Control system for a motor vehicle engine to prevent slipping of the vehicle drive wheels during acceleration

A system for automatically overriding operator control of engine power delivered to the drive wheels of a motor vehicle when a wheel slip condition is detected during vehicle acceleration. A pneumatic actuator in the engine fuel control circuit is operated in a controlled manner to cause the engine fuel lever to initially decrease power at a relatively fast rate and then at a relatively slow rate to alleviate the wheel slip. Once the wheel slip condition is corrected, the actuator is reset in a controlled manner, which allows the fuel lever to restore engine power, initially at a relatively fast rate and subsequently at a relatively slow rate, such rate controlled adjustment of engine power during each wheel slip control cycle providing less cyclic control of the wheel slip correction process, and accordingly a smoother acceleration.

BACKGROUND OF THE INVENTION 
The invention relates to a method and an apparatus for start-up control on 
motor vehicles. 
Start-up control systems of the prior art are intended to prevent an 
uncontrolled slipping of the drive wheels when movement of the vehicle is 
started on a smooth surface (DE-PS No. 18 08 799). Such slipping 
unnecessarily prolongs the time required to accelerate the vehicle to 
running speed and reduces its traction, as well as lateral stability. 
The slipping of the drive wheels is measured by rotation sensors located on 
the wheels and is evaluated in an electronic system. If only one wheel is 
slipping, the corresponding wheel brake is activated, e.g., via a valve 
(differential brakes). A drive torque is thereby transmitted via the wheel 
differential to the other stopped wheel. 
However, if both wheels are slipping, the power of the engine is adjusted 
downward. For this purpose, an intervention in the carburetor throttle 
control must be made, and the value set by the driver must be reduced. 
This occurs, for example, by means of interposed electrical solenoid 
actuators or a pneumatic or hydraulic work cylinder. 
With the configuration described above, the gas is taken away from the 
engine as soon as one wheel on the drive axle starts to slip. This is 
recognized by the occurrence of a +b control signal (acceleration signal 
of one wheel). Then, as soon as the +b signal has disappeared, the gas 
setting desired by the driver is re-established. 
Such a control concept (black-white control) naturally causes a relatively 
uncomfortable acceleration of the vehicle. 
The object of the invention, therefore, is to provide a system by means of 
which the vehicle start-up operation can be executed without passenger 
discomfort. A pre-requisite, however, is that, as in the prior art, there 
is only one black-white signal present to indicate the slipping of the 
drive wheels.

DESCRIPTION AND OPERATION 
As shown in FIG. 1, a gas pedal 6 is connected via a mechanical linkage 12 
and via an actuator cylinder 4 with a lever 5 of an injection pump 7. The 
injection pump 7 regulates the fuel feed to an engine (not shown). The 
lever 5 can be placed in the positions zero-load (NL), idle (LL) and 
full-load (VL). There is a stop cylinder 14 so that the lever 5 is not 
allowed to drop below the idle position (LL) while the vehicle is in 
motion. 
The actuator cylinder 4 in the carburetor control linkage 12 reduces the 
fuel fed to it by the driver, if necessary, as when the drive wheels slip. 
Normally, the piston 13 of the actuator cylinder 4 is centered by springs 
15 and 16 in a middle position. When the accelerator pedal pressure 
applied to the actuator cylinder 4 via linkage 12 decreases, piston 13 is 
retracted, whereupon the lever 5 of the injection pump 7 is moved in the 
direction of lower power. 
The actuator cylinder 4 is supplied by a pressure medium from a reservoir 1 
via a control valve 2. The control valve 2 is electrically activated by an 
electronic system 3. It is designed as a 2-position, 3-way valve. Its 
output is connected to the actuator cylinder 4 by means of a shuttle 
valve. There is also a connection to the stop cylinder 14. A motor brake 
valve is also connected to the shuttle valve 21. 
