WO1991005675A1

WO1991005675A1 - Vehicle accessory drive clutch control

Info

Publication number: WO1991005675A1
Application number: PCT/AU1990/000482
Authority: WO
Inventors: Andrew John Doig; Maurice Alafaci
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-10-11
Filing date: 1990-10-09
Publication date: 1991-05-02
Anticipated expiration: 1992-04-11

Abstract

A control system for a vehicle air conditioner uses a manifold pressure sensing device to detect conditions of low power demand by the driver where the engine is acting as a brake. During these times the air conditioner is engaged to use energy supplied by the momemtum of the vehicle. At other times of higher power demand from the engine the air conditioner is disengaged from the engine except when the vehicle cabin temperature exceeds a predetermined upper limit.

Description

VEHICLE ACCESSORY DRIVE 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 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 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. (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. 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 R1 and fixed resistor R11 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 IC11a 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 IC11b 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 IC11c 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 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 LED1, LED2 and LED3, driven by transistors T1, 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, IC12b, 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 IC12c 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 air conditioner off. BCOMP RESETS this particular output (see Fig. 5), when the intake manifold pressure reduces to below 13 psi.

Both VCOMP 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 CMOS network of four NAND gates IC13a,b,c and d, providing the following truth table as a function of (LCOMP, HCOMP,

VCOMP):

LCOMP HCOMP 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 Celsius 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.

4. TO provide an OFF CONDITION to the car cooling system in the following cases (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.

b. Cabin temperature is between 20 and

26 degrees Celsius and the intake manifold pressure is greater than 10 psi.

c . Intake manifold pressure is greater than 13 psi irrespective of

temperature.

A delay and driver subsystem as illustrated in Fig. 5 is also provided and comprises a basic voltage comparator designed to provide an ON CONDITION at the output of IC11d a few seconds after a positive input is applied (say +8 Volts). This is achieved by an RC time constant circuit (R53 + C6) driven by transistor T6 which charges the RC circuit to a preselected reference voltage. The output of IC11d is duffered by transistor T5 to drive the

conditioning system relay to operate the compressor

clutch. Light emitting diode LED5 indicates the state of the air conditioning system drive relay. The function of this subsystem is threefold:

1 . To prevent brief excursions to the OFF

CONDITION of the cooling system above during very short periods of high power demand

(e.g., high intake manifold pressures during gear changes etc.).

2 . To 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 relay or other driver to switch the air conditioning system clutch on and off

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-

1. A control system for a vehicle accessory, wherein the accessory is arranged to be fitted to a vehicle powered by a motor and the accessory being powered directly or indirectly via power transmission means connected to the motor, the control system being arranged to cause

engagement and disengagement of the power transmission means, the control system comprising demand assessment means to assess a level of power demand by the vehicle for propulsion and accessory connection control means

responsive to the assessment means to control the

engagement and disengagement of the transmission means such that the accessory is predominantly connected to the motor only when the assessment means indicates a level of power demand by the vehicle which is below a predetermined level.

2. The control system of claim 1 wherein the accessory is connected to the motor predominantly only when the power demanded by the vehicle is negative.

3. The control system of claim 1 wherein the vehicle is powered by an internal combustion engine and the vehicle power demand is measured by measuring manifold pressure.

4. The control system of claim 3 wherein the accessory is connected to the engine predominantly only when the manifold pressure is below a level exhibited when the engine is idling.

5. The control system of claim 1 wherein the vehicle power demand is measured by measuring the position of a throttle connected to the motor.

6. The control system of claim 5 wherein the accessory is connected to the motor predominantly only when the throttle is within a preset range indicating a zero or negative power demand by the vehicle.

7. The control system of claim 1 wherein the vehicle power demand is measured by an accelerometer and the accessory is connected to "the motor predominantly only when the vehicle is decelerating.

8. The control system of claim 1 wherein the demand assessment means includes delay means arranged to prevent connection of the accessory to the motor during brief periods of low vehicle power demand.

9. The accessory control system of claim 1 wherein the accessory is an air conditioner having temperature sensing means arranged to indicate when the temperature within the vehicle is within a predetermined preferred range.

10. The accessory control system of claim 9 wherein override means are provided responsive to the temperature sensing means to continuously leave the air conditioner engaged when the temperature in the vehicle increases above a

predetermined upper temperature.

11. The accessory control system of claim 10 wherein the override means is also responsive to the temperature sensing means to continuously leave the air conditioner disengaged when the temperature in the vehicle decreases below a further predetermined lower temperature.

12. The accessory control system of claim 1 wherein the accessory is an electrical power generation unit for charging an electrical storage cell, said power generating unit having voltage sensing means arranged to indicate when the voltage of the storage cell is within a predetermined range and the control system being further arranged to control engagement and disengagement of the power transmission means in response to the sensing means.