Motorized throttle body

Throttle body in which on the internal wall of the feed pipe there is provided at least one channel the base of which defines together with external edge of the butterfly valve at least one limp-home flow and in which on the internal wall of the feed pipe there is provided a curvilinear section, adjacent to the channel, the base of which defines together with the external edge of the butterfly valve at least one idling flow.

BACKGROUND OF THE INVENTION 
The invention relates to a motorized throttle body, particularly a throttle 
body suitable for being inserted along an intake manifold of an internal 
combustion engine, to which the discussion which follows will make 
explicit reference without thereby losing generality. 
Motorized throttle bodies are currently known which comprise a feed pipe, 
through which a comburent fluid (air), or a comburent fluid/fuel mixture 
reaches the engine's intake manifold; a butterfly valve housed in a 
movable manner inside the feed pipe and suitable for choking the flow of 
comburent fluid as a function of its position; and an operating device 
suitable for selectively moving the butterfly valve to control the flow of 
the comburent fluid. 
FIG. 1 shows the flow curve of a throttle body which uses a complex 
kinematic mechanism which is required to achieve the equilibrium position 
at point LH, which defines the state in which the actuator used to move 
the butterfly valve malfunctions or is not supplied at all because of a 
breakdown in the current supply unit (limp-home state). In FIG. 1 the 
angle .alpha..sub.mn, which defines the angle at which there is the 
minimum flow Q.sub.mn, is close to the minimum angle achievable by the 
butterfly, whilst the angle .alpha..sub.lh, which denotes the limp-home 
angle, is positive and greater than the preceding angle. The system 
proposed to control the angular movement of the butterfly valve is rather 
complex to operate in that the characteristics of the springs used have a 
discontinuity around the angle .alpha..sub.lh. 
FIG. 2 shows the curve of operation of a negative limp-home system. In this 
case the minimum flow Q.sub.mn corresponds to zero (.alpha..sub.mn =0) 
whilst in general the opening of the butterfly valve itay range from 
-90.degree. and +90.degree.. Although there are undoubted advanstages of 
simplicity, with this system it is, however, extremely critical to 
guarantee that the flow at the low point is situated at a very precise 
value defined by specification; contact between butterfly valve and pipe 
in correspondence with the angle .alpha.=0.degree. is also possible if the 
butterfly valve has not been fitted correctly. 
From the above it will be clear that even though the system works with the 
flow curves shown in FIG. 1 or FIG. 2, it is difficult to operate and 
involves considerable complications in the electronic devices used to 
control it. 
SUMMARY OF THE INVENTION 
The object of the invention is to remedy the above-mentioned disadvantages 
in a simple and effective manner. 
The invention provides a motorized throttle body suitable for being fitted 
along an intake manifold of an internal combustion engine; this throttle 
body comprising a feed pipe, a butterfly valve housed in movable manner 
inside the feed pipe so as to define between its internal wall and the 
external edge of the butterfly valve a plurality of states of supply of a 
comburent fluid or of a comburent fluid/fuel mixture; this throttle body 
further comprising an operating device suitable for selectively moving the 
butterfly valve; throttle body characterized in that on the internal wall 
of the pipe there is provided a channel the base of which defines together 
with the external edge of the butterfly valve a limp-home flow (Q.sub.lh) 
and further characterized in that on the internal wall of the pipe there 
is provided a curvilinear section, adjacent to the channel, the base of 
which defines together with the external edge of the butterfly valve an 
idling flow (Q.sub.mn).

DETAILED DESCRIPTION OF THE INVENTION 
With reference to FIGS. 4, 5, in its entirety 1 denotes a motorized 
throttle body preferably suitable for being inserted along an intake 
manifold (not shown) of an internal combustion engine (not shown). 
