DE10023519A1 - Cooling system for vehicles - Google Patents

Abstract

The invention is based on a cooling system (1) for vehicles with an internal combustion engine (2) and a transmission (15), the cooling system (1) having at least one fan and a coolant pump (6), which is dependent on one at least one point of the cooling system (1) is controlled, has a heat exchanger (3, 5, 16), a coolant distributor device (7, 8, 20) and a plurality of coolant circuits. DOLLAR A It is proposed that the speed of the coolant pump (6) increases with the power of the internal combustion engine (2) and the speed of the fan follows the speed of the coolant pump (6) by the fan only at a lower limit speed of the coolant pump (6) starts and only reaches its maximum speed when the coolant pump (6) has already reached its maximum speed for a while.

Description

The invention relates to a cooling system for vehicles according to the preamble of claim 1.

Today's cooling systems for vehicles are standard moderately equipped with a coolant pump through a constant ratio with the speed of a drive machine, usually an internal combustion engine, coupled is. There is also a heat exchanger designed as a cooler provided by which the coolant is conveyed and the from a speed-controlled fan with cooling air is struck. To get an optimal one as quickly as possible Operating temperature of the internal combustion engine is to be reached A bypass line is provided parallel to the cooler using a thermostat at low coolant temperature passed at least part of the coolant flow becomes. As soon as the optimal operating temperature is reached, the fan starts or its speed changes accordingly regulated the heat accumulation.

Because the entire cooling system for the maximum occurring Heat quantity must be designed, it is for the partial load rich in which vehicle drives usually work over dimensioned. Due to the high cooling capacity, the overall efficiency of the vehicle drive especially in this loading drive area deteriorated. In addition, the response hold thermostatic valves, especially expansion material valves, relatively sluggish. Therefore the setpoint temperature structures well below the maximum permissible temperatures be adjusted to avoid damage to the units the.  

DE 196 41 558 A1 describes a cooling system for a Internal combustion engine of a motor vehicle known in the the speed of a coolant pump as a function of egg ner temperature of the internal combustion engine is set in such a way is that a predetermined maximum temperature value is not is exceeded. An electric motor can use the coolant pump that is connected to the electrical circuit of the Vehicle is connected. It can also have multiple cooling medium pumps may be provided, one or more of which are speed controlled.

One or more temperature sensors measure the tem temperatures at various points on the internal combustion engine or the coolant line. You are about Signallei lines connected to a control device. Parallel to A bypass line is provided in the cooler, at the branch a three / two-way valve is arranged. This has the Function to control the coolant flow so that it escapes the through the cooler or through the bypass line on Cooler can be passed. In an operating phase the valve controls the cooling flow with high heat dissipation partially or mostly to the cooler. The valve can be used as Expansion valve or as an electrical or pneumatic constant regulating valve.

The cooling system further includes a retarder, the Working medium is the coolant. The retarder can both be a primary retarder, the speed of which depends on the Speed of the internal combustion engine is, or a secondary tarder, whose speed depends on the driving speed is. It is also possible that the coolant is not also the retarder's tool, but is only passed through a heat exchanger from  Equipment of the retarder is flowed through, and from there absorbs the heat generated by the retarder during braking becomes.

DE 198 21 100 A1 describes a fan for cooling systems of a motor vehicle known. The internal combustion engine ne drives with a belt drive with different Ratios on the fan. For that they have assigned pulleys each a clutch, whereby both the different gear ratios nisse are produced as well as the fan wheel can be tet.

It is also known from DE 195 33 642 A1 for Regulation of the fan before a fluid friction clutch watching. Have such so-called viscous couplings basically a large hysteresis behavior and quite long cold start phase due to the correspondingly high Vis liquid viscosity.

Finally, from DE 196 28 742 A1 is a fan known in which the speed by a hydrostatic Gear is regulated.

The invention is based on the object Reduce cooling system-related efficiency losses. she is according to the invention by the features of claim 1 solved. Further refinements result from the sub claims.

According to the invention, the speed of the coolant pump pe regulated so that it matches the performance of the internal combustion engine Schine increases, the speed of the fan the speed  the coolant pump follows. However, the fan only starts at a lower limit speed of the coolant pump and reaches its maximum speed when the coolant pump has reached its maximum speed for a while.

