OIL SYSTEM WITH TWO PUMPS AND MEANS FOR CONTROLLING CONNECTING PASSAGES IN A TWO-STOKE, OPPOSED-PISTON ENGINE

The subject matter relates to an opposed-piston engine that incorporates a pair of oil pumps, a piston thermal management (PMT) pump and a pump for lubricating all engine bearings and a means for controlling their respective outputs according to engine load demands by sharing the PTM pump output with the second pump output to ensure adequate lubrication of all bearings during low load engine condition such as engine idle mode.

Inventor: John Kessler

Disclosure Numbers: D460

Date of This Draft: 06/15/2016

Prepared by: Joel F. Lemke

ABSTRACT

The subject matter relates to an opposed-piston engine that incorporates a pair of oil pumps, a piston thermal management (PMT) pump and a pump for lubricating all engine bearings and a means for controlling their respective outputs according to engine load demands by sharing the PTM pump output with the second pump output to ensure adequate lubrication of all bearings during low load engine condition such as engine idle mode.

BACKGROUND

In opposed-piston engines the oil system must be designed to provide sufficient lubrication and cooling to the pistons reciprocating in the bore of the cylinder as well as lubrication to all of the bearings of the engine under varying load conditions.   Conventional engines typically employ a single pump to supply all required oil to the engine including the pistons, wristpins and all bearings.  The Achates opposed-piston engine however employs two, separate oil supply pumps to meet the demands for sufficient cooling and lubrication to all of these areas to efficiently meet all engine load conditions.  Since combustion events increase heat in the piston area at high engine loads, a separate PTM pump for cooling the pistons is necessary.  However, during low load conditions, such as engine idle, the large PTM pump may supply more oil than needed to the pistons. This excess oil increases engine “windage” friction.  It may also result in extra oil draining down the bore of the cylinder after the engine is stopped – a definite unfavorable situation.  To offset this, a shutoff valve is used to stop PTM oil from flowing into the piston area during engine idle, or other low load conditions. During the period when the shutoff valve is energized the oil being delivered by the PTM valve must be diverted somewhere. This is accomplished by adding a pressure relief valve across the PTM pump to shunt oil from the pump back to the oil sump.  When engine loads again dictate that piston cooling oil is required, the shutoff valve is opened.  There also may be moments during low load, and/or idle, conditions when lubrication being supplied to all engine bearings by the second oil pump may be insufficient to keep these bearing adequately lubricated.  Traditionally, this is addressed by sizing the lubrication pump larger than otherwise necessary.  This increases engine weight and also increases oil pumping friction at higher engine speeds.  It therefore would be advantageous if a design scheme could provide for controlling the amount of oil delivered to the pistons during varying load conditions while also ensuring that adequate oil is delivered to all engine bearings to ensure adequate lubrication during the varying engine load conditions. This publication presents a scheme to achieve these goals in an opposed-piston engine by modifying the current lubrication scheme utilized in the Achates Power opposed-piston engine.

DESCRIPTION

The following figure is a block diagram representation of a two-pump means for controlling oil lubrication connecting passages in an opposed-piston engine.   The PTM valve output includes an electronically controlled on/off valve (shutoff valve) to interrupt oil flow to the pistons during low engine load conditions.

D460 Image

A second pump, (Lube Pump), supplies oil to all bearing surfaces in the engine.  Both pumps have independent PRV valves that return oil to the sump when downstream pressures exceed their respective set points.

Conditions may arise during PTM valve shutoff (engine low load moments, including engine startup) when the amount of oil available from the Lube Pump may be insufficient to properly pressurize the lube circuit feed galleys.  If such conditions occur, a One-Way Valve that couples the output of the PTM pump, prior to the shutoff valve, to the output of the Lube pump would divert any available oil from the PTM pump to be mixed with the lube circuit oil.  In order for this to happen it is necessary that a relationship between the two PRV valves and the One-Way-Valve operating pressure levels be as shown, or similar to, the respective 1 bar, 5 bar, 0.3 bar shown in the figure.