There is an ever-increasing requirement to ensure motor vehicles operate in their most efficient and environmentally friendly condition whilst simplifying manufacture of vehicles, particularly across a model range.

Thus, typically a modern motor vehicle will include an vehicle or engine management system associated with the vehicle and engine in order to ensure that exhaust emissions are as low as possible whilst fuel economy and performance are remain acceptable. Alternatively, there may be at least a memory device used to indicate engine and/or gearbox combinations for determination of specific operation of the vehicle. Furthermore, it will also be understood that the load and performance of an engine may vary during its life and even an individual journey. For example, the engine must reach its operating temperature from a cold start and will be required to quickly propel the motor vehicle from a crawling speed to those associated with highway travel.

As indicated above, an engine management system which monitors various parameters within a motor vehicle can provide some adaptation with regard to engine performance in order to achieve the necessary efficiency, etc. However, one of the greatest determining factors, with regard to engine performance in particular, is naturally the driver of the motor vehicle. Thus, such a driver should be made aware of the operating 5 conditions of the engine in order to allow better control. Traditionally, a tachometer in a motor vehicle has included a red line warning. This warning illustrates an engine speed, in terms of revolutions per minute (rpm) condition, which can be damaging to the engine. Normally, this red line has been determined as a compromise in terms of known engine 10 performance and expected operating conditions. Furthermore, these operating conditions may change from cold start up to sustained high speed driving. The red line is generally not a true indicator of the limit of acceptable operating conditions.

It will also be understood that generally different engine and gearbox 15 combinations will have different limitations. However, it is inconvenient to have different tachometers for respective models in a motor vehicle model range.

It is an object of the present invention to provide a motor vehicle tachometer with a red line warning which allows ready adaptation to 20 varying current engine operating conditions and for a'standard'tachometer

to be used for different engine and gearbox combinations in a vehicle model range.

In accordance with the present invention there is provided a motor vehicle tachometer whereby, when coupled to an engine, the engine speed (rpm) of said engine can be displayed upon a scale, said tachometer including a plurality of independently operable illuminating elements, said tachometer being coupled to interrogation means whereby the specific engine/gearbox combination and/or operation can be monitored in order to determine their type or an operating condition thereof and said plurality of illuminating elements being operated to indicate upon said scale of the tachometer the limit of the range of acceptable, or efficient, engine speed (rpm) for that specific engine/gearbox combination dependent upon the specific engine/gearbox combination identification or the operating condition monitored by the interrogation means.

The interrogation means may monitor revolutions per minute (rpm) and/or coolant condition, e. g. temperature/flow and/or lubrication conditions, e. g. temperature/flow rate and/or engine manifold pressure and/or air temperature/flow rate and/or ignition spark condition and/or dwell time and/or advance/retard position for ignition and/or fuel injection in terms of volume, dispersion and rate and/or exhaust emissions/temperatures, etc.

The interrogation means may be incorporated within an existing engine

management system of the motor vehicle. Alternatively, and possibly solely, the interrogation means may simply determine the engine and gearbox combination to operate only that illuminating element appropriate for that engine and/or gearbox combination.

The interrogation means may predict future engine operation conditions by projection or from previous behaviour monitored by the interrogation means in order to appropriately operate the illuminating element required.

For the acceptable engine speed (rpm) for each incremental operation condition, a respective red line warning may be provided by one illuminating element to indicate the upper limit of acceptable engine speed (rpm) whilst a green line may be provided by another illuminating element to indicate the ideal engine speed (rpm) for the operating condition determined by the interrogation means. This ideal engine speed (rpm) or green line illuminating element may also indicate the desirability to change gear for best vehicle performance.

As described above, a single tachometer including a plurality of illuminating elements may be provided for a range of engine types and gearbox combinations by providing that, dependent upon engine and gearbox type combination identification only, determined by the interrogation means, one illuminating element is actuated to define that engines"red-line"limit of acceptable rpm.

The illuminating elements may be light-emitting diodes (LED).

An embodiment of the present invention will now be described by way 5 of example only with reference to the attached drawing of a schematic representation illustrating the cascade manner of present tachometer operation.

The use of tachometers in motor vehicles is well known in order to provide, in association with the speedometer, a wide range of information to 10 the driver in terms of engine and gearbox operating conditions. The speedometer alone would not indicate whether the motor vehicle is being excessively rewed such that damage may occur through misfires, wear or localise overheating/temperature differentials within the engine.

As indicated above, typically, a red line warning is provided upon the 15 tachometer to indicate the acceptable limit of engine speed (rpm) for that engine and gearbox combination. Previously, this red line limit was a compromise based upon the designer's expected operating conditions for the motor vehicle engine. Thus, cold start up and other transient factors which effect engine condition and performance would not normally be considered.

