Fluid-pressure and analogous brake systems – Speed-controlled – Four-wheel drive or all wheel drive
Patent
1996-07-02
1998-05-19
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Speed-controlled
Four-wheel drive or all wheel drive
303139, 180197, 192 85, B60K 2816
Patent
active
057527539
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates generally to a wheel slip control system (ASR-system) and more specifically to a wheel slip control system in combination with a pneumatically operated limited-slip differential lock.
For motor vehicles with connectible drives and/or for connectible locks for axle and central differentials, locking clutches are used in order to avoid the disadvantages of large friction clutches.
Based on this technological background, limited-slip differentials were developed with jaw clutches (European Patent Document EP-0510457 A1 corresponding to U.S. Pat. No. 5,335,764), in which the clutch jaws are shaped such that an engaging of the differential lock is also possible at differential rotational speeds of up to approximately 150 r.p.m without destroying the clutch jaws. The engaging of the differential lock takes place by a compressed-air cylinder which presses together the jaws of the clutch by a mechanical linkage until these jaws engage. When the jaws are engaged, no actuating force of the compressed-air cylinder is necessary since, because of the special shaping of the clutch jaws, these will not be released as long as a drive torque is transmitted by the engine of the vehicle. In the case of an actuation, the compressed-air cylinder is acted upon by compressed air via a simple electropneumatic 3/2-way valve.
In the case of commercial vehicles equipped with differential locks of the above-mentioned type, which vehicles are also used off-the-road, wheel slip control systems (ASR-systems) with a pneumatic brake control are increasingly used. In this case, as required, a brake control is activated at vehicle speeds below 40 km/h. Here, by opening the so-called wheel slip control valve of the wheel to be braked, stored pressure is provided; a pressure control valve arranged behind, the brake pressure on this drive wheel is then controlled such that an optimal differential brake effect is achieved.
The object of the present inventions consists of further developing vehicles equipped with antilock/wheel slip control systems, particularly commercial vehicles, which have automatic differential locks of the above-mentioned type, with respect to their electronic control systems in such a manner that, without significant additional expenditures, in addition to the automatic locking switching for the differential lock, the conventional antilock system/wheel slip control system brake control can also be carried out. As a result, it is to be achieved, among other things, that, when starting on a hill on .mu.-split roads (roads with different friction values of the road sides), the vehicle can also be accelerated when, because of excessive rotational speed differences, the lock is not yet engaged. Also, the "soft" starting on a .mu.-split road is to be permitted without the danger of stalling the engine.
The objects are achieved by modifying the antilock system/wheel slip control system while changing the logic of the antilock system/wheel slip control system control unit to use a pressure below a pressure level predetermined essentially by the spring restoring force of the limited-slip differential to operate the conventional brake control on the driving wheels of the vehicle. That is, the actuating valve of the compressed-air cylinder for the limited-slip differential acts as a normal wheel slip control valve when the control logic recognizes a coefficient of adhesion difference between the left and the right driving wheel and wants to modulate it. In this case, the logic is designed such that the brake control is maintained until preferably two conditions are met which are specified for engaging the differential lock. It is only then that the actuating or wheel-slip control valve is fully opened in order to engage the lock at the differential. As a result, stalling of the engine is reliably avoided. With respect to their stability, the jaws of the lock are also stressed far less because the rotational speeds of the driving wheels are synchronized before the lock is
REFERENCES:
patent: 4700797 (1987-10-01), Leiber
patent: 4753131 (1988-06-01), Wupper
patent: 5105903 (1992-04-01), Buschmann
patent: 5220975 (1993-06-01), Zimmer et al.
patent: 5335764 (1994-08-01), Leitner et al.
patent: 5431241 (1995-07-01), May et al.
Klement Roland
Mederer Martin
Utzt Alfred
Graham Matthew C.
Knorr-Bremse Systeme Fur Nutzfahrzeuge GmbH
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