Abstract:
A multi-cylinder diesel engine provides split mode operation in which one or more cylinders function as air pumps. Compressed air supplied by the cylinders is amplified and stored to a high pressure air tank from which it may be used to run air brakes or other systems. Improved energy density is achieved over prior art vehicle air systems and an auxiliary air compressor is eliminated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to air compression systems and more particularly, to a pressure amplifying pneumatic pump system operating off of air pumped by a non-firing cylinder of an internal combustion engine. 
     2. Description of the Problem 
     Designers of internal combustion engines have long appreciated that such engines can function as air pumps. For example, U.S. Pat. No. 3,365,014 to Clingerman describes a multi-cylinder diesel engine adapted to operate as a self-powered air compressor. This engine provides for shutting off the flow of fuel to a bank of cylinders and then diverting the air pumped by the cylinders to an auxiliary outlet for use. The cylinders continuing to receive fuel power the vehicle and the air pumping cylinders. The compressed air made available can be used to operate auxiliary equipment on the vehicle. 
     An example of an opportunity to recapture kinetic energy of a vehicle which is otherwise lost during braking would be to use the engine as a pump to compress air. Engine compression braking has long been used as an auxiliary braking system on diesel engine equipped trucks. An example of such a system is the widely used Jepsen engine brake. Engine compression braking operates by cutting off fuel to the cylinders and coupling the vehicle&#39;s momentum back to the pistons through the drive shaft. The cylinders&#39; intake valves operate to allow air to be drawn for compression strokes, but the cylinders&#39; exhaust valves are opened at or just before top dead center (TDC) of the pistons&#39; cycles to exhaust the compressed air. The energy expended to compress the air in the cylinders is lost through the exhaust and no rebound energy is returned to the crankshaft through the pistons during the expansion portions of the piston strokes. In this way a substantial portion of an engine&#39;s rated power can be applied to braking. An engine incorporating engine compression braking would seem well adapted for operating as an engine pump to recover a proportion of vehicle energy otherwise wasted during braking. 
     Unfortunately, diverting engine cylinders for use as air compression pumps provides relatively little practical pressure gain. A non-firing cylinder in a diesel engine reliably generates a pressure of about 200 psi and can, under some circumstances, develop 300 psi. Absent modification of the cylinder not even these limited pressures are available for use though. The air typically must be released to some portion of the exhaust system, resulting in a substantial pressure drop. Assuming diversion of the air using a butterfly valve and check valve positioned as close to the exhaust valve from the cylinder as practical, an exhausted air pressure of perhaps 100 psi will be generated. Such low pressures have worked against using the engine itself an air compressor. 
     As a consequence, pressurized air is usually provided from an auxiliary pump driven by a belt off of the engine. Unless the pump is clutched, this arrangement constitutes a parasitic drag on the engine and has been criticized for this reason. If the system is clutched it adds weight and complexity to the vehicle. Baguelin, U.S. Pat. No. 4,492,192, proposed modifying one cylinder of a diesel engine to introduce an extra valve as an outlet for compressed air to make the cylinder more effective as an air pump. Such a cylinder, while achieving better pressures than 100 psi, is still limited by the compression ratio of the engine. It is also possible to couple air pumps to the vehicle wheels with clutches to provide kinetic energy recapture during braking. These proposals are mechanically complex. 
     SUMMARY OF THE INVENTION 
     One object of the invention is to improve the efficiency of motor vehicles equipped with internal combustion engines. 
     Another object of the invention is to provide an engine driven, high pressure air compression system for use on a motor vehicle. 
     Still another object of the invention is to eliminate the need for auxiliary, belt driven air compressors. 
     Yet another object of the invention is to provide a vehicle braking system providing energy recovery. 
     Another object of the invention is to reduce the need for stored vehicle electrical power. 
     The invention provides for these and other objects with an engine exhaust driven fluidic amplifier which operates as a high pressure air pump. The engine is preferably a multi-cylinder diesel engine which can be operated in a split mode with one or more cylinders diverted to operation as first stage air compressors. Cylinders operate as air compressors upon cut off of fuel injection to the cylinders. Air exhausted from one or more of the cylinders can be applied by selective positioning of an escape valve as an input to one or more pneumatic amplifiers. The pneumatic amplifiers draw air from the environment and compress the air by a substantial amount over the pressure of the air exhausted from the engine. The output of the pneumatic amplifiers is delivered to a high pressure storage tank. A pneumatic amplifier comprises a shuttle piston having a large area piston head exposed to the exhaust chamber and a small area head exposed to a compression or pumping chamber. A check valve passes air from the pumping chamber to the pressure tank. The fluidic amplifier allows pressurization of a storage tank to levels of 1600 to 1800 psi or higher. Air compressor operation is triggered by reduced air pressure in the storage tank occurring concurrently with the engine operating at a low or negative load. 
