Cam engine

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A cam engine is a reciprocating engine where instead of the conventional crankshaft, the pistons deliver their force to a cam that is then caused to rotate. The output work of the engine is driven by this cam. [1]

Contents

A variation of the cam engine, the swashplate engine (also the closely related wobble-plate engine), was briefly popular. [2]

Cam engines are generally thought of as internal combustion engines, although they have also been used as hydraulic and pneumatic motors. Hydraulic motors, particularly the swashplate form, are widely and successfully used. Internal combustion engines, though, remain almost unknown.

Historical Background

The history of cam engines is connected to the development of engines, especially in the late 19th and early 20th centuries. Engineers and inventors explored different mechanical designs to improve engine performance. One of the earliest recorded cam engine concepts dates back to the 19th century, during the industrial revolution.

In 1862, a French engineer named Alphonse Beau de Rochas, who is credited with the four-stroke engine, also explored using cams in engines. His work laid the foundation for later developments in internal combustion engines. [3] Another notable figure is Felix Wankel, the German engineer known for inventing the Wankel rotary engine. Wankel's work on unconventional engine designs included experiments with cam-based mechanisms, although his rotary engine became more prominent. [4]

In the early 20th century, there were many patents filed for different cam engine designs. These designs were especially important for aviation and industrial applications. During World War I and World War II, there was a lot of interest in alternative engine designs. These designs could offer advantages in power-to-weight ratios, durability, and fuel efficiency. However, cam engines never became widely used. This was mainly due to the complexity of their design and the durability issues with the cam and follower mechanisms. [5]

Mechanical Design

The mechanical design of a cam engine is different from the conventional crankshaft-driven internal combustion engines. The engine's design uses a cam mechanism instead of a crankshaft. This introduces unique challenges and opportunities for optimizing performance.

Cam Mechanism

The cam mechanism is at the heart of the cam engine. This mechanism plays a crucial role. It converts the linear motion of the pistons into rotational motion. This task is traditionally handled by a crankshaft in conventional engines. The cam is a rotating or sliding component. It is part of a mechanical linkage. The cam imparts a desired motion to a follower by direct contact. In the context of a cam engine, the cam is typically designed as a rotating disk or cylinder. It has a specially shaped profile. This profile interacts with the pistons. The cam's profile is carefully engineered. It controls the timing and movement of the pistons. The pistons reciprocate within the engine's cylinders. As the cam rotates, its profile pushes against a cam follower. The cam follower rides on the cam surface. This causes the follower to move up and down. This movement is transmitted to the pistons. This makes the pistons reciprocate. The cam's shape determines the piston's stroke length, timing, and speed. These factors directly influence the engine's performance characteristics. In a cam engine, the cam is connected to a drive mechanism, usually a shaft. This shaft rotates the cam at a specific speed. The rotation of the cam is synchronized with the engine's combustion cycle. This ensures that the pistons are in the correct position to use the energy from the combustion process. The careful design and synchronization of the cam mechanism are crucial for the efficient operation of the engine. Any deviation can lead to performance issues or mechanical failure. [6]

Types of Cam Designs

The design of the cam profile is very important for a cam engine. The cam profile directly affects the engine's performance, such as torque, power output, and efficiency. There are several types of cam designs, each with its unique advantages and challenges:

  1. Flat Cams:

Design: Flat cams, also called plate cams, have a flat surface. The edge of the surface is contoured. The contour of the edge determines the motion of the cam follower. This, in turn, determines the motion of the piston.

Performance Impact: Flat cams are easy to design and manufacture. This makes them a popular choice for early cam engine experiments. However, they have limitations. They cannot produce complex motion profiles. This can restrict the engine's efficiency and power output. [7]

2. Cylindrical Cams

3. Conical Cams:

Design: Conical cams have a tapered, cone-shaped surface that interacts with the cam follower. The varying radius of the cone influences the motion of the follower. This allows for creating intricate motion profiles.

Performance Impact: Conical cams can generate highly specialized motion profiles. These profiles can optimize the engine's performance for specific applications. However, the complexity of their design and the precision required in manufacturing can make them challenging to implement in practice. [8]

4. Barrel Cams:

Design: Barrel cams have a barrel-shaped surface, which is a variation of cylindrical cams. The cam follower moves along a track or groove on the curved surface. This converts the rotational motion into linear motion.

Performance Impact: Barrel cams can provide a high degree of control over the piston's motion, similar to cylindrical cams. Their design allows for the creation of motion profiles that can enhance the engine's torque output at specific points in the cycle. [9]

Operation

Operating cycle

Some cam engines are two-stroke engines, rather than four-stroke. In a two-stroke engine, the forces on the piston act uniformly downwards, throughout the cycle. In a four-stroke engine, these forces reverse cyclically: In the induction phase, the piston is forced upwards, against the reduced induction depression. The simple cam mechanism only works with a force in one direction. In the first Michel engines, the cam had two surfaces, a main surface on which the pistons worked when running and another ring inside this that gave a desmodromic action to constrain the piston position during engine startup. [10]

Usually, only one cam is required, even for multiple cylinders. Most cam engines were thus opposed twin or radial engines. An early version of the Michel engine was a rotary engine, a form of radial engine where the cylinders rotate around a fixed crank.