By controlling the speed of the coolant pump is enough that the power consumption of the coolant pump increases with the performance of the internal combustion engine and thus relatively low in the partial load range of the internal combustion engine is. This results in a relatively good overall effect degree of vehicle drive. Furthermore, the internal combustion engine reaches machine due to the lower cooling at the start quickly their optimal operating temperature.

The increase in coolant flow is no longer sufficient off, an optimal temperature of the internal combustion engine hold, and if this is exceeded, the fan is ge starts and also depending on suitable para Regulated meters of the drive train, for. B. the performance or the temperature. If the coolant pump and the fan have reached their maximum speeds is the maximum Cooling capacity of the cooling system reached. This capacity must be sufficient, even in unfavorable conditions Temperatures of the internal combustion engine below the permissible To maintain maximum values.

With simple cooling systems, an otherwise usual by pass line with a thermostatic valve is not required. To one Vehicle heating in a parallel to the radiator To be able to operate the heating line with sufficient pressure NEN, is between a branch of the heating cable and the Radiator inlet a control valve in the form of a pressure regulating valve tils arranged depending on the pressure in the upstream  Coolant line opens. This pressure is depending on the volume flow or the speed of the coolant pump. The vehicle heater forms a second coolant circulation. This coolant circuit is controlled by a tax valve switched on, with a small volume flow of the coolant pump before the coolant circuit is switched on via the cooler.

In high-performance gearboxes for motor vehicles, the often include an integrated retarder, and for auto it is advisable to cool the gear oil and heat exchange via a gearbox heat exchanger to provide for the cooling circuit of the internal combustion engine. because through the cooling devices of the internal combustion engine can also be used for the gearbox and the retarder. This is particularly advantageous in retarder operation because of the This time the heat accumulation in the internal combustion engine is low and the performance of the coolant pump and the fan can be used to brake the vehicle. there can the gearbox heat exchanger in the direction of flow or behind the coolant pump and / or before or after the Internal combustion engine can be arranged.

It is also useful in the inventive Cooling system a common bypass line parallel to the cooler and to provide the internal combustion engine. The bypass line serves especially when starting the internal combustion engine in a small coolant circuit as quickly as possible to reach the optimal temperature of the internal combustion engine. According to the invention is at the branch point of the bypass line a control valve arranged as a coolant flow distributor ler is designed and with low coolant flow and correspondingly low pressure in the coolant line  Internal combustion engine opens the bypass and the radiator inlet closes.

The coolant flow distributor is advantageously as Flap valve formed, the flap about an axis of rotation is pivotable and so loaded by a spring that the completely or almost completely closes the radiator inlet if the Coolant flow is below a limit volume flow, so the remaining coolant flow through the bypass line tung flows. Cooling exercises above the limit volume flow medium current such a pressure on the flap that the spring force is exceeded and the flap Radiator inlet continues to increase with increasing volume flow releases.

In addition to the spring, other active elements can be in shape of magnets, a bimetal spring or bimetal elements Additional forces on the flap in the opening or closing direction exercise. The magnet that acts as a permanent magnet or Electromagnet can be formed is arranged that the flap is in the rest position without volume flow declines, but is maintained at a volume flow, such as it occurs when the engine is idling. Becomes if an electromagnet is used, it can be controlled by a tax electronics of any relevant control parameters or depending on the integrated thermal switch Coolant temperature can be switched.

The bimetal spring also loads the flap in Direction of the first spring, so that its force with decreasing coolant temperature and reduced coolant telstrom increases.  

According to a further embodiment of the invention attached to the edges of the flap bimetallic elements, so that the edges change depending on the coolant temperature bulge differently and thus in the coolant flow desired additional forces in the opening or closing direction produce.

In addition, the flap can have a wing that directed against the flow direction of the coolant and which encloses an angle with the flap. before in part, the wing is also a bimetal, so that the angle between the flap and the wing changes depending on the temperature, especially at high temperatures tures and large coolant flow increases, so that the cooling medium current exerts a large force on the flap when it opens the radiator inlet and closes the bypass line.

According to a further embodiment of the invention the flap is divided transversely to the axis of rotation, with the flap penteile can act different active elements. Springs, magnets and bimetals come in as active elements Question that differ in size, strength and control characteristics can distinguish. The distribution of the flap, the purpose is moderately asymmetrical, and the choice of knives elements allow great flexibility in control characteristic over a wide temperature range.

