VEHICLE ΔCCESSORy EKIWE CLUTCH CONTROL FIELD OF THE INVENTION The present invention relates generally to the efficient use of accessories fitted to motorized vehicles and in particular to the control of such accessories whereby a substantial portion of the energy required to drive the accessory is provided by the momentum of the vehicle while the vehicle is not being driven by its motor, hereinafter referred to as a backoff mode.

In a particularly useful embodiment of the invention an air conditioning unit in an automobile is controlled to provide a substantial portion of its cooling during backoff periods when the accelerator pedal is released and the vehicle is moving under its own momentum.

PRIOR ART In prior art automobile air conditioning equipment the possibility that fuel savings could result from the preferential operation of the car-cooler during the vehicles backoff mode has not been recognized.

US Patent 3186184 to Pruitt is the first of many patents which discloses switching off the power to the clutch of the car cooler during periods where high engine power is required, for example during overtaking other vehicles on the road or climbing steep hills. Other patents disclose improvements to this system: US Patent 4155225 to Upchurch Jnr. uses a mercury switch to detect acceleration of the vehicle for controlling car cooler as stated in US Patent 3186184.

US Patent 4596121 to Ogata discloses a mechanical device for detecting high power demand on diesel engines for controlling the car .cooler as stated above.

US Patent 3462964 to Haroldson discloses a vacuum operated switch which would detect a high power requirement and switch off the car cooler during this demand. US Patent 4424682 to F.S. Miska & J.A. Duddles

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discloses a car-cooler device that uses a timed cyclic override at a preselected ambient temperature and vehicle speed.

Other car-cooler control devices that operate on a similar principle as US Patent 3186184 are disclosed in US Patents 4269033, 4355523 and 4445341.

SUMMARY OF THE INVENTION The present invention consists in a control system for a vehicle accessory adapted to be driven by the engine of an automotive vehicle, the control system being arranged to cause engagement and disengagement of the accessory from the engine whereby the accessory is driven predominantly when the vehicle is operating in backoff mode. Throughout this specification the term "backoff mode" will be used to describe an operating condition where the engine is not being used to power the vehicle but rather the momentum of the vehicle is turning the engine. In the case of an automobile the backoff mode occurs when the accelerator pedal is released while the vehicle is in motion.

In a preferred embodiment of the invention, backoff mode is sensed by detecting manifold pressure that is considered below normal idle manifold pressure. In another embodiment of the invention the referred backoff mode is sensed by detecting a preselected range of throttle positions.

In a further embodiment of the invention the referred backoff mode is detected by using an accelerometer such as a mercury switch to detect a condition of deceleration. In preferred embodiments the accessory is an air conditioning system in which the internal cabin temperature of the vehicle is detected by a thermistor in conjunction with a stable voltage supply and selectable switching comparators to indicate an operational cabin

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temperature range window.

In another embodiment incorporating an automotive air conditioning system, the internal cabin temperature is detected by the usage of an expandable chamber filled with a gas such that the expansion of the chamber is proportional to the temperature of the surrounding air, this chamber actuating an electrical switch to activate (turn on) or deactivate (turn off) the switch at a set temperature. In a preferred automotive air conditioning system the activation of the auto accessory during backoff is overridden when the temperature range of the cabin falls outside the selected temperature range. The overriding effect is as follows: a) When the cabin temperature is above the selected range the accessory will remain on regardless of backoff mode, b) When the cabin temperature is below the selected range the accessory will remain off regardless of backoff mode.

In the preferred automotive air conditioning system according to the present invention the auto accessory is automatically shut off during periods when the operation of the engine approaches its maximum capacity as indicated by the occurrence of high pressure in the inlet manifold of the engine.

Preferably, embodiments of the invention will be arranged to avoid response to false backoff mode signals by preventing signals which are shorter than a preselected length from being relayed to control of the auto accessory thereby saving clutch life and enhancing passenger comfort,

In further embodiments of car air conditioning systems, a heater is controlled such that heating is enabled when the cabin temperature is below the desired range window.

