GB2147959A

GB2147959A - Gear lock-out devices

Info

Publication number: GB2147959A
Application number: GB08327623A
Authority: GB
Inventors: Johannes Sorg
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1982-04-21
Filing date: 1983-10-14
Publication date: 1985-05-22
Also published as: GB2147959B; SE8305352L; DE3214710C2; SE445320B; FR2553853B1; FR2553853A1; DE3214710A1; GB8327623D0; SE8305352D0

Abstract

A vehicle transmission (not shown) is provided with a device for preventing the engagement of a gear (such as reverse) at a too high speed. A speed selector 1 compares a speed analogue signal F from a transmitter 3 with a threshold value. if the speed is above a predetermined level, the selector 1 generates a first input signal V and feeds it to a logic selector 2. A state-of-the-transmission indicator 4 generates a second input signal S to the selector 2 when a gear-shift lever is actuated. The selector 2 allows an output signal A to actuate a warning device 5 or a lock-out device to prevent the shift if the first signal V is present prior to the second signal S. <IMAGE>

Description

SPECIFICATION Gear lock-out devices The invention relates to devices for preventing transmissions from engaging a gear at a speed which is too high. Such a gear change, particularly into reverse gear in a vehicle, can damage the transmission.

Our Patent Specification DE 3042920A1 describes such a device in which the engagement particularly of a reverse gear is prevented by an electromagnet actuated as a function of speed which inhibits the gear change via an output signal. This device is relatively expensive to produce, and difficult to adapt to downward gear changes besides changes into reverse.

A device according to the invention comprises means for generating a first input signal when the speed is above a predetermined level, means for generating a second input signal when a gear-shift lever is actuated towards the gear, and means for allowing an output signal to actuate a warning and/or lock-out device if the first input signal is present prior to the second input signal.

Such a device can be adapted to various gear changes at little additional cost. In many cases it is sufficient if a warning signal attracts the driver's attention to a downward gear-change which is not permitted while he is preparing for the change. This enables the driver to interrupt his gear-changing for as long as is required for an acceptable speed condition to be achieved.

By braking or merely waiting, for example, the necessary conditions can be produced.

A warning signal is produced only if a downward gear-change is attempted at a speed above the permitted threshold. If the threshold speed is reached after the change-down has taken place, no signal is produced. For more stringent requirements with regard to change-down safety, the output signal may be used to actuate a lock-out device or a lock-out device in addition to a warning device. The warning device may comprise an audible signal transmitter which may already be present in the vehicle for other reasons, for example for a frost warning.

With a lock-out device, a visual signal transmitter to give information to the driver should preferably also be provided. The switch for the reverse light can also be used in producing the second input signal when the gear-shift lever is actuated towards reverse. A warning signal may be produced as early as the movement of the gear-shift lever into the next lower lane, so that initiation of a faulty move can be cancelled with great safety.

The first input signal is preferably generated by continuously comparing speed with a predetermined threshold. The means for allowing the output signal to actuate a warning and/or lock-out device is preferably a logic selector fed by the first and second input signals.

The first input signal may be generated by an integrated module fed with a frequency analogue of speed with a threshold frequency adjustable by means of a potentiometer and/or fixable by means of a resistor. The means for allowing the output signal to actuate the warning and/or lock-out device may comprise a transistor, and a relay actuable when the first input signal is present at the transistor, the transistor connecting the second input signal to the output when the transistor is de-energized. In a preferred arrangement, the means for generating the first signal comprises a number of potentiometers and/or resistors for generating different selection thresholds. A number of switches may be provided for controlling the second input signal.Thus it is possible to provide warning and/or lock-out devices for downward-gear changes into a lane including a reverse gear or a lower group of gears. To simplify the changeover, the potentiometers may be arranged in the area of the gear-shift lever.

DRAWINGS: Figure 1 is a block wiring diagram of a device according to the invention; Figure 2 is a more detailed circuit diagram of the same device as Fig. 1; Figure 3 is a circuit diagram corresponding to a part of Fig. 2 but modified so as to include a number of potentiometers; and Figure 4 is a schematic illustration of a transmission provided with a device according to the invention.

