What is IMA? What is VTM-4?
Thread Starter
Cost Drivers!!!!
Joined: Mar 2001
Posts: 19,392
Likes: 1
From: burbs of philly
What is IMA? What is VTM-4?
To clarify for those who don't know:
VTM-4(AWD)
IMA
VTM-4(AWD)
VARIABLE TORQUE MANAGEMENT 4-WHEEL-DRIVE (VTM-4(TM)) SYSTEM
After studying various all-wheel- and four-wheel-drive systems offered by the wide variety of SUVs on the market today, MDX engineers concluded that virtually every one had functional shortcomings and was undesirably bulky and heavy. The direct result of that research was the creation of an innovative system that automatically and proactively distributes torque to all four wheels as needed. Called Variable Torque Management 4-wheel-drive (VTM-4(TM)), this new system provides front-wheel drive for dry-pavement cruising conditions and engages all-wheel drive when needed to improve stability or maneuverability. Unlike many competitive systems that use an engagement strategy triggered by wheel slippage, the MDX's VTM-4 system anticipates the need for all-wheel drive and engages the rear wheels before slippage begins.
Additional torque is redistributed to the rear for improved performance, especially on low friction surfaces. In addition, the VSA system provides a limited-slip differential effect by applying braking force to a slipping front wheel thereby directing driving force to the wheel with more grip.
Another special feature is a lock button, which temporarily holds engagement of the rear wheels to aid extraction from a slippery ditch or a snow bank.
To avoid the weight and bulk of a conventional transfer case, VTM-4's torque transfer unit is a compact cast-aluminum housing bolted directly to MDX's transaxle. Since this vehicle is engineered for medium-duty off-road capability, the transfer case is a single-speed permanently-engaged device without a low-range. Attached to the front wheel differential's ring gear is a helical gear that provides input torque to the transfer unit. A short horizontal shaft and a hypoid gear set within the case turn the drive ninety degrees, move it to the vehicle center line, and lower its axis by approximately 3.75-inches.
There are three distinct modes of VTM-4 engagement. The first - called the acceleration torque control (ATC) mode - is unique to this system. It works even on dry pavement to proactively distribute driving torque to all four wheels as the MDX accelerates from a stop to cruising speed. One notable benefit of this mode is that traction is immediately available to move the vehicle from rest through a slippery intersection before slippage occurs. (Once a wheel slips, the traction available for forward propulsion and lateral restraint is significantly diminished.) A second advantage is that apportioning drive torque among all four wheels greatly diminishes the likelihood of torque steer. Handling dynamics are also improved. Reducing the propulsive force carried by the front tires leaves more adhesion for steering the vehicle into a tight bend or for holding cornering arc in the middle of a turn. In other words, the MDX's dynamic balance is greatly enhanced by ATC logic.
Rear wheel torque rises smoothly from zero to the maximum setting in proportion to vehicle acceleration (both forward and reverse). At higher speeds, the front wheels are capable of providing the desired thrust with excellent handling so torque delivered to the rear wheels automatically diminishes with speed. While cruising, all driving torque is delivered by the front wheels in the interests of smoothness, quietness, and fuel efficiency.
The second engagement mode uses wheel slippage control logic. If the difference in rotational speed between front and rear wheels rises because of a slippery surface or poor traction at the front of the vehicle, that condition is detected by wheel-speed sensors which are monitored by VTM-4's ECU. In response, the ECU commands an increasing amount of torque for the rear wheels. Torque is proportional to both slip rate and the rate at which the slip rate is increasing. This operation is similar to conventional slip-based all-wheel-drive systems already on the market.
The third mode of all-wheel-drive engagement activates when the driver presses the lock button mounted on the instrument panel. The maximum amount of rear-drive torque is locked in until the vehicle gets moving and exceeds six mph, at which time rear drive torque is gradually diminished. By 18 mph, the lock mode is fully disengaged. When vehicle speed drops below 18 mph, the lock mode automatically reengages. The shift lever must be in the first, second, or reverse-gear position to use the lock mode.
