Patent Publication Number: US-3877223-A

Title: Pressurized hot air choke

Description:
United States Patent [1 1 Layton Apr. 15, 1975 PRESSURIZED HOT AIR CHOKE [75] Inventor: John M. Layton, Howell, Mich.  
 [731 Assignee: General Motors Corporation,  
 Detroit, Mich.  
 [22] Filed: Feb. 27, 1974 21 Appl. No.2 446,282  
 [56] References Cited UNITED STATES PATENTS 5/1956 Hutchison 123/119 F 6/1965 Manning 123/119 F Primary Examiner-Douglas Hart Attorney, Agent, or Firm-J. C. Evans [57] ABSTRACT An improved choke control system for an internal combustion engine includes a two stage, hot air supply for heating a sealed thermostatic housing around a choke control coil. During high intake manifold vacuum at engine start, with the choke valve closed, hot air is drawn from a heat tube in an exhaust crossover passageway through the thermostatic housing by high engine intake vacuum. Following uncoiling of the choke coil and positioning of the choke valve in an open position, hot air recirculation across the unwound coil is maintained under reduced intake manifold vacuum conditions by operation of a reactor air pump at a higher discharge pressure to produce a positive pressure flow of air from the pump through the heat tube to force hot air through the thermostatic housing and out a manifold vacuum port to the thermostatic housing.  
 2 Claims, 1 Drawing Figure PRESSURIZED HOT AIR CHOKE This invention relates to internal combustion engine fuel supply systems of the type having thermostatic choke coils for positioning the carburetor choke valve between an engine start, closed position and an open position following engine start and more particularly to such systems which have a sealed thermostatic housing around the choke coil and means for directing circulation of hot air across the coil to unwind the coil to open said choke valve once the engine has attained a predetermined operating temperature.  
  Thermostatically controlled choke valves in carburetors have a flow of heated air across the thermostatic coil of the choke valve controller maintained by. a sealed thermostatic housing connected to a source of vacuum such as the intake manifold of a vehicle. In such systems, hot air circulation is maintained across the coil by means of the high intake manifold vacuum that is produced under engine start conditions with the choke valve closed. However, in such systems, when the choke valve is opened and the engine is operated under wide open throttle, it is possible &#39;to reduce the intake manifold vacuum to a level where hot air is no longer drawn through the sealed thermostatic housing. Accordingly, the choke coil may cool so as to cause the choke valve to move into a closed position to produce unexpected enrichment of the air-fuel ratio to the in take manifold with a resultant flooding of the engine.  
  Accordingly. an object of the present invention is to include means in association with a sealed thermostatic housing of a choke coil controlled carburetor choke valve with means to maintain a continuous circulation of hot air through the sealed thermostatic housing under reduced intake manifold vacuum conditions so as to prevent a reduction in the temperature of the thermostatic coil that might close the carburetor choke valve to flood the engine.  
  Still another object of the present invention is to include means to sustain recirculation of hot air through the thermostatic coil housing ofa choke valve with the intake manifold vacuum substantially reduced under wide open throttle operation and to do so by means that require little or no modification to existing engine components.  
  Still another object of the present invention is to provide an improved combination reactor air injection pump supply system and vacuum induced hot air recirculation through a thermostatically controlled choke valve wherein means are provided to cause recirculation of air from the outlet of an engine driven reactor air injection pump through a heat pipe thence through a sealed thermostatic choke coil enclosure in response to reduced vacuum in the intake manifold of the engine so as to cause hot air flow across a thermostatic coil to open a choke blade following engine start and wherein the heat flow is maintained across the choke valve thermostatic coil during wide open throttle conditions by maintenance of an increased pressure level at the discharge of the engine driven reactor air injection pump during wide open throttle conditions so as to maintain a pressure differential across the heat pipe during wide open throttle conditions that will maintain a circulation of heated air across the coil back to the intake manifold of the vehicle to prevent cooling of the choke COll and a resultant movement of the choke valve toward a closed position to flood the engine.  
  Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.  
 IN THE DRAWING The single illustration is a diagrammatic. view of an automatic choke system for an internal combustion engine including the present invention.  
  In the drawing, a carburetor 10 is illustrated having a bore 12 therein for directing air into the intake manifold of an internal combustion engine. A choke valve 14 is pivotally mounted by means of a pin 16 in the upper end of the bore 12. It is under the control of a thermostatic controller 18 having a spiral formed bimetallic element or choke coil 20. The choke coil 20 is fixed at one end to a pin 22 on a cover 24. It has the opposite end 26 thereof connected to a lever 28 which is moved arcuately as heat increases to unwind the coil 20. The lever 28 is connected to a fast idle cam 29 and a choke rod 30, to an upper choke lever 32. Lever 32, as viewed in the drawing, will be rotated in a clockwise direction as the coil 20 unwinds so as to move the choke valve 14 from its engine start closed position into an open position after the engine is heated.  
  In the illustrated arrangement, the coil 20 is enclosed by a cup-shaped housing 34 with cover 24 secured thereon by means of a plurality of screws 36. The cover 24 and housing 34 define a sealed space 38 within the housing 34 which is in communication with a vacuum bleed opening 40 that communicates with the intake manifold of the internal combustion engine.  
  The housing further includes a heat inlet port 42 with a fitting 44 thereon to which hot air is supplied during both a high vacuum condition within the space 38 which occurs under engine start conditions and a reduced intake vacuum condition as may occur under wide open throttle conditions with the choke valve 14 open. More particularly, the heat inlet fitting 44 is in communication with a two. stage hot air source 46 including a reactor air injection pump 48 operated in accordance with engine speed to supply air to an engine exhaust valve reactor system (not shown). The air reactor pump 48 has an inlet 50 from atmosphere and an outlet conduit 52 to the exhaust valve reactor ports. In the illustrated arrangement, the outlet conduit 52 includes a tee fitting 54 therein connected to a conduit 56. The conduit 56 is in communication with the inlet of a choke heat tube 58 supported within the interior of an exhaust heat cross-over passage 60 formed in the intake manifold 62 of an internal combustion engine so as to produce a heat source for preheat of an air supply to the thermostatic controller 18. The heat tube 58 has an outlet connected to a heat supply pipe 64 which is connected to the inlet heat fitting 44 to the thermostatic housing 34.  
  During a startup phase of operation, the thermostatic coil 20 is wound so as to position the lever&#39;28 to.move the choke rod 30 upwardly as shown in the illustrated figure. This rotates the choke valve 14 into a closed position under cold engine conditions. Thus, the bore 12 is sealed and an increased intake manifold vacuum will be produced at the port 40. This produces a reduced pressure condition in the chamber 38 of the theremostatic controller 18. Under these engine start conditions, the reactor air injection pump 48 is operated at fast idle but well below acceleration conditions that might occur under operating engine conditions. The increased vacuum within the chamber 38 at engine start will, however, be sufficient to draw air from the outlet conduit 52 of the pump 48 thence through the conduit 56, the heat tube 58 and the pipe 64. The input air from the compressor discharge conduit 52 is heated in the tube 58 and will be drawn through the enclosure 38 and across the coil 20 so as to cause it to heat and unwind. When the coil is unwound, it will move the choke valve 14 to an open position once the engine is at operating temperature. Thus, during this phase of operation, irrespective of the speed of operation of the reactor air injection pump 48, air will be drawn continuously by the high level intake manifold vacuum through the heat pipe 58 by the sucking action of the vacuum 40 in the housing 34. Thus, when the engine is running at high vacuum levels, there is always a stream of hot air on the choke coil.  
  In such systems, however, when the accelerator is positioned in wide open throttle positions, the intake manifold vacuum will be substantially reduced so that there is no effective vacuum to suck air through the hot air source 46. Under such circumstances, it is possible for the choke coil 20 to cool and thereby position the choke valve 14 closed producing a resultant unexpected enrichment of the fuel supply to the intake manifold system to flood the engine.  
