Camless Engine Essay Sample
Car makers have recognized the via medias associated with engines that are governed by the rotary motion of a camshaft. This rotary motion. the velocity of which is relative to the engine velocity. determines the timing of the engine valves. For this ground. automotive applied scientists must do a determination early in the design procedure that dictates the public presentation of the car. The engine will either hold powerful public presentation or increased fuel economic system. but with the bing engineering it is hard to accomplish both at the same time.
In response to the demands of improved engines. some makers have designed mechanical devices to accomplish some variable valve timing. These devices are basically camshafts with multiple Cam lobes or engines with multiple camshafts. For illustration. the Honda VTEC uses three lobes. low. mid. and high to make a broader power set. This does stand for an increased degree of edification. but still limits the engine timing to a few distinct alterations.
The construct of variable valve timing has existed for some clip. Unfortunately. the ability to accomplish genuinely variable valve timing has eluded automotive makers. Most variable timing mechanisms were created as tools for the automotive applied scientist. Their usage was limited to the research lab as a agency of proving multiple. “virtual” cam profiles. These early Camless engines allowed for the interior decorators to take the best Cam for the engine under examination. but were less than energy efficient. Furthermore. they were one research lab machines and were non capable of being mass produced or utilized in an car
Chapter Two: Introduction to Camshaft Technology
Since the inception of the car. the internal burning engine has evolved well. However. one invariable has remained throughout the decennaries of ICE development. The camshaft has been the primary agencies of commanding the valve propulsion and timing. and hence. act uponing the overall public presentation of the vehicle.
The camshaft is attached to the crankshaft of an ICE and rotates comparative to the rotary motion of the crankshaft. Therefore. as the vehicle increases is speed. the crankshaft must turn more rapidly. and finally the camshaft rotates faster. This dependance on the rotational speed of the crankshaft provides the primary restriction on the usage of camshafts.
As the camshaft rotates. Cam lobes. attached to the camshaft. interface with the engine’s valves. This interface may take topographic point via a mechanical linkage. but the consequence is. as the Cam rotates it forces the valve unfastened. The spring return closes the valve when the Cam is no longer providing the gap force. Figure 1 shows a schematic of a individual valve and Cam on a camshaft.
Figure 1: Single Cam and Valve
Since the timing of the engine is dependent on the form of the Cam lobes and the rotational speed of the camshaft. applied scientists must do determinations early in the car development procedure that affect the engine’s public presentation. The ensuing design represents a via media between fuel efficiency and engine power. Since maximal efficiency and maximal power require alone timing features. the cam design must compromise between the two extremes.
This via media is a premier consideration when consumers purchase cars. Some persons value power and thin toward the purchase of a high public presentation athleticss auto or towing capable trucks. while others value fuel economic system and vehicles that will supply more stat mis per gallon.
Acknowledging this via media. car makers have been trying to supply vehicles capable of cylinder inactivation. variable valve timing ( VVT ) . or variable camshaft timing ( VCT ) . These new designs are largely mechanical in nature. Although they do supply an increased degree of edification. most are still limited to discrete valve timing alterations over a limited scope.
Early on in the development of variable engines. Cadillac introduced its V-8-6-4 engine. This 1981 engine was based on a 6. 0 liter V-8. but was capable of operating as a 4. 5 liter V-6 or a 3. 0 liter V-4. The engine alterations were made while running and were controlled by the on-board computer’s finding of power demands. The engine changed the figure of active cylinders by seting the place of the rocker-arm fulcrum. To disenable a cylinder. the fulcrum was moved via a hydraulic solenoid valve to the contact point of the rocker-arm and engine valve root. This prevented the revolving camshaft from providing adequate force to open the engine valve. The computing machine so made accommodations to the fuel injection rates to counterbalance for the alteration in fuel demands.
The Cadillac V-8-6-4 was the standard engine for all 1981 Cadillac theoretical accounts. but the engine experienced a short production tally. Due to consumer ailments about the engine response and operation. particularly when altering from one manner to another. Cadillac discontinued its variable engine.
As an update to the short lived Cadillac V-8-6-4. GM introduced its “Displacement on Demand” engines in their 2004 theoretical accounts. The construct is similar to the earlier Cadillac effort. but this design limits the engine to run either as a V-8 or a V-4. With the addition of calculating power. GM states the design is more sophisticated. and they promise that the alteration from 8 to 4 to 8 cylinders will be virtually unobtrusive to the driver.
The new GM engine incorporates a particular valve lifter. designed by Eaton Corporation. This lifter is a multi-shaft constituent capable of telescoping. A hydraulicly actuated locking pin. when engaged. prevents the lifter from fall ining. This allows the Cam to open the engine valve. When the lockup pin is hydraulicly removed. the Cam merely collapses the lifter and can non trip the engine valve.