The maximum torque delivered to the rear wheels is sufficient to climb the steepest grade observed on any public road in America - 31 degrees (60-percent slope) - with a two-passenger load on board. The MDX will also move from rest up a 28-degree (53-percent slope) dirt grade. On a split-friction grade (different amounts of traction at each wheel), VTM-4 automatically provides sufficient rear-wheel torque to help the vehicle climb a steep, slippery driveway to enter a garage.
PROPELLER SHAFT AND HALF-SHAFTS
The two-piece propeller shaft that carries drive torque from the transfer case to the rear-drive unit is made of high-strength steel tubing to permit a smaller diameter, thereby improving both ground clearance and interior room. The cross yokes attached at each end by friction welding are forged steel for high strength and low weight. The center support bearing is rubber isolated to block the transmission of driveline noise from the interior of the vehicle. A low-friction plunger joint located near the center of the propeller shaft accommodates relative motion between front- and rear-mounted driveline components. A tuned-mass damper inside the front portion of the propeller shaft cancels any bending tendency in response to powertrain vibrations.
Equal-length, front-wheel half-shafts have a plunger joint at their inboard end and a ball-type universal joint at the wheel end. Rear half-shafts are similar in design but use a double-offset joint at the inboard end and a ball joint at the outboard end. All universal joints are constant-velocity type.
REAR AXLE DRIVE UNIT
The MDX's rear final-drive unit does not use a conventional differential. Instead, a hypoid ring-and-pinion gear set supported by a cast-aluminum housing switches torque from the propeller shaft's longitudinal orientation to the lateral orientation necessary to drive the rear wheels. Surface grinding the ring and pinion gear teeth yields the quiet operation expected of a luxury SUV wearing an Acura nameplate.
A connection from the ring gear to each wheel's half-shaft is made by left- and right-side clutches. Each drive clutch consists of three elements: an electromagnetic coil, a ball-cam device, and a set of 19 wet clutch plates which are similar in design to clutches used in an automatic transmission. Ten of the plates are splined (mechanically connected) to the ring gear while nine of the plates are splined to a half shaft. Left and right clutches are identical.
The VTM-4 system's electronic control unit (ECU) determines torque which is to be distributed to the rear wheels, then electric current is sent to the two electromagnetic coils. The resulting magnetic field moves a rotating steel plate toward each fixed coil. Friction between that steel plate and an adjoining cam plate causes the cam plate to begin turning. As it does, three balls per clutch roll up curved ramps, creating an axial thrust against a clutch-engagement plate. This thrust force compresses the wet clutch plates, thereby engaging drive to the corresponding rear wheel.
Unlike mechanically actuated four-wheel drive systems, the VTM-4 system is infinitely variable. The amount of torque provided to the rear wheels is directly proportional to the electric current sent from the ECU and can be adjusted from zero to a preset maximum. This current constantly changes to deliver the optimum rear torque calculated by the ECU. An internal gear pump circulates VTM-4 fluid to cool and lubricate the clutches, bearings, and gears within the rear drive unit. Use of high-strength, low-weight materials - such as die-cast aluminum for the housing - minimizes the bulk and weight of this hardware, helping to keep the weight of the entire all-wheel-drive system to about 212-pounds.
After studying various all-wheel- and four-wheel-drive systems offered by the wide variety of SUVs on the market today, MDX engineers concluded that virtually every one had functional shortcomings and was undesirably bulky and heavy. The direct result of that research was the creation of an innovative system that automatically and proactively distributes torque to all four wheels as needed. Called Variable Torque Management 4-wheel-drive (VTM-4(TM)), this new system provides front-wheel drive for dry-pavement cruising conditions and engages all-wheel drive when needed to improve stability or maneuverability. Unlike many competitive systems that use an engagement strategy triggered by wheel slippage, the MDX's VTM-4 system anticipates the need for all-wheel drive and engages the rear wheels before slippage begins.
