Direct fuel injection basics

Direct fuel injection is a fuel-delivery technology that allows gasoline engines to burn fuel more efficiently, resulting in more power, cleaner emissions, and increased fuel economy to meet today's evolving EPA standards.

How direct fuel injection works

Gasoline internal combustion engines work by sucking a mixture of gasoline and air into a cylinder, compressing it with a piston, and igniting it with a spark, the resulting explosion drives the piston downwards, producing the power. Traditional (indirect) fuel injection systems pre-mix the gasoline and air in a chamber just outside the cylinder in the intake manifold.  In a direct-injection system, the air and gasoline are not pre-mixed, air comes in via the intake manifold, while the gasoline is injected directly into the cylinder.

Advantages of direct fuel injection

Combined with precise computer management, direct injection allows more accurate control over fuel metering (the amount of fuel injected) and injection timing (exactly when the fuel is introduced into the cylinder). The location of the injector also allows for a more optimal spray pattern that breaks the gasoline up into smaller droplets. The result provides a more complete combustion process -- in other words, more of the gasoline is burned, which translates to more power and less pollution.

Disadvantages of direct fuel injection

The primary disadvantages of direct injection engines are complexity and cost. Direct injection systems are more expensive to build because their components must be more rugged to include engine computer ECU management> The direct injection system also handle fuel at significantly higher pressures than indirect injection systems and the injectors themselves must be able to withstand the heat and pressure of combustion inside the cylinder.

Driver assistance systems

Over the past several years, driver assistance features have become commonplace. The functionality and convenience of these systems continue to help develop vehicle collision avoidance capabilities. By their very nature, driver assistance systems are designed to help detect, judge and react to anticipated collision scenarios.
Anti-lock braking system (ABS) is probably the best known driver assistance feature. ABS has evolved from simple lockup control only during braking to more advanced systems that control traction during acceleration, braking and cornering by braking wheels individually while integrating other vehicle operating factors such as engine power output.
Most new vehicles are equipped with ABS these days, but ABS is not a one-size-fits-all system. ABS can include a number of additional features, which are found on a number of Toyota vehicles:
  • Electronic Brake-force Distribution (EBD) -- modifies braking force at individual wheels to compensate both for changes in vehicle load (occupants and cargo) and to help increase braking efficiency during cornering.
  • Brake Assist (BA) -- monitors the force with which the driver depresses the brake pedal and provides additional brake fluid pressure when the system detects an emergency stop.
  • Traction Control (TRAC) -- helps reduce drive wheel spin during acceleration using ABS and control of engine power output.
  • Vehicle Stability Control (VSC) -- helps prevent skidding or spinning while cornering by controlling ABS and engine power output to help keep the vehicle traveling in the steered direction, even if the driver enters a turn too fast or steers the vehicle too sharply for road conditions.
  • Vehicle Dynamics Integration Management (VDIM) -- combines a range of vehicle stability control functions into a single, seamless process to help provide overall vehicle dynamic drivability.

SUVs and trucks, such as the Toyota Tundra and 4Runner, may be equipped with specialized ABS-based functions such as:
  • Active TRAC (A-TRAC) -- During 4-wheel-drive operation on a snow-covered road or in rugged off-road conditions, A-TRAC controls engine output and brake fluid pressure so that the drive force is distributed to the wheels that have traction. This enhances drivability in extreme road conditions, an effect that is similar to a Limited Slip Differential (LSD). Off-road drivability is equivalent to having the center differential locked and a Limited Slip Differential on both front and rear axles.
  • Auto Limited Slip Differential (Auto LSD) -- Auto LSD uses the TRAC system to achieve the capability of a Limited Slip Differential (LSD) when driving in 2WD mode. (On a 4WD vehicle, Auto LSD only operates when the vehicle is being driven in 2WD mode.) Because Auto LSD and Rear Differential Lock perform similar functions, vehicles may have one system or the other, but not both. While Auto LSD components are similar to those in the TRAC system, there are important differences.
  • Downhill Assist Control (DAC) -- DAC allows the vehicle to descend a steep hill in a stable manner without the wheels locking. It does this by controlling hydraulic brake pressure at all four wheels, helping to maintain a constant, low vehicle speed.
  • Hill-start Assist Control (HAC) -- The basic function of the HAC system is to help increase control on steep upgrades and stopping and starting on slippery surfaces. The HAC system is designed to help prevent the vehicle from rolling backward or slipping sideways during transition from a stopped position to climbing an upgrade.