Throttle Control: past, present and future

It seems a long time ago – thirty years to be precise – while studying Electrical Engineering at Brunel University, that I realised I was working towards the wrong degree.

Rather than learning about microprocessors and fibre-optic circuits, I found myself reading L.J.K. Setright’s Valve mechanisms for high-speed engines: their design and development. As a student (on a budget), I was forever searching for a few more horsepower (for my Alfasud Sprint) through the black art of porting and polishing and modifying the throttle body to take in more fuel and air.

If you can relate to that kind of obsession, then you’ll probably enjoy the latest technical feature from Renault Sport F1.

They start by explaining the purpose of the throttle in an F1 engine:

RENAULT F1:  A throttle is a hydraulically operated mechanism used to increase or decrease inlet gases to the engine. The throttle valves (all eight of them in the RS27 engine) are controlled via the accelerator pedal but the demand for power is sent via a signal to the ECU that then directly controls the exact position of the throttle valve through a number of maps.

* * *

Their are parallels between the mechanism used in the RS27 and that in a typical road. BMW has been using a “drive by wire” throttle control mechanism for years, where the opening and closing of throttles is achieved via an electronic signal – this in turn is controlled by the central engine management unit. In road cars it results in smoother, steadier power delivery, plus lower emissions and improved fuel efficiency.

In an F1 engine, the main benefits are better air-fuel mixture preparation, leading to improved driveability – especially in slower corners.

While most road cars use a butterfly type throttle valve, F1 has experimented with several alternatives. The simple reason is that of power. In a butterfly throttle, the valve is hinged, where at full throttle the valve is vertical but when closed the valve swings into a horizontal position like a butterfly wing opening and closing. The valve remains in the air flow (even when fully open), which slows down the flow and costs precious power.

The main alternative is the barrel valve, where rounded barrels roll into the cylinder to stop the flow of air, but when the throttle is wide open they retract fully from the intake chamber. This results in more power but less sensitivity and control.

RENAULT F1: The difference between the two systems is in the region of four to five horsepower and Renault believed greater gains could be found with the butterflies by delivering more stability and therefore tyre slip control and grip in the slower corners when the throttles are only partially open.

* * *

To lessen the downside of using butterfly valves, F1 engine makers have been making the element from thinner and thinner materials. With such advances, the loss in power has fallen from 10bhp to around 4bhp today (when compared to the more efficient barrel system).

RENAULT F1: In the early 2000s, the valve was approximately three times thicker than it is today, with the material changing from steel to titanium/aluminium and now to a composite plastic.

* * *

But perhaps the most fascinating insight is where throttle control systems would have evolved to in F1, if the engine freeze hadn’t halted development.

RENAULT F1: Without any regulations you probably would not have throttles any more in F1. In 2011 when teams were using maps to power off throttle blown floors, throttles were left (more or less) open the entire lap to maintain exhaust flow, and torque and ignition maps alone were used to control the torque produced. If the rules had not been clarified, then the air intake would have been left fully opened and torque would have been controlled completely by ignition.

* * *

Sound like rocket science? Well, perhaps this is one area where road cars may have actually overtaken F1.

BMW’s Valvetronic system, does precisely that – replacing the conventional throttle butterfly with an electrical unit that controls the lift of each cylinder’s intake valves. The butterfly valve is no longer needed to control air supply – although for safety reasons it is still fitted as an emergency back-up.

In this case, the primary means of controlling the engine’s power output is transferred from the throttle to the intake valvetrain, improving fuel efficiency and providing more granular control of the engine’s power delivery.