Additional torque is redistributed to the rear for improved performance, especially on low friction surfaces. In addition, the VSA system provides a limited-slip differential effect by applying braking force to a slipping front wheel thereby directing driving force to the wheel with more grip.
Another special feature is a lock button, which temporarily holds engagement of the rear wheels to aid extraction from a slippery ditch or a snow bank.
To avoid the weight and bulk of a conventional transfer case, VTM-4's torque transfer unit is a compact cast-aluminum housing bolted directly to MDX's transaxle. Since this vehicle is engineered for medium-duty off-road capability, the transfer case is a single-speed permanently-engaged device without a low-range. Attached to the front wheel differential's ring gear is a helical gear that provides input torque to the transfer unit. A short horizontal shaft and a hypoid gear set within the case turn the drive ninety degrees, move it to the vehicle center line, and lower its axis by approximately 3.75-inches.
There are three distinct modes of VTM-4 engagement. The first - called the acceleration torque control (ATC) mode - is unique to this system. It works even on dry pavement to proactively distribute driving torque to all four wheels as the MDX accelerates from a stop to cruising speed. One notable benefit of this mode is that traction is immediately available to move the vehicle from rest through a slippery intersection before slippage occurs. (Once a wheel slips, the traction available for forward propulsion and lateral restraint is significantly diminished.) A second advantage is that apportioning drive torque among all four wheels greatly diminishes the likelihood of torque steer. Handling dynamics are also improved. Reducing the propulsive force carried by the front tires leaves more adhesion for steering the vehicle into a tight bend or for holding cornering arc in the middle of a turn. In other words, the MDX's dynamic balance is greatly enhanced by ATC logic.
Rear wheel torque rises smoothly from zero to the maximum setting in proportion to vehicle acceleration (both forward and reverse). At higher speeds, the front wheels are capable of providing the desired thrust with excellent handling so torque delivered to the rear wheels automatically diminishes with speed. While cruising, all driving torque is delivered by the front wheels in the interests of smoothness, quietness, and fuel efficiency.
The second engagement mode uses wheel slippage control logic. If the difference in rotational speed between front and rear wheels rises because of a slippery surface or poor traction at the front of the vehicle, that condition is detected by wheel-speed sensors which are monitored by VTM-4's ECU. In response, the ECU commands an increasing amount of torque for the rear wheels. Torque is proportional to both slip rate and the rate at which the slip rate is increasing. This operation is similar to conventional slip-based all-wheel-drive systems already on the market.
The third mode of all-wheel-drive engagement activates when the driver presses the lock button mounted on the instrument panel. The maximum amount of rear-drive torque is locked in until the vehicle gets moving and exceeds six mph, at which time rear drive torque is gradually diminished. By 18 mph, the lock mode is fully disengaged. When vehicle speed drops below 18 mph, the lock mode automatically reengages. The shift lever must be in the first, second, or reverse-gear position to use the lock mode.
The maximum torque delivered to the rear wheels is sufficient to climb the steepest grade observed on any public road in America - 31 degrees (60-percent slope) - with a two-passenger load on board. The MDX will also move from rest up a 28-degree (53-percent slope) dirt grade. On a split-friction grade (different amounts of traction at each wheel), VTM-4 automatically provides sufficient rear-wheel torque to help the vehicle climb a steep, slippery driveway to enter a garage.
PROPELLER SHAFT AND HALF-SHAFTS
The two-piece propeller shaft that carries drive torque from the transfer case to the rear-drive unit is made of high-strength steel tubing to permit a smaller diameter, thereby improving both ground clearance and interior room. The cross yokes attached at each end by friction welding are forged steel for high strength and low weight. The center support bearing is rubber isolated to block the transmission of driveline noise from the interior of the vehicle. A low-friction plunger joint located near the center of the propeller shaft accommodates relative motion between front- and rear-mounted driveline components. A tuned-mass damper inside the front portion of the propeller shaft cancels any bending tendency in response to powertrain vibrations.
