GB2058967A - Safety devices for vehicle transmissions - Google Patents

Abstract

A safety device for an electronic- hydraulically controlled range transmission for vehicles comprises a pressure switch 10 monitoring the hydraulic circuit of each clutch or brake and communicating with a comparator 5. The comparator 5 compares the information received with control pulses transmitted from an electronic control unit 1 to a hydraulic control unit 2, and if a fault is found switches off the supply. <IMAGE>

Description

SPECIFICATION Safety devices for vehicles The invention relates to safety devices for electronic-hydraulically controlled range transmissions for vehicles with an electronic control unit comprising a programmable permanent memory, an output amplifier and a comparator.

Electronic-hydraulic control systems for automatic range transmissions with several clutches and brakes must comply with stringent safety requirements, since in transmissions of this kind only a certain number of clutches or brakes-e.g. two-may be acted upon simultaneously. Similarly only certain fixed combinations of acted-upon clutches and brakes are admissible. If more clutches or brakes than admissible, or inadmissible combinations of clutches and brakes, are activated the transmission may be blocked and lead to damage or a dangerous traffic situation.

Known electronic measures are, of course available for monitoring the operability of the electronic control unit at its output and for cutting off the supply voltage at its output, if inadmissible operating states occur. This would make it possible to prevent clutches and/or brakes in the range transmission from being acted upon erroneously and so preventing blockage. However, the remaining disadvantage is that the hydraulic control part of the transmission is not monitored or safeguarded. If an error occurs in the hydraulic control, it will not be registered by the electronic control unit or the safety device monitoring it, and therefore no counter measures can be initiated, and the possibility that the transmission will be blocked remains.

In a control unit according to the invention the hydraulic circuit of each clutch is provided with a pressure switch having an electronic contact the operating states of which is communicated to the comparator and compared with control pulses transmitted from the electronic control unit to the hydraulic unit and, if a fault is found, transmits control pulses to a device for switching off the supply voltage for the hydraulic control unit. Thus the device not only monitors the output of the control electronics but also the hydraulic control, and switches off the supply voltage if an erroneous operating state occurs. It is possible to build such a safety device with a minimum of additional work with respect not only to the control electronics but also to its wiring between the electronic control unit and the hydraulic control part.

Including the hydraulic control part in the monitoring system offers the advantage that an electronic-hydraulically controlled range transmission is made very safe in operation and that malfunction in either the electrical and/or hydraulic control system leads to a switch-off of the supply voltage, safely avoiding a blockage of the range transmission. The skilful use of electronic control elements eliminates costly wiring between the electronic control unit and the hydraulic control part, so that hardly any additional cables between the control units are necessary.

DRAWINGS Figure 1 is a schematic illustration of an electronic control unit with a comparator and of a section of the hydraulic control unit with a pressure switch according to the invention for reporting the operating state of a pilot and pressure control valve back to the electronic control unit; Figure 2 is a further schematic illustration, similar to Fig. 1, but including an additional memory in the electronic control unit for storing admissible combinations of acted-upon clutches and brakes of the transmission; Figure 3 is a diagram of the time flow for a fault recognition in the unit of Figs. 1 and 2; Figure 4 is a circuit diagram linking several pressure switches in the unit of Figs. 1 and 2, the operating states of which are reported via a single electrical line to the unit.

Fig. 1 shows a simple arrangement of an electronic-hydraulically controlled range transmission having hydraulically parallel control circuits for activating the clutches and brakes engaged in the respective gear range. It has only one pilot and pressure control valve 9, whilst the transmission is provided with a number of control circuits. The valve 9 is activated from an output amplifier via a line 6, a solenoid valve 7 and a pre-control valve 8. A number of output amplifiers are provided in an output amplifier unit 4 corresponding to the number of pilot and pressure control valves. The unit 4 receives control signals from the output of a permanent memory 3 (PROM) via a line 1 6. The control signals (to the permanent memory) are supplied from functional elements via a line 1 8.

The unit 4 is monitored by transmitting the signals appearing at its output via a line 1 5 to a comparator 5 which, via a line 13, compares the input of the unit with its output. Fig.

1 shows only one broken line 15, but the line 1 5 will correspond to the number of amplifier stages required for monitoring the individual outputs of the unit 4. If the information supplied to the comparator 5 via the line 1 3 does not match that supplied via line 1 5 a signal is created at the output 1 4 of the comparator 5 which switches off the power supply. If the comparator 5 is used in this way, only the operating state of the unit 4 is monitored.

The operating states of the clutches and brakes are controlled by monitoring their hydraulic circuits. The pressure on the clutches and brakes is registered by providing each pilot and pressure control valve 9 with a separate pressure switch 10 which has an electrical contact 11. The contact 11 of the pressure switch 10 is an on-off switch, one connection of which is connected to a reference electrical potential (not shown in the drawing) and the other connection of which is in communication with the comparator 5 via the line 1 2. This enables the comparator 5 to compare the control signals at the input of the unit 4 with the information from the corresponding line 1 2. The line 1 5 for monitoring the output of the unit 4 may therefore be omitted, since the comparator 5 receives an answer signal on the actual state of the respective pressure switch 10 and thus of the respective pilot and pressure control valve 9.