The throttle body 1 comprises a feed pipe 2 inside which there flows, in 
the example shown, a comburent fluid or a comburent fluid/fuel mixture, 
which passes through the said intake manifold (not shown) of the internal 
combustion engine; a butterfly valve 3, housed in movable manner inside 
the pipe 2 and suitable for choking the flow of the comburent fluid as a 
function of its angular position inside the said pipe 2; and an operating 
device (not shown in the accompanying drawings) suitable for selectively 
moving the butterfly valve 3 to control the flow of fluid. In its turn the 
operating device is controlled by a control unit which is also not shown. 
It should be said incidentally that in FIG. 4, the anti-clockwise direction 
defined by the arrow 4 has been considered as the positive direction of 
rotation of the butterfly valve 3; the various elements and positions will 
therefore be defined, one with respect to the other, by the order in which 
they are located with respect to this direction of rotation. 
In FIGS. 4 and 5 the extension of the central line of symmetry of the 
butterfly valve 3 meets, in particular, the wall 5 of the feed pipe 2 at: 
a point IM, defined as the point of impact of the valve 3 at which there is 
the impacting of the valve 3 in the pipe 2; in other words it is at point 
IM that there is contact between the valve 3 and the pipe 2; 
a point LH, defined as the limp-home point, for which a flow is assured 
such as to permit the operation of the engine even in the event of 
breakdown or lack of supply to the actuator which acts on the valve 3; and 
a point MN, such as to permit a minimum flow of supply to the engine. 
FIG. 5 shows a channel 6, the base 7 of which defines together with the 
circular external edge 8 of the butterfly valve 3 a flow Q.sub.lh such as 
to permit the running of the motor vehicle even if there is no supply to 
or poor operation of the operating device of the butterfly valve 3. 
The butterfly valve 3 is adjusted from point IM to point LH by means of an 
adjusting screw not shown in the accompanying drawings. 
The LH position of the butterfly valve 3 in the limp-home position, which 
defines the limp-home flow Q.sub.lh as has been said, must comply with two 
conditions at the same time: 
(A) the relative angle between the LH position and the IM position must be 
such as to prevent impacts during the operation of the device 1; 
(B) the flow Q.sub.lh at the LH point (or position) must comply with a very 
accurate value (limp-home value) defined by the specification which is 
usually dependent on the requirements of the internal combustion engine. 
A suitable dimensioning of the channel 6 enables the position of the LH 
point to be defined so that the above-mentioned conditions A and B are 
met. 
It should be understood that even though only one channel 6 is shown in the 
accompanying drawings, the arguments put forward in this description apply 
to any number of channels 6. 
The optimum values for the dimensions of the channel 6 found by the 
Applicant will be defined in greater detail below. 
The channel 6 may be obtained directly by moulding or with specific working 
on a machine tool. 
If the butterfly valve 3 is not controlled because the actuator used to 
move it is not operating, this butterfly valve 3 is placed in the LH 
position by a return spring which is not shown in the accompanying 
drawings. 
When the engine is to operate in normal conditions, however, the actuator 
suitable for moving the valve 3 will position it in the desired positions, 
all above the MN conditions, and it will be operated if the engine is to 
idle. 
The section above the MN point will have a form suitable for producing, 
together with the external edge of the butterfly valve 3, a curve of flow 
as a function of the angle defined by the specification and dependent on 
the engine's requirements. 
The MN position must comply with the following condition: 
(C) the flow of the comburent air or of the mixture in correspondence with 
it must comply with an established value (blow-by flow) defined by the 
specification of the device and usually dependent on the dimensions of the 
feed pipe 2. 
It is easy to check from a study of FIG. 3 that the value of the flow Qlh 
when the butterfly valve 3 is at point LH is greater than that, Q.sub.mn, 
which there is when the said butterfly valve 3 is at the point MN 
corresponding to the case of engine idling. In other words, this means 
that the flow of comburent air Q.sub.lh for the limp-home situation is 
greater than that which there is when the internal combustion engine 
supplied by the pipe 2 is idling (Q.sub.mn). 