Advantages

  1. Perfect balance, a crank system is impossible to dynamically balance, because one cannot attenuate a reciprocal force or action with a rotary reaction or force.
  2. A more ideal combustion dynamic, a look at a PV diagram of the "ideal IC engine" and one will find that the combustion event ideally should be a more-or-less "constant volume event". [11]

The short dwell time that a crank produces does not provide a more-or-less constant volume for the combustion event to take place in. A crank system reaches significant mechanical advantage at 6° before TDC; it then reaches maximum advantage at 45° to 50°. This limits the burn time to less than 60°. Also, the quickly descending piston lowers the pressure ahead of the flame front, reducing the burn time. This means less time to burn under lower pressure. This dynamic is why in all crank engines a significant amount of the fuel is burned not above the piston, where its power can be extracted, but in the catalytic converter, which only produces heat.

A modern cam can be manufactured with computer numerical control (CNC) technology so as to have a delayed mechanical advantage.

Other advantages of modern cam engines include:

After extensive testing by the United States government, the Fairchild Model 447-C radial-cam engine had the distinction of receiving the very first Department of Commerce Approved Type Certificate. At a time when aircraft crank engine had a life of 30 to 50 hours, the Model 447-C was far more robust than any other aircraft engine then in production. [12] However, in this pre-CNC age it had a very poor cam profile, which meant it shook too severely for the wood propellers and the wood, wire, and cloth airframes of the time.

One advantage is that the bearing surface area can be larger than for a crankshaft. In the early days of bearing material development, the reduced bearing pressure this allowed could give better reliability. A relatively successful swashplate cam engine was developed by the bearing expert George Michell, who also developed the slipper-pad thrust block. [2] [13]

The Michel engine (no relation) began with roller cam followers, but switched during development to plain bearing followers. [14] [15]

Unlike a crankshaft, a cam may easily have more than one throw per rotation. This allows more than one piston stroke per revolution. For aircraft use, this was an alternative to using a propeller speed reduction unit: high engine speed for an improved power-to-weight ratio, combined with a slower propeller speed for an efficient propeller. In practice, the cam engine design weighed more than the combination of a conventional engine and gearbox.

Swashplate and wobble plate engines

The only internal combustion cam engines that have been remotely successful were the swashplate engines. [2] These were almost all axial engines, where the cylinders are arranged parallel to the engine axis, in one or two rings. The purpose of such engines was usually to achieve this axial or "barrel" layout, making an engine with a very compact frontal area. There were plans at one time to use barrel engines as aircraft engines, with their reduced frontal area allowing a smaller fuselage and lower drag.

A similar engine to the swashplate engine is the wobble plate engine, also known as nutator or Z-crank drive. This uses a bearing that purely nutates, rather than also rotating as for the swashplate. The wobble plate is separated from the output shaft by a rotary bearing. [2] Wobble plate engines are thus not cam engines.

Pistonless rotary engines

Most piston-less engines relying on cams, such as the Rand cam engine, use the cam mechanism to control the motion of sealing vanes. Combustion pressure against these vanes causes a vane carrier, separate from the cam, to rotate. In the Rand engine, the camshaft moves the vanes so that they have a varying length exposed and so enclose a combustion chamber of varying volume as the engine rotates. [16] The work done in rotating the engine to cause this expansion is the thermodynamic work done by the engine and what causes the engine to rotate.

Related Research Articles

<span class="mw-page-title-main">Crankshaft</span> Mechanism for converting reciprocating motion to rotation

A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting rods.

<span class="mw-page-title-main">Piston</span> Machine component used to compress or contain expanding fluids in a cylinder

A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder.

<span class="mw-page-title-main">Reciprocating engine</span> Engine utilising one or more reciprocating pistons

A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common features of all types. The main types are: the internal combustion engine, used extensively in motor vehicles; the steam engine, the mainstay of the Industrial Revolution; and the Stirling engine for niche applications. Internal combustion engines are further classified in two ways: either a spark-ignition (SI) engine, where the spark plug initiates the combustion; or a compression-ignition (CI) engine, where the air within the cylinder is compressed, thus heating it, so that the heated air ignites fuel that is injected then or earlier.

<span class="mw-page-title-main">Cam (mechanism)</span> Rotating or sliding component that transmits variable motion to a follower

A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to a steam hammer, for example, or an eccentric disc or other shape that produces a smooth reciprocating motion in the follower, which is a lever making contact with the cam. A cam timer is similar, and were widely used for electric machine control before the advent of inexpensive electronics, microcontrollers, integrated circuits, programmable logic controllers and digital control.

