Essay: Performance engine operation – camshafts and valve timing

Essay details:

  • Subject area(s): Engineering essays
  • Reading time: 10 minutes
  • Price: Free download
  • Published: November 24, 2020*
  • File format: Text
  • Words: 2,784 (approx)
  • Number of pages: 12 (approx)
  • Performance engine operation - camshafts and valve timing
    0.0 rating based on 12,345 ratings
    Overall rating: 0 out of 5 based on 0 reviews.

Text preview of this essay:

This page of the essay has 2,784 words. Download the full version above.

 

Introduction

 

Engine inspection refers to the analysis of different engine processes. In this paper, we are interested in understanding the use of camshafts and the process of valve timing in performance engines. When an engine is running, each cylinder has valves which open and close at certain times allowing the inflow or rejection of air, this is controlled by the camshafts. (Nagaya, 2016). As Kim (2014) points out when the piston goes down during the intake stroke, the valve is supposed to open to allow for pressure balance within the cylinder. In the same way, as the piston comes up in a compression stroke, the valves are supposed to close to prevent pressure leakage which can lead to the engine not gathering as much torque as it is supposed to. This is the process referred to as valve timing. The other factor of the valves affected by the camshaft is the valve lift, this is how much a valve can open.

In this paper, we shall address in details the process of valve timing and its relevance towards the functioning of a performance engine. In addition, we shall compare two engines and collect data related to them in terms of the relationship between crank angle and valve lift. Here we shall be interested in establishing whether there is any relationship that can be established between the two variables.

Material selection in the making of camshafts

 

As we have already pointed out, camshafts are a vital part of the engine used to control the motion of valves to attain efficiency and performance in an engine. As Jiang and Yilmaz (2010) pointed out, the functioning of an engine depends on the opening and closing of its valves. When compression is too much in the cylinder, the valves are supposed to open to create a balance of pressure. On the other hand, when more compression is required, these valves are supposed to close allowing pressure to accumulate in the inside.

The exact area for location of a camshaft is just above the engine block on the upper region of the engine. Per Nam and Choi (2012) camshafts are strategically placed to allow valves to open from the upper part where the piston requires pressure variation. This is an area where there are high temperatures and pressure to withstand these, the camshaft should be made from a strong material that is not affected by extreme temperatures. In most engines, the most applicable material is cast iron. One of the reasons why cast iron is preferred is its resistance to extreme temperature and pressure. The other reason is that cast iron does not conduct electricity hence the engine is not charged (Jiang and Yilmaz, 2010). This is the same material that is used to make the engine block to protect the engine from the impact of charge variations.

From my research in the sector of Materials, I believe that if I were to start with steel billets and machine out the camshafts. Then use the inductive hardening process (a process used to harden the surface of steel using a magnetic field. I could end up with a very strong camshaft capable of taking on huge mechanical load (even at high RPMs) and at the same time have a hard surface effectively increasing the camshaft working life.

 

 

 

 

Components of the valve train

 

There are several components that make up the valve timing system these will be defined below. The components complement each other to ensure that the exhaust and inlet valves are actuated in the correct sequence in relation to the positions of the relative pistons. Below are the components that make up the valve timing system.

Pushrods – These are rods that are pushed by the cam lobes to actuate valves. Due to the high temperature and pressure inside the cylinder, these rods are pushed hard to allow valves to open. When the pressure allied on them has released the rods valves close automatically and the rods go back to their original position. Usually, in a single cylinder, there are two pushrods. One of the rods is used to control the inlet valve while the other is used to control the exhaust valve.

I believe that the use of pushrod in high-performance vehicles with a v-configuration engine is very useful for the purpose of keeping the camshafts (a large mass) lower down in the engine, thus lowering the center of gravity and making the engine physically smaller and more compact.

 

 

Cam lobes – The cam lobes are what control the lift and opening/closing pattern of the valves. Although many shapes have been designed the most common shape used in modern performance engines is the teardrop. This was found to be the most effective in the gradual opening and closing of the valves.

The Part of the camshaft lobe that determines the valve duration (how long the valve opens for) is the nose. The larger the nose the longer the duration will be. The size of the lobe determines the valve lift. The larger the lobe the more lift the valve undergoes.

Ends – These are the points at which the camshaft is attached to the block. Due to the extreme circular movement that is made by the camshaft, ends are fitted with a bearing to reduce friction and increase engine efficiency.

In my opinion, the use of Silicon Nitride or Silicon Carbide bearings instead of regular bearings could be of great advantage in performance as they are very slippery, can run without lubrication and have a working temperature limit much higher than that of the engine.