The apparatus illustrated in FIG. 1 operates as follows: 
As soon as the drive wheels of the vehicle begin to slip, i.e., as soon as 
their velocity exceeds the vehicle speed by a specified velocity .DELTA.V, 
the electronic system transmits a signal to the control valve 2. The 
latter then opens and connects the reservoir 1 with the actuator cylinder 
4. The actuator cylinder is shortened until the lever 5 of the injection 
pump 6 is pivoted into the idle position LL. In this position, the lever 5 
is held by the stop cylinder 15. 
On account of the power reduction of the engine effected in this manner, 
the speed of the drive wheels again approaches the speed of the vehicle. 
Then the slip signal of the electronic system 3 disappears, the control 
valve 2 evacuates the actuator cylinder 4, and the acceleration originally 
set by the driver is resumed. This control sequence (black-white 
regulation) is repeated until the drive wheels cease slipping. 
A disadvantage with the black-white regulation described is that relatively 
steep gradients result for the wheel velocities of the drive wheels, 
therefore causing a wheel slip which on one side is relatively large and 
on the other side is practically zero. The resulting large slip amplitudes 
reduce the stability of the vehicle during the start-up process. On the 
other hand, the temporary absense of a drive slip leads to a discontinuous 
acceleration of the vehicle. The overall result, therefore, is an 
uncomfortable control curve. 
To achieve a better control characteristic of the start-up regulation, the 
slip amplitudes must, if possible, be kept in an optimal slip range of 
approximately 20%, and the wheel velocitities must exhibit gradients which 
are as flat as possible, and in the control pauses, the drive wheels 
should not equal the vehicle speed, and thus zero slip. 
This is achieved by the invention in that the pressure in the actuator 
cylinder 4 is controlled in the form of a steep-drop characteristic curve. 
An apparatus by means of which this can be achieved is illustrated 
schematically in FIG. 2. 
As shown in FIG. 2, between the reservoir 1 and the control valve 2, there 
is a first flow restrictor 8, as well as a first volume 9. In the 
evacuation line of the control valve 2, there is a second volume 11 and a 
second flow restrictor 10. Otherwise, the apparatus shown in FIG. 2 is the 
same as in FIG. 1, whereby components which are not directly part of the 
invention are not shown. 
The operation of the apparatus illustrated in FIG. 2 is explained in 
greater detail below, in connection with the diagrams presented in FIG. 3. 
It is assumed that the slipping of the wheels begins at time t.sub.0. At 
this time, therefore, the wheel velocity V.sub.R begins to differ from the 
vehicle velocity V.sub.F. At time t.sub.1, the difference between the 
wheel velocity and the vehicle velocity is already so large that a 
predetermined threshold value .DELTA.V is reached. At this point, the 
first phase of a wheel slip control cycle is initiated during which the 
electronic system 3 gives a signal to the control valve 2, which thereupon 
switches into the position which pressurizes the actuator cylinder 4. The 
first volume 9 is connected to cylinder 4, which initially leads to a 
rapid pressure increase of the pressure p in the actuator cylinder 4. At 
time t.sub.2 (steep drop K), the pressure of first volume 9 has been 
reduced by pressure equalization with the actuator cylinder 4. After this 
initial steep pressure increase, the action of the first flow restrictor 8 
leads to a further gradual pressure increase, since now the higher 
pressure in volume 1 flows to volume 9, and hence to cylinder 4, via flow 
restrictor 8. This first phase of the wheel slip control cycle, is 
terminated at time t.sub.3, at which point the wheel velocity V.sub.R 
corresponds to the threshold value . 
At time t.sub.3 the electronic system 3 recognizes that the wheel velocity 
V.sub.R begins to fall below the threshold value .DELTA.V, and switches 
the control valve 2 back into the initial position (shown). This initiates 
a second phase of the wheel slip control cycle. In this position, the 
actuator cylinder 4 is evacutated. The evacuation takes place, initially 
rapidly, into the second volume 11, which is void of pressure. After the 
steep-drop K (volume equalization) is reached, at time t.sub.4 evacuation 
continues to take place at a slower rate via the second flow restrictor 10 
until, at time t.sub.5, the wheel velocity V.sub.R again increases to a 
value that exceeds the wheel slip threshold value .DELTA.V and the control 
cycle is repeated. 