<span class="mw-page-title-main">Two-stroke engine</span> Internal combustion engine type

A two-strokeengine is a type of internal combustion engine that completes a power cycle with two strokes of the piston in one revolution of the crankshaft. A four-stroke engine requires four strokes of the piston to complete a power cycle in two crankshaft revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time.

<span class="mw-page-title-main">Radial engine</span> Reciprocating engine with cylinders arranged radially from a single crankshaft

The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is called a "star engine" in some other languages.

<span class="mw-page-title-main">Camshaft</span> Mechanical component that converts rotational motion to reciprocal motion

A camshaft is a shaft that contains a row of pointed cams in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines, mechanically controlled ignition systems and early electric motor speed controllers.

The engine configuration describes the fundamental operating principles by which internal combustion engines are categorized.

<span class="mw-page-title-main">Connecting rod</span> Piston engine component which connects the piston to the crankshaft

A connecting rod, also called a 'con rod', is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the crankshaft. The connecting rod is required to transmit the compressive and tensile forces from the piston. In its most common form, in an internal combustion engine, it allows pivoting on the piston end and rotation on the shaft end.

<span class="mw-page-title-main">Sarich orbital engine</span> Type of internal combustion engine

The Sarich orbital engine is a type of internal combustion engine, invented in 1972 by Ralph Sarich, an engineer from Perth, Australia, which features orbital rather than reciprocating motion of its central piston. It differs from the conceptually similar Wankel engine by using a generally prismatic shaped piston that orbits the axis of the engine, without rotation, rather than the rotating trilobular rotor of the Wankel.

<span class="mw-page-title-main">Variable valve timing</span> Process of altering the timing of a valve lift event

Variable valve timing (VVT) is the process of altering the timing of a valve lift event in an internal combustion engine, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with variable valve lift systems. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems. Increasingly strict emissions regulations are causing many automotive manufacturers to use VVT systems.

<span class="mw-page-title-main">Reciprocating motion</span> Repetitive back-and-forth linear motion

Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth linear motion. It is found in a wide range of mechanisms, including reciprocating engines and pumps. The two opposite motions that comprise a single reciprocation cycle are called strokes.

<span class="mw-page-title-main">Crankpin</span> Crankshaft section where connecting rods are attached

A crankpin or crank pin, also known as a rod bearing journal, is a mechanical device in an engine which connects the crankshaft to the connecting rod for each cylinder. It has a cylindrical surface, to allow the crankpin to rotate relative to the "big end" of the connecting rod.

<span class="mw-page-title-main">Axial engine</span> Type of reciprocating engine

An axial engine is a type of reciprocating engine with pistons arranged around an output shaft with their axes parallel to the shaft. Barrel refers to the cylindrical shape of the cylinder group whilst the Z-crank alludes to the shape of the crankshaft.

A swing-piston engine is a type of internal combustion engine in which the pistons move in a circular motion inside a ring-shaped "cylinder", moving closer and further from each other to provide compression and expansion. Generally two sets of pistons are used, geared to move in a fixed relationship as they rotate around the cylinder. In some versions the pistons oscillate around a fixed center, as opposed to rotating around the entire engine. The design has also been referred to as a oscillating piston engine, vibratory engine when the pistons oscillate instead of rotate, or toroidal engine based on the shape of the "cylinder".

<span class="mw-page-title-main">Swashplate</span> Mechanism to convert between reciprocating and rotary motion

A swashplate, also known as slant disk, is a mechanical engineering device used to translate the motion of a rotating shaft into reciprocating motion, or vice versa. The working principle is similar to crankshaft, Scotch yoke, or wobble, nutator, and Z-crank drives in engine designs. It was originally invented to replace a crankshaft, and is one of the most popular concepts used in crankless engines. It was invented by Anthony Michell in 1917.

<span class="mw-page-title-main">Dead centre (engineering)</span> The positions of an engines piston at the top or bottom of its stroke

In a reciprocating engine, the dead centre is the position of a piston in which it is either farthest from, or nearest to, the crankshaft. The former is known as top dead centre (TDC) while the latter is known as bottom dead centre (BDC).

<span class="mw-page-title-main">Hydraulic motor</span> Machine converting flow into rotation

A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement (rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder as a linear actuator. Most broadly, the category of devices called hydraulic motors has sometimes included those that run on hydropower but in today's terminology the name usually refers more specifically to motors that use hydraulic fluid as part of closed hydraulic circuits in modern hydraulic machinery.

The Michel engine was an unusual form of opposed-piston engine. It was unique in that its cylinders, instead of being open-ended cylinders containing two pistons, were instead joined in a Y-shape and had three pistons working within them.

<span class="mw-page-title-main">Internal combustion engine</span> Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber

An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance. This process transforms chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.

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