The invention relates to a speed limiter system for an automobile or the like. The invention in particular relates to a speed limiter system adapted for use in vehicles in which an electromechanical throttle actuator including a mechanical actuator such as an accelerator pedal is associated with suitable signal generation means and is coupled to and controls the operating engine speed electronically rather than by direct mechanical linkage.
Automobile vehicles are widely used for personal and public transportation and for the transportation of goods. It is well established that for a variety of reasons an owner or operator of a vehicle might wish to limit the speed of the vehicle to a predetermined maximum, for example for economical or safety reasons, to comply with legislative or regulatory regimes, or for some other purpose.
Vehicle speed is usually controlled and varied by operation of a driver-operated system which acts to vary the engine speed and consequently the speed transmitted to the drive system. Such a system is commonly called a throttle system. Most commonly, the speed contract or throttle system is actuated by a foot-operated accelerator or gas pedal that can be depressed by the driver, the extent of the depression being set up to control engine speed. Manual accelerator devices such as handles are also known.
In traditional mechanically driven speed control or throttle systems, the accelerator pedal, handle or the like was mechanically coupled to a throttle valve in the fuel/air delivery system such that depression or other operation of the pedal, handle or the like opened the valve, increased the fuel/air supply, and caused an increase in engine and hence vehicle speed. From the throttling action of the valve, the term came to be used loosely for the entire engine speed control system. In such mechanical throttle systems, the speed can be limited in a number of mechanically driven ways, for example by providing a secondary means to limit the extent to which the valve can open, by disengaging the throttle pedal or handle from the valve at the desired speed etc. In particular, speed limiter systems might be fitted which acted to limit fuel or fuel/air flow into the system, for example by a suitably placed valve means fitted within a fuel supply line.
Newer vehicles increasingly operate so-called “drive-by-wire” engine speed control systems in which a direct mechanical link between the mechanical accelerator actuator and a throttle valve or other control mechanism is no longer present. Instead, an indirect electronic or electromechanical system is used, typically incorporating an electromechanical accelerator actuator unit. This electromechanical system is set up so that when a mechanically actuated throttle actuator such as an accelerator/gas pedal or handle is depressed or otherwise operated in the usual way an electrical signal is generated which can be processed via an engine management system to control the engine speed in any suitable manner, for example by control of fuel and/or air intake or otherwise. As used herein, “throttle” is used in the broadest loose sense to refer to the actuation system to control engine speed, and does not imply only a system where the engine has a classical throttled carburettor intake, but is intended to cover any actuation system to control engine speed, in particular by controlling the fuel and/or air intake of the engine in any manner.
In electronic systems, the signal generated by the throttle actuator still varies in some functional relationship with the extent of actuation, and for example with the extent to which an accelerator pedal or handle is depressed or otherwise operated. As in fully mechanical systems, the system will be configured such that a greater extent of actuation, for example greater depression of the accelerator pedal, generates a greater signal that will tend to be interpreted by the engine management system as instructing a greater engine speed. However, there is no direct mechanical actuation link between the accelerator pedal, handle or other throttle means and a throttle valve, fuel injection system, or other control means controlling engine speed.
For the reasons set out above, a number of circumstances are still likely to arise where there might be perceived to be a need to limit the vehicle speed to a predetermined maximum. However, there is no longer a direct mechanical link within the throttle system, and purely mechanically limiting devices of the sort which have been developed for such direct mechanical throttle systems are no longer necessarily applicable.
Most drive-by-wire vehicles include complex electronic engine management systems which have as only one of their functions the receipt of an input signal from the electromechanical throttle means and the use of this signal to control engine speed. Such engine management systems might include more complex capabilities associated with a cruise control function and the setting of a cruise control speed. While such engine management systems could therefore be used, subject to modification, to set a maximum speed, they are likely to be an unnecessary complex and expensive alternative where only a simple predetermined upper limit speed is required. When a simple limit speed is desired, an option that does not necessarily require a complex engine management computer is desirable.
Difficulties can arise with fitment of a simple secondary limit device in vehicles with a complex engine management system, especially where the device is of a type that acts to limit fuel or fuel/air flow into the engine. Many conventional complex engine management systems are likely to treat such an unexpected variation in fuel flow as a fault, and may shut the engine down or revert to some safe mode of operation. Other systems may continue to operate, but in a such a manner, given the unexpected variation in fuel flow, as to risk long term damage. Thus, fitment of a secondary system that restricts or interrupts fuel supply might not be compatible with a vehicle engine management system.
As a secondary consideration, which is especially encountered for large vehicles likely to handle multiple terrain conditions, such as trucks or wagons for both road and off road (for example, quarry/mine/construction site) use is the desire to have a lower limit speed applied to the rough terrain. Again, it is desirable that a vehicle speed limiter system can provide a simple mechanism to effect a limit at either speed with a throttle system that does not have a direct mechanical link. Again, since a simple limit speed is desired, an option which does not necessarily require complex modifications to an engine management computer is desirable.