     Additional effects, features and advantages will be apparent in the written description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a truck with which the invention is advantageously employed. 
     FIG. 2 is a high level schematic diagram showing an exhaust diversion system and compression system in accordance with the invention. 
     FIGS. 3A-D are schematics of a fluidic amplifier illustrating principals of its operation in accordance with the teachings of the invention. 
     FIG. 4 is a cross sectional view of a shuttle piston for a preferred embodiment of the fluidic amplifier. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates in a perspective view a truck tractor  10  comprising a cab  11  mounted on a chassis  12 . A plurality of wheels  13  depend from the chassis. Associated with wheels  13  are a plurality of wheel speed sensors and pneumatic brakes under the control of a conventional anti-lock brake system. Tractor  10  includes the other conventional major systems of a vehicle, including a diesel engine and a transmission and may include an air starter or other air powered devices, as described below. The invention is preferably applied to medium and large trucks which have utilized compressed air systems for brake operation or for starting. These vehicles are typically equipped with a multi-cylinder diesel, which is often adapted for engine compression braking, and compressed air tanks. It will be understood that while the invention is preferably applied to diesels, it would also work, with modification, on internal combustion engines using spark initiated combustion. It may also be advantageously applied to delivery trucks and other vehicles used heavily for stop and go driving. 
     Referring now to FIG. 2 an engine air compression and diversion system  18  is illustrated. Compression system  18  uses one or more of the cylinders  32  of a bank  24  of cylinders of a multi-cylinder diesel engine as a first stage pump. In normal operation a piston  102  moves in a conventional, reciprocating fashion within a cylinder  32  with the result that space  104  between the piston and valves  106  and  110  varies in volume. A diesel is conventionally operated as a four cycle engine. Unless stated otherwise in the discussion that follows, intake valve  106  and exhaust valve  110  may be assumed closed. The first cycle is initiated with piston  102  at the top of its travel in cylinder  32  (referred to conventionally as top dead center (“TDC”). Intake valve  106  is opened and air is drawn into cylinder  32  with the following downstroke of piston  102  through the opened intake valve  106  from an intake manifold  108 . Intake valve  106  is closed when piston  102  reaches the bottom of its travel in the piston and the air is compressed by the subsequent upward movement of piston  102 . This compression stroke of piston  102  develops an approximately 25 to 1 compression ratio of air in the cylinder, raising the temperature of the air above the ignition point of the fuel. Compression ignition of the fuel which is injected into cylinder  32  as the piston approaches TDC results. The burning air fuel mixture substantially raises pressure in cylinder  32  generating a downward force on piston  102 . This produces a downward power stroke of piston  104 . An upward exhaust stroke of piston  102  follows for which exhaust valve  110  is opened. During the exhaust stroke the combustion byproduct is exhausted through exhaust valve  110  into a cylinder exhaust chamber  112 . Exhaust chamber  112  can pass air or combustion byproducts from cylinder  32  to an exhaust manifold  17 , which collects exhaust gas from bank  24  of cylinders, or retain the air for use of the fluidic amplifier  83 . The four cycles repeat as long as the cylinder is firing. 
     Contemporary practice provides for computer based control of many vehicle and engine functions. An engine controller  20  monitors and controls the operation of diesel  16 . Engine controller  20  times fuel injection to each cylinder  32  using a fuel injection controller  48 . A camshaft rotates in synchronous with a crank shaft, which in turn is coupled to the pistons in cylinders  32 . Thus camshaft position is related to the phase of each piston relative to TDC. Fuel injection is timed in relation to the cam phase position, provided by a cam phase (engine position) sensor  42 . Fuel injection is handled by an injector controller  48 . The timing of closing and opening of the intake valve  106  and an exhaust valve  110  are effected by engine controller  20  through valve actuators  124  and  126 , respectively. Engine controller  20  is also used to operate a starter  50 . Engine control module  20  controls a solenoid  87  which positions a valve  85  connecting compressed air tank  70  to air starter  50 . The pistons of an engine are connected to a rotatable crankshaft (not shown) which is connectable to the drive train and which operates to maintain movement of the pistons during none power strokes. 