The cooling system according to the invention is not restricted on flap valves. There are other types of tax valves applicable. According to one embodiment, the com Combination of a flap valve with a spool struck, in which the flap the radiator inlet and the Slide controls the bypass line. The flap and the Sliders are coupled together by a handlebar, so  that an adjustment of the flap a corresponding Ver pushing the slide causes.

Further advantages result from the following drawing planning description. In the drawing is an execution example shown game of the invention. The description and the Claims contain numerous features in combination of the Those skilled in the art will expediently also individually consider and together to useful further combinations summarized.

Show it:

Fig. 1 shows a schematic structure of a cooling system according to Inventive,

Fig. 2 shows a variant of Fig. 1 with a gearbox and gearbox heat exchanger,

Fig. 3 to 8 variants to Fig. 2,

Fig. 9 shows a coolant flow distribution as a flap valve,

Fig. 10 is a butterfly valve of Fig. 9, in which a radiator inlet is open propagated

Fig. 11 is a flap valve with a flow direction opposite to the facing wing,

FIGS. 12 and 13 different positions of the flap valve of Fig. 11,

Fig. 14 is a flap valve in combination with a slide for a bypass line and

Fig. 15 shows an embodiment according to FIG. 14, but with ge connected bypass line.

The cooling system 1 shown in FIG. 1 has an internal combustion engine 2 provided with a radiator inlet 13 of a heat exchanger designed as a condenser 3 is connected via a coolant line 25. The coolant of the engine 2 is conveyed 6 and passes through a radiator return line 14 to the internal combustion engine 2 back telpumpe of a speed-controlled Kühlmit. Arrows 37 indicate the direction of flow of the coolant. The cooler 3 is flowed through and cooled by an air flow 4, which is generated by a fan, also not shown, which is also speed-regulated.

The essential temperatures in front of the internal combustion engine 2 are detected by a temperature sensor 10 , while the corresponding temperatures of the coolant after the internal combustion engine 2 are detected by a temperature sensor 9 . The temperature sensors 9 and 10 are connected via signal lines, not shown, to a central control unit or to control elements which are integrated in the coolant pump 6 or the fan or correspond to the actuators.

The cooling circuit of the cooling system 1 is divided by a heating conduit 12 that branches off at a branching point 11 of the refrigerant pipe 25 and the coolant pipe connects to the radiator return line 14 25th A heat exchanger designed as a vehicle heater 5 is provided in the heating line 12 . A control valve 8 controls the flow through the vehicle heater 5 in accordance with requirements that are set manually or via the control unit. A pressure-dependent control valve 7 is arranged in the cooler inlet 13 and opens more when the pressure in the coolant line 25 rises due to the increasing flow rate of the speed-controlled coolant pump 6 . The coolant flow of the coolant pump 6 increases with their speed, which in turn is controlled as a function of the temperatures that are detected by the sensors 9 and 10 . If the temperature of the internal combustion engine 2 exceeds the optimum temperature, even though the speed control of the coolant pump 6 reaches the maximum speed, the fan is started and the optimum temperature is guaranteed by the speed control of the air flow 4 .

The embodiment according to FIG. 2 differs from that according to FIG. 1 in that a transmission heat exchanger 16 is provided in the cooling system 1 for a transmission 15 . A Ge transmission pump 17 promotes the transmission oil via oil lines 19 from the transmission 15 to the heat exchanger 16 and back. Temperature sensors 18 and 24 detect the transmission oil temperature at the output of the transmission 15 or at the input of the heat exchanger 16 and in the oil sump of the transmission 15 . If the temperatures of the transmission oil exceed predetermined limit values, the coolant flow in the cooling system 1 is increased in order to be able to dissipate the amount of heat in the transmission heat exchanger 16 faster due to a larger temperature gradient.

The transmission heat exchanger 16 can be switched on in the flow direction of the coolant upstream of the coolant pump 6 or afterwards in the cooling circuit. Furthermore, as shown in FIG. 2, it can be arranged in front of the internal combustion engine 2 or, as shown in the embodiment according to FIG. 3, after the internal combustion engine 2 .

