Control system for an automatic all wheel drive vehicle
AssigneeDaimler-Benz Aktiengesellschaft
InventorsManfred Burckhardt, Richard Zimmer
Life of this patent
Estimating the term…
Abstract
A reference signal generation circuit for providing a vehicle reference speed signal to an antilocking system in a vehicle having automatic selectable all wheel drive is provided. A reference signal generator is put into various operational states to increase, decrease or hold the reference signal in response to various operating conditions of the vehicle and the road conditions, in order to provide a more accurate vehicle reference speed signal to the antilocking control system, even when the vehicle wheels are spinning.
Claims17
A process for generating a reference signal representing the speed of a vehicle, said vehicle having selectable automatic on- and off all wheel drive with wheel sensors, each of which delivers wheel speed signals in proportion to the speed, with an antilocking control system;
- having a first electronic control unit that evaluates the wheel speed signals and delivers control signals for decreasing, keeping constant or increasing brake pressure, with an all wheel drive control apparatus;
- having a second electronic control unit that evaluates the wheel speed signals and:
- (1) switches to two axle drive if at least one of the wheels of a permanently driven axle spins,
- (2) in the case of continuous spinning of at least one wheel of the two axles, locks a longitudinal differential in the power train between front and rear axles;
- the reference signal of the vehicle speed being generated from the wheel speed signals of non-driven wheels, provided only one axle is driven and the reference signal is routed to both control units;
- said process including:
- (a) increasing the reference signal of the vehicle speed at a rate of change, limited by a predetermined acceleration threshold value of approximately 4 m/s.sup.2, if both axles are drive-coupled via the longitudinal differential and the wheel speed signals change with a value that exceeds said threshold value;
- (b) restricting the reference signal of the vehicle speed to a maximum value present during the locking of the longitudinal differential;
- (c) increasing the reference signal at a rate of change of 4 m/s.sup.2 if a test cycle, which periodically uncouples an axle from the power train, yields that the largest wheel speed signal is higher than the reference signal;
- and
- (d) reducing the reference signal at a high rate of change down to the largest wheel speed signal if the reference signal, generated according to steps (a) to (c), is greater than the largest wheel speed signal.
Apparatus for providing a reference signal to an antilocking control system in an automatic all wheel drive vehicle, comprising:
- a reference signal generator means, which can be driven by output signals of electronic control units of the antilocking system and the automatic all wheel drive, said reference signal generator means delivering from a reference signal output, a reference signal which corresponds to the reference speed, as long as the power train of the vehicle is shifted to one axle drive;
- a logical switching circuit, provided to drive said reference signal generator means, said circuit including a first AND gate having a first input for receiving a high level signal when a brake is activated, and a second input for receiving an output signal of the automatic all wheel drive control unit, and providing a high output signal indicating that the all wheel drive and a longitudinal differential lock are switched on;
- wherein for a duration of a high output signal of the AND gate, the reference signal generator means is driven by said AND gate to deliver a reference speed signal which decreases at a first preselected rate of change, and after a delay time span,
- following a fall of a signal from the electronic control unit of the antilocking system, the reference signal generator means generates reference speed output signals which decrease at a second rate of change higher than said first rate of change.
A process for generating a reference signal representing a vehicle speed of a vehicle, said vehicle having an automatic selectable all wheel drive including a lockable longitudinal differential;
- an antilocking control system;
- and wheel sensors for detecting circumferential wheel speeds and producing wheel speed signals corresponding to said detected wheel speeds, said process including the steps of:
- (a) increasing the reference signal at a rate limited by a predetermined threshold rate if both axles are drive coupled via the longitudinal differential and a wheel speed signal increases faster than the threshold rate.
An arrangement for generating and providing a reference signal representing an estimated vehicle speed in a vehicle having selectable automatic all wheel drive and an antilocking control system, comprising:
- means for detecting circumferential speeds of each vehicle wheel;
- all wheel drive control means for placing the vehicle in an all wheel drive mode and for locking a longitudinal differential;
- antilocking control means for controlling operation of the antilocking system;
- and reference signal generating means for producing said reference signal, connected to both said all wheel drive control means and said antilocking controls means;
- first operational state control means for controlling said reference signal generating means to produce a reference signal that either increases or decreases to match increases and decreases in the detected circumferential speeds of non-driven wheels when said vehicle is being driven by a single axle only;
- second operational state control means for controlling said reference signal generating means to produce a reference signal that is either held constant at a highest value of the reference signal attained during transition of said reference signal generating means from first to second operational state, or is gradually lowered, in response to locking of the longitudinal differential in combination with nonactivation of a vehicle brake;
- and
- third operational state means for controlling said reference signal generating means to lower the reference signal produced when said reference signal is larger than the largest of the detected circumferential wheel speeds.
Dependencies are inferred from the claim text.