The form of the section 9 will be chosen on the basis of the desired 
specifications of flow Q.sub.mn. 
To obtain low values of Q.sub.mn, this profile must be of curvilinear form. 
Reference should be made to FIG. 6 in this connection, which compares the 
flow curves when the section 9 is shaped according to a cylindrical 
profile (continuous curve A) and according to a curvilinear profile 
(continuous curve B). These curves are superimposed on those which would 
be obtained in the absence of the channel 6 and which are shown in broken 
lines. It will be noted how in the presence of the channel 6 (continuous 
line curves A, B) the curvilinear form of the section 9 is essential for 
the purpose of obtaining low flow values. 
To have an order of magnitude it can be stated that for a feed pipe of 44 
mm diameter fitted with channel 6, the curvilinear section 9 may enable 
flows Q.sub.mn &lt;6 kg/hr to be obtained. 
For greater clarity FIG. 3 shows a diagram which has the angle .alpha. in 
degrees on the abscissa and the flow Q of the fluid passing through the 
feed pipe 2 on the ordinate. 
Like FIGS. 1 and 2, FIG. 3, which shows the fluid flow curve as has been 
said, denotes by .alpha..sub.lh the angle corresponding to the position LH 
in which there is a flow Q.sub.lh, whilst .alpha..sub.mn denotes the angle 
corresponding to the position MN at which there is a flow Q.sub.mn. 
The following relationship exists between the moduli of these angles: 
EQU .alpha..sub.lh &lt;.alpha..sub.mn 
Furthermore, with reference to the various positions shown in FIGS. 4 and 5 
and assuming as positive the angles in the anti-clockwise direction 
defined by the arrow 4, the result is that: 
EQU .alpha..sub.lh &gt;0 .alpha..sub.mn &gt;0 
If, as has already been stated, Q.sub.lh and Q.sub.mn denote the flows in 
the position LH and the position MN respectively, there is the following 
relationship: 
EQU Q.sub.lh &gt;Q.sub.mn 
To have an order of magnitude it can be said that with a feed pipe 2 of 44 
mm diameter it is possible to have a value of Q.sub.lh equal to 10 kg/hr 
and of Q.sub.mn equal to 4 kg/hr. 
From FIG. 3 it is also clear that the device for adjusting the angle 
relating to the position LH (not shown in the drawings) enables the flow 
Q.sub.lh to be accurately regulated and that the value of this flow may be 
different with equal geometry of the pipe 2, of the diameter of the 
butterfly valve 3 and of the geometry of the channel 6; in fact, by acting 
on the above-mentioned adjustment and thus varying the value of the angle 
which determines the position LH, the section of passage of the air or 
mixture is varied; the value which the flow Q.sub.lh may assume varies 
between Q.sub.im and Q.sub.mn and complies with the following equation: 
EQU Q.sub.im &gt;Q.sub.lh &gt;Q.sub.mn 
where Q.sub.im is the flow relating to the position IM of the valve 3. 
By comparing FIG. 3 with FIGS. 1 and 2 already discussed above and showing 
the most common embodiments of the prior art, it may be noted that the 
throttle body 1 produced according to the specifications of FIG. 3 has a 
flow curve that is completely different from those relating to the known 
devices. 
In fact, in the case of the throttle body 1 to which the invention relates 
and which is shown in FIGS. 3, 4 and 5, the butterfly valve 3 is subjected 
to the action of a spring or of a group of springs (not shown in the 
accompanying drawings) which all act in the same direction of rotation. 
The elastic characteristic of this spring is shown in FIG. 7. 
By using one or more springs of the same direction, the problems relating 
to the control of the operating device suitable for moving the butterfly 
valve 3 during the transient phases of passage from one state to another 
are solved in a simple and effective manner. As has been said, this spring 
has the task of pushing the butterfly valve 3 into the position LH when 
there is a breakdown of the actuator or no supply, a condition in which 
the said actuator is no longer capable of controlling the position of the 
valve 3.