
the driver of the vehicle; supplying the first variable and additional 
operating variables to an electronic control unit; computing the torque 
and power of the drive unit in dependence upon the operating variables 
utilizing the electronic control unit; determining the maximum permissible 
torque and the maximum permissible power utilizing the electronic control 
unit; and, initiating a fault reaction when the computed torque and power 
exceed the maximum permissible torque and the maximum permissible power. 
The solution provided by the invention makes possible a reliable monitoring 
of the control of the drive unit in all operating states and even in the 
presence of a complete decoupling of the position of the accelerator pedal 
and engine power. 
In this way, the operating reliability of the control is ensured also in 
those operating states wherein the power deviates from the input via the 
accelerator pedal (for example, for heating of the catalytic converter in 
the cold start with a retarded ignition angle and increased air supply and 
for lean operation of the engine with increased air supply compared to a 
.lambda.=1 operation and for power increasing measures such as engine drag 
torque control et cetera). 
Monitoring is made significantly more precise by considering the ignition 
angle because the ignition angle significantly affects the efficiency of 
the engine. The consideration of the ignition angle becomes advantageous 
especially for catalytic converter heating measures via retarded ignition 
angle with a simultaneous increase of the supplied air. 
Furthermore, and in contrast to the known position comparison, tolerances 
in the characteristic of the angle sensors, which affect the precision of 
the comparison, do not have to be considered. 
Influences caused by charging (such as via a turbo charger), which operate 
on the power of the engine, are automatically taken into account by 
considering the actual air/fuel mixture drawn by the engine for the 
monitoring of the control of the drive unit. 
It is especially advantageous that the solution provided by the invention 
can be utilized for the drive unit for different embodiments of the 
control arrangement. In these embodiments, individual functions can be 
executed separately from each other. 
Monitoring on the basis of torque values or power values is especially 
advantageous because these values are determined via an engine simulation 
and can be checked in this manner irrespective of whether the driver 
command has been converted into the correct power or into the correct 
torque. 
It is especially advantageous to carry out monitoring during idle of the 
drive unit because, in this operating state, an increased power can be 
especially critical. Outside of idle, a driver would react to increased 
power by releasing the accelerator pedal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
FIG. 1 shows an overview block circuit diagram of a control apparatus 10 as 
it can be configured in the arrangement according to the invention. The 
control apparatus 10 includes a microcomputer having subprograms or 
program steps which are shown as function blocks in FIG. 1. For reasons of 
clarity, only those elements are shown which are needed to explain the 
solution of the invention. The control apparatus 10 includes all the 
elements which are needed according to the state of the art to control a 
drive unit and preferably an internal combustion engine. 
At least one input line 12 from at least one measuring device 14 is 
connected to the control apparatus 10 or microcomputer. The measuring 
device 14 detects the position of an operator-controlled element 16 
actuated by the driver. An input line 20 connects an rpm measuring device 
18 to the control apparatus 10 and a line 24 connects a control unit 22 to 
the control apparatus 10 and a line 28 connects a measuring device 26 to 
the control apparatus 10. The control unit 22 can, for example, control 
the engine drag torque. The line 28 connects measuring device 26 for 
detecting the engine load, for example, from an air-quantity sensor, an 
air mass sensor, a throttle flap position sensor or a sensor for detecting 
intake pipe pressure or combustion chamber pressure or the quantity of 
fuel injected. 
In the preferred embodiment, the control apparatus 10 influences the air 
supply to an internal combustion engine via at least one output line 30. 
The control apparatus 10 can influence the air supply to the engine via an 
electrically actuable throttle flap 32 and the metered fuel and the 
ignition of the engine via the output lines 34 and 36, respectively. 
The input line 12 and the input line 20 are connected to a 
characteristic-field element 44. The input line 20 branches into the lines 
38, 40 and 42. The output line 46 of the characteristic-field element 44 
leads to a comparator element 48. The input line 24 and, if needed, at 
least one further input line 50 (shown dotted in FIG. 1) is connected to 
the comparator element 48. The output line 52 of the comparator element 48 
branches into a line 54 and into a line 56. The line 54 is connected to 
the control element 58 having an output line representing at least the 
output line 30 of the control apparatus. 
