GB2083610A

GB2083610A - Method of controlling a vehicle ventilating air flow

Info

Publication number: GB2083610A
Application number: GB8125040A
Authority: GB
Original assignee: Behr GmbH and Co KG
Current assignee: Mahle Behr GmbH and Co KG
Priority date: 1980-09-15
Filing date: 1981-08-17
Publication date: 1982-03-24
Also published as: FR2490160B1; DE3034786C2; FR2490160A1; DE3034786A1; GB2083610B

Abstract

In a method of controlling the quantity of air for ventilating or air conditioning the passenger compartment of a vehicle, i) the flow of air in a channel subject to dynamic air pressure is controlled by altering, by means of flaps (7, 8, 9) the air flow cross-section, and ii) the air flow rate in the channel is controlled by altering the speed of rotation of a fan (12). In dependence on vehicle speed, the air flow cross-section is altered in at least two steps and the fan rotation speed is infinitely varied, the rotation speed also jumping from one value to another when the air flow cross-section is abruptly changed. The flap adjustment drives (4, 5, 6) and the fan motor (11) are controlled by electronic control means (1, 10) which can be regulated from a tachometer (2) and a setting device (3). The arrangement is such that the variation of air flow cross-section as a function of vehicle speed follows a stepwise path, while the variation of the fan rotation speed as a function of vehicle speed follows a saw-tooth path. <IMAGE>

Description

SPECIFICATION Method of controlling a ventilating airflow This invention relates to a method for controlling the quantity of air for ventilating or air conditioning a vehicle. The invention also includes apparatus for carrying out the method.

One problem in ventilating or air conditioning a vehicle is to maintain the air stream required for ventilating or air conditioning for instance a passenger compartment at a constant preselected nominal value. Any change in the speed of the vehicle is accompanied by a change in the dynamic air pressure in the air inlet channel of the vehicle and hence a change in the rate of flow of air through the channel, unless measures are taken to compensate for this pressure, for example by alteration of the cross section of the channel by means of flaps andlor an alteration in the speed of rotation of a fan driving the air stream in the channel.

A method of adjusting the quantity of air by means of a manually operated air quantity control device is disclosed in German Patent Specification No.

2,654,552. The switch is adjusted to a particular setting depending on the individual comfort requirements of the passenger to provide for a particular cross section of airflow or position of the flap and a particular fan speed. Although the passenger has the choice of six different settings, these do not remain constant when there is a change in the speed of the vehicle and the deviation of the actual value from the set value must then be corrected by manual readjustment of the air quantity control device. This not only distracts the driver but is also an impairment of comfort.

An automatic control device for maintaining the air stream constant has been disclosed in German Patent Specification No. 1,680,228, in which both the speed of rotation of the fan and the position of the air flap are infinitely variable in dependence upon vehicle speed. This control device has an elaborate adjustment drive (i.e. a coil with a plunger-type armature) involving return of the flap by electrical means. Moreover, the range of control of this device is limited by the range of the fan speed. For present day vehicles with their wide speed range, such a control device would lose its effectiveness, i.e. its quality of control, in the upper speed range.

It is an object of the invention to provide an improved method of controlling the air quantity and also to provide an apparatus for carrying out this method, so that a constant air quantity preselected at a given value is automatically maintained in the vehicle at every vehicle speed.

According to this invention there is provided a method of controlling the quantity of air for ventilating or air conditioning a vehicle by controlling i) the flow of air in an air supply channel subject to dynamic air pressure by altering the airflow crosssection of the channel, and ii) the airflow rate by altering the speed of rotation of a fan, wherein the air flow cross-section is altered in at least two steps in dependence upon vehicle speed, and the fan rotation speed is substantially infinitely varied between the two steps, the fan rotation speed also jumping from one extreme value to another when the airflow cross-section is abruptly altered, so that variation of airflow cross-section as a function of vehicle speed follows a stepwise path and variation of the fan rotation speed as a function of vehicle speed follows a saw-tooth path.

This automatic control operating in dependence on velocity can provide a constant air stream over the whole speed range of the vehicle without the driver having to make any manual adjustment as the speed changes, apart from the initial preselection of the given or nominal value. The requirement for comfort is thus largely fu If i I led and the driver is relieved of a task which could impair his concentration. Since the control of the airflow cross-section is step-wise, it is possible to use simple devices such as flaps with adjustment drives, for example vacuum boxes, but a constant air quantity is nevertheless ensured due to the abrupt changes in the speed of fan rotation, i.e. the saw-tooth variation in speed.

The entire range of speeds of the fan can be utilized for each step, with the result that the quality of the control of air quantity is improved over the whole speed range of the vehicle.