     The intake and exhaust valves may be hydraulically actuated using pressurized engine oil, with the camshaft used to operate hydraulic valves controlling intake and exhaust valve operation. Hydraulic valve control may then be overridden by engine controller  20  through valve controllers  124  and  126 . For future camless engines, crankshaft phase position may be substituted for cam phase position to the same effect in coordinating the injection of fuel with piston phase and valve timing. In a camless engine hydraulic valve control uses pressurized engine oil under the control of valve actuators  124  and  126 . The position of an exhaust collection or retention valve  34  is coordinated by engine controller  20  using a solenoid  35  as described below. 
     The engine can be operated in a split mode, or used for engine compression braking, by cutting off fuel to one or more cylinders  32 . After fuel is cut off to a pumping cylinder, the cam actuated lifters can continue to operate intake and exhaust valves  106  and  110 , however, for more efficient engine compression braking, the intake valve is open during every down stroke and the exhaust valve is briefly opened as the piston  102  approaches TDC. Under conditions where some engine power is required, but air pressure status indicates a need for air, valve operation may be altered, and still allow operation of the high pressure compression system of the invention. It is not usually necessary under these conditions to draw air to a pumping cylinder  32  and it is preferable not to draw air away from the firing cylinders, or to impose as large a load on the engine as would occur if the one cylinder of the engine was operating in effect as a compression brake. For a preferred embodiment of a fluidic amplifier  83 , the intake valve  106  may be left closed and the exhaust valve  110  left open after an initial air charge is drawn into cylinder  32  and the fluidic amplifier  83  will continue to supply high pressure air, at least as long as the charge does not leak away. To compensate for such leakage the charge in the pumping cylinder  32  may be occasionally refreshed by opening intake valve  106 . 
     Cylinder  32  operates as an air pump when at least some of the remaining cylinders of the engine continue to fire, or when vehicle momentum is coupled to the engine crankshaft from the transmission. To make use of the compressed air from cylinder  32  with modification of the cylinder, some modification of the exhaust manifold  17 , or to the exhaust chamber  112  from an individual cylinder, is required to divert the air to a functional element. An exhaust collection valve  34  is located in the wall of exhaust chamber  112  and connects the chamber with exhaust manifold  17 . A fluidic amplifier  83  communicates with the exhaust chamber  112 . Modification of the exhaust system for one cylinder  32  to accommodate one exhaust collection valve  34  and fluidic amplifier  83  is illustrated, but it will be understood that an exhaust system can be modified allowing more than one of cylinders  32  to operate as first stage air pumps. It will also be understood that cylinders may have more than one intake or exhaust valve and that illustration of and reference to the cylinders as having a single valve for exhaust and a single valve for intake has been done for the sake of simplicity in illustration only and that provision for additional valves in no way alters the application of the invention to an engine. 
     Routing of the air exhausted or pumped from cylinder  32  is effected by opening and closing exhaust collection valve  34 . A control solenoid  40 , under the control of engine controller  20 , positions valve  34 . When valve  34  is closed, and fuel cut off from cylinder  32 , air is pumped from cylinder  32  during an exhaust stroke into fluidic or pneumatic amplifier  83 . Pneumatic amplifier draws air from the environment through an intake  183 , compresses the air and exhausts the compressed air through a check valve  120  into a high pressure air tank  70 . Fluidic amplifier  83  should have a pressure gain factor of about 20 and thus be able to deliver air to compressed air tank at pressures in excess of 2000 psi or twenty times the expected pressure of air from cylinder  32 . Exhaust collection valve  34  also operates to release air from the input side of pneumatic amplifier  83  as described hereinafter. Fluid amplifier  83  could in theory be run from combustion by product exhaust gas from cylinder  32  at substantially higher pressures, however, such an arrangement would substantially increase back pressure from the exhaust system and thereby reduce the efficiency of the engine. The 2000 psi pressure level is chosen as the contemporary practical limit for a motor vehicle compressed air storage system. A higher pressure could be used given progress in seals and tank strength at affordable prices for a mass produced vehicle. 