Alternatively of the cylinder operating alterations offered by the new GM engine. Honda has introduced its VTEC engines to turn to the demand for greater degrees of engine edification. This design incorporates three Cam lobes and three rocker-arms for each engine valve ; see figure 2 for a schematic of the Honda VTEC. The unit locks the rocker-arms together as engine demands change. One rocker-arm is in contact with the engine valve root and is straight responsible for the propulsion of the engine valve. As engine demands change due to increased engine velocity. the next rocker-arms are linked. so the valve timing becomes a map of the 2nd Cam and rocker-arm brace. This procedure is repeated for higher rpm’s. so the 3rd Cam controls the timing of the engine valve. A hydraulic bobbin valve connects the rocker weaponries together by driving a pin through the units. The three Cam lobes are designated for low. mid. and high revolutions per minute demands. There use generates more consistent torsion end product and increase fuel efficiency by supplying better valve timing at three different runing scopes.
Figure 2: Honda VTEC Schematic
As another attack to VVT. Lexus has developed a “variable valve timing. intelligent” ( VVT. I ) system for its engines. They claim to hold produced the following degree of edification by presenting continuously VVT. The on-board computing machine proctors the engine demands and continuously adjusts the timing and convergence of the consumption and exhaust valves.
Regardless of the VVT engineering differences among the taking automotive makers. the premier similarity of a camshaft remains. Therefore. restrictions continue. since the timing is still a map of engine velocity.
These restrictions have initiated research into Camless engine engineering. The undermentioned subdivision outlines some recent achievements of other research workers in an effort to develop genuinely independent VVT.
Chapter Three: Working of Camless Engine
Engine valve propulsion is achieved through the undermentioned process. An electric urge from the control hardware will do the piezoelectric stack to spread out. This additive enlargement will be transferred into motion of a hydraulic bobbin valve. The little motion of the bobbin valve will deviate hydraulic fluid and force per unit area to one side of a hydraulic amplifier. The sudden addition of force per unit area in the hydraulic amplifier will be transmitted into additive gesture by agencies of a Piston. The motion of the Piston acts as the actuator and is straight attached to an engine valve.
Variable valve timing is achieved by changing the input electromotive force signal to the piezoelectric tonss. This discrepancy alters the velocity of response and warp of the tonss. Therefore. the motion of the bobbin valve is varied and alters the flow of hydraulic fluid. It is this combination that allows for the independent control of valves. their supplanting. and their gap and shutting speed.
The system outlined above is required to get the better of the displacement restrictions of the piezoelectric stack. while working its efficiency and easiness of accurate control. The piezoelectric will offer the needful response for precise rapid alterations in way. but it can non present the force over the needed supplanting needed for usage as an engine valve actuator. Therefore. fluid mechanicss is introduced as a proved engineering. capable of triping the engine valves.
Chapter Four: Literature Reappraisal
Originally. camless engines were developed for usage as a design adjutant to automotive engine makers. The usage of a camless engine allowed the applied scientist to experiment with valve timing as a agency of planing Cam profiles. These early units were non limited by dimensional or power ingestion restraints. Alternatively. they were entirely developed for research lab usage as a design tool.
Aside from research lab usage. history shows that the thought of a camless internal burning engine had its beginnings every bit early as 1899. when designs of variable valve timing surfaced. It was suggested that independent control of valve propulsion could ensue in increased engine power. More late. nevertheless. the focal point of increased power has broadened to include energy nest eggs. pollution decrease. and dependability.
To supply the benefits listed supra. research workers throughout the old decennary have been suggesting. prototyping. and proving new versions of valve propulsion for the internal burning engine. Their designs have taken on a assortment of signifiers. from electro-pneumatic to electro-hydraulic. These designs are based on electric solenoids opening and shutting either pneumatic or hydraulic valves. The controlled fluid so actuates the engine valves. Much of the staying certification trades with either the control of the solenoids or the computing machine mold of such control systems. The research on the control of the solenoids is important since their preciseness and response is a restricting factor to the development of earlier camless valve actuators.
A comprehensive undertaking utilizing solenoid control of pneumatic actuators was completed in 1991. This research included the development of the actuators. a 16 spot microprocessor for control. and comparative testing between a standard Ford. 1. 9liter. flicker ignition. port fuel injected four cylinder engine and the same engine modified for camless propulsion. Testing compared the unmodified engine to that of the same engine. altered to include eight pneumatic actuators in topographic point of the criterion camshaft.