Flaps and the fan speed may be controlled by an electronic control unit into which is fed an electrical input signal, firstly from a tachometer indicating the vehicle speed and secondly from a setting device indicating the nominal value for the quantity of air when the vehicle is stationary. This ensures by simple means that each speed value is associated with a particular fan speed and with a particular position of the flaps so that the quantity of air remains constant.

The fan speed may be controlled by the voltage of the electric motor, i.e. by simple, known means, although the constant part of the saw-tooth function may also represent any function produced by the electronic control unit.

Certain vehicle specific parameters may be stored in the electronic control unit, e.g. the speed values at which the step-wise changes take place. This enables the method of control to be adapted to different vehicles, in particular to their different speed ranges.

The step-wise changes may be associated with particular speeds of fan rotation, the difference in speed of rotation (step-wise change in speed) depending upon the difference in the cross sections of airflow (step-wise change in cross section) and the velocity (dynamic pressure) at the position of step-wise change. This ensures constancy of the air stream in spite of any unsteadiness in the adjustment means, flaps and fan. An increase in comfort may thus be achieved.

An embodiment ofthe invention will now be described by way of example, with reference to the drawings, in which: Fig. la is a graph showing the variation of blower speed n with vehicle speed v; Fig. 1b is a graph showing the variation in crosssection of air flow A with vehicle speed v; Fig. 1c is a graph showing the variation in rate of airflow m with vehicle speed v; Fig. 2 is a block circuit diagram containing the components of a control unit; and Fig. 3 is a diagram of a ventilating system with adjustment elements and adjustment drives.

Referring to the drawings, Figures 1 a, b and c show the three functions, blower speed n, air flow cross section A and airflow rate m each plotted against the same abscissa, the vehicle speed v, which is sub-divided into three ranges, 0 to I, I to II and ll to Ill.

Figure 1a shows the blower speed n varying continuously within each range, 0 to I, I to II and II to Ill from a maximum value nmax to a minimum value nmin. At the points of transition I, II and Ill from one range to the next, the speed of rotation jumps abruptly from one extreme value to another, viz from n,mjn to nimax, from niimin to niimax and from n",mjn to niiimax or conversely, so that a saw-toothed profile is obtained over the whole velocity range v from 0 to Ill.Above the point of change Ill, the speed of rotation remains constant in this particular embodiment because the influence of the dynamic pressure is virtually eliminated when the cross section of air flow is closed; in that case, any leakage air still present is delivered at a constant blower speed.

Figure 1 b shows the step-wise variation ofthe air flow cross section A plotted against the several ranges from 0 to Ill and upwards. The airflow cross sectionAthus remainsconstantwithin each range0 to I, I toll and II to Ill, and changes abruptly at the points of change I, ll and lil. The air flow cross section is at a maximal in the range 0 to I, as indicated by Ao and is approximately half closed in the range I to II as indicated by A,, while in the range II to Ill it amounts to only ca. 20% that of Ao, as indicated by A". At velocities above that of Ill, the air flow cross section is closed although there is some airflow due to leakage but in this highest velocity range this flow is virtually constant, i.e. independent of the dynamic pressure.

In Figure 1 c, the airflow rate m inside the vehicle is plotted over the whole range of vehicle velocities.

The air flow remains constant at the nominal value mnom, as can be seen from the graph. In the first velocity range from 0 to I, for example, this is due to the fact that while the air flow cross section Ao remains constant within this range, the fan speed n decreases continuously from a maximum speed nO to a minimum speed nimin in inverse ratio to the increase in dynamic pressure.When the first position of stepwise change I is reached, which may correspond, for example, to a vehicle speed of 80 km/h, the cross section of air flow Ao is abruptly reduced to A1 while the speed ofthefan is abruptly increased to a maximum value n,,,,. Thereafter, the speed n continuously decreases with increasing vehicle speed v until it reaches a minimum value n"mjn at the next point of change Il while the cross section of air flow A, remains constant.

At this point, the cross section of airflow A1 is abruptly reduced to A" and at the same time the fan speed is abruptly raised to a maximum value niimax.

As the vehicle speed v continues to increase, the fan speed again falls continuously until it reaches a minimum value n",mjn at the change point Ill. At this point Ill, the cross section of airflow is abruptly reduced from A11 to A111, i.e. it is closed completely and only a leakage cross section remains. At the same time, the fan speed is abruptly increased to ni'imax and from this point Ill onwards it can remain constant even if the vehicle velocity continues to rise since the quantity of leakage air entering the cross section is virtually constant.The conditions of transition must be fulfilled at all the change points I, II and Ill, namely that the rate of air flow at the larger cross section of airflow and lower fan speed must be equal to the rate of air flow at the smaller cross section of air flow and high fan speed. It is this condition which results in the differences in speed of rotation and height of the steps at the change points l, ll and Ill. The various fan speed differences nimax - flimin at point I and ni'max- n11min at point II in proportion to the corresponding differences in cross section Ao-A and A, - A" result from the pronounced nonlinearities of the quantities of inflowing air.