The comparator 5 compares these answer signals with the desired settings and decides whether an error exits. If this is the case, a corresponding signal is transmitted via a line 1 4 to a device which switches off the supply voltage.

Although the unit 4 is constantly monitored, there remains the possibility that the safety device is put out of action by failure of the signals supplied by the permanent memory 3 (PROM), as the permanent memory 3 (PROM) also activates the comparator 5.

Therefore the safety circuit can be extended as shown in Fig. 2.

The hydraulic control unit 2 remains the same, while the electronic control unit 1 has been extended by the memory 1 9. This memory serves as an additional store for admissible combinations of activated clutches and brakes in the transmission. It may also store the maximum number of clutches and/or brakes to be activated. By using the memory 1 9 it is no longer necessary to ascertain the information appearing at the input of the output amplifier unit 4. The line 1 2 transmits the answer signal from the relevant pressure switch 10 and the associated contact 11, concerning the operating state of the pilot and pressure control valve 9, to the comparator 5.

The value supplied is compared with the values stored in the additional memory 19, and the comparator 5 ascertains whether the combination reported is correct, whether it is inadmissible, incorrect or whether it is admissible, incorrect. If there is no inadmissible, incorrect combination, the comparator 5 will not emit a signal. If, however, the combination reported is inadmissible, incorrect, the comparator emits a signal from its output 14 which is transmitted to a facility for switching off the supply voltage. If an inadmissible incorrect combination is reported, or if the number of clutches activated is higher than the maximum admissible number, then all clutches are released.

When using an additional memory 1 9 there is no need for separate monitoring of the output amplifier unit 4, as it is already monitored due to the monitoring of the actual values occurring at the pressure switches 10 and their contacts 11. Since the comparator 5 receives its reference signals from the memory 19, the safety circuit is not put out of action, if the permanent memory 3 (PROM) fails.

In Fig. 3 diagram A shows the current of the solenoid valve 7 switched off at the point in time T,. From this moment onwards there is no more activation of the solenoid valve, and the pressure in the clutch should return to zerowith a certain time delay inherent in the system. A time T1 is thus available for carrying out a check via the pressure switch 10. If according to diagram B the clutch pressure ascertained via presure switch 10 continues to hold after the time T1 (that is the time T2) then a fault signal is ascertained via the check on the pressure switch 10 at the end of time T1, and the safety device is able to respond. The safety device responds after a certain time delay indicated by the time T3.

The delay for the response of the safety device must be rated such that the slowness of the system in dropping the pressure during switch-off of the solenoid valve 7 has not already triggered a response from the safety device. If with a non-activated solenoid valve 7 the pressure in the clutch remains present as per diagram C an error signal will, of course, be supplied to the comparator 5 via the pressure switch 10 and its contact 11.

The line 6, being the connection between the output amplifier unit 4 and the various solenoid valves 7, must be multiplied several times corresponding to the number of clutches employed. In order to simplify the illustration only one line 6 appears in the drawings. If e.g. seven clutches are employed, then seven lines 6 must also be employed.

There is no need, however, to multiply the line 1 2 for the answer signal of the information coming from the pressure switch 10 and concerning the hydraulic pressure for the clutch, and this makes possible a saving in lines and plug connections.

Turning now to Fig. 4, the electronic control unit 1 in Fig. 1 ascertains through the comparator 5, by means of a comparison between the information content appearing at the input and the outputs at the output amplifier unit 4, whether the unit 4 is in order. In Fig. 2, with the additional memory 19 and by measuring the outputs of the output amplifier unit 4, the electronic control unit 1 determines whether the maximum admissible number of clutches to be acted upon has been exceeded, whether the present combinations of clutches and brakes are correct or whether the present combinations of clutches and brakes are perhaps incorrect. The hydraulic control unit 1 is checked as to whether the actual pressure conditions in the transmission are in accordance with the control signals for the solenoid valve 7 which the unit 4 supplies via the line(s) 6.The check is carried out separately for each clutch. When the comparator 5 has recognised that the correct clutches, i.e. only a certain maximum number of clutches, correct combinations etc., have been activated via the unit 4, when the pressure switches 10 have reported the respective pressure conditions to the comparator 5 and when it is ascertained that the signals emitted by the electronic control unit 1 are in accordance with the information received from the pressure switches 10, the desired pressure conditions in the transmission are correct.