The actuators used during the research required an off-engine power beginning because an engine mounted compressor was non executable. The researches found that for engine operation at 1500 revolutions per minute. the eight actuators used a sum of 2. 5 kilowatt of power. This compares really high to the 140 Watts of power consumed by comparable production engines. As Gould et Al. provinces. their work can non be considered executable for execution due to the high power demands of the actuator.
For their undertaking. pneumatic actuators were chosen after running comparing trials among different methods. Pressurized air was chosen due to its low mass. leting fast response and stableness over a wide temperature scope. The research workers found that hydraulic systems had sulky response. particularly at low temperatures.
The pressurized air was controlled by electromagnetic valves. All flow way distances were minimized to increase the response clip of the actuator by cut downing the volume of air required for propulsion. The pressurized air opened the engine valves based on the timed electrical signal input to the “electromagnetic latch. ” Residual air was compressed during valve seating and provided a agency of decelerating the valve for a soft place.
The research workers concluded that the trial engine produced about 11 % greater torsion at low engine velocities ( below 2000 revolutions per minute ) compared to a conventional engine. Furthermore. the camless engine was capable of cut downing emanation gasses. specifically “brake specific azotic oxide emissions” ( bsNOx ) . but merely by degrading the burning procedure.
In 1996 the following coevals of camless engine was completed at the Ford Research Laboratory by. chiefly. Michael Schechter and Michael Levin. Ford’s work has taken a elaborate expression at the overplus of parametric quantities associated with consistent. dependable engine operation. The first half of the paper depicting their work is focused on the base parametric quantities of valve timing and convergence. This information will function as good information during the farther development of the paradigm at the University of South Carolina.
Beyond the rudimentss. Schechter and Levin introduce a new construct of the hydraulic pendulum. It is stated that the usage of a hydraulic pendulum decreases the system’s energy ingestion by change overing the kinetic energy of a shutting valve into possible energy stored in the pressurized fluid. This reduces the energy required for pumping the hydraulic fluid. Through this transition of energy. the writers predict that a 16-valve. 2. 0 L engine will devour about 125 W to run at light tonss.
The hydraulic pendulum besides allows for the solenoid-based-system to decelerate valve speed. This consequences in soft siting the valve and is a favourable property of the new system. Another benefit is the ability to change the gap and shutting speed of the valve. This allows for increased fluctuation to engine valve parametric quantities.
A schematic of the hydraulic pendulum is shown in Figure 3. High and low force per unit area hydraulic reservoirs are connected to the engine valve’s triping Piston. The control of this fluid is accomplished by agencies of two solenoids and two cheque valves. High force per unit area fluid is ever in contact with the lower side of the Piston. and either high or low force per unit area fluid is in contact with the upper side of the Piston. The difference in force per unit area contact country is utilized in concurrence with the hydraulic force per unit area to change the actuating forces.
Figure 3: Hydraulic Pendulum Schematic
The writers provide a elaborate description of the valve propulsion rhythm. This is summarized as follows. To open the engine valve. the high force per unit area solenoid opens to let high force per unit area hydraulic fluid into the upper chamber. Due to the difference in force per unit area contact country. the valve opens. Next. the high force per unit area solenoid stopping points. but the valve’s impulse continues to open the engine farther. This causes a decrease of force per unit area in the upper chamber and allows the low force per unit area cheque valve to open. The engine valve decelerates as it pumps the high force per unit area fluid from the lower pit back to the high force per unit area reservoir. This procedure both slows the valves and recovers some energy by change overing the kinetic energy of the engine valve into possible energy in the high force per unit area fluid. Once the upper pit force per unit area equalizes with the low force per unit area reservoir. the cheque valve stopping points and the upper pit fluid is inactive. This allows the engine valve to be held unfastened.
Closing the valve is initiated by the gap of the low force per unit area solenoid valve. The engine valve accelerates toward its closed place based on the force derived function between the high force per unit area lower pit and the low force per unit area upper pit. The upper pit fluid is pumped back toward the low force per unit area reservoir. Energy is once more cured and the engine valve is soft-seated through a similar slowing procedure. By shuting the low force per unit area solenoid valve. the upward impulse of the engine valve pressurizes the upper pit fluid. This addition in force per unit area opens the high force per unit area cheque valve and allows the upper pit fluid to be pumped back to the high force per unit area reservoir. Again. energy is converted from kinetic to possible and the valve is decelerated.
The best timing of this procedure would let for the kinetic energy of the engine valve to be exhausted precisely when it closes. However. the research workers provide an alternate to such preciseness. Alternatively. they suggest halting the engine valve merely prior to reach with the place. and so briefly opening the high force per unit area solenoid to finish the rhythm.