With reference to Fig. 1, a speed selector 1 compares a speed analogue signal F from a transmitter 3 with a threshold value. If the speed is above a predetermined level, the selector 1 generates a first input signal V and feeds it to a logic selector 2. A state-of-the-transmission indicator 4 generates a second input signal S to the selector 2 when a gear-shift lever is actuated. The selector 2 allows an output signal A to actuate a warning device 5 if the first signal V is present prior to the second signal S. Thus: Threshold (V) Change-down signal (S) Output signal (A) 0 0 0 0 1 0 0 0 0 1 ,1 1 1 1 0 1 0 1 1 0 In Fig. 2, the speed selector 1 can be seen to comprise a frequency switch 11 in the form of an integrated module IC1, a potentiometer 12 and a power supply 71.The speed analogue signal F is input from a reed switch 31 of the transmitter 3 which does not appear in Fig. 2.

The signal F is continuously supplied to the frequency switch 11, and there compared with a threshold frequency which may be adjusted by means of the potentiometer 12. If the frequency supplied to the switch 11 is below the threshold, the first digital input signal V is generated and fed to the logic selector 2. The frequency threshold is generally determined as corresponding to a particular speed, and may be fixed by means of a resistor. The logic selector 2 comprises a transistor 21 representing a switch for a relay 22 connected to the first input signal V. In its deenergized state, the relay 22 connects the second input signal S via a contact 23 to produce the output signal A. In the energized state, the relay 22 interrupts this connection. The second input signal S is derived from the state-of-the-transmission indicator 4 which is represented by a switch 41.The switch 41 is closed if a downward gear-change is intended. The output signal A is fed to the warning device 5, or lock-out device 6. which is fed directly from a power source 7. The power source 7 also feeds through a line 71 the frequency switch 11 and relay 22. The remaining resistor, capacitors and diodes in Fig. 2 adapt and protect the frequency switch 11, transistor 21 and relay 22.

Operation If the contact 23 of the relay 22 is in the de-energized condition shown, for example in a forward drive speed condition of above 10 kilometres per hour at which a downward gearchange into reverse is not permitted, a shift of a gear lever 81 (Fig. 4) into the reverse lane leads to closure of the switch 41, or if it is coupled with a reversing light switch, also to the closure of a switch 42 which causes the warning device 5 to emit an alarm. This urges the driver to discontinue the gear-change operation, and initially to reduce speed. Once the speed has dropped below a threshold of for example 10 kilometres per hour, the relay 22 is operated by the transistor 21, and the connection of the second input signal S to the output A is interrupted. If a downward gear-change is then initiated, no warning signal is generated.If the speed in the reverse direction is subsequently increased, the position of the relay 22 remains unchanged because the increase in speed did not occur until after the closure of the switch 41 or 42, and because the relay 22 is held in the energized state via the switch 41 or 42 even after the transistor 21 has interrupted the connection.

Fig. 3 shows a modification in which a number of potentiometers 120,121, and 1 22 are connected via a switching device 82 with the integrated module IC1, represented by a frequency switch 110, thus facilitating the selection of different thresholds. The switching device 82 may be in the speed selector 1, or in the area of the gear lever 81 where it can be mechanically actuated when a gear-change is initiated.

Fig. 4 shows a locking magnet 61 provided as a lock-out device for a gear-change unit 83 of a transmission 8 for inhibiting downward gear-changes which are not permitted.

Claims

1. A device for preventing a transmission from engaging a gear at a speed which is too high, which device comprises means for generating a first input signal when the speed is above a predetermined level, means for generating a second input signal when a gear-shift lever is actuated towards the gear, and means for allowing an output signal to actuate a warning and/or lock-out device if the first input signal is present prior to the second input signal.

2. A device according to claim 1 in which the first input signal is generated by continuously comparing speed with a predetermined threshold.

3. A device according to claim 1 or claim 2 in which the means for allowing the output signal to actuate is a logic selector fed by the first and second input signals.

4. A device according to any preceding claim in which the first input signal is generated by an integrated module fed with a frequency analogue of speed and with a threshold frequency adjustable by means of a potentiometer and/or fixable by means of a resistor.

5. A device according to any preceding claim in which the means for allowing the output signal to actuate comprises a transistor, and a relay actuable when the first input signal is present at the transistor, the transistor connecting the second input signal to the output when the transistor is de-energized.

6. A device according to any preceding claim in which the means for generating the first signal comprises a number of potentiometers and/or resistors for generating different selection thresholds.

7. A device according to claim 6 comprising a number of switches for controlling the second input signal.

8. A device for preventing a transmission from engaging a gear as herein described with reference to Figs. 1, 2 and 4 of the drawings.

9. A device according to clam 8 as modified by Fig. 3 of the drawings.