Embodiments of the present invention provide a car-cooler clutch control apparatus in which the compressor can be engaged or disengaged from the engine so that less engine power is required to drive the compressor whilst still maintaining suitable passenger comfort. This is achieved by preferentially engaging the compressor to the engine whilst the momentum of the car is driving the engine and hence the car-cooler compressor (i.e., during backoff mode). An. embodiment of the car-cooler apparatus comprises of a vacuum switch to sense backoff mode, a timing circuit, temperature sensor, an electronic logic circuit and relays.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail with reference to the accompanying drawings in which:-

Fig. 1 illustrates a circuit schematic for a voltage regulator subsystem of a preferred embodiment of an accessory control system;

Fig. 2 illustrates a circuit schematic for a temperature control subsystem of the preferred embodiment of an accessory control system;

Fig. 3 illustrates a circuit schematic for a vacuum subsystem of the preferred embodiment of an accessory control system; Fig. 4 illustrates a circuit schematic for a logic subsystem of the preferred embodiment of an accessory control system;

Fig. 5 illustrates a circuit schematic for a delay/driver subsystem of the preferred embodiment of an accessory control system.

DETAILED DESCRIPTION It is a well known fact that car air conditioning systems require a substantial fraction of the power generated by the car engine for their operation. Consequently the added power requirement for driving the

air conditioning system reduces the fuel efficiency and compromises car performance during periods of high power demands (e.g. when overtaking).

Embodiments of the present invention provide an improved electronic detection and control system that switches the compressor of an automotive air conditioning system in such a way as to achieve required temperature control of the car's interior, increased responsiveness of the car during periods of high power demand, and improved fuel efficiency. Some benefits of the preferred embodiment of the invention are outlined below: (a) Improved fuel consumption - Gained by preferentially switching on the air conditioning system compressor when the car's momentum is driving the engine (this is referred to as backoff mode). In backoff mode the accelerator pedal is not depressed whilst the vehicle is in gear and in motion (i.e. , no additional fuel consumption is required to drive the air conditioning system's compressor). (b) Increased responsiveness and improved fuel consumption of the car during periods of high power demands on the engine - This is achieved by sensing the engine intake manifold vacuum together with driver cabin temperature and processing these two inputs using the logic subsystem (to be described later). The air conditioning system compressor is then preferentially switched off during periods of high power demand (e.g., when the car is overtaking corresponding to a low vacuum state). By switching off the compressor, power generated by the engine is available for propulsion of the car in response to the power demand instead of being diverted to interior cooling needs. After the period of high power demand is over the intake manifold vacuum will increase and the compressor will automatically switch on to maintain temperature control.

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(c) Preservation of the longevity of the air conditioning system compressor clutch and maintain a more stable temperature control - The preferred embodiment of the invention has the capability of discriminating between extended periods of high power demands and short term or instantaneous high power demands (say less than a few seconds e.g., gear changes). In the event of instantaneous high power demands the compressor will not be switched off in order to preserve the longevity of the air conditioning system compressor clutch, and to maintain a more uniform temperature control.

(d) Maintain vehicle cabin temperature control - The temperature sensor installed in the interior of the car continuously monitors cabin temperature. The driver can preselect the temperature at which the air conditioner should switch on and the preferred embodiment of the invention maintains the cabin temperature to below this preselected value (option 1). In the event that the vehicle has heating as well as air conditioning, the driver can select a temperature range to which the cabin should be maintained and the embodiment of the invention will control both the heater and air conditioner in such a way as to maintain the required temperature range (option 2) .

(e) Increased responsiveness override during excessively hot days - The increased responsiveness described at paragraph (b) above can be overriden if the car cabin temperature is sufficiently excessive to necessitate that the need for cooling of the car interior has priority over car performance during periods of high power demands. The driver can select a temperature threshold at which this override condition is to occur .