     Air compression occurs in response to a need for compressed air and availability of engine power to provide energy for pumping. Engine operation as an air pump requires coordination of the operation of fuel injectors, intake valves, exhaust valves and the exhaust diversion valves. Compressed air may be applied to vehicle systems such as an air brake system  95  used by a trailer or by an air starter  50  used for starting a diesel engine. The need for air may thus be equated with a downward variance from the maximum pressure limit for air tank  70 . To provide air tank  70  pressure readings, a pressure sensor  91  is provided in fluid communication with air tank  70 . Pressure sensor  91  reports air pressure in the tank to a computer such as a body controller computer  30  or to an engine control module  20 , depending upon the particular control arrangements provided on a given vehicle. The air pressure in air tank  70  being below the maximum allowed is taken as a request for operating air compression system  18 . The degree to which the air pressure falls below the maximum allowed may also be used as an indication of the priority of the request. In order to avoid frequent cycling of the system on and off, air pressure in tank  70  may be required to fall a certain minimum amount below the maximum limit before an air compression system  18  engages. A number of control regimens may be implemented and which regimen is used at a given time may depend upon the pressure level variance. Described here are the mechanisms useful in implementing the regimens. 
     Finding the preferred periods for operation of the air compression system  18  also requires determining engine load or some other related factor indicative of spare engine capacity. If engine load is low, or better still negative, air compression system  18  can be run at little penalty, or even allow energy to be recaptured. Periods of engine compression braking are an ideal opportunity for air compression operation. Body controller  30  can estimate engine load from engine speed, derived from the output of the engine (or cam phase) position sensor  42 , and the fuel flow output from engine control module  20 . Body controller  30  also receives inputs from an accelerator pedal/torque request input  54 , a starter button  56 , an ignition switch  58 , a brake pedal position switch  58  and a vehicle speed source  59 , all of which may be used to determine other opportunities to initiate air pumping. Under cruising conditions where air tank  70  is fully pressurized, and no demands for air power occur, ESC  30  may determine leakage rates for air tank  70  from periodic sampling of readings from pressure sensor  91 . 
     A preferred embodiment of the invention will now be described with reference particularly to FIGS. 3A-C where a schematic of the pneumatic amplifier  83  and exhaust collection valve  34  are illustrated. Pneumatic amplifier  83  comprises an exhaust chamber  112  functions as a pneumatic amplifier back pressure input chamber. Exhaust chamber  112  is exposed to a working surface  308  of a shuttle piston  304 . Shuttle piston  304  is positioned between chamber  112  and pumping chamber  320 . Shuttle piston  304  is mounted to reciprocate in the directions indicated by the double headed arrow “C” allowing air in a pumping chamber  320  to be compressed. A working surface  310  of piston  312  is exposed to pumping chamber  320 . Working surface  308  has approximately 20 times the exposed surface area of working surface  310  meaning that the pressure in pumping chamber  320  balances the pressure in chamber  302  when it is about 20 times as great, less the rebound force generated by a compression spring  312 . Spring  312  is disposed to urge shuttle piston  304  in the direction “D” up to a limit of the shuttle piston&#39;s travel. An intake  183  is provided to the pumping chamber  320 , which admits air to the chamber through a one way check valve  314 . The air drawn into the chamber is preferably dried ambient air. The spring constant of compression spring  312  is selected to substantially prevent movement of shuttle piston  304  during the relatively low transient pressures occurring during the exhaust of combustion gases. Piston  304  may be attached to the interior walls of pneumatic amplifier  83  by a membrane, which would reduce wear and promote a long service life. 
     An exhaust collection valve  34  is located in the wall of exhaust chamber  112  and is positioned to control pressurization of the chamber and operation of fluidic amplifier  83 . Exhaust chamber  112  should be made as small as practical to minimize the pressure drop occurring in gas exhausted from cylinder  32  when exhaust collection valve  34  is closed. As illustrated in FIG. 3A, valve  34  is in its opened position, allowing combustion by-products to escape from cylinder  32 . With valves  32  and  34  open, reciprocating piston  102  can force exhaust gas from cylinder  32  through the opened exhaust valve  110  as indicated by arrow “A” into cylinder exhaust chamber  112  and out of exhaust chamber  112  through valve  34  as indicated by the arrow “B” to an exhaust manifold  17 . 
