Apparatus for preventing excessive running speed for internal combustion engine, especially for motor vehicles

Apparatus for preventing overspeeding of an engine is provided. In preferred embodiments, an hydraulically actuable clutch is controlled by a piston-cylinder arrangement connected to a driver operable clutch pedal. The rear side of the piston in this arrangement is selectively communicated with a high pressure air source and an exhaust space by means of a solenoid valve. The solenoid valve is controlled by a tachometer switch so that the same communicates the high pressure medium to automatically actuate the disengagement of the clutch whenever a predetermined set engine speed is exceeded. The pressure medium space at the side of the piston is also communicated with a further piston-cylinder arrangement for automatically forcing an engine accelerator pedal toward a no-load engine running condition at the same time the clutch is automatically disengaged. An emergency switch is provided for overriding the clutch disengaging apparatus so as to accommodate intentional usage of the engine as a brake.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to apparatus for the avoidance of 
overspeeding of a combustion engine, especially an internal combustion 
engine for an automotive vehicle. More particularly, the invention relates 
to such an apparatus which utilizes a disengageable clutch which is 
connected in a drive train for the drive of an automotive vehicle, such as 
in conjunction with the shifting transmission. 
It is known that considerable damage can result to an engine when it is 
operated at speeds above its highest desirable speed or rotational speed, 
especially if so operated for a long period of time. In certain 
circumstances with automotive vehicle engines, such damage can affect the 
safety of the vehicle, the vehicle passengers, and also other traffic 
vehicles. Since such overspeeding results often only from inattentiveness, 
the invention is directed to the problem of creating an arrangement which 
automatically undertakes the supervision of the running speed and the 
automatic initiation of appropriate counter-measures. Such an arrangement 
should preferably be simply constructable and operationally safe. 
According to the invention, these above-noted problems are solved by 
providing effective adjustment apparatus for the clutch so as to 
automatically disengage the clutch upon the reaching of a predetermined 
speed of the engine. The selected predetermined speed for the apparatus is 
advantageously chosen such that it is slightly under the permissible 
highest operational speed of the engine, so that, considering the inertia 
of the apparatus, a proper disengagement of the gears is possible. 
According to preferred embodiments of the invention, the control is such 
that the clutch can be mechanical, pneumatic, hydraulic or electric. The 
control can also be specifically directly for the clutch itself, as well 
as also for its existent activating part or linkage. 
The invention also contemplates the general idea of separating or 
interrupting the drive train from the engine or motor to the driving 
wheels automatically, in dependence on the reaching of a predetermined 
critical engine speed. The disengaging impulse for the drive train can, in 
practical appropriate embodiments, be controlled by engine speed dependent 
frequencies; e.g., in dependence upon the generator or a mechanical 
control signal. It is also contemplated within the framework of the 
invention for the selected predetermined engine speed to be made to be 
adjustable so as to accommodate certain desired different driving styles 
(sport driving or maximum economy driving, for example). It is also 
contemplated to coordinate different predetermined engine speeds for 
individual gears in order to prevent excessive speed operation in the 
lower gears during acceleration. 
According to a further development of the inventive concept, the 
arrangement can be so constructed that the arrangement for activating the 
clutch is also effective to regulate the engine in the sense of an 
adjustment for no-load running. In this way, it is established in each 
case that the engine will not by chance run away (excessive overspeeding) 
if, for whatever reasons, the driver keeps his foot on the throttle pedal 
upon activation of the clutch disengaging apparatus of the invention. 
Further, there are driving situations where, for safety reasons, an 
overrunning or overspeeding of the engine beyond the predetermined highest 
desired operational speed is necessary. For example, if the brakes fail, 
such intentional overspeeding may be required for braking purposes. For 
this reason, the present invention further proposes that an emergency 
switch or the like be provided for the intentional shut-off or cut-out of 
the control apparatus for the disengagement of the clutch. 
Modern vehicle clutches are frequently hydraulically operated in such a 
manner that a first piston-cylinder arrangement directly controls the 
engagement and disengagement of the clutch, with a second piston-cylinder 
arrangement being operated by a clutch pedal in such a manner as to 
selectively apply pressure to the first cylinder arrangement. With such a 
clutch arrangement, the invention proposes that the second or activating 
cylinder connected with the clutch pedal, on the back side thereof, is 
pressurizable by a pressure medium controlled by a solenoid valve with the 
activating circuit for such solenoid valve being controlled in response to 
an engine speed responsive switch (tachometer switch) set to close the 
activating circuit when the engine exceeds a predetermined set speed. 
The engine tachometer switch, in accordance with a first embodiment of the 
invention, operates so as to control the reengagement of the clutch after 
the slowing down of the engine below a selected speed, with consequent 
advantages of automatic continuous operation of the vehicle system. 
However, in accordance with a second preferred embodiment of the 
invention, the clutch is maintained in a disengaged position until further 
intentional activation of same by the vehicle driver. In this 
last-mentioned arrangement, the control of a relay for the solenoid valve 
is to be equipped with a stopping circuit, including a switch for 
controlling deactuation of the solenoid valve. 
