Concentric Camshafts - Independent VVT On A Single Cam
Our concentric camshafts enable dual-independent Variable Valve Timing or VVT on a single camshaft. Both the intake and exhaust centerline timings can be controlled to give optimum engine performance over the complete operating range. These cam assemblies form a key part of many of our VVA systems, but they are ideal for cam in block pushrod engines.
Our concentric camshafts are:
- In volume production. The new Dodge Viper engine uses a concentric cam.
- The best and most cost-effective solution for phasing adjacent cams on a single camshaft.
- Essential for Dual Independent cam phasing in cam-in-block engines.
- Used in our variable lift and duration system (VLD).
Concentric Cam Key Points
- 1000 hours durability
- Direct camshaft replacement
- Many differing applications
- Continuously variable
How a Concentric Cam Works
An SCP camshaft is two concentric camshafts in a single assembly - A cam within a cam.
SCP cams are made from a solid inner camshaft and an outer cam tube assembly. They contain two types of cam lobe:
- Fixed cams: These are fixed to the outer cam tube.
- Moving cams: These are pinned to the inner camshaft through slots in the outer tube.
The phase of the moving cams is then controlled by the inner camshaft and the phase of the fixed cams is controlled by the outer cam tube.
Please download the following PDF summarising the benefits of concentric camshaft technologyConcentric Camshafts
Concentric Cam Video Media
View these videos to understand more about SCP cams...
See the key individual elements of an SCP camshaft assembled together and then see how they move. Watch now
Assembly to a Cam Phaser
See how a cam in block SCP camshaft assembles to our twin vane phaser for dual independent control. Watch now
Dual Independent Cam Phasing
See a lift curve animation showing dual independent control Watch now
VVT Extends the Life of Cam In Block Engines
So why is dual-independent VVT essential to the future of cam in block engines?
Cam timing on a fixed camshaft is a delicate balance between the following conflicting engine requirements:
- Meeting emissions regulations
- Allowing for good fuel economy
- Producing acceptable power and torque
- Maintaining good idle quality
No single cam timing will give optimum results under all engine operating conditions. A compromise timing is therefore chosen depending on the specific engine application.
Cam in block engines with dual-independent VVT are freed from this constraint, essentially allowing for the same performance and emissions improvements that have been successfully implemented in double over-head cam engines.
Some of the basic principles associated with these benefits are summarised in the sections below. Please note, however, that this is only intended to give an overview of how cam timing can affect engine operation.
VVT For Power and Torque
At any specific speed and load, increasing the intake of air into the combustion chamber allows us to burn more fuel, thus resulting in more power being produced. This is measured in terms of an engines volumetric efficiency (the actual volume induced / the static cylinder volume).
During normal engine operation, pressure pulses are set up within both the intake and exhaust manifolds from the continuous opening and closing of the valves and the intermittent motion of the gasses into and out of the combustion chamber.
To get the best volumetric efficiency at a particular operating point, one must tune the valve events to be in-sync with these pulses. Unfortunately, the frequency, magnitude and timing of these pulses varies with speed, so the volumetric efficiency of an engine with fixed valve timing will only be optimum at one speed.
With dual-independent VVT, however, the engine can be optimised at all speeds. This will yield significant improvements in low speed torque and top end power.
VVT For Fuel Economy and Emissions
Control of valve overlap is a key factor in improving engine fuel economy and emissions. Valve overlap is the point near piston TDC in the 4-stroke cycle where both the intake and the exhaust valves are open at the same time.
At low speed, the effect of valve overlap is to re-introduce exhaust gasses into the combustion chamber. This is known as generating internal exhaust gas re-circulation or internal EGR. The benefits from internal EGR are two-fold:
Firstly, internal EGR benefits part load fuel economy by diluting the charge within the cylinder, thus restricting output without the need for increased throttling and its associated pumping losses.
Secondly, internal EGR also reduces hydrocarbon and NOX emissions by the re-circulation of un-burnt exhaust gasses. The retained exhaust gasses tend to be very rich in un-burnt Hydrocarbons, as they typically come from crevice volumes that are expelled at the end of the exhaust stroke. This strategy can therefore be quite effective at reducing emissions.
Variable valve timing can also be used to reduce the work required by the piston to pump the combustion gasses into and out of the combustion chamber. This may yield further fuel economy benefits.
VVT For Idle Quality
Control of valve overlap is also the key to good idle quality.
The resulting internal EGR from high valve overlap tends to reduce engine stability at very light load (e.g. idle). This increases idle emissions and fuel consumption, whilst making the engine sound and feel poorly tuned. Reducing overlap reduces the internal EGR and hence improves idle stability.
This can be a particular problem for high performance high-output pushrod engines. These engines often have long duration high-lift profiles, with more valve overlap than would be desirable at low speed. Idle performance can therefore be significantly compromised as a result.
With dual-independent VVT, these engines can now benefit from overlap control and significantly improved idle quality at low speed.
Requiring More Detailed Information ?
If you require a more in-depth look at how the timing of valve events affects engiine performance and emissions, please click on the following link. The impact of valve events on engine performance and emissions