Equal-length, front-wheel half-shafts have a plunger joint at their inboard end and a ball-type universal joint at the wheel end. Rear half-shafts are similar in design but use a double-offset joint at the inboard end and a ball joint at the outboard end. All universal joints are constant-velocity type.
REAR AXLE DRIVE UNIT
The MDX's rear final-drive unit does not use a conventional differential. Instead, a hypoid ring-and-pinion gear set supported by a cast-aluminum housing switches torque from the propeller shaft's longitudinal orientation to the lateral orientation necessary to drive the rear wheels. Surface grinding the ring and pinion gear teeth yields the quiet operation expected of a luxury SUV wearing an Acura nameplate.
A connection from the ring gear to each wheel's half-shaft is made by left- and right-side clutches. Each drive clutch consists of three elements: an electromagnetic coil, a ball-cam device, and a set of 19 wet clutch plates which are similar in design to clutches used in an automatic transmission. Ten of the plates are splined (mechanically connected) to the ring gear while nine of the plates are splined to a half shaft. Left and right clutches are identical.
The VTM-4 system's electronic control unit (ECU) determines torque which is to be distributed to the rear wheels, then electric current is sent to the two electromagnetic coils. The resulting magnetic field moves a rotating steel plate toward each fixed coil. Friction between that steel plate and an adjoining cam plate causes the cam plate to begin turning. As it does, three balls per clutch roll up curved ramps, creating an axial thrust against a clutch-engagement plate. This thrust force compresses the wet clutch plates, thereby engaging drive to the corresponding rear wheel.
Unlike mechanically actuated four-wheel drive systems, the VTM-4 system is infinitely variable. The amount of torque provided to the rear wheels is directly proportional to the electric current sent from the ECU and can be adjusted from zero to a preset maximum. This current constantly changes to deliver the optimum rear torque calculated by the ECU. An internal gear pump circulates VTM-4 fluid to cool and lubricate the clutches, bearings, and gears within the rear drive unit. Use of high-strength, low-weight materials - such as die-cast aluminum for the housing - minimizes the bulk and weight of this hardware, helping to keep the weight of the entire all-wheel-drive system to about 212-pounds.
IMA
INTEGRATED MOTOR ASSIST (IMA)
System Overview
The new, more advanced version of Honda's patented Integrated Motor Assist (IMA) system represents the second generation of IMA technology from Honda. The new IMA system uses technology that delivers increased performance and provides enhanced packaging flexibility within the vehicle.
Primary motive power for the Civic Hybrid is provided by the system's 1.3-liter i-DSI gasoline engine. Although the engine alone provides sufficient driving performance, even in sustained uphill driving, the electric motor mounted between the engine and transmission provides power assistance under a broad range of conditions, such as initial acceleration from a stop. And since the electric motor is used only for power assistance and not for primary motive power, it too can be made smaller and lighter (along with the batteries) compared to the full-size traction motors in other hybrid systems.
As the IMA gasoline engine enters its cruising operating range, the electric motor assist has a minimal role and the engine supplies the power required. Power for the electric motor is mainly generated by capturing energy from the forward momentum of the vehicle rather than from the gasoline engine. When the Civic Hybrid is coasting or its brakes are applied when the engine is in gear, its electric-assist motor becomes a generator, converting forward momentum (kinetic energy) into electrical energy, instead of wasting it as heat during conventional braking. Energy is stored in the system's NiMH battery pack located behind the rear seat in the trunk. If the charge state of the IMA battery is low, the motor generator will also recharge while the Civic Hybrid is cruising.
