EMISSION CONTROL SYSTEM FOR THE VARIOUS U.S. MODELS
The achievement of good mixture distribution among cylinders as well as a good overall richness, whatever the engine operating conditions may be, has made the achievement of good emission control results much easier though, with a view to complying with the very low US emission levels, it has been necessary to equip the engine with several extra emission control systems, whose main features are mentioned below:
US models are equipped either with the breakerless transistorized ignition system or with the fully electronic ignition system described in Ignition (less risk of misfiring, durability of catalytic converters).
The anti-evaporation system consists of a canister and a fuel tank pressurizing system.
Some models are equipped with a purge valve, which both prevents carbon canister purging at idle speed and, henceforth, improves operation under such conditions.
EXHAUST GAS RECIRCULATION
The EGR systems used are of two types: "on-off" or proportional (in the latter case, the vacuum in a venturi located in the air intake system or carburetor is used for controlling recirculation valve opening).
Extra devices can be used so as to prevent any recirculation during operation periods: at idling speed, with a cold engine, or at full load.
SECONDARY AIR INJECTION
The air injection device is of a conventional type comprising a belt-driven vane air pump, a diverted valve (which acts as a relief valve at high engine speeds and removes air injection during decelerations) a check value (in order to protect the pump against possible exhaust back flow or backfiring).
The catalytic converters used are oxidation catalysts.
The active catalytic substance is comprised of a platinum/palladium mixture deposited on al monolith ceramic substrate.
This paper has explained the reasons for development and the particular characteristics of the P.R.V. V6 engine; the main objectives in the design process have been: minimized weight, and minimized overall dimensions.
Thanks to its ease of application derived from its two overhead camshafts, an the sturdiness of its moving parts, Peugeot, Renault and Volvo will be able to technically meet emission control regulations and to achieve the performances required by commercial policies. These three companies will be able to accomplish this at reasonable cost because of the advanced features and production methods of this engine.
NOTE: Basic specifications are found in Appendix 1.
Basic Engine Specifications
|Bore and Stroke||88 x 73 mm.|
|Cylinder Bore Spacing||108 mm.|
|Compression RAtio||8.65/l - Europe|
8.2/1 - USA
|Camshaft||One overhead camshaft per bank|
(One separate chain drives each of the camshafts)
|Crankshaft||Graphite spheroidal cast-iron|
|Main Bearing Diameter||70 mm.|
|Crankpin Bearing Diameter||52.3 mm.|
|Oil pump output @ RPM||14 dm3 @ 1000 RPM|
|Valve Timing||Left Bank / Right Bank|
| Intake opens BTDC||9° / 7°|
| Intake closes ABDC||45° / 43°|
| Exhaust opens BRDC||45° / 43°|
| Exbaust closes ATDC||9° / 7°|
| Firing order||1-6-3-5-2-4|
1 2 3
4 5 6
|Length (L)||466,5 mm.|
(Distance between first belt working plane and clutch disc friction areas - See Figure 18)
|Height (H)||623 mm.|
(Distance between oil pan and upper air intake areas of carburetors - see Figure 19)
|Width (W)||632 mm.|
(Total width meaeured at level of the exhaust manifolds - See Figure 19)
(Total weight of carburetor European version - with air filter, flywheel, water pump, alternator, fluid drive type cooling fan, starter motor and oil, but without engine mounts and brackets)
|Performance Data of Existing Versions:|| |
| Gross horsepower (DIN)||125-140 HP|
| Gross torque (DIN)||20-21.5 daN.|
Fuel Injection System Description
Referring to the numbers in the diagram (Figure 20), of the fuel lnjection system is as follows:
An electrically driven roller type fuel pump (15) pumps fuel at a pressure of about 5 daN/cm2 via a pressure accumulator (16) and fuel filter (17) to the fuel metering device. The objective of the pressure accumulator is to maintain fuel pressure after the engine is stopped, in order to prevent vapor lock, which otherwise could cause hot-start problems.
The air metering device consists of an air metering plate in the form of a disc (3) attached to a pivoted arm (2) which moves in the conical tube (1). (Also see Figure 21 - bottom.) The movement of the air is proportional to the air flow into the engine which is conventionally controlled by the driver via a throttle plate (4). As the air flow depresses the arm (2), the fuel control piston (6) of the fuel metering device allows fuel to flow equally to the six injectors (20) via the six rectangular fuel metering slots (32). The pivoted arm (2) is counter-balanced by a weight and also by means of hydraulic counterbalancing force on top of the fuel metering piston (6).
The ratio between the fuel and air flow, and thus air/fuel ratio, is controlled by the profile of the conical tube (1) of the air metering device.
Pressure regulator (19) maintains the fuel feed system at a pressure of 4.5 daN/cm2 and a diaphragm valve (11) controls the pressure drop over the metering slots at a constant drop of 0.1 daN/cm2.
Under cold starting conditions, a bi-metallic strip (24) within the control pressure regulator (22) reduces the control pressure working on the top side of the fuel metering piston (6), thus providing a diminished force opposing the movement of the air metering plate. A specific air flow results in a larger opening of the fuel metering slots and a richer mixture. During warm up the bi-metallic strip is heated both by engine and electrical heat and raises the counterbalancing control pressure progressively to weaken the air/fuel mixture.
For extra enrichment during "key on" condition, an additional injector (31) is provided behind the throttle plates. This injector has a maximum injection time limit to prevent flooding.
An extra fast idle air supply is provided via throttle by-pass circuit controlled by a disc valve (27). An electrically heated bi-metallic strip (29) opens a rotating air valve (29) at low temperature, which is closed again by a combination of electrical and engine-produced heat as the motor warms up.
Full throttle enrichment is also provided by the control pressure regulator (22), which senses the low manifold depression, and reduces the control pressure to enrich the fuel mixture (as during choke operation).
On switching off, the fuel supply is positively cut off to prevent engine run-on.