GB2264995A

GB2264995A - Throttle assembly

Info

Publication number: GB2264995A
Application number: GB9205637A
Authority: GB
Inventors: David Pickman
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1992-03-14
Filing date: 1992-03-14
Publication date: 1993-09-15
Also published as: GB9205637D0

Abstract

A throttle assembly has a throttle body 10 defining a bore of generally rectangular cross section and a shaft 12 journalled in the throttle body for rotation about an axis perpendicular to the axis of the bore 14. The diameter of the shaft 12 corresponds to the length of one side of the cross section of the rectangular bore 14 and a part of the shaft disposed within the bore is waisted in such a manner that the shaft substantially obstructs the rectangular bore when in one angular position and opens the bore progressively as the shaft 12 is rotated from the latter position. The edge of the wasted portion is aerodynamically shaped. <IMAGE>

Description

THROTTLE ASSEMBLY Field of the invention The present invention relates to a throttle assembly for regulating the air flow to an engine.

Background of the invention The conventional way to control the air supply to an engine is by means of a so-called butterfly throttle. This comprises a throttle body with a circular through bore and a shaft journalled in the body for rotation about an axis perpendicular to the through bore. An arcuately profiled plate of a diameter slightly smaller than the bore is fitted to the shaft and can be rotated by the shaft between a closed position in which it substantially blocks all gas flow along the bore and a fully open position in which the plate lies parallel to the gas flow along the bore and presents a minimum obstruction.

Current design philosophies for throttle bodies suffer from several disadvantages relating primarily from the increased demands placed upon vehicle systems. With the adoption of electronic engine management and fuel injection systems, precise control of air flow is of increasing significance; especially within the idle / off idle region which controls low speed drivability.

This is compounded by the need to reduce idle speed in order to reduce emission levels, resulting in lower idle air flow requirements.

Within the idle / off idle region, the gap between the plate and housing (leakage path) has a significant effect on air flow.

A careful balance must therefore be maintained between minimising plate leakage and maintaining adequate clearance to ensure avoidance of potential plate on wall condition which can lead to throttle stiction at idle. This leads to increased design complexity with associated manufacturing costs. Furthermore, mounting of the butterfly plate on its shaft can only be carried out after the shaft has been inserted into the throttle body and this results in a labour intensive and costly assembly.

Object of the invention The present invention seeks to mitigate the foregoing disadvantages of a conventional butterfly throttle.

Summary of the invention According to the present invention, there is provided a throttle assembly having a throttle body defining a bore of generally rectangular cross section and a shaft journalled in the throttle body for rotation about an axis perpendicular to the axis of the bore, wherein the diameter of the shaft corresponds to the length of one side of the cross section of the rectangular bore and a part of the shaft disposed within the bore is waisted in such a manner that the shaft fully obstructs the rectangular bore when in one angular position and opens the bore progressively as the shaft is rotated from the latter position.

Preferably, the waisted portion of the shaft defines a thin rectangular plate lying on the diametral plane of the shaft and having the same dimensions as the cross section of the bore.

The throttle of the invention can be seen to differ from a conventional butterfly throttle in that the throttle bore is rectangular and in that the throttle plate is as wide as the diameter of the shaft that turns it. The fact the throttle plate is as wide as its shaft means that there is no problem sealing around the sides of the plate and the plate can be formed as an integral part of the shaft thereby simplifying its construction and assembly. The large diameter shaft allows accurate positioning of the throttle plate and sealing of the shaft relative to the throttle body can be effected simply by means of O-rings.

The cross section of the plate may be aerodynamically shaped to minimise obstruction to gas flow in the wide open throttle position and/or reduce the rate of increase in air flow with throttle plate rotation within the idle / off idle region.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an exploded side view of a throttle assembly of the invention, Figure 2 is a plan view of the throttle shaft and throttle plate of assembly shown in Figure 1, Figure 3 is a plan view of the assembled throttle body, and Figure 4 is a sectional side view of the throttle assembly in the wide open position.

The illustrated throttle assembly comprises a throttle body 10 which, as shown in Figure 3, has a rectangular through bore 14 through which air flows to the engine. A shaft 14 is mounted in the body 10 to intersect the bore 14. At each end, the shaft 12 comprises a circular support portion 12a, 12b received within a bearing 16, 18 in the throttle body 10 to allow the shaft 12 to be rotated about its own axis. A plate 12c defined by a waisted central portion of the shaft 12 extends between the support portions 12a, 12b and serves the same function as the butterfly plate in a conventional butterfly throttle.

When the throttle is closed, the shaft 12 is turned into a position in which the plate 12c substantially blocks the rectangular bore 14. In this position, plate leakage is minimised as the shorter sides of the plate are integral with the shaft and the ends of the shafts are sealed by Orings 20 in the bearings 16 and 18 so that full sealing can be effected around the entire periphery of the plate 12c.

When the shaft is rotated to wide open throttle from this position about its own axis, the plate lies edge on in the bore 14 and its cross section is aerodynamically shaped to minimise obstruction to air flow.

In the preferred embodiment illustrated, the throttle is provided with motor control and a sensor for providing a position feedback signal to the control circuitry. The sensor 40 is mounted on the throttle body 10 to the right of the shaft, as viewed in Figure 4. The shaft 12 has a splined end 12d which is acts as an input drive to the sensor 40. The sensor may be of any desired type, for example it may comprise a variable resistor or variable capacitance, which produces a signal representing the angular position of its input drive.

The other end 12b of the shaft 12 can be operated by a conventional cable but in the drawings is driven by a motor 40 also secured to the body 10 of the throttle unit. The motor 50 has an output cog 52 which meshes with an idler reduction gear 54 which is freely journalled about a pin 56 in the throttle body 10 by means of a bearing 58. The smaller diameter portion of the reduction gear 54 meshes with a toothed quadrant on a cap 62 which is fast in rotation with the end 12b of the shaft 12. A torsion spring 64 acts as a return spring biassing the quadrant 60 into a close throttle position against a stop.

When no current flows through the motor 50, the spring 64 biases the shaft 12 into a closed position. When current is supplied to the motor, as the motor output cog 52 turns, it drives the reduction gear 54 which in turn rotates the shaft 12 by acting on the toothed quadrant 60. The position of the shaft 12 is then sensed by the sensor 40 which then supplies a feedback signal to the control electronics to allow closed loop control of the throttle aperture.

Claims

1. A throttle assembly having a throttle body defining a bore of generally rectangular cross section and a shaft journalled in the throttle body for rotation about an axis perpendicular to the axis of the bore, wherein the diameter of the shaft corresponds to the length of one side of the cross section of the rectangular bore and a part of the shaft disposed within the bore is waisted in such a manner that the shaft fully obstructs the rectangular bore when in one angular position and opens the bore progressively as the shaft is rotated from the latter position.

2. A throttle assembly as claimed in claim 1, wherein the waisted portion of the shaft defines a thin rectangular plate lying on the diametral plane of the shaft and having substantially the same dimensions as the cross section of the bore.

3. A throttle assembly as claimed in claim 2, wherein the cross section of the plate is aerodynamically shaped to minimise obstruction to gas flow in the wide open throttle position and/or reduce the rate of increase in air flow with throttle plate rotation within the idle / off idle region.

4. A throttle assembly as claimed in any preceding claim, further comprising an angular position sensor for sensing the angular position of the shaft.

5. A throttle assembly as claimed in any preceding claim, further comprising an electric motor for rotating the shaft.

6. A throttle assembly constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.