These short term divergences would be accepted provide such conditions did not persist for too long a time period and so overly wear the engine or gear box. Clearly, whilst these conditions persist it will also be appreciated that the vehicle may have exhaust emissions which would not be acceptable in normal operation.

It will also be understood that different engines and gearbox combinations will present different limitations so that varying red line warning positions will be required in the tachometer scale. Clearly, it is at least inconvenient to have individual distinct tachometers for each of such combinations in a vehicle model range.

In order to meet more stringent exhaust emissions control and to increase reliability and performance, a large number of current motor vehicles include vehicle management systems. These systems interrogate and monitor various parameters within a motor vehicle in order to adapt principally the ignition, air volumes and the fuel requirements for a motor vehicle engine in comparison with an identified engine type and gearbox combination. Thus, a reasonable understanding of the motor vehicles operating conditions can be determined from the sensors used to determine these parameters. This information can be utilise in order to adapt the ignition, air volumes and fuel presentation within the motor vehicle engine.

Clearly, these management systems also interrogate or know, as requested,

identities for functional vehicle components such as the engine and gearbox type. Thus, vehicle operation can then be effected in accordance with that engine and gearbox combination. This identification of the engine and gearbox is clearly normally fixed for a vehicle model but nevertheless is known and identified by the management system as required for operational purposes.

In accordance with the present invention, engine monitoring and identifying facilities of the vehicle management system are utilise in order to interrogate the vehicle engine and possibly gearbox in order to provide a red line warning within the tachometer scale. This red line may vary dependent upon the current engine operating conditions, or may be substantially fixed for a particular engine and gearbox combination. In either event the driver will be able to adapt his driving performance accordingly.

Each red line warning will generally be incremental in terms of the engine operating conditions or engine/gearbox combination type and will comprise an independently operable illumination element such as a light emitting diode (LED). These LEDs will be configured in a"secret till lit" format. Typically, three illuminating elements, as described later, will be provided for respective relevant engine operating conditions or engine/gearbox combination types.

The engine operating conditions which typically may be monitored to include the engine speed in terms of revolutions per minute (rpm) of the engine itself along with coolant condition and/or lubrication condition and/or manifold pressure and/or air temperature/flow rate and/or ignition spark condition and/or dwell time and/or advance/retard position and/or fuel injection performance and/or exhaust emissions/temperature and/or battery conditions, etc. From these monitored parameters, the vehicle or engine management system through the interrogation means can determine the limit of acceptable engine speed (rpm) for that engine/gearbox combination.

The interrogation means incorporated in the management system will determine current operating conditions and powertrain i. e. engine and gearbox combination. Thus, the interrogation means will ensure the appropriate illuminating element is operated in the tachometer scale.

The interrogation means in order to operate or trigger the illuminating element appropriate to the monitored operating conditions or engine and gearbox combination will generally utilise either an appropriate algorithm or a look-up table type profile held in its memory or use some sort of fuzzy logic in order to determine the appropriate illuminating element to be triggered. Alternatively, the interrogation means may simply identify a particular engine and gearbox combination in order to illuminate an appropriate illumination element. It will be appreciated that any operating condition profile may be adapted over the life of the engine in order to

account for variations in the engine performance during that lifetime.

Alternatively, the operating condition profile could be stored in a read-only memory (ROM) device for a specific engine and gearbox combination and simply referred to by the interrogation means in order to find the appropriate illuminating element to be triggered, and maintain that illumination over the full range of operating conditions.

It will be appreciated from the above, a further advantage of the present invention is that a single tachometer with several illuminating elements could be used for a wide range of engine and gearbox combinations used in different motor vehicle models. In such circumstances, only one illuminating element may ever be operated but the necessity of providing different red lines warnings in specific tachometer scale ranges for each engine type in each model range is eliminated and so the parts inventory necessary for the motor vehicle manufacturer is reduced. The interrogation means would simply determine the particular engine and gearbox combination and operate the appropriate illuminating element for that combination in a generic tachometer.

In terms of operation, the tachometer in accordance with the present invention will generally operate as follows.

Upon ignition, a pre-determined illuminating element will be triggered and so a red line warning relevant to that condition is presented in the tachometer range. This will normally occur upon the general start-up bulb check within a motor vehicle. This illuminating element may then be 5 switched off until the engine speed is increased or rewed to a pre-set level.

Thus, the illuminating element will be reactivated and so triggered to present a red line warning in the tachometer range. However, more normally, an illuminating element will remain lit during normal driving operations.

10 A tachometer is used to display the engine speed of the vehicle in revolutions per minute (rpm). The displayed speed will be derived from a received engine speed signal from the vehicle management system. Thus, the tachometer operates as follows:- Ignition position 0 (engine off)-the tachometer will point to 0 RPM.

15 Ignition position 1 (auxiliary equipment powered but engine still off)- the tachometer will point to 0 RPM.

Ignition position II (normal engine operation condition)-the tachometer will point to the current engine speed.