Through the usage of a hydraulic pendulum. a complete four cylinder ICE was produced and found some success. However. the system is complicated and requires multiple constituents. The usage of a hydraulic pendulum requires two solenoids and two cheque valves per engine valve and both a high force per unit area and low force per unit area hydraulic fluid supply. ( Schechter et al. province that two solenoids can run a brace of valves as-long-as the brace is synchronized. However. this detracts from the construct of independent valve control. )
The camless engine developed by Ford and described above was so enhanced at the University of Illinois at Urbana-Champaign. The focal point of the undertaking was to progress the hydraulic-pendulum-based CLE actuator by developing an adaptative feedback control. Their research is focused on the electronics and algorithms of informations acquisition and control and extends beyond the range of the current stage of research here at the University of South Carolina. However. as a comparing. some of the consequences are presented here. The complete system was limited to runing at 3000 revolutions per minute. Valve lift greater than 5 millimeters could non be systematically controlled.
There have been a few efforts at developing production theoretical accounts of Camless engines. most notably by Ford. but the usage of solenoids has impeded their execution. Using solenoids to command hydraulic fluid and finally the gap and shutting of the engine valves introduces its ain restrictions. The solenoids consume considerable energy and are a binary control device – they are either on or off. Therefore the hydraulic fluid. controlled by the solenoids. is either fluxing or blocked. This design allows for some discrepancy of valve timing. but is still limited by the response capablenesss of the solenoids. Furthermore. it can non straight address valve speed or supplanting alterations.
The development of the Camless engine overcomes these restrictions through the usage of piezoelectric tonss. a spool valve. and a hydraulic amplifier alternatively of solenoids. This combination consequences in a device capable of about boundlessly variable valve timing. altered valve supplanting. and governable valve speed.
Chapter Five: Conceptual Development
The construct was to utilize piezoelectric tonss to supply the supplanting of a hydraulic bobbin valve. The motion of the bobbin valve would command the flow of hydraulic fluid. To use the hydraulic fluid flow from the bobbin valve. a hydraulic amplifier would be required. This would make the needed force and supplanting for triping an ICE valve. The original expectancy of design demands presented during the conceptual development stage was stated as follows.
• ICE valve travel requires 8 millimeter. Design the system for 10 millimeter.
• Forces encountered will be due to internal force per unit area within the ICE cylinder and from the valve closing spring. Design for 8 saloon moving on a valve caput diameter of 28 millimeters and a spring rate of 35 N/mm.
• ICE velocity of 6000 revolutions per minute. This equates to valve propulsion of 50 Hz.
• Develop control for the system that can change valve displacement speed and timing.
As the ICE valve opens. the forces due to coerce cut down dramatically while the spring force additions linearly. This is shown pictorially in Figure 4.
Figure 4: Resistive Engine Forces V. Valve Displacement
The spring is designed to shut the ICE valve when no force is being applied to open it. This is similar to bing engine valves. but finally may turn out to be an obstruction to get the better of. Even during the conceptual development. the replacing of spring-return with hydraulic-return was discussed. Figure 5 shows a schematic of the engine valve with a spring return. This is similar to the valve used on the trial rig.
Figure 5: Engine Valve Schematic
The usage of a compaction spring. as shown in Figure 2. allows for thermic enlargement of valve constituents while keeping valve closing. If the spring is to be removed. the control system must be able to supervise the seal unity and suit any supplanting alterations due to thermic enlargement. During cogent evidence of construct proving. a spring return was maintained. as to non
present further control complexness.
Aside from the provided spring return valve attach toing the trial rig. the other major design restraint was the hook-up demands for linking to the bobbin valve. The bing bobbin valve had a four port interface based on ISO 4401: Hydraulic Fluid Power – Four Port Directional Control Valves – Mounting Surfaces. Figure 6 represents a schematic of the four port interface.
Figure 6: Four Port Directional Control Valve Mounting Surface
From Figure 6. it can be seen that there are four bolt holes and the four hydraulic ports labeled A. B. P. and T. These represent the followers.
• Ports A and B are the end product ports for hydraulic fluid. Fluid flow is directed to A or B depending on the place of the bobbin. For the Camless engine application. ports A and B provide hydraulic force per unit area to the top and underside of the hydraulic amplifier’s Piston. severally.
• Port P is the input port. It is connected to the end product of a hydraulic pump.
• Port T is the return port. It is connected to the input of a hydraulic fluid reservoir.
The construct develops a hydraulic actuator that would link to ports A and B of the provided bobbin valve. By making a hydraulic actuator based on a Piston – cylinder agreement. hydraulic fluid from ports A or B would do supplanting of the Piston. This is shown schematically in Figure 7.