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The preferred embodiment of the invention provides an apparatus that controls motor vehicle accessories such as air conditioning/heating systems. Typical control is achieved through strategic operation of the clutch in the air conditioner and valve in the heating system. An electronic controlling device incorporating the five subsystems described below is used to achieve the overall aims of this embodiment. These are to enhance car responsiveness during periods of high power demands, maintain cabin temperature control, and save fuel by using energy otherwise used in braking or slowing down the vehicle to drive the air conditioning system compressor.

The embodiment of this electronic controlling apparatus which is described herein can be fitted in the drivers cabin of the vehicle and is described below in terms of its five component subsystems:

(a) Power supply and voltage regulator

(b) Temperature detection and control

(c) Vacuum sensing and control (d) Logic subsystem

(e) Delay and driver

An operational description of each of the abovementioned subsystems is given below with reference to the accompanying drawings. Referring to Fig. 1, the power supply and voltage regulator (PSVR) of the preferred embodiment is illustrated. Since a typical car battery system does not provide the sufficiently accurate voltage regulation required by the electronic components used in the control apparatus of the present invention, an independent voltage regulator is implement. Voltage regulation is achieved using a standard three pin positive regulator IC10 (LM317) with a voltage setting of 8 Volts set by variable resistor Rl and fixed resistor Rll which form a divider network to set the level on the regulator reference input. The

regulation voltage of 8 Volts was chosen to provide an accurate reference voltage for the comparators used in the apparatus and to provide effective baissing of the temperature transducer. Drivers for relays and LEDs use a less regulated 12 Volt supply.

The temperature detection and control subsystem (TDC) illustrated in Fig. 2 may be implemented in one of two forms. In its first form of the TDC, which is the simplest, two basic analogue comparators "LCOMP" and "HCOMP" are provided. LCOMP senses the LOWER temperature threshold of the car's interior and provides an ON CONDITION at the output of IClla when the temperature sensed by the temperature transducer TT, is greater than 20 degrees Celsius (nominal). The LCOMP temperature threshold may be preselected by the user adjusting variable resistor R2 to suit personal thermal preferences. HCOMP however, senses the UPPER threshold temperature which provides an ON CONDITION at the output of ICllb when the temperature as sensed by the temperature transducer TT exceeds a nominal temperature of 27 degrees Celsius. As with LCOMP, the HCOMP temperature threshold may be preselected by the user by adjusting variable resistor R3.

In its second form the TDC is arranged to achieve total climate control through the use of a third comparator associated with the car heating system. This comparator "WCOMP", can be configured such that an ON CONDITION is provided at the output of ICllc when the temperature as sensed by the temperature transducer TT is below a certain nominal threshold, say 15 degrees

Celsius. If this condition arises the car heater will automatically switch on. The WCOMP temperature threshold may be preselected by the user by adjusting variable resistor R4. A temperature detection subsystem that includes the

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second form of the TDC enables total automatic temperature control to be achieved. The user is able to select a "Thermal Comfort Zone" TCZ by varying resistors R2 and R4 to suit personal thermal comfort requirements based on individual metabolic rates (i.e., maintain cabin temperature between say 15 degrees Celsius and 20 degrees Celsius) .

The output states of comparator circuits LCOMP, HCOMP and WCOMP are respectively indicated by light emitting diodes LEDl, LED2 and LED3, driven by transistors Tl, T2 and T3.