In the embodiment of Fig. 4 is a Bypasslei is device 21 is provided which is arranged parallel to the radiator 3 and the engine 2. At the branch point of the bypass line 21 , a control valve in the form of a coolant flow distributor 20 is arranged in the coolant line 25 . This distributes the coolant flow as a function of its size to the bypass line 21 or to the cooler inlet 13 . Increases the coolant pump 6 due to increasing temperatures of the coolant, the coolant flow by increasing their speed, the coolant flow increases and with it the coolant pressure in the coolant line 25 . This acts directly or indirectly on the actuator in the form of a flap 26 of the coolant flow distributor 20th It is also possible that the flow through the coolant line 25 is detected by means of a flow sensor that supplies a signal for an actuator of the coolant flow distributor 20 .

Since only a low heat output is transferred into the coolant when the internal combustion engine 2 is idling, the coolant flow generated by the coolant pump 6 can be low. In the case of a cold internal combustion engine 2 , a coolant flow can be dispensed with at times in order to shorten the heating time of the internal combustion engine 2 . At this operating point, the coolant pump 6 does not run or only runs at a low speed. The fan is switched off. When the engine 2 is warm, the speed of the coolant pump 6 is increased and the coolant flow is increased with increasing temperature of the engine 2 and / or performance. The coolant flow is now also used to operate a vehicle heater 5 . In the operating state in which the coolant pump 6 is running at a low speed, the fan is switched off or is also running at a low speed.

Also, in the partial load operation of the internal combustion engine 2, current can at low ambient temperatures with a reduced coolant to be driven, since the quantity of heat in this case in addition to the heat transport via the coolant and by convection of the heated surface of the internal combustion engine 2 occurs. Likewise, the vehicle heater 5 , if it is switched on, contributes to the cooling of the greedy internal combustion engine 2 . The coolant flow is increased with increasing outside temperatures and thus increasing coolant temperatures. The coolant pump 6 and the fan run at low to medium speed.

The same applies to the full load operation of the internal combustion engine 2 , but at a higher speed level of the coolant pump 5 and the fan.

In the embodiment of Fig. 5 of the transmission heat exchanger is switched telkreislauf 16 after the internal combustion engine 2 in the Kühlmit. If the transmission 15 has a retarder 22 ( FIGS. 7 and 8), the maximum coolant flow is set in the retarder mode. If necessary, the coolant temperature can be regulated via the fan speed. The braking power of the retarder 22 is increased by the power consumption of the coolant pump 6 and the fan.

If the gearbox heat exchanger 16 is arranged after the internal combustion engine 2 , the coolant temperature can drop too much during operation of the retarder 22 . A partial coolant flow is therefore directed past the internal combustion engine 2 to the transmission heat exchanger 16 via a pressure control valve 23 . The pressure control valve 23 opens as soon as the predetermined pressure is exceeded. As is low during the Re tarderbetriebs the accumulation of heat in the internal combustion engine 2, a jump in temperature is decreased in the internal combustion engine 2 by this measure.

In the embodiment of FIG. 6 of the transmission heat exchanger 16 is disposed in the radiator return overflow 14. Since clotting gem refrigerant flow must also in this arrangement, nor the Ge gearbox heat exchanger flows through 16 with coolant, the coolant flow distributor 20 is embodied in this case, so that always a minimum flow of coolant flowing through the radiator. 3

In order to bring the temperature of the internal combustion engine 2 into the optimal temperature operating point, an electronic control can be provided. For this purpose, the electronic control takes on characteristic values of the drive train, the internal combustion engine 2 and the transmission 15 as well as the retarder 22 and determines the requirements for the coolant pump 6 and the fan. The optimal control strategy can be determined with a transient cooling system computing model.

FIGS. 9 to 15 show embodiments of a cooling medium flow distributor 20 in the form of a flap valve. In the embodiments according to FIGS. 9 to 13, a flap 26 is mounted about a central axis of rotation 27 pivotally so that they Annae in its first end position of the coolant inlet 13 hernd or completely closes while processing the Bypasslei 21 releases. A spring 28 loads the flap 26 in the direction of the first end position ( FIG. 9).

In a second end position ( FIG. 10), the flap 26 largely releases the radiator inlet 13 while it closes the bypass line 21 . This is caused by the fact that the coolant flow in the direction of arrow 37 increases the volume of the flap 26 in the direction of the second end position. If the coolant flow decreases, the spring 28 moves the flap 26 back in the direction of the first end position.

