14-08-2014, 12:42 PM
A SEMINAR REPOR ON CAMLESS ENGINE
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ABSTRACT
Presented within is a synopsis of the conceptual development, design, manufacture, and analysis of a piezoelectric controlled hydraulic actuator. This actuator was developed for use as a replacement for the camshaft in an internal combustion engine (ICE). Its development results in a new device; called, the camless engine (CLE).
The objective of the project was to design and manufacture a device that proved the concept of a CLE. More specifically, it is a electro/hydraulic device capable of producing engine valve displacement at typical automotive demands. The goals for maximum displacement and frequency are 10 mm and 50 Hz, respectively. In general, the unit must be capable of varying engine valve displacement and valve timing.
The system design utilized a customized piezoelectric stack and hydraulic spool valve combined with an in-house designed hydraulic amplifier. Control is facilitated by afunction generator, and feedback is monitored with an oscilloscope.
The resulting system is capable of displacing an engine valve to nearly 11 mm, and frequencies up to 500 Hz have been obtained. The proof of concept can be considered successful, as it demonstrates the ability of piezoelectric control of hydraulics for use as an ICE valve actuator. Furthermore, the device has demonstrated potential areas of improvement that can be implemented in a second generation camless engine.
Introduction
Automobile manufacturers have recognized the compromises associated with engines that are governed by the rotation of a camshaft. This rotation, the speed of which is proportional to the engine’s speed, determines the timing of the engine valves. For this reason, automotive engineers must make a decision early in the design process that dictates the performance of the automobile. The engine will either have powerful performance or increased fuel economy, but with the existing technology it is difficult to achieve both simultaneously.
In response to the needs of improved engines, some manufacturers have designed mechanical devices to achieve some variable valve timingThese devices are essentially camshafts with multiple cam lobes or engines with multiple camshafts. For example, the Honda VTEC uses three lobes, low, mid, and high to create a broader power band. This does represent an increased level of sophistication, but still limits the engine timing to a few discrete changes.
The concept of variable valve timing has existed for some time. Unfortunately, the ability to achieve truly variable valve timing has eluded automotive manufacturers. Most variable timing mechanisms were created as tools for the automotive engineer. Their use was limited to the laboratory as a means of testing multiple, “virtual” cam profiles.
Conceptual Development
The University of South Carolina, Department of Mechanical Engineering was approached in 2000 to consider the development of a device that would be capable of replacing the camshaft in an internal combustion engine. The original idea was to use hydraulics as a means of actuating the intake and exhaust valves in an ICE. This was not the first attempt at producing such a device; however, the proposal to use the developing technology of piezoelectric stacks provided the project’s distinctiveness. It was proposed that piezoelectric stacks could control the movement, either directly or indirectly, of an engine valve. Due to the limited displacement of existing piezoelectric stacks, it was decided that they would not be used to directly actuate an engine valve for this phase of the project. Instead of direct actuation, the concept was to use
Literature Review of Camless Engine Development
Originally, camless engines were developed for use as a design aide to automotive engine manufacturers. The use of a camless engine allowed the engineer to experiment with valve timing as a means of designing cam profiles. These early units were not limited by dimensional or power consumption restraints. Instead, they were solely developed for laboratory use as a design tool.
Aside from laboratory use, history shows that the idea of a camless internal combustion engine had its origins as early as 1899, when designs of variable valve timing surfaced [5]. It was suggested that independent control of valve actuation could result in increased engine power. More recently, however, the focus of increased power has broadened to include energy savings, pollution reduction, and reliability.
To provide the benefits listed above, researchers throughout the previous decade have been proposing, prototyping, and testing new versions of valve actuation for the internal combustion engine.
Design Process
This chapter summarizes the design process in, roughly, chronological order. Some designs were initiated and later altered or abandoned as more information about the project was discovered. The entire process is outlined as a historic reference and is written considering that the project will continue into a second design phase. Therefore, earlier work that did not appear in the proof-of-concept design may have significance in future development.
Initially, the boundary interface of the design had to be well defined. This is divided into three discrete components. First, the connections to the spool valve needed to be outlined. Next, the interface with the engine valve stem needed to be studied. Finally, the systems envelope needed to fit within the available space on the test stand.