The initially steep pressure gradient in the actuator cylinder 4 is 
primarily intended to overcome the hysteresis of the overall activation 
mechanism, and to brake or accelerate the drive wheels as rapidly as 
possible. The subsequent gradual pressure gradient then causes the motor 
and thus the drive wheels not to react in an uncontrolled manner, and the 
control point is reached relatively precisely, without significant 
over-control or under-control. The resulting control frequency is 
approximately 2 to 3 Hz. 
The steep-drop characteristic of the pressure in the actuator cylinder 4 
achieved by the invention can also be achieved in another way. It is 
conceivable, for example, to use a proportional valve instead of the 
2-position, 3-way control valve. The proportional valve would then be 
controlled by the electronic system 3 so that first of all, a large cross 
section flow path would be set, and after a predetermined time had 
elapsed, the flow path would be reduced to a smaller value. The same would 
be true both for the pressurization and for the evacuation of the actuator 
cylinder 4. 
Another possibility would be to use an electrically-operated solenoid 
actuator instead of the actuator cylinder 4, and to apply an appropriately 
graduated current to it by means of the electronic system 3. 
Instead of using the separate volumes and flow restrictors shown, it is 
also possible to replace these components by means of a corresponding 
configuration of the length and the diameter of the connecting lines of 
the control valve 2. 
FIG. 4 shows another arrangement of the start-up control. In FIG. 4, the 
lever 5 of the injection pump is not activated by means of a mechanical 
linkage, but pneumatically. During normal travel, the driver controls the 
gas pedal 6, which here is designed as a pedal-operated valve, and which 
supplies a graduated control pressure from the reservoir 1 via a 
normally-open 2-position, 2-way valve 19 to an actuator cylinder 4. The 
piston of the actuator cylinder 4 is connected with the adjustment lever 5 
of the injection pump. When the piston moves out of the actuator cylinder 
4, the adjustment lever 5 is moved to the right against the force of a 
spring 20, whereupon the power of the motor is increased. 
If now, during starting, the drive wheels of the vehicle begin to slip, the 
situation is recognized by the electronic system 3. The electronic system 
3 then emits a signal to valve 19 and to control valve 2. In the 
electrical control line to the multiway valve 19, there is a timer 18 with 
a delay. 
In the evacuation line of control valve 2, there is again a second volume 
11 and a second flow restrictor 10. The input line of the control valve 2 
is connected with the output of the pedal-operated valve 6 via a first 
volume 9 and a first flow restrictor 8. Finally, the multiway valve 19 is 
bridged by a check valve 17. 
The apparatus illustrated in FIG. 4 operates as follows: 
The illustrated situation is normal operation, in which the driver can give 
gas to the engine unhindered through the open multiway valve 19. 
As soon as the electronic system 3 recognizes a slipping of the drive 
wheels, the position of both valves 2 and 19 is reversed. The multiway 
valve 19 closes, and the driver's direct influence on the engine is 
overridden. The control valve 2 is switched to evacuate. The actuating 
cylinder 4 is thereby evacuated via the second volume 11 and the seconf 
flow restrictor 10, by pressure equalization between volume 11 and 
actuating cylinder 4 and then slowly by flow of this equalized pressure 
via choke 4, so that the steep-drop characteristic mentioned above is 
achieved. 
As soon as the electronic system 3 recognizes that the slipping of the 
drive wheels has stopped, the control valve 2 is switched back into the 
position shown. The multiway valve 19, as a result of the delay of the 
timer 18, remains in the closed position, however. The renewed 
pressurization of the actuator cylinder 4 is now accomplished initially by 
the contents of the volume 9 and then by the volume 1 via the first flow 
restrictor 8. Here, too, pressurization is accomplished first rapidly by 
pressure equalization between volume 9 and actuating cylinder 4, and then 
slowly by restricted pressure equalization from additional volume 1. 
The check valve 17 makes certain that the driver, if necessary, can let up 
on the gas at any time, even if the multiway valve 19 is closed. In this 
case, the actuator cylinder 4 is evacuated via the check valve 17 and the 
pedal-operated valve 6.