Figure 2 is a block circuit diagram showing the main components of apparatus for carrying out the method of the invention. It includes an electronic control unit 1 which is supplied with signals proportional to the vehicle speed from a tachometer 2. This unit I in addition receives an input signal representing the nominal value for the air quantity, a value which can be preselected as desired by a setting device 3.

Adjustment drives 4, 5 and 6 which control flaps 7, 8 and 9 in the air channel are electrically connected to the electronic control unit 1. These flaps vary the airflow cross section step-wise. The adjustment drives are preferably in the form of vacuum boxes activated by all or nothing magnetic valves. The electronic control unit 1 is also connected with an electronic fan control 10 which transmits its output signals to an electric motor 11 which in turn drives a fan 12 to move the air stream in the air channel. The electronic control unit 1 is supplied with certain vehicle specific parameters, such as the particularvehicle speeds associated with the various change points l, ll and Ill and the fan speeds associated with those speeds as illustrated in Figure 1a.When the vehicle reaches these speeds, the flaps 7, 8 and 9 are successively opened or closed to produce the step-wise variation in cross section of airflow represented in Figure Ib. The continuous control of fan speed in accordance with a particular function is carried out by way of the electronic fan control 10 and which also receives its input signals dependent upon the vehicle speed from the electronic control unit 1.

Figure 3 illustrates that part of a ventilating or air conditioning system of a vehicle which contains the adjustment elements, adjustment drives and control devices necessary for carrying out the method of the invention. An air channel 13 has two air inlets 14 and 15 opening into itthrough airinletchannels 16 and 17. The air channel 13 contains a fan with a motor 18 and a fan wheel 19 which may be an axial wheel or a radial wheel. The air inlet channel 16 contains a flap 20 which may be moved into the closed position and the open position 20' indicated in broken lines by means of a vacuum box 22 with a magnetic valve (not shown). The other air inlet channel 17 contains a flap 21 which may be moved into three different pos itions, 21,21' and 21", by means of a double vacuum box 23 with magnetic valves (not shown). The flap 21 may therefore assume a mid-position 21' in addition to its fully closed and fully open positions. The magnetic valves (not shown) which control the vacuum boxes 22 and 23 are connected to an electronic control unit 28 by electric leads 24, 25 and 26. This control unit 28 also has an electric connection 27 to the electric motor for the fan wheel 19 by way of an electronic fan control 29.

Claims

1. A method of controlling the quantity of air for ventilating or air conditioning a vehicle by controlling i) the flow of air in an air supply channel subject to dynamic air pressure by altering the air flow cross-section ofthe channel, and ii) the airflow rate by altering the speed of rotation of a fan, wherein the air flow cross-section is altered in at least two steps in dependence upon vehicle speed, and the fan rotation speed is substantially infinitely varied between the two steps, the fan rotation speed also jumping from one extreme value to another when the airflow cross-section is abruptly altered, so that variation of airflow cross-section as a function of vehicle speed follows a stepwise path and variation of the fan rotation speed as a function of vehicle speed follows a saw-tooth path.

2. A method according to claim 1, wherein the flow of air in the channel is controlled by at least two flaps and the fan is driven by an electric motor, the flaps and motor being controlled by an electronic control unit which receives its input signals both from a tachometer of the vehicle and from a setting device.

3. A method according to claim 1 or claim 2, wherein the substantially infinitely variable control of fan rotation speed within one step is carried out by means of an electronic fan control which alters the voltage of an electric motor of the fan.

4. Apparatus for carrying out a method according to any of claims 1 to 3, comprising an air supply channel subject to dynamic air pressure, at least two flaps in the channel to control airflow therein by altering the airflow cross section of the channel in at least two steps in dependence upon vehicle speed, and an electric motor driven fan whose speed of rotation is substantially infinitely variable between two steps, and which speed also jumps from one extreme value to another when the airflow crosssection is abruptly changed, and an electronic control unit for causing movement of the flaps to alter the air flow cross-section and for altering the motor speed, whereby variation of the air flow crosssection as a function of vehicle speed follows a stepwise path and variation of the motor speed follows a saw-tooth path, and wherein the electronic control unit has a vehicle specific programme into which are fed certain vehicle velocities which determine the stepwise changes.

5. Apparatus according to claim 4, wherein the particular vehicle speeds or the various stepwise changes are associated with particular fan rotation speeds.

6. A method of controlling the quantity of air for ventilating or air conditioning the passenger compartment of a vehicle substantially as herein described with reference to the drawings.

7. Apparatus for controlling the quantity of air for ventilating or air conditioning the passenger compartment of a vehicle, the apparatus being constructed and arranged substantially as herein described and shown in the drawings.