  By use of the two stage source 46, however, under wide open throttle conditions the pump 48 will follow engine speed and will thereby produce an increased discharge pressure of approximately psig. This represents a pressure stage that is sufficient to produce a pressure differential across the tube 58 to cause hot air to continue to flow from the discharge conduit 52, through the conduit 56, the heat tube 58 and the heat supply pipe 64 through the inlet heat fitting 44. As a result, notwithstanding the reduction of inlet vacuum in the chamber 40, hot air recirculation is maintained through the chamber 38 and is discharged through the vacuum port 40 into the inlet manifold. Thus, under wide open throttle conditions a constant flow of warm air is maintained on the choke coil 20. Accordingly, it will be maintained unwound so as to hold the choke valve in an open position thereby to prevent a transient open throttle cooling of the coil. As a result, the engine will have a proper fuel supply ratio maintained thereto under both engine start and wide open throttle conditions irrespective of the vacuum conditions within the intake manifold of the vehicle.  
  While the embodiments of the present invention, as herein disclosed, constitute a preferred form, it is to be understood that other forms might be adopted.  
 What is claimed is:  
  1. In an automatic choke of the type including a choke valve, and means including a thermostatic choke coil to operate the valve in accordance with engine heated air directed to a thermostatic housing enclosing the choke coil through a heat inlet fitting on said thermostatic housing, thence to an inlet manifold vacuum port connected to said thermostatic housing for pro ducing a vacuum therein, the improvement comprising:  
 means defining an exhaust crossover passage, a heat tube located within said exhaust crossover passage hav&#39; ing an inlet and outlet, a heat pipe connected to the outlet of said heat tube and including an outlet end thereon connected to the heat inlet fitting, a reactor air injection pump having a discharge conduit, means driving said pump in accordance with engine speed, means communicating said discharge conduit with the inlet of said heat tube, the manifold vacuum port in said thermostatic housing being operative when the engine is running at high intake manifold vacuum levels to suck a stream of hot air from the pump discharge conduit through said heat tube for heating air therein by exchange from the exhaust crossover passageway thence through &#39;said heat inlet for heating said cho&#39;ke coil to cause it to operate said choke valve into an open position, said reactor air injection pump operating at increased speed at wide open throttle conditions to produce an increased pressure in said discharge conduit and at the inlet of said heat tube to cause air to be directed therethrough for discharge through said heat inlet to said thermostatic housing when there is a reduced engine vacuum whereby hot air circulation through said thermostatic housing is maintained to produce a constant flow of air on the choke coil to prevent windup of the choke coil to close the choke valve following engine start operation.  
  2. In an internal combustion engine fuel supply system of the type including an air-fuel bore with a choke valve therein operated by a choke control mechanism including a thermostatic choke coil having a surrounding thermostatic housing with a vacuum opening therein connected to engine intake manifold vacuum and a heat inlet fitting thereto the improvement comprising: means forming an exhaust crossover passage, a heat tube located within said crossover passageway including an inlet and an outlet, an air pressure pump for supplying reactor air to the engine including an outlet therefrom, means for communicating the outlet of said pump to the inlet of said heat tube, means for connecting the outlet of said heat tube to the heat inlet fitting of said thermostatic housing, said air reactor pump having a reduced discharge pressure under engine start conditions and said thermostatic housing having a high engine vacuum directed thereto when the choke valve is closed to draw air from the pump outlet through said heat tube into the thermostatic housing to cause a flow of warm air across the choke coil to produce an unwinding of the coil and a resultant positioning of the choke valve in an open position following engine start, said pump being operative in response to wide open throttle conditions to produce an increased discharge pressure level operative to maintain flow of air through said heat tube during reduced vacuum conditions within said thermostatic housing following engine start to produce a continuous recirculation of hot air through the housing so as to maintain the thermostatic coil in an unwound position to prevent engine flooding produced by closure of the choke valve during reduced intake manifold vacuum conditions following engine start.