HowardOR

I purchased the 450h because it was - according to the dealer - capable of towing a trailer and boat not exceeding 3500 lbs. However what he failed to mention was that in reverse, the torque and power to backup with a boat and trailer is not equal to the forward power. I found this out when the front of my car was at the water's edge and would not move an inch backing up a relatively steep incline with a boat and trailer attached. Long story short, I had to have a tow truck pull me out. If anyone has had a similar experience and found a solution, please let me know.

Cruiter

Do you have FWD or AWD and what was the load you were pulling? Only the AWD is rated for towing. I wanted a Lexus hitch on my FWD (h) just for mounting a device to carry my Segway. Dealer wouldn't do it as it would void the warranty unless it was an AWD.

DunWkg

I don't know anything about it, but I'm asking, "what about snow mode?" Does the AWD snow mode work in reverse?

I tried digging around the on-line manual, but didn't find the answer.

HowardOR

I have an AWD and used snow mode. As I mentioned, pulling 3500 lbs up an incline works well. But the same weight on the same incline in reverse does not. My discussion with Lexus customer svc sympathized with my disapointment with the dealer, but did not have a solution. This remains a problem for me because I need to take the boat out of the lake each winter and launch it each spring. The configuration of he ramp requires me to both pull and push the boat up the ramp. (a time consuming operation using dollys an a winch) Why would the car not have the same power at slow speeds in reverse as it does moving forward?

TorontoIS

So the RX 450h uses only the rear electric motor for reverse? It doesn't use the gas engine at all in reverse even if it requires more power?

wa3cuj

The ICE runs in reverse if required. When I start the vehicle and back out of the garage, the ICE usually only starts after I am part way out the door in reverse.

I usually hit the start button and wait until all of the dash lights "normalize" before putting it in reverse. I had several occassions where I put it in reverse right away and found that braking was extremely hard. I am not sure what the issue is but it has never happened to me when I wait that extra 1-2 seconds before shifting into reverse.

lucasb7

The only motive force in reverse is from MG2 or in the AWD cases MG2 and 3. In some situations (e.g warm up or charging the battery) the ICE will fire and rotate MG1 to charge the battery but it cannot put any direct power to the wheels in reverse. The best it could do is maybe fire up to charge the batteries to give juice to the motors.

The only suggestion I could give you is to do a force charge of the battery before you try to push the boat up the ramp. To do this, in drive press the gas and brake at the same time. You can watch the battery's state of charge increase on the display. With all bars, the car should theoretically be able to put down more power. You might try this somewhere where you could just go forward if this doesn't work to avoid the tow...

That is certainly a downside I never considered when I was looking at the RX450h.

TorontoIS

I never considered this either, who would have thought that this is how it worked. Fortunately I don't need to tow anything.

RXSF

i have to back out every morning up a steep hill. the engine fires but doesnt power the wheels directly. because of this, the car feels like it has little to no power going up, and Im usually pretty deep in the pedal pressure.

TorontoIS

It does sound a bit worrisome actually. What if one were to get stuck in deep snow or mud and had to rock the car to get it out? Would the electric motors have enough power to power in reverse?

lucasb7

You shouldn't have any problem making the tires slip in reverse on snow or mud. The limited friction in these situations means that the car can't put out much torque before slipping. In fact, it could be beneficial because you can't go crazy with wheel spin.

The only situation this affects is where traction is not limiting and it is just putting enough power/torque to actually move the load.

This is something they will have to change if they hope to put HSD in the LX or GX because this would be unacceptable. I'm lucky I thought the RX was too small for my needs because I could be in this very situation myself. I have to back my 3500 lb trailer up a hill at my home to store it. Even this action makes me feel bad for the transmissions on the MDX and RX.

DunWkg

Now I'm confused. Are you saying Motor Generator (MG) 1, 2, and 3 ?

I was thinking there is only one in front and one in the back on an all-wheel drive.

JimH2

Excerpt from carshowroom web site:

"RX 450h has three separate electric motors (MG1, MG2 and MGR) with MG1 used exclusively as a generator to charge the batteries. MG2 provides up to 123kW/335Nm and drives the front wheels while MGR drives the rear wheels with up to 50kW/139Nm."

lucasb7

Yes, there are two electric motors in the front transaxle.

The two electric motors spin in various directions based on the demands of the ICE and other things. MG2, or in some cases 3, is the only motor that has direct, mechanical connection to the wheels. For instance, if you are driving on electric only MG2 is providing motive force, MG1 has to spin backwards to keep the ICE stopped. You'll see on the sliders (below) that at ~42 MPH MG1's redline is reached and the ICE has to be started.

You can read and play with a really cool sliders at http://eahart.com/prius/psd/. The numbers may be a bit different for the 450h's planetary gearbox but the principles are all the same.

The brilliance of the design is really astonishing. Very simple but it clearly too good engineering to make it work. I learn new things about synergy drive every day!

It looks like if the ICE is idling, you are limited to about 15 MPH in reverse.If it is charging (~1500 RPM) you are limited to around 4 MPH.

wa3cuj

Thanks for posting the web site. This clearly shows that I had some major misconceptions as to how the CVT in the 450h worked. It also helps explain some of the display changes in the fuel consumption display.

This shows why us engineers are such good conversation at parties!!!!!