 

Timing belt/chain – This is a very important component of the valve timing system. This component is what keeps the camshaft in sync with the rest of the engine. This motion is sustained by the crankshaft through the belt and in some cases timing chain. This belt is very delicate and must be installed with precision and accuracy. In situations where the belt is not fitted as required, the engine does not function effectively. Nam and Choi (2012) pointed out that in these situations valves are opened and closed at inappropriate times leading to poor fuel efficiency and exhaust of unburnt fuel. In extreme cases, may result in engine damage.

If I were to design a performance engine I would try to utilize gears to drive the camshafts instead of a belt or chain. This is because I hypothesize that a gear driven system, although more complicated, would be much stronger, reliable and work at a much higher rpm as the risk of failure would be far less.

 

The diagram below shows the components explained.

 

 

Fig 1: Components of a valve control system

 

 

 

 

 

 

Cam lobe design and formulation

 

As it has already been stated above, cam lobes are one of the main components in the process of valve timing. These lobes are put on the surface of the camshaft to exert pressure on the rocker arm which in turn exerts pressure on the push rod or valve. The push rod is connected directly to the valves and any pressure exerted on it is subsequently exerted on the valve. When the lobe releases the rocker arm, this pressure is withdrawn and the valve returns to its position due to the pressure from the return spring. This pressure always keeps the valve shut. The diagram below shows the design of a camshaft including cam lobes.

 

 

 

 

Fig 2: Design of a camshaft

 

From the above diagram, it is possible to note the profiling of cam lobes along the camshaft. The cam lobes have an oval shape at the end that is supposed to exert pressure on the rocker arm. Another salient feature that can be noted is that the camshaft has pairs of similar lobes. These are designed based on engine characteristics and the number of pistons in the engine. At the end of the camshaft, one can see three bores. These are the bores where the camshaft is attached to the engine block. There is a smooth round surface at the end of the shaft to facilitate revolution of the shaft by reducing friction with the surface of the end bearing.

 

Valve and camshaft arrangement

 

The diagram below shows how the valves are connected to the camshafts to facilitate valve opening.

 

 

Fig 3: Showing valve and camshaft arrangement

 

 

From the above diagram, there are several observations that can be made. It can be clearly observed that the design has one camshaft. The camshaft is directly connected to a rocker arm which is responsible for controlling valves. There is a return spring that is fitted in every push rod. This return spring is the one that is responsible for closing the valve after pressure from cam lobe is released.

The advantage of this system is that you reduce the rotational mass in the engine by only using one camshaft but utilizing the pushrod system to mimic having two camshafts. On the right side, there is a cogged wheel that can be seen. This is the gear that is fitted with a timing belt. The belt transmits power from crankshaft into the camshaft. This is what facilitates opening and closing of valves. Jiang and Yilmaz (2010) noted the engine is designed in such a way that it can be regarded as self-sustaining. The power that is exerted by piston movement and transmitted through the crankshaft is used to control air in and out of the engine component.

Different camshaft arrangements

 

There are two main camshaft arrangements. These include Pushrod (OHV), Single Overhead Camshaft (SOHC) and Double Overhead Camshaft (DOHC). SOHC has a single camshaft that sits on top of the valves. A SOHC has a complex cam lobe profiling to ensure that it opens both exhaust valves and inlet valves at the required time intervals. DOHC, on the other hand, is an arrangement where there are two camshafts. Here, one camshaft has cam lobes for opening and closing of the inlet valve and the other has cam lobes for control of exhaust valves. In an OHV engine, the camshafts sit lower down in the engine, connected to pushrods which engaged and disengage the rocker arms. In all three cases, the same objective is achieved. The main objective here is to ensure that the valves open and close at different points in time. The diagram below shows different arrangements.

 

Fig 4: Different camshaft arrangements

 

 

 

 

 

Fig 5: SOHC timing

 

From the above diagram, there are several observations that can be made. To begin with, the model has one camshaft meaning that both valves are controlled by the same shaft. As it can be observed, there are two cam lobes in every position. One of the cam lobes is for the inlet valve while the other is for the exhaust valve. Inlet valve cam lobe and exhaust valve cam lobe are arranged in such a way that, opening and closing of the valves will be done at the appropriate time.

 

 

DOHC timing

 

This, as it has already been stated, is a timing arrangement that uses two camshafts. The figure below shows this arrangement

Fig 6: DOHC timing

 

The above diagram is an illustration of a DOHC engine. As it can be observed, in this engine, valve control is mainly done by two camshafts. It is also clear from the above diagram that the shafts have one cam lobe at every point. One of the shafts is supposed to control the inlet valve while the other one is supposed to control the exhaust valve. It can also be noted that there is timing chain that s attached to both shafts. The chain controls both the inlet and outlet.