The control characteristic of the flap 26 can be influenced in addition to the characteristic of the spring 28 by further active elements, for. B. by magnets 29 in the form of a permanent magnet and / or electromagnet and by bimetallic springs 30 and bimetallic elements 36th The Magne te 29 , are arranged so that they keep the flap 26 to a coolant flow, which corresponds to the idle operation of the internal combustion engine 2 , in the first end position, wherein the electromagnet can be switched on / off by control electronics or by temperature switches.

The bimetal spring 30 acts in the direction of the spring 28 . Your influence on the flap 26 decreases with increasing temperature, so that the flap 26 increasingly releases the cooler inlet 13 with increasing temperature of the coolant. To determine the effect of the coolant flow to the flap 26 in from the temperature dependence to modify, the flap 26 has at its edges 35 bimetal elements 36, which are more or less bend according to the temperature against the flow direction 37 of the coolant, and thus a variable, temperature dependent flow resistance form.

A similar purpose is followed by the arrangement of a wing 31 , which is arranged on the upstream side of the flap 26 and is directed against the flow direction 37 of the coolant and advantageously consists of bimetal. It causes the coolant flow to exert a sufficiently large force on the flap 26, in particular when the Klap pe 26 reaches its second end position and almost all of the coolant current flows through the radiator. 3 In this state, the coolant is very warm, so that due to the bimetallic property of the wing 31 there is a large angle ϕ between the flap 26 and the wing 31 ( FIG. 13), which increases the effect of the coolant flow on the flap 26 ,

In the embodiment of Fig. 14 and 15, a Klap is pe 32 pivotable about an axis of rotation 27, which is on the edge of the flap 32. The flap 32 controls the cooler inlet 13 and is brought into a first end position by the spring 28 , in which the cooler inlet 13 is closed. To the flap 32 a slide 34 is articulated by means of a link 33, which in the first end position of the Klap pe 32 (Fig. 14), the bypass line 21 clears.

With increasing coolant flow in the direction of arrow 37 , the flap 32 opens and pulls the slide 34 via the handlebar 33 into a second end position in which the cooler inlet 13 is open and the bypass line 21 is closed ( FIG. 15). In this case too, the above-described active elements 29 , 30 , 36 can be provided on the flap 32 in addition to the spring 28 .

The coolant flow distributor 20 in the form of a flap valve is suitable for both circular and rectangular cross sections. The flaps 26 and 32 can be divided transversely to the axis of rotation 27 . The subdivision allows good control characteristics to be achieved over a wide temperature range. In this case, differently designed active elements 28 , 30 and 36 can be provided on the parts of the flaps 26 and 32 .

reference numeral

1

cooling system

2

Internal combustion engine

3

cooler

4

airflow

5

car heater

6

Coolant pump

7

control valve

8th

control valve

9

temperature sensor

10

temperature sensor

11

branching point

12

heating

13

radiator inlet

14

Cooler return

15

transmission

16

Transmission heat exchanger

17

transmission pump

18

temperature sensor

19

oil line

20

Kühlmittelstromverteiter

21

bypass line

22

retarder

23

Pressure control valve

24

temperature sensor

25

Coolant line

26

flap

28

feather

29

magnet

30

bimetallic

31

wing

32

flap

33

handlebars

34

pusher

35

edge

36

bimetallic

37

arrow
ϕ angle

Claims (17)

1. Cooling system (1) for vehicles with an internal combustion engine (2) and a transmission (15), wherein the Kühlsy stem (1) at least one fan, a coolant pump (6) in response to an at least one point of the cooling system ( 1 ) measured temperature is controlled, at least one heat exchanger ( 3 , 5 , 16 ), at least one coolant control device ( 7 , 8 , 20 ) and several coolant circuits, characterized in that the speed of the coolant pump ( 6 ) with the power the internal combustion engine ( 2 ) increases and the speed of the fan follows the speed of the coolant pump ( 6 ) by the fan only starting at a lower limit speed of the coolant pump ( 6 ) and only reaching its maximum speed when the coolant pump ( 6 ) has already reached maximum speed for a while. 2. Cooling system ( 1 ) according to claim 1, characterized in that a control valve ( 7 ) is arranged in front of a heat exchanger designed as a cooler ( 3 ), which opens depending on the pressure in an upstream coolant line ( 25 ). 3. Cooling system ( 1 ) according to claim 2, characterized in that a transmission heat exchanger ( 16 ) is arranged in the flow direction upstream or downstream of the coolant pump ( 6 ) and / or the internal combustion engine ( 2 ). 4. Cooling system ( 1 ) according to claim 3, characterized in that the transmission ( 15 ) has a re tarder ( 22 ) and that during operation of the retarder ( 22 ), the coolant pump ( 6 ) and / or the fan at maximum speed operate. 5. Cooling system ( 1 ) according to claim 4, characterized in that the gear heat exchanger ( 16 ) is arranged after the internal combustion engine ( 2 ) and a partial coolant flow via a pressure control valve ( 23 ) on the internal combustion engine ( 2 ) to the gear heat exchanger ( 16 ) is passed as soon as a predetermined pressure of the coolant in front of the internal combustion engine ( 2 ) is exceeded. 6. Cooling system ( 1 ) according to one of claims 3 to 5, characterized in that the coolant telpump ( 6 ) and the fan are operated at maximum speed when the temperature of the transmission oil in an oil sump of the transmission ( 15 ) or at the output of the gearbox heat exchanger ( 16 ) is above a predetermined limit. 7. Cooling system ( 1 ) according to one of the preceding claims, characterized in that a vehicle heater ( 5 ) is provided parallel to the cooler ( 3 ) and to the internal combustion engine ( 2 ). 8. Cooling system ( 1 ) according to one of the preceding claims, characterized in that a bypass line ( 21 ) is provided parallel to the cooler ( 3 ), a coolant flow distributor ( 20 ) at a branch point of the bypass line ( 21 ) in the coolant line ( 25 ) is arranged and the cooler inlet ( 13 ) opens with increasing pressure in the coolant line ( 25 ), while the bypass line ( 21 ) is closed accordingly. 9. Cooling system ( 1 ) according to claim 8, characterized in that the coolant flow distributor ( 20 ) is designed as a flap valve, the flap pe ( 26 , 32 ) is loaded by a spring ( 28 ) so that it is in a first end position closes the cooler inlet ( 13 ) completely or to a minimum volume flow below a limit volume flow and the remaining volume flow flows through the bypass line ( 21 ), while above the limit volume flow the flap ( 26 , 32 ) to a second end position the cooler inlet ( 13 ) continuously releases with increasing volume flow. 10. Cooling system ( 1 ) according to claim 9, characterized in that the flap ( 26 , 32 ) is held in the first end position by a magnet ( 29 ) which closes the cooler inlet ( 13 ), as long as the volume flow one Volume flow when the internal combustion engine ( 2 ) is idle. 11. Cooling system ( 1 ) according to one of claims 10, characterized in that the magnet ( 29 ) is an electromagnet which is controlled by an electronic control unit or an integrated thermal switch. 12. Cooling system ( 1 ) according to one of claims 9 to 11, characterized in that on the flap pe ( 26 , 32 ) a bimetallic spring ( 30 ) is provided, which at low temperatures additionally in the direction of the spring ( 28 ) on the flap ( 26 , 32 ) works. 13. Cooling system ( 1 ) according to one of claims 9 to 12, characterized in that the flap pe ( 26 , 32 ) at its edges ( 35 ) has bimetallic elements ( 36 ) which bend under the influence of the coolant temperature so that the coolant flow generates a desired additional force in the opening or closing direction. 14. Cooling system ( 1 ) according to one of claims 9 to 13, characterized in that the flap pe ( 26 , 32 ) is divided transversely to an axis of rotation ( 27 ), with different active elements ( 28 , 29 , 30 ) acting on the flap parts , 15. Cooling system ( 1 ) according to one of claims 9 to 14, characterized in that the flap pe ( 26 ) has a against the flow direction of the coolant means wing ( 31 ) which with the flap ( 26 ) an angle (χ) includes. 16. Cooling system ( 1 ) according to claim 15, characterized in that the wing ( 31 ) is made of bimetal and the angle (ϕ) changes depending on the temperature. 17. Cooling system ( 1 ) according to one of claims 9 to 14, characterized in that the flap pe ( 32 ) controls only the cooler inlet ( 13 ) and is connected via a link ( 33 ) to a slide ( 34 ) which connects the bypass line ( 21 ) controls.