It is the purpose of the circuit of Fig. 4 to carry out a comparison between the control signals transmitted from the electronic control unit 1 via the line 6 to the hydraulic control unit and thus to the transmission, and the actual pressure conditions prevailing in the transmission. To illustrate this circuit arrangement the output amplifier unit 4 (Fig. 4) is shown as incorporating contacts, 38, 39, 40 of which one connection is connected to the supply voltage of + 24 V and of which the other connections lead to coils of solenoid valves 7, 37, 47, whereby the same connections of the solenoid valves 7, 37, 47 are connected to the cathodes of diodes 32, 33, 34.The anodes of these diodes lead to a connection of each contact 11, 31, 41 representing the contacts of the pressure switches 1 0. The other connections of the contacts 11, 31, 41 of the pressure switches are connected via the line 1 2 with the comparator 5.

The comparator 5 contains a current sensor 20 (Fig. 4) which is also connected via a line 35 to the supply voltage of + 24 V. In the example the current sensor 1 2 supplies a voltage of + 5 V to the line 12. If one or several of the contacts 38, 39, 40 in the unit 4 are closed, then a corresponding current passes over the coil of the solenoid valves 7, 37, 47, the diodes 32, 33, 34 are blocked, independently of whether one or several of the contacts 11,31,41 of the pressure switches 10 are open or closed.

If on the other hand, the contact 38 in the output amplifier unit 4 is open-the solenoid valve 7 should therefore not be activated but if the contact 11 of pressure switch 10 is closed thereby indicating that there is pressure present in the respective clutch, then a current flows from the line 1 2 via the closed contact 11 and the extended diode 32 over the coil of the solenoid valve 7, the second connection of which is connected to ground.

The current sensor 20 ascertains that a clutch is being acted upon.

If all contacts 38, 39, 40 in the output amplifier unit 4 are open and if the contacts 11, 31, 41 of the pressure switches are closed, then a correspondingly strong current flows through line 12, which is evaluated by the current sensor 20 in the comparator 5 as proof for the fact that three clutches are acted upon by pressure. If, however, it is only admissible to connect two clutches in the transmission, then the safety device is activated. Therefore one line 1 2 is sufficient, in order to ascertain, by means of the amperage in this line, whether clutches are acted upon by pressure, although they should not be according to the activation via the unit 4, or whether pressure is present in the hydraulic line system on too many clutches.

If the contact 38 in the output amplifier unit 4 is closed, but the corresponding clutch is not under pressure, then contact 11 of the pressure switch 10 is not closed, this too would be an error. This error would not be reported via the line 1 2 to the current sensor 20 and thus to the comparator 5. However, this missing information would not be disadvantageous to the transmission, since a released clutch could not lead to blockage of the transmission.

By opening the previously closed contact 38 of the unit 4, the energizing of the coil of solenoid valve 7 is interrupted. The drop in pressure on the corresponding clutch, due to the nature of the system, cannot immediately follow the interruption of the current, but requires a certain time period. In order to prevent the safety device from immediately responding during this time period, the error signal is initially transmitted by the current sensor 20 via a line 25 to a delay circuit 21 and from there transmitted via a line 26 to the safety device.

By way of line 36 the error signal is also transmitted to a flip-flop 22 which is able to accept the error at a certain time and to store it for indication. A test signal is sent to it via another line 27. The purpose of this circuit detail is merely that when the pressure conditions are altered, the pressure switch of each clutch and its contact ought to be actuated, leading to the occurrence of a corresponding error signal-at least for a short time which could be used for checking the operability of the pressure switches. A line 28 and an amplifier 23 could be used to indicate, via a further line 29, a pressure switch fault, should the pressure switch not operate.

Claims (9)

1. A safety device for an electronic-hydraulically controlled range transmission for vehicles comprising an electronic control unit, a programmable permanent memory, an output amplifier, and a comparator, the hydraulic circuit of each clutch being provided with a pressure switch having an electrical contact the operating state of which is communicated to the comparator and compared with control pulses transmitted from the electronic control unit to the hydraulic unit and, if a fault is found, transmits control pulses to a device for switching off the supply voltage for the hydraulic control unit.

2. A device according to claim 1 in which the comparator evaluates the control pulses emitted from the electronic control unit as reference signals, in which form they are directly available at the output of the permanent memory.

3. A device according to claim 1 or claim 2 in which the comparator evaluates information from an additional memory as reference signals.

4. A device according to claim 3 in which the additional memory includes the maximum admissible number of acted-upon clutches and/or inadmissible combinations of brakes and clutches.

5. A device according to claim 4 in which the information in the maximum admissible number of activated clutches and/or inadmissible combination of acted-upon clutches and brakes is compared in the comparator with the control pulses appearing at the output of the electronic control unit.

6. A device according to any preceding claim in which several contacts of pressure switches are in communication with the comparator via a common single line from one of their connections, whilst an other connection of each contact is connected via a diode with the control input of a solenoid valve which is activated by the electronic control unit.

7. A device according to any preceding claim in which the error signal is initially transmitted to a delaying device.

8. A device according to any preceding claim in which the error signal together with a test signal is transmitted to a flip-flop.

9. A safety device as herein described with reference to Fig. 1, 3 and 4 of the drawings.

1 0. A safety device according to claim 9 as modified by Fig. 2 of the drawings.