Electric Motor
The 13-horsepower, 144-volt ultra thin DC brushless electric motor's function is to boost the output of the ultra efficient gasoline engine in order to provide powerful acceleration. The electric motor does not provide primary motivation, and in fact, the Civic Hybrid will continue to operate with reasonably good performance on the gasoline engine alone.
The performance characteristics of the electric motor, which has a width of 2.55 inches (65 mm), results in high amounts of torque across a wide rpm range with peak torque available at 1000 rpm (46-lb.-ft @ 1000 rpm). It produces a peak of 13 horsepower at mid range engine rpms. The gasoline engine excels at providing horsepower at higher rpms, and in the case of the i-DSI engine, it supplies reasonably good torque, too. The most significant contribution the electric motor makes to the overall performance of the vehicle is it adds significant amounts of torque at lower rpms.
The electric motor is positioned between the gasoline engine and the transmission. The output shaft of the engine connects directly to the electric motor and the output shaft of the electric motor attaches directly to the transmission. The electric motor and the gasoline engine always turn in tandem since they are connected together.
Intelligent Processing Unit (IPU)
The Intelligent Processing Unit (IPU) is the nerve center that controls the power of the IMA system. The IPU houses the Power Control Unit (PCU), motor Electric Control Unit (ECU), energy storage module (battery), and a compact cooling system.
System Overview
The new, more advanced version of Honda's patented Integrated Motor Assist (IMA) system represents the second generation of IMA technology from Honda. The new IMA system uses technology that delivers increased performance and provides enhanced packaging flexibility within the vehicle.
Primary motive power for the Civic Hybrid is provided by the system's 1.3-liter i-DSI gasoline engine. Although the engine alone provides sufficient driving performance, even in sustained uphill driving, the electric motor mounted between the engine and transmission provides power assistance under a broad range of conditions, such as initial acceleration from a stop. And since the electric motor is used only for power assistance and not for primary motive power, it too can be made smaller and lighter (along with the batteries) compared to the full-size traction motors in other hybrid systems.
As the IMA gasoline engine enters its cruising operating range, the electric motor assist has a minimal role and the engine supplies the power required. Power for the electric motor is mainly generated by capturing energy from the forward momentum of the vehicle rather than from the gasoline engine. When the Civic Hybrid is coasting or its brakes are applied when the engine is in gear, its electric-assist motor becomes a generator, converting forward momentum (kinetic energy) into electrical energy, instead of wasting it as heat during conventional braking. Energy is stored in the system's NiMH battery pack located behind the rear seat in the trunk. If the charge state of the IMA battery is low, the motor generator will also recharge while the Civic Hybrid is cruising.
Electric Motor
The 13-horsepower, 144-volt ultra thin DC brushless electric motor's function is to boost the output of the ultra efficient gasoline engine in order to provide powerful acceleration. The electric motor does not provide primary motivation, and in fact, the Civic Hybrid will continue to operate with reasonably good performance on the gasoline engine alone.
The performance characteristics of the electric motor, which has a width of 2.55 inches (65 mm), results in high amounts of torque across a wide rpm range with peak torque available at 1000 rpm (46-lb.-ft @ 1000 rpm). It produces a peak of 13 horsepower at mid range engine rpms. The gasoline engine excels at providing horsepower at higher rpms, and in the case of the i-DSI engine, it supplies reasonably good torque, too. The most significant contribution the electric motor makes to the overall performance of the vehicle is it adds significant amounts of torque at lower rpms.
The electric motor is positioned between the gasoline engine and the transmission. The output shaft of the engine connects directly to the electric motor and the output shaft of the electric motor attaches directly to the transmission. The electric motor and the gasoline engine always turn in tandem since they are connected together.
Intelligent Processing Unit (IPU)
The Intelligent Processing Unit (IPU) is the nerve center that controls the power of the IMA system. The IPU houses the Power Control Unit (PCU), motor Electric Control Unit (ECU), energy storage module (battery), and a compact cooling system.
Thread
Thread Starter
Forum
Replies
Last Post