In addition, the element 58 influences the metering of fuel via the line 82 
and/or the ignition angle via lines 88 to 90. The line 56 is connected to 
a characteristic line or characteristic-field element 60. At least one 
further operating variable such as the engine rpm is supplied to the 
element 60, as required, via at least one line 62 (shown as a broken 
line). The output line 64 of the element 60 is connected to a second 
comparator element 66. A line 68 is connected to the comparator element 66 
which defines the output line of a computing element 70. The line 40 
connects as an input line to the computing element 70 and branches off the 
line 20. The line 72 is connected to the computing element 70 and branches 
off line 28. A line 76 is also connected to the computing element 70 and, 
in an advantageous embodiment, at least one further line 78 (shown as a 
broken line) is also connected to computing element 70. The line 76 
branches from line 36 for influencing the ignition angle. The line 36 is 
the output line of a characteristic field and computing element 80 which, 
in turn, has input line 42 and the line 74 branching from line 28 as well 
as at least one further line 82 (shown as a broken line). 
For influencing the metering of fuel, the output line 84 of the comparator 
element 66 is connected to an element 86 (shown by a broken line) for 
computing the metered fuel. At least input lines 88 to 90 are connected to 
the element 86 and the output line thereof is shown as line 34. In an 
advantageous embodiment, and as alternative or supplementary, a line 92 
branches from the output line 84 and is connected to control element 58. 
The basic idea of the monitoring measures provided by the invention is 
that, in the context of engine simulation, a check is made as to whether 
the control system converts the pregiven desired value into the correct 
power. In this motor simulation, all data which are relevant to engine 
power and which are available, are considered. The desired value is 
pregiven by the driver or from additional control systems (engine drag 
torque control, idle control, et cetera). 
In the preferred embodiment, the engine simulation takes place in the 
context of the estimate of the engine torque outputted or generated by the 
drive unit or the power which is generated by the drive unit (while 
considering the rpm) or the power which is outputted by the drive unit. 
The computed or estimated actual value is compared to a limit value 
derived from the driver command (driver input or input value of an 
additional control system). A fault is detected when the actual value 
exceeds the limit value. 
A preferred embodiment is shown in FIG. 1 for the control of an internal 
combustion engine wherein the torque of the engine is adjusted in 
accordance with a pregiven desired torque as disclosed in U.S. Pat. No. 
5,558,178 and incorporated herein by reference. For this purpose, a 
measured variable representing the position of the accelerator pedal as 
well as a variable representing the engine rpm are supplied to the 
characteristic-field element 44. There, a characteristic field is stored 
which, from the supplied signal quantities, determines a desired torque 
pregiven by the driver and outputs the desired torque via the line 46. 
With the determination of the desired torque, additional data such as data 
relative to gear position, vehicle road speed, et cetera, can be used in 
the determination of the desired torque. The characteristic field, which 
is utilized to form the driver desired torque value, is predetermined in 
accordance with the desired driving performance and with the power 
capacity of the vehicle. 
Modern control systems for motor vehicles exhibit functions which reduce 
the engine torque independently of the input of the driver (for example, 
drive slip control, transmission control et cetera) or increase the engine 
torque (for example, engine drag torque control, idle control et cetera). 
Only the last mentioned are of interest with respect to the monitoring 
measures according to the invention. For this reason, a maximum value 
selection is determined between the supplied variables for forming the 
actual torque desired value (Mdes) in the comparator element 48. The 
largest value from this maximum value selection is outputted via the line 
52. The desired torque value determined in this manner is translated by 
the control unit 58 in accordance with the known procedure primarily into 
the adjustment of the air supply and, if required, while correcting the 
fuel injection (one of the lines 88 to 90) and the ignition angle (one of 
the lines 82). 
To compute the actual torque value, and as in the known state of the art, 
at least the signal, which represents the engine load, the engine rpm as 
well as the actual adjusted ignition angle are considered. In addition, 
and in an advantageous manner, the number of active cylinders is also 
considered in the determination of the actual torque. 
If the comparison of the input torque and the actual torque is not made on 
the basis of the indicated torque (that is, the torque generated by the 
engine via combustion), and is instead made on the basis of the torque 
(clutch torque) outputted by the drive unit, then the following is 
considered in an advantageous manner and in addition to the 
above-mentioned variables: variables which influence the outputted torque 
such as the friction torque of the engine (which is temperature and rpm 
dependent) or the torque requirement of ancillary equipment (climate 
control system, windshield heating, et cetera). 
The determined desired torque value is supplied to the characteristic line 
(characteristic field) 60 for monitoring purposes. There, a maximum 
permissible engine torque is stored as a limit value in dependence upon 
the input value. This limit value is then the basis of the comparison to 
the computed actual torque. In an advantageous manner, the engine rpm is 
also considered (line 62). This is done preferably in that, for engine 
rpms in the region of idle rpm or lower, the maximum permissible engine 
torque is comparatively greater than at higher -engine rpms. For this 
reason, the flexibility of the monitoring measures for a vehicle at 
standstill or a rolling vehicle is significantly increased because, 
especially in this range, via idle control and additional ancillary 
functions (such as catalytic converter heating measures), an actual torque 
can occur which deviates significantly from the driver command (at idle 
this torque is as a rule 0). In general, the limit value increases with 
increasing engine rpm. 
A corresponding signal is transmitted via the line 84 when the determined 
actual torque exceeds the maximum permissible engine torque. This signal 
is considered in the computation of the metering of fuel by switching off 
the metering of fuel to individual cylinders or to all cylinders and/or is 
considered in the control unit 58 which cuts off the current of the 
actuator for the throttle flap or limits the position of the throttle 
flap. This computation is shown symbolically in FIG. 1 by the block 86. 
The determination of ignition angle is represented symbolically by block 80 
and determines, in a manner known per se, the ignition angle to be 
adjusted from the following: engine load, engine rpm, corrected 
interventions such as knock control, ignition angle correction via control 
unit 58, catalytic converter heating measures et cetera. The ignition 
angle to be adjusted is considered via the line 76 for the determination 
of the actual engine torque. 
To improve the function of the monitoring measures, the fault reaction 
measures are only initiated when the actual value has exceeded the desired 
value for a pregiven time duration. This is shown in the flowchart of FIG. 
2. In addition, and to provide improvement when negative torque changes 
take place (that is, when the driver releases the accelerator pedal), it 
is provided that a time-dependent delay or a dead time element is 
effective when there is a change of the permissible torque in the 
direction toward lower values. 
In addition to the embodiment shown which operates on the basis of engine 
torque, the motor control is carried out on the basis of power values in 
other advantageous embodiments. The measures undertaken then correspond 
because the interrelationship between engine torque and engine power is 
given by the engine rpm. Furthermore, and in other embodiments, a 
conventional position control of the throttle flap can also be carried out 
in dependence upon position desired values. In these conventional control 
concepts, the monitoring measures of the invention are determined by 
determining the desired torque values from the input values (especially 
from the accelerator pedal position) and the actual torque values as shown 
above and the desired and actual values of torque are compared to each 
other. 
The flowchart of FIG. 2 shows how the solution of the invention can be 
realized as a computer program. After the start of the subprogram at 
pregiven time points, operating variables are read in in the first step 
200. These operating variables preferably include the engine torque 
desired value Mdes, the engine rpm Nmot, the actual adjusted ignition 
angle ZW, the determined engine load TL and, as required, further 
operating variables (engine temperature, status of ancillary equipment, et 
cetera). 
In the next step 202, and in the preferred embodiment, the maximum 
permissible engine torque Mmotmax is formed from the preprogrammed 
characteristic field in dependence upon engine desired torque Mmotdes and 
engine rpm Nmot. Thereafter, in step 204, and in accordance with the 
procedure known from the state of the art, the actual torque value Mmotact 
is computed in accordance with engine rpm, engine load, ignition angle 
and, if required, additional operating variables. In the next inquiry step 
206, a check is made as to whether the maximum permissible torque value 
Mmotmax is greater than the determined torque actual value Mmotact. If 
this is the case, the subprogram is ended and repeated at a pregiven time. 
If the actual torque value exceeds the permissible value for a pregiven 
time, then, in accordance with step 208, fault reaction measures are 
initiated. These measures can include, for example, fuel interruption, 
cylinder suppression, limiting or cutting off the air supply et cetera. 
The subprogram is ended after step 208. 
In the preferred embodiment, after step 202, inquiry step 210 provides 
inquiring as to the direction of the change of the maximum permissible 
engine torque. This takes place with respect to determined maximum values 
of two sequential program runthroughs. Alternatively, the change of the 
accelerator pedal position or the desired torque can be applied. If the 
maximum permissible engine torque becomes less (that is, the actual value 
is less than the previous value), a dead time or delay time in accordance 
with step 212 is provided before the program continues with step 204. 
A further advantageous embodiment and for the determination of the actual 
engine torque in step 204, a filtering or a mean value formation of the 
determined values is undertaken in correspondence to step 214 in order to 
further increase the reliability and precision of the monitoring measure. 
In an advantageous embodiment, the accelerator pedal position is detected 
via redundant sensors on the accelerator pedal. Both sensor data are 
supplied to the control apparatus 10. In the preferred embodiment, one of 
the pieces of sensor data is used to determine the desired torque value 
and to control the air supply and, if necessary, the metering of fuel 
and/or the ignition angle; whereas, from the remaining sensor data, the 
maximum permissible torque value, which is applied for monitoring, is 
determined. 
