A variety of methods and arrangements for improving the fuel efficiency of internal combustion engines based on skip fire operation of the engine are described. In one aspect the skip fire decisions are made on a working cycle by working cycle basis. During selected skipped working cycles, the corresponding cylinders are deactivated such that air is not pumped through the cylinder during the selected skipped working cycles. In some implementations, the cylinders are deactivated by holding associated intake and exhaust valves closed such that an air charge is not present in the working chamber during the selected skipped working cycles.

Systems and methods for operating an engine in a variety of different cylinder operating modes are presented. In one example, an actual total number of available cylinder modes is increased in response to a vehicle's suspension setting and road roughness. By increasing the available cylinder modes, the engine may be operated in a higher number of modes where one or more engine cylinders may be deactivated to conserve fuel. The number of cylinder modes is increased during conditions where vehicle occupants may be less likely to object to operating the engine with fewer active cylinders.

The invention concerns a method for controlling the fuel supply to an internal combustion engine at start-up. The fuel supply system can be set in at least two start modes, a lean mode and a rich mode, and the selection of mode is based on an evaluation of a previous start attempt or successful run. The invention also concerns a carburettor (10) having a fuel supply system including a main fuel path (13) with an actively controlled fuel valve (26) and an idling fuel path (14) branching off from the main fuel path (13) downstream of the valve (26). The fuel supply system further includes a start fuel line (23, 423) starting upstream (FIG. 1) or downstream (FIG. 4) of the fuel valve (26) and ending in at least one start fuel outlet near and downstream of a choke valve.

In one aspect, a method for controlling operation of an internal combustion engine is described. The engine is operated in a skip fire manner such that selected skipped working cycles are skipped and selected active working cycles are fired to deliver a desired engine output. A particular level of torque output is selected for each of the fired working chambers. Various methods, engine controllers, arrangements and systems related to the above method are also described.

A compression ignition engine, commercial vehicle comprising such an engine, and a method for improving starting behaviour of such an engine. The engine is operable in a normal mode or a cold start mode. In the normal mode, a fuel injection system is controlled to inject a main fuel injection in a single pulse. In the cold start mode, the main fuel injection is split into a first split main and a second split main. The fuel injection system is controlled to inject the first and second split main in two distinct pulses, wherein the first split main is injected at a delayed timing for initiating a diffusion combustion phase in the pressurized combustion chamber, and wherein the second split main is injected during the diffusion combustion phase into the already combusting air-fuel mix.

A variety of methods and arrangements for improving the fuel efficiency of internal combustion engines based on skip fire operation of the engine are described. In one aspect the skip fire decisions are made on a working cycle by working cycle basis. During selected skipped working cycles, the corresponding cylinders are deactivated such that air is not pumped through the cylinder during the selected skipped working cycles. In some implementations, the cylinders are deactivated by holding associated intake and exhaust valves closed such that an air charge is not present in the working chamber during the selected skipped working cycles.

An engine torque estimator for an internal combustion engine, includes a cylinder internal pressure sensor, an indicated-torque calculator, a pump loss torque calculator, and an engine torque calculator. The cylinder internal pressure sensor detects a cylinder internal pressure in a cylinder. The indicated-torque calculator calculates an indicated torque in a second combustion cycle based on the cylinder internal pressure detected in a period from an exhaust stroke in a first combustion cycle to an expansion stroke in the second combustion cycle. The second combustion cycle that follows the first combustion cycle. The pump loss torque calculator calculates a pump loss torque in the second combustion cycle based on the cylinder internal pressure detected in the period. The engine torque calculator calculates an engine torque of the internal combustion based on the indicated torque and the pump loss torque.

A combined-cycle combustion control type three-cylinder engine includes: a cylinder block; and cylinders arranged in a row in the cylinder block and consisting of first, second, and third cylinders so that four-cycle combustion is performed in two of the first, second, and third cylinders and two-cycle combustion is performed in the remaining cylinder. A crankshaft is provided in first, second, and third pistons and converting reciprocating motions of the respective first, second, and third cylinders into rotational motions. A camshaft receives a rotational force from the crankshaft to control intake and exhaust timings for each of the first, second, and third cylinders

Methods of operation of liquid and gaseous multi-fuel compression ignition engines that may be operated on a gaseous fuel or a liquid fuel, or a combination of both a gaseous fuel and a liquid fuel at the same time and in some embodiments, in the same combustion event. Various embodiments are disclosed.

A variety of methods and arrangements for improving the fuel efficiency of internal combustion engines based on skip fire operation of the engine are described. In one aspect the skip fire decisions are made on a working cycle by working cycle basis. During selected skipped working cycles, the corresponding cylinders are deactivated such that air is not pumped through the cylinder during the selected skipped working cycles. In some implementations, the cylinders are deactivated by holding associated intake and exhaust valves closed such that an air charge is not present in the working chamber during the selected skipped working cycles.