The piston went through several design iterations to develop both the overall dimensions and satisfy the means of manufacture. Due to the close clearance needed between the piston and the bore, manufacturing capabilities were scrutinized to develop a design that could act as a metal-to-metal reciprocating seal and could be aligned with multiple components (cylinder block, two bore plates, and the valve stem). Of greatest concern was the ability to center the shafts of the piston through the bore plates and maintain the minimal clearance within the bore. This obstacle was directly related to the ability of the manufacturer to maintain a concentricity tolerance between the piston diameter and the shaft diameter.
The first proposed solution was to develop a three part piston assembly. This assembly would be made of a male rod, female rod, and piston. With ample clearance between the rods and a hole through the piston, the unit could be assembled with, essentially, two separate centerlines. One centerline could pass through t the rods, while the other centerline passed through the cylinder. This would allow for the rods to align to the center of the bore plate holes and the piston to align to the center of the bore, even if the bore plate and bore centers were out of alignment.
Assembly of the Hydraulic System
The camless engine actuator assembly outlined in the previous section was mounted onto the hydraulic test stand. Hydraulic connections were made via the standard hydraulic threaded connection ¼ - 19 BSP (British Straight Pipe). The system flows hydraulic fluid from a pump and back to a reservoir and is a self contained scheme.
Hydraulic fluid is pumped through a ball valve and into the side port of the cylinder block. This connection is directly routed to the P port of the spool valve. From there, the position of the spool valve determines where the pressurized fluid goes. In the neutral position, the fluid is dead-headed, and aside fr When the spool valve translates up, fluid flows through the B port and pressurizes the upper cavity of the cylinder block. This pressurization results in the downward translation of the piston. In turn, the engine valve is being opened om any leakage p the spool, the fluid is static. as the piston translates down The opposite
Complete System Overview and Operation
Through the effort outlined in the previous chapters, a complete system was created. This system was capable of actuating a single engine valve and met the original parameters outlined for the project. This chapter reviews the hydraulics and controls introduced during the previous chapter and develops their usefulness as part of the complete system.
The goal of the design, troubleshooting, and development of the system during phase one was to actuate a single engine valve. This actuation needed to have a displacement of 10 mm with variable timing up to 50 Hz. Initial qualitative testing revealed several parameters that would require adjustments to reach the project’s goal. These tests are outlined in the next chapter; however, some qualitative results are presented here to explain the working of the camless engine
System Testing
Flow rate testing can be divided into multiple phases. For all testing, the experiments were divided into three distinct runs – both pumps, right pump only, and left pump only. Since the pumps themselves are together, the distinction of left and right is based on the location of their isolation ball valve.
Initially, flow rate testing was done to determine the flow output of the pump systems. These measurements were necessary to ascertain the maximum flow rate available to the camless engine system. For these measurements, fl
flow was diverted from the camless system, just prior to its entrance into the cylinder block, into a graduated cylinder. Practice runs were made to determine the length of time to use for each run without overflowing the graduated cylinder. When running both pumps, a time limit of 5 seconds was used for each test. The tests were repeated a minimum of five times to establish consistency in volumetric readings. These readings were established for a variety of pressures. Pump pressures were set with the isolation valves closed.
ADVANTAGES OF CAMLESS ENGINE
Electro hydraulic camless valve train offers a continuously variable and independent control of all aspects of valve motion. This is a significant advancement over the conventional mechanical valve train. It brings about a system that allows independent scheduling of valve lift, valve open duration, and placement of the event in the engine cycle, thus creating an engine with a totally uncompromised operation. Additionally, the ECV system is capable of controlling the valve velocity, perform selective valve deactivation, and vary the activation frequency. It also offers advantages in packaging. Freedom to optimize all parameters of valve motion for each engine operating condition without compromise is expected to result in better fuel economy, higher torque and power, improved idle stability, lower exhaust emissions and a number of other benefits and possibilities. Camless engines have a number of advantages over conventional engines. In a conventional engine, the camshaft controls intake and exhaust valves. Valve timing
CONCLUSIONS
1. An electro hydraulic camless valve train was developed for a camless engine. Initial development confirmed its functional ability to control the valve timing, lift, velocity, and event duration, as well as to perform selectively variable deactivation in a four-valve multicylinder engine.
2. The system employs the hydraulic pendulum principle, which contributes to low hydraulic energy consumption.
3. The electro hydraulic valve train is integral with the cylinder head, which lowers the head height and improves the engine packaging.
4. Review of the benefits expected from a camless engine points to substantial improvements in performance, fuel economy, and emissions over and above what is achievable in engines with camshaft-based valve trains.