According to a further preferred embodiment of the invention, it is further 
proposed that the pressure medium supplied to the activating cylinder for 
controlling the clutch is also connected to a further pressure medium 
cylinder, the piston of which further cylinder is operable to move an 
engine speed control rod in a direction corresponding to a decreasing 
engine load upon the pressurization of the mentioned cylinders. In this 
way it will be in each case assured that the engine is returned to a 
no-load running speed situation irrespective of the position that the 
driver maintains his foot on the accelerator pedal.

Clutch 10 is hydraulically controlled, and includes engaging and 
disengaging linkage connected with piston-cylinder arrangement 11. 
Piston-cylinder arrangement 11 is pressurized in response to the pressure 
in piston-cylinder arrangement 12, which in turn is controlled by clutch 
pedal 13. A reservoir 14 is coordinated to the cylinder 12 in order to 
compensate for any eventual leakage losses of the hydraulic fluid. The 
just-described hydraulic clutch control operation is in itself known and 
therefore is not the subject of the present invention by itself. 
The piston 15 in cylinder 12, which is normally activated by clutch pedal 
13, has a space 12a at the rear thereof which is connected with line 16 
for supplying pressurized air thereto. A solenoid valve 17 is arranged in 
the supply to line 16, which solenoid valve is configured to normally 
exhaust line 16 via line 18. However, upon actuation of solenoid valve 17, 
the supply to line 16 is connected with a pressurized air container 19. 
The space 12a in cylinder 12 is at the same time connected through the 
line 20 with a further pressure medium cylinder 21. The piston 22 in 
cylinder 21 is connected with an engine accelerator pedal or drive pedal 
23 in such a manner that, upon pressurization of lines 16 and 20, the 
drive pedal 23 is automatically adjusted in the sense of a decreasing load 
(in the direction of no-load running of the motor). 
The activating circuit 24 for the solenoid valve 17 is controlled by 
contact switch 25 of a relay 26. The activating circuit 27 for relay 26 is 
responsive to speed switch (tachometer or rotational speed responsive 
switch) 28. The tachometer switch 28 is preset at a predetermined engine 
speed which is slightly under the highest desired permissible speed for 
the engine. The tachometer switch 28 is usually in a position so as not to 
close the circuit 24 controlling the solenoid valve 17, but is movable in 
response to excessive engine speed over the predetermined set engine speed 
to activate the circuit 24 for the solenoid valve 17, with the resultant 
communication of high pressure chamber 19 with line 16. Activating circuit 
for solenoid 17 is also provided with an emergency switch 29, which is 
normally closed. The vehicle driver can intentionally open this switch 29 
when he wishes to render the apparatus for deactivating the clutch 
inoperational. 
As long as the engine operates under the preset selected speed for the 
tachometer switch 28, the solenoid valve 17 remains in the shown position. 
That means that the space 12a behind piston 15 is unpressurized. 
Consequently, the clutch 10 can be operated in the normal usual manner by 
way of clutch pedal 13, into and out of engagement. In the event the 
preset highest speed for the engine is exceeded, as determined by the 
tachometer switch 28, the relay 26 is automatically activated to close 
with its contact 25 the circuit 24 of the solenoid valve 17. The solenoid 
valve 17 operates against the spring 30 to move to its other position in 
which the space 12a of cylinder 12 is pressurized with high pressure air 
from the chamber 19. The piston 15 in cylinder 12 will also, in a manner 
exactly as if activated by clutch pedal 13, move so that the 
piston-cylinder arrangement 11 releases the clutch 10. This will separate 
the connection between the motor and the transmission so that the motor 
cannot exceed its highest desired speed. Simultaneously, the piston 22 in 
cylinder 21 is pressurized to therefore control the movement of 
accelerator pedal 23 in the direction of no-load running of the motor. 
Upon disengagement of the clutch, the motor returns to its no-load 
rotational speed or at least to a substantially reduced rotational speed. 
Now if the tachometer 28 senses reduction of the engine speed below the 
predetermined high speed, the relay 26 is deactivated and the activating 
circuit 24 for the solenoid valve 17 is opened so that this valve 17 is 
switched again to the shown released condition. The space 12a then becomes 
again unpressurized and the clutch 10 is again engaged. In this situation 
it is very advantageous, according to the preferred embodiments of the 
invention, if special precautions are made to prevent oscillations of the 
system. For example, such can be provided at the tachometer 28 itself by 
way of a certain hysteresis in the tachometer system. Other possibilities 
contemplated by the invention are the arrangement of throttles in the 
exhaust lines 18 and, finally, the provision of a stopping circuit for the 
relay 26, which stopping circuit can only intentionally be further 
separated after the closing of switch 25 by relay 26. This last-mentioned 
arrangement is advantageous if one wants to undertake the reengagement of 
the clutch intentionally anyhow. 
When it becomes absolutely necessary due to certain reasons of travel 
conditions to have an overspeeding of the engine, such as in the case of 
failure of brakes, then the driver can open the emergency switch 29 so as 
to separate and deactivate the circuit 24. In this condition, activation 
of the solenoid valve 17 is impossible by way of the tachometer switch 28 
so that disengagement of the clutch is not effected and the motor can be 
used for braking. 
While we have shown and described several embodiments in accordance with 
the present invention, it is understood that the same is not limited 
thereto but is susceptible of numerous changes and modifications as known 
to those skilled in the art and we therefore do not wish to be limited to 
the details shown and described herein but intend to cover all such 
changes and modifications as are encompassed by the scope of the appended 
claims.