Ignition position III (starter motor activated to crank engine)-the tachometer will freeze in its current position and will resume when engine cranking is finished.

The tachometer pointer will respond at a rate allowing it to remain 5 within 2% of the engine speed signal during periods of changing engine speed. The tachometer pointer response rate will be limited to a tacho max response rate which balances accuracy with inherent volatility of engine speed as the vehicle is driven.

With regard to the red line illumination, for example, there are for 10 example three sectors constituted by distinct illuminating elements within the red line area of the tachometer which will be illuminated at successively greater engine speeds.

Ignition position 0 (Off) and ignition position 1 (Aux)-all red line illuminating elements will be extinguished.

15 Ignition position II (On)-The red line area will remain hidden until the tachometer pointer exceeds a first engine speed threshold upon which the first illuminating element is illuminated. As each engine speed threshold is exceeded a successive illuminating element will be illuminated and the normally previous elements extinguished. Each red line element will

remain illuminated until the engine speed has fallen below the red line threshold by the value of a pre-determined red line hysteresis.

Ignition position III (Crank)-the red line illuminating elements will remain in their current state until engine cranking has finished.

Permanent red line illumination-if a red line actuation engine speed threshold for the tachometer is set to 0 RPM then at least the first red line illuminating element will be illuminated for the duration of ignition i. e. engine operation.

As indicated previously, the red line may be fixed for a particular engine type or may vary incrementally dependent upon the varying engine operating conditions determined by the interrogation means.

The interrogation means may also be arranged to predict future engine operating conditions and so vary the triggered illuminating elements accordingly.

By utilising the vehicle management system in order to determine the appropriate red line limit for a motor vehicle engine in accordance with the presented operating conditions, it will also be appreciated by those skilled in the art that the vehicle management system through the interrogation

means may also be able to predict the ideal engine speed or rpm level for the current engine conditions. Thus, in the present invention, the tachometer range may incorporate a plurality of red illuminating elements to indicate the appropriate limit of acceptable rpm for that engine and gearbox combination and possibly related to the presented operating conditions whilst a plurality of green illuminating elements indicate the ideal engine speed (rpm) for the engine under those conditions.

The preferred illuminating element is a light-emitting diode (LED) due to its relatively low electrical power consumption and long operational life.

It will be understood that the illuminating element at the appropriate red line or ideal operation rpm level may be illuminated for considerable periods of time or intermittently so the relative reliability of LED devices is advantageous.

In the attached drawing of a schematic representation of tachometer operation is illustrated. It will be noted that ignition activates both a red line lamp check timer 1 and a red line illumination qualification module 2.

The timer 1 checks the illuminating elements 3,4,5 i. e. LEDs are working by presenting a check flag for each illuminating elements 3,4,5 through the module 2. Thus, timer 1 operation generally only occurs at engine ignition start up as described above.

Assuming all the elements 3,4,5 are functional, then an engine speed signal is presented to the module 2 and this module determines which illuminating element 3,4,5 in the tachometer 6 is illuminated. Thus, the tachometer 6 has a red line provided by a respective illuminating element 3, 4,5 dependent upon module 2 determination of interrogated engine speed and identification knowledge of the engine/gearbox combination.

As indicated above, the module 2 may also determine which element 3, 4,5 is operated dependent upon monitored engine conditions such as coolant temperature. However, generally after initialisation, it will be engine speed which determines respective element 3,4,5 operation. Thus, if S1= illuminating element extinguished and S2= illuminating element operated then there are illuminating element transitions T1 and T2 where T1 defines the criteria for illuminating element operation whilst T2 defines such element's extinguishing criteria. In such circumstances, by judicious choice of the engine speed thresholds for T1 and T2, operation and extinguishing of each element 3,4,5 can be achieved. It will be appreciated that typically for each transition T1 and T2 it will be necessary to have vehicle engine ignition and a confirmation flag signal from the lamp check timer 1 that the illuminating element 3,4,5 is working. However, the distinguishing feature for each operation transition T1 for a respective element 3,4,5 will be the engine speed exceeding a threshold for each element's 3,4,5 operation. Similarly, the distinguishing features between extinguish transitions T2 for elements 3,4,5 will be the engine speed falling below that threshold for operation (i. e. T1) minus a hysteresis rpm value to provide an in-built response lag to the red line determined by the element 3, 4,5 and to avoid'gear-change'transients etc., adversely effecting the 5 tachometer red line response.

It will be appreciated that the engine speed threshold could be set at 0 rpm for transitions T1 and T2 in order that any of the elements 3,4,5 could be permanently illuminated for a particular engine/gearbox combination identified by the module 2 through interrogation. Thus, the same 10 tachometer 6 could be used for different engine and gearbox combinations with the module 2, through interrogation of the vehicle management system and by choice of engine speed thresholds for transitions T1, T2, determining which element 3,4,5 is illuminated to present a pre-set red line in the tachometer 6.