Furthermore, in an advantageous embodiment, it is provided that the check 
only takes place at one operating point, namely, at idle. In the case 
where the accelerator pedal is released, the maximum permissible torque 
value is determined and compared to the determined actual torque value. 
In a preferred embodiment, monitoring, however, takes place at every 
operating point of the engine. However, it is possible to input only 
selected operating points or operating ranges (for example, in the idle 
range, in the pregiven part-load range and/or in the full-load range). 
When these operating points or ranges are reached, the monitoring measures 
are carried out. 
In FIGS. 3a and 3b, the solution provided by the invention is explained 
further with reference to exemplary signal traces. In FIG. 3a, the 
following pregiven desired torque values are shown: from the driver (solid 
line), from the idle controller (dash line) and from the engine torque 
controller (dot-dash line). FIG. 3b shows the computed actual value (solid 
line) as well as the maximum permissible torque (dotted line). 
FIGS. 3a and 3b show how the driver accelerates the motor vehicle to the 
desired speed by actuating the accelerator pedal. Thereafter, the 
accelerator pedal is released and the vehicle is in overrun operation 
during which the engine drag torque controller increases the output torque 
of the engine. The release of the accelerator pedal at time T.sub.0 leads 
to a rapid reduction of the actual torque; whereas, the maximum desired 
torque tracks with a delay. 
In FIG. 3b, two operating situations are introduced in which a fault 
occurs. The first operating situation is after the release of the 
accelerator pedal when the engine power has suddenly again increased. The 
engine power exceeds the maximum permissible torque so that at time point 
T.sub.1 and after a pregiven time has elapsed, the fault reaction measures 
are initiated. The other operating situation shows the vehicle in idle. 
Here, the engine torque exceeds the maximum permissible value so that at 
time point T.sub.2 a fault reaction takes place after the elapse of a 
pregiven time. 
FIG. 4 shows embodiments of the control apparatus 10. 
In the first embodiment, the control apparatus 10 comprises two 
microcomputers 400 and 402 which are interconnected via a communication 
system 404 for mutually exchanging data and information. The microcomputer 
400 adjusts the air supply, the ignition and the fuel metering via output 
lines 406, 408 and 410, respectively. 
A first measuring device 414 for detecting the accelerator pedal position 
is connected via input line 412 to the microcomputer 400. Also, measuring 
devices 420 to 422 for detecting the operating variables known from FIG. 1 
are connected to the microcomputer 400 via input lines 416 to 418, 
respectively. 
In the microcomputer 400, all functions needed to control the internal 
combustion engine are carried out, that is, fuel metering, ignition angle 
and the adjustment of the air supply in dependence upon operating 
variables which are read in. The second microcomputer 402 operates to 
carry out the monitoring measures according to the invention. For this 
purpose, a second sensor 426 detects the accelerator pedal position and is 
connected via input line 424 to the microcomputer 402. In a first 
preferred embodiment, the lines 428 to 430, which are branched from input 
lines 416 to 418, respectively, are also connected to the second 
microcomputer 402. 
In this embodiment, the microcomputer 402 executes all monitoring measures 
including the determination of the actual torque value and the maximum 
permissible torque value as well as the comparison of the torque values. 
The fault data is transmitted via the communication system to the first 
microcomputer which executes the reaction. 
The input lines 428 and 430 are omitted in another embodiment. In this 
other embodiment, the microcomputer 400 computes the actual torque and 
transmits this value via the interface 404 to the microcomputer 402. The 
microcomputer 402 forms the maximum permissible engine torque from the 
driver command signal and executes the comparison of the torque values. 
Alternatively, the microcomputer 402 transmits the operating variables to 
the second microcomputer which determines the actual torque. 
In a further advantageous embodiment, the two microcomputers are combined 
and have mutually separate program blocks. Here too, in a first 
embodiment, all information is read into the two program blocks 400 and 
402. Also, the possibility is provided that the operating variables for 
determining the actual torque are read in only by program block 400. This 
program block 400 then transmits these variables or the determined actual 
torque or both to the program block 402. 
In all embodiments, any hardware and software errors of the computer 
element 400 as well as of the periphery (measuring devices and actuators) 
can be detected with the aid of the invention. 
The solution provided by the invention can be applied advantageously to 
spark-ignition engines as well as to diesel engines or electric vehicles. 
It is understood that the foregoing description is that of the preferred 
embodiments of the invention and that various changes and modifications 
may be made thereto without departing from the spirit and scope of the 
invention as defined in the appended claims.