Throttle positioning system

A valve is positioned by a control diaphragm which senses manifold pressure in an automotive engine and by an opposing biasing spring to create a control pressure, and a servo diaphragm positions the throttle in response to variations in the control pressure to thereby maintain the manifold pressure at a value determined by the spring bias. The vehicle operator positions the accelerator pedal to vary the spring bias and thus determine the value at which the manifold pressure is maintained.

TECHNICAL FIELD 
This invention relates to a throttle positioning system particularly 
suitable for use on an automotive engine. 
BACKGROUND 
The conventional throttle positioning system on an automotive engine is a 
mechanical linkage between the throttle and an operator control such as an 
accelerator pedal. In the conventional system, an input from the engine 
operator is directly converted to a particular throttle position, and 
abrupt movements of the accelerator pedal cause abrupt changes in throttle 
position and in the pressure in the engine induction manifold downstream 
of the throttle. In addition, changes in engine load cause the operator to 
move the accelerator pedal and throttle in search of a new throttle 
position which will provide the desired engine operation. 
It is well known that abrupt and unnecessary changes in throttle position 
and manifold pressure inhibit operation with minimum emissions and fuel 
consumptions and, in addition, lead to annoying shift patterns with some 
automatic transmissions. The operator of the conventional throttle 
positioning system therefore has the burden of avoiding abrupt and 
unnecessary changes in throttle position to enjoy minimum emissions and 
fuel consumption and smooth vehicle operation. 
SUMMARY OF THE INVENTION 
In the throttle positioning system provided by this invention, on the other 
hand, an input from the engine operator is interpreted as a command for a 
particular pressure in the engine induction manifold downstream of the 
throttle, and the throttle is positioned automatically to maintain that 
manifold pressure. 
The throttle positioning system provided by this invention is thus 
effective to maintain a substantially constant manifold pressure during 
nontransient engine operating conditions and to smoothly increase or 
decrease the manifold pressure during transient engine operating 
conditions. As a result, the engine is better able to operate with minimum 
emissions and fuel consumption and to provide smooth vehicle operation. 
In the preferred embodiment of this invention, a valve is positioned by a 
control diaphragm which senses the manifold pressure and by an opposing 
biasing spring to create a control pressure, and a servo diaphragm 
positions the throttle in response to variations in the control pressure 
to thereby maintain the manifold pressure at a value determined by the 
spring bias. The operator control--the accelerator pedal, for 
example--varies the spring bias and thus determines the value at which the 
manifold pressure is maintained. 
The details as well as other features and advantages of this invention are 
set forth in the remainder of the specification and are shown in the 
accompanying drawing.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to the drawing, an automotive engine induction passage 10 has a 
throttle 12 secured to a throttle shaft 14. A throttle lever 16 is 
operatively connected to throttle shaft 14, and a return spring 18 biases 
lever 16 against an adjustable stop 20 to move throttle 12 to the closed 
position shown. 
Throttle lever 16 is connected by a link 22 to a servo diaphragm 24 which 
forms a portion of a control pressure chamber 26. Control pressure chamber 
26 has a restricted connection 28 for sensing the subatmospheric manifold 
pressure in induction passage 10 downstream of throttle 12 and a 
restricted air bleed 30 sensing atmospheric pressure. 
Flow through air bleed 30 is controlled by a valve 32 mounted on a bracket 
34 which is secured to a control diaphragm 36. Control diaphgram 36 forms 
a portion of a chamber 38 which senses the manifold pressure in induction 
passage 10 downstream of throttle 12. Control diaphragm 36 exerts a force 
porportional to (and varying inversely with) manifold pressure in a 
direction tending to position valve 32 to reduce air flow through air 
bleed 30. The force exerted by control diaphragm 36 is opposed by the bias 
exerted by a spring 40 connected between bracket 34 and a vehicle 
accelerator pedal 42. Accelerator pedal 42 is biased to the position shown 
by a torsion spring 44. 
In operation, when the vehicle operator depresses accelerator pedal 42, 
moving it slightly counterclockwise to reduce the tension of spring 40, 
valve 32 moves leftwardly and reduces air flow through air bleed 30 which 
thereby reduces the subatmospheric control pressure in control pressure 
chamber 26. Servo diaphragm 24 then pulls throttle 12 counterclockwise 
against the return force of spring 18 to permit additional air flow 
through induction passage 10. The additional air flow increases the 
manifold pressure sensed by control diaphragm 36, and the force exerted by 
control diaphragm 36 is thus reduced to balance the force exerted by 
spring 40. 
Should the manifold pressure increase due to an increase in load, the force 
exerted by control diaphragm 36 will be reduced and valve 32 will be 
pulled rightwardly by spring 40 to increase air flow through air bleed 30. 
The increased control pressure sensed by servo diaphragm 24 will then 
allow return spring 18 to move throttle 12 in a closing direction to 
reduce the manifold pressure to the value determined by spring 40. 
Similarly, should the manifold pressure reduce due to a decrease in load, 
the force exerted by control diaphragm 36 will be increased to move valve 
32 leftwardly against the force exerted by spring 40 and reduce air flow 
through air bleed 30. The reduced control pressure sensed by servo 
diaphragm 24 will then open throttle 12 to increase the manifold pressure 
to the value determined by spring 40. 
When the operator releases accelerator pedal 42 and it is rotated clockwise 
by spring 44, the tension of spring 40 is increased to move valve 32 
rightwardly. The resulting increase in air flow through air bleed 30 
increases the control pressure sensed by servo diaphragm 24, and spring 18 
closes throttle 12 to reduce the induction passage pressure to the new 
value determined by spring 40. 
A valve 46 is provided to disconnect control pressure chamber 26 from the 
subatmospheric pressure sensed through connection 28 and to apply 
atmospheric pressure to control pressure chamber 26. At such times, servo 
diaphragm 24 exerts no opening force on throttle 12, and spring 18 returns 
throttle 12 to the closed position shown. Valve 46 is so operated whenever 
the vehicle brakes are applied. It will be appreciated that valve 46 need 
not necessarily disconnect control pressure chamber 26 from the 
subatmospheric pressure sensed through connection 28 by instead may simply 
open a large air bleed into control pressure chamber 26. 
It will be noted that in the preferred embodiment of this invention, the 
left side of servo diaphragm 24 forms a control pressure chamber 26 which 
senses subatmospheric pressure through connection 28 and atmospheric 
pressure through air bleed 30. It will be appreciated that, as an 
alternative, the right side of servo diaphragm 24 could form a control 
pressure chamber sensing superatmospheric pressure (from an air pump not 
shown) and atmospheric pressure through air bleed 30. The important 
characteristics of a throttle positioning system provided according to 
this invention are that the servo diaphragm exert a force which varies in 
inverse relation to the biasing force of a spring such as 40 and in direct 
relation to the force exerted by control diaphragm 36 and that the servo 
diaphragm move throttle 12 to vary the manifold pressure in direct 
relation to the force exerted by the servo diaphragm. In this manner, the 
system is effective to position the throttle to maintain the manifold 
pressure at the value determined by the force of spring 40. 
Thus it will be appreciated that this invention may be employed in a 
variety of other embodiments within the scope of the following claims.