When a car with a manual transmission is in motion with the clutch engaged, there is a mechanical connection between the engine and wheels which keeps them in sync with each other. When shifting, however, depressing the clutch is required. This disconnects the engine from the wheels, and the engine speed is no longer linked to that of the wheels. When upshifting, this is usually not a problem, as the tendency of the engine to reduce speed itself without gas will slow it to loosely match the lower speed of the higher gear. However, when downshifting, the engine needs to speed up to come to speed with the wheels. If the accelerator is not "blipped" (or briefly and quickly pressed to speed up the disengaged engine), the engine will have to take power from the wheels and momentum of the car to come to speed, which is often accompanied by a sudden deceleration of the vehicle due to the power suddenly going to the engine, often described as a "lurch" or "jolt". This sudden external acceleration of the engine through the transmission also causes increased wear on the mechanics of the car. Therefore, a staple of advanced or professional manual-transmission driving is the "rev match", or "throttle-blip", in which the driver quickly brings the engine up to speed with the wheels by use of the throttle. As downshifting is often necessary when accelerating into or out of a curve or other slow-down, advanced techniques such as the "heel-toe method" are often required, in which the toe of the right foot presses on the brake pedal, while the heel of the same foot blips the throttle.
Nissan's SynchroRev Match system makes such throttle blipping and advanced techniques by the driver unnecessary and accomplishes engine rev-matching automatically.
Implementation and experience
The system employs sensors on the clutch pedal, gear shift, and transmission, and is coordinated by the ECU. When the clutch pedal is depressed, the system waits for the user to either move the shifter to a different position or to re-engage the clutch. If a new gear is never selected but the clutch has been depressed long enough for the engine to lose speed, the system will bring the engine back to speed for the same gear if the driver begins to raise the clutch. If the shifter is moved to a higher gear and the clutch is re-engaged quickly, the system will let the natural deceleration of the engine sync the drive train with the higher gear. If the clutch is depressed long enough for the engine to fall below the speed of the higher new gear, the computer will blip the throttle to bring the engine back to speed. Most usefully, if a new, lower gear is selected, the computer will accelerate the engine to the new estimated speed, even to the point of redline.
In all cases, the computer continues to adjust the throttle to match the ever-changing target speed of the wheels when the clutch is partially engaged, as the vehicle speed may often change while shifting (for example due to shifting while going up or down a hill). In actual execution, the computer is able to "blip" the throttle due to the presence of an electronic throttle, in which the computer has direct control over both the fuel and air inputs to the engine. As the accelerator pedal in such a system has no direct mechanical connection to the throttle valve, the engagement of the system to change engine speeds is apparent to the driver via sound and tachometer cues only, and the feel or weight of the accelerator pedal remains constant. Regardless of the previous operation, the involvement of the system is ended when the clutch pedal reaches a certain point of re-engagement to ensure the system does not interfere with the driver's intended power output to the wheels. In any case, Nissan has provided a switch to disengage the system, for example in the case of the driver preferring to perform their own rev-matching.
Related Research Articles
Double-clutching is a method of shifting gears used primarily for vehicles with an unsynchronized manual transmission, such as commercial trucks and specialty vehicles. While double clutching is not necessary in a vehicle that has a synchronized manual transmission, the technique can be advantageous for smoothly downshifting in order to accelerate and, when done correctly, it prevents wear on the synchronizers which normally equalize transmission input and output speeds to allow downshifting.
Heel-and-toe shifting is an advanced driving technique used mostly in performance driving with a manual gearbox, although some drivers use it on the road in everyday conditions in the interest of effectiveness. It involves operating the throttle and brake pedals simultaneously with the right foot, while facilitating normal activation of the clutch with the left foot. It is used when braking and downshifting simultaneously, and allows the driver to "blip" the throttle to raise the engine speed and smoothly engage the lower gear.
An automatic transmission is a multi-speed transmission used in motor vehicles that does not require any input from the driver to change forward gears under normal driving conditions.
A manual transmission (MT), also known as manual gearbox, standard transmission, or stick shift, is a multi-speed motor vehicle transmission system, where gear changes require the driver to manually select the gears by operating a gear stick and clutch.
In mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. An overdrive is sometimes mistakenly called a freewheel, but is otherwise unrelated.
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Redline refers to the maximum engine speed at which an internal combustion engine or traction motor and its components are designed to operate without causing damage to the components themselves or other parts of the engine. The redline of an engine depends on various factors such as stroke, mass of the components, displacement, composition of components, and balance of components.
Engine braking occurs when the retarding forces within an internal combustion engine are used to slow down a motor vehicle, as opposed to using additional external braking mechanisms such as friction brakes or magnetic brakes.
The modern usage of the automotive term manumatic denotes an automatic transmission that allows the driver to select a specific gear, typically using paddle-shifters, steering wheel-mounted push-buttons, or "+" and "-" controls on the gear selector.
A direct-shift gearbox is an electronically-controlled, dual-clutch, multiple-shaft, automatic gearbox, in either a transaxle or traditional transmission layout, with automated clutch operation, and with fully-automatic or semi-manual gear selection. The first dual-clutch transmissions were derived from Porsche in-house development for the Porsche 962 in the 1980s.
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A transmission control unit (TCU), also known as a transmission control module (TCM), or a gearbox control unit (GCU), is a type of automotive ECU that is used to control electronic automatic transmissions. Similar systems are used in conjunction with various semi-automatic transmissions, purely for clutch automation and actuation. A TCU in a modern automatic transmission generally uses sensors from the vehicle, as well as data provided by the engine control unit (ECU), to calculate how and when to change gears in the vehicle for optimum performance, fuel economy and shift quality.
Powershifting, also known as full-throttle shifting or flat-shifting, is a method of shifting used with manual transmissions to reduce the time where the driving wheels are not powered. Unlike a normal gearchange, in a powershift the driver does not let off the accelerator. The clutch is briefly depressed while the shift lever is rapidly shifted into a higher gear, keeping the engine in its power band. Keeping the engine in its powerband allows it to put down power quicker when the clutch is "dropped" and power returns to the transmission. In most cases, there is a method of cutting the ignition or fuel delivery, in a manner similar to a rev-limiter, which prevents the engine from over-revving when the load from the transmission is removed. Many aftermarket engine management systems provide this functionality as either a standard feature or as an option, usually combined with launch control.
The name Autostick has been used for a Volkswagen semi-automatic transmission, which is a vacuum-operated automatic clutch system, coupled with a conventional 3-speed manual transmission. The "AutoStick" system designed by Chrysler allows for manual selection of gears with a standard hydraulic automatic transmission, also known as a manumatic.
Clutch control refers to the act of controlling the speed of a vehicle with a manual transmission by partially engaging the clutch plate, using the clutch pedal instead of the accelerator pedal. The purpose of a clutch is in part to allow such control; in particular, a clutch provides transfer of torque between shafts spinning at different speeds. In the extreme, clutch control is used in performance driving, such as starting from a dead stop with the engine producing maximum torque at high RPM.
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Car controls are the components in automobiles and other powered road vehicles, such as trucks and buses, used for driving and parking.
Float shifting or floating gears, also called "slip shifting", "dead sticking", or "bang shifting", is the process of changing gears, in typically a non-synchronous transmission, without depressing the clutch. Shifting in this manner is also used with synchronous manual transmissions, particularly after a clutch failure, to prevent destroying the synchromeshes with the power of the engine.
A quickshifter is a device that eliminates the need to use the clutch or throttle when shifting gears on a manual transmission. This can increase the safety and comfort of the vehicle and allow for faster gear shifting and is thus a popular performance enhancement for motorcycles.
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