Technology bases valve timing techniques

 

There are technological advancements that have been done to the process of valve timing in order to provide better performance and more efficiency. As Kim (2014) pointed out, the functionality of an engine is based on air to fuel ratio. This is the ratio of fuel and air allowed into the cylinder. In order to control this further and streamline on performance, engine manufacturers have come with VVT and VVL engines. These are engines that do not only rely on camshaft and cam lobes only for air valve control. Instead, these engines have advanced technologies that are applied to control air intake and outlet. VVT engines are those engines that are designed to vary the amount of air entering or leaving the engine according to RPM. This means that for this class of engines, there is no fixed amount of air that is allowed into the engine. Instead, this air is varied depending on the drive status of the engine. This is done by opening using an auxiliary pushrod to induce extra lift in the valves thus allowing greater flow in and out of the engine to increase torque levels. VVL, on the other hand, is a technology that is mostly applied by Nissan Company. It works on the same principals, however, uses hydraulic pressure switches to control intake valves. The switch works between two different sets of camshaft lobes.

 

The Problem with Return Springs

 

Return springs are widely used in modern engines. The main purpose is to hold the engine valves closed whenever they are not opened by the Camshaft or valve train. The main difficulty when designing return springs for performance engines is that springs are not instantaneous so there may be a slight delay with valve motion under high RPMs. Another issue is that springs act elastically and there for at high RPMs may bounce around causing valve flutter and in extreme cases causing the piston and valves to collide.

In my opinion, the solution to this is simple. I would remove the spring and develop a method by which the camshaft will have an additional lobe profiled inversely to the valve lobe which will push on and inversely mounted rocker. This inversely mounted rocker will be connected to a grove on the valve stem and thus shut the valve closed when the valve no longer needs to stay open.

 

Results

Below are data collected from two engines of the same manufacturer (Suzuki). One engine is from a GSXR600 (600cc race bike) and a GS500 (500cc cruiser).

 

 

 

 

Discussion

 

Several things about valve lift and timing can be deduced from the collected data. As a start you can see that the GS500 have a considerably higher value for intake valve lift when compared to the GSXR600 this is due to it being a cruiser. This is because it is not required to run at high rpm but needs high levels of torque. Hence the large intake valve lift to allow as much air into the cylinder as possible and thus maximum torque. I have also noticed that on the GS500 engine the valves on both intake and exhaust tend to open earlier than on the GSXR600 helping the engine build torque lower down in the rpm range.

On the other hand, the GSXR engine must rev high and hold power all the way through its power band. To achieve this a slightly larger exhaust valve lift is utilized to quickly expel fumes from the cylinder and keep cylinder temperatures safe.

Analyzing the circular graphs, you can see that the GS500 has a much larger lead to create more torque at lower RPMs. The GSXR600 has a more significant lag so that it can generate more power at higher RPMs. You can also see that the overlap on the GS500 is far more significant to that of the GSXR600 as it requires a lot of air to create the high torque and in that requires a substantial overlap to flush out a large amount of fumes generated by the combustion process.

Conclusion

 

In this paper, I have taken a step by step approach to understanding performance engine operation as far as camshafts and valve timing are concerned. It has been established that intake of air and exhaust is very crucial for running of an engine. In a situation where no air gets into the engine, the engine cannot keep running. It has also been noted that the opening and closing of valves should be done in the appropriate timing. If proper timing is not done, it will not be possible to run the engine as there will not be sufficient pressure inside the cylinder. The research has compared SOHC, DOHC and OHV engines regarding engine efficiency, performance, and best application. I have also measured and analyzed valve lift concerning crank angle for two different engines used for various purposes; both built with performance in mind.

 

About Essay Sauce

Essay Sauce is the free student essay website for college and university students. We've got thousands of real essay examples for you to use as inspiration for your own work, all free to access and download.

...(download the rest of the essay above)

About this essay:

If you use part of this page in your own work, you need to provide a citation, as follows:

Essay Sauce, Performance engine operation – camshafts and valve timing. Available from:<https://www.essaysauce.com/engineering-essays/performance-engine-operation-camshafts-and-valve-timing/> [Accessed 28-01-22].

These Engineering essays have been submitted to us by students in order to help you with your studies.

* This essay may have been previously published on Essay.uk.com at an earlier date.

Review this essay:

Please note that the above text is only a preview of this essay.

Name
Email
Rating
Review Content

Latest reviews: