GB1561093A

GB1561093A - Anti-lock brake control system

Info

Publication number: GB1561093A
Application number: GB4212276A
Authority: GB
Original assignee: WABCO WESTINGHOUSE GmbH
Current assignee: WABCO WESTINGHOUSE GmbH
Priority date: 1975-10-11
Filing date: 1976-10-11
Publication date: 1980-02-13
Also published as: IT1071217B; JPS5247176A; FR2327123A1; DE2545593A1

Description

(54) ANTI-LOCK BRAKE CONTROL SYSTEM (71) We, WABCO WESTINGHOUSE G.m.b.H., a Company organised according to the laws of the Federal Republic of Germany, of 3000 Hannover 91, Postfach 91 12 80, Federal Republic of Germany; do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to an anti-lock brake control system for pressure mediumactuated vehicle brakes.

There has been proposed a braking system in which there are arranged devices which during a braking action alter the brake pressure in the front wheel brake cylinders in dependence upon the rotational behaviour of the front wheels. The brake lines which lead from the control devices to the wheel brake cylinders of the front wheels are also connected to the wheel brake cylinders of the rear wheels via additional brake lines. As a result, a control of the brake force at all brakable wheels of the vehicle is achieved in response to the rotational behaviour of the front wheels.

With vehicles having a very small wheel base a reliable control of the pressure can be achieved with such a brake pressure control system.

However, this system cannot be successfully applied to vehicles having a long wheelbase, and in particular not to multipleaxle vehicles, using compressed-air brake systems, because long brake lines render impossible both the rapid control of the brake pressure and a rapid release of air.

In addition, with such a brake pressure control system changing axle loads dependent on the extent to which the vehicle is loaded cannot be taken into account. It is also a disadvantage that having devices responsive to the rotational behaviour of the front wheels only of the vehicle, the rotational behaviour of the rear wheels, which may for a short time be upon a surface of a different frictional value from that of the surface on which the front wheels are, is not taken into account in the brake pressure control. This circumstance may make itself felt, for example when the front wheels are upon a surface of high frictional value and the rear wheels are upon a surface of low frictional value, by permitting the rear wheels to be excessively braked and lock for a short time, with the result that the vehicle becomes unstable.If conversely the front wheels are upon a surface of low frictional value and there is a high frictional value at the rear wheels, only a low brake pressure is introduced into the wheel brake cylinders of the front wheels and thus also into those of the rear wheels, so that the entire brake force is small and the braking path is lengthened unnecessarily.

It has also been proposed that signalgenerating devices be arranged at diagonally opposite wheels of a vehicle, the output signals of which signal-generating devices influence via an evaluation circuit and a control valve unit the brake pressure at all brakable wheels of the vehicle, wherein to effect the control, the output signals of both signal-generating devices are evaluated in one evaluation circuit so that it is always only one osutput signal which is used for the control. However, such an anti-lock control system has the drawback that the output signal of the signal-generating device of the wheel which first shows a tendency to lock determines the brake pressure.If, for example, in the case of a heavily loaded vehicle, the right-hand front wheel comes upon a part of the road surface of lower frictional value than the part that the left-hand rear wheel is on, the brake pressure to all wheels is consequently reduced to suit the lower frictional value. A maximum utilization of the possible brake force at the wheels which are upon parts of the surfaces having higher frictional value is therefore prevented. the result is a longer braking path. Without additional expensive devices, as anti-lock control which takes into account the different axle loads is moreover not possible in such a system.

A system has been proposed in which the above difficulties are overcome and is arranged so that the brake pressure at each of two wheels of a first axle is controlled jointly by the output signals of the signalgenerating devices of one wheel of the first axle and one wheel of a second axle via an electrical evaluation circuit, and that the signal-generating devices are arranged at the diagonally opposite wheels of the two axles, whereby, for example in the case of a lorry, the different loads on the front and rear axle (or axles) and different frictional values upon which the wheels of the front and rear axles may possibly come, are taken into account during the anti-lock control of the brakes.

Whilst appreciating all the advantages given by this solution and also obtained in experiments, it may, however, still happen that under extreme driving conditions the uncontrolled wheel of an axle may lock.

Above all in the case of roadways having different frictional coefficients on the left and the right-hand sides, it is quite possible for a vehicle braked on such a roadway, when, for example the sensed wheel is on the side with the high frictional coefficient and shows a perfect braking behaviour whereas the other wheel on the side with the low frictional coefficient may lock, which especially in the case of the rear axle leads to the vehicle becoming directionally unstable.

The same thing may occur in the case of a brake system actuated when driving round a bend, wherein there takes place a transfer of the load from the vehicle wheels on the inside of the bend to the wheels on the outer side of the bend, which adds to the effect of the different frictional coefficient of the left and right-hand wheels. If, for example the sensed wheel on the outer side of the bend exhibits normal control behaviour, then the wheel from which loading has been transferred on the inner side of the bend may lock.

If on the contrary, the sensed wheel is on the inner side of the bend, and if this wheel exhibits normal control behaviour, the wheel on the opposite side may not be sufficiently strongly braked.

The criteria given here are, in relation to the front axle, the lesser evil, since when a front wheel locks the driver may react with the steering accordingly, but the locking of a rear wheel may tend to make the vehicle unstable, vehicles having a short wheelbase and a low moment of inertia about the vertical axis being especially difficult to control under these circumstances.

It is an object of the invention to provide an anti-lock brake control system whIch as a further development of the so-called diagonal control avoids at least some of the difficulties described above.

According to the present invention there is provided an anti-lock brake control system for a pressure medium actuated vehicle brake system, especially for road vehicles having at least a front axle and a rear axle, in which the rotational wheel behaviour during a braking action is observed by sensors and evaluating signal-generating devices connected to the sensors are arranged to produce output signals which influence the wheel brake pressure, wherein a first sensor is provided responsive to the rotational behaviour of at least one wheel of the front axle and a second sensor is provided coupled to, and responsive to the rotational behaviour of, a drive shaft of the rear axle and that wheel brake cylinders of the wheels of the front axle are interconnected to receive a first brake pressure and wheel brake cylinders of the wheels of the rear axle are interconnected to receive a second brake pressure, the first and second brake pressures each being controlled by at least one respective valve control unit, the sensors being connected to the valve control units through an electronic evaluation circuit.

In the following description references to axles of a vehicle should be understood to include references to the wheels on the axles concerned. In addition the sensing of a wheel or an axle means the deriving of signals representing the rotational behaviour of that wheel or the wheels on that axle.

An especial advantage of the anti-lock control system according to the invention is that while retaining the principle of diagonal control at the front axle, by the measuring of the wheel spin at the rear axle, the braking effort for both rear wheels is controlled jointly in response to one mean value, so that in the case of emergency braking on a uniform roadway, and on roadways having parts with different frictional coefficients and on bends, the rear axle is prevented from sliding. With a four-wheel drive vehicle, the principle of diagonal control can be implemented with a front wheel sensor coupled to the front driven axle instead of a front wheel.

In order that the invention may be fully understood and readily carried into effect, several embodiments will now be described with reference to the accompanying drawings, of which: Figure I shows a schematic representation of the brake system of a two-axles vehicle whose right-hand front wheel is sensed and in which the sensing of the rear axle takes place at the drive shaft thereof Figure 2 shows a schematic representation of a two-axled vehicle with two driven axles, whose sensing is carried out at the two drive shafts; Figure 3 shows a schematic representation of the brake system of a three-axled vehicle with two driven rear axles, the right-hand front wheel of which vehicle is sensed, and in which the sensing of the rear axles is carried out at the two drive shafts;; Figure 4 shows a schematic representation of the brake system of a three-axled vehicle with a live rear axle and a dead rear axle, the right-hand front wheel of which vehicle is sensed, and in which a sensing of the live axle alone is carried out at the drive shaft thereof, whereas the dead axle is cocontrolled by the anti-lock control device of the driving axle; Figure 5 shows the schematic representation of the brake system of a three-axled vehicle as in Figure 4 with a sensed righthand front wheel and a sensed drive shaft of the driven rear axle, in which the left-hand wheel of the dead rear axle of the vehicle is also sensed; Figure 6 shows the schematic representation of the brake system of a three-axled vehicle as in Figure 4 with a dead rear axle which is braked directly from the brake valve; and Figure 7 shows the schematic representation of the brake system of a two-axled vehicle as in Figure 1, in which one control valve unit is provided for each brakable wheel.

In Figure 1 the wheels of a two-axled vehicle are denoted by the reference numerals 1, 2, 3 and 4. Brake cylinders 8 and 9 of the wheels 1 and 2 of a front axle VA of the vehicle are directly connected to eqch other by means of a brake line 7. A brake line 6 is attached to the brake line 7 and joins it to a control valve unit 5. Wheel brake cylinders 10 and 11 of the wheels 3 and 4 of a rear axle HA of the vehicle are likewise joined together by means of a brake line 14. A brake line 13 attached to the brake line 14 leads to a control valve unit 12. At the right-hand wheel 2 of the front axles VA and at a drive shaft 15 of the rear axle HA there are arranged sensors 16 and 17, respectively.The sensor 16 of the wheel 2 is connected by an electrical lead 18 to an electronic evaluation circuit 19a, and the sensor 17 is connected by an electrical lead 20 to an electronic evaluation circuit 19b.

An output of the electronic evaluation circuit 19a is applied by an electrical control lead 21 to the control valve unit 5; an output of the electronic evaluation circuit 19b is applied by an electrical control lead 22 to the control valve unit 12. From a pressure medium supply container, not shown, there is provided a pressure line 23 connected to a pedal-operated brake valve 24 through which line 23 is joined to the control valve unit 5 by a pressure line 25, to the input of the control valve unit 12 by a pressure line 26.

During a braking action initiated by actuating the pedal valve 24. compressed air, for example, flows from the pressure medium supply container via the pressure line 23, the pedal valve 24, the pressure line 25 and the control valve unit 5 into the wheel brake cylinders 8, 9 of the wheels 1,2 of the front axle VA and from the valve 24 via the pressure line 26 and the control valve unit 12 to the cylinders 10, 11 of the wheels 3 and 4 of the rear axle HA. The sensor 16 of the wheel 2 senses the rotational behaviour of the wheel 2 during the braking action and when the wheel 2 shows a tendency to lock delivers a signal via the electrical lead 18 to the electronic evaluation circuit 19a.The output signal of the electronic evaluation circuit 19a passes via the electrical control lead 21 to the control valve unit 5, which under the control of these signals effects a limitation of pressure by blocking further supply of compressed air, a reduction of the pressure by letting it out of the wheel brake cylinders, or, after the wheel 2 has started to turn again, and in response to release of the blocking of the supply of compressed air, effects an increase in the brake pressure at the wheel brake cylinders 8 and 9 of wheels 1 and 2 of the front axles VA.In the same manner the brake pressure at the wheel brake cylinders 10 and 11 of the wheels 3 and 4 of the rear axle HA is influenced by the output signals of the sensor 17 in response to the rotational behaviour of the drive shaft 15 of the rear axle when one of the two wheels 3 and 4 shows a tendency to lock. by means of the electronic evaluation circuit 19b and the control valve unit 12.

In Figure 2 the wheels of a two-axled, four-wheel drive vehicle are denoted by the reference numerals 31, 32, 33 and 34. Brake cylinders 38 and 39 of the wheels 31, 32 of the front axle VA of the vehicle are connected directly together via a brake line 37.

A brake line 36 is connected from the brake line 37 to a control valve unit 35. Wheel brake cylinders 40 and 41 of the wheels 33, 34 of the rear axle HA of the vehicle are likewise joined together via a brake line 44.

A brake line 43 is connected from this brake line 44 to a control valve unit 42. Sensors 47 and 48 are arranged at the drive shaft 45 of the front axle VA and at the drive shaft 46 of the rear axle HA respectively. An electrical lead 49 joins the output of the sensor 47 of the drive shaft 45 to an electronic evaluation circuit 50a; an electrical lead 51 joins the output of the sensor 48 to an electronic evaluation circuit 50b. The output of the electronic evaluation 50a is applied via an electrical control lead 52 to the control valve unit 35; the output of the electronic evaluation circuit 50b is applied to the control valve unit 42 via the electrical control lead 53.From a pressure medium supply container, not shown, a pressure line 54 leads to a pedal-operated brake valve 55, which is connected to the input of the control valve unit 35 via a pressure line 56 and the input of the control valve 42 via a pressure line 57.

During a braking action initiated by actuating the pedal valve 55, compressed air flows from the pressure medium supply container via pressure line 54, pedal valve 55, pressure line 56 and the control valve unit 35 into the wheel brake cylinder of the wheels 31, 32 of the front axle VA, and from the valve 55 via the pressure line 57 and the control valve unit 42 to the brake cylinders of the wheels 33, 34 of the rear axle HA.

The sensor 47 of the drive shaft 45 establishes the rotational behaviour of the drive shaft 45 and hence the front wheels 31, 32 during the braking action and when one of the wheels 31 or 32 shows a tendency to lock, delivers a signal via the electrical line 49 to the electronic evaluation circuit 50a.

The output signal of the electronic evaluation circuit 50a passes via the electrical control lead 52 to the control valve unit 35, which in response to these signals effects a limitation of pressure by blocking further supply of pressure medium, a reduction of the pressure by letting it out of the wheel brake cylinders, or after the wheels 32 have resumed rotation and as a result of releasing the blocking of the compressed air supply, effects an increase in brake pressure at the wheel brake cylinders 38 and 39 of the wheels 31 and 32 of the front axle VA.In the same manner the brake pressure at the wheel brake cylinders 40 and 41 of the wheels 33 and 34 of the rear axle HA is influenced by the output signals of the sensor 48 of the drive shaft 46 of the rear axle HA when one of the two wheels 33, 34 shows a tendency to lock, by means of the electronic evaluation circuit SOb and the control valve unit 42.

The embodiment shown in Figure 3 is concerned with the control of the brake pressure of a three-axled vehicle, wherein the rotational behaviour of the right-hand front wheel and of the drive shafts of the rear axles, both of which are driven, is sensed.

In Figure 3 the wheels of a front axle VA are denoted by 60 and 61, those of a second axle 62 by 63 and 64, those of a third axle 65 by 66 and 67. Axles 62 and 65 are the rear axles of the vehicle. A control valve unit 68 is connected via a brake line 69 to a brake line 72 directly interconnecting wheel brake cylinders 70, 71 of the wheels 60, 61 of the front axle VA. In the same manner a brake line 73 establishes a connection between a control valve unit 74 and a brake line 77 directly interconnecting wheel brake cylinders 75 and 76 of the wheels 63, 64 of the second axle 62. Wheel brake cylinders 78, 79 of the third axle 65 are joined together directly via a brake line 80 and are joined to a control valve unit 82 via a brake line 81 branching off the brake line 80 joining the two wheel brake cylinders, 78, 79.

Pressure lines 84 and 85 lead to the control valve units 68, 74 and 82 from a pedal-operated brake valve 83. The pedal valve 83 is joined to a source of pressure medium which is not shown and from which it applies pressure to the lines 84 and 85.

Sensors 88, 89 and 90 are allocated to the right-hand wheel 61 of the axle VA, to the drive shaft 86 of the second axle 62 and to the drive shaft 87 of the third axle 65, respectively. Electrical leads 91, 92 and 93 respectively connect the sensors 88, 89 and 90 to inputs of associated electronic evaluation circuits 94a, 94b and 94c. The outputs of the electronic evaluation circuits 94a, 94b and 94c are joined to the control valve units 68, 74 and 82 via electrical control leads 95, 96 and 97, respectively.

During a braking action the rotational behaviour of the sensed wheel or of the sensed drive shafts of the two rear axles is monitored by means of the associated evaluation circuits. When a sensed wheel or a wheel of a sensed rear axle shows a tendency to lock, a signal is sent from the evaluation circuit to the corresponding control valve unit and the wheel brake pressure of both wheels on the particular axle is controlled as described above to reduce the tendency to lock.

The embodiment shown in Figure 4 is concerned with the control of the brake pressure in response to the rotational behaviour of the right-hand front wheel of a three-axled vehicle having a driven rear and a dead rear axle. The braking of the dead rear axle is co-controlled by the anti-lock control device for the brakes of the driven rear axle.

Wheel brake cylinders 101 and 102 of the wheels 103 and 104 of the front axle VA of a three-axled vehicle are joined to the brake line 105 leads to a control valve unit 107. A brake line 113 interconnects wheel brake cylinders 108 and 109 of wheels 110 and 111 of a second axle 112 and a brake line 114 connects the brake line 113 a connection is produced between the wheel brake cylinders 108, 109 and a control valve unit 115. A pressure line 116 leads from a pressure medium supply container, not shown, to a pedal valve 117, which is connected to the input of the control valve unit 107 by means o a pressure line 118, and by means of a pressure line 119 to the control valve unit 115 of the wheels 110, 111 of the second axle 112.At the right-hand wheel 104 of the front axle VA there is arranged a sensor 120 whose output signals are passed via an electrical lead 121 to an input of an electronic evaluation circuit 122a. The output signals of a sensor 124 arranged at the drive shaft 123 of the second axle 112 are delivered via an electrical lead 125 to an input of an electronic evaluation circuit 122b. An electrical control lead 126 connects the output of the evaluation circuit 112a to the control valve unit 107. An electrical control lead 127 connects the output of the electronic evaluation circuit 122b to the control valve unit 115. Wheel brake cylinders 128 and 129 of the wheels 130, 131 of a third vehicle axle 132 are connected to the control valve unit 115 via brake lines 114a and 114.

The wheel brake pressure at the brake cylinders of the wheels of the first axle and of the second axle is controlled in the same manner as already described in the embodiment according to Figure 1. The wheel brake cylinders of the wheels of the third axle are acted upon by the pressure regulated for the second axle. It will be understood that the loadings on the second and third axles will be similarly affected by the load carried by the vehicle, and the close spacing of these axles will mean that the wheels on the axles will probably be on parts of the roadway affording the same friction.

Figure 5 shows an anti-lock brake control system of a three-axled vehicle in which the rotational behaviour of the right-hand front wheel, at the drive shaft of the driven rear axle and the left-hand wheel of the dead rear axle is sensed and used to control the braking of the respective axles independently.

In the diagram, the wheels of a front axle VA are denoted by 140 and 141, those of a driven rear axles 142 by the numerals 143 and 144 and those of a dead rear axle 145 by the numerals 146 and 147. A control valve unit 148 is joined via a brake line 149 to a brake line 152 directly interconnecting wheel brake cylinders 150, 151 of the wheels 140, 141 of the front axle VA. In the same manner a brake line 153 connects a control valve unit 154 to a brake line 157 which directly interconnects the wheel brake cylinders 155 and 156 of the wheels 143, 144 of the driven rear axle 142. Wheel brake cylinders 158 and 159 of the wheels 146, 147 of the dead rear axle 145 are joined directly together via a brake line 160 and connected by a brake line 161 branching off the brake line 160 to a control valve unit 162.

Pressure lines 164, 165 lead from a pedal valve 163 to the control valve units 148, 154 and 162. The pedal valve 163 is joined to a source of pressure medium not shown.

Sensors 167, 168 and 169 are allocated respectively to the right-hand wheel 141 of the front axle VA, to a drive shaft 166 of the driven rear axle 142 and to the left-hand wheel 146 of the dead rear axle 145.

Electrical leads 170, 171 and 172 are connected respectively from the sensors 167, 168 and 169 to the inputs of associated electronic evaluation circuits 173a, 173b and 173c. The outputs of the electronic evaluation circuits 173a, 173b, 173c are respectively joined to the control valve units 148, 154 and 162 by electrical control leads 174, 175, 176.

In Figure 6 a three-axled vehicle is illustrated whose front axle and driven rear axle are controlled in the same way as the vehicle described with reference to Figure 1. The wheel brakes of the second and dead rear axle are not joined to the anti-lock brake control system but are controlled directly by the pedal-operated brake valve.

The description of the construction and function of Figure 6 corresponds to the description given with reference to figure 4, except that the brake cylinders 128 and 129 are connected directly to the pressure line 119 and not to the control valve 115 which controls the brake pressure for the brake cylinders 108 and 109 of the wheels 110 and 111 of the driven rear axle 112. Thus during braking the brake cylinders 128 and 129 of the dead rear axle 132 are acted upon directly by the compressed air controlled by the brake valve 117.

Figure 7 shows schematically the brake system of a two-axled vehicle similar to that shown in Figure 1 but in which for each brakable wheel there is provided a separate control valve unit instead of having a control valve unit for each axle as in Figure 1.