In the vacuum sensing and control subsystem (VSC) which is illustrated in Fig. 3, a pressure transducer PT senses intake manifold vacuum levels in a range between 2 and 14 psi. The voltage output from this pressure transducer is amplified by a differential amplifier and gain stage formed by operational amplifiers IC12a, ICl2b, and IC14a. This output is then fed into two separate comparators "VCOMP" and "BCOMP" which switch at preselected voltage thresholds corresponding to required intake manifold vacuum levels. The comparator VCOMP is configured to provide an ON CONDITION (+8 Volts) at the output of ICl2c when the intake manifold pressure is GREATER THAN say 10 psi (nominal) corresponding to a state of HIGH POWER DEMAND. If the intake manifold pressure is LESS THAN this 10 psi nominal value, then VCOMP will provide an OFF CONDITION (0 Volts). The output from VCOMP is fed into the logic subsystem together with the corresponding outputs from the TT (see TDC and logic subsystem) .

The comparator BCOMP provides an ON CONDITION at the output of IC12d when the intake manifold pressure is GREATER THAN 13 psi (nominal). This particular ON CONDITION DISABLES the output to the air conditioning system clutch control apparatus (see Fig. 5) turning the

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air conditioner off. BCOMP RESETS this particular output ₍ see _F ig. 5 ₎ , when the intake manifold pressure reduces to below 13 psi.

_B oth VCOM _P and BCOMP thresholds can be set by the user by varying R5 and R6 respectively.

Light Emitting Diode LED4, driven by transistor T4 indicates the output state of the VCOMP comparator.

Referring to Fig. 4, the logic subsystem is a ^C MO ^S network of four _NA ND gates IC13a,b,c and d, providing the following truth table as a function of (LCOMP, HCOMP,

VCOMP) :

L _CO MP H _C OMP VCOMP ACCESSORY ON

1 0 0 1

1 1 0 1 1 1 1 1

It can be seen from the truth table above that the logic subsystem together with the TDC and VSC subsystems are combined to produce the following:

1. To provide an ON CONDITION to the car cooling system in cases where the cabin temperature is between 20 and 26 degrees _C elsius and intake manifold pressure corresponds to less than 10 psi.

2. τo provide an ON CONDITION to the car cooling system in cases where the cabin temperature exceeds 27 degrees Celsius and the intake manifold pressure is less than 10 psi.

3. To provide an ON CONDITION to the car cooling system in cases where the cabin temperature exceeds 27 degrees Celsius and the intake manifold pressure is between 10 and 13 psi. _{ι O} provide an OFF CONDITION to the car cooling system in the following cases

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⁽ complementary to the cases described at sub-paragraphs 1, 2, and 3 above ₎ : ^a - Cabin temperature is less than 20 degrees Celsius irrespective of intake manifold pressure. Cabin temperature is between 20 and 26 degrees Celsius and the intake manifold pressure is greater than 10 psi. ⁱ ntake manifold pressure is greater than 13 psi irrespective of temperature. is ai ^delay - ^{dt iV} " ^{SUbsysten as} "Crated _{in Fig s} ⁱ s also provided and comprises a t,,. , - * . a ., e csi ^. „ed to provide an oκ c -Z ^WWU _._ ^A _ ^1U W _ at tIhIe ou '!tpu '∞t o" _f " _TΠ *" _{I Λ}

. l. l ^' c.?_ i ^ls T ^{ιevea by an EC tiπe} " ^»• * ^•» * ^«i ««ιt i u t I a . ^{y tranS t} - *« *ich cha. _ges the Re

cond ⁱ tioning system relay to ooera _f . *■», clutch _r ^ _K . _• _. _• ae a e the compressor clutch. L ⁱ ght em ⁱ tting diode LED5 indicates the state o _f the a ⁱ r conditioning system drive relay _The this subsystem is threefold- ^UnCtl ° ⁿ ° ^f

1.

To prevent brief excursions to the _O FF ^CO ND ^IT I ^O N of the cooling system above during very short periods of high power demand ⁽ e.g., high intake manifold pressures during gear changes etc.).

T ^O buffer and preserve the mechanical clutch that drives the car cooling system from excessive wear and tear due to unnecessary, and SHORT INTERVALS ON and OFF switching

3. To provide the necessary power to drive the "lay or other driver to switch the air conditioning system clutch on and off