     In FIG. 3B pumping of compressed air into compressed air tank  70  is illustrated. Following cessation of fuel injection to cylinder  32  and having drawn a charge of air into cylinder  32 , and concurrent with compression stroke of piston  102 , exhaust valve  110  opens to allow air to be forced from cylinder  32  indicated by arrow “A”. Exhaust collection valve  34  closes access to exhaust manifold  17  preventing the flow of air into the exhaust manifold. As pressure in exhaust chamber  112  increases, the resistance of spring  312  is overcome and shuttle piston  304  is forced in the direction indicated by the letter “E”, compressing the air in pumping chamber  320  until check valve  120  admits (arrow “G”) the air to compressed air tank  70 . Again the gain provided by the difference in exposed surface areas of the two ends of the pistons results in a gain of about 20 to 1 in pressurization. The relative volumes of the exhaust chamber  302  and the pumping chamber  320  and the travel of shuttle piston  304  are chosen so that shuttle piston  304  does not bottom against spring  312  before pressure in the chamber  320  increases sufficiently to balance the pressure in input chamber  302 . 
     In FIG. 3C a pumping stroke of shuttle piston  304  has completed. Fluidic amplifier  83  may be operated without drawing fresh air with each cycle into cylinder  32 . Once a charge of air is drawn into cylinder  32 , valves  106  and  34  are kept closed, and valve  110  left open. For subsequent pumping steps, as piston  104  moves downwardly, air is drawn from chamber  112  through exhaust valve  110  back into cylinder  32 , pulling shuttle piston  304  back into chamber  302 , and thereby drawing air in pumping chamber  320  by a now open check valve  314  as indicated by the arrow “I”. Piston  102  reciprocates in cylinder  32  resulting in the same charge of air being forced in and out of exhaust chamber  112 . Using this operational sequence it may be possible to eliminate compression spring  312 , simplifying pneumatic amplifier  83 . The effectiveness of such an arrangement will depend upon the quality of the seal formed by valve  34  and some leakage from exhaust chamber  112  is to be expected. Pumping in this manner may require pressure monitoring in chamber  112  or an occasional opening of intake valve  106  to replenish the charge may be used. A pressurized first stage system might be employed where, rather than drawing a fresh air charge, pumping begins with a charge of combustion by product from cylinder  32 . Again the intake valve  106  and exhaust collection valve  34  remain closed and valve  110  would remain open while piston  102  reciprocates. Pumping with valve  106  held closed and valve  110  held open is preferably employed when the engine is under a positive load and it is undesirable that pumping mimic a compression brake or divert air from the firing cylinders. 
     FIG. 3D reflects the configuration of pumping system  18  for recharging fluidic amplifier  83  or for an intake stroke when the engine is being used for a compression brake. Exhaust valve  110  to cylinder  32  has closed and intake valve  106  has opened as piston  102  begins an intake stroke, drawing air from intake manifold  108  into chamber  104 . Exhaust collection valve  34  opens allowing air in exhaust chamber  112  and exhaust pipe  118  to escape to the exhaust manifold  17 . This results in a pressure drop in chamber  112  which allows a combination of air pressure in pumping chamber  320  and spring  312  to return shuttle piston  304  in the direction indicated by the letter “F” to a neutral position. With movement of the shuttle piston  304 , air pressure drops below ambient pressure in pumping chamber  320  and air is drawn through intake  183  and check valve  314  into the pumping chamber. 
     FIG. 4 is a detailed schematic illustration of a shuttle piston  1304 . Shuttle piston  1304  preferably is of low mass and is suspended in a manner minimizing resistance to its movement. Were piston  1304  considered analogous to a filter or loudspeaker it would minimally damped and have good high frequency response. Piston  1304  and its supporting structures must also be resistant to high temperatures encountered in a vehicle exhaust. To meet these objectives a shuttle piston  1304  comprises two piston heads  408  and  410  mounted on opposite ends of a thin connecting rod  412 . Piston heads  408  and  410  are preferably fabricated from a light weight, high temperature resistant aluminum alloy or a ceramic material. They are shaped as thin disks oriented to present a major surface toward the exhaust chamber  112  and the compression or pumping chamber  320 , respectively. Piston heads  408  and  410  are suspended from the interior walls of the fluidic amplifier  83  by flexible membranes  414  and  416 , respectively, to minimize resistance. 
     The invention provides for amplifying the output of air pumped by an engine&#39;s cylinders to allow higher density energy storage. This improves the efficiency of internal combustion engines used in applications of varying load, particularly applications involving negative loads, as can occur when an engine is used for compression braking by recapturing energy. The invention reduces or eliminates the need for auxiliary air compressors and can be used to reduce the demands for vehicle electrical power. 
     While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.