The description of the construction and the function of Figure 7 corresponds to the description given above for Figure 1. The only difference is that to each brake cylinder 8 and 9 of the front axle VA and to each brake cylinder 10 and 11 of the rear axle HA, there are allocated separate control valve units Sa, Sb and 12a, 12b, respectively, instead of the arrangement of Figure 1 of one control valve unit 5 and 12 common to each axle. Accordingly, separate electrical leads 21a and 21b are connected from the output of the electronic evaluation circuit 19a to the control valve units 5a and 5b and carry the same signals to that units; instead of one line 21 to the control valve unit 5 as in Figure 1.With reference to the rear axle HA, separate electrical control leads 22a, 22b are connected from the output of the electronic evaluation circuit 19b to the control valve units 12a and 12b and carry the same signals to those units, instead of one line 22 to the control valve unit 12 as in Figure 1.

WHAT WE CLAIM IS: 1. An anti-lock brake control system for a pressure medium actuated vehicle brake system, especially for road vehicles having at least a front axle and a rear axle, in which the rotational wheel behaviour during a braking action is observed by sensors and evaluating signal-generating devices connected to the sensors are arranged to produce output signals which influence the wheel brake pressure, wherein a first sensor is provided responsive to the rotational behaviour of at least one wheel of the front axle and a second sensor is provided coupled to, and responsive to the rotational behaviour of, a drive shaft of the rear axle and that wheel brake cylinders of the wheels of the front axle are interconnected to receive a first brake pressure and wheel brake cylinders of the wheels of the rear axle are interconnected to receive a second brake pressure, the first and second brake pressures each being controlled by at least one respective valve control unit, the sensors being connected to the valve control units through an electronic evaluation circuit.

2. A system according to claim 1 including a plurality of evaluation circuits and a plurality of control valve units wherein the sensors are connected to respective evaluation circuits and the outputs of the evaluation circuits are connected to respective control valve circuits whereby the brake cylinders of wheels of a particular axle receive pressure regulated by a sensor re sponsive to one or more wheels of that axle.

3. A system according to claim 1 or 2 wherein for a vehicle having a driven front axle the sensor for at least one wheel of the front axle is responsive to the rotational behaviour of a drive shaft of the front axle.

4. A system according to claim 1, 2 or 3 wherein for a vehicle having a dead rear axle there is provided a sensor responsive to the rotational behaviour of one wheel of the dead rear axle.

5. A system according to claim 4 having a sensor responsive to the rotational be haviour of one wheel of the front axle, wherein the wheels of the front axle and the dead rear axle having sensors are diagonally opposite to one another.

6. A system according to claim 1, 2 or 3 for a vehicle having a driven rear axle and a dead rear axle, wherein brake cylinders of the wheels of the dead rear axle are directly connected to a pressure medium connection of the wheels of the driven rear axle.

7. A system according to claim 1, 2, or 3 for a vehicle having a dead rear axle and a driven rear axle wherein wheel brake cylinders of the dead rear axle are in direct pressure medium connection with a driver operated brake valve and are not subject to anti-lock control.

8. A system according to any of claims 1 to 6, wherein each braked wheel has an individual control valve unit and electrical leads are provided to connect the control valve units of each axle to an electronic evaluation circuit for that axle, which circuit is connected to a sensor responsive to the rotational behaviour of at least one wheel on that axle.

9. An anti-lock brake control system substantially as described herein with reference to any of the Figures of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. same signals to those units, instead of one line 22 to the control valve unit 12 as in Figure 1. WHAT WE CLAIM IS:

1. An anti-lock brake control system for a pressure medium actuated vehicle brake system, especially for road vehicles having at least a front axle and a rear axle, in which the rotational wheel behaviour during a braking action is observed by sensors and evaluating signal-generating devices connected to the sensors are arranged to produce output signals which influence the wheel brake pressure, wherein a first sensor is provided responsive to the rotational behaviour of at least one wheel of the front axle and a second sensor is provided coupled to, and responsive to the rotational behaviour of, a drive shaft of the rear axle and that wheel brake cylinders of the wheels of the front axle are interconnected to receive a first brake pressure and wheel brake cylinders of the wheels of the rear axle are interconnected to receive a second brake pressure, the first and second brake pressures each being controlled by at least one respective valve control unit, the sensors being connected to the valve control units through an electronic evaluation circuit.