Figure 7: Hydraulic Actuator Schematic
As shown in Figure 7. if hydraulic force per unit area is introduced through port Angstrom from the bobbin valve. the Piston will travel down. Hydraulic force per unit area applied to port B will do the Piston to travel up. Furthermore. hydraulic fluid must be able to run out out of the cylinder through the port antonym of that being pressurized. For illustration. as hydraulic force per unit area and fluid is applied through port A. the Piston moves down. Since the hydraulic fluid is basically incompressible. the fluid must be able to run out through port B.
Sing this construct. the ICE valve would merely be attached to the terminal of the Piston. This would make additive propulsion. Length of shot would merely be dependent on the Piston surface country in contact with the hydraulic fluid. the force per unit area of the fluid. and the resistive forces associated with opening the ICE valve. The major constituents that make-up the camless engine actuator are two bore home bases. one cylinder block. one Piston. and the piezoelectric controlled spool valve. Extra elements include the fasteners. o-rings. and PTFE lip seals. The consequence of the camless engine actuator assembly is shown below in Figure 8.
Figure 8: Hydraulic Actuator and Mounting Block Assembly
Figure 8 shows a cutaway position of the camless engine actuator assembly. Because it is cutaway. the bobbin valve and the ISO 4401 port connexions are non seeable. In this position. the bobbin valve would be coming out of the paper toward the reader. The camless engine actuator assembly and mounting block were so attached to the hydraulic system. Hydraulic connexions and layout are addressed in the following subdivision.
Chapter Six: Assembly of the Hydraulic System
The camless engine actuator assembly outlined in the old subdivision was mounted onto the hydraulic system. Hydraulic connexions were made via the standard hydraulic threaded connexion ? – 19 BSP ( British Straight Pipe ) . The system flows hydraulic fluid from a pump and back to a reservoir and is a ego contained strategy.
Hydraulic fluid is pumped through a ball valve and into the side port of the cylinder block. This connexion is straight routed to the P port of the bobbin valve. From at that place. the place of the bobbin valve determines where the pressurized fluid goes. In the impersonal place. the fluid is dead-headed. and aside from any escape past the bobbin. the fluid is inactive. See Figure 9.
Figure 9: Hydraulic Amplifier Schematic
When the bobbin valve translates up. fluid flows through the B port and pressurizes the upper pit of the cylinder block. This pressurization consequences in the downward interlingual rendition of the Piston. In bend. the engine valve is being opened as the Piston translates down. This is shown in Figure 10.
Figure 10: Hydraulic Amplifier – Spool Valve Up
The opposite occurs as the bobbin valve translates down. Fluid flows through the A port and pressurizes the lower pit of the cylinder block. This force per unit area causes the Piston to lift and allows the engine valve to shut. See Figure 11.
[ movie ] Figure 11: Hydraulic Amplifier – Spool Valve Down
Drain of fluid from the cylinder block takes topographic point through the A or B port. whichever is non being pressurized by the bobbin valve. As the Piston translates toward the non-pressurized port. hydraulic fluid is forced back into the bobbin valve. This fluid is so routed straight to the T port ( drain ) and returns to the reservoir. From the reservoir. the fluid is pumped back into the system. and the procedure repetitions.
It is the ability to change valve timing that will supply enormous betterments to the following coevals of internal burning engines. An engine will be capable of supplying increased power when needed. increased fuel efficiency when allowable. and overall decreased emanations. For illustration. when come ining onto a busy freeway. the onboard computing machine will feel the demand for greater power. This consequences in valve timing alterations to change the convergence between consumption and exhaust valves. Making so will momentarily sacrifice efficiency for power. Then. one time the car is cruising on the freeway. the computing machine will change the timing once more to cut down power and increase fuel efficiency. Furthermore. the timing can be optimized for a more complete burn ; therefore the engine will bring forth fewer emanations. Fuel economic system can farther be increased by closing down unnecessary cylinders. When an car is cruising at a changeless velocity. it does non necessitate all cylinders to be operational. With this freshly developed piezoelectric controlled camless engineering. complete cylinders can be removed from the timing rhythm.
It is this combination of fluid mechanicss and piezoelectric tonss that constitutes a spring in automotive engine engineering. A working paradigm to trip a individual valve has been completed. and proving has proven that the system is a feasible option to a camshaft.
The overall consequences of a complete Camless engine will supply the consumer with a vehicle that performs to outlooks. but facilitates increased fuel economic system. This combination is indispensable. since grounds shows consumers are non prepared to compromise on public presentation. while at the